*Article* **Parametric Study for Thermal and Catalytic Methane Pyrolysis for Hydrogen Production: Techno-Economic and Scenario Analysis**

**Seunghyun Cheon 1,†, Manhee Byun 1,†, Dongjun Lim 1, Hyunjun Lee 1 and Hankwon Lim 1,2,\***

**Abstract:** As many countries have tried to construct a hydrogen (H2) society to escape the conventional energy paradigm by using fossil fuels, methane pyrolysis (MP) has received a lot of attention owing to its ability to produce H2 with no CO2 emission. In this study, a techno-economic analysis including a process simulation, itemized cost estimation, and sensitivity and scenario analysis was conducted for the system of thermal-based and catalyst-based MP (TMP-S1 and CMP-S2), and the system with the additional H2 production processes of carbon (C) gasification and water–gas shift (WGS) reaction (TMPG-S3 and CMPG-S4). Based on the technical performance expressed by H2 and C production rate, the ratio of H2 combusted to supply the heat required and the ratio of reactants for the gasifier (C, Air, and water (H2O)), unit H2 production costs of USD 2.14, 3.66, 3.53, and 3.82 kgH2 −1 from TMP-S1, CMP-S2, TMPG-S3, and CMPG-S4, respectively, were obtained at 40% H2 combusted and a reactants ratio for C-Air-H2O of 1:1:2. Moreover, trends of unit H2 production cost were obtained and key economic parameters of the MP reactor, reactant, and C selling price were represented by sensitivity analysis. In particular, economic competitiveness compared with commercialized H2 production methods was reported in the scenario analysis for the H2 production scale and C selling price.

**Keywords:** thermal methane pyrolysis; catalytic methane pyrolysis; H2 production; process simulation; economic analysis; unit H2 production cost


*4.1. Verification of the Validity of the 4.75-Hydrate Crystal Structure*

The published crystal structures of pentahydrate, 4.75H, and tetrahydrate have very similar lattice constants but different water contents. Moreover, the space group of 4.75H is *P*21, whereas those of the pentahydrate and tetrahydrate forms are both *P*21/*m* [33,35]. The crystal structure of DIC-Na 4.75H contains a pseudo-mirror plane between two corresponding DIC anions. However, the shape of the cluster of Na+ ions and water molecules is greatly distorted from the mirror symmetry, so it is not suitable to set the mirror plane on this cluster. The published pentahydrate structure was solved in the *P*21/*m* space group by employing a disordered model at the position of Na+ ions [33]. However, this assignment of the occupancy of disordered water may have been incorrect. The present study revealed that, in one unit cell, four DIC-Na molecules are associated with not 20 but 19 water molecules (4.75 water molecules for one DIC anion) in the hydrated solid state. Notably, the 4.75H structure model reported by Llinàs et al. was validated by a low *R* factor in their structural refinement [34].

Figure 13 shows the Na–O coordination network observed in the crystal structure of DIC-Na 4.75H. Three 6-coordinated sodium ions (Na1, Na2, and Na3) form a waving [Na– O–Na–O] chain structure, while a 5-coordinated sodium ion (Na4, orange) is connected to the chain via water. The lower panel in Figure 13 displays the chain seen from the direction parallel to the pseudo-mirror plane. Although most atoms have a corresponding atom across the pseudo-mirror plane, one water molecule (red) does not. A different Fourier map exhibited a 0.36 eÅ−3 residual electron peak at the corresponding position, which might indicate a water oxygen. However, refining such a model was difficult because the occupancy factor decreased to less than 8%, and the position was unstable. Thus, we concluded that the residual error is not significant, and the phase contains 4.75 water molecules.

**Figure 13.** Na–O chain observed in the crystal structure of 4.75H. Three 6-coordinated sodium ions (Na1, Na2, and Na3) form a waving [Na–O–Na–O] chain structure. Red water molecules do not have an associated atom across the pseudo-mirror plane (non-paired water molecule). Figures were drawn with crystallographic a, b, c-axis marks.


*3.3. Structural Dynamic Characteristics*

The first eight orders of vibration modes simulated and analyzed by the finite element model are shown in Figure 4. The natural frequency and participating mass ratios in the main directions are shown in Table 1. It can be seen from the model analysis that the first-order vibration mode demonstrates the torsion of the middle ring cable, the second one as the torsion of the inner and outer ring cables, the third as the torsion of the inner ring cable, the fourth as the antisymmetric vertical vibration of the whole roof along the short span, the fifth as the antisymmetric vertical vibration of the whole roof along the long span, the sixth as the symmetric vertical vibration of the whole roof along 45 degree, the seventh as the outer vibration of the south outer ring cables, and the eighth as the coupling of the translational motion and antisymmetric vibration of roof along the long-span direction. Therefore, the first three vibration modes are dominated by the torsional deformation of square ring cables while the last five ones are mainly the overall roof plane vibration and antisymmetric vibration.

**Figure 4.** Schematic diagram of the first eight-order vibration modes. (**a**) First-order; (**b**) second-order; (**c**) third-order; (**d**) fourth-order; (**e**)fifth-order; (**f**) sixth-order; (**g**) seventh-order; (**h**) eighth-order.


**Acknowledgements**

Finally, in order to evaluate the electrical properties of the thin films, the four-point technique was employed, using the glass substrate with an ITO conducting contact. This study was performed on the sample labelled *Thin Film 7*, which was the one having the lowest optical

versus photon energy *hν* of *Thin Film 7*.

**Figure 7.** *I*-*V* characteristics of *Thin Film 7:* (a) ITO is positively biased and (b) ITO is negatively biased.

*Film 7* under different illumination types (yellow light, white, blue, orange, green, infrared, UV and dark [no light]). Regardless of the wavelength of the incident radiation, the thin film follows the same behaviour. At lower voltages (around 10 V), ohmic conduction is evident, while space-charge limited conductivity (SCLC) governed by an exponential trap distribution is found at higher voltages. On the other hand, the *I-V* characteristics display symmetric

. **Figure 7** shows the *I-V* characteristics of *Thin*

gap. The film had a surface area of 2.16 cm2

**Figure 6.** Plot of **(α***h***ν)1/2** and **(α***h***ν)2**

38 Phthalocyanines and Some Current Applications

The authors wish to thank the technical support of M.I. Mariel Leyva-Esqueda (Universidad Anáhuac) for technical help. María Elena Sánchez-Vergara gratefully acknowledges the financial support of Universidad Anáhuac México under grant INNADBSEVM140129141.


**8. References**

quinolinolato)aluminum and hole-transporting molecular materials with low ionization potentials. Appl. Phys. Lett. 1998; 72(6) 636-638.

Exciplex Electroluminescence of the New Organic Materials for Light-Emitting Diodes 193

[25] Noda T, Ogawa H, Shirota Y. A blue-emitting organic electroluminescent device using a novel emitting amorphous molecular material, 5,5′-bis(dimesitylboryl)-2,2′-bithiophene.

[26] Li G, Kim CH, Zhou Z, Shinar J, Okumoto K, Shirota Y. Combinatorial study of exciplex formation at the interface between two wide band gap organic semiconductors. Appl.

[27] Liao S-H, Shiu J-R, Liu S-W, Yeh S-J, Chen Y-H, Chen C-T, Chow TJ, Wu C-I: Hydroxynaphthyridine-derived group III metal chelates: wide band gap and deep blue analogues of green Alq3 (Tris(8-hydroxyquinolate)aluminum) and their versatile

[28] Li M, Li W, Chen L, Kong Z, Chu B, Li B, Hu Z, Zhang Z. Tuning emission color of electroluminescence from two organic interfacial exciplexes by modulating the thickness of middle gadolinium complex layer. Appl. Phys. Lett. 2006; 88(9) 091108-3. [29] Yu J, Lou S, Wen W, Jiang Y, Zhang Q. Color-tunable organic light-emitting diodes

[30] Kulkarni, A.P., Jenekhe, S.A. Blue-green, orange, and white organic light-emitting diodes based on exciplex electroluminescence of an oligoquinoline acceptor and different hole-transport materials. Journal of Physical Chemistry C 2008; 112(13) 5174-

[31] Feng J, Li F, Gao W, Liu S. White light emission from exciplex using tris-8 hydroxyquinoline aluminum as chromaticity-tuning layer. Appl Phys Lett 2001; 78(25)

[32] Yang S, Jiang M. White light generation combining emissions from exciplex, excimer and electromer in TAPC-based organic light-emitting diodes. Chemical Physics Letters

[33] Zhu J, Li W, Han L, Chu B, Zhang G, Yang D, Chen Y, Su Z, Wang J, Wu S, Tsuboi T. Very broad white-emission spectrum based organic light-emitting diodes by four

[34] Zhou G, Wong W-Y, Suo S. Recent progress and current challenges in phosphorescent white organic light-emitting diodes (WOLEDs). Journal of Photochemistry and

[35] Kumar A, Srivastava R, Bawa SS, Singh D, Singh K, Chauhan G, Singh I, Kamalasanan MN. White organic light emitting diodes based on DCM dye sandwiched in 2-methyl-8-

[37] Tong QX, Lai SL, Chan MY, Tang JX, Kwong HL, Lee CS, Lee ST. High-efficiency nondoped white organic light-emitting devices. Appl. Phys. Lett 2007; 91(2) 023503-3.

hydroxyquinolinolatolithium Journal of Luminescence 2010; 130(8) 1516-1520 [36] Liu Y, Guo J, Zhang H, Wang Y. Highly efficient white organic electroluminescence from a double-lay device based on a boron hydroxyphenylpyridine complex. Angew

exciplex emission bands. Optics Letters 2009; 34(19) 2946-2948.

Photobiology C: Photochemistry Reviews 2010; 11(4)133-156.

applications for organic light-emitting diodes. J Am Chem Soc 2009, 131:763.

based on exciplex emission. Proceedings of SPIE 2009; 7282, 728234-7.

Advanced Materials 1999; 11(4) 283-285.

Phys. Lett. 2006; 88(25) 253505-3.

5184.

3947–3949

2009; 484(1-3) 54-58.

Chem Int Ed 2002; 41(1) 182-184.

[25] Noda T, Ogawa H, Shirota Y. A blue-emitting organic electroluminescent device using a novel emitting amorphous molecular material, 5,5′-bis(dimesitylboryl)-2,2′-bithiophene. Advanced Materials 1999; 11(4) 283-285.

192 Organic Light Emitting Devices

82(3) 334-336

8104.

2461.

043508-3.

541-546

potentials. Appl. Phys. Lett. 1998; 72(6) 636-638.

Physics 2005; 98(1) 013512-5.

light-emitting diode?. Appl. Phys. Lett. 2001; 79(5) 560-562.

mechanisms. Synthetic Metals 2003; 139 (3) 675-677.

Proceedings of SPIE 2010; 7658, 76583V-6.

quinolinolato)aluminum and hole-transporting molecular materials with low ionization

[12] Thompson J, Blyth RIR, Mazzeo M, Anni M, Gigli G, Clinigolani R. White light emission from blends of blue-emitting organic molecules: a general route to the white organic

[13] Salerno M, Blyth RIR, Thompson J, Cingolani R, Gigli G. Surface morphology and optical properties of thin films of thiophene-based binary blends Journal of Applied

[14] Mazzeo M, Pisignano D, Della Sala F, Thompson J, Blyth RIR, Gigli G, Cingolani R, Sotgiu G., Barbarella G. Organic single-layer white light-emitting diodes by exciplex emission from spin-coated blends of blue-emitting molecules Appl. Phys. Lett. 2003;

[15] Mazzeo M, Pisignano D, Favaretto L, Sotgiu G, Barbarella G, Cingolani R, Gigli G. White emission from organic light emitting diodes based on energy down-convertion

[16] Granlund T, Pettersson LAA, Anderson MR, Inganäs O. Interference phenomenon determines the color in an organic light emitting diode. J. Appl. Phys. 1997; 81(12) 8097-

[17] Zhang W, Yu J, Yuan K, Jiang Y, Zhang Q, Cao K. Acceptor thickness effect of exciplex and electroplex emission at heterojunction interface in organic light-emitting diodes

[18] Zhu H, Xu Z, Zhang F, Zhao S, Wang Z, Song D. White organic light-emitting diodes via mixing exciplex and electroplex emissions Synthetic Metals 2009; 159(23-24), 2458-

[19] Zhao D-W, Xu Z, Zhang F-J, Song S-F, Zhao S-L, Wang Y, Yuan G-C, Zhang Y-F, Xu HH. The effect of electric field strength on electroplex emission at the interface of NPB/PBD organic light-emitting diodes. Applied Surface Science 2007; 253(8) 4025-4028 [20] Matsumoto N, Adachi C. Exciplex formations at the HTL/Alq3 interface in an organic light-emitting diode: Influence of the electron-hole recombination zone and electric

[21] Seo JH, Kim HM, Choi EY, Choi DH, Park JH, Yoo HS, Kang HJ, Lee KH, Yoon SS, Kim YK. Phosphorescent organic light-emitting diodes with simplified device architecture

[22] Su WM, Li WL, Xin Q, Su ZS, Chu B, Bi DF, He H, Niu JH. Effect of acceptor on efficiencies of exciplex-type organic light emitting diodes. Appl. Phys. Lett. 2007; 91(4)

[23] Wang H, Klubek KP, Tang CW. Current efficiency in organic light-emitting diodes with

[24] Lai SL, Tong QX, Chan MY, Ng TW, Lo MF, Ko CC, Lee ST. Lee CS. Carbazole-pyrene derivatives for undoped organic light-emitting devices Organic Electronics 2011; 12(3)

field. Journal of Physical Chemistry C 2010; 114(10) 4652-4658.

Japanese Journal of Applied Physics 2010; 49(8 part 2) 08JG04-4.

a hole-injection layer Applied Physics Letters 2008; 93 (9), 093306-3.

[38] Lai SL, Chan MY, Tong QX, Fung MK, Wang PF, Lee CS, Lee ST. Approaches for achieving highly efficient exciplex-based organic light-emitting devices Appl. Phys. Lett. 2008; 93(14) 143301-3.

Exciplex Electroluminescence of the New Organic Materials for Light-Emitting Diodes 195

[51] Kalinowski J, Cocchi M, Di Marco P, Stampor W, Giro G, Fattori V. Impact of high electric fields on the charge recombination process in organic light-emitting diodes. J.

[52] Zhao D, Zhang F, Xu C, Sun J, Song S, Xu Z, Sun X. Exciplex emission in the blend of two blue luminescent materials Applied Surface Science 2008; 254(11) 3548-3552. [53] Qian J, Yu J, Lou S, Jiang Y, Zhang Q. Influence of hole transporter doping on electroluminescent property of novel fluorene molecular material. Proceedings of SPIE

[54] Xu X, Chen S, Yu G, Di C, You H, Ma D, Liu Y. High-efficiency blue light-emitting diodes based on a polyphenylphenyl compound with strong electron-accepting groups

[55] Zhang W, Yu J-S, Huang J, Jiang Y-D, Zhang Q, Cao K.-L. Exciplex elimination in an organic light-emitting diode based on a fluorene derivative by inserting 4,4'-N,N' dicarbazole-biphenylinto donor/acceptor interface Chinese Physics 2010; B19(4) 047802-

[56] Horvath A, Stevenson KL. Transition metal complex exciplexes. Coord. Chem. Rev.

[57] Hill IG, Rajagopai A, Kahn A. Energy-level alignment at interfaces between metals and the organic semiconductor 4,48-N, N8-dicarbazolyl-biphenyl. J Appl Phys 1998; 84(6)

[58] Baldo MA, Lamansky S, Burrows PE, Thompson ME, Forrest SR. Very high-efficiency green organic light-emitting devices based on electrophosphorescence. Appl Phys Lett

[59] Brutting W, Berleb S, Muckl AG. Device physics of organic light-emitting diodes based

[60] Lee M-T, Yen C-K, Yang W-P, Chen H-H, Liao C-H, Tsai C-H, Chen CH. Efficient green coumarin dopants for organic light-emitting devices. Organic Letters 2004; 6(8) 1241-

[61] Kim JY, Kim M, Kim HM, Joo J, Choi J-H. Electrical and optical studies of organic light emitting devices using SWCNTs-polymer nanocomposites. Optical Materials 2002; 21,

[62] Divayana Y, Sun XW, Chen BJ, Sarma KR. Improved organic light-emitting device with tris-(8-hydroxyquinoline) aluminium inserted between hole-injection layer and hole-

[64] Yang S, Zhang X, Lou Z, Hou Y. Influence of heterojunction interface on exciplex emission from organic light-emitting diodes under electric fields Applied Physics A:

transporting layer. Journal of Physics D: Applied Physics 2007; 40(1) 183-186. [63] Lee KS, Choo DC, Kim TW. White organic light-emitting devices with tunable color emission fabricated utilizing exciplex formation at heterointerfaces including m-

on molecular materials. Organic Electronics 2001; 2(1) 1–36.

MDATA Thin Solid Films 2011; 519(15) 5257-5259.

Materials Science and Processing 2008; 90(3) 475-478.

Phys. D. Appl. Phys. 2000; 33(19), 2379-2387.

Advanced Materials 2007; 19(9) 1281-1285.

2009; 7282, 72823F-5

1996; 153, 57-82.

3236-3241.

1244.

147-151.

1999; 75(1) 4-6.

7.

[51] Kalinowski J, Cocchi M, Di Marco P, Stampor W, Giro G, Fattori V. Impact of high electric fields on the charge recombination process in organic light-emitting diodes. J. Phys. D. Appl. Phys. 2000; 33(19), 2379-2387.

194 Organic Light Emitting Devices

Lett. 2008; 93(14) 143301-3.

160(7-8) 722-727.

535(1) 212-219.

Physics Letters 2008; 92(5) 053304-3

Mol Cryst Liq Cryst 2008; 497(1) 211-217.

Research Letters 2012; 7(1), 206-8.

diodes. High Energy Chemistry 2008; 42(7) 563-565.

substituted ligands. High Energ Chem 2009; 43(7) 536-539.

oxadiazole. Current Applied Physics 2009; 9(5) 1038-1041.

an oxadiazole derivative. Chem. Phys. Lett. 2000; 318(1-3) 137-141

[38] Lai SL, Chan MY, Tong QX, Fung MK, Wang PF, Lee CS, Lee ST. Approaches for achieving highly efficient exciplex-based organic light-emitting devices Appl. Phys.

[39] Wang D, Li W, Chu B, Su Z, Bi D, Zhang D, Zhu J, Yan F, Chen Y, Tsuboi T. Highly efficient green organic light-emitting diodes from single exciplex emission Applied

[40] Nayak PK, Agarwal N, Periasamy N, Patankar MP, Narasimhan KL. Pure exciplex electroluminescence in blended film of small organic molecules. Synthetic Metals 2010;

[41] Yakushchenko IK, Kaplunov MG, Krasnikova SS, Roshchupkina OS, Pivovarov AP. A New class of electroluminescent metal complexes based on quinoline ligands

[43] Kaplunov MG, Yakushchenko IK, Krasnikova SS, Pivovarov AP, Balashova IO. Electroluminescent materials based on new metal complexes for organic light-emitting

[44] Kaplunov MG, Krasnikova SS, Balashova IO, Yakushchenko IK. Exciplex Electroluminescence Spectra of the New Organic Materials Based on Zinc Complexes of Sulphanylamino-Substituted Ligands, Molecular Crystals and Liquid Crystals 2011;

[45] Kaplunov MG, Krasnikova SS, Nikitenko SL, Sermakasheva NL, Yakushchenko IK. Exciplex electroluminescence and photoluminescence spectra of the new organic materials based on zinc complexes of sulphanylamino-substituted ligands. Nanoscale

[46] Krasnikova SS, Kaplunov MG, Yakushchenko IK: Exciplex electroluminescence spectra of organic light emitting diodes based on zinc complexes with sulfonylamino

[47] Adamovich V, Brooks J, Tamayo A, Alexander AM, Djurovich PI, D'Andrade BW, Adachi C, Forrest SR, Thompson ME. High efficiency single dopant white

[49] Yap CC, Yahaya M, Salleh MM. The effect of driving voltage on the electroluminescent property of a blend of poly(9-vinylcarbazole) and 2-(4-biphenylyl)-5-phenyl-1,3,4-

[50] Giro G, Cocchi M, Kalinowski J, Di Marco P, Fattori V. Multicomponent emission from organic light emitting diodes based on polymer dispersion of an aromatic diamine and

electrophosphorescent light emitting diodes. New J Chem 2002; 26,1171-1178. [48] Yakushchenko IK, Kaplunov MG, Efimov ON, Belov MY, Shamaev SN. Polytriphenylamine derivatives as materials for hole transporting layers in

electroluminescent devices. Phys. Chem. Chem. Phys. 1999; 1, 1783-1785.

containing the sulfanylamino group. Russ. J. Coord. Chem. 2009; 35(4) 312-316. [42] Kaplunov MG, Yakushchenko IK, Krasnikova SS, Pivovarov AP. Electroluminescent devices based on novel zinc complexes of sulphonylamino substituted heterocycles.

[65] Chen, T-R. Luminescence and electroluminescence of bis (2-(benzimidazol-2-yl) quinolinato) zinc. Exciplex formation and energy transfer in mixed film of bis (2- (benzimidazol-2-yl) quinolinato) zinc and N,N'-bis-(1-naphthyl)-N, N'-diphenyl-1,1' biphenyl-4,4'-diamine. Journal of Molecular Structure 2005; 737(1) 35-41.

**Chapter 8**

© 2012 Zarins et al., licensee InTech. This is an open access chapter 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.

© 2012 Zarins et al., licensee InTech. This is a paper 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.

**Synthesis and Physical Properties of Red**

Elmars Zarins, Aivars Vembris, Valdis Kokars and Inta Muzikante

Additional information is available at the end of the chapter

emitting compounds have been introduced by us [28-32].

http://dx.doi.org/10.5772/53462

**1. Introduction**

**Luminescent Glass Forming Pyranylidene and**

**Isophorene Fragment Containing Derivatives**

Low molecular mass organic compounds with internal charge transfer properties are widely adopted for organic photonics such as materials for the creation of molecular electronics elements, organic magnets, solar cells and organic light emitting diodes (OLEDs) for full display panels [1-3]. One of the most widely used red light-emitting materials contains pyranylidene (4*H*-pyran-4-ylidene) or isophorene (5,5-dimethylcyclohex-2-enylidene) fragments as backbone of the molecule (see Fig.1), which are conjugated in a system with electron acceptor and electron donor fragments [1,4-24]. In many cases the light-emitting layer from such commercially available compounds is prepared by thermal evaporation in vacuum [1-2, 25-27]. Some of them are used as dopants in a polymer matrix and spin-coated onto a hole transport layer from solution [1,12]. However the doping amount of luminescent compound is limited by self crystallization and photoluminescence quenching at higher concentrations which reduce the quantum efficiency of fabricated devices significantly [11- 12]. Therefore it is important to synthesize low molecular mass light-emitting organic compounds which do not crystallize and form thin amorphous solid films from volatile organic solvents. Such compounds, which can make a solid-state glassy structure prepared from solutions, could facilitate technological processes in the production of many devices in optoelectronics, for example, light emitting devices by low-cost deposition such as wet casting methods and easier light-emitting material synthesis. Some of these red light-

In this chapter we present complete synthesis, thermal, optical, photoelectrical and glass forming properties of new organic glass-forming pyranylidene and isophorene fragment containing derivatives with bulky trityloxy groups in their molecules. The optical properties, both in solution and solid state, are compared. The dependance of


**Figure 5.** Concordance analysis for the term 'Explainability'. **Figure 5.** Concordance analysis for the term 'Explainability'.

#### **5. Discussion**

The findings from the results highlight critical tenets regarding the concept of explainability in AI. From the results, it is evident that specific keywords were prominently featured compared to others. Notably, words such as 'use', 'explanation', and 'model', as highlighted in Figure 2, confirm increased usability. The findings are key in addressing the shortcoming of the whole concept of explainability as reported by Soni et al. [5]. Similar results are reported in the case of Figure 3, which identifies notable words such as 'use', 'model', 'learn', and 'data'. The analysis reveals that the AI communities approach the concept of explainability differently, but with some general resemblance. The term is used to assist in evaluating the mechanism of machine language systems, such as understanding the working of the system, yet, at other times, to relate to concepts of particular inputs like determining how a given input was mapped to an output. From the analysis, certain key observations were made.

#### *5.1. Opaque Systems*

Mainly, this refers to a system where mapping inputs to outputs are not visible to the user. It can be perceived as a mechanism that only predicts an input, without stating why and how the predictions are made. Opaque systems exist, for example, when closed-source AI systems are licensed by an organization where the licensor prefers to keep their workings private. Additionally, black-box methodologies are categorized as opaque because they use algorithms that do not give insight into the actual reasoning for the system mapping of inputs to outputs [21].

#### *5.2. Interpretable Systems*

This refers to AI systems where clients cannot see, understand, and study how mathematical concepts are used to map inputs to the output. Thus, related issues include transparency and understanding. Regression models are considered interpretable, for instance, in comparing covariate heights to determine the significance of each aspect to the mapping. However, deep neural networks' functioning may not be interpretable, especially regarding the fact that input features are mostly based on automatic non-linear models [21].

#### *5.3. Comprehensible Systems*

Comprehensible AI models emit symbols without the use of inputs. These symbols are mostly words and allow the user to relate input properties to the outputs. Thus, the user can compile and understand the symbols relying on personal reasoning and knowledge about them. Thus, comprehensibility becomes a graded notion, with the extent of clarity being the difficulty or ease of use. The required form of knowledge from the user's side relates to the cognitive intuition concerning how the output, inputs, and symbols relate to each other [21]. Interpretable and comprehensible systems are improvements over opaque systems. The concept of interpretation and comprehension are separate: interpretation mostly relies on the transparency of system models, whereas comprehension requires emitting symbols that allow a user to reason and think [21]. Most present-day AI systems can produce accurate output but are also highly sophisticated if not outright opaque, making their workings incomprehensible and difficult to interpret. As part of the efforts to renew user trust in AI systems, there are calls to increase system explainability.

There is an increasing need to enhance user confidence in AI systems [25]. User confidence and trust are cited as the primary reasons for pursuing explainable AI. System users seek explanations for various reasons—to manage social interactions, assign responsibility, and persuade others. A critical aspect of explainable AI is that it creates an opportunity for personalized human–computer interaction. Instead of the brick and mortar models of decision-making techniques that cannot be understood or interpreted by humans, explainability ensures that the customer journey through machine learning and AI systems is modeled in a way that mimics human interactions. There is a need for machine learning to explain why and how individual recommendations or decisions are made [26]. The implication is that

consumers' activity on AI systems will be complemented to make better and accurate decisions faster. Thus, organizations will be able to leverage customer value. When giving advice, recommendations, or even descriptive aspects, looking for justifications and reasons behind the recommended action is important. It is not enough to predict or suggest outcomes as the best or the preferred action without showing connections between the data and the factors involved to arrive at the decisions [26]. better and accurate decisions faster. Thus, organizations will be able to leverage customer value. When giving advice, recommendations, or even descriptive aspects, looking for justifications and reasons behind the recommended action is important. It is not enough to predict or suggest outcomes as the best or the preferred action without showing connections between the data and the factors involved to arrive at the decisions [26].

*Future Internet* **2020**, *12*, x FOR PEER REVIEW 13 of 15

McNaught and Lam [22] state that most people have the perception that a doctor is 'a kind of black box' who transforms symptoms of illnesses and related test outcomes into the best diagnosis for treatment. Doctors deliver diagnostic recommendations to patients without explaining why and how they arrived at such decisions. Mostly, doctors use high-level indicators or symptoms (which, in the context of AI systems, denote system symbols). However, when handling a patient, the doctor should be like a comprehensible model. When interacting with medical staff and other physicians, the doctor may be like an interpretable model. Other doctors will interpret the technical analysis like an analyst would do to a ML system to ensure that the decisions arrived at are backed up by the reasonable assessment of the evidence provided. McNaught and Lam [22] state that most people have the perception that a doctor is 'a kind of black box' who transforms symptoms of illnesses and related test outcomes into the best diagnosis for treatment. Doctors deliver diagnostic recommendations to patients without explaining why and how they arrived at such decisions. Mostly, doctors use high-level indicators or symptoms (which, in the context of AI systems, denote system symbols). However, when handling a patient, the doctor should be like a comprehensible model. When interacting with medical staff and other physicians, the doctor may be like an interpretable model. Other doctors will interpret the technical analysis like an analyst would do to a ML system to ensure that the decisions arrived at are backed up by the reasonable assessment of the evidence provided.

Thus, XAI ensures that the information provided is accurate and personalized, to engage with targeted users in the most optimal manner [26]. In this way, XAI will increase the offer's relevance, thus enhancing user engagement and interest. Additionally, XAI will offer aspects that drive predicted outcomes, allowing real-time adjustment of primary business aspects to optimize gains and corporate outcomes. Transparency and reasoning will contribute to a decrease in abandoned products and an increase in order value, and thus higher revenue and conversion rates. Therefore, this research proposes implementing XAI frameworks that possess the following features: interpretability and comprehensibility. However, responsible XAI is more than just the ML features: user-related aspects of external AI features that should be considered are trust, fairness, confidence, ethics, and safety, as highlighted in So [27]. Moreover, the actual meaning of XAI is dependent on the perspective of the user, as highlighted by So [27] in Figure 6. As illustrated in Figure 6, XAI utilizes customer data to support the process of decision-making, with the impact being witnessed in improved business outcomes. Thus, XAI ensures that the information provided is accurate and personalized, to engage with targeted users in the most optimal manner [26]. In this way, XAI will increase the offer's relevance, thus enhancing user engagement and interest. Additionally, XAI will offer aspects that drive predicted outcomes, allowing real-time adjustment of primary business aspects to optimize gains and corporate outcomes. Transparency and reasoning will contribute to a decrease in abandoned products and an increase in order value, and thus higher revenue and conversion rates. Therefore, this research proposes implementing XAI frameworks that possess the following features: interpretability and comprehensibility. However, responsible XAI is more than just the ML features: user-related aspects of external AI features that should be considered are trust, fairness, confidence, ethics, and safety, as highlighted in So [27]. Moreover, the actual meaning of XAI is dependent on the perspective of the user, as highlighted by So [27] in Figure 6. As illustrated in Figure 6, XAI utilizes customer data to support the process of decision-making, with the impact being witnessed in improved business outcomes.

**Figure 6.** An analogy showing the differences between present-day AI and XAI models. **Figure 6.** An analogy showing the differences between present-day AI and XAI models.

#### **6. Conclusions 6. Conclusions**

The study's main purpose was to lay the foundation for a universal definition of the term 'explainability'. The analyzed data from the word cloud plots revealed that the term 'explainability' is mainly associated with words such as model, explanation, and use. These were the most prominent words exhibited in the corpus generated from the word cloud. In the corpus from word cloud 1, they include emotion, design decision, data, control, image, variance, interpret, decision, show, result, control, estimate, data, predict, method, train, study, use, learn, model, explanation, and system. In The study's main purpose was to lay the foundation for a universal definition of the term 'explainability'. The analyzed data from the word cloud plots revealed that the term 'explainability' is mainly associated with words such as model, explanation, and use. These were the most prominent words exhibited in the corpus generated from the word cloud. In the corpus from word cloud 1, they include emotion, design decision, data, control, image, variance, interpret, decision, show, result, control, estimate, data, predict, method, train, study, use, learn, model, explanation, and system.

corpus word cloud 2, they include model, use, learn, data, method, predict, behavior, task, perform,

In corpus word cloud 2, they include model, use, learn, data, method, predict, behavior, task, perform, base, show, infer, image, algorithm, propose, optimal, object, general, explain, network. After the Voyant analysis was conducted, the most prominent words that appeared on word cloud 1 included control, data, decision, design, and emotion, while in word cloud 2, they included algorithm, base, behavior, data, and explain. When the words obtained from the Voyant analysis were combined, they provided specific meanings of the word 'explainability'. The main definitions obtained from the combination of the most frequent words include 'an algorithm that explains data behavior' or 'an algorithm behavior that is based on data explanation' or 'a design of data control that enhances decision making' or 'designing and controlling data in such a way that enhances emotion and decisions'.

The application of AI in e-commerce stands to expand in the future, as businesses are appreciating their role in influencing consumer demands. The rapid development of research technology and increased access to the internet present e-commerce businesses with an opportunity to expand their various platforms. Notably, the influence of AI in e-commerce spills over to customer retention and satisfaction. The customers are at the center of the changes and adoption of AI in e-commerce. Hence, e-commerce can further develop contact with customers and establish developed customer relationship management systems.

The researcher of this study has made an effort to provide a critical outline of the key tenets of AI and its role in e-commerce, as well as a comprehensive insight regarding the role of AI in addressing the needs of consumers in the e-commerce industry. Even though the study has attempted to provide a universal meaning of ' explainability', the actual impact of AI on consumers' decisions is not yet clear, considering the notion of the "black box", i.e., if the decisions arrived at cannot be explained and the reasons behind such actions given, it will be difficult for people to trust AI systems. Therefore, there is a need for future studies further to examine the need for explainable AI systems in e-commerce and find solutions to the 'black box' issue.

For future research, this study may serve as a 'template' for the definition of an explainable system that characterizes three aspects: opaque systems where users have no access to insights that define the involved algorithmic mechanism; interpretable systems where users have access to the mathematical algorithmic mechanism, and comprehensible systems where users have access to symbols that enhance their decision making.

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

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

#### **References**

**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/).


*Flow Cytometry Applied to the Diagnosis of Primary Immunodeficiencies DOI: http://dx.doi.org/10.5772/intechopen.89743*

before adding the detection antibody. This fixation/permeabilization treatment allows the antibody to pass through the plasma membrane into the cell while maintaining morphological characteristics. While this technique is informative and very useful to identify total defects of a particular protein, detecting expression does not rule out the defect, as there may be mutations that do not alter the expression but the function. Some examples of this type of application to PID diagnosis are the evaluation of the following proteins:

For intracellular staining, there are several commercial options, including laboratory permeability and fixation reagents. It is important to take into account that not all commercial kits work the same way for different cell types or for different techniques. It is therefore necessary to adjust the conditions in each particular case.

Intracellular staining protocol:

*Innovations in Cell Research and Therapy*

group of congenital defects of the number or function of phagocytes in which the following leukocyte populations are affected: CD56bright NK cell, B lymphocytes, monocytes and peripheral dendritic cells populations are affected. Patients with this PID have susceptibility to infections by mycobacteria and human papillomavirus (HPV), histoplasmosis, alveolar proteinosis, myelodysplastic syndromes such

*NK/monocytes/DC dendritic cells (DC) gating strategy. NK cells and monocyte populations were analyzed in the CD3−CD19− gate. NK subpopulations (NKdim and NKbright) were studied using CD56 and CD16 expression markers. The markers CD16 and CD14 were used to identify classical monocytes (CD14+CD16−) and non-classical monocytes (CD16+CD14−). DCs were studied selecting the population negative for the following markers: CD3, CD14, CD16, CD19, CD20, and CD56. High expression of HLA-DR and CD11c and CD123 was used to identify plasmacytoid DCs (HLA-DR+CD123+) and myeloid DCs (HLA-DR+CD11c+).*

**3. Evaluation of intracellular proteins and activation markers involved**

Intracellular protein and specific cell surface antigen detection is a screening test for PIDs. Depending on the specific clinical presentation of the patient, the diagnostic suspicion can be assessed by evaluating the expression of the affected protein by flow cytometry. The most widely used procedure for staining intracellular molecules requires the fixation of cells in suspension and subsequent permeabilization

acute myelogenous leukemia and lymphedema [24]. See the immunophenotype protocol in Section 2.

**3.1 Evaluation of intracellular proteins**

**34**

**in immunity**

**Figure 5.**

(This protocol may change slightly depending on the commercial kit used).


**Author details**

concern is that some infusions or extracts used as household remedies lose their antidepressant or anxiolytic effects when fractioned [96]. These findings indicate that in some cases it may be necessary to keep the metabolites together at the concentrations present in the original infusion or extract that has a proven therapeutic effect. As explained herein, some metabolites share pharmacological targets, which explains why they lose their effect when separated and emphasizes the importance of using standardized extracts with demonstrated therapeutic effects in animal and human studies [97, 98]. Unfortunately, very few clinical studies have evaluated the potential antidepressant or anxiolytic effects of isolated metabolites,

Several observations suggest that active metabolites share the mechanism of action of antidepressant and anxiolytic drugs like SSRIs, SNRIs, MAOIs, DDNRI, and BZDs, but we should emphasize that some metabolites—at least in preclinical studies—produced better effects than conventional drugs, even at lower doses, while others presented a pharmacological synergism between both types at suboptimal doses that improved the effects exerted separately at higher doses. A second shared characteristic is that they contain active stereoisomers and probably, some metabolites, once metabolized, could become more active. This encourages us to consider a significant number of substances with anxiolytic and/or antidepressant pharmacological profiles and invites us to take on the challenge of evaluating

In conclusion, terpenes, flavonoids, alkaloids, and sterols share mechanisms of action that include activation of the critical enzyme for catecholamine synthesis (e.g., tyrosine hydroxylase) or the inhibition of their limiting enzymes, MAO-A and MAO-B, and transporters, thus stimulating the vesicular storage monoamine and the release of neurotransmitters toward the synaptic cleft. Finally, they can prevent the production of ROS and inhibit NO synthesis and, further downstream, interact with the 5-HT1A, 5-HT2A, D1, D2, GABAA receptors, and α1, α2, β-adrenoceptors that contribute to stimulating PKA. One consequence is that CREB increases BDNF levels, which foster the appearance of dendritic contacts that improve cerebral

This chapter discusses the efficacy of some plant metabolites in treating anxiety and depression disorders, as demonstrated in preclinical studies. In the future, this option for treating such disorders will allow us to reduce treatment costs and moderate the side effects produced by drugs currently in use. However, our review also points out that few clinical studies have focused on the pharmacokinetic and pharmacodynamic processes involving metabolites that would permit the safe use of these extracts. Despite this, research has shown that traditional medicine, especially forms that use medicinal plants that have been passed down through several

generations, constitutes an important alternative for health care.

The third author received (Ramos-Molina Ana Raquel) fellowships from Consejo Nacional de Ciencia y Tecnología (CONACyT) for postgraduate studies in

so a great deal of work remains to be done.

*Behavioral Pharmacology - From Basic to Clinical Research*

their pharmacokinetics, pharmacodynamics, and safety.

neurotransmission and modulate the emotions.

**10. Perspective**

**Acknowledgements**

**114**

Science and Technology (Reg. 631048).

Rosa Isela García-Ríos1 \*, Armando Mora-Pérez1 , Ana Raquel Ramos-Molina2 and Cesar Soria-Fregozo1

1 Laboratory of Psychobiology, University Center of Los Lagos, University of Guadalajara, Lagos de Moreno, Jalisco, Mexico

2 University Center of Los Lagos, University of Guadalajara, Lagos de Moreno, Jalisco, Mexico

\*Address all correspondence to<EMAIL_ADDRESS>
© 2020 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.


**4. Narcissism**

certain analysis and predictions. The CIT was considered useful methodology for the phenomenon, dark side of leadership, because the techniques has built in inductive tendency, does not need a hypothesis, does not carry any cultural bias and yields impartial results for study [29]. It was used carefully with the 32 school teachers of Pakistani schools from both public and private sectors to explore the influence of dark traits of leadership on the morale and work attitudes. Semi-structured interviews were conducted with all participants who had willingly decided to participate in this study. The protocol was constructed in a way that allowed the teachers to choose any story from their past and narrate it to us without any cues

The participants were given total freedom to tell their story to any length, with probes to reach to a common understanding to their lived experience [30]. Hence, teachers chose those incidents from their life which carried certain significance in their lives and which they could easily relate to us [31]. The aim of using CIT was to use interpretivist approach not only for induction of suitable inferences from the data, but it provided us a fair chance to problematize existing theory and contribute something original and novel to the theory of Dark Triad of leadership. After transcribing all interviews, the suitable themes were generated. In the first step, dark triad of traits was identified through examples identifying the behaviors of supervisors and leaders. In the second step, the outcomes and implications of these behaviors are discussed. Thus, by applying these techniques critically, researcher was able to get new insight into the phenomenon of dark side of leadership and its impact on teachers that may not have been known otherwise [32]. In the following sections, the Dark Triad is discussed with relevant examples from critical incidents reported by the school teachers, the partici-

Machiavellianism is linked with weakening organizational, supervisory and team commitment [33]; most of such managers are reported as abusive supervisors by the people who work under them [34]. All they want is 100% compliance; they cannot listen to what they have

*A teacher narrated an incident: she was writing something on board and could not pay attention to a boy's mischief; she did not miss the chance to insult me; she came into the class and delivered lecture on classroom discipline, whereas, she could have controlled the student herself with a simple eye gesture; but how would she get a chance to braggart about her knowledge. In another incident, a teacher of a boarding school went to attend a marriage ceremony. She had to return by 9:00 pm but she got late. Next day the principal called for a written explanation, which is usually taken on a major offense.*

*Another teacher told her story: Five months back, I was appointed as ESE teacher. I had experience of teaching but not in public institutions, that's why I took special one month training. I learned during training that learning is contextual and performance depends upon previous status of learning and there is always step by step improvement. We have to correlate our teaching strategies to the school environment is compatible with background of students. I was given the responsibility of class three. The previous class result was pathetic that's why I had to work hard to improve result. I did not have any idea of the expectations; neither school head told me any. I tried my level best to fulfill my duty*

not expected and lose temper. Some incidents narrated by teachers are related below:

from the researcher [28].

10 Dark Sides of Organizational Behavior and Leadership

pants of the research.

**3. Machiavellianism**

The narcissists differ greatly in self-adoration, self-evaluation, and sense of self-grandeur [42, 43]. They are perceived as vain, egocentric, and domineering personality who do not tend to look beyond where their nose ends. The narcissists have an endless desire to get recognized for their intelligence, superiority and excellent character and personality [1]. They want to prove that they are the best of all and can do what others cannot; narcissists invite envy, acknowledgment, approval and flattery [44, 45]. Narcissists exaggerate their creative intelligence, leading ability and capacity, in comparison with their peers [46–48]. Their preoccupations with themselves confuse and disturb others [1, 15]. Although narcissists are charismatic and most sociable of all DTs, their indirect need for power [47] seems unethical [49, 50] in managers.

*Many teachers had disclosed that seniority is very much celebrated attribute in Pakistani schools. Most of the conflicts among teachers are about seniority and personal worth in terms of work experience and not diversity of knowledge; it seems all knowledge and experience is about managing negative attitudes of others, how to bear insults and injustice and how to tolerate degradation and zero appreciation of your hard work. There is a long and hard way to go to earn respect from other colleagues.*

*Some young teachers complained that they are more qualified than head teachers especially in case of freshly hired teachers who are MPhil. Their high qualification is often ridiculed, targeted to make them realize that they don't know enough and they are not doing things right, so that they can be disciplined unless someone is related to any high ranked officer or has some strong political connection.*

A narcissist would never endear intellectuals near him/her—any person who is more intelligent or creative than them. A narcissist is the person who aspires to claim all credit unto him/ herself. They would hesitate to say: we did it. He or she will keep the person tight folded and hard bound. Therefore, there is always lack of talent around them; either people deliberately underperform to remain at peace with them or remain wary of being discredited of their hard efforts. Narcissists have a high element of pride attached with their work. They are good listeners; they listen carefully when people give feedback on their performance and later judge whether or not their remarks were sincere.

*A teacher told her story: One day principal called me in her office and told me that head of another campus wanted me to be transferred to him as an accountant but I don't want to send you so I myself must deny the offer as it was not much feasible either. Then she started telling me about certain negative factors about the other campus. She didn't want to deny the other principal risking her professional relationships. She wanted me to stay with her as I am shy and comply with her work demands and attitudes. She knew that I will adjust very well there but insisted on keeping me with her, in spite of the fact that I was very much interested in the transfer. I wondered that people are seeking personal benefit*

Dark Side of Leadership in Educational Setting http://dx.doi.org/10.5772/intechopen.78790 13

*Finally, I decided to join the other campus as an accountant realizing that teachers are less valued than the accountants. Before leaving I had to take 10 days training for accountancy, which I took but I was not passed in the test and could never go to other branch. Later, I had to do double duty for my madam, both of teaching and accountancy to stay in the job.  People become vindictive for a life time if you oppose them even for a minor reason.* Psychopaths can target people for their specific aims; they enjoy making fools of others,

*A teacher recounted: Once an officer came for school inspection and the school head was not present there, she had gone on a visit to another branch. The officer commander her immediate return and reprimanded her without even listening to her. At last, when he cooled down and acknowledged that she was right, he did not apologize and left. The headmistress then turned toward us to displace her anger*

*The other told her story: The school head was on a usual school round; she saw a key book on a child's desk and started shouting that why are you using key book for teaching. She was told that it is necessary to teach grammar but she did not listen and insulted us all. She tagged me as rude and ill-mannered as*

They are always scheming and planning to get advantage and would attempt to ruin whoever comes in their way. They are masters in diverting attention of others by successfully masking

*one teacher reported that her headmistress removed all staff reporting to higher ups that the teachers were caught during helping students in cheating for their exams. Teachers are oppressed and depressed; there is a general comment: Nobody is accepting and respecting the role of teachers in education. Anybody can easily take a step against teachers. Another teacher reported that she went to the washroom for two minutes. The headmistress was on round; she came to her class and started to ask the students where*

DTs may demonstrate soft reaction (e.g., ungratefulness and irrationality) or hard measures (e.g., assertiveness and direct manipulations) while pursuing their personal goals [1]. Whether characterized by an impulse of using force, being "hard" and "pushing" or being soft distinguished by glib charm and manipulativeness. However, leaders occupy much stronger positions in the middle and upper hierarchy, more than what could be desired for [1, 53, 58]. Machiavellianism and primary psychopathy appear to be completely identical psychological concepts [62] for their uncontrolled ambition and aggression, exploitation, tendency to harm others both physically and psychologically. Psychopaths are more unscrupulous in taking

unmindful of the harm and psychological pain they cause others [10].

*and blamed all of us for her insult. Where would we turn? To our students…?*

themselves in sweetness and smartness. They can lie shamelessly, as

*your teacher is. When I returned, she started to insult me in front of the class.*

**6. Overlapping characteristics of the dark triad**

*and completely ignoring what I had wanted.*

*I had tried to explain.*


Contents

Preface

This book is a select collection of works on the homology modeling technique,

Molecular modeling by homology is a technique that has been growing and becoming popular in several fields of science such as structural bioinformatics,

Through this tool, it is possible to predict the three-dimensional structure of a protein from its primary sequence of amino acids, as long as there is a threedimensional structure already known of a homologous protein to be used as a

The theoretical models obtained by the homology modeling technique have numerous uses. One is that knowledge of the 3D structure of a protein is crucial for understanding its function and behavior. Thus, theoretical models of proteins are formidable for a good understanding of biological systems and intra- and

This book is aimed at researchers and academic students in areas related to molecular modeling, biotechnology, and molecular biology. It consists of seven

Section 1 contains the introductory chapter (Chapter 1), in which the editor and co-editors of the book make a synthetic and objective approach to the technique of

Section 2 presents two excellent review chapters that address fascinating topics in molecular modeling. Chapter 2 presents the Normal Mode Analysis technique, with examples and excellent didactic-scientific description. Chapter 3 takes a great

In Section 3, readers will be able to find scientific works with in silico experiments that used the modeling technique. This section consists of two chapters, where readers can find practical use in real academic work using molecular protein

Section 4 contains two chapters that address applications associated with modeling.

approach to using force fields to validate three-dimensional models.

Other applications are in the field of biotechnology and drug discovery. Theoretical models of target proteins for drugs or with applicability in genetic engineering can accelerate several discoveries of importance for biotechnological and therapeutic advances. Simulation studies of docking and molecule dynamics using theoretical

theoretical and biochemical chemistry, and computational biophysics.

also called comparative modeling.

extracellular processes of living organisms.

chapters carefully selected and reviewed.

comparative modeling, presenting this tool to the reader.

models have grown enormously.

modeling techniques.

template.

Energy Minimization *by Budhayash Gautam*


*Article* **Investigation of 3D-Moldability of Flax Fiber Reinforced Beech Plywood**

**Johannes Jorda 1,2, Günther Kain 1,\*, Marius-Catalin Barbu 1,3, Matthias Haupt 1 and L'uboš Krišt'ák 4**

Received: 30 October 2020; Accepted: 26 November 2020; Published: 29 November 2020

**Abstract:** The current work deals with three dimensionally molded plywood formed parts. These are prepared in two different geometries using cut-outs and relief cuts in the areas of the highest deformation. Moreover, the effect of flax fiber reinforcement on the occurrence and position of cracks, delamination, maximum load capacity, and on the modulus of elasticity is studied. The results show that designs with cut-outs are to be preferred when molding complex geometries and that flax fiber reinforcement is a promising way of increasing load capacity and stiffness of plywood formed parts by respectively 76 and 38% on average.

**Keywords:** plywood; veneer 3D moldability; natural fiber reinforcement

## **1. Introduction**

The world is not flat-driven by the rising consumer awareness for the ecological product footprint, designers are set to bid and overcome the limits for material applications. Composite materials are developed to surpass single inferior material properties in order to combine quality characteristics for specific maximum performance. A broadly available, natural composite material resource is wood-defined as a natural polymeric, cellular fiber composite with superior advantages compared to other engineering materials [1]. Various wood-based products, such as cross laminated timber (CLT), particleboard, oriented strand boards (OSB) or fiberboards, resolve solid wood disadvantages, respectively anisotropy, biodegradability, and dimensional limitations [2].

Plywood, with its multilayered veneer-based laminar structure, is considered to be the oldest and the most important wood-based composite material with two distinct fields of application—construction purposes and multidimensional forming for interior and exterior products. Plywood can be bent by steaming a panel before forming, thin panels can be threaded and glued together or veneer layers are mechanically modified when producing 3D-molded parts [3]. To enhance veneer-based products (plywood and laminated veneer lumber) mechanical load bearing capacity, several experimental studies were conducted addressing synthetic glass, carbon, or other artificial fiber reinforcement [4–8]. Results revealed significantly improved mechanical properties for modulus of elasticity (MOE) and modulus of rupture (MOR), dimensional stability, and especially splitting strength [9–11]. Currently, the focus on fiber reinforcement shifted to more ecofriendly, fiber sources based on renewable

resources. Flax (*Linum usitatissium*), ramie (*Boehmeria nivea*), hemp (*Cannabis sativa*), sisal (*Agave sisalana*), kenaf (*Hisbiscus cannabinus*), jute (*Corhorus capsularis*) or bamboo are characterized by biodegradability, cost effectiveness, natural availability [12,13]. Natural fibers are emerging at low cost, lightweight and apparently environmentally superior alternatives to glass fibers in composites. The current mass-based price of raw processed glass fibers with a density of 2.6 g/cm3 is approximately 2 to 4 times greater than that of e.g., flax fibers with a density of 1.5 g/cm3 [14,15]. The elevated mechanical properties of lightness, stiffness to weight ratio, and high tensile strength of natural fibers are advantageous for high performance composites [16,17]. For instance, flax with a density of 1.50 g/cm3 , tensile strength between 345 to 1100 N/mm2 , and an MOE of 27,600 to 64,500 N/mm2 [18] is characterized by a relatively high stiffness, load capacity, and damping performance and shows comparable mechanical performance as e-glass and s-glass fibers. Moreover, flax is flexible and preferred for complicated geometries [19]. B˝ohm et al. [20] evaluated the bending characteristics of sandwich composite materials based on balsa plywood reinforced with flax (2 × 2 twill, 400 g/m2 ) and glass fibers (roving fabric, 390 g/m2 ) with epoxy resin. Reinforcement of the balsa plywood with both types of fibers significantly increased the modulus of elasticity and bending strength. Whilst for flax fibers, the flexural modulus was 7.5% higher than for glass fibers, the bending strength values of glass fibers were 26.5% lower compared to flax fibers. Research confirmed that flax fibers with less environmental impact may be a material that is used as an adequate replacement of glass fibers. Papadopoulos and Hague [21] prepared single-layer particleboards made from various wood chip/flax mixtures bonded with urea formaldehyde resin. The strength properties of boards containing up to 30% (mass-based) flax particles meet the minimum European standard (EN 310, 317, 319) requirements for interior particleboards. In the research of Susainathan et al. [22,23], glass fiber, carbon fiber, and flax fiber were used as the surface layer, poplar and okoume as the core layer to make wood-based sandwich structures. The impact and bending properties of the boards with flax fiber reinforcement showed comparable bending strength and stiffness as glass fiber reinforced samples. Research on fiber reinforcement primarily focuses on two-dimensional panel applications [24–26].

Bendability (formability) of two-dimensional curvature for wood is well investigated [27]. Three-dimensional (3D) molding of wood is considered as one of the most complicated chipless methods of shaping wood [28,29]. In general, limitations for veneer formability are set by the anisotropic character of wood and influenced by the MOE and tensile strength for the two directions parallel and perpendicular to grain. Wagenführ et al. [30] revealed a correlation between bending radius and veneer thickness for two-dimensional bending with a significant increase for the minimal possible radius with increasing veneer thickness and dependence on grain direction for non-modified veneers. Additional research on non-modified two-dimensional veneer bending suggested a higher suitability of tangential veneers for molding [31]. 3D veneer moldability is furthermore limited by the anisotropic nature, varying tensile strength, and plastic deformation of veneers [30]. Other relevant parameters are wood species, moisture content, sample and molding geometry in this respect. Deciduous wood species like beech (*Fagus sylvatica* L.) are considered more suitable for 3D-molding due to wood anatomy and plasticizing ability. Wood moisture content, heat pressing, moistening of wood are process variables which are relevant for surface quality in 3D wood molding [32]. It was shown that the 3D formability of veneer can be improved by 12 to 50% by increasing veneer moisture content and steaming. Birch (*Betula pendula Roth*) veneer showed better forming properties than beech (*Fagus sylvatica* L.) and ash (*Fraxinus excelsior*) [33]. Warping and cracking in the forming process depends strongly on veneer thickness [29]. According to Fekiaˇc and Gáborík [27], there is no clear preference between radial and tangential veneers for 3D molding. Another way to increase the moldability of the wood is surface densification, hydrothermal plasticizing, thermal modification, reinforcement by natural fibers, and the optimization of the pressing process [34]. Zerbst et al. [35] successfully applied the Nakjima test to evaluate the deep drawing capacity of veneer laminate, which can be used for forming simulations. The authors found that cracks in veneer laminate sheets occur in the early wood zone and propagate in grain direction.

The aim of the study is to determine the influence of woven natural flax fiber reinforcement on 3D molded beech veneer-based plywood with a specific molding geometry. The occurrence of surface cracks and delamination as well as 3D-bending behavior for maximum load and MOE with the factors mold geometry and fiber-reinforcement are investigated. The aim of the study is to determine the influence of woven natural flax fiber reinforcement on 3D molded beech veneer-based plywood with a specific molding geometry. The occurrence of surface cracks and delamination as well as 3D-bending behavior for maximum load and MOE with the factors mold geometry and fiber-reinforcement are investigated. cracks and delamination as well as 3D-bending behavior for maximum load and MOE with the factors mold geometry and fiber-reinforcement are investigated. **2. Materials and Methods**

3D molded beech veneer-based plywood with a specific molding geometry. The occurrence of surface

*Polymers* **2020**, *12*, 2852 3 of 12

#### **2. Materials and Methods 2. Materials and Methods**  *2.1. Sample Preparation*

#### *2.1. Sample Preparation 2.1. Sample Preparation*  Pre-conditioned (20 °C, 65% relative humidity) radial sliced zero defect beech (*Fagus sylvatica L.*)

Pre-conditioned (20 ◦C, 65% relative humidity) radial sliced zero defect beech (*Fagus sylvatica* L.) veneers with a thickness of 0.6 mm, an average density of 0.67 g/cm3 , and an average moisture content of 10.2 (SD = 0.3) % were used as wooden raw material in this study due to its superior bending strength and MOE performance compared to birch (*Betula pendula Roth)*. Twill flax fabric LINEO FlaxPly Balanced Fabric 200 (Ecotechnilin, Valliquerville, France) with a thickness of 0.4 mm, a density of 1.27 g/cm3 , and a grammage of 200 g/m2 acted as fiber reinforcement. The flax moisture content accounted for 11 (SD = 0.3) %. West Systems International (Romsey, England) 105 Epoxy Resin and 207 Special Coating Hardener were used as adhesive. Two kinds of lay-ups were introduced (Figure 1). The unreinforced reference samples existed of ninety degree cross layered veneer layers, whereas the flax fiber reinforced samples consisted of the identical ninety cross layered veneer layers with additional four layers of flax fabric. These were located at the first and second glue line on each side in order to improve the tensile strength under bending and to minimize the influence of shear stresses. The calculated amount of epoxy resin per glue line was set to 200 g/m2 for the veneer to veneer layers and 400 g/m2 for flax fiber to veneer. Pre-conditioned (20 °C, 65% relative humidity) radial sliced zero defect beech (*Fagus sylvatica L.*) veneers with a thickness of 0.6 mm, an average density of 0.67 g/cm3, and an average moisture content of 10.2 (SD = 0.3) % were used as wooden raw material in this study due to its superior bending strength and MOE performance compared to birch (*Betula pendula Roth)*. Twill flax fabric LINEO FlaxPly Balanced Fabric 200 (Ecotechnilin, Valliquerville, France) with a thickness of 0.4 mm, a density of 1.27 g/cm3, and a grammage of 200 g/m2 acted as fiber reinforcement. The flax moisture content accounted for 11 (SD = 0.3) %. West Systems International (Romsey, England) 105 Epoxy Resin and 207 Special Coating Hardener were used as adhesive. Two kinds of lay-ups were introduced (Figure 1). The unreinforced reference samples existed of ninety degree cross layered veneer layers, whereas the flax fiber reinforced samples consisted of the identical ninety cross layered veneer layers with additional four layers of flax fabric. These were located at the first and second glue line on each side in order to improve the tensile strength under bending and to minimize the influence of shear stresses. The calculated amount of epoxy resin per glue line was set to 200 g/m² for the veneer to veneer layers and 400 g/m2 for flax fiber to veneer. veneers with a thickness of 0.6 mm, an average density of 0.67 g/cm3, and an average moisture content of 10.2 (SD = 0.3) % were used as wooden raw material in this study due to its superior bending strength and MOE performance compared to birch (*Betula pendula Roth)*. Twill flax fabric LINEO FlaxPly Balanced Fabric 200 (Ecotechnilin, Valliquerville, France) with a thickness of 0.4 mm, a density of 1.27 g/cm3, and a grammage of 200 g/m2 acted as fiber reinforcement. The flax moisture content accounted for 11 (SD = 0.3) %. West Systems International (Romsey, England) 105 Epoxy Resin and 207 Special Coating Hardener were used as adhesive. Two kinds of lay-ups were introduced (Figure 1). The unreinforced reference samples existed of ninety degree cross layered veneer layers, whereas the flax fiber reinforced samples consisted of the identical ninety cross layered veneer layers with additional four layers of flax fabric. These were located at the first and second glue line on each side in order to improve the tensile strength under bending and to minimize the influence of shear stresses. The calculated amount of epoxy resin per glue line was set to 200 g/m² for the veneer to veneer layers and 400 g/m2 for flax fiber to veneer.

**Figure 1.** Veneer layup reference (**a**), with flax fiber reinforcement (**b**).

**Figure 1.** Veneer layup reference (**a**), with flax fiber reinforcement (**b**). **Figure 1.** Veneer layup reference (**a**), with flax fiber reinforcement (**b**).

The specimens were designed focusing on the use of the molded parts as car seat shells (Figure

The specimens were designed focusing on the use of the molded parts as car seat shells (Figure 2). A transition section between seating and back was considered in the design of the specimens. The seating shell was split in the center, and looking in driving direction, the left part of the shell was considered. The size of the raw veneer sheets accounted for 20 × 27.5 cm. The specimens were designed focusing on the use of the molded parts as car seat shells (Figure 2). A transition section between seating and back was considered in the design of the specimens. The seating shell was split in the center, and looking in driving direction, the left part of the shell was considered. The size of the raw veneer sheets accounted for 20 × 27.5 cm. 2). A transition section between seating and back was considered in the design of the specimens. The seating shell was split in the center, and looking in driving direction, the left part of the shell was considered. The size of the raw veneer sheets accounted for 20 × 27.5 cm.

**Figure 2.** Dimension of the 3D molded specimens (dimensions in mm). **Figure 2.** Dimension of the 3D molded specimens (dimensions in mm).

**Figure 2.** Dimension of the 3D molded specimens (dimensions in mm).

To overcome the veneer warping during molding, two different options where used. First, a minimal leaving out of the critical curvature was applied (Figure 3). To overcome the veneer warping during molding, two different options where used. First, a minimal leaving out of the critical curvature was applied (Figure 3). minimal leaving out of the critical curvature was applied (Figure 3).

To overcome the veneer warping during molding, two different options where used. First, a

**Figure 3.** Cut-out of specimens (**a**) reference, (**b**) with flax fiber reinforcement. **Figure 3.** Cut-out of specimens (**a**) reference, (**b**) with flax fiber reinforcement. **Figure 3.** Cut-out of specimens (**a**) reference, (**b**) with flax fiber reinforcement.

Second, relief cuts at the critical curvature were provided (Figure 4). These were filled with an Epoxy filler (Molto 2-components wood replacement) after pressing. In total, four different types of setups with three samples each were tested. Second, relief cuts at the critical curvature were provided (Figure 4). These were filled with an Epoxy filler (Molto 2-components wood replacement) after pressing. In total, four different types of setups with three samples each were tested. Second, relief cuts at the critical curvature were provided (Figure 4). These were filled with an Epoxy filler (Molto 2-components wood replacement) after pressing. In total, four different types of setups with three samples each were tested.

**Figure 4.** Relief cut of specimens (**a**) reference, (**b**) with flax fiber reinforcement. **Figure 4.** Relief cut of specimens (**a**) reference, (**b**) with flax fiber reinforcement.

**Figure 4.** Relief cut of specimens (**a**) reference, (**b**) with flax fiber reinforcement. The lay-up of the veneer laminates and the glue application were conducted manually. The calculated areal glue amount spreading per layer was checked by a scales KERN PRS 620-6 (Kern & Sohn GmbH, Ballingen-Frommern, Germany). The controlled molding was carried out using a HÖFLER (Taiskirchen, Austria) HLOP 280 press to reach the target thickness of 10 mm within 15 h of cold pressing. The applied pressure during molding was 2.5 N/mm2 for the reference samples and 2.8 N/mm2 for the flax fiber reinforced samples. The temperature was kept constant at 20 °C. No pretreatment of the veneers was applied to improve the bending performance. Before further testing, the samples were stored for seven days under constant standard climate conditions (20 °C, 65% The lay-up of the veneer laminates and the glue application were conducted manually. The calculated areal glue amount spreading per layer was checked by a scales KERN PRS 620-6 (Kern & Sohn GmbH, Ballingen-Frommern, Germany). The controlled molding was carried out using a HÖFLER (Taiskirchen, Austria) HLOP 280 press to reach the target thickness of 10 mm within 15 h of cold pressing. The applied pressure during molding was 2.5 N/mm2 for the reference samples and 2.8 N/mm2 for the flax fiber reinforced samples. The temperature was kept constant at 20 °C. No pretreatment of the veneers was applied to improve the bending performance. Before further testing, the samples were stored for seven days under constant standard climate conditions (20 °C, 65% relative humidity). The lay-up of the veneer laminates and the glue application were conducted manually. The calculated areal glue amount spreading per layer was checked by a scales KERN PRS 620-6 (Kern & Sohn GmbH, Ballingen-Frommern, Germany). The controlled molding was carried out using a HÖFLER (Taiskirchen, Austria) HLOP 280 press to reach the target thickness of 10 mm within 15 h of cold pressing. The applied pressure during molding was 2.5 N/mm2 for the reference samples and 2.8 N/mm2 for the flax fiber reinforced samples. The temperature was kept constant at 20 ◦C. No pretreatment of the veneers was applied to improve the bending performance. Before further testing, the samples were stored for seven days under constant standard climate conditions (20 ◦C, 65% relative humidity).

#### relative humidity). *2.2. Testing of Surface Cracks and Delamination 2.2. Testing of Surface Cracks and Delamination*

*2.2. Testing of Surface Cracks and Delamination*  Surface cracks and delamination were determined after pressing and conditioning of the formed Surface cracks and delamination were determined after pressing and conditioning of the formed Surface cracks and delamination were determined after pressing and conditioning of the formed parts. Samples were trimmed to equal size before proceeding to the 3D bending test.

parts. Samples were trimmed to equal size before proceeding to the 3D bending test. To determine the surface crack length and widths, pictures were taken with a digital camera (Rollei Compactline 750) and a scale positioned on the formed parts. For the exact determination of length and width, MATLAB R2018a was used according to Equation (1). On each picture taken, a parts. Samples were trimmed to equal size before proceeding to the 3D bending test. To determine the surface crack length and widths, pictures were taken with a digital camera (Rollei Compactline 750) and a scale positioned on the formed parts. For the exact determination of length and width, MATLAB R2018a was used according to Equation (1). On each picture taken, a scale was installed, to determine the dimensions of cracks and delamination considering the pixel-To determine the surface crack length and widths, pictures were taken with a digital camera (Rollei Compactline 750) and a scale positioned on the formed parts. For the exact determination of length and width, MATLAB R2018a was used according to Equation (1). On each picture taken, a scale was installed, to determine the dimensions of cracks and delamination considering the pixel-based

length of the defect *lpixel*, the pixel-based length of the reference scale *lre f*. *pixel*, and the known length of the scale *lre f*. The delamination length was determined using the identical formula. In addition, a verbal nomenklatura was introduced to describe the location of surface cracks and delamination in order to locate critical spots of failure. First of all, cracks and delamination were categorized whether they occurred (1–1) on the front or (1–2) back of the formed part. Second, it was described whether they occurred (2–1) on the back shell or (2–2) on the seat. Third, defects were assessed regarding their position relative to the transition radius; (3–1) transition radius, (3–2) above transition radius, (3–3) below transition radius. Finally, defects on edges were assessed using the attributes (4–1) outer edge, (4–2) edge cut-out. All measurements were taken from formed parts to exclude influences caused by post-processing. delamination in order to locate critical spots of failure. First of all, cracks and delamination were categorized whether they occurred (1–1) on the front or (1–2) back of the formed part. Second, it was described whether they occurred (2–1) on the back shell or (2–2) on the seat. Third, defects were assessed regarding their position relative to the transition radius; (3–1) transition radius, (3–2) above transition radius, (3–3) below transition radius. Finally, defects on edges were assessed using the attributes (4–1) outer edge, (4–2) edge cut-out. All measurements were taken from formed parts to exclude influences caused by post-processing. = ௫ .௫ × . (1)

*Polymers* **2020**, *12*, 2852 5 of 12

based length of the defect ௫, the pixel-based length of the reference scale .௫, and the known

addition, a verbal nomenklatura was introduced to describe the location of surface cracks and

$$l = \frac{l\_{\text{pixel}}}{l\_{\text{ref. pixel}}} \times l\_{\text{ref.}} \tag{1}$$

#### *2.3. Three-Dimensional Bending Test* the direction of force for spreading was implemented. For testing, the samples were placed with the

*2.3. Three-Dimensional Bending Test*

A modified bending test following UN/ECE Regulations Nr. 17 [36] with a variation regarding the direction of force for spreading was implemented. For testing, the samples were placed with the small faces on an aluminum block due to its low friction coefficient to reduce influences on internal stress distribution (Figure 5). Constant linear force with a speed of 10 mm/min was applied by a pressure disc (ø 135 mm) parallel to the supports using a Zwick/Röll Z 250. The maximum load (Fmax) and the modulus of elasticity (MOE) were determined following EN 310:2005 [37]. small faces on an aluminum block due to its low friction coefficient to reduce influences on internal stress distribution (Figure 5). Constant linear force with a speed of 10 mm/min was applied by a pressure disc (ø 135 mm) parallel to the supports using a Zwick/Röll Z 250. The maximum load (Fmax) and the modulus of elasticity (MOE) were determined following EN 310:2005 [37]. The statistical significance of the factors molding geometry and fiber-reinforcement was determined using two-way ANOVAs with consideration of interaction effects of first order.

A modified bending test following UN/ECE Regulations Nr. 17 [36] with a variation regarding

**Figure 5.** Bending test for 3D molded plywood samples. **Figure 5.** Bending test for 3D molded plywood samples.

**3. Results and Discussion**  The statistical significance of the factors molding geometry and fiber-reinforcement was determined using two-way ANOVAs with consideration of interaction effects of first order.

The finished specimens showed up to 6 cracks and between 1 and 2 delamination after pressing.

#### *3.1. Number of Surface Cracks and Delamination*  **3. Results and Discussion**

#### Comparing the number of counted surface cracks for each of the four groups, it was assumed that *3.1. Number of Surface Cracks and Delamination*

there is an influence of the factors molding geometry and fiber reinforcement. Based on a two-way ANOVA to prove the statistical significance of the factors molding geometry (*p*-value 0.074) and fiber reinforcement (*p*-value 0.334) displayed that there is no significant influence. In addition, there is no significant interaction effect of the factors. This can be explained by the high variation of crack numbers between specimens (Table 1). The finished specimens showed up to 6 cracks and between 1 and 2 delamination after pressing. Comparing the number of counted surface cracks for each of the four groups, it was assumed that there is an influence of the factors molding geometry and fiber reinforcement. Based on a two-way ANOVA to prove the statistical significance of the factors molding geometry (*p*-value 0.074) and fiber reinforcement (*p*-value 0.334) displayed that there is no significant influence. In addition, there is no significant interaction effect of the factors. This can be explained by the high variation of crack numbers between specimens (Table 1).

**Table 1.** Number of cracks and crack geometry after bending (SD in brackets).

To determine the influence of the factors molding geometry and fiber reinforcement on the number of delamination, the same procedure as for the surface cracks was applied. The two-way ANOVA displayed a significant influence of the molding geometry with a *p*-value of 0.037. On average, formed parts with a cut-out showed one delamination, whilst parts with relief cuts had two delaminations after pressing (Table 2). The fiber-reinforcement (*p*-value 0.631) such as the factor interaction (*p*-value 0.631) in contrast had no significant influence on the number of delaminations.

**Table 2.** Number and length of delamination after bending (SD in brackets).

Considering these statistics, it seems that the cracks and delamination are predominantly caused by deformations occurring during the molding process rather than ineffective gluing between composite layers.

#### *3.2. Length and Width of Surface Cracks and Delamination*

The effect of the factors molding geometry and fiber reinforcement on the length of cracks was assessed using a two-way ANOVA. Only specimens with cracks were considered. According to the ANOVA, the *p*-value for the interaction between the factors is significant with 0.030, stating the fact that the level effect of one factor is dependent on the level of the other factor. Cracks on fiber reinforced parts with cut-out have an average length of 6.7 (SD = 2.3) mm, 64% lower than their unreinforced counterpart—a coherence that could not be shown for formed parts with relief cuts.

In contrast, the results of the surface crack widths had no statistically significant factor effect or interaction (*p*-value 0.196) between the two factors molding geometry and fiber reinforcement. This is underlined by the singular *p*-value for molding geometry with 0.774 and fiber reinforcement with a *p*-value 0.864.

Based on the comparison of the mean and standard deviations of the factors, the two-way ANOVA revealed no statistically significant influence on the delamination length. Molding geometry (*p*-value 0.587) and fiber reinforcement (*p*-value 0.203) showed no significant interaction effect (*p*-value of 0.450).

The sum of the crack length of a specimen is significantly (*p*-value 0.034) affected by the molding geometry, showing that it accounts for 16.6 (SD = 27.9) mm with formed parts with cut-out compared to 64.6 (SD = 33.5) mm with relief cut. The cumulated crack width per sample is not significantly affected by the mold geometry or fiber reinforcement. The effect of molding geometry on the cumulated length of delamination is narrowly not significant (*p*-value 0.053). The average sum of delamination length accounts for 12.9 (SD = 10.5) mm when using cut-outs and 23.6 (SD = 4.0) mm when relief cuts are applied (Table 3). Summarized, it was found that molded parts with relief cut have more and additionally more significant cracks and delamination than parts with a cut-out. The sum of the

crack lengths is two thirds lower when applying fiber reinforcement for parts with cut-out, whereas no advantage of fiber reinforcement could be detected for parts with relief cuts. The investigation of cracks and delamination shows that the total sum of defect characteristics is higher for parts with relief cuts. This is due to the fact that a greater part of the critical sector of the transition zone is covered. The forced deformations are greater with the relief cut formed parts and exceed more often the strength of the veneer. The fiber reinforced parts with cut-out show lower crack and delamination length, probably due to the fact that fabric with twill weave is easily shear formable and has good draping properties [38]. *Polymers* **2020**, *12*, 2852 7 of 12 out, whereas no advantage of fiber reinforcement could be detected for parts with relief cuts. The investigation of cracks and delamination shows that the total sum of defect characteristics is higher for parts with relief cuts. This is due to the fact that a greater part of the critical sector of the transition zone is covered. The forced deformations are greater with the relief cut formed parts and exceed more often the strength of the veneer. The fiber reinforced parts with cut-out show lower crack and delamination length, probably due to the fact that fabric with twill weave is easily shear formable and has good draping properties [38].

**Table 3.** Number and length of delamination after bending (SD in brackets). **Table 3.** Number and length of delamination after bending (SD in brackets).

#### *3.3. Location and Orientation of Defects 3.3. Location and Orientation of Defects*

Surface cracks occurred with a relative frequency of 67 (SD = 31) % on the inner (positive) side of the molding with the shorter radius. Ninety-seven (SD = 11) percent are located at the "transition radius" due to the sharp radius and the change of direction into three different dimensions. Seventy-six (SD = 22) percent are placed on the outer edges of the molding (Figure 6). The reason is, that tensions cannot be transferred to neighboring veneer layers in the corner range which results in cracks. All surface cracks are oriented in grain direction, because the tensile strength of beech veneer orthogonally to grain direction is 20 times lower than in grain direction [39], which is confirmed by Zerbst et al. [35] finding the same phenomenon when producing molded veneer laminates. Surface cracks occurred with a relative frequency of 67 (SD = 31) % on the inner (positive) side of the molding with the shorter radius. Ninety-seven (SD = 11) percent are located at the "transition radius" due to the sharp radius and the change of direction into three different dimensions. Seventysix (SD = 22) percent are placed on the outer edges of the molding (Figure 6). The reason is, that tensions cannot be transferred to neighboring veneer layers in the corner range which results in cracks. All surface cracks are oriented in grain direction, because the tensile strength of beech veneer orthogonally to grain direction is 20 times lower than in grain direction [39], which is confirmed by Zerbst et al. [35] finding the same phenomenon when producing molded veneer laminates.

**Figure 6.** Heat map of crack number and position. **Figure 6.** Heat map of crack number and position.

Cracks are not acceptable in molded parts due to structural and aesthetic reasons. A possible optimization is to create micro cracks and collapsed cells in veneer layers before molding to prevent the formation of macro cracks. It is important to note that a collapsed cell not necessarily goes along with a broken cell wall [30]. Cracks are not acceptable in molded parts due to structural and aesthetic reasons. A possible optimization is to create micro cracks and collapsed cells in veneer layers before molding to prevent the formation of macro cracks. It is important to note that a collapsed cell not necessarily goes along with a broken cell wall [30].

Delaminations were predominantly found on the inner (front) side as well (Figure 7). Seventyseven (SD = 26) percent occurred on the more strongly bent inner side. All of them were found above the transition radius on the formed parts where the shear strengths were strongest. For the same reason, these occurred in large part with some distance to the cut-out referenced to the edge position. Ninety-five percent of all delaminations were found near the outer edge of the formed parts. The use of rigid press forms results in an uneven pressure distribution because the application of uniaxial Delaminations were predominantly found on the inner (front) side as well (Figure 7). Seventy-seven (SD = 26) percent occurred on the more strongly bent inner side. All of them were found above the transition radius on the formed parts where the shear strengths were strongest. For the same reason, these occurred in large part with some distance to the cut-out referenced to the edge position. Ninety-five percent of all delaminations were found near the outer edge of the formed parts. The use of rigid press forms results in an uneven pressure distribution because the application of uniaxial vertical

vertical pressure results in uneven orthogonal pressure referred to the curved surface of the formed

pressure results in uneven orthogonal pressure referred to the curved surface of the formed part [40]. The maximal angle of the form parts used in this study is 50 degrees on the outer edge and the pressure was therefore 36% [40] reduced in this area, as an explanation for the less efficient bonding. The strong influence of the mold geometry on the quality of plywood formed parts was discussed by Comsa [41], suggesting deformation modeling using finite element methods. This shows an interesting opportunity for the current mold part to lower crack and delamination formation during molding. Finally, the use of plasticized veneer (at least the outer layers) before pressing suggests to lower the risk for cracks [34]. *Polymers* **2020**, *12*, 2852 8 of 12 bonding. The strong influence of the mold geometry on the quality of plywood formed parts was discussed by Comsa [41], suggesting deformation modeling using finite element methods. This shows an interesting opportunity for the current mold part to lower crack and delamination formation during molding. Finally, the use of plasticized veneer (at least the outer layers) before pressing suggests to lower the risk for cracks [34]. *Polymers* **2020**, *12*, 2852 8 of 12 bonding. The strong influence of the mold geometry on the quality of plywood formed parts was discussed by Comsa [41], suggesting deformation modeling using finite element methods. This shows an interesting opportunity for the current mold part to lower crack and delamination formation during molding. Finally, the use of plasticized veneer (at least the outer layers) before pressing suggests to lower the risk for cracks [34].

**Figure 7.** Heat map of delamination number and position in the 3D-molded plywood samples after forming. **Figure 7.** Heat map of delamination number and position in the 3D-molded plywood samples after forming. forming. *3.4. 3D Bending Test*

#### *3.4. 3D Bending Test 3.4. 3D Bending Test* Based on the load-deformation curvature, two thirds of the samples with cut-outs showed a

Based on the load-deformation curvature, two thirds of the samples with cut-outs showed a linear-elastic deformation behavior and a nondescriptive fracture with a mixture of delaminations and failures within the beech veneer (Figure 8). One third of samples had a partial fracture behavior within the linear-elastic deformation with a notable tension failure. The load-deformation curve for relief cut samples revealed a semi-fracture at the end of the linear-elastic range caused by the failure of the filler regardless of fiber reinforcement, followed by a further plastic deformation. Fiber reinforcement resulted in an increase in force for both cut-out and relief cut samples in the plastic deformation range, whereas unreinforced samples of both groups more or less stagnated. These findings validate research by Wagenführ et al. [30] considering that veneer laminates behave Based on the load-deformation curvature, two thirds of the samples with cut-outs showed a linear-elastic deformation behavior and a nondescriptive fracture with a mixture of delaminations and failures within the beech veneer (Figure 8). One third of samples had a partial fracture behavior within the linear-elastic deformation with a notable tension failure. The load-deformation curve for relief cut samples revealed a semi-fracture at the end of the linear-elastic range caused by the failure of the filler regardless of fiber reinforcement, followed by a further plastic deformation. Fiber reinforcement resulted in an increase in force for both cut-out and relief cut samples in the plastic deformation range, whereas unreinforced samples of both groups more or less stagnated. These findings validate research by Wagenführ et al. [30] considering that veneer laminates behave predominantly elastically. linear-elastic deformation behavior and a nondescriptive fracture with a mixture of delaminations and failures within the beech veneer (Figure 8). One third of samples had a partial fracture behavior within the linear-elastic deformation with a notable tension failure. The load-deformation curve for relief cut samples revealed a semi-fracture at the end of the linear-elastic range caused by the failure of the filler regardless of fiber reinforcement, followed by a further plastic deformation. Fiber reinforcement resulted in an increase in force for both cut-out and relief cut samples in the plastic deformation range, whereas unreinforced samples of both groups more or less stagnated. These findings validate research by Wagenführ et al. [30] considering that veneer laminates behave predominantly elastically.

**Figure 8.** Force-path diagram for specimens with cut-out (**a**) and relief cut (**b**). **Figure 8.** Force-path diagram for specimens with cut-out (**a**) and relief cut (**b**).

**Figure 8.** Force-path diagram for specimens with cut-out (**a**) and relief cut (**b**). The results of maximum load displayed a significant influence of the molding geometry (*p*-value 0.010) as well as the fiber reinforcement (*p*-value 0.001). Moldings with cut-outs resulted in 58 and 36% higher bending strength than their counterparts with relief cuts. Fiber reinforcement lead to 65 The results of maximum load displayed a significant influence of the molding geometry (*p*-value 0.010) as well as the fiber reinforcement (*p*-value 0.001). Moldings with cut-outs resulted in 58 and 36% higher bending strength than their counterparts with relief cuts. Fiber reinforcement lead to 65 and 92% higher bending strength compared with the unreinforced part, respectively (Table 4). The results of maximum load displayed a significant influence of the molding geometry (*p*-value 0.010) as well as the fiber reinforcement (*p*-value 0.001). Moldings with cut-outs resulted in 58 and 36% higher bending strength than their counterparts with relief cuts. Fiber reinforcement lead to 65 and 92% higher bending strength compared with the unreinforced part, respectively (Table 4).

and 92% higher bending strength compared with the unreinforced part, respectively (Table 4).

**Table 4.** Results of the bending test (SD in brackets).

The reason for the significant increase in the maximal load capacity through flax fiber reinforcement is the high tensile strength of flax fibers, approximately 5 times as high as the one of the wood fiber [38]. This increased tensile strength affects especially the inner side of the formed part which is tensile-loaded in the current experimental situation. As the relief cuts are an interruption in the fiber reinforcement, the filler grouts fail early and are an explanation for the lower performance of such parts.

Regarding the results of the MOE, similar effects are given. The influence of the fiber reinforcement is highly significant (*p*-value 0.001), whereas the influence of the molding geometry—in contrast to the maximum load capacity—was statistically not significant (*p*-value 0.168). Formed parts which are fiber reinforced had an MOE on average 76% higher than the unreinforced parts (Table 4). The mold geometry does not have an effect in this respect, because failures occur above 40% of the maximal force and up to this point the part shows linear-elastic behavior.

A significant correlation between the sum of crack width in a part and the MOE was observed (*p*-value 0.024, R2 = 0.41). The higher the cumulated crack width, the higher the MOE. Moreover, a higher number of cracks result in a not significant higher MOE. A rationale for this coherence is that crack formation during the forming process results in an improved layer contact due to a compensation of the deformations in the transition zones.