The energy constituents of J. curcas are wood, fruit as whole and parts of fruit such as shells, seed husks, and kernel (Singh et al. 2008) which are direct sources of fuel. All these products have different energy values. The energy value of these products increases upon processing, but unless a use for by-products is found a decrease in overall energy availability occurs. A schematic illustration of these energy components is shown in Fig. 17.1.

Several pretreatment processes combine physical and chemical elements. The most common of physicochemical pretreatments used are steam explosion: SO2-steam explosion, Liquid hot water, ammonia fiber explosion (AFEX), Microwave pretreat­ment, Ultrasound pretreatment, and carbon dioxide (CO2) explosion.

Steam explosion is the most widely employed physicochemical pretreatment for lignocellulosic biomass. It is a hydrothermal pretreatment in which the biomass is subjected to pressurized steam for a period of time ranging from seconds to several minutes, and then suddenly depressurized. This pretreatment combines mechanical forces and chemical effects due to the hydrolysis (autohydrolysis) of acetyl groups present in hemicellulose. Autohydrolysis takes place when high temperatures promote the formation of acetic acid from acetyl groups; furthermore, water can also act as an acid at high temperatures.

Addition of dilute acid in steam explosion can effectively improve enzymatic hydrolysis, decrease the production of inhibitory compounds, and lead to more complete removal of hemicellulose.

The most important factors affecting the effectiveness of steam explosion are particle size, temperature, residence time, and the combined effect of both tempera­ture and time (Alfani et al. 2000). Higher temperatures result in an increased removal of hemicelluloses from the solid fraction and an enhanced cellulose digestibility; they also promote higher sugar degradation.

AFEX involves liquid ammonia and steam explosion. A typical AFEX process is carried out with 1-2 kg ammonia/kg dry biomass at 90 °C pH values (<12.0) during 30 min. It reduces the lignin content and removes some hemicellulose while decrys — tallizing cellulose. The important advantages of AFEX include: (1) producing neg­ligible inhibitors for the downstream biological processes, so water wash is not necessary (Mes-Hartree et al. 1988); and (2) requiring no particle size reduction. However, ammonia must be recycled after the AFEX pretreatment based on the considerations of both the ammonia cost and environmental protection. Therefore, both ammonia cost and the cost of recovery processes drive up the cost of the AFEX pretreatment (Holtzapple et al. 1992).

Carbon dioxide (CO2) explosion acts similar to steam and ammonia explosion: high-pressure CO2 is injected into the batch reactor and then liberated by an explo­sive decompression. It is believed that CO2 reacts to carbonic acid (carbon dioxide in water), thereby improving the hydrolysis rate. The glucose yields in the later enzymatic hydrolysis are low (75 %) compared to steam and ammonia explosion. Overall however (CO2 ) explosion is more cost-effective than ammonia explosion and does not cause the formation of inhibitors as in steam explosion.

Bamboo processing is a lengthy process and has the following requirements:

1. Machine for separating rough bamboo fiber

2. High temperature pressure-cooking pot

3. Pool for bleaching and softening

4. Steam boiler

5. Equipments for washing

6. Drying room

7. Dehydrator

Several technologies are available for the processing of bamboo fibers. Each of them has its own merits, demerits, and specifications and employs a different pro­cess. The following paragraphs include the details of the five of the technologies used for the processing of the bamboo.

1. Although the cultivation of abaca plants is being currently practiced on large scale in Philippines, Ecuador, and other adjacent areas where its plantation is done in the humid regions having an altitude upto 500 m, the studies have also revealed that its cultivation could be extended upto 1,000 m latitudinal extent which is suggestive of the fact that there is a great scope for expanding the culti­vation practice of abaca in other neighboring regions or regions with similar climatic conditions so that its production could be increased to the extent that the gap between the demand and supply will be minimized or nullified.

2. Abaca plants in Philippines are generally propagated from vegetative propagules or seeds in a traditional way (without any modern agricultural practice). However, the recent studies have revealed that the use of fertilizers leads to enhancement of growth in abaca thereby paving way for higher fiber yields. Moreover, FIDA (Philippines) is also providing the micropropagated plant material for successful cultivation of abaca.

3. Although about 200 varieties of abaca are known to exist, only a few varieties are cultivated on commercial scale because most of the varieties are either low — yielding or yield fiber of inferior quality. Now, NARC (National Abaca Research Centre, Philippines) and FIDA have been and are promoting research programs so that better (high yielding and good fiber quality) varieties will be introduced to overcome the problem.

4. Keeping in view the advantages of abaca fibers and the processed products over synthetic ones, there is a great expectation that there will be a continuous increase in its demand in the national and international markets. To manage the increasing demands, the most important thing is to increase the supplies but during the last few years, the trend in abaca supply or production has been found otherwise. The main reasons have been found to be the low-income generation from the abaca cultivation, burdensome fiber extraction, and the natural calamities like typhoon or disease-incidence. As far as the income generation (for farmers) and fiber extraction is concerned, the Philippine government as well as the agencies like FIDA and NARC has a role to play. For the control of disease-incidence, differ­ent conventional plant breeding approaches coupled with the modern biotechno­logical techniques should be employed to produce disease-resistant varieties as has been recently initiated in two abaca cultivars Tangongon (TG) and Tinawagan Pula (TP) to produce virus-resistant (BBTV and BBrMV) abaca cultivars.

5. Abaca fiber is considered as the strongest natural fiber and known for its exceptional mechanical strength, durability, and long fiber length. It is because of these properties that it has become an important raw material for various industries like paper and pulp industry, furnishing industry, textile industry, automobile industry, etc. where it is being used in the production of many industrial or domestic products like cordage products, fabrics, speciality papers, bank notes, carpets, rugs, baskets, fiber boards, insulators (for wires/ cables), and automobile components. It is also used as a fuel (Musafel). As per the estimates, paper and pulp industry consumes maximum share (about 80 %) of the fiber production. With the advancement in technology, currently the pro­duction of abaca-reinforced polymers is gaining more importance due to their superiority over pure fibers and the synthetic counterparts like nylon, rayon, etc. Keeping in view the above mentioned applications of abaca fibers in vari­ous industrial or domestic activities, it has a great potential to be used as an important renewable bio-resource.

6. The production of abaca fibers or its composites is eco-friendly, energy — efficient, and biodegradable, thereby posing no major threat to the environ­ment. Moreover, abaca plantations have been used to control soil erosion and to promote biodiversity rehabilitation. Wastes produced from abaca plant find its use as organic fertilizer to maintain the fertility of soil.

In conclusion, it can be stated that the abaca industry holds a great scope in national as well as international markets providing employment or economic bene­fits to a large number of people (including farmers, traders, exporters, manufactur­ers, etc.). The production of high-quality fibers by industrial units creates multiple job opportunities and increase in the income of farmers and laborers. Being renew­able natural fiber and superior in qualities, its market demand is expected to strengthen as far as its industrial applications are concerned. Also, the use of abaca fiber composites for automotive and other industrial applications carries ecological as well as economic benefits, thereby leading to sustainable development program. As abaca is mainly grown in Philippines and other adjacent areas, both government and the private sector should coordinate and extend its support in developing the abaca markets at the domestic and international level so that its unfulfilled potential will be attained in future.

As the “low-carbon” concept prevails, abundant kapok fiber has received increasing attention as an eco-friendly textile material for its intrinsic superiorities such as finest and lightest quality, highest hollowness, and most warm nature. With the focus on this green cellulosic fiber, more studies will be carried out to expand the application fields for kapok fiber by combining its higher hollowness and hydrophobic — oleophilic characteristics.

Acknowledgment We are grateful for the support of the National Natural Science Foundation of China (No. 21107116).

10.3.1 Thermosetting Phenol Formaldehyde Resin

Thermosetting and thermoplastic polymers are usually used for making natural fibre composites. These both types of polymers have different applications for their versatile properties. Both polymers have structural similarity as they con­tain long chains. But the major difference is that thermosetting polymers possess

cross-linking chain which gives higher tensile strength and rigidity. That is why they are usually used in structural application and thermoplastics are considered for nonstructural products (Ganga Rao et al. 2007). The application of thermosetting polymers in natural fibre composites is shown in Table 10.2. Thermoset polymers, those that are used as matrices in composites, have sufficient viscosity to flow at some point during the cure process. They can be cast into plate forms to provide blanks. The finished specimens can be machined or moulded into even more complex geometries if necessary to create net-dimension specimens (Fig. 10.3).

The properties and structure of thermosetting resins mostly depends on polycon­densation condition. A number of polycondensation resins such as polyester, polyurethane, melamine formaldehyde, urea formaldehyde (UF) and phenol

formaldehyde (PF) are commercially available today (Pizzi et al. 1999). Among them, phenolic resins are well known for their tremendous mechanical properties, chemical resistance, thermal stability and strong adhesive capacity (Satapathy and Bijwe 2006; Park et al. 2006). This resin has been keeping its outstanding perfor­mance in synthetic polymer industry from the last 90 years (Shafizadeh et al. 1999). Resol is the commercial name of PF resin, which is produced by polycon­densation reaction of formaldehyde and phenol under alkaline medium. A wide range of uses in wood industry, impregnation, thermal insulation and moulding is found for its highly cross-linked, versatile, cure capability and stable nature (Holopainen et al. 1997).

In case of heterotrophic cultivation, the culture has a high chance of getting contami­nated especially in open pond cultivations. Apart from this, carbon source is also purchased at a high cost. Photoautotrophic system of algae cultivation is the most frequently used method for biomass growth. It is easy to scale up and can easily take carbon dioxide from the surface air.

13.3 Cultivation Systems

There are two main cultivation systems used for the production of algal biomass:

13.3.1 Open Ponds

The average volumetric yield for this system lies between 0.06 and 0.42 g/L per day. The efficiency of the system depends upon the configuration of the pond and the algal specie that is being cultivated. Open tanks or naturally existing water bod­ies (ponds, lakes, lagoons, etc.) are collectively termed as open ponds and are unproblematic to construct and maneuver. These ponds are kept shallow for the easy penetration of solar radiations. Water and nutrients are continuously circulated in the culture. Output of the pond is measured by calculating the biomass produced each day per unit area. Circular ponds and raceways have an area of about 1 ha whereas extensive ponds can be about 200 ha. Artificial open ponds are further categorized as:

Some rigid carbon materials like carbon nanotubes, graphene, ordered mesoporous carbon, and activated carbon are relatively hard to be sulfonated. Concentrated H2SO4 and fuming H2SO4 are used as the sulfonating agents. However the CBSC prepared with fuming H2SO4 possess much higher catalytic activity (Dehkhoda et al. 2010; Kastner et al. 2012). Researchers have extensively studied the influence of different parameters like sulfonating agent, sulfonation time, and carbon precur­sor on the activity of such catalysts by direct sulfonation. Directly pyrolysis of the carbon precursors and sulfonation is concentrated at high H2SO4 temperatures, pro­duces sulfonated carbons with low in acid density, lower specific surface area, and poor reusability (Konwar et al. 2013). Figure 15.5 shows the way for the preparation of SO3H-carbon (Konwar et al. 2014).

Studies also indicated that the catalytic activity is primarily determined by total acid density, — SO2H density, surface functional groups, and pore structure. It is established that a high — SO3H density and pore volume favored high activity. These properties in turn are directly influenced by the carbonization temperature (Konwar et al. 2014). Apart from these there are numerous other reports on the preparation of similar sulfonated carbons catalysts, by one-step hydrothermal carbonization/

sulfonation (Xiao et al. 2010), polymerization followed by sulfonation and carbon­ization (Zhao et al. 2010) , by the thermal treatment of p-toluene sulfonic acid (Zhang et al. 2010) etc.

Here we discussed different system of microalgal biomass production, their prob­lems and future considerations, which is summarized in Table 18.2.

18.2.1 Open Pond Production

Open pond production is achieved through using a special type of pond called “race­way pond” that is a shallow artificial pond and is commonly used for the cultivation of microalgae. The pond is formed into a rectangular grid, containing an oval chan­nel resembling to an automotive raceway circuit. From an aerial view, many ponds look like a rounded-corner maze (like a puzzle in which we find the way in a closed circuit). It contains a paddle wheel to make the water flow continuously around the circuit (Fig. 18.2).

Raceway ponds (RP) have been used for mass culture of microalgae (Acien Fernandez et al. 1999) since last six decades. A best suited RP for microalgal culti­vation is usually 0.3 m deep. Paddle wheel provides mixing and circulation of water in the pond. They are built with solid concrete to avoid water seepage and the floor is lined with a white sheet for enhanced light reflection (to improve the light use efficiency in photosynthesis). Culture is fed continuously in front of paddle wheel during day light and broth is harvested on completion of the loop behind the paddle wheel. The continuous (24/7) operation of paddle wheel prevents the culture sedi­mentation (Spolaore et al. 2006). Evaporation of water from the RP is a necessary evil, because it is source of water loss but also helps to maintain temperature. Because, in summer cooling effect of evaporation lowers the temperature and in winter heat-retaining capacity of water does not allow the temperature to go too low. Overall, mitigation of water loss in raceway ponds due to seepage and evaporation is an engineering challenge.

Contamination of heterotrophic microbes is another offending challenge in open cultivation systems since it may strongly influence microalgae productivity as the contaminant microbes (bacteria, fungi etc.) become parasite on microalgae. Moreover, RPs may have poor mixing of atmospheric CO2 and least penetration of sunlight (because waste water has a dark color) keeping most of the cells in dark zone. Subsequently, low biomass is produced as compared to the theoretical yield calculated for a raceway pond based on its engineering dimensions. The mixing may be improved by using an aeration system and light penetration may be enhanced by decreasing the depth of pond (maybe 0.2 m instead of 0.3 m). Despite these facts,

production of microalgal biomass for making biodiesel has been extensively studied in RPs (Sheehan et al. 1998) . Although RPs have a low biomass productivity compared with photo-bioreactors yet they balance the equation by lowering the cost of production (Terry and Raymond 1985).

Short bamboo fiber reinforced epoxy composites with varying fiber length, when tested for resistance to acetic acid, hydrochloric acid, toluene, carbon tetrachloride, benzene, ammonia, sodium carbonate, sodium hydroxide, and nitric acid show varia­tion in tensile load. This proves that bamboo fiber length affects the tensile load. The tensile load is found to be maximum at the fiber length of 30 mm (Rajulu et al. 1998).

2.4.5 Tensile Modulus

The tensile modulus of permanganate treated bamboo polyester fiber is seen to be increased by 118 % and that treated with benzoyl chloride is 118 % (Kushwaha and Kumar 2010). Bamboo fiber reinforced polypropylene composites show a signifi­cant increase in tensile modulus after addition of maleic anhydride polypropylene (MAPP) content in concentration of 24 % by weight. The composite is shown to have the tensile modulus of 5-6 GPa (Chen et al. 1998) . Due to high tensile modulus, bamboo fibers are excellent material for making composites (Rao and Rao 2007). By the addition of glass fiber by 20 % mass the tensile modulus of bamboo glass fiber reinforced polypropylene composite increases by 12.5 %. The reduction of tensile modulus in bamboo glass fiber reinforced poly propylene hybrid composites is two times more than reduction of tensile modulus in bamboo fiber reinforced poly propylene composites after 1,200 h of aging in water (Thwe and Liao 2002b). Tensile modulus of poly propylene based bamboo composites which use steam exploded fibers increases to about 30 %, due to well impregnation and reduction in void numbers (Okubo et al. 2004). The tensile modulus improves significantly with the addition of silane coupling agent Si69 in bamboo fibers (Ismail et al. 2002).