**3. On-farm–produced organic amendments**

### **3.1. SOM source and modified C:N ratio of added residues**

Leguminous green manure has long been used as a SOM source as a component of cropping system in Africa, Asia, and Latin American. Cover crops and intercropping increase C sequestration in the soil [21]. Another possible benefit of legumes is the result of N fixation by the root nodules, which the amount of biological fixed N is a somewhat contentious issue in some case studies, but most of the organic N can be available to plants after residues have been composted [22]. Generally green manure can produce a dry weight of 5-9 tons or more biomass ha–1 year–1; about 40% of dry matter is C and 2-4% is N. While the N productivity of several major cultivated legumes has been reported as from 80 kg (berseem clover) to 190 kg (subc‐ lover) ha–1 [23-25]. The ability of biological N fixation ranges from 40 to 200 kg in aboveground tissues ha–1 due to the species of legume, bacterial strain, and agricultural conditions, such as climate and soil (Table 2).

Factors that influence the ability of microorganisms to break down added plant materials includes the C:N ratio of organic matter and components of organic C and N [26]. The C:N ratio of plant tissue reflects the kind and age of a plant from which it was derived. Non-legume plants may have a high C:N ratio, over 60 (cow straw), up to even 250 (wood tissue) [27,28]. Non-leguminous green manure with high a C:N ratio (over 25), will cause microorganisms to tie up available N in the soil. Thus, added materials with C:N ratios above 25:1 can result in N being bound by soil microbes in the breakdown of C-rich crop residues, thus pulling N away from the root zone of crop plants. Legumes usually have a low C:N ratio (about 10-15) and can help to modify the SOM C:N ratio to an adequate level. The optimal C:N ratio for rapid decomposition of organic matter is between 15:1 and 25:1 [29]. The addition of N-rich plant residues, such as legume plants, to aid the decomposition process may be advisable with these high-C residues: the lower the C:N ratio, the more N will be released into the soil for immediate crop use [30].

**Table 2.** Yearly average biomass yields and nitrogen yields of several legumes.

#### **3.2. Intercropping with green manure**

Intercropping refers to multiple crops planted at same time on the same land, growing and interacting with each other during the whole or part of the growing season within a crop system [31,32]. Intercrops or mixture crops influence the farming system in ways including the lower density of each species helping to reduce plant pathogen infection opportunities, raising land productivity as a result of reducing the effects of unsuitable conditions, which may be not so unsuitable to other intercrops, positive effects on weed control, border effects, and enhancing plant nutrient and soil humidity use efficiency. Intercropping can be regarded as a method of weed suppression and offering habitats for beneficial organisms. According to space arrange‐ ments and temporal practices, intercropping is commonly divided into four subcategories [31]:

Crop mixtures may gather more light and plant nutrients than pure standing crops, as a result of differing root depth and stem height. Generally, the land equivalent ratio (LER) is one of the major measures to judge how complementary crops are under intercropping. The mathe‐ matical equation is stated as [33]:

$$\text{LER} = (\text{Yiji} + \text{Yji} \, / \, \text{Yji} + \text{Yii})\_{\prime \prime}$$

where Yij is the grain yield per unit area of species i grown in a mixture with species j, Yii is the grain yield per unit area of species i grown in a pure stand, Yji is the grain yield per unit area of species j grown in mixture with species i, and Yjj is the grain yield per unit area of species j grown in a pure stand.

When the LER is below 1, it indicates that competition exists between different components rather than them being complementary. Generally, under a well-managed intercropping system, the LER is 1.2-1.5 and sometimes even above 1.5. These results are due to the rational use of natural resources for crop growth. As Paolini et al. reported, after 2-year case studies on mixture crops of sunflower and chickpea, total LER figures averaged 1.16 as to aboveground biomass yield and 1.25 as to grain yield [34]. They also pointed out that an unfavorable climate for one species is not so unfavorable to another. The conclusion can be made that when the climate or other agricultural factor becomes the key limiting factor for one crop, the other crop will likely get sufficient plant nutrients and soil moisture water supply; one species will be more tolerant of the unfavorable condition than the other.

Altieri found that in Mexico, 1.73 ha of land had to be planted with maize to produce as much food as 1 ha planted with a mixture of maize, squash, and beans [35]. Additionally, maize + squash + bean polyculture can produce up to 4 tons ha–1 of dry matter for plowing into the soil as compared with 2 tons in a maize monoculture. In Brazil, a maize or sorghum mixture with cowpeas or beans can lead to LER values of 1.25-1.58 [35]. Sometimes under intercropping management, a major crop cannot get the maximum yield obtainable in a monoculture due to competition from the other crop or a lower density versus a pure stand. By interplanting, farmers achieve several production and conservation objectives simultaneously [36]. Polycul‐ tures produce more combined yield in a given area than could be obtained from monocultures of the component species; sometimes, the LER can be above 1.5, although the yield variability of cereal + legume polycultures are much lower than that for monocultures of the components [37]. The intercrop treatments represented the highest LER was 1.52 for baby corn/pea intercropping system [38]. And other maize/bean intercropping achieved LER values were 1.76 and 1.92 [39]. Cover cropping is also considered as a the practice of growing pure or mixed strands of legumes, cereals, or natural vegetation to protect the soil against erosion, ameliorate soil structure issues, enhance soil fertility, and suppress pests, including weeds, insects, and pathogens [31]. The cover crop approach has been used for thousands years ago and is regarded as a sustainable method of agricultural production.

#### **3.3. Living mulch**

decomposition of organic matter is between 15:1 and 25:1 [29]. The addition of N-rich plant residues, such as legume plants, to aid the decomposition process may be advisable with these high-C residues: the lower the C:N ratio, the more N will be released into the soil for immediate

**(tons ha–1)**

Intercropping refers to multiple crops planted at same time on the same land, growing and interacting with each other during the whole or part of the growing season within a crop system [31,32]. Intercrops or mixture crops influence the farming system in ways including the lower density of each species helping to reduce plant pathogen infection opportunities, raising land productivity as a result of reducing the effects of unsuitable conditions, which may be not so unsuitable to other intercrops, positive effects on weed control, border effects, and enhancing plant nutrient and soil humidity use efficiency. Intercropping can be regarded as a method of weed suppression and offering habitats for beneficial organisms. According to space arrange‐ ments and temporal practices, intercropping is commonly divided into four subcategories [31]: **1.** *Row intercropping*: growing two or more crops at the same time with at least one crop

**2.** *Stripe intercropping*: growing more than one crop together in stripes wide enough to permit separate crop production using machines but close enough for the crops to interact with

**4.** *Relay cropping*: planting a second crop in a standing crop at a time when the standing crop is at its reproductive stage but before harvest. According to plant density or land features, the crop with high seeding rates is called the major crop, and the other crop is the

Crop mixtures may gather more light and plant nutrients than pure standing crops, as a result of differing root depth and stem height. Generally, the land equivalent ratio (LER) is one of

**3.** *Mixed intercropping*: growing two or more crops with no distinct row arrangement.

Sweet clover 4.3 130 Berseem clover 2.7 75 Crimson clover 3.5 108 Hair vetch 4.3 118 Subclover 5.4–10.1 184

**Nitrogen (kg ha–1)**

crop use [30].

\*

**Crop Biomass\***

294 Organic Fertilizers - From Basic Concepts to Applied Outcomes

Dry weight of plant aboveground material (sources: [2325])

**3.2. Intercropping with green manure**

planted in rows.

secondary crop.

each other.

**Table 2.** Yearly average biomass yields and nitrogen yields of several legumes.

Living mulch refers to a legume cover-crop, which is undersown with an annual crop. Common living mulches include white clover, hairy vetch, and red clover. A living mulch can improve soil structure and water penetration, prevent soil erosion, modify the microclimate, and reduce weed competition [40]. An ideal crop occupies underused time or space in an existing system. It does not compete with the cash crop for light, water, or nutrients, and attracts beneficial organisms, while keeping harmful pests away. It should be readily estab‐ lished and grow rapidly. It should produce an abundant growth of both shoots and roots in a short time, and its growth habits should encourage ground cover soon after its establishment [41]. Common living mulches can offer soil cover, especially during the seedling period and after harvest of the target crop when the crop plant does not cover most of the soil surface. Subclover planted as a living mulch was able to regenerate and provide the succeeding crop with abundant and N-rich residues [42]. The main benefits of living mulches include enhance‐ ment of soil structure, improvement of soil fertility, and positive effects on pest management and environmental quality [43].

Changing from a monoculture to an intercropping system requires several important man‐ agement practices based on natural laws. Successful management requires investment in experience and research to modify the system into an economically acceptable, ecologically sustainable, and technologically practicable one. In the case of winter wheat, a major crop around the world, legumes, as rotation crops or intercrops, have been tested for the establish‐ ment of the cropping systems. According to Caporali and Campiglia, in search of strategies for increasing sustainability in cropping systems, they have been focusing for 10 years on the use of plant resources, such as self-reseeding winter annual legumes (*Trifolium* and *Medicago* species) native to the Mediterranean environment [44]. Although subclover and annual medics are well-known forage crops in cereal-lay farming systems under the Mediterranean climate around the world, their use is practically unknown in more intensive cash-crop sequences, such as the 2-year rotation between a winter cereal (wheat, barley) and a summer crop (rainfed sunflower, irrigated corn), as is common in central Italy. In this rotation, an annual legume is used as a living mulch in winter cereals, and after its self-reseeding, as either a green manure or living mulch for the succeeding summer crop. This alternative cropping system has proved to have the potential to induce a significant shift toward a less energy-intensive and a more environmentally friendly management type, while maintaining the same cash-crop sequence of the conventional one [44].

The foundation of the system began with the screening of self-reseeding legumes species and cultivars and ended with the implementation and performance assessment of an entire alternative cropping system (winter cereal/summer crop rotation). The yield of winter wheat intercropped with subclover was not significantly different from that of a pure wheat stand in a drier crop year, while in the wetter year the grain yield of the intercropping system was significantly higher than the pure stand. However, in both crop years, grain yields were significantly lower that obtained using 130 kg ha–1 mineral N fertilizer, by 11% and 23%, respectively. Additionally, a positive correlation between the amount of subclover biomass plowed in and the vegetative and productive characteristic of sunflower was found in dry and wet years. Subclover green manure was so effective that sunflower yield in the alternative system was higher than that of the conventional one fertilized with 130 kg ha–1 of inorganic N. Subclover green manure also affected biomass and the composition of the weed community in the sunflower crop. Subclover mulch from a sod strip intercropping system with wheat was also effective in positively influencing the aboveground biomass production of the succeeding crops, the effect being dependent on the amount of dry mulch left by the different subclover species and cultivars [44].

## **3.4. Competition between intercrops and intercropping principles**

and reduce weed competition [40]. An ideal crop occupies underused time or space in an existing system. It does not compete with the cash crop for light, water, or nutrients, and attracts beneficial organisms, while keeping harmful pests away. It should be readily estab‐ lished and grow rapidly. It should produce an abundant growth of both shoots and roots in a short time, and its growth habits should encourage ground cover soon after its establishment [41]. Common living mulches can offer soil cover, especially during the seedling period and after harvest of the target crop when the crop plant does not cover most of the soil surface. Subclover planted as a living mulch was able to regenerate and provide the succeeding crop with abundant and N-rich residues [42]. The main benefits of living mulches include enhance‐ ment of soil structure, improvement of soil fertility, and positive effects on pest management

Changing from a monoculture to an intercropping system requires several important man‐ agement practices based on natural laws. Successful management requires investment in experience and research to modify the system into an economically acceptable, ecologically sustainable, and technologically practicable one. In the case of winter wheat, a major crop around the world, legumes, as rotation crops or intercrops, have been tested for the establish‐ ment of the cropping systems. According to Caporali and Campiglia, in search of strategies for increasing sustainability in cropping systems, they have been focusing for 10 years on the use of plant resources, such as self-reseeding winter annual legumes (*Trifolium* and *Medicago* species) native to the Mediterranean environment [44]. Although subclover and annual medics are well-known forage crops in cereal-lay farming systems under the Mediterranean climate around the world, their use is practically unknown in more intensive cash-crop sequences, such as the 2-year rotation between a winter cereal (wheat, barley) and a summer crop (rainfed sunflower, irrigated corn), as is common in central Italy. In this rotation, an annual legume is used as a living mulch in winter cereals, and after its self-reseeding, as either a green manure or living mulch for the succeeding summer crop. This alternative cropping system has proved to have the potential to induce a significant shift toward a less energy-intensive and a more environmentally friendly management type, while maintaining the same cash-crop sequence

The foundation of the system began with the screening of self-reseeding legumes species and cultivars and ended with the implementation and performance assessment of an entire alternative cropping system (winter cereal/summer crop rotation). The yield of winter wheat intercropped with subclover was not significantly different from that of a pure wheat stand in a drier crop year, while in the wetter year the grain yield of the intercropping system was significantly higher than the pure stand. However, in both crop years, grain yields were significantly lower that obtained using 130 kg ha–1 mineral N fertilizer, by 11% and 23%, respectively. Additionally, a positive correlation between the amount of subclover biomass plowed in and the vegetative and productive characteristic of sunflower was found in dry and wet years. Subclover green manure was so effective that sunflower yield in the alternative system was higher than that of the conventional one fertilized with 130 kg ha–1 of inorganic N. Subclover green manure also affected biomass and the composition of the weed community in the sunflower crop. Subclover mulch from a sod strip intercropping system with wheat was

and environmental quality [43].

296 Organic Fertilizers - From Basic Concepts to Applied Outcomes

of the conventional one [44].

The struggle for nature's resources is always an issue within any crop system because plant growth needs not only space and time, but also light, mineral nutrients, and water. The competition can be considered to have two main aspects: aboveground competition and root system competition. In rain-fed agriculture, under limited water conditions, a major compe‐ tition can occur between the target crop and legumes for water resource. The wheat yield under intercropping conditions with legumes reportedly decreases with less water availability versus a pure stand, although legume intercropping with a major crop can enhance the N content of the soil [45]. Mc Gowan and Williams found that subclover depleted soil moisture more than barley. At 19 weeks after sowing, maximal soil moisture was observed when barley was in a high density and a pure stand, 7.5% at 5-15 cm and 9.9% at 15-30 cm depth, while for subclover in a pure stand, it was 6.2% at 5-15 cm and 8% at 15-30 cm depth [46]. Taking into account negative effects between intercrops, how to best balance between competition and companion effects is a task for experimental research.

As Altieri and Rosset pointed out, a production system must be designed to reduce nutrient losses by effectively containing leaching, runoff, and erosion, and improving nutrient recycling mechanisms [40]. Diversity is a natural design, while monoculture is an anthropogenic creation. So intercropping should be organized according to natural laws. The cultivars within a cropping system must be suitable for the local climate and soil conditions. Under the circumstances of intercropping, cooperation between different species is also required; at least, competition should be eliminated as much as possible. As the main competition between two crops is canopy competition and root system competition, the principles of a well-managed intercropping system can be summarized as follows:

Tall and short crops are growing together to minimize struggle for sunlight and reduce air humidity of the microclimate. Crops with deep and strong root systems intercropped with the species with sallow root systems can reduce underground competition. The density of a major crop should be reduced to adjust the growth of itself and leaving optimum space for another intercrop.

Select different maturity dates to minimize competition as much as possible [47].

When crops are planted together according to these principles, competition between different species will be less than would exist within the same species. The success of intercropping systems at low levels of interspecific competition has also been explained in terms of more balanced and efficient use of soil moisture due to temporal complimentarily in water require‐ ments of the two species [48]. In the case of legume intercropping, high companion effects between the two crops are caused by biological N fixation, producing N that benefits the target crop and offering soil cover. Simultaneously, the negative effects of legumes on the major crop should be reduced by a well-managed system.


**Author details**

Seiki Chiba1 \* and Mikio Waki2

1 Chiba Science Institute, Yagumo, Meguro Ward, Tokyo, Japan

2 Wits Inc., Oshiage, Sakura, Tochigi, Japan

\*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.


The authors dealing with ionic liquids have already reported on the degradability of cellulose with ionic liquids, and based on this knowledge, ionic liquids were also used for the purpose of cellulose decomposition. For example, Swatloski et al. [21] found that the ILs can dissolve cellulose in a microwave oven as well as in a conventional oven. They reported about initial results that demonstrate that cellulose can be dissolved without activation or pre-treatment in, and regenerated from, 1-butyl-3 methylimidazolium chloride and other hydrophilic ionic liquids. This may enable the application of ionic liquids as alternatives to environmentally undesirable solvents currently used for dissolution of this important bioresource. Ren et al. [22] reported that imidazolium-based chloride ILs can be used to dissolve and regenerate cellulose into a variety of physical forms. They found that 1-allyl-3-methylimidazolium chloride ([AMIM]Cl) showed better capability for dissolving cellulose than [BMIM]Cl. Zhang et al. [23] also found that [AMIM] Cl can be used as solvent for the dissolution and regeneration of cellulose without any pre-treatment or activation. The research results indicated that cellulose with a degree of polymerisation as high as 650 can be dissolved in [AMIM] Cl within 30 min. In these applications, recycling of IL is highly necessary from the points of view of economics, IL disposal and toxicity.

It should be emphasised again that this property of ionic liquids is more or less known to experts in the field of chemistry, to those who deal with ionic liquids. Experts in the field of construction of hydraulic devices, who encounter this type of liquid during their first applications, certainly not.

To test the compatibility of the cellulose-based filter material, a 47 mm diameter membrane white filter paper was used, gridded (to facilitate possible deformation of the filter paper) with a pore size of 0.8 μm and made of mixed cellulose ester (MCE), manufactured by Millipore.

Five different types of ionic liquids were used to test the compatibility of ionic liquids with the cellulose filter material: IL1 (Trioctylmethylammonium dibutyl phosphate,) IL2 (EMIM EtSO4), IL3(B2001®), IL4 (B2002a®) and IL5 (B2002b®). All mentioned ionic liquids are from the manufacturer proionic. For this purpose, the filter paper was covered with 3 ml of ionic liquid, and the effect of the liquid on the filter material was observed after 1 hour and after 2 days (at normal ambient air conditions). The results of the simple test of the compatibility of tested ionic liquids with a cellulose filter, based on visual observation, are shown in **Figure 5**.

In the present case of testing, the compatibility of the ionic liquid with the cellulose-based filter material, in all cases the deformation of the filter paper occurred

**Figure 5.** *Effect of ionic liquid on cellulose-based filter material.*

first, followed a little later by the disintegration of the paper or another type of deformation. As a result of greater or lesser degradation of the cellulose membrane, a part of the cellulose is definitely present in the ionic liquid and was not visible to the naked eye. We did not measure the amount of cellulose in the ionic hydraulic fluid, because in this case the compatibility of the cellulose filter was in the foreground. The resulting deformation and decomposition are a big enough warning that ionic liquids are not compatible with cellulose filters, which is why it is necessary to use another type of filter material.

## **4. Tests related to filters and filterability test**

There are a wide range of fluid filters used in industry, especially in the filtration of fuel, water and lubricants, including hydraulic filters. Hydraulic filters are required to be compliant with the international contamination code of cleanliness for the fluid contamination levels (ISO 4406) and corresponding filtration standards (e.g. ASTM D3948–14). The required filtration efficiency and dirt holding capacity for the removal of solid particles, water droplets and water moisture from lubricants depend on the filtration system used, the required cleanliness levels of the fluid and the fluid properties (e.g. type, viscosity, surface tension, etc.), which influence the fibre wetting process in fluid filtration. There are many Standards defining performance requirements and test methods for fuel and lubricant filtration [24].

For example, methods for characterising the porous structure and integrity of a filter are defined in ISO 2942 and EN 24003; different methods of testing filtration efficiency and retention capacity are defined in the ISO 4548-12, ISO 16889, ISO 19438 and ISO 23369 Standards; the other test standards also include diesel fuel–water separator performance (ISO 16332 and SAE J1488/J1839), performance of fuel filters for diesel engines (for road vehicles) (ISO 4020), an online automatic particle counter calibration test rig (ISO 11943) and single-pass/gravimetric fuel filter test rigs (SAE J1985 and SAE J905).

In addition to the mentioned standardised tests, the filterability test is important for determining the efficiency of the filter material. The filterability of hydraulic oils is a measure of the ability of a clean fluid to pass through a standard filter without clogging or plugging. Solid additives in hydraulic oils affect filterability largely. This is

### *Compatibility of Filter Materials Used with Ionic Liquids' Uses in Hydraulic… DOI: http://dx.doi.org/10.5772/intechopen.107962*

especially important, because modern hydraulic systems with narrow gap tolerances, high operating pressures and ever finer filters place increasing demands on the filterability of hydraulic oils. To determine this precisely, the filterability test has been developed in accordance with ISO 13357 and included in the DIN 51524 Standard for HLP hydraulic oils [25].

Using filterability tests in which oil flows through a filter, often under intensified conditions, the interaction between the filter membrane and oil is examined in more detail. Most 'static' filterability tests are carried out as internal tests, due to the lack of a Standard, using different membrane pore sizes and liquid volumes under a vacuum or pressure conditions. However, the results can vary enormously according to the procedure used and often depend on the individual experiences of the laboratory. Since the early 1980s, scientists have been searching for a test capable of becoming a Standard. This has now been passed as the ISO 13357 filterability test parts 1 and 2 [26, 27].

The ISO 13357 Standard test is intended for fresh hydraulic oils with a viscosity grade up to ISO VG 100. The test is divided into the 'wet' filterability test, in which the oil is replaced by water (ISO 13357, part 1) and the test with 'dry' oil (ISO 13357, part 2). The quantity of 300 ml of hydraulic oil is flowed – filtered through a dried 0.8 μm membrane filter under the pressure specified in the Standard. The filtration volume and time are recorded during this process. The filterability is calculated by determining the volume-time relationships at the start, for a test duration of between 10 and 50 seconds (level I) and between 200 and 300 seconds (level II). The test ends when the required data have been recorded or the filtration time exceeds 2 hours. The filterability is indicated by the letter 'F'. If the value is F > 50, the test is concluded as 'passed' according to the Standard. The closer 'F' is to 100, the better the filterability. If F < 50, the test is deemed to have 'failed'. If the filtration time exceeds 2 hours, the test liquid must be marked as 'unable to filter'.

As already mentioned, Standard ISO 13357-1 and ISO 13357-2 prescribe the use of a cellulose membrane filter with the specified pore size of 0.8 μm, which is not problematic in case of the testing of mineral-based oils and HFD fluids. However, it is not known what may happen in the case of testing the filterability of another type of hydraulic fluid. As shown in Section 3.3, ionic liquids (at least tested), including ionic hydraulic fluids, are not compatible with cellulosic filter materials, as they deform rapidly and, in some cases, degrade completely.

According to the results when testing the filterability in conformity with the ISO 13357 Standard and compatibility with the cellulose filter paper discussed at this point, it can be concluded that the ionic liquids are incompatible with the cellulose filter paper. Therefore, the use of cellulose filter elements in hydraulic systems is not recommended. The filterability in the case of using the filter elements from other materials, for example, glass fibres, should not be problematic; however, they still need to be tested.

The same applies to all other systems that use a certain type of ionic liquid as a liquid which also needs to be filtered. Because there are many types of ionic liquids used for different purposes and in different processes, care must be taken when using cellulose-based materials. It is best to avoid them carefully or, at least, to check the compatibility of the ionic liquid with the cellulose filter before use.

However, regarding standard filterability testing strictly according to the ISO 13357 Standard, it is not feasible, as the use of a cellulose membrane filter is problematic. Other types of filter materials are usually used in today's hydraulic devices. The filterability through filter elements made from other material, for example, glass

fibres, should not be a problem regarding filter material and fluid compatibility. However, the compatibility test must still be established and, of course, to supplement the standard filterability test procedure for these types of fluids.

## **5. Conclusion**

The trend of development of modern hydraulic systems is moving towards more efficient systems with higher energy density and the use of new, high-tech hydraulic fluids. Modern hydraulic components are, thus, made with ever narrower tolerances, smaller gaps between internal moving parts, better materials are used and better surface quality. As a result, higher operating pressures can be used, making hydraulic components smaller, lighter and less space consuming. Due to the smaller tanks, a smaller amount of hydraulic fluid is also used, which is, therefore, much more loaded. As well as in the field of hydraulic fluids, development is taking place in the direction of more energy-efficient fluids, with better lubricating properties, a wider temperature operating range, non-flammability and greater environmental friendliness.

Thus, new types of hydraulic fluids are appearing, which have certain physical and chemical properties that are much better than classic hydraulic fluids. Among them certainly belong ionic liquids suitable for use in hydraulic systems – ionic hydraulic fluids.

Regardless of the type of hydraulic fluid, effective filtering is crucial to achieve adequate operational reliability and a long service life of the components and the entire system. Thus, the average pore size of filters has been reduced from 10 to 20 μm to today's 3 to 12 μm, and new and better filter materials are being used. In the case of new hydraulic fluids, however, the question arises of their compatibility with the materials used commonly in hydraulic components, including filters.

The paper discusses in more detail the issue of compatibility of new ionic hydraulic fluids with the materials used in filters. The emphasis is on return filter materials, which are considered an indispensable component of any hydraulic system.

Extensive research has shown that no problems can be expected with the metal materials we use for filter housings. Corrosion of steel parts can occur in certain cases only if moisture is present. However, since the filter housing is usually filled with liquid, this problem is not to be expected. However, a problem may arise if the inside of the filter housing is painted with protective paint. In certain cases, softening, wrinkling and peeling of the paint can occur, which can be problematic. It is necessary to individually check the compatibility of a certain type of ionic hydraulic fluid with a certain type of paint before use. If the filter housing and other metal materials of the filter are not painted or are made of other materials (for example, based on copper or stainless steel), these problems do not exist.

We have also not detected any compatibility issues of ionic hydraulic fluids with the plastic materials present on the filter. The same applies to the seals, if they are made of NBR or Viton, the seal material most often found in the filter.

However, it is necessary to be careful with the material of the filter cartridges. In the event that plastic, fibreglass or micro glass (e.g. Polyester, Nylon, Dacron...) is used as the filter material, we did not detect any problems during durability testing on a real device under real operating conditions. However, a compatibility problem arises when using cellulose-based filters. These are considered the most efficient in the field *Compatibility of Filter Materials Used with Ionic Liquids' Uses in Hydraulic… DOI: http://dx.doi.org/10.5772/intechopen.107962*

of hydraulics, but unfortunately ionic hydraulic fluids degrade them (deform and partially decompose).

Cellulose filter membranes are also used in the case of the use of portable off-line devices to determine the cleanliness class of hydraulic fluid. Cellulose-based filter material has proven to be incompatible with ionic liquids.

However, cellulose membranes are also prescribed for determination a very important parameter of filter efficiency, i.e. its filterability. The test is standardised but is mainly intended for testing the filterability of conventional fluids, including hydraulic fluids. Since ionic liquids degrade cellulose-based materials, it will be necessary to update the standardised filterability test for cases where ionic hydraulic fluids are used.

Findings regarding the compatibility of filter materials must be considered, not only when determining the filterability but also when choosing the materials of all filter components. This is true in general and especially in all cases where we do not use classic hydraulic and other technical fluids.

## **Acknowledgements**

This research was supported by the company proionic GmbH from Grambach, Austria, which provided all the samples of ionic liquids and was a very cooperative partner in the IL-selection process, for sharing their wisdom with us. We are also grateful to the company OLMA d.o.o. from Ljubljana, Slovenia, which allowed us to use their equipment and facilities, as well as the personnel to carry out very extensive experimental work. We are thankful to all colleagues in both companies who provided their expertise and skills that assisted this research greatly.

## **Author details**

Darko Lovrec\* and Vito Tič Faculty of Mechanical Engineering, University of Maribor, Maribor, Slovenia

\*Address all correspondence to<EMAIL_ADDRESS>
© 2022 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.

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[13] Kalb SR. Toward industrialization of ionic liquids. In: Commercial Applications of Ionic Liquids; Green Chemistry and Sustainable Technology. Cham, Switzerland: Springer; 2020. pp. 261-282. DOI: 10.1007/978-3- 030-35245-5\_11

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Comparison of several properties with those of conventional oil. Lubrication Science. 2014;**26**(7–8):488-499

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## **Chapter 7**

## Development of Low-Friction Ion Gels for Industrial Applications

*Toshio Kamijo, Hiroyuki Arafune, Takashi Morinaga and Takaya Sato*

## **Abstract**

Friction reduction is imperative for improving the service life and energy efficiency of mechanical systems. Ion gels using ionic liquids (ILs) as swelling agents are expected to be stable gel lubricants owing to the high thermal stability and negligible volatility of ILs; they can maintain their swollen state even under harsh conditions. Therefore, we investigated two types of ion gels: an IL-substituted double-network gel (DN ion S-gel), in which the water in the DN hydrogel is replaced by the IL 3-ethyl-1-methyl-imidazolium ethylsulfate; and a DN ion gel containing N,Ndiethyl-N-(2-methoxyethyl)-N-methyl-ammonium bis(trifluoromethylsulfonyl) imide (DEME-TFSI), where one of the polymer backbones is a network of poly(N,Ndiethyl-N-(2-methacryloylethyl)-N-methylammonium bis(trifluoromethylsulfonyl) imide), an IL-type polymer based on our previous synthetic study of IL polymer technology. The DN ion S-gel and DN ion gel achieved compression strengths of 25 and 30 MPa, respectively, and were thermally stable until 196°C and 335°C (10% weight-loss temperature), respectively. The coefficient of friction remained stable and low (0.02) after repeated measurements under harsh conditions (high temperature or vacuum conditions), affirming the durability of the DN ion gel.

**Keywords:** double-network gel, ionic liquid, low friction, highly robust, high vacuum

## **1. Introduction**

Low-friction materials are demanded for energy and resource conservation. As 75% of machine failures are attributed to friction wear [1], friction reduction would improve the service life and energy efficiency of mechanical systems [2]. Low-friction materials can be modeled on the human joint, which has a low coefficient of friction (CoF = 10−3) at pressures above 102 atm and remains lubricated for decades [3]. The gel-like structure of human joints, comprising proteoglycans and collagen fibers with a high water content (75–80 wt%), has inspired extensive research on gel lubricants [2–4]. In the early 2000s, researchers in Japan developed hydrogels with high mechanical strength [4–7], promoting the application of gel as biomaterials. Double-network (DN) hydrogels with high mechanical strength, low friction, and biocompatibility are representative gel-lubricant materials [8] and suitable candidates for artificial human joints or cartilages [9]. However, the evaporation of the solvent (water) and

consequent loss of the swollen state have limited the industrial exploitation of gels with these benefits.

Previously, we developed ion gels comprising monodisperse silica nanoparticles and ionic liquids (ILs). In these gels, the silica surface is densely grafted by a welldefined polymer, forming a colloidal self-assembled crystal with a face-centered cubic structure [10]. The ionic conductivity and diffusion coefficients of our gels exceeded those of the bulk polymer. We thus considered the possibility of introducing the highly mobile ions in ion gels to a low-frictional gel surface. To test this idea, we combined ILs with gel lubricants. Owing to their high thermal and oxidative stability, ultralow volatility, and low friction [11–13], IL swelling agents are expected to retain the swelling state of low-friction gels. Whereas DN hydrogels have been targeted as tough hydrogels for biomaterial applications [14], DN ion gels have been mainly studied as gas separation membranes obtained by replacing the water in DN hydrogels with amino-acid-based ILs [15]. As shown in our recent study, IL-based lubrication systems and compatible polymer brushes grafted on Si substrates are efficient and robust lubricants [16]. These lubricants are composed of an IL called N,N-diethyl-N-(2-methoxyethyl)-N-methyl-ammonium bis(trifluoromethylsulfonyl)imide (DEME-TFSI) and high-density IL-type polymer brushes comprising N,N-diethyl-N-(2-methacryloylethyl)-N-methylammonium bis(trifluoromethyl-sulfonyl)imide (DEMM-TFSI), which is a derivative of DEME-TFSI with a polymerizable group. The CoF of the IL-type polymer brushes remained as low as 0.003 over 4,000 cycles.

The present study proposes two types of DN ion gels: an IL-substituted gel in which the water in the DN hydrogel is replaced by an IL [17], and a gel in which one of the polymer backbones of the DN ion gel is a network of poly(DEMM-TFSI) (hereafter, these two gels will be named DN ion S-gel and DN ion gel, respectively). The IL-type polymer in the latter gel is based on our previous synthetic study [18].

The ILs we used, 3-ethyl-1-methylimidazolium ethyl sulfate (EMI-EtSulf) and DEME-TFSI, are commercially readily available and were selected for their compatibility with the gel networks. EMI-EtSulf was also chosen because it can easily substitute water in the hydrogels and has low toxicity. DEME-TFSI has been used for a long time in our material development due to its low viscosity and high electrochemical and thermal stability [13, 16–20]. We are also considering its eventual industrial applications. This IL has been approved by the Japan Chemical Substances Control Law, thereby indicating its potential for industrial mass production and significant cost reductions. Considering the compatibility with this IL, we designed monomers and developed polymerization technology. Therefore, we are developing functional materials by combining DEME-TFSI and poly(DEMM-TFSI) with a maximum consideration of compatibility.

The present study discusses and compares the different tribological properties of DN hydrogels, DN ion S-gels, and DN ion gels. Specifically, it evaluates the gel immobilization techniques of the gels on substrates, the mechanical and thermal stabilities of the ion gels, their lubrication properties in a vacuum, and other required functions for industrial applications.

## **2. Two types of DN ion gels for industrial applications**

### **2.1 IL-substituted DN gel (DN ion S-gel)**

**Figure 1** is a schematic of an IL-substituted DN gel. First, a DN hydrogel was fabricated via sequential photopolymerization [6]. A solution of 2-acrylamido

*Development of Low-Friction Ion Gels for Industrial Applications DOI: http://dx.doi.org/10.5772/intechopen.107942*

**Figure 1.** *Schematic of the IL-substituted DN gel (DN ion S-gel).*

methylpropane sulfonic acid (AMPS) as the first monomer, α-Ketoglutaric acid as the initiator, N,N-methylene bisacrylamide (MBAA) as the cross-linker, and water as the solvent was mixed and transferred to a Schlenk tube. Using an injection syringe, the solution was inserted into a reaction cell formed by sandwiching 1-mm-thick Si rubber between two glass plates. After 18 h of rotation under ultraviolet (UV) irradiation, the first gel was obtained. This gel was polymerized under Ar atmosphere, then immersed in a second gel solution comprising dimethylacrylamide as a second monomer, α-Ketoglutaric acid as the initiator, MBAA as the cross-linker, and water as the solvent. Once swelling equilibrium was reached, the second gel solution (i.e., the swelled first gel) was set in the reaction cell and rotated for 18 h under UV light irradiation. The obtained gel was washed with acetonitrile and EMI-EtSulf (volume ratio 1:1), then vacuum-dried at 70°C for 12 h to obtain the substituted DN ion gel. The gel prepared using this method is called DN ion S-gel. The synthesis is detailed elsewhere [17].

## **2.2 DN ion gel comprising IL and IL polymer, DN ion gel**

**Figure 2** schematizes the DN ion gel comprising an IL and its polymer (DN ion gel). The first and second networks were composed of DEMM-TFSI and poly (methylmethacrylate) (PMMA), respectively. DEMM-TFSI as the IL monomer, IRGACURE 369 as the initiator, triethyleneglycol dimethacrylate (TEGDMA) as the cross-linker, and DEME-TFSI as the solvent were mixed in a Schlenk tube and deoxygenated by Ar bubbling for 5 min. Using an injection syringe, the solution was injected into a reaction cell formed by sandwiching 2-mm-thick Si rubber between a pair of glass plates. The first gel was rotated for 18 h under UV light irradiation to promote polymerization in an Ar atmosphere. The polymerized gel was washed with acetonitrile to remove impurities and then swollen with DEME-TFSI (poly(DEMM-TFSI) gel as a reference material. PMMA gel was prepared similarly by replacing DEMM-TFSI with methyl methacrylate (MMA) at the same weight ratio. The first gel was polymerized and immersed in a second gel solution comprising MMA monomer, benzophenone

**Figure 2.** *Schematic of the DN ion gel composed of an IL and an IL polymer (DN ion gel).*

as the initiator, TEGDMA as the cross-linker, and propylene carbonate as the solvent. After immersion for 2 days to reach swelling equilibrium, the swollen first gel was placed in a reaction cell and rotated for 18 h under UV irradiation. The resulting second gel was washed with an acetonitrile and DEME-TFSI (volume ratio 1:1) to remove the impurities and then vacuum-dried at 70°C for 12 h. The resulting DN ion gel was rich in DEME-TFSI (75 wt%). The synthesis is detailed elsewhere [18].

## **2.3 Gel immobilization technology on substrates**

**Figure 3** is a schematic of the gel immobilization technique. The DN ion gels were covalently immobilized on glass substrates via a silane coupling reaction [21]. Briefly, a mixture of ethanol and 3-(trimethoxysilylpropyl)methacrylate was slowly dropped into mixed ethanol and 25-wt% ammonia solution while stirring. The solution was used to immerse a washed glass substrate for 16 h at room temperature to impart the vinyl moieties that covalently anchor the gel to the glass surface. The resulting substrate coated one side of the reaction cell. During the second gel synthesis, the DN ion gel was covalently bonded to the surface silanol groups of a glass substrate. The same technique can prepare DN hydrogels. It is also applicable to other substrates if their surfaces possess hydroxyl groups that can be modified by a silane coupling reagent with vinyl groups, which can help anchor the gel.

## **3. Characterization of DN and DN ion gels**

## **3.1 Mechanical properties from stress-strain curves**

The mechanical strengths of the DN ion gels were evaluated at 25°C and 40% relative humidity using a universal testing machine (Instron 3342, Instron Japan, Kawasaki, Japan). From the stress-strain curves, the compression fracture stresses of the DN

*Development of Low-Friction Ion Gels for Industrial Applications DOI: http://dx.doi.org/10.5772/intechopen.107942*

#### **Figure 3.**

*Schematic of gel immobilization technology.*

#### **Figure 4.**

*Stress-strain curves of DN hydrogel (blue), DN ion S-gel (green), single DEMM-TFSI gel (brown), and DN ion gel (red). Inset is an expansion of the change region of the curves.*

hydrogel and DN ion S-gel were found to be 20 and 25 MPa, respectively (**Figure 4**), which were comparable to those of DN ion gel substituted with tetrabutylphosphonium prolinate [14]. The stress-strain curve of DN ion gel presented a smaller initial slope than that of DN hydrogel; the loss of hydration force softened the DN ion gel. PAMPS is an electrolyte polymer that swells in pure water via hydration of negatively charged AMPS. In addition, its surface charge is easily shielded in ionic salt at high concentration. The DN ion gel shrank after displacement, suggesting that it softened through loss of hydration power caused by the high ionic strength of EMI-EtSulf.

Moreover, the compressive fracture stress of the DN ion gel was 30 MPa at 87% strain (**Figure 4**), which is 10 MPa higher than that of the DN hydrogel (20 MPa) and DN ion S-gel (25 MPa). The compressive fracture stresses of single-network gels were much lower (1 MPa for poly(DEMM-TFSI) and 3 MPa for PMMA), suggesting that the high mechanical strength of the combined materials derives from the formed DN structure. Because conventional DN gels substituted with amino-acid-based

ILs exhibit similarly high mechanical strengths (>25 MPa) [14], we concluded that combining ILs with compatible polymers can boost the mechanical strength without hydration assistance from electrolyte polymers.

## **3.2 Thermal properties of the gels**

The thermal properties of DN ion S-gel, DN ion gel, and DN hydrogel were evaluated using thermogravimetric analysis (TGA), and the results were compared with those of pure ILs and the conventional lubricants poly-α-olefin (PAO) and glycerol. **Figure 5** compares the TGA curves of DN hydrogel (blue), DN ion S-gel (light blue), EMI-EtSulf (green), DN ion gel (red), DEME-TFSI (light green), PAO (gray), and glycerol (black). The initial weight loss (up to 100°C) in the TGA curves of DN ion S-gel and EMI-EtSulf was attributed to release of absorbed moisture. The secondary weight loss at ~150°C indicated pyrolysis of the sulfonate and sulfate portion of PAMPS and EMI-EtSulf [22]. The 10% weight-loss temperatures (T10) of DN ion S-gel and EMI-EtSulf were determined as 196°C and 247°C, respectively. The T10 of DN hydrogel was much lower (39°C), thereby indicating that replacing water with ILs decidedly improves the thermal stability of DN gels (ΔT10, DN ion S-gel = 157°C). The DN ion gel thermally decomposed at nearly 300°C with a weight loss 10% at 335°C. The obtained T10 value of DN ion gel was much higher than that of the DN hydrogel (ΔT10, DN ion gel = 295°C) and 139°C higher than that of the S-gel. The 10% weight loss of DN ion gels occurred at a much higher temperature than that of glycerol (165°C) and PAO (241°C); therefore, DN ion gel can be used as stable and efficient lubricant under high-temperature conditions for industrial applications.

## **4. Tribological properties of the DN ion gel**

## **4.1 Sliding-speed dependence of CoF on gel properties**

For the friction test using a ball-on-plate-type reciprocating tribometer (Shinto Scientific Co., Ltd, Tokyo, Japan), the gel sample was fixed on a sliding table and a glass ball sample (ϕ10 mm) was placed in a ball holder connected to a load cell. To

## **Figure 5.**

*TGA curves of DN hydrogel (blue), DN ion S-gel (right blue), EMI-EtSulf (green line), DN ion gel (red), DEME-TFSI (light green), PAO (gray), and glycerol (black).*

*Development of Low-Friction Ion Gels for Industrial Applications DOI: http://dx.doi.org/10.5772/intechopen.107942*

#### **Figure 6.**

*Sliding-speed dependence of CoF at glass ball/DN hydrogel (light blue circles), glass ball/DN ion S-gel (green circles), and glass ball/DN ion gel (red circles).*

evaluate the lubrication properties, the ball/substrate frictional force was measured at different loads and sliding speeds. **Figure 6** plots the CoFs as functions of sliding speed for the ball/DN hydrogel (light blue circles), glass ball/DN ion S-gel (green circles), and glass ball/DN ion gel (red circles) under an applied load of 0.98 N. The CoF of the glass ball/DN hydrogel remained within 0.01–0.02 over the range of measured sliding speeds. The minimum CoF at 3.0 × 10−2 ms−1 indicated a shift from the elastic lubrication regime to mixed lubrication. By contrast, the CoFs of the glass ball/DN ion S-gel ranged from 0.04 to 0.05 over the sliding-speed range and were minimized at a speed six times slower (5.0 × 10−3 ms−1) than that of the DN hydrogel. These results can be attributed to the following factors: (1) high viscosity of the swelling agent incorporated in the DN gels, and (2) increased polymer adhesion after substituting water with IL. As the viscosities of water and EMI-EtSulf at 25°C are 0.89 and 71 MPa·s, respectively, a fluid film of IL is much thicker than a water film. Therefore, the viscosity change could not explain the disparate lubrication properties of DN ion S-gel and DN hydrogel. Regarding factor (2), PAMPS and the glass surface easily dissociate to produce negative charges in pure water, and the fluid film thickness is preserved by electrostatic repulsion between the glass surface and PAMPS [23, 24]. Electrostatic repulsion is essential for lowering the friction at an electrolyte interface. Using a surface force apparatus, Raviv et al. [23] studied the friction between polymer brush layers adsorbed on a molecularly smooth mica surface in water. The friction induced by the sheer force between the polyelectrolyte brush layers (CoF = 0.0006–0.001) was lower than that induced between neutral brush layers. In the former case, friction was decreased by electrostatic repulsion between the negatively charged tribopaired polymer brushes. Dunlop et al. [24] measured the normal and shear forces between polyelectrolyte brush layers grafted on a mica surface. After examining the contribution of ionic strength to friction, they found that salt at high concentrations shielded the electric double layer, thereby increasing the shear forces. Being fully composed of cations and anions, EMI-EtSulf has a high salt concentration (≈5 molar); therefore, it shielded almost all of the hydroxyl groups on the glass surface and the sulfonate groups on PAMPS. The higher friction of the DN ion gel than of the DN hydrogel was thus attributed to polymer adhesion on the glass surface, enabled by electrostatic shielding of the glass and PAMPS surfaces.

The red circles in **Figure 6** plot the relationship between CoF and sliding speed of the glass ball/DN ion gel under a 0.98-N load. The CoF decreased as the sliding velocity increased to 1.5 × 10−3 ms−1 and increased slowly thereafter, indicating a transition from a mixed (elastic fluid) to a fluid lubrication regime. The higher CoF of the DN ion gel than of the hydrogels and DN ion S-gel at sliding velocities above 5.0 × 10−3 ms−1 may be explained by the smaller elastic deformation (and consequent entry to the fluid lubrication regime) of the synthesized DN ion gel. The CoF of the DN ion gel exceeded those of the DN hydrogel and ion S-gel in the same velocity region. Meanwhile, the effect of surface-to-surface contact becomes significant at velocities below 1.5 × 10−3 ms−1 (in the mixed lubrication regime). The smaller CoF of the DN ion gel than that of the DN ion S-gel in the slow-velocity region means a smaller interaction between the glass surface and DN ion gel than between the glass surface and DN ion S-gel; however, the former interaction exceeded the interaction between the glass surface and DN hydrogel. The CoF of the DN hydrogel was lower at room temperature when water was not volatilized (that is, under the experimental conditions of the present study).

## **4.2 Repeated durability and thermal stability of gels**

**Figure 7** shows the temporal changes in the measured CoFs of glass balls/DN ion S-gel and glass balls/DN ion gel at different temperatures under a 0.98 N load and a sliding speed of 5.0 × 10−3 ms−1. At 25°C, 80°C, and 100°C, the CoF values of the glass ball/DN ion S-gel were 0.067, 0.054, and 0.037, respectively, and those of the glass balls/DN ion gel were 0.025, 0.017, and 0.013, respectively. Both sets of CoFs monotonically decreased with increasing temperature. Higher temperatures promote gel softening and decrease the average contact pressure. They also increase the fluid film thickness and hence the viscous resistance. Therefore, decreased polymer adhesion is considered as the main cause of the friction reduction. At 50°C, the CoF of the DN hydrogels jumped by more than 10-fold during repeated measurements, probably due to thermal aggregation of the dried polymer [18] as the water solvent evaporated. In contrast, the CoF of the DN ion gel remained stable after 500 friction cycles even at 100°C because it did not volatilize, indicating that the DN ion S-gel and DN ion gels were more thermally stable than the DN hydrogel. Therefore, they can potentially be applied as lubricating gels in high-temperature applications that are unsuitable for hydrogels.

## **4.3 Lubricating properties of gels in a vacuum and future development of gel materials**

**Figure 8** shows the stability of the DN ion gel under a high vacuum during repeated friction measurements of glass balls/DN ion gel. The sliding velocity, load, and pressure were 5.0× 10−3 ms−1, 0.20 N, and 2.2×10−4 Pa, respectively. For this test, a custom-made ball-on-plate-type tribometer was installed in a vacuum chamber [25].  Along with the temperature stability results in **Figure 7**, this result affirms that DN ion gels can reduce the friction and improve the energy efficiency of mechanical systems operating under high-temperature and high-vacuum conditions, such as bearings and mechanical seals.

*Development of Low-Friction Ion Gels for Industrial Applications DOI: http://dx.doi.org/10.5772/intechopen.107942*

#### **Figure 7.**

*CoF versus number of friction cycles for glass ball/DN ion S-gel (black: 25°C, red: 80°C, green: 100°C) and glass ball/DN ion gel (gray: 25°C, pink: 80°C, yellow–green: 100°C). All measurements were taken at 5.0 × 10−3 ms−1 under a load of 0.98 N.*

Thus, we combined DN gels and ILs and evolved them into an industrially viable material. For widespread usage of this material, we must halt the metal corrosion of ILs and replace the expensive ILs with cheaper alternatives such as deep eutectic solvents (DES) [26]. In DES compounds, hydrogen-bond donors are mixed with hydrogen-bond acceptors (either or both solid) at a certain ratio, forming a liquid at room temperature. DESs exhibit similar properties to ILs but are inexpensive and their combination possibilities are numerous. We plan to develop new materials based on DESs.

In addition, the DN gel with IL in this study requires a two-step preparation, which is difficult to synthesize in large quantities. This issue must also be resolved in industrial preparations. Currently, we are developing a one-step preparation method for DN gels [27].

#### **Figure 8.**

*CoF versus number of friction cycles for glass ball/DN ion gel (black) and SUJ2 ball/DN ion gel (red), measured at 5.0 × 10−3 ms−1 under a 0.20 N load and 2.2 × 10−4 Pa.*

## **5. Conclusion**

In this study, we investigated gels comprising two types of ILs for industrial applications: DN ion S-gel in which the water in the hydro-DN gel is replaced by an IL EMI-EtSulf, and DN ion gel containing IL DEME-TFSI where one of the polymer backbones of the DN ion gel becomes a network of poly(DEMM-TFSI), an IL-type polymer developed through our previous IL polymer technology.

The obtained DN ion S-gel and DN ion gel achieved high compression strengths (25 and 30 MPa, respectively) and were thermally stable up to 196°C and 335°C (the 10% weight-loss temperature), respectively. The decomposition behavior of the DN ion S-gel and DN ion gel reflects their thermal stabilities after incorporating EMI-EtSulf and DEME-TFSI, respectively. This phenomenon is commonly observed in ion gels. The CoF of the DN ion gel was low (0.02) and stable after repeated measurements at high temperature and under vacuum conditions, confirming the durability of this gel even under harsh conditions.

This study elucidated the fabrication of lubricant gels with high mechanical strength and robustness. The gels are expected to reduce the energy and resource consumption of materials in the temperature range at which conventional hydrogels cannot be used (DN ion S-gel: ΔT10, DN ion S-gel = 157°C, DN ion gel; ΔT10, DN ion gel = 295°C).

## **Acknowledgements**

This study was supported in part by the e "Green Tribology Innovation Network" Advanced Environmental Materials Area, Green Network of Excellence (GRENE) Program, the ACCEL program and Grants-in-Aid for Scientific Research (No.20H02060, No. 25810091, and No. 26820034) sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) in Japan. The authors would like to thank Enago (www.enago.jp) for the English language review.

## **Author details**

Toshio Kamijo\*, Hiroyuki Arafune, Takashi Morinaga and Takaya Sato Department of Creative Engineering, National Institute of Technology, Tsuruoka College, Tsuruoka, Japan

\*Address all correspondence to<EMAIL_ADDRESS>
© 2022 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.

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[16] Arafune H, Kamijo T, Morinaga T, Honma S, Sato T, Tsujii Y. A robust lubrication system using an ionic liquid polymer brush. Advanced Materials Interfaces. 2015;**2**:1500187. DOI: 10.1002/admi.201500187

[17] Arafune H, Muto F, Kamijo T, Honma S, Morinaga T, Sato T. Tribological properties of doublenetwork gels substituted by ionic liquids. Lubricants. 2018;**6**:89. DOI: 10.3390/ lubricants6040089

[18] Arafune H, Honma S, Morinaga T, Kamijo T, Miura M, Furukawa H, et al. Highly robust and low frictional double-network ion gel. Advanced Materials Interfaces. 2017;**4**:1700074. DOI: 10.1002/admi.201700074

[19] Sato T, Masuda G, Takagi K. Electrochemical properties of novel ionic liquids for electric double layer capacitor applications. Electrochimica Acta. 2004;**49**:3603-3611. DOI: 10.1016/j. electacta.2004.03.030

[20] Maruyama Y, Marukane S, Morinaga T, Honma S, Kamijo T, Shomura R, et al. New design of polyvalent ammonium salts for a highcapacity electric double layer capacitor. Journal of Power Sources. 2019;**412**:18- 28. DOI: 10.1016/j.jpowsour.2018.10.093

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## *Edited by Fabrice Mutelet*

Due to their very low volatility, high thermal stability, and ability to dissolve a wide variety of compounds, ionic liquids appear to meet the rigorous criteria for industrial applications. Among other uses, ionic liquids appear to be efficient for gas capture, biomass pretreatment, separation problems, and electrochemistry. They are also used in electrolytes, as lubricants, catalysts, or as antistatic agents. This book discusses the various uses of ionic liquids. Chapters discuss such topics as the use of ionic liquids in batteries, new mono, di, and trimeric imidazolium and pyridinium ionic liquids as catalysts in organic chemistry, the physico-chemical properties of ionic liquid-substituted double-network gels for industrial applications, the use of paramagnetic ionic liquids in magnetic resonance imaging, the compatibility of filter materials used with ionic liquids, and the development of low-friction ion gels for industrial applications.

Published in London, UK © 2023 IntechOpen © neirfy / iStock

Industrial Applications of Ionic Liquids

Industrial Applications of

Ionic Liquids

*Edited by Fabrice Mutelet*


**5. Conclusions and perspectives**

Attributed to the importance of DNWs, several efforts have been driven by experts to apply in diverse semiconductor and biological applications. In this way, those DNWs were effectively developed through different methods such as reactive-ion etching, chemical vapor deposition, from sp2 carbon and sp3 diamondoids and wet chemical route. Among them, the template-assisted synthesis of DNWs seems to be impressive to produce highly precise nanostructures. On the other hand, the cost-effective wet chemical route still remains a challenging task in terms of reproducibility and obtaining the unique structures. From experimental and theoretical studies, it has been found that DNWs have the exceptional structural, mechanical, thermal conductivity, electronic and electrochemical properties. However, structural studies on hybrid G-DNWs require exclusive focus for future applications. Subsequently, those DNWs also possess the unique applications such as EFE device, high-performance NEM switches, conductivity and electrochemical biosensor and so on. However, with respect to practicality, those applications remain unsatisfied. For instance, the reported DNW-based electrochemical biomolecules monitoring was affected by its stability; hence, still it is a challenging task to fabricate the DNW-based device for real-time continuous determination.

So far, except the wet chemical route, the reported synthetic techniques for DNWs are costly, and hence their development is still a challenging task. Therefore, much effort needed to develop the DNWs at large scale, which can be attained by the collaboration of diverse technical fields such as electro-biochemistry, nanoelectronics and analytical techniques, etc. For example, attempts are needed to develop hybrid G-DNWs by the association of CVD and wet chemical pathways. Such investigations may direct the DNWs toward diverse opto-electronic applications.


*4.3. Seed Setting Rate*

After maturation, the marked spikes from ten plants were harvested separately for each genotype within each treatment. The number of empty and filled grains was recorded, with the seed set rate represented as the percentage of filled grains in all grains. The effect of heat stress on seed set was indicated by the relative seed setting rate, being seed setting rate at high temperature/seed setting rate at normal temperature × 100%.

#### *4.4. Sample Collection for RNA-Seq and Real-Time PCR*

A total of 75 plants per genotype were used for sample collection. When three or more panicles extended from flag leaves by approximately 2 cm, the panicles were labeled, and the plants transferred to the growth chamber for the HS treatment. The labeled spikes were harvested before HS treatment (0 h) and 1, 2, 6, and 12 h after the initiation of the HS treatment, respectively, and placed on ice before anther extraction. The treatments were designated WD\_0 and 9311\_0, WD\_1 and 9311\_1, WD\_2 and 9311\_2, WD\_6 and 9311\_6, and WD\_12 and 9311\_12 for SDWG005 and 9311, respectively. One hour and 2 h were considered as short-term, 6 and 12 h were considered as intermediate and long-term heat treatments, respectively. For each treatment, 15 independent plants were sampled, and mature anthers which ascending to the top of glume from five independent plants pooled as one biological replicate, such that there were three biological replicates per treatment. The labeled panicles from each time point in each treatment were collected on ice, with the mature anthers from the panicles isolated, immediately suspended in liquid nitrogen, and stored at −80 ◦C until RNA extraction.


Acknowledgements

We like to thank Dr. Su-ChingLin, Dr. Jian-GuoBau, Dr. Bo-Shiu Chen, Dr.Yuen-Chun Lo, and Dr. Mao Sheng Sun for their help and inspirations. We also want to thank Miss Davy Kuo, Ariel Yu, and Sherry Ho. This study was funded by Ministry of Technology (no: MOST 106-2511-S-371-001) and Changhua Christian Hospital (no: 106-CCH-MST-133).


**4. Case studies of forest disturbances from different parts of India**

Forests are an invaluable resource that is being subjected to so many threats. In order to protect our forests, it is very much necessary to understand the reasons behind their destruction. Differentiating the agents and causes of deforestation will enable in understanding the same [36]. Several disturbances within the forest directly or indirectly contribute in destruction of the forest. This can be interpreted from the results obtained while surveying in different forest patches in India.

#### **4.1 Disturbances in the forests of Arunachal Pradesh**

Arunachal Pradesh is one of the states that has more than 75% forest cover and has the maximum very dense forest cover type [44]. The state is highly diverse in terms of climate as well as forest cover with tropical, sub-tropical, temperate and alpine forests having higher NDVI (≥7.0) [46]. However, the pressure on forest resources is consistently increasing with the rise in population, development

**Figure 5.** *Major disturbances in the forests of Arunachal Pradesh.*

activities, large number of wood-based industries and unsustainable land use practices resulting in their degradation [47]. This has also resulted in decrease in the forest cover of the state [44]. Several disturbances were being observed during the field survey in the forests of Arunachal Pradesh during 2007 to 2010. The major disturbances that were found include lopping, cut stumps, litter collection, soil removal, grazing, fire, NTFP collection and fuelwood collection (**Figure 5**). Of these, fuelwood collection was found to be the most recurrent activity followed by grazing. Generally, fuelwood collection has not been considered as the major cause of deforestation but leads to the same in certain regions with reduced forest area such as in the Philippines, Thailand and parts of Central America [36]. Forest fire has also been observed as an occasional event in certain parts of Arunachal Pradesh. Fires are generally used as a tool in clearing the forest for shifting cultivation which is one of the major agricultural practices performed in the state. Fires when used responsibly act as a valuable tool in managing forest and agriculture, but when abused, it can lead to deforestation [48, 49]. Other disturbances that can be an indicator of deforestation include NTFP collection and presence of cut stumps in certain forests. Forests of the state are highly diverse in endemic as well as nonendemic species, which need intensive monitoring and management to conserve the species-rich ecosystems from ever increasing anthropogenic pressure and changing climatic conditions [50].

#### **4.2 Disturbances in the forests of Madhya Pradesh**

Madhya Pradesh is among one of the states of India which is endowed with rich and diverse forests and comprises the largest forest cover in the country [44]. This is mainly because of the efforts that the state has put in to conserve and harness this invaluable resource through innovative measures like community participation and decentralization (MP) [51]. Even after these continuous efforts, there are certain regions within the state where the occurrence of several types of disturbances in the forest has been found. The common disturbances that were being observed

**61**

productivity of the forest.

**Figure 6.**

**4.3 Disturbances in the forests of Jharkhand**

*Major disturbances in the forests of Madhya Pradesh.*

*Deforestation in India: Consequences and Sustainable Solutions*

during the field survey (2017–2019) include fire, grazing, fuelwood collection, forage removal, litter collection, NTFP collection, lopping, thatch collection, root collection, soil removal, etc. (**Figure 6**). Among all these fire has been found as the major recurrent type of disturbance in the forests of Madhya Pradesh. Other major disturbances were grazing followed by fuelwood collection. Since every type of deforestation is not intentional but some which are the results of amalgamation of anthropogenic and natural factors like wildfires and subsequent overgrazing can prevent the growth of young trees [52] and thus eventually degrade the quality and

The name of the state 'Jharkhand' itself connotes 'area of land covered with forests' and has been exhibiting a unique relation with forests since time immemorial [53]. During the forest cover assessment [44], a net increase of 29 sq. km in the forest cover has been observed in the state which is mainly because of the plantation and conservation efforts within recorded forest areas. Although, there was an increment of 314 sq. km in the forest cover within the recorded forest areas, because of the felling of trees outside the forests area, its effect on forest cover has been offset. Also, several types of disturbances can be seen within the forest areas during the field survey (2016–2018), and the major disturbances were fuelwood collection, grazing, forage removal, lopping, cut stumps, thatch collection, root collection, soil removal, litter collection and NTFPs collection (**Figure 7**). Most of these disturbances were occasional in nature. Although these disturbances are not that recurrent, a regular check is necessary in order to prevent the forests from degrading and in achieving a sustainable forest cover. The forest management strategies should focus on the increasing demands of different timber and non-timber forest produce to conserve the plant diversity of the natural forests of the state [54].

*DOI: http://dx.doi.org/10.5772/intechopen.85804*

*Deforestation in India: Consequences and Sustainable Solutions DOI: http://dx.doi.org/10.5772/intechopen.85804*

*Forest Degradation Around the World*

activities, large number of wood-based industries and unsustainable land use practices resulting in their degradation [47]. This has also resulted in decrease in the forest cover of the state [44]. Several disturbances were being observed during the field survey in the forests of Arunachal Pradesh during 2007 to 2010. The major disturbances that were found include lopping, cut stumps, litter collection, soil removal, grazing, fire, NTFP collection and fuelwood collection (**Figure 5**). Of these, fuelwood collection was found to be the most recurrent activity followed by grazing. Generally, fuelwood collection has not been considered as the major cause of deforestation but leads to the same in certain regions with reduced forest area such as in the Philippines, Thailand and parts of Central America [36]. Forest fire has also been observed as an occasional event in certain parts of Arunachal Pradesh. Fires are generally used as a tool in clearing the forest for shifting cultivation which is one of the major agricultural practices performed in the state. Fires when used responsibly act as a valuable tool in managing forest and agriculture, but when abused, it can lead to deforestation [48, 49]. Other disturbances that can be an indicator of deforestation include NTFP collection and presence of cut stumps in certain forests. Forests of the state are highly diverse in endemic as well as nonendemic species, which need intensive monitoring and management to conserve the species-rich ecosystems from ever increasing anthropogenic pressure and changing

Madhya Pradesh is among one of the states of India which is endowed with rich and diverse forests and comprises the largest forest cover in the country [44]. This is mainly because of the efforts that the state has put in to conserve and harness this invaluable resource through innovative measures like community participation and decentralization (MP) [51]. Even after these continuous efforts, there are certain regions within the state where the occurrence of several types of disturbances in the forest has been found. The common disturbances that were being observed

**60**

climatic conditions [50].

**Figure 5.**

*Major disturbances in the forests of Arunachal Pradesh.*

**4.2 Disturbances in the forests of Madhya Pradesh**

**Figure 6.** *Major disturbances in the forests of Madhya Pradesh.*

during the field survey (2017–2019) include fire, grazing, fuelwood collection, forage removal, litter collection, NTFP collection, lopping, thatch collection, root collection, soil removal, etc. (**Figure 6**). Among all these fire has been found as the major recurrent type of disturbance in the forests of Madhya Pradesh. Other major disturbances were grazing followed by fuelwood collection. Since every type of deforestation is not intentional but some which are the results of amalgamation of anthropogenic and natural factors like wildfires and subsequent overgrazing can prevent the growth of young trees [52] and thus eventually degrade the quality and productivity of the forest.

#### **4.3 Disturbances in the forests of Jharkhand**

The name of the state 'Jharkhand' itself connotes 'area of land covered with forests' and has been exhibiting a unique relation with forests since time immemorial [53]. During the forest cover assessment [44], a net increase of 29 sq. km in the forest cover has been observed in the state which is mainly because of the plantation and conservation efforts within recorded forest areas. Although, there was an increment of 314 sq. km in the forest cover within the recorded forest areas, because of the felling of trees outside the forests area, its effect on forest cover has been offset. Also, several types of disturbances can be seen within the forest areas during the field survey (2016–2018), and the major disturbances were fuelwood collection, grazing, forage removal, lopping, cut stumps, thatch collection, root collection, soil removal, litter collection and NTFPs collection (**Figure 7**). Most of these disturbances were occasional in nature. Although these disturbances are not that recurrent, a regular check is necessary in order to prevent the forests from degrading and in achieving a sustainable forest cover. The forest management strategies should focus on the increasing demands of different timber and non-timber forest produce to conserve the plant diversity of the natural forests of the state [54].

**Figure 7.** *Major disturbances in the forests of Jharkhand.*


**Education Improvement Promoting Human Capabilities Development in Post-Neoliberal Period**

Editors

**Edward P. St. John Luxi Chen Zachary Taylor Lijing Yang Chen Wang**

Basel • Beijing • Wuhan • Barcelona • Belgrade • Novi Sad • Cluj • Manchester

*Editors* Edward P. St. John University of Michigan Ann Arbor, MI, USA

Lijing Yang Ohio University Athens, GA, USA Luxi Chen Beijing Normal University Beijing, China

Chen Wang Beijing Normal University Beijing, China

Zachary Taylor University of Southern Mississippi Hattiesburg, MS, USA

*Editorial Office* MDPI St. Alban-Anlage 66 4052 Basel, Switzerland

This is a reprint of articles from the Special Issue published online in the open access journal *Education Sciences* (ISSN 2227-7102) (available at: https://www.mdpi.com/journal/education/ special issues/Social Capital Edu Inequality).

For citation purposes, cite each article independently as indicated on the article page online and as indicated below:

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**ISBN 978-3-0365-9486-6 (Hbk) ISBN 978-3-0365-9487-3 (PDF) doi.org/10.3390/books978-3-0365-9487-3**

Cover image courtesy of Chen Wang

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