**3.2 Carboprost**

Carboprost is used as IM injection in 250 μg doses; can be repeated up to eight such doses (i.e. maximum 2 mg). Side effects are nausea, vomiting, diarrhoea, fever, bronchospasm and hypertension. It is used as a last resort. It should also be used with caution in active hepatic or cardiovascular disease.

### **3.3 Misoprostol**

This prostaglandin analogue can replace oxytocin, if not available. It is used at a dose of 600 μg orally or sublingually in PPH. Diarrhoea, shivering, pyrexia and headache are some of the side effects. The drug is second-line agent when methylergometrine is contraindicated such as in preeclampsia.


**Edward Narayan 1,2**

Received: 30 November 2020; Accepted: 2 December 2020; Published: 3 December 2020

Wild animals under human care as well as domesticated farm production animals are often exposed to environmental changes (e.g., capture and transportation). Short-term or acute changes in physiological indices (e.g., heart rate, respiration, body temperatures, immune cells and stress hormonal biomarkers) provide crucial information regarding the responses of animals to novel environments, and they could provide crucial determining factors for evaluating the long-term health and welfare of animals. The goal of this special issue is to provide examples of new research and techniques that can be used to monitor short- and long-term environmental adaptation of animals under human care. Examples of research include applications of physiological indices and welfare assessment methods (e.g., morphological and morphometric data, behavioural assessments, thermal profiles and physiological markers) in any wildlife or production animal (e.g., rescued and rehabilitating animals, pets, competition animals, farm animals and zoo animals), in response to environmental and management-related factors.

This book is a reprint of the papers published in the Special Issue: "Assessing the Environmental Adaptation of Wildlife and Production Animals: Applications of Physiological Indices and Welfare Assessment Tools".

Chapter 1—This research was based on a retrospective analysis of clinical data and characterises this based on categories of stress experienced by avian wildlife patients. It demonstrated the factors associated with urbanization, which exposes avian wildlife to an array of environmental stressors that result in clinical admission and hospitalisation. It showed that the most common outcome of avian patients that suffered from vehicle-related injuries or other impact injuries was euthanasia. Immobility and abnormal behaviour were the most commonly occurring primary stressors of avian patients. Finally, trauma and fractures were the most common occurring secondary stressors in avian patients. The most common outcome of all these stressors was euthanasia. This study also provided a categorisation system for the stressors (preliminary, primary and secondary) that may be used to monitor the stress categories of wildlife patients and gain a deeper understanding of the complex notion of stress.

Chapter 2—Artificial insemination programs are used to improve reproductive output in livestock animals. This study showed the possible influence of ejaculation collection in breeding boars on their oxytocin profiles. Using saliva collection, the research measured total (protein bound) and free oxytocin in pigs. Research showed that ejaculation influences the salivary oxytocin concentrations in breeding boars, although this influence varies according to age, libido and breed.

Chapter 3—Pharmacological and biological validation are important for establishing minimally invasive stress hormone evaluation in animals. Here, researchers were able to validate two faecal

glucocorticoid enzyme immunoassays (faecal corticosterone metabolites-FCMs, EIAs; a corticosterone EIA, and a group-specific 5 α-pregnane-3β,11β,21-triol-20-one EIA) in deermice (*Peromyscus maniculatus*) by challenging individuals with dexamethasone and adrenocorticotropic hormone (ACTH). Researchers discuss the need for careful physiological/biological validation of assays prior to applications in animal studies.

Chapter 4—Veterinary intervention is an important aspect of wildlife rescue and rehabilitation programs. In this research case study on the roe deer (*Capreolus capreolus*) from Italy, researchers identified a potential biomarker (whole blood lactate concentrations) as an early indicator of lactataemia status to predict the outcome of clinical intervention. Biomarkers such as these should be used in conjunction with clinical veterinary intervention to provide appropriate care and outcome decisions for rescued wildlife.

Chapter 5—Quantification of acute stress is an important component of wildlife management and care in zoos. In this research, the investigators compared the glucocorticoid concentrations in response to various types of potential stressors present during the standard operation of a temporary housing facility between three species, namely, ring-tailed lemurs, collared brown lemurs and white-headed lemurs. Researchers employed polyclonal antibodies directed against the metabolite 11-oxo-etiocholanolone I. Researchers found some species-related di fferences in the physiological stress responses of the lemurs, however, the general patterns across treatments were similar, but individual reproductive status may also influence the stress responses in grouped housing situation.

Chapter 6—Wildlife hunting is an example of intensive human–animal interaction which can generate physiological stress in animals. Red deer (*Cervus elaphus*) is the target of intensive seasonal hunting in the Lousã Mountain region, Portugal. Using a combination of sample types (blood, faeces and hair), researchers in this study quantified glucocorticoid levels in red deer across hunting seasons. The researchers discuss the applications of specific sample types for evaluating acute and chronic stress responses of red deer in the hunting season.

Chapter 7—Tigers (*Panthera tigris*) are an endangered species and it is crucial to obtain vital health indices of tigers for rescue, rehabilitation and captive management programs. In this pilot study, the researchers demonstrated the application of serum protein electrophoresis as a useful tool in monitoring the health of tigers.

Chapter 8—Stress endocrine response can influence immune response in animals. Similarily, immune response biomarkers can be used to index stress responses in animals. For example, salivary immunoglobulin A (sIgA) has been proposed as a potential indicator of welfare for various species, including Asian elephants, and may be related to adrenal cortisol responses. Here, researchers distinguished circadian rhythm e ffects on sIgA in male and female Asian elephants and compared patterns to those of salivary cortisol, information that could potentially have welfare implications. Researchers discovered a daily quartic pattern of SIgA in elephants, which can be important information for designing future experiments to standardize field data collection.

Chapter 9—Wild mammals can be highly cryptic and there remains substantial knowledge gaps regarding the physiological control of reproduction in species, such as red deer (*Cervus elaphus* L., 1758). Researchers evaluated the concentration of cortisol and progesterone, extracted from blood and hair, in 10 wild and pregnant red deer females. Researchers successfully quantified cortisol and progesterone in hair samples obtained from the hinds of deer sampled during a regional selective hunting plan. It may be possible the deer were actively breeding during the sampled period and the methods could be used to evaluate the reproductive ecology and welfare of deers used for human hunting purposes.

Chapter 10—The current study developed a baseline welfare assessment protocol for captive Punjab urial adapted from the welfare protocol for domestic sheep from the Welfare Quality ® project. It was able to apply the protocol for Punjab urial across two facilities and provided recommendations for areas of improvement for captive management and breeding.

Chapter 11—Koalas (*Phascolarctos cinereus*) are Australia's iconic marsupial species and they face heightened threats from anthropogenic induced environmental change. In this study, the researchers validated the application of a thermal imaging technology (FLIR530TM IR thermal imaging camera) to evaluate heat signatures in koalas in a captive zoo housing facility. The study discussed the technical limitations and applications of this method for tracking heat stress in koalas in zoos.

Chapter 12—Wildlife are commonly impacted by parasites from their surroundings and they can also serve as hosts for zoonotic pathogens. Parasites activate immune responses of wildlife which can be quantified using morphological, blood and tissue analysis. Here, the researchers evaluated the relative impact of parasite pressure vs. parasite load on di fferent host species, using bank voles (*Myodes glareolus*) and wood mice (*Apodemus sylvaticus*) as study species. The researchers sampled sub-adult males to quantify their immune function, infestation load for ectoparasites and gastrointestinal parasites, and infection status for vector-borne microparasites. They used regression trees to find out whether variation in immune indices could be explained by among-site di fferences (parasite pressure), among-individual di fferences in infestation intensity and infection status (parasite load) or other intrinsic factors. The research outcome showed that both parasite pressure and parasite load influence the immune system of wild rodents.

Chapter 13—It is important to validate minimally invasive stress hormone assays for each species due to potential species-specific di fferences in metabolism and excretion of steroids. In this study, the researchers physiologically validated a faecal cortisol metabolite (FCM) enzyme-immunoassay for male reindeer. Researchers conducted a physiological validation of an 11-oxoaetiocholanolone enzyme immunoassay (EIA) for measuring faecal cortisol metabolites (FCMs) in male reindeer by the administration of an adrenocorticotrophic hormone. Researchers also identified the faecal samples belonging to individual animals using DNA analysis across time. This study reports a successful validation of a non-invasive technique for measuring stress in reindeer, which can be applied in future studies in the fields of biology, ethology, ecology, animal conservation and welfare.

Chapter 14—Minimally invasive hormone monitoring methods can be used to evaluate the physiological responses of aquatic fish species to habitat quality. Here, the researchers validated mucous cortisol assays in wild freshwater fish (Catalan chub, *Squalius laietanus*) living across a pollution gradient. They compared the mucous cortisol levels with cortisol levels in blood and haematological parameters. The results showed that the variation in cortisol in skin mucus followed a similar pattern of response to that detected by the quantification of cortisol levels in blood and the hematological parameters, such as erythrocytic alterations and neutrophil to lymphocyte ratios. Skin mucus could be potentially used as a biomarker in fish welfare evaluation.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The author declares no conflict of interest.

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

©2020 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).


**4. Experimental Results**

#### *4.1. Description of the Experimental Prototype*

A 300 W prototype was built to demonstrate the feasibility of the proposed converter. The parameters and components used in the setup are listed in Table 1. The converter is designed for the target operating range shown in Figure 7b, which suits the PV applications and is similar to the previous studies [18–20]. Only generic Si MOSFETs are used in the input side to reduce the converter cost. The use of SiC devices at the output side is unavoidable due to high switching frequency.

The isolating transformer was built on an ETD39 core of 3C95 ferrite material. The transformer turns ratio *n* = 6 yields the output voltage of 350 V according to (18), which results in the boost mode at the input voltage below 30 V. The value of the output voltage is suitable for the integration with residential DC microgrids. The number of primary and secondary turns equals 9 and 54, respectively. This design yields the maximum flux density of the core of 60 mT in the worst case. Therefore, the core losses can be minimized. To reduce the skin e ffect and proximity losses in the transformer, 90 × 0.2 and 90 × 0.1 litz wires were used for the primary and secondary windings, respectively. They were interleaved to reduce the leakage inductance and insulated by the Kapton polyimide tape to minimize the capacitance between the layers. An external inductor was connected in series with the secondary winding of the transformer to increase the resonance inductance. The resonance frequency of the converter was aimed close to the switching frequency to ensure the ZVS of the primary-side MOSFETs [9]. The dead-time period between *S*1, *S*2 or *S*3, *S*4 equaled 190 ns. The PWM control signals were generated using the low-cost microcontroller STM32F334. The system e fficiency was measured by a Yokogawa WT1800 precision power analyzer.

$$m = \frac{V\_{OUT}}{2V\_{INm}}.\tag{18}$$


**1. Introduction**

Nephrolithiasis is a common disease, typically occurring between 30 and 60 years of age. It is the most often‐diagnosed chronic condition involving the kidney, after hypertension. The symptoms and consequences are not life threatening for the majority of patients, but stones in the urinary tract are a major cause of morbidity, hospitalization, and days lost from work [1]. The incidence of nephrolithiasis is increasing. In Italy, for example, the number of patients given hospital treatment for this condition rose between 1988 and 1993 from 60,000 to 80,000 a year. About 12,000 patients a year required surgical treatment or urological maneuvers, and the number of extracorporeal shock wave lithotripsy sessions administered amounted to approximately 50,000 a year [2].

The metabolic characteristics of the urinary stones identified in patients with nephrolithiasis vary, but the most common (accounting for 75% of all cases) are calcium‐containing stones. Calcium oxalate (CaOx) is the primary component of most stones [3], often combined with some calcium phosphate (CaP), which may form the stone's initial nidus. Crystal retention in the kidney is essential to stone formation and this occurs with several different patterns of deposition in the kidneys of stone formers, each pattern being associated with specific types of stone. Patients with idiopathic CaOx stones have white deposits on their papillae called "Randall's plaque" [4]. Biopsies of these areas reveal interstitial deposits of CaP in the form of biological apatite, which first develop in the basement membrane of the thin loops of Henle and which contain layers of protein matrix. These deposits may extend down to the tip of the papilla and, if the overlying urothelium is denuded, the exposed plaque can become an attachment site for stones [5]. Stones seem to start as deposits of amorphous CaP overlying the exposed plaque, interspersed with urinary proteins. With time, more layers of protein and mineral are deposited, and the mineral phase becomes predominantly CaOx.

By contrast, in patients whose stones consist mainly of CaP (apatite or brushite), these stones are not attached to plaque. Instead, many collecting ducts fill with crystal deposits that occupy the tubule lumen and may protrude from the openings in the ducts of Bellini. Generally speaking, most stone formers studied to date have had crystal deposits in the med‐ ullary collecting ducts, with the exception of those with idiopathic CaOx stones, who have no intratubular deposits, but abundant deposits of apatite in the papillary interstitium.

Calcium nephrolithiasis, the most common renal form of stone disease, is defined as the for‐ mation of macroscopic concretions of inorganic and organic material in the renal calyces and/ or pelvis. Many *in vitro* and *in vivo* studies on the mechanisms underlying calcium nephroli‐ thiasis have produced evidence of this condition frequently being associated with nephrocal‐ cinosis, a condition involving microscopic renal crystal deposition.


*6.4.2. Design philosophy*

428 Ultra-Wideband Radio Technologies for Communications, Localization and Sensor Applications

UWB sensor unit with portable power supply and UWB reflectometer (ILMSENS).

**6.4. Single-chip sensor head**

radar electronics into one silicon die.

*6.4.1. UWB single-chip head architecture*

**Figure 58.** Left-hand side: 1Tx 2 Rx UWB sensor unit (MEODAT). Middle and right-hand side: 1Tx 2Rx

The ability to create an optimized multi chip sensor is apparent, but the manufacturability of such system is much more difficult with a longer parts list and more complex assembly as for instance in the case of the construction of complex MIMO sensing systems (see 8Tx 16Rx system in the chapter 11). One promising way is to realize all active high-frequency system components (i.e. components on the primary RF board – see Fig. 57 left-hand side) onto one chip. This will enhance the overall system performance, reliability, robustness and assembling yields. By contrast, however, increased complexity on the single die means more second-order effects that have not been studied so far. For example, undesired on-chip coupling interactions between the different constituent system components become more pronounced and are more challenging to manage especially because of dealing with ultrawideband signals. Such unwanted signal coupling or cross-talk can degrade the performance of the sensitive receive circuitry and, consequently, of the whole system. The aim to study such interactions which have not been considered so far, the expected advantages but also the knowledge gained from multi-chip approach analyses, have motivated the first monolithic integration of the complete RF-part of the M-sequence UWB

Fig. 59 shows the simplified block topology of the realized M-Sequence based single-chip transceiver head (alias System-on-Chip, SoC head). In correspondence with the system topology depicted in Fig. 4, the M-sequence transceiver SoC contains one transmitter and

According to our experience, the 1Tx-2Rx topology of the primary sensor cell represents the optimum regarding achievable performance and circuit complexity. Moreover, the implementation of 1Tx 2Rx structure on one die has the advantage of permitting both crosstalk investigations between active and passive circuit parts (i.e. transmitter and receiver) as well as between two passive parts (i.e. receiver 1 and 2). From a practical point of view, the stand-alone 1Tx 2Tx devices are suitable for implementations where two receive channels are needed a priori, e.g. for simple localization tasks or in material testing (see chapter 11) in

two receiver circuits (commonly assigned as 1Tx 2Rx configuration).

It is apparent that the presented single chip architecture envisages ultra-fast switching cells (i.e. stimulus generator and synchronization unit) with their relatively high signal swing output buffers as well as very sensitive analog input blocks integrated on the same chip substrate. So, the undesired signal coupling or cross-talk can degrade the performance of the sensitive receive circuitry and, consequently, of the whole system. Especially in the case of analog devices, which handle the ultra-wideband signals, the on-chip interferences can be catastrophic. For example, intermodulation/interaction of noise components with the measured signal within the frequency band of interest may cause device saturation. Therefore, special emphasis is put on the isolation of the SoC channels during the design phase ,as discussed in [2] or [49].

### *6.4.3. Individual functional block peculiarities*

Particular functional circuit cores of the SoC transceiver components are designed to fulfill at minimum the parameters of the demonstrator plug-in blocks discussed above. Additionally, the SoC transceiver includes additional build-in options to open further functionalities as e.g. (equivalent time) oversampling [51] or frequency conversion in order to meet the UWB radiation rules [52]-[55]. In particular, the SoC concept is intended for very

### 430 Ultra-Wideband Radio Technologies for Communications, Localization and Sensor Applications

wideband material investigations and MIMO-applications like in medical microwave imaging [56]-[61].

HaLoS – Integrated RF-Hardware Components for Ultra-Wideband Localization and Sensing 431

an area of about 2000 1200 *µm µm* and the build-in circuits consume in total about 300 mA

**Figure 60.** Microphotograph of the SiGe M-Sequence based transceiver head die with depicted

For the sensor head prototype evaluation, the transceiver chip has been measured on wafer as well as packaged with well-established chip-on-board technology using an optimized composite 4-layer carrier made from Rogers 4003C™, FR4 laminate and ultrasonic bonding procedure with 1-mil aluminum wires. The bond wire landing areas for RF ports on the board are designed to match as closely as possible (i.e. realizable) the pitch on the IC to avoid long wire connections. The cavity approach has not been implemented because of challenging technological realization on the selected carrier board. Fig. 61 shows the test board whereat the wired die is zoomed out for better visualization. The die is located in the center of the photo and top glue is used to protect the bond wires. It is mounted on a metal patch which is connected with VEE. This allows a direct connection between the substrate and the board's lowest potential. The top layer is mainly used for RF signal routing whereas the bottom layer is used for control lines. The inner plane layer below the top layer is the common board GND, and it also provides the GND reference for the RF signal lines. The other inner plane is the supply layer. The supply is bypassed to the GND with a 0.1 µF

A basic test set-up for the sensor head prototype parameter evaluation is symbolically depicted in Fig. 62. The photograph on the right side shows an example of such test assembly. The evaluation board is connected to a 10-bit data "digitizer" (ADC), FPGA control and pre-processing unit which is equipped also with the PC interface. Moreover, for the parameter characterization, stable sinusoidal reference has to be connected to the system

particular functional blocks. The die size is 2 1.2 mm2.

ceramic capacitor placed as close as possible to the die.

*6.4.4. Single chip transceiver head evaluation*

from 3 V supply.

In summary, the goals of the single-chip integration are:

Thus, to achieve the desired MIMO usability, the shift register may be enabled and disabled, and transmitter buffers can be switched off (power down) by simple TTL-signals so that no external RF-switch is required to operate in a MIMO system. The transceivers are designed in such a way that they may either work while being driven individually or they may be cascaded with respect to the master system clock so that all units of a MIMO array work synchronously. Once the array is calibrated, a power down feature will be used for active transmitter selection. Thus, all receivers of MIMO array work in parallel and capture permanently data in order to get maximum measurement speed. As shown in Fig. 59, the transceiver IC is equipped with a wideband multiplier which optionally allows the sensor stimulus frequency band to be shifted and doubled ([2] or [49], [55]) or the operational band to be adapted to a specific application [50] in conformity with regulation requirements [52] - [54]. The channel is designed for operation up to 18 GHz.

Moreover, the multiplier can invert the stimulus M-sequence by implementing simple ECL signals on the control port. This feature may be useful to provide uncorrelated transmit signals in MIMO arrays. In addition, the sampling timing control chain is equipped with optional switchable shunt path. This add-on allows direct clock supplying from chip periphery. Thereby, user-selectable sampling rates or enhanced signal capturing approaches (e. g. equivalent time oversampling approach [50]) are possible without IC redesign. The analog receivers are designed to operate with wideband signals up to 18 GHz. The maximum linear operation input signal peak-peak swing is 60 mV.

Fig. 60 shows the chip die micrograph of the discussed transceiver with marked particular functional blocks and well visible top metal of a decoupling guard between the transmitter and receiver (line in the middle). The transmitter and receiver cores as well as their particular I/O pads are placed on the opposite die sides to minimize mutual on-chip coupling as well as inductive coupling between the bond wires after packaging. As extensively discussed in [62] or [63], [64], the decoupling guard is a guard well in a trench between the noisy transmitter and sensitive receivers. In the final assembly, the guard is connected to the quiet potential in order to fix the voltage of the substrate between the Tx and Rx die part by absorbing potential substrate fluctuations. The transceiver die occupies an area of about 2000 1200 *µm µm* and the build-in circuits consume in total about 300 mA from 3 V supply.

**Figure 60.**  The die size is 2 1.2 mm2.


*2.2. Kinetics of Rafting*

In the heart of rafting is a stress-limited diffusion process, depending on applied stress, σ*A*, lattice misfit, δ, and the difference between the mechanical property of γ and γ' phases, Δ*G* [3,40]. Both applied stress and inherent misfit stress play important roles in the distribution of internal stress in the grains/crystals consisting of γ and γ' phases due to the dependence of chemical potential on local stress state [40]. Under tensile loading, the difference of the chemical potentials between the γ' phase and the γ phase (γ channels) drives the forming atoms of the γ' phase (Al, Ti, Ta, etc.) in horizontal γ channels into vertical γ channels and drives nearly insoluble atoms (Co, Cr, Mo, Re, W, etc.) away from vertical γ channels. This results in the formation of raft structures perpendicular to the tensile loading, as shown in Figure 6 [41,42].

**Figure 6.** Schematic for the migration of solute atoms under tension in <001> direction.

Assuming that the stress-limited diffusion process is the dominant mechanism controlling the rafting, Fan et al. [34] proposed a von-Mises stress-based criterion in determining the rafting direction. Under concurrent action of external stress and misfit stress, the von-Mises stress in different γ channels can be calculated according to the formulations in Table 1. Dislocations can easily accumulate in γ channels under a large stress, leading to the relief of the misfit stress through the migration of the γ/γ' interface and the directional coarsening in the γ channels with maximum von-Mises stress [34,43].

**Table 1.** Calculation of the von-Mises stress in γ channels under uniaxial loading. Here, σ0 is applied stress in the global coordinate system, σ*i* is the magnitude of the misfit stress, and α is a reduction factor. Adapted from [34].

Geometrical characteristics of the microstructures have been used to determine the degree of rafting, such as the width of γ channels [34,44], the dimension of γ' phase [45], and the shape of γ' phase [46]. The images of the microstructures can be captured through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the geometrical characteristics of the microstructures can be then analyzed via image-processing algorithms. There are a few algorithms commonly used to analyze the SEM and TEM images, including Connectivity number method [46], AutoCorrelation Method [47,48], Rotational Intercept Method [48], Fourier analysis [9], and Moment invariants method [49].

Fedelich et al. [44] introduced a dimensionless variable ξ for the analysis of rafting as

$$\xi = \frac{w(t) - w\_{\text{cube}}}{w\_{\text{raft}} - w\_{\text{cube}}} \tag{1}$$

where *w*(*t*) is the width of the γ channel at time *t*, *wcube* and *wra f t* are the channel widths of the cubic structure and the raft structure, respectively. Their numerical values are correlated to the volume fraction of γ' phase, *f*γ, and the microstructure periodicity, λ. The dimensionless variable, ξ, varies in a range of 0 (initial cubic morphology) to 1 (complete raft morphology).

Tinga et al. [45] proposed an evolution law for the dimension of γ' phase under the action of a multiaxial stress as

$$\dot{L}\_{i} = \frac{-3}{2} L\_{i} \left[ \frac{\sigma\_{\text{ii}}^{\prime}}{\sigma\_{M} + \sigma\_{\delta}} \right] \frac{A^{\*}}{L\_{0}} exp \left[ \frac{-Q - \sigma\_{M} l L\_{T}}{RT} \right] \text{ ( $i = 1, 2, 3$ )}\tag{2}$$

where *Li* are the dimensions of γ' phase along three orthogonal directions, σ *ii* are the diagonal components of deviatoric stress tensor, σ*M* is von-Mises stress, and *UT* is thermal shear-activation volume, *Q*,*R*, and *T* are activation energy, gas constant, and absolute temperature, respectively, *A*∗ and σδ are constants, and *L*0 is the dimension of γ' precipitate in cubic shape. Desmorat et al. [50] used the width of γ channel and the dimensions of γ' phase as internal variables in the framework of thermodynamics with elasto-visco-plasticity and Orowan stress (dislocation mechanics). They calculated the Orowan stress τ*or*, which acts as a resistance to the dislocation motion in γ matrices, during the rafting in the following formulation,

$$
\tau\_{\rm or} = a\_{\rm or} \frac{\mu b}{w} \tag{3}
$$

where αor is a material constant ranging from 0.238 to 2.15 [51], and μ and *b* are the shear modulus and the magnitude of Burgers vector, respectively. Their simulation results provided quantitative description of the rafting behavior in nickel-based single crystal superalloys.

There exists the interaction between rafting and dislocation motion. Rafting leads to the accumulation of dislocations in the γ channels, resulting in the relief of the misfit stress through the migration of the γ/γ' interface and the directional coarsening of γ' precipitates. Without mechanical loading, rafting can also prevail at high temperature if the plastic strain in superalloys reaches a threshold value [52,53]. The deformation field (plastic strain) is associated with the presence of dislocations in crystal, even though there is no external loading. The dislocation motion in superalloys at high temperature relieves the misfit stress and promotes the directional coarsening of γ' precipitates through rafting. It is the plastic deformation in the γ matrices (channels) that determines the rafting process and the microstructure evolution.


**Author details**

Anwar Ali1 \*, Quratul Ain2 , Ayesha Saeed2 , Waseem Khalid3 , Munir Ahmed4 and Ahmed Bostani5

1 Department of Epidemiology and Health Statistics, Xingya School of Public Health, Central South University, Changsha, China

2 Department of Biochemistry, Government College University, Faisalabad, Pakistan

3 Department of Food Science and Technology, Government College University, Faisalabad, Pakistan

4 Department of Food Science and Engineering, Yangzhou University, Yangzhou, China

5 Department of Tourism and Hospitality Management, Dongbei University of Finance and Economics, Dalian, China

\*Address all correspondence to<EMAIL_ADDRESS>
© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


*3.1.7. Hydrogenation of benzoic acid with cobalt catalysts*

Cobalt metal catalyst has been reported for the hydrogenation of carboxylic acid to alcohols [6]. Hydrogenation of benzoic acid was carried out with 5%Co/C, Co metal, and Ru-Co catalysts. These catalysts were, however, found to be inactive for the hydrogenation of both aromatic and carboxylic groups of BZA under the conditions mentioned in **Table 1**.

**Table 2.** Hydrogenation of benzoic acid with 5% Ru on different supports.

**Scheme 4.** Hydrogenation of benzoic acid with 5%Ru-29%Sn/Al2 O3 catalyst.


**1. Introduction**

With the development of technologies such as industrial robots and computer image processing, a series of research and experiments on intelligent picking robots have been carried out in Japan and other related countries, such as tomato, apple, and grape picking robots [1]. Research on picking robots has focused on two parts: the first is a hardware device that can achieve rapid picking, that is, how to design a stable, efficient, and adaptable mechanical and visual sensing system, and the second is to design intelligent software for continuous operations, that is, to accurately identify, distinguish, and locate targets and to solve the problem of task planning and task scheduling during continuous picking operations.

In the research field of picking robots, Kondo et al. [2] designed a tomato picking robot using a 7-degree-of-freedom manipulator. It used fingers and pneumatic nozzles in conjunction with a color camera to complete the picking operation. The experiment achieved a picking success rate of about 70% [3]. Tanigaki et al. [4]

developed a cherry picking robot using a four-degree-of-freedom manipulator and a specially designed end effector with suction and shear functions. The visual part uses a light emitter, a photodetector, and a scanning device. The fruit was picked in 14 s, and the success rate was about 84%. The CROPS plan completed in 2014 was jointly completed by many European countries and units and aims to develop a modular picking robot system for different mission scenarios. The greenhouse bell pepper picking robot platform completed in the experiment in the Netherlands [5] used a 9-degree-of-freedom manipulator, two color CCD cameras and a depth-measuring camera, and its end effector was also equipped with a small camera to complete the picking with higher accuracy. Taqi et al. [6] have developed small household cherry tomato picking robots that can achieve very accurate picking tasks in specific environments.

The continuous operation of the picking robot can make intelligent decisions on multi-task under multi-objective scenarios and plan the operation according to the picking needs. The research goal is that the picking robot system can intelligently select and pick fruits that meet the picking conditions, thereby greatly improving the degree of automation of the picking process and improving the quality of the harvested fruits. Because the picking robot is still in the laboratory research stage, the research on continuous operation is also very limited, and it is basically in its infancy. Japan's Nagata et al. [7] used the shape to judge and classify strawberry quality. The accuracy in the experiment is acceptable, but the speed is much slower than artificial. Zhao et al. [8] investigated the visual recognition of apple maturity, using multi-spectral laser beams to complete fruit identification and positioning and ripeness judgment. Guo [9] and others judged strawberry maturity based on HIS color space algorithm. In the field test, the accuracy of the goal of picking fruits with maturity of 80% or more was more than 90%. Wang [10] and Ling et al. [11] carried out research on selective harvest information acquisition and path planning of tomato picking robots. Multi-sensor information fusion method was used for tomato quality detection and classification and selective picking decision. The appearance maturity of the fruit is detected by the H-means in the computer image, the fruits are classified in real time according to the agricultural industry standards, and the selective harvesting decision is made through the progressive identification of feature information and the fusion decision. At harvest time, path planning is performed on multiple targets through an optimization algorithm and then boxed by level.

This chapter mainly focuses on developing an intelligent software system for the continuous operation of the dual-arm picking robot in a plant factory. Typically, the semi-structure environment of the greenhouse poses challenges for autonomous operations of the robot, and the complex tasks mainly include identification and positioning under variable light conditions, selective picking in multi-cluster growth environment, and complex multi-task programming. For the difficulty of developing the software system, a hierarchical modular software system framework is designed. Moreover, a scheduling method of functional modules is designed based on the idea of finite state machine for the complex multi-task planning problem of tomato continuous picking process. The task scheduling design based on the Finite State Machine (FSM) reduces the difficulty of development work and improves the efficiency of development.

This chapter is organized as follows: Section 2 briefly describes the hardware structure of a dual-arm robot, and Section 3 presents the software framework with the highlights of deploying SMACH- and ViSP-based nodes in a ROS development environment. The experimental results are also included at the end of Section 3.

**111**

**Figure 1.**

*The structure of the robot body.*

*Manipulating Complex Robot Behavior for Autonomous and Continuous Operations*

The semi-structured operating environment in the plant factory is relatively complicated, such as the occlusion of fruit branches and leaves, the challenging grasping shape of the fruit, the changing light, and the variety of tasks, which requires to consider the multi-tasking ability of the robot when designing the hardware of the picking robot. At the same time, the complexity of the picking environment requires that the execution of the robot be robust to the environment in which the target is located, only in this way can it pick fruits in different states. Based on the above two design goals, we designed a dual-arm picking robot to

The mechanical structure of the robot body mimics human arms, and the left and right arms each have three joints: a vertical lift joint, a boom rotation joint, and a forearm rotation joint. The vertical lifting joint is driven by a servo motor to drive the roller screw. The actual effective stroke is about 300 mm. The big and small arm joints are driven by a servo motor connected to a harmonic reducer. There is a waist joint between the body and the base, which can provide 360° rotary motion. The single-arm movement of the robot is similar to that of the SCARA robot. The vertical positioning is achieved by the lifting joint, and the rotation of the large and small arms realizes the positioning in the plane. There are three degrees of freedom in motion. Each of the left and right forearms is designed with a mounting flange surface, and end effectors can be installed as required. The dual-arm robot base is installed on a mobile cart and is transported along the track to different picking

Due to the limitation of the freedom of the robot body, for complex tomato picking environments, it is not enough to rely only on the freedom of the arms, so we can use the design of the end effector to increase the freedom of our robot and enable the robot to flexibly complete the picking operation. We designed a shearing end effector on the cutting hand of the dual-arm robot and designed a suction-type end sleeve on the auxiliary hand to fix the target tomato and assist the hand in

*DOI: http://dx.doi.org/10.5772/intechopen.92254*

simulate human picking operations.

**2.1 Design of dual-arm robot body**

points for picking operations.

picking (**Figure 1**).

**2. Hardware design of a dual-arm robot**

*Manipulating Complex Robot Behavior for Autonomous and Continuous Operations DOI: http://dx.doi.org/10.5772/intechopen.92254*


**7. Conclusion**

*Environmental Issues and Sustainable Development*

*6.3.1 Principles of integrated sustainable waste management*

All citizens should be exposed to appropriate waste management system for

The major concern of waste management is to maximize the benefits, lower the costs and optimize the use of resources, taking into account, equity, effectiveness

The waste management system is appropriate to the local conditions and feasible from a technical, environmental, social, economic, financial, institutional and political perspective. It can maintain itself overtime without exhausting the

*6.3.2 Components of integrated sustainable waste management*

2.The (practical and technical) elements of the waste system

The waste management model should ensure safe removal of waste.

**176**

*<IP_ADDRESS> Equity*

**Figure 6.**

*<IP_ADDRESS> Effectiveness*

*<IP_ADDRESS> Efficiency*

and sustainability.

*<IP_ADDRESS> Sustainability*

resources upon which it depends.

1.The stakeholders

environmental health reasons.

*Integrated sustainable waste management.*

The main prospective of hazardous waste management program is to change the way of managing hazardous waste so that they can be stored, transported and dispose in an environmentally safe manner. The focus of managing hazardous waste comes in an effort to address potential threats to public health and environment. Hazardous waste management must have an initiative beyond disposing directly into the land surface. Industries are encouraged to generate less amount of hazardous waste as a part of manufacturing process. Because the toxic wastes cannot be completely eliminated and only possible way is to minimizing, recycling, and treating wastes. So steps should be taken to use the modern technology without causing any threat to environment. Minimizing, recycling, and treating wastes.


**4. The differences between functional foods and herbs with edited genomes**

Scientific evidence shows a great relationship between functional foods and improvement of physiological condition. It is also important to achieve health-related results, particularly in the case of chronic diseases and pandemics. Several studies and clinical trials for herbal nutrition exist. In fact, functional foods have been accepted as mainstream medicine for generations. Based on the literature review, it may be suggested that functional foods are safe to use. They have several health benefits such as preventing adverse effects, increasing the beneficial effect on health, and improving health status [1, 2, 9, 10, 15].

Genome editing of herbs is an exciting innovation for agricultural, nutritional, and pharmacological areas. Some foods designed to modify the genome have been in use for 25 years. This technology is addressed in the cultivation of first-generation transgenic crops, and it permits gene deletion, insertion, silencing, and gene knock-out. The main problem in genome editing is off-target effect. The off-target effect results in inadequacy and typing error, and undesired mutations occur. These off-target activities may change in organisms. However, any such mismatches can be guessed through computer programs [67]. There have been several studies to decrease these effects [68, 69].

Unlike random recombinant methods, CRISPR/Cas9 editing technology is accepted as target-specific. On the contrary, especially in rice, the off-target sites of CRISPR/ Cas9 editing are still unknown [70]. However, studies have shown that there are no nontarget DNA changes in rice mutants generated by CRISPR/Cas9, which should be important for the regulation of gene-modified breeding [71, 72]. In addition, it was reported that besides rice, *Arabidopsis*, cotton, and tobacco have indicated off-target mutations rarely [73]. However, some studies have indicated that off-target mutations are possible. Thus, genome editing still leaves room for improvement for the future.


*Article* **Waste Wood Particles from Primary Wood Processing as a Filler of Insulation PUR Foams**

**Radosław Mirski , Dorota Dukarska \* , Joanna Walkiewicz \* and Adam Derkowski**

Department of Wood Based Materials, Faculty of Forestry and Wood Technology, Pozna ´n University of Life Sciences, Wojska Polskiego 38/42, 60-627 Pozna ´n, Poland<EMAIL_ADDRESS>(R.M<EMAIL_ADDRESS>(A.D.)

**\*** Correspondence<EMAIL_ADDRESS>(D.D<EMAIL_ADDRESS>(J.W.)

**Abstract:** A significant part of the work carried out so far in the field of production of biocomposite polyurethane foams (PUR) with the use of various types of lignocellulosic fillers mainly concerns rigid PUR foams with a closed-cell structure. In this work, the possibility of using waste wood particles (WP) from primary wood processing as a filler for PUR foams with open-cell structure was investigated. For this purpose, a wood particle fraction of 0.315–1.25 mm was added to the foam in concentrations of 0, 5, 10, 15 and 20%. The foaming course of the modified PUR foams (PUR-WP) was characterized on the basis of the duration of the process' successive stages at the maximum foaming temperature. In order to explain the observed phenomena, a cellular structure was characterized using microscopic analysis such as SEM and light microscope. Computed tomography was also applied to determine the distribution of wood particles in PUR-WP materials. It was observed that the addition of WP to the open-cell PUR foam influences the kinetics of the foaming process of the PUR-WP composition and their morphology, density, compressive strength and thermal properties. The performed tests showed that the addition of WP at an the amount of 10% leads to the increase in the PUR foam's compressive strength by 30% (parallel to foam's growth direction) and reduce the thermal conductivity coefficient by 10%.

**Keywords:** polyurethane foams; filler; wood particles; structure; properties

#### **1. Introduction**

In recent years, people's environmental awareness has been increasing, which has led to the search for solutions that will allow the use of technologically processed byproducts. Due to the increasing development in the wood industry, waste generation is a common problem. Two by-products of wood processing are dust and wood particles. Despite the fact that research is carried out with the use of wood dust in the context of various materials, this material is still a nuisance waste. Nowadays, the most popular composite containing wood (of any form) is a wood plastic composite (WPC) [1]. Research concerning the application of WP was also conducted in order to enhance the properties of thermoplastic starch [2]; as a component in adhesive mixtures for 3D printing [3]; in concrete as a partial replacement for sand [4]; and in the production of new polyurethane foams from liquefied wood powder [5]. Wood waste can also be applied as a potential filler for loose-fill building isolation [6].

PUR represents a wide class of polymeric materials [7,8]. Polyurethane foams account for 2/3 of the world's production of polyurethanes, and because of their numerous applications in the form of rigid, semi-rigid and flexible foams, they are continuously highly ranked among all of available foams [9]. PUR foams are the product of the addition polymerization of polyols and polyisocyanates. Catalysts, surfactants and foaming agents are also used during the production of PUR. These foams may differ in composition, density, color and mechanical properties. There are also studies where fillers were used to lower the cost and increase mechanical properties, e.g., the modulus and strength or density [10].

**Citation:** Mirski, R.; Dukarska, D.; Walkiewicz, J.; Derkowski, A. Waste Wood Particles from Primary Wood Processing as a Filler of Insulation PUR Foams. *Materials* **2021**, *14*, 4781. https://doi.org/10.3390/ma14174781

Academic Editors: Réh Roman, L'uboš Krišt'ák and Petar Antov

Received: 11 August 2021 Accepted: 20 August 2021 Published: 24 August 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Polyurethane foams, particularly flexible polyurethane foams, are commonly used in the building, automotive, furniture and packaging industries [11–15]. These foams have many advantages, such as a wide range of flexibility, good shock absorption and high durability in use. Moreover, they can be easily formed into various shapes, and they are characterized by a low density. However, they are not cheap. It is also worth adding that there is an opportunity to easily control and manage their parameters by changing their composition or using fillers [16].

Literature data clearly indicate that the organic or inorganic fillers can significantly improve the mechanical and thermal properties of PUR composites [17–20]. The introduction of inorganic fillers such as glass fibers or carbon fibers in polyurethane foams is a well-known process [21]. The fillers strongly affect the physical properties of foam. Not only inorganic fillers are used in foam formulations, but they can also be filled with materials of natural origin, such as plant and agricultural waste. Agricultural waste has the potential to be used in the production of PUR foams as renewable bio-based fillers [17]. Członka et al., Kerche et al., and De Avila Delucis et al. [19,22,23] claimed that the use of agricultural waste in the production of PUR materials can result in a new approach in the application path and provide a new opportunity for creating a new class of green materials. Paciorek-Sadowska et al. [17] used rapeseed cake as an addition for PUR composite production. Authors observed that 30–60% incorporation of rapeseed cake significantly influenced the apparent density and mechanical properties. Modified sunflower cake was added to PUR foam, and it was found that the addition of plant waste had an impact on the improvement of the mechanical properties, while it did not cause a significant deterioration of the insulating properties [24]. Funabashi et al. [21] researched the effect of filler types on mechanical properties of a rigid polyurethane composite. For this purpose, authors used particles from plant wastes (e.g., bamboo powder, coffee grounds, wood meal and cellulose). Zieleniewska et al. [25] obtained the composites of rigid polyurethane foams (RPURF) with the use of waste hazelnut shells, suitable for applications in the cosmetics industry. Moreover, rice plant wastes were used as a reinforcing material in the concentrations of 5%, 10%, 15% and 20% [26]. According to the literature, wood waste can also be a valuable raw material for the production of biocomposite PUR foams. According to Augaitis et al. [6], their application is beneficial due to their high availability, low cost and content of free hydroxyl groups capable of reacting with isocyanate groups. These authors showed that a biocomposite PUR foam with an apparent density of 150 kg/m3 and a PUR to pinewood sawdust ratio of 0.7 is characterized by very good physical and insulating properties and high strength. In turn, in this paper, an innovative solution has been proposed to use waste wood particles from primary wood processing as a filler for PUR foam. To the best of our knowledge, this type of filler has not been used in the process of producing insulating PUR foams with open-cell structure so far. It seems that such operations are beneficial from an economic and technological perspective. They enable us to increase the rational utilization of wood waste as full-value raw material without the need for their further processing (e.g., fragmentation, gluing, etc.). It should be emphasized that, for many years, there has been a growing interest in the use of wood waste, mainly in the wood, paper, polymer-wood composite, and energy industries. This is due to the necessity of sustainable management of this type of waste, whose resources increase with the development of the wood industry and the demand for wood-based products. This is evidenced, among others, by current technological trends in the production of wood-based materials and numerous studies indicating the possibility of producing full-value products from recycled wood or directly from primary wood processing [27–33].

The aim of this study was to apply the waste wood particles (WP) from primary wood processing as a filler of open-cell PUR foams. The effects of wood waste's introduction on the apparent density, cellular morphology, mechanical and thermal properties of PUR foams were examined and discussed.

This paper is a continuation of the previous research conducted by the authors concerning the possibility of using by-products from wood processing in order to manufacture

materials with improved properties, which are used, e.g., in construction and in the production of interior design elements [30–32]. ture materials with improved properties, which are used, e.g., in construction and in the production of interior design elements [30–32]. ture materials with improved properties, which are used, e.g., in construction and in the production of interior design elements [30–32].

This paper is a continuation of the previous research conducted by the authors concerning the possibility of using by-products from wood processing in order to manufac-

This paper is a continuation of the previous research conducted by the authors concerning the possibility of using by-products from wood processing in order to manufac-

*Materials* **2021**, *14*, x FOR PEER REVIEW 3 of 14

*Materials* **2021**, *14*, x FOR PEER REVIEW 3 of 14

#### **2. Materials and Methods 2. Materials and Methods 2. Materials and Methods**

#### *2.1. Materials 2.1. Materials 2.1. Materials*

A two-component foam system for the production of open-cell polyurethane thermal insulation PUREX-WG 2017 (Polychem System, Pozna´n, Poland) was used in the research. One of the components was a polyol (A component). The isocyanate component (B component) was polymeric methylenediphenyl-4,40 -diisocyanate consisting of 31.14% free isocyanate groups (NCO). A two-component foam system for the production of open-cell polyurethane thermal insulation PUREX-WG 2017 (Polychem System, Poznań, Poland) was used in the research. One of the components was a polyol (A component). The isocyanate component (B component) was polymeric methylenediphenyl-4,4′-diisocyanate consisting of 31.14% free isocyanate groups (NCO). A two-component foam system for the production of open-cell polyurethane thermal insulation PUREX-WG 2017 (Polychem System, Poznań, Poland) was used in the research. One of the components was a polyol (A component). The isocyanate component (B component) was polymeric methylenediphenyl-4,4′-diisocyanate consisting of 31.14% free isocyanate groups (NCO).

Wood particles (WP) representing a dimensional fraction of 0.315–1.25 mm were used as a filler (Figure 1). WP were obtained as a result of sorting sawdust intended for the production of chipboard. The moisture content of WP ranged between 0.2% and 0.5%. Figure 2 presents their fractional composition. The largest shares were observed for the fractions of 0.315 and 0.630 mm. The wood particles were added to the foam at the concentrations of 0, 5, 10, 15 and 20% determined according to a weight ratio. The amount of filler was determined based on preliminary studies and a literature review on the manufacture of biocomposite PUR foams [6,17,34,35]. Wood particles (WP) representing a dimensional fraction of 0.315–1.25 mm were used as a filler (Figure 1). WP were obtained as a result of sorting sawdust intended for the production of chipboard. The moisture content of WP ranged between 0.2% and 0.5%. Figure 2 presents their fractional composition. The largest shares were observed for the fractions of 0.315 and 0.630 mm. The wood particle*s* were added to the foam at the concentrations of 0, 5, 10*,* 15 and 20% determined according to a weight ratio. The amount of filler was determined based on preliminary studies and a literature review on the manufacture of biocomposite PUR foams [6,17,34,35]. Wood particles (WP) representing a dimensional fraction of 0.315–1.25 mm were used as a filler (Figure 1). WP were obtained as a result of sorting sawdust intended for the production of chipboard. The moisture content of WP ranged between 0.2% and 0.5%. Figure 2 presents their fractional composition. The largest shares were observed for the fractions of 0.315 and 0.630 mm. The wood particle*s* were added to the foam at the concentrations of 0, 5, 10*,* 15 and 20% determined according to a weight ratio. The amount of filler was determined based on preliminary studies and a literature review on the manufacture of biocomposite PUR foams [6,17,34,35].

**Figure 1.** Wood particles used as a filler for PUR foams. **Figure 1.** Wood particles used as a filler for PUR foams. **Figure 1.** Wood particles used as a filler for PUR foams.

**Figure 2.** Fractional composition of wood particles added to PUR foams. **Figure 2.** Fractional composition of wood particles added to PUR foams. **Figure 2.** Fractional composition of wood particles added to PUR foams.

#### *2.2. Synthesis of PUR Composite Foams 2.2. Synthesis of PUR Composite Foams*

*2.2. Synthesis of PUR Composite Foams*  The course of foaming of the modified PUR foams was characterized on the basis of the times of the successive stages of this process and the maximum foaming temperature. The course of foaming of the modified PUR foams was characterized on the basis of the times of the successive stages of this process and the maximum foaming temperature. The course of foaming of the modified PUR foams was characterized on the basis of the times of the successive stages of this process and the maximum foaming temperature. For this purpose, the foam components were mixed in a weight ratio premised in accordance with the manufacturer's recommendations, i.e., A:B = 100:100. The reaction mixture was prepared by mixing the appropriate amounts of wood particles with component B and

then adding component A (Figure 3). The reaction mixture was stirred with a low-speed mechanical stirrer at 1200 rpm for 10 s, at a temperature of 23 ◦C, and then poured into a form with internal dimensions of 250 × 250 × 130 mm3 . After that, PUR-WP composites were allowed to grow and were left at room temperature for 24 h. Each foam variant was prepared in two replicates. The obtained foams were cut with a band saw (Holzstar, Hallstadt, Germany) into specimens of dimensions necessary for testing their properties. and then adding component A (Figure 3). The reaction mixture was stirred with a lowspeed mechanical stirrer at 1200 rpm for 10 s, at a temperature of 23 °C, and then poured into a form with internal dimensions of 250 × 250 × 130 mm3. After that, PUR-WP composites were allowed to grow and were left at room temperature for 24 h. Each foam variant was prepared in two replicates. The obtained foams were cut with a band saw (Holzstar, Hallstadt, Germany) into specimens of dimensions necessary for testing their properties.

For this purpose, the foam components were mixed in a weight ratio premised in accordance with the manufacturer's recommendations, i.e., A:B = 100:100. The reaction mixture was prepared by mixing the appropriate amounts of wood particles with component B

*Materials* **2021**, *14*, x FOR PEER REVIEW 4 of 14

**Figure 3.** Scheme of PUR manufacturing (A—polyol; B—isocyanate; WP—wood particle*s*). **Figure 3.** Scheme of PUR manufacturing (A—polyol; B—isocyanate; WP—wood particles).

#### *2.3. Kinetic of PUR Foaming 2.3. Kinetic of PUR Foaming*

The influence of wood filler on the foaming process of PUR foams was determined by measuring the following times: The influence of wood filler on the foaming process of PUR foams was determined by measuring the following times:

• tack-free—the time measured until the foam solidified completely. The foaming temperatures were measured with a thermocouple immersed in the reaction mixture. The temperature was always read after the foam growth was completed. At the end, the average of 5 individual measurements was evaluated. The foaming temperatures were measured with a thermocouple immersed in the reaction mixture. The temperature was always read after the foam growth was completed. At the end, the average of 5 individual measurements was evaluated.

#### *2.4. Characterization of PUR Sample*

*2.4. Characterization of PUR Sample*  The density of neat PUR foam and PUR-WP composites, defined as the ratio of the sample mass to its volume, was determined in accordance with the PN-EN ISO 845 standard. Samples with the dimensions 50 × 50 × 50 mm3 were used. The samples were measured with a thickness gauge with an accuracy of 0.01 mm and weighed on an analytical The density of neat PUR foam and PUR-WP composites, defined as the ratio of the sample mass to its volume, was determined in accordance with the PN-EN ISO 845 standard. Samples with the dimensions 50 × 50 × 50 mm3 were used. The samples were measured with a thickness gauge with an accuracy of 0.01 mm and weighed on an analytical weight with an accuracy of 0.001 g.

weight with an accuracy of 0.001 g. The compressive strength in parallel direction to the foam's growth was investigated in accordance with the recommendations of EN 826 standard using a Tinius Olsen H10KT testing machine (Tinius Olsen Ltd., Salfords, UK). The test covered foam samples with dimensions of 50 × 50 × 50 mm3, which were compressed in the direction of foam growth at a rate of 5 mm/min and the load cell of 250 N. The compressive strength (σ10%) was defined as the maximum compressive force achieved when the relative deformation at deflection was less than 10% (based on the initial cross-sectional area of the specimen). The compressive strength in parallel direction to the foam's growth was investigated in accordance with the recommendations of EN 826 standard using a Tinius Olsen H10KT testing machine (Tinius Olsen Ltd., Salfords, UK). The test covered foam samples with dimensions of 50 × 50 × 50 mm3 , which were compressed in the direction of foam growth at a rate of 5 mm/min and the load cell of 250 N. The compressive strength (σ10%) was defined as the maximum compressive force achieved when the relative deformation at deflection was less than 10% (based on the initial cross-sectional area of the specimen). The means of the compressive strength were evaluated based on the 7 individual measurements.

The means of the compressive strength were evaluated based on the 7 individual measurements. The thermal conduction coefficient was determined using a heat flux density sensor type ALMEMO 117 company Ahlborn (Holzkirchen, Germany), with plate dimensions of 100 × 30 × 3 mm3 . The average values of the thermal conduction coefficient were evaluated on the basis of 5 individual measurements. A detailed description of the research method was presented in the previous works by the authors [36,37].

In order to determine the cellular structure, a scanning electron microscope (SEM) and a light microscope were used. SEM analyses were carried out with the use of an SU3500 Hitachi microscope. The images of the sample plane were prepared using a computer image analyzer equipped with a stereoscopic optical microscope (Motic SMZ-168, Hongkong, China) and a camera (Moticam 5.0, Barcelona, Spain). The image of the structure was transferred by a camera to the monitor screen, and then pictures were taken using the Motic Images Plus 3.0 program (Hongkong, China). The cell sizes of pure PUR foam and PUR-WP composite foams were determined using the same equipment.

The samples with the dimensions 50 × 50 × 50 mm3 were collected in order to evaluate the dispersion of WP in PUR foam using computer tomography which is a type of X-ray tomography allowing to obtain cross-sections of the examined object. Scanning was performed with the use of a Hyperion X9Pro tomography, with objects scanned at a resolution of 0.3 mm at a lamp voltage of 90 kV.

The yielded test results of PUR foams with wood particles addition were analyzed statistically using STATISTICA software v.13.1(StatSoft Inc., Tulsa, OK, USA). Mean values of the parameters were compared in a one-factor analysis of variance—post hoc Tukey's test allowed us to distinguish homogeneous groups of mean values for each parameter for *p* = 0.05.

#### **3. Results and discussion**

#### *3.1. The Impact of WP Filler on PUR Foams Manufacture*

The parameters characterizing the foaming process of the tested foams are presented in Figures 4 and 5. It can be concluded that the addition of wood particles to the open-cell PUR foam influences the kinetics of the foaming process of the PUR-WP composition. It was observed that the addition of this type of filler accelerates the onset of foam growth. This phenomenon is particularly evident in the case of PUR-WP compositions containing 10% and 15% of particles. In the case of these variants, a reduction in the starting time by approx. 29% was observed. These statistically significant differences were confirmed by the post hoc test. Statistical analysis allowed for the identification of four different groups of average foam expansion start times for the tested variants. However, mixing the foam components with wood particles had an adverse effect, and it led to extensions in the foams increases the growth time and their gelling times. With the maximum addition of wood particles, the growth time was extended by 23%, and the gel time by 33%. The extension of these times is the effect of slowing down the exothermic reaction, which is also evidenced by the decrease in the maximum foaming temperature of the foams. As shown in Figure 5, the addition of wood particles to the components of foamed PUR foam caused a decrease in the foaming temperature from 95 to 82 ◦C. According to the literature, the reduction in the maximum foaming temperature of PUR foams results from the reduced amount of heat generated during the reactions occurring in the latent stages and growth, used at the stage of foam stabilization and maturation. In addition, as shown in previous studies, organic fillers introduced into PUR foams can absorb some of the heat generated during synthesis, thus lowering the temperature of their foaming [19,38]. An insufficient amount of heat could slow down the cross-linking reaction and, consequently, extend the time required to achieve a track-free time, which is also confirmed by the data presented in Figure 4 [9]. Moreover, the presence of the wood particles and their relatively large dimensions undoubtedly limited both the growth of the foam cells and the susceptibility of the composition to the foaming process. According to Str ˛akowska et al. [24], the presence of fillers also limits the mobility of the polymer and the speed of the polymerization reaction. Moreover, as reported by Członka et al. [39], hydroxyl groups present in lignocellulosic fillers can react with highly reactive isocyanate groups. This affects the stoichiometry of the system and reduces the number of isocyanate groups capable of reacting with water, which results in a reduction in the amount of CO2 released.

with water, which results in a reduction in the amount of CO2 released.

with water, which results in a reduction in the amount of CO2 released.

*Materials* **2021**, *14*, x FOR PEER REVIEW 6 of 14

reaction. Moreover, as reported by Członka et al. [39], hydroxyl groups present in lignocellulosic fillers can react with highly reactive isocyanate groups. This affects the stoichiometry of the system and reduces the number of isocyanate groups capable of reacting

reaction. Moreover, as reported by Członka et al. [39], hydroxyl groups present in lignocellulosic fillers can react with highly reactive isocyanate groups. This affects the stoichiometry of the system and reduces the number of isocyanate groups capable of reacting

**Figure 5.** Values of the maximum foaming temperature of PUR-WP composition depending on wood particle content. **Figure 5.** Values of the maximum foaming temperature of PUR-WP composition depending on wood particle content. **Figure 5.** Values of the maximum foaming temperature of PUR-WP composition depending on wood particle content.

#### *3.2. Density, Thermal Conductivity and Microstructure of PUR Foams 3.2. Density, Thermal Conductivity and Microstructure of PUR Foams*

*3.2. Density, Thermal Conductivity and Microstructure of PUR Foams*  As expected, the addition of the wood particles causes a significant increase in the density of the PUR-WP composite. The apparent density of pure PUR foam was 20 kg/m3 (Figure 6). The introduction of 5% wood filler particles into its structure caused a slight increase in its density; however, the HSD Tukey test did not confirm statistically significant differences. The mean density values obtained for these two variants belong to the same homogeneous groups. A significant increase in the density of the produced foams was noticed only when larger amounts of wood particles were used, i.e., from 10% and As expected, the addition of the wood particles causes a significant increase in the density of the PUR-WP composite. The apparent density of pure PUR foam was 20 kg/m3 (Figure 6). The introduction of 5% wood filler particles into its structure caused a slight increase in its density; however, the HSD Tukey test did not confirm statistically significant differences. The mean density values obtained for these two variants belong to the same homogeneous groups. A significant increase in the density of the produced foams was noticed only when larger amounts of wood particles were used, i.e., from 10% and As expected, the addition of the wood particles causes a significant increase in the density of the PUR-WP composite. The apparent density of pure PUR foam was 20 kg/m3 (Figure 6). The introduction of 5% wood filler particles into its structure caused a slight increase in its density; however, the HSD Tukey test did not confirm statistically significant differences. The mean density values obtained for these two variants belong to the same homogeneous groups. A significant increase in the density of the produced foams was noticed only when larger amounts of wood particles were used, i.e., from 10% and more. With their addition in the amount of 20%, the average apparent density of the foam was 34.6 kg/m3 , i.e., it increased in comparison to pure foam by as much as 73%.

**Figure 6.** Thermal conductivity and density of PUR-WP composition depending on wood particle content. Different letters indicate homogeneous groups of mean values determined by one-factor ANOVA with Tukey's test. **Figure 6.** Thermal conductivity and density of PUR-WP composition depending on wood particle content. Different letters indicate homogeneous groups of mean values determined by one-factor ANOVA with Tukey's test.

more. With their addition in the amount of 20%, the average apparent density of the foam

Along with the increase in the density of the tested foams, the statistically significant changes in their thermal insulation, determined by the thermal conductivity coefficient λ, were also observed. This is confirmed by the results of the post hoc test and the homogeneous groups of mean values λ distinguished on its basis. Moreover, the test probability level was significantly lower than the assumed level of statistical significance, i.e., <0.05. As follows from the data presented in Figure 6, the use of wood particles as a filler for PUR foam at an amount of up to 10% leads to the reduction in the average λ value by approx. 10%, which proves the improvement of thermal insulation of this type of foam.

was 34.6 kg/m3, i.e., it increased in comparison to pure foam by as much as 73%.

Unfortunately, a further increase in the wood particle content results in a gradual increase in the value of λ. In the case of the 15% addition of wood filler, the value of λ was lower than the coefficient which the pure foam was characterized by, but higher than that of foams with 10% of wood particles. It should be noted that even with the maximum concentration of wood particles used in the tests (i.e., 20%), the value of the thermal conductivity coefficient was at a level comparable to that of pure PUR foam. Similar observations were made by Tao et al. [34]. The authors noted a decrease in the value of the coefficient λ by as much as 50%, while higher amount of lignocellulosic fibers (up to 20 php) Along with the increase in the density of the tested foams, the statistically significant changes in their thermal insulation, determined by the thermal conductivity coefficient λ, were also observed. This is confirmed by the results of the post hoc test and the homogeneous groups of mean values λ distinguished on its basis. Moreover, the test probability level was significantly lower than the assumed level of statistical significance, i.e., <0.05. As follows from the data presented in Figure 6, the use of wood particles as a filler for PUR foam at an amount of up to 10% leads to the reduction in the average λ value by approx. 10%, which proves the improvement of thermal insulation of this type of foam.

resulted in a gradual increase in thermal conductivity to a level exceeding that of pure PUR foam. This method of shaping the thermal insulation properties of the tested PUR-WP compositions may result mainly from disturbances in the cell structure of the foams. This might be manifested by changes in the distribution of cell sizes. As shown in the literature, such changes have a significant impact on the insulation properties and mechanical strength of PUR foams. As shown in Figure 7, pure PUR foam is characterized by a uniform cell size distribution, mainly within the range of 150–450 µm. The mean cell size in the range of the highest frequency is 224 µm. Introducing relatively small amount of wood Unfortunately, a further increase in the wood particle content results in a gradual increase in the value of λ. In the case of the 15% addition of wood filler, the value of λ was lower than the coefficient which the pure foam was characterized by, but higher than that of foams with 10% of wood particles. It should be noted that even with the maximum concentration of wood particles used in the tests (i.e., 20%), the value of the thermal conductivity coefficient was at a level comparable to that of pure PUR foam. Similar observations were made by Tao et al. [34]. The authors noted a decrease in the value of the coefficient λ by as much as 50%, while higher amount of lignocellulosic fibers (up to 20 php) resulted in a gradual increase in thermal conductivity to a level exceeding that of pure PUR foam.

particles (i.e., 5 wt.%) to the system reduces the number of cells in the size range of 200– 250 µm. At the same time, it increases the number of cells above this range, i.e., within the range of 300–450 µm. However, the mean cell size with the highest frequency is still in the This method of shaping the thermal insulation properties of the tested PUR-WP compositions may result mainly from disturbances in the cell structure of the foams. This might be manifested by changes in the distribution of cell sizes. As shown in the literature, such changes have a significant impact on the insulation properties and mechanical strength of PUR foams. As shown in Figure 7, pure PUR foam is characterized by a uniform cell size distribution, mainly within the range of 150–450 µm. The mean cell size in the range of the highest frequency is 224 µm. Introducing relatively small amount of wood particles (i.e., 5 wt.%) to the system reduces the number of cells in the size range of 200–250 µm. At the same time, it increases the number of cells above this range, i.e., within the range of 300–450 µm. However, the mean cell size with the highest frequency is still in the range of 200–250 µm. A further increase in the proportion of wood shavings in the PUR-WP composition in the amount of up to 10% of the weight results in the shifting of the mean cell size from 250 to 300 µm (average cell size 276 µm). However, taking into account the photos taken with a light microscope and SEM (Figures 8 and 9), it can be concluded that

despite the noted changes in the cell size distribution, the structure of foams with the 5% and 10% wood filler added is relatively well-developed, which allows for high thermal insulation parameters. The insulating properties of the wood filler itself are likely to be important as well. Wood itself is an excellent insulator, and also has a heat capacity greater than the PUR foam.

A further increase in the amount of wood filler to 15% and 20% causes a significant disturbance of the foam structure and formation of larger and more irregular pores. In these variants, the cell structure of the composite foams is disturbed by the presence of cells sized above 450 µm. This is particularly visible in the case of variants containing 20% of wood particles (Figures 7 and 8), although a collapse of the cellular structure of the foam is visible even with a filler content of 15%. The presence of larger cells and damage to the structure of the foams result in increased air permeability. As a result, it increases the heat transfer and thus reduces the thermal insulation of this type of foam [6,34]. Similar observations in the case of the modification of closed-cell PUR foam with various types of lignocellulosic fillers were made by Str ˛akowska et al. and Członka et al. [24,39]. Additionally, as shown in the literature, such disturbances in the morphology of the PUR foam due to the introduction of the organic filler, such as straw particles, may result from poor interfacial adhesion between the polymer matrix and the filler surface, which consequently disrupts the foaming process and, as a result, the structure of modified PUR foams [40]. Additionally, according to Sung et al. [41], during the cell structure formation of PUR foams, the interaction between the filler surface and the polymer matrix can determine the final average cell sizes. The higher the hydrophilicity of the filler surface, as in the case of wood filler, the larger the cell sizes in the microstructure of foams. Moreover, the filler particles may constitute a nucleating agent and cause the nucleation pattern to change from homogeneous to heterogeneous and reduce the nucleation energy. For this reason, smaller cells are formed in the foam structure [42,43]. In the case of our research, the formation of cells of a small size, i.e., about 100 and 150 µm in size, was also noted. *Materials* **2021**, *14*, x FOR PEER REVIEW 8 of 14 range of 200–250 µm. A further increase in the proportion of wood shavings in the PUR-WP composition in the amount of up to 10% of the weight results in the shifting of the mean cell size from 250 to 300 µm (average cell size 276 µm). However, taking into account the photos taken with a light microscope and SEM (Figures 8 and 9), it can be concluded that despite the noted changes in the cell size distribution, the structure of foams with the 5% and 10% wood filler added is relatively well-developed, which allows for high thermal insulation parameters. The insulating properties of the wood filler itself are likely to be important as well. Wood itself is an excellent insulator, and also has a heat capacity greater than the PUR foam.

**Figure 7.** Cell size and cell size distribution of PUR foam depending on wood particle (WP) content: (**a**) control; (**b**) 5%; (**c**) 10%; (**d**) 15%; (**e**) 20% **Figure 7.** Cell size and cell size distribution of PUR foam depending on wood particle (WP) content: (**a**) control; (**b**) 5%; (**c**) 10%; (**d**) 15%; (**e**) 20%.

*Materials* **2021**, *14*, x FOR PEER REVIEW 9 of 14

**Figure 8.** Light microscope photos of PUR samples with addition of different amount of WP: (**a**) control; (**b**) 5%; (**c**) 10%; (**d**) 15%; (**e**) 20% (green arrow—wood particles; red circle—structure disorders,large pores). All scale bars of figures are the same. **Figure 8.** Light microscope photos of PUR samples with addition of different amount of WP: (**a**) control; (**b**) 5%; (**c**) 10%; (**d**) 15%; (**e**) 20% (green arrow—wood particles; red circle—structure disorders, large pores). All scale bars of figures are the same. **Figure 8.** Light microscope photos of PUR samples with addition of different amount of WP: (**a**) control; (**b**) 5%; (**c**) 10%; (**d**) 15%; (**e**) 20% (green arrow—wood particles; red circle—structure disorders,large pores). All scale bars of figures are the same.

tion. All scale bars of figures are the same. **Figure 9.** SEM images of PUR samples: (**a**) control sample; (**b**) 10% WP addition; (**c**) 15% WP addition. All scale bars of figures are the same. **Figure 9.** SEM images of PUR samples: (**a**) control sample; (**b**) 10% WP addition; (**c**) 15% WP addition. All scale bars of figures are the same.

This can also be confirmed by the analysis of the cell size distribution and SEM (Figures 7 and 9). It also proves a significant differentiation of the cell size distribution of PUR-WP composite foams. The formation of this type of cell may result from the attachment of filler particles to the foam cell, which leads to damage and weakening of the foam microstructure, and thus lowers its strength. Analyzing the structure of the produced foams, attention should also be paid to the dispersions of wood particles. As a rule, fillers with smaller particle sizes (e.g., nano-scale) tend to agglomerate, which also interferes with the foaming process and the morphology

structure, and thus lowers its strength.

mation of cells of a small size, i.e., about 100 and 150 µm in size, was also noted.

This can also be confirmed by the analysis of the cell size distribution and SEM (Fig-

ures 7 and 9). It also proves a significant differentiation of the cell size distribution of PUR-WP composite foams. The formation of this type of cell may result from the attachment of filler particles to the foam cell, which leads to damage and weakening of the foam micro-

*Materials* **2021**, *14*, x FOR PEER REVIEW 10 of 14

A further increase in the amount of wood filler to 15% and 20% causes a significant disturbance of the foam structure and formation of larger and more irregular pores. In these variants, the cell structure of the composite foams is disturbed by the presence of cells sized above 450 µm. This is particularly visible in the case of variants containing 20% of wood particles (Figures 7 and 8), although a collapse of the cellular structure of the foam is visible even with a filler content of 15%. The presence of larger cells and damage to the structure of the foams result in increased air permeability. As a result, it increases the heat transfer and thus reduces the thermal insulation of this type of foam [6,34]. Similar observations in the case of the modification of closed-cell PUR foam with various types of lignocellulosic fillers were made by Strąkowska et al. and Członka et al. [24,39]. Additionally, as shown in the literature, such disturbances in the morphology of the PUR foam due to the introduction of the organic filler, such as straw particles, may result from poor interfacial adhesion between the polymer matrix and the filler surface, which consequently disrupts the foaming process and, as a result, the structure of modified PUR foams [40]. Additionally, according to Sung et al. [41], during the cell structure formation of PUR foams, the interaction between the filler surface and the polymer matrix can determine the final average cell sizes. The higher the hydrophilicity of the filler surface, as in the case of wood filler, the larger the cell sizes in the microstructure of foams. Moreover, the filler particles may constitute a nucleating agent and cause the nucleation pattern to change from homogeneous to heterogeneous and reduce the nucleation energy. For this reason, smaller cells are formed in the foam structure [42,43]. In the case of our research, the for-

Analyzing the structure of the produced foams, attention should also be paid to the dispersions of wood particles. As a rule, fillers with smaller particle sizes (e.g., nano-scale) tend to agglomerate, which also interferes with the foaming process and the morphology of PUR foams. The filler of relatively large dimensions and irregular shape used in the research allows for a high degree of dispersion of its particles in the polyurethane matrix. This is evidenced by the 3D photos of foams with 5% and 20% addition of wood particles. The photos were made with the use of the computed tomography technique, presented in Figure 10. of PUR foams. The filler of relatively large dimensions and irregular shape used in the research allows for a high degree of dispersion of its particles in the polyurethane matrix. This is evidenced by the 3D photos of foams with 5% and 20% addition of wood particles. The photos were made with the use of the computed tomography technique, presented in Figure 10.

**Figure 10.** Image of foam with the addition of wood particles made with a computer tomograph: (**a**) 5% WP addition; (**b**) 20 addition WP. **Figure 10.** Image of foam with the addition of wood particles made with a computer tomograph: (**a**) 5% WP addition; (**b**) 20 addition WP.

#### *3.3. Compressive Strength*

*3.3. Compressive Strength*  The results of the structure and thermal insulation properties of the produced foams correspond with the results of the analysis of the compressive strength measurements. As shown in Figures 11 and 12, the maximum increase in the mean value of compressive strength was recorded for the composition with a 10% share of foam wood particles—an The results of the structure and thermal insulation properties of the produced foams correspond with the results of the analysis of the compressive strength measurements. As shown in Figures 11 and 12, the maximum increase in the mean value of compressive strength was recorded for the composition with a 10% share of foam wood particles—an increase in σ10% by approx. 30% in comparison with control PUR foam. With a 15% addition of wood filler, a tendency towards a reduction in compressive strength can be noticed, but it should be emphasized that the HSD Tukey analysis did not confirm the statistically significant differences noted for the compositions containing 10% and 15% of wood particles (the same homogeneous group b). A statistically significant decrease in compressive strength was noticed only for the composition containing 20% wood particles. It should be emphasized that in this case, the compressive strength was comparable to control samples (the same homogeneous group-a). The increase in the compressive strength of compositions containing up to 10% wood filler can be explained by an increase in the apparent density of the tested foams. At the same time, the foam still has a well-developed cell structure, which is also confirmed by the analysis of the cell size distribution of the tested foams and the photos in Figures 7–9.

Despite a significant increase in the apparent density of foams, a further increase in the amount of wood particles reduced the strength of PUR-WP. Such shaping of the compressive strength of the tested compositions proves that this type of parameter is influenced not only by the apparent density of the foam, but also by its structure. This is confirmed by the research of other authors [38,39,44] and the additionally estimated specific compressive strength of the produced PUR-WP compositions, which is defined as the ratio of the compressive strength σ10% to the density of the tested foams [39]. As demonstrated by the analysis, the use of waste wood particles of such large dimensions as PUR foam filler increases the specific compressive strength by up to 5%. Above this amount, the value of this parameter gradually decreases.

the value of this parameter gradually decreases.

foams and the photos in Figures 7–9.

**Figure 11.** Compression strength of PUR-WD composition depending on wood particle content. Different letters indicate homogeneous groups of mean values determined by one-factor ANOVA with Tukey's test. **Figure 11.** Compression strength of PUR-WP composition depending on wood particle content. Different letters indicate homogeneous groups of mean values determined by one-factor ANOVA with Tukey's test. *Materials* **2021**, *14*, x FOR PEER REVIEW 12 of 14

increase in σ10% by approx. 30% in comparison with control PUR foam. With a 15% addition of wood filler, a tendency towards a reduction in compressive strength can be noticed, but it should be emphasized that the HSD Tukey analysis did not confirm the statistically significant differences noted for the compositions containing 10% and 15% of wood particles (the same homogeneous group b). A statistically significant decrease in compressive strength was noticed only for the composition containing 20% wood particles. It should be emphasized that in this case, the compressive strength was comparable to control samples (the same homogeneous group-a). The increase in the compressive strength of compositions containing up to 10% wood filler can be explained by an increase in the apparent density of the tested foams. At the same time, the foam still has a well-developed cell structure, which is also confirmed by the analysis of the cell size distribution of the tested

Despite a significant increase in the apparent density of foams, a further increase in the amount of wood particles reduced the strength of PUR-WP. Such shaping of the compressive strength of the tested compositions proves that this type of parameter is influenced not only by the apparent density of the foam, but also by its structure. This is confirmed by the research of other authors [38,39,44] and the additionally estimated specific compressive strength of the produced PUR-WP compositions, which is defined as the ratio of the compressive strength σ10% to the density of the tested foams [39]. As demonstrated by the analysis, the use of waste wood particles of such large dimensions as PUR foam filler increases the specific compressive strength by up to 5%. Above this amount,

**Figure 12.** Compression specific strength of PUR-WD composition depending on wood particle con-**Figure 12.** Compression specific strength of PUR-WP composition depending on wood particle content.

This is due to the fact that foams with 5% of wood filler have a homogeneous structure with a narrow range of cell size distribution (like pure foam). The proper filler dispersion with a well-formed foam structure probably facilitates the transfer of strain under compressive load and thus increases its strength. As mentioned earlier, higher filler additions result in a broadening of the range of the cell size distribution and the presence of numerous structural disorders (especially at 15% and 20% of the WP activity). Despite the This is due to the fact that foams with 5% of wood filler have a homogeneous structure with a narrow range of cell size distribution (like pure foam). The proper filler dispersion with a well-formed foam structure probably facilitates the transfer of strain under compressive load and thus increases its strength. As mentioned earlier, higher filler additions result in a broadening of the range of the cell size distribution and the presence of numerous structural disorders (especially at 15% and 20% of the WP activity). Despite the increase in density, these foams are characterized by lower compressive strength.

#### increase in density, these foams are characterized by lower compressive strength. **4. Conclusions**

buildings.

tent.

**4. Conclusions**  This article presents the influence of wood particles as a filler in PUR foams. The WP was added in different amounts, i.e., 0, 5, 10, 15 and 20% to PUR and apparent density, cellular morphology, mechanical properties and thermal property were conducted. As expected, the addition of the wood particles causes a significant increase in the density of the PUR-WP composite. A significant increase in the density of the produced foams was noticed only when larger amounts of wood particles were used, i.e., from 10% and more. Along with the increase in the density of the tested foams, statistically significant changes in their thermal insulation were observed. The addition of wood filler in the amount of This article presents the influence of wood particles as a filler in PUR foams. The WP was added in different amounts, i.e., 0, 5, 10, 15 and 20% to PUR and apparent density, cellular morphology, mechanical properties and thermal property were conducted. As expected, the addition of the wood particles causes a significant increase in the density of the PUR-WP composite. A significant increase in the density of the produced foams was noticed only when larger amounts of wood particles were used, i.e., from 10% and more. Along with the increase in the density of the tested foams, statistically significant changes in their thermal insulation were observed. The addition of wood filler in the amount of 10% allows us to improve the insulation properties of PUR foam, which is manifested by a

10% allows us to improve the insulation properties of PUR foam, which is manifested by a decrease in the value of the thermal conductivity coefficient by 10%. It should be noted

value of the thermal conductivity coefficient was at a level comparable to that of pure PUR foam. Moreover, the results of the compressive strength in the parallel direction to the foam's growth showed that addition of 10% WP to the foam lead to the increase in σ10% by approx. 30% in comparison with the control PUR foam. The increase in the compressive strength of compositions containing up to 10% can be explained by an increase in the apparent density of the tested foams. Thus, the conducted studies indicated the possibility of using wood waste as fillers for PUR foams with open-cell structure. Such composite foams with 10 wt.% of waste wood particles from primary wood processing can be used as thermal insulation of open diffusivity building partitions in modern prefabricated

**Author Contributions:** Conceptualization, R.M.; methodology, R.M., D.D. and J.W.; validation, R.M.; formal analysis, R.M., D.D., J.W. and A.D.; investigation, D.D., J.W. and A.D.; resources, R.M., D.D., J.W.; writing—original draft preparation, D.D., J.W.; writing—review and editing R.M., D.D. and J.W.; visualization, D.D., J.W. and A.D.; project administration, R.M.; funding acquisition, R.M.

All authors have read and agreed to the published version of the manuscript.

decrease in the value of the thermal conductivity coefficient by 10%. It should be noted that even with the maximum amount of wood particles used in the tests (i.e., 20%), the value of the thermal conductivity coefficient was at a level comparable to that of pure PUR foam. Moreover, the results of the compressive strength in the parallel direction to the foam's growth showed that addition of 10% WP to the foam lead to the increase in σ10% by approx. 30% in comparison with the control PUR foam. The increase in the compressive strength of compositions containing up to 10% can be explained by an increase in the apparent density of the tested foams. Thus, the conducted studies indicated the possibility of using wood waste as fillers for PUR foams with open-cell structure. Such composite foams with 10 wt.% of waste wood particles from primary wood processing can be used as thermal insulation of open diffusivity building partitions in modern prefabricated buildings.

**Author Contributions:** Conceptualization, R.M.; methodology, R.M., D.D. and J.W.; validation, R.M.; formal analysis, R.M., D.D., J.W. and A.D.; investigation, D.D., J.W. and A.D.; resources, R.M., D.D., J.W.; writing—original draft preparation, D.D., J.W.; writing—review and editing R.M., D.D. and J.W.; visualization, D.D., J.W. and A.D.; project administration, R.M.; funding acquisition, R.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Center for Research and Development, grant number BIOSTRATEG3/344303/14/NCBR/2018.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


*3.7.3 Piezoelectric buzzers*

Piezoelectric buzzers are similar to piezoelectric speakers, but they are usually designed with lower fidelity to produce a louder volume over a narrower frequency range. Buzzers are used in a seemingly endless array of electronic devices.