Mechanical properties of natural fibers can be strongly affected and determined by several important variables such as structure, microfibrillar angle, chemical compo­sition, cell dimensions, and defects (Azwa et al. 2013 ; Dittenber and GangaRao 2011; John and Anandjiwala 2007; Wong et al. 2010). Microfibrillar angle is the angle between fiber axis and the micro-fibrils. These angles are responsible for the mechanical properties of the fibers. The smaller the angle the higher strength and stiffness of the fiber while larger angles provide usually higher ductility. Generally, natural fibers with higher mechanical strength possess higher cellulose content, lon­ger cell length, higher degree of polymerization of cellulose, and lower microfibril­lar angle. Important mechanical properties like tensile strength and Young’s modulus usually increase as cellulose content and cell length increase (John and Thomas 2008; Methacanon et al. 2010). The mechanical properties of the date palm fiber and other natural fiber types can be shown in Table 1.4.

Waseem Shahri, Inayatullah Tahir, and Burhan Ahad

Contents

3.1 Introduction……………………………………………………………………………………………………… 48

3.2 Morphology of Abaca (Musa textilis) Plant………………………………………………………………. 49

3.3 Abaca Cultivation………………………………………………………………………………………………. 49

3.4 Harvesting of Abaca Fiber and the Recommended Varieties……………………………………………… 51

3.5 Applications of Abaca Fiber…………………………………………………………………………………… 53

3.6 Potential Areas of Abaca-Fiber Application…………………………………………………………………. 56

3.7 Abaca Market Demand and Supply…………………………………………………………………………… 57

3.8 Ecological Implications………………………………………………………………………………………… 57

3.9 Conclusions and Future Prospectus…………………………………………………………………………. 58

References …………………………………………………………………………………………………………. 59

Abstract Of the various fibers obtained from natural sources, fibers obtained from abaca offer a great potential to be used as a renewable bio-resource for various industrial or extra-industrial applications due to their high mechanical strength, durability, flexibility, and long fiber length. The fiber is obtained from the leaf sheaths or petioles of the abaca plant (Musa texitilis), a plant native to Asia (Philippines). The plant grows well in shady and humid areas (altitude below 500 m and temperature 27 °C) and requires well-drained loamy soil for cultivation. It can be propagated by seeds, suckers or corm, or through tissue culture techniques. Since the cultivation of abaca is mainly confined to Philippines and other adjacent areas, it has also been introduced to other regions like Malaysia, Indonesia, etc. The top­most producer of abaca fiber is Catanduanes province. As far as its extent of cultiva­tion is concerned, it is being grown on about 172,524 ha providing employment to a large number of farmers and other associated traders, exporters, or manufacturers.

W. Shahri (*) • I. Tahir • B. Ahad

Department of Botany, University of Kashmir, Srinagar,

Jammu and Kashmir 190 006, India

e-mail: waseem. bot@gmail. com

K. R. Hakeem et al. (eds.), Biomass and Bioenergy: Processing and Properties,

DOI 10.1007/978-3-319-07641-6_3, © Springer International Publishing Switzerland 2014

The harvesting and extraction of fiber from abaca is laborious process which involves many operations like tuxying, stripping, drying, and final processing. Stripping and drying of fibers is either done manually or mechanically. After extraction, different grades of fibers are obtained which are then accordingly used for different set of industrial activities. Abaca fiber is chemically composed of cellulose, pectin, lignin, and significant quantities of glycerides, ketones, fatty acids, and other compounds. Being regarded as the strongest natural fiber in the world, it can be put into various modern sophisticated technologies like automobile industry and as a raw material for other important industries like paper and pulp industry, textile industry, and fur­nishing industry, besides being used as a fuel. Now-a-days, abaca-reinforced poly­mers are used and preferred over synthetic polymers. In the ecological perspective, the products obtained from abaca fibers are eco-friendly and the production of abaca-fiber composites is energy-efficient as it has been found to save 60 % energy besides reducing CO2 emissions. Moreover, abaca plantations are used to prevent soil erosion and in promoting biodiversity rehabilitation. Waste material produced from abaca plants is also used as organic fertilizers to replenish the soil fertility.

Keywords Bio-resource • Cordage • Eco-friendly • Fiber • Polymer • Propagation • Textile

3.1 Introduction

Today we are familiar with a number of natural fibers obtained from various plant sources like cotton, jute, cannabis, pineapple, sisal, bamboo, coconut, etc. These fibers because of their extraordinary mechanical and tensile properties find their use in many industries for the production of numerous commodities like fabrics, carry bags, and also as filling material for furniture items (Pothan et al. 2003). Despite the advantages of using these natural fibers, their mechanical degradation or thermal degradation during processing makes them unsuitable for various applications and thus limits their utility (Espert et al. 2004; Majid et al. 2008). Of the various fiber — yielding plants, abaca is one of the potential candidates that offer a good quality fiber with high mechanical strength and durability and is regarded as the strongest natural fiber in the world (Umali and Brewbaker 1956; Hadi et al. 2011). Keeping in view the applications of natural fibers like abaca fibers in various industrial and miscellaneous activities, there is a need to present a comprehensive review on the various aspects of abaca ranging from its morphology, cultivation, fiber extraction, applications, and other related aspects. In the present chapter, we therefore attempt to consolidate the information scattered in various research papers, conference pro­ceedings, and FIDA (Fiber Industry Development Authority, Philippines) annual reports to discuss the role of abaca as a potential renewable bio-resource for various applications of industrial and other domestic importance.

Wise development of agricultural biomass within prudential excellence should have some elements to ensure that the sustainability of the environment with other living thing is not affected in terms of quality and quantity. Elements of ecology, economy and technology as shown in Fig. 5.12 are determined based on the importance and the effectiveness of the product life cycle, processes and properties of raw material from excellent research by scientists.

Environmental issues often become a hot topic of the international community every year since rapid urbanization has resulted in the loss of conventional raw materials due to lack of natural resources. The world is confronted with serious environmental hazard problems such as environmental pollution, global warming, greenhouse gas emissions, ozone depletion, acid rain, extinction of habitat, flora and fauna also cause less health. The main key of all these problems is closely related to the sustainability of the world’s ecology which was declining dramati­cally each year due to the ineffective management system of natural waste material (Kramer 2012) . The industrial world has expanded exponentially over the past

Fig. 5.12 Three elements of agricultural biomass raw materials for sustainable economical development

century involving raw materials usage without emphasizing universal aspects of sustainability, but only profit oriented that may soon become a silent killer to the world ecology cycle.

All levels in the ecology of the world will receive a direct impact on development, agricultural waste resource operation that involved in different stages. This concept can be illustrated based on the increase demand by society for the product, preserva­tion of balance of the forest, the diversity of material resources and benefits ( Bovea and Vidal 2004). Previous research demonstrated that the use of composite biomass — based products in the market can sustain the ecology and economy of a country and the effect caused very less damage to ecosystems and natural resources. Society awareness can be achieved by evaluating the advantages of using agricultural bio­mass materials and its impact on the environment. The perspective of the product life cycle in terms of raw materials manufacturing process, marketing and disposal should also be considered. Transformation of low impact materials such as kenaf, oil palm, coconut fibre, and bagasse is necessary to diversify the market by providing alternative sources of fibre that has many advantages in mechanical properties for advanced applications. This can increase the market potential of the new manufac­turing industry in developing sustainable solutions (Kar and Jacobson 2012).

Agriculture is one of the world’s largest industry also a lifeblood of the econ­omy of each country as it involves a lot of the manufacturing sector, such as food (e. g. wheat, sugar, oil), construction (e. g. buildings, automotive) and the produc­tion of products (e. g. furniture, clothing, tools packaging). Agriculture is one of the world’s largest industry also a lifeblood of the economy of each country as it involves a lot of the manufacturing sector, such as food (e. g. wheat, sugar, oil),

construction (e. g. buildings, automotive) and the production of products (e. g. furniture, clothing, tools packaging). Pawlak (2007) detected the importance of the economic transformation for country depends on how the success of the product. Economics is an important factor related to the development of the country, and the demand of natural fibres using appropriate technology to produce quality fibre reinforced for use in concrete construction is gaining high score. Among the exam­ples of countries Japan and America who excel in a variety of advanced design and high demand in the world market successfully provide economic incentives and strengthen the country’s agricultural and industrial sectors. On the other hand, the economy had jumped up along with the effectiveness of economic development based on sustainability, and product can be evaluated based on the production pro­cess of a product from base till the end by provided at minimal cost. The “waste to profit” step is very important to exploit biomass raw material in the production of value-added and innovative new products.

As shown in Fig. 5.13, the global exports trend for biomass-based manufactur­ing sector continues to increase every 5 years from 2005 to 2016 (Lucintel 2011). Electrical and electronic sector, pharmaceutical, textile and other significant con­tributors in the export value of 90 % compared to wood-based industry sector and only 10 % biocomposites. Continues scenario will be able to bring a stronger econ­omy for the world market. Many factors such as easy planting and care, short-term crops, easy handling and minimal cost might benefit two fold compared with con­ventional materials (Majeed et al. 2013). For example, an oil palm biomass crop that is widely grown in ASEAN countries such as Malaysia and Indonesia can be used and converted into various products that would create an optimal supply of raw materials cycle continuously through a secure supply of quality and can pre­
vent wastage of raw materials. Raw material costs were seen to be at the highest with carbon fibre at the price of between MYR20,000 and 50,000 per tonne, fol­lowed by fibre glass with the price starting from MYR6,000 to 10,000 per tonne, and at the lowest was oil palm fibre with the cost ranging from MYR600 to 1,000 per tonne. Advantages of agricultural waste-based manufacturing industry can have a positive impact on society and the country creates many job opportunities and is able to raise the living standards of the community (Kar and Jacobson 2012). Well-income communities while increasing consumer purchasing power and domestic sources of raw materials might be able to help reduce the loss of imports.

Over recent years, many researchers have focused on research related to agricul­tural waste to solve the environmental problems due to the disposal of the biomass waste material. Agricultural waste biomass have become an interesting research field and led to the creation of new solutions and materials through research and development in science and technology. The research continued to become impor­tant for producing a new generation of processes and innovative composite products with the features of a more sustainable and improved quality (Kramer 2012). Advances in science and technology enable the world’s manufacturing industry to manipulate matter at the policy level to improve the overall properties of alternative materials to replace conventional materials. Technology-based research with a focus on biomass species variety with high potentialities can be grown to be applied in various industries for energy, pulp and paper, textiles, composites, cosmetic, con­struction, nanotechnology and pharmaceutical. This activity can make a huge impact not only on the product and the community, but to the transformation of technology development (Lane and Fagg 2010).

5.3 Conclusions

Agricultural biomass raw materials are highly potential candidates either as replace­ment or as complement to synthetic fibre in various applications due to their com­parable properties. This integrated biomass technology is not only devoted in minimizing the environmental impact but in maximizing the performance and func­tionality of fibres, sustainability of resources and profitability. The growing enthu­siasm to fully exploit agricultural biomass as material for green product also benefiting towards people as its generating many posts and opportunities. Agricultural biomass as a fascinating material brings the possibility to gain plenty of interest application in multidisciplinary fields. Until now, there have been a vast amount of well-established applications of agricultural biomass especially in con­struction, automotive, etc. However, the potential applicability of this raw material is unlimited and rapidly expanding due to their variety of unique characteristic which offered many properties that meet different requirements.

Even though a large potential of energy is associated with straw of sugarcane, so far, very minute efforts have been made in order to establish a suitable route from collec­tion to harness such potential. Similar to the corn stover in the USA (Atchison and Hettenhaus 2004), for sugarcane straw to become an energy source for large biore­fineries, innovations are required between the field and delivery to the processors in the areas of collection, storage, and transportation. As the attention is directed toward the cane harvesting mostly, it is not very clear which way to opt for the collection of straw for energy applications on industrial level. A set of field tests were performed in 1990s by the former Copersucar Technology Center (CTC) in order to evaluate some unburned cane harvesting routes proposed in the recovery of straw. Initially, five routes for collection purposes were evaluated with main intent of use of straw for generation of electricity (Hassuani et al. 2005). As a result of the poor harvester per­formance, when dealing with yield higher than 70 mg ha-1, the routes that were based on whole harvesting of stalks were thrown away and discarded and the other three were subjected to further analyses which are briefly explained below:

Route 1: harvesting of unburned chopped cane with removal of straw in the harvester. This is the conventional cleaning—harvester’s primary and extractor fans on. Chopped cane is transported to the mill of sugarcane. Straw is baled and transported.

Route 2: harvesting of unburned chopped cane without removal of straw in the har­vester (harvester’s extractor fans turned off). Cane stalks along with the straw are transferred to trucks and then transported to the mill. In the dry cleaning station of the mill, stalks and straw are separated.

Route 3: harvesting of unburned chopped cane with partial cleaning (harvester’s primary extractor fan operates at reduced speed and secondary extractor is turned off). A certain amount of straw is left on the ground, while the remaining is transported to the mill with cane stalks. At the mill, stalks and straw are separated in a dry cleaning station (Leal et al. 2013).

The main reason behind the dry cleaning station is to allow and enhance the sepa­ration of mineral (soil) impurities and vegetal (straw) from stalks of cane at the mill. Once these are separated, straw can act as a complementary fuel to bagasse or as feedstock in other applications. These collection routes investigated by CTC led to extremely different percentages of recovery efficiencies. For instance, in Route 2, 95 % of the total available straw can be collected, but, instead, only 66 % can undergo separation in the mill, whereas the rest of the 29 % would be squelched and crushed with the stalks to eventually compose the bagasse. Even though the efficiencies of Routes 1 and 3 are lower, in accordance with the analysis performed by CTC, both of these present lower cost. The cost is dependent upon the impact in the field of sugarcane caused by straw removal such as loss of productivity in agricultural sector due to compaction of soil and the loss of herbicide to the blanket of straw, among others (Leal et al. 2013).

In another study, the six different recovery routes were assessed (Michelazzo 2005). A model was generated to estimate the recovery cost of straw stimulating the capacity of field, consumption of fuel, repair and maintenance, depreciation, and required labor for the operation in field and transport. Results revealed the lowest recovery costs while handling together, cane billets and straw, followed by handling of chopped straw in bulk, the round bale, the giant bale, and lastly the pellet and briquette system.

The routes indicated by these studies are based on the combined stalk handling of the straw from the cane. This is an effective alternative in which mills may even­tually find more than one appropriate route, along with the knowledge of recovery level of straw may not be uniform over cane field (Braunbeck and Neto 2010). CGEE presented an analysis report after investigating three conditions of storage. It concluded that “the densification method was one of the leading factors for final cost of biomass.” Based on the recovery costs identified by CTC, the cost of final biomass including straw storing operations was calculated to be in the range between 17.9 and 39.2 $/mg, depending on the route of recovery and storage methods (Braunbeck and Neto 2010). Even though it is indicated in these studies that the route that is based on the handling of stalks of cane and straw combined should turn out to be an alternative toward cost-effectiveness, mills may eventually find appro­priate to utilize more than one route, also keeping in mind that the level of recovery of straw may not be uniform all over the field of cane. Improvements in the technologies used for straw recovery and incorporation of other biomass aspects can result in the expected reduction in costs. According to a research, for instance,

estimation was made that the total cost on delivery of switch grass was estimated to be 80.46 mg. This was calculated using balancing technology. Nearly 8.5 % of energy input of the feedstock is required (Atchison and Hettenhaus 2004). Mature technology reduces the total delivery. Cost would be reduced to 71.16 $/mg with input of required feedstock to be 7.8 % for corn stover. Investigations have also been done on finding innovative methods for collection. Hess et al. (2009) described designs showing advanced uniform format that would enable lignocellulosic biomass trading and supply to biorefineries in a market of commodity type similar to that of grain. Apart from cost, the methods of recovery and storage must also consider its impacts on quality of biomass for its intended use. Studies estimate that nearly 40-50 % of straw is available in the field to be utilized as an additional fuel to bagasse. Estimation showed that the total electricity surplus from mills of sugar­cane can reach up to 468-670 MJ mg-1 of cane (Seabra and Macedo 2011; Dias et al.

2011) . Certain challenges with the combustion and handling of straw in large amounts in boilers of bagasse at industrial level are being faced and are still sub­jected to investigation. Alternative technologies are based on the straw conversion into biofuels and chemicals via biochemical and thermochemical ways. For the longer term, they are expected to become available on commercial scale. In BIG/GT-CC (biomass integrated gasification/gas turbine-combined cycles), systems may also get adapted to substantial generation of power at the mills. According to a study, surplus of electricity would reach up to 1,048 MJ mg-1 of cane. This analysis was made when 103 kg of straw (dry mass) per milligram of cane was used along with the bagasse in sugarcane mills with installed BIG/GT-CC system. Regarding bio­fuel production, the biochemical conversion of residues of sugarcane could affect the yield possibly by increasing it from 124 to 132 L mg-1 in case of ethanol. Further assumption is made that recovery is almost 40-50 % of straw (Dias et al. 2011; Seabra et al. 2010). If thermochemical state conversion is considered, a reduc­tion to 116 L mg-1 value can be observed for ethanol and 115 MJ mg-1 canes for production of electricity. These rates result in 4 L of more production of higher alcohols per mg of cane (Seabra and Macedo 2011). These yields are characteristics of biomass so that the industrial performance may be affected by recovery route of straw (Seabra et al. 2010). A compromise is therefore required to be considered between the methods of collection and use of biomass of straw.

The microwave interacting vegetation surfaces are composed of layered media and is made up of the layers of consecutive leaves, branches, roots and stems of varying dielectric constants situated at a certain level above the surface of earth (Woodhouse 2006a, b; Santoro et al. 2005; Moghaddam 2009). The microwave interacting woody vegetation with variable dielectric constants (due to compositional change) may lead to a change in the direction of reflected microwaves at least to some extent. The microwaves following the interference with woody vegetation, the reflected signal properties such as the wavelength, incidence angle, polarization and terrain surfaces are greatly influenced by the surface roughness, local incidence angle, dielectric constant and surface morphology, respectively (Raney 1998; Leckie

1998) . In order to address the reflection properties of a relatively smooth surface from any part of the vegetation, the Fresnel reflectivity can be employed. For under­standing, the schematic representation of the Fresnel reflection in two different media of varying dielectric constants for air and homogeneous soil which corre­sponds to the refractive indices, n and n2 (respectively) is shown in Fig. 12.1 (Hajnsek and Papathanassiou 2005). Based on this, the following Eqs. 12.13 and 12.14
can be used to calculate the Fresnel reflection constants for horizontal and vertical polarization, respectively.

Where e corresponds to the dielectric constant and м is the unit applied to a natural material of non-ferromagnetic behaviour (natural soil).

The physical and chemical activation are the two most common methods involved for the activated carbon preparation (Prauchner and Rodrfguez-Reinoso 2012) though, mutual treatments might enhance the surface properties of the adsorbent, therefore increasing its adsorption capacity (Diasa et al. 2007). Chemical activation can be completed in a single step by carrying out thermal decomposition of raw

material with chemical reagents. Dehydrating agents such as sulfuric acid (H2SO4), zinc chloride (ZnCl2) , phosphoric acid (H3PO4) and KCl (Al-Khalid 1995), and potassium hydroxide/carbonate (KOH/K2CO3) (U? ar et al. 2009) are the most widely used chemical agents.

Steam, nitrogen, or carbon dioxide are employed for mild oxidation of the carbo­naceous matter in the physical activation. The process is usually involved two stages, carbonization stage is the first stage followed by an activation stage of the resulting char in the presence of activating agents (Haimour and Emeish 2006).

The physical activation occurs at relatively higher temperature in comparison to chemical activation, thus chemical activation results a perfect and improved pore development in the carbon structure. Generally chemical activation results higher carbon yields than physical ones (Sudaryanto et al. 2006). Table 15.4 shows the different raw materials, activating agent and their corresponding references that have been already studied. Catalytic properties of activated carbon such as acid site density and strength, crystalline structure, surface area, and pore volume greatly

Table 15.4 (continued)

Raw materials Activation agent References

affected by calcination temperature (Hattori 2001) . As sulfonic acid groups are hydrophilic in nature its number greatly enhanced the activity of the solid acid acti­vated carbon.

In terms of Brunauer-Emmett-Teller (BET) surface area and pore volume the activated carbons prepared under vacuum condition are better than those produced under nitrogen atmosphere (Yang and Lua 2006). Biomass derivatives are abundant and inexpensive (generally agricultural residues) obtained from renewable sources and hence they are quite remarkable raw materials (Prauchner and Rodrfguez — Reinoso 2012) thus they are important to meet the growing world demand.

Seed contains about 35-40 % oil (Kandpal and Madan 1995; Jongschaap et al. 2007), which can be extracted by pressure, heat, or solvents. One hectare of Jatropha plantation can produce about 900 kg of oil. Raw seed oil of J. curcas has been exten­sively studied because of its promising potential to substitute fossil diesel (Achten et al. 2008). J. curcas raw oil is cost effective, environmentally safe, renewable non­conventional source of energy and has fuel properties comparable to fossil diesel (Table 17.1).

These properties, particularly calorific value of J. curcas oil which is akin to fossil diesel and greater than coal (Gubitz et al. 1999; Rosenblum 2000; Sotolongo et al. 2009), vindicates its use both in unmodified and modified diesel engines as a substitute for petro-diesel.

However the high kinematic viscosity of raw oil 49.93 mm2 s-1 compared to die­sel fuel which is 1.3-4.1 mm2 s-1 results in less satisfactory use of raw oil in diesel engines (Shahid and Jamal 2008; Kywe and Oo 2009) as it causes several problems in diesel engines such as increasing fuel spray and reduction in fuel atomization, which causes choking of injectors, engine deposits, thickening of lubricating oil, and piston ring sticking (Shahid and Jamal 2008; Kywe and Oo 2009). Notwithstanding these problems, raw oil is used with success in slow-speed station­ary diesel engines such as generators and pumps (Tomomatsu and Brent 2007). Prasad et al. (2000) reported that use of raw J. curcas oil in diesel engine results in lower GHG emissions than fossil diesel which is beneficial for environment. To improve the use of raw Jatropha oil as fuel, its viscosity is reduced by either blend­ing raw oil with fossil diesel or preheating it (Achten et al. 2008). Apart from trans­portation fuel, raw oil also finds its use in lamps and cooking stoves. Thus, the most common uses of raw J. curcas oil are lighting lamps combustion, in stationary die­sel engines and cooking stoves; however to counter low absorbance capacity and high viscosity of oil, they have to be modified slightly.

Jatropha seed oil in raw form without any modification can be used directly in agri­cultural machinery. However, conversion to biodiesel first, will result in very little long-term problems (Harwood 1984). High content of unsaturated fatty acids (78— 84 %) makes J. curcas seed oil suitable for biodiesel production (Salimon and Abdullah 2008). Pure biodiesel and its blends with petro-diesel can be used in any petroleum diesel engine without the need for modification. The oil can be used in machines and engines as a direct replacement for fuel, in addition to many other commercial and industrial uses (Cerrate et al. 2006; Ndong et al. 2009).

The most common technology to produce biodiesel J. curcas oil is Trans­esterification (Meher et al. 2006). The J. curcas oil in trans-esterified form gives comparable results to fossil diesel (Prasad et al. 2000). The suitability of Jatropha oil for trans-esterification into biodiesel has been demonstrated (Achten et al. 2008; Shahid and Jamal 2008). In trans-esterification process, under heat using alcohol and a strong base usually NaOH as catalyst, J. curcas oil is converted to esters and glycerine. The ester usually formed is methyl esters (Singh et al. 2008). The process involves three successive reversible reactions. In the first reaction diglycerides are formed from triglycerides, and then former is converted to monoglycerides which finally forms glycerine. In all the three reactions, esters are produced. Raw oil type, temperature of reaction, alcohol to ratio, catalyst type and quantity, and mixing intensity are different variables in process of trans-esterification (Marchetti et al. 2007). Acids, alkali, lipases, or supercritical alcohol all can be used as catalysts. The stoichiometric ratio of oil and alcohol is usually 1:3 (Marchetti et al. 2007). Ethanol is preferred usually as it is CO2 neutral and also renewable. Trans­esterification transforms 92-98 % of the original oil to biodiesel and also reduces its viscosity from 49.93 to 4.59 mm2 s-1. Thus one hectare of Jatropha plantation can produce about 828 kg biodiesel, representing about 32 GJ ha-1 energy. The eco­nomic evaluation showed that the production of biodiesel from Jatropha oil is prof­itable provided the by-products of production process are also commercialized as valuable energy products (Eisa 1997; Foidl and Eder 1997).

Acid-Catalyzed Hydrolysis: Hydrolysis of cellulosic materials can be catalyzed by either a dilute or concentrated acid. Sulfuric acid is the most investigated acid, although other acids such as hydrochloric acid have also been applied. The acid reacts with cellulose to produce glucose and short chain molecules which is further transformed to the desired fuel grade bioethanol.

Dilute acid hydrolysis is a method that can be used either as a pretreatment preced­ing enzymatic hydrolysis or as the actual method of hydrolyzing lignocelluloses to sugars (Qureshi and Manderson 1995). The process is conducted under high tempera­ture and pressure, and the reaction time is in the range of seconds or minutes, which facilitates continuous processing (Lee et al. 1999). Although the process shows low acid consumption, the combination of acid and high temperature and pressure may cause the degradation of glucose to undesirable by-products such as levulinic acid, acetic acid, formic acid, and furfural, decreasing the yield of glucose.

On the other hand, concentrated acid hydrolysis occurs in relatively mild tem­peratures and atmospheric pressure. The process is more efficient and produces high sugar recovery efficiency, which can be on the order of over 90 % of both hemicel- lulose and cellulose sugars. Typically, 1 % of sulfuric acid is used at elevated pres­sure (42.0 MPa) and temperature (493 K). An advantage of this process over enzymatic hydrolysis is the high hydrolysis rate, with residence times of the order of several seconds. The mild temperatures and pressures employed allow the use of relatively low-cost materials. Unfortunately, the process is time-consuming, taking up to 120 h to complete. Also, the acid catalyst after the reaction is difficult to recover generating acid wastes (Fig. 20.3).

Solid Acid-Catalyzed Hydrolysis: Homogeneous catalysts such as sulfuric acid and enzymes produce glucose from cellulose in high yields; however, these processes suffer from the complicated product recovery and high production costs. The low selectivity of product due to the further degradation of glucose in harsh conditions should also be improved. Solid acid catalysts are expected to overcome these prob­lems as various types of the catalysts can be designed and applied in a wide range of reaction conditions. Furthermore, solid catalysts are easily recovered and reused.

Solid acids, e. g., zeolites, sulfonated zirconia and sulfonated carbons, can carry a high concentration of strong Bronsted acid sites, creating a very acidic environment in the catalyst pores or close to the catalyst surface. H-form zeolites and sulfonated mesoporous silicas were used as solid acid catalysts for the hydrolysis of soluble oligosaccharides and starch. Sulfonated activated-carbon catalysts showed a remarkably high yield of glucose, which was due to the high hydrothermal stability

Fig. 20.3 Reaction route of cellulose to glucose

and the excellent catalytic property attributed to the strong acid sites of SO3H func­tional groups and the hydrophobic planes, selectivity 90 % (Onda et al. 2008). The hydrolysis of cellulose with a highly active solid acid catalyst bearing SO3H, COOH, and OH groups was also investigated at 323-393 K using an artificial neural net­work (ANN) and a response surface methodology (RSM). The study shows that hydrolysis reaction depends largely on the amount of water as the solvent. The glucose yield by the solid acid catalyst reaches a maximum with an amount of water comparable to the catalyst weight. The reaction efficiency increases with increasing reaction temperature up to 363 K and does not increase in proportion to the reaction temperature above 363 K, suggesting that degradation of the cellulose surface by the acid catalyst prevents efficient hydrolysis of cellulose (Yamaguchi et al. 2009).

Recently, many new catalysts have emerged as powerful tools for the hydrolysis of cellulose to sugars. Ferrate CaFe2O4 was used as a solid catalyst for cellulose hydrolysis giving a glucose yield of 37 and 74 % selectivity. Ionic liquid was used for pretreatment to reduce the crystallinity of cellulose. The reaction was carried out at 423 K over 24 h. Hydrolysis of cellulose using hydrotalcite [Mg4Al2(OH)12CO3-4 H2O] activated by saturated Ca(OH)2 showed the conversion and glucose selectivity of 46.6 % and 85.3 %, respectively. The reaction was carried out at 423 K over 24 h with ball-milled cellulose. The solid acid catalyst could be reused four times and the catalytic activity remained. Compared with carbon-based solid acids, the activated hydrotalcite catalyst is more stable and can be separated more easily from the reaction mixture (Fang et al. 2011).

20.3.1 Fermentation

In 2005, Yao Wenbin and Zhang Wei of Zhejiang Forestry College put forward the cracking technology of bamboo fiber pyrolysis and separating (Yao and Zhang 2011).

Firstly, using high pressure-cooking vessel softens bamboo slices and then micro-cracks are formed. The slices are delaminated by splitting the bamboo through machine and the cracks and delamination expand along the direction paral­lel to the fiber leading to bamboo detaching. In external load synergies, the macro­crack of bamboo continues to expand, achieve its interfacial debonding stratified and obtain crude fiber bamboo. Coarse bamboo fibers become fine fibers after soft­ening, carding and a series of processes (Yao and Zhang 2011).

The notable feature in this method is small damage to the fiber intensity, fiber product has even type, and also very adaptable. Bamboo fiber processed by this method has the length of 50-90 cm and the fineness of 0.06 mm (Yao and Zhang 2011). The quality and yield of bamboo fiber produced by this method is shown in Table 2.1.

A tropical climate is necessary for the production or cultivation of sugarcane with minimum 24 in. of moisture annually. In growing regions, such as Mauritius, Dominican Republic, India, Peru, Brazil, Bolivia, Cuba, El Salvador, and Hawaii, sugarcane crop produces over 15 kg of cane per square meter of sunshine.

The cultivation of sugarcane is only possible in the tropical and subtropical areas with 6-7 months continuous supply of water through natural resources like rainfall or artificial resources like irrigation (George et al. 1917). The production of cane is only possible in the presence of plentiful sunshine and water supplies. This condi­tion provides good irrigation facilities to the countries where less availability of water supply is the major problem such as Egypt. Fig. 4.1 shows a general picture of sugarcane crops.

Sugarcane cultivation can be done by both mechanically and manually, i. e., by hand. Hand harvesting accounts for more than half of production. The process of hand harvesting involves the field to set on fire and burns dry leaves without harm­ing the stalks and roots. Harvesters then cut the cane manually by knives just above ground-level. The mechanical cutters cut the cane at the base of the stalk and take off the leaves, cut the cane into regular lengths and deposit it into a transporter. The structure of bagasse is shown in Fig. 4.2. From Fig. 4.2 it is observed that the bagasse mainly consists of cellulose and lignin (Fig. 4.2, b, respectively).

Figure 4.3a showed the morphology of the washed raw bagasse obtained from the sugarcane mill. The composition of this consists of a mixture of cellulosic short fibers and fine particles. The removal of lignin (Fig. 4.3b) makes the material fairly hard, coarse cellulosic particulates. The modified bagasse fibers shown in Fig. 4.3c display fluffy soft texture.