Lignin displays high structural complexity characterized succinctly by a seemingly random (highly polydisperse), highly cross-linked polymeric network composed of monomeric phenylpropane units cross-linked through ether linkages and carbon — carbon bonds. It is an amorphous component of plants able to confer strength and rigidity to the cell wall. In addition to the multiplicity of lignin forms potentially available based on their origin, lignin structures and content vary widely depend­ing on the plant. In the case of wood, the amount of lignin ranges from ca. 12% to 39%.27

The monomer structures in lignin consist of phenylpropane units, but differ in the degree of oxygen substitution on the phenyl ring. Basically, three structures of lignin; H-subunit (4-hydroxy phenyl), G-subunit (guaiacyl) and the S-subunit (sy — ringyl) are conjugated to produce a three-dimensional lignin polymer that has been proposed by the majority of scientists to arise by radical (combinatorial) biosynthe­sis (Fig. 14.6). Thus, because enzymatic pathways for lignification have not been unequivocally identified, lignin is not expected to have a putative regular structure such as cellulose or other major macromolecules and therefore is a physically and chemically heterogeneous material with an unknown chemical structure.27

Historically, lignin has been considered as an unwelcome by-product from the pulping process, because the main objective of pulping is to extract cellulose from wood. However, based on the biorefinery portfolio, an effective and cost-saving utilization of industrial lignin it is essential, because lignin has the possibility to even partly replace petroleum-based products because of its chemical similarity and potential cost-performance benefits.

The extraction of lignin from lignocellulosic materials always leads to frag­ments of low molecular weight, due to the method of extraction, thus changing its physic-chemical properties. Besides, the method of isolation, the source from which lignin is obtained also has an influence on its properties. Lignin itself possesses very attractive chemical motifs that allow it to be modified. For example, its phenolic hydroxyl is a reactive site for cross-coupling, networking, modification, and polym­erization. A variety of polymers such as polyurethanes can be effectively produced from it. Indeed, by judicious control of decomposition (chemical and thermal) a panoply of chemicals can be derived for use as monomers to construct popular and valuable polymers such as polyesters, polyetheres, and polystyrenes.27

Manufacturing products from lignin depends on its physicochemical properties. Because of its wide varying functionality, parameters such as functional groups dis­tribution are relevant to end-use properties of lignin. The reactivities of these lignins will impact on the attributes of the end products. Table 14.4 shows molecular weight and functional groups of lignins.28

The Tg is a critical parameter to evaluate for any polymer because it is an in­direct measure of crystallinity degree and crosslinking (higher crosslinking would lead to a higher temperature for phase transition to liquid state) that relate to the rubbery region of the material.29 For example, comparing hardwood and softwood milled wood lignin, hardwoods presents a Tg lower (110-130°C) than softwoods (138-160°C). The value of the Tg will to a great degree depend on the moisture content and chemical functionalization and will be lower if the lignin has greater mobility. In addition, a greater molecular weight of the polymer typically translates to a higher Tg, but for lignin the impact of structural variation will need to be calculated into the overall rheological characteristics because it influences degree of polymerization.

The ability to introduce lignin into composite blends is greatly enhanced if its miscibility is increased; the miscibility of a hydrophobic polymer like lignin into a more hydrophilic matrix can be increased by appropriate modification of the phe­nolic group (hydroxypropyl, butyrate, etc.)30 or it can be introduced into hydropho­bic matrices by the formation of lignin copolymers.28 At a value of 4 GPa, the me­chanical properties of lignin are significantly lower compared to cellulose pulp (40 GPa).31 Therefore, lignin itself is not appropriate to be used as reinforcing material as has been demonstrated for cellulose. On the other hand, many commercial ap­plications of low-value lignin already require it to be tailored for specific end goals with high value (extrusion moldings, composites, etc.).

CH is currently sold in the USA as a dietary supplement to aid weight loss and lower cholesterol and is approved as food additive in Japan, Italy, and Finland. However, although pure CH has very attractive properties, it lacks bioactivity and is mechani­cally weak.20 These drawbacks limit its biomedical applications. For these reasons, it is highly desirable to develop a hybrid material made of CH and appropriate filler, hoping that it can combine the favorable properties of the materials, and further en­hance tissue regenerative efficacy. Of particular relevance is that CH is ideally suit­ed to complex with anionic form of cellulose (carboxymethyl cellulose), to enable a number of applications and can be conjugated with functional molecules, antibod­ies, biotin, and heparin.2125 The advantage of blending CH is not only to improve its biodegradability and its antibacterial activity, but also the hydrophilicity, which is introduced by addition of the polar groups able to form secondary interactions (-OH and — NH2 groups involved in H bonds with other polymers). The most promising developments at present are in pharmaceutical and tissue engineering areas.

Clay based biocomposites using biopolymers as matrices are continuously gaining widespread attention from scientific and industrial world. Montmorillon — ite (MMT) clay and chitosan nanocomposites have been reported to possess excel­lent mechanical, thermal and bioactive properties.1112 Cellulose nanocrystals, have attracted a great deal of interest in the development of nanocomposites owing to

their appealing intrinsic properties such as nanoscale dimensions, high surface area, unique morphology, low density, and mechanical strength. Furthermore, they are easily modified, readily available, renewable, and biodegradable and are known to improve the limited mechanical and barrier properties of biopolymers.26’27

Although the Chinese have farmed cocoon silk from Bombyx mori for over 5,000 years, the ability to farm spider silk is impractical for several reasons. Firstly, the cannibalistic, territorial, and venomous nature of spiders is less than desirable when considering managing a farm of spiders. Secondly, the “milking” of spiders is labor intensive and yields relatively small quantities of silks. For example, it took 70 in­dividuals over 4 years to collect silk from more than 1 million golden orb-weaver spiders to produce enough material to assemble an 11’ x 4’ textile. The estimated cost for the single tapestry was approximately $500,000, which from an economical perspective, is staggering. Therefore, attempts to obtain large quantities of spider silk proteins have turned to the implementation of molecular biological approaches.

A variety of different expression systems have been explored to determine whether silk proteins can be expressed at high levels. Both eukaryotic and prokary­otic expressions systems offer advantages and disadvantages. Eukaryotic expression systems offer the benefit of posttranslational modifications, which include glyco — sylation and phosphorylation. However, the role and importance of these modifi­cations to silk proteins and their necessity for fiber production remains unclear. Thus far, no posttranslational modifications have been shown to be necessary for spidroin function. Prokaryotic systems offer the advantage of faster growth rates, easier genetic manipulation, and custom optimization for expression. Most existing expression systems have focused on producing truncated fibroins that only contain reduced numbers of the internal block repeats. In some cases, the C-terminus has been included in the protein constructs. Synthesizing full-length silk spidroins has been challenging due to their large molecular mass and their bias towards specific amino acids. Native proteins can exceed 3000 amino acids in length and, in the case for MaSpl, have amino acid content that surpasses more than 60% alanine and glycine.8a In fact, both DNA replication and expression of spider silk cDNAs have been hampered by their long, repetitive and guanine and cytosine rich nature. Attempts to circumvent the translational challenges via codon optimization have been used with limited success. In the literature, there have been several successful reports of partial or truncated silk fibroins being expressed in prokaryotes. Most of these studies have used Escherichia coli as the host. Miniature recombinant proteins that contain C-termini and internal block repeats have been demonstrated to be ex­pressed in prokaryotic organisms as well.58

The expression of full-length spidroin cDNAs has not been reported from either prokaryotic or eukaryotic systems. However, a metabolically engineered strain of E. coli has been shown to synthesize a large molecular weight recombinant fibroin that approaches the predicted size of native MaSpl.41 Mammalian and insect cell culture systems have shown promising results involving the expression of large molecu­lar weight spidroins using transformed cells lines from bovine mammary epithe­lial alveolar cells and Spodoptera frugiperda cells, respectively.59 Transgenic goats that express and secrete fibroins into the milk have also been generated; however, purification of the proteins from the milk has been challenging and expensive to maintain the transgenic goats. In addition, both transgenic mice and silkworms that express spider silk proteins have also been reported.60 Transgenic silkworms have shown promising possibilities, but some current barriers need to be resolved, such as improving the quantities of the spider silk protein deposited in the final spun product, which is still approximately 94% (w/w) B. mori natural product.606 The methylotrophic yeast Pichia pastoris is a robust eukaryotic expression system that allows for recombinant proteins to be secreted into liquid growth media, and it would appear to offer many advantages. These include the ability to grow the cells at high densities, harvest the protein without breaking or lysing the cells, and cheaper methods for protein purification, making yeast one of the more readily adaptable systems for producing spider silk proteins on an industrial scale.61

When the commercial MFC containing 90% water was directly added to a 50% ethanol solution of ESO and TA, some ESO-rich component was phase-separated and homogeneous cured material was not obtained. When the mixture was cured af­ter freeze-drying, the relatively homogeneous ESO/TA/MFC composite with MFC content 5 wt.% was obtained. However, the composite had much lower tan 5 peak temperature (42 °C) and tensile strength (4.0 MPa) than the control ESO/TA(1/1.4) (58 °C, 15.1 MPa). Therefore, the water in MFC aqueous suspension was substi­tuted with ethanol and the obtained ethanol suspension of MFC was added to a mixture of ESO and TA, as is described in the experimental section. By this method, a homogeneous composite with a higher performance than the control-cured resin was obtained.23

Figure 4.19 shows the relationship between tensile properties and fiber content for ESO/TA(1/1.4)/MFC composites. Tensile modulus of the composites increased with increasing fiber content, and reached 1.33 GPa at MFC content 11 wt.%. On the other hand, elongation at break decreased with an increase of MFC content. Re­garding tensile strength, although all the ESO/TA(1/1.4)/MFC composites had high­er value than the control ESO/TA(1/1.4), a clear tendency between tensile strength and MFC content was not elucidated. As a result, highest tensile strength (26.3 MPa) was obtained when the MFC content is 9 wt.%.

Figure 4.20 shows FE-SEM images of the fractured surfaces of ESO/TA(1/1.4) and ESO/TA(1/1.4) /MFC biocomposites with MFC content 9 and 11 wt.%. The surface of ESO/TA(1/1.4) was very smooth except for the fractured pattern. On the other hand, the surface of ESO/TA(1/1.4)/MFC9 is very rough, suggesting the MFC is homogeneously dispersed in the matrix polymer. However, the surface of ESO/ TA(1/1.4)/MFC11 is heterogeneous and several microcracks were observed, sug­gesting that some aggregation of MFC occurs and the space between the aggregated fibrils is not fully filled out with the epoxy resin because of the high volume frac­tion of MFC. The difference of morphology is responsible for the fact that tensile strength of ESO/TA(1/1.4)/MFC11 is lower than that of ESO/TA(1/1.4)/MFC9.

ESO/TA(1/1.4)

ESO/TA(1/1.4)/MFC9

ESO/TA(1/1.4)/MFC11

Figure 4.21 shows the temperature dependency of E’ and tan d for ESO/ TA(1/1.4)/MFC composites. The E’ at the rubbery plateau region over 100 °C in­creased with MFC content, suggesting a good dispersion of MFC in the matrix is attained. The tan d peak temperature corresponding to Tg increased a little with MFC content over the range from 5 to 9 wt.% (see also Table 7), indicating that there is some interaction between MFC and crosslinked ESO/TA. However, the tan d peak temperature of ESO/TA(1/1.4)/MFC11 was rather lower than that of ESO/ TA(1/1.4) /MFC9. This result is attributed to the heterogeneous morphology of the former composite. Table 4.7 summarizes the results of TMA and TGA measure­ments of ESO/TA(1/1.4)/MFC composites. The Tg measured by TMA exhibited a similar tendency to the tan d peak temperature measured by DMA. The coefficient of thermal expansion’s (CTE’s) below Tg and above Tg somewhat increased with MFC content. Considering that crystalline cellulose has much lower CTE than ESO/ TA(1/1.4),67 it is thought that micro bubbles or voids are contaminated into the com­posites. Although 5 wt.% loss temperature measured by TGA for ESO/TA(1/1.4)/ MFC decreased with increasing MFC content, their values were higher than that of dried MFC (315.1 °C).

Traditionally noise control materials have three distinct properties: sound absorb­ing, sound blocking and sound damping. The very first step in noise control is to identify and characterize the noise source in term of its radiated sound pressure level and frequency. Designers make an effort to ensure that the products and associated components do not radiate high levels of noise. The noise which is received by the receiver propagates in the medium between the source and the receiver as elastic waves. Thus the sound energy is transferred between the source and the receiver by such waves. In order to reduce this transfer of energy, acoustical treatment can be done in the path between the source and the receiver by using the above noise control materials. For industrial noise control, materials like glass wool, elastomers and heavy sheet metal are used. Biocomposites made of natural materials are an excellent replacement for the above materials since they are abundantly available in nature and are economic to process. In order to use biocomposites for noise control their two important acoustical properties need to be known, normal specific sound absorption coefficient and the sound transmission loss. Another important property of the material, which is used to control the vibration of the structure generating noise is its damping factor. There exist standards by which all the above properties can be measured in the laboratory.

In recent years, there is a growing interest in the development of new materials, which enhance optimal utilization of natural resources, and particularly, of renew­able resources and the research on the natural fiber reinforced composite is on the forefront due to its significant properties like economical, biodegradable, recyclable and ecofriendly. For instance, in the year 2013 for 1 US dollar around 25 kg of raw jute fiber can be procured in India. Naturally, the composites reinforced with natural fibers like jute, sisal, banana and coir thus have been subjected to intense study for their low density and low cost application in contrast to synthetic reinforced com­posites. These materials have potential to replace traditional noise synthetic noise control materials because of their comparable acoustical and mechanical properties.

Human beings exposed to high levels of noise for a prolonged time can have per­manent damage done to their ears. The human ear is nonlinear and the perception of sound heard by human being is to be clearly understood for implementing an effective noise control solution. Traditionally noise control has been done using expensive synthetic polymer based materials. However efforts are being made to use biocomposites for industrial noise control. Researchers around the globe are moving towards greener ecofriendly biocomposite materials for their use in various industrial noise control applications. Biocomposites based on ecofriendly materials like jute, coir, cotton, hemp and so forth are being used.

The three important elements in sound generation, propagation and reception are the source of sound, the path of sound and the receiver of sound. There can be an acoustical energy transfer between any of the three elements. The very basic step in noise control is to identify these three elements and then to rank and characterize the noise sources in terms of the amplitude of the sound and its frequency content.

Many experimental methods currently exist for the noise source identification like the sound pressure level mapping, the sound intensity mapping and acoustical ho­lography.

In this chapter the application ofjute a plant based fiber and its derivatives in the form of composites in industrial noise control has been discussed. The jute deriva­tives can be in the form of chopped pieces, fibers, felts, yarns, textile and composite panels. The physical, mechanical, thermal and acoustical properties of jute deriva­tives have been reported. Most of the values reported in this chapter are from actual measurements done at the various facilities of the Indian Institute of Technology Kharagpur as per international standards. For noise control, the jute derivatives can either be used as sound absorbers or sound barriers. The sound absorbers are quan­tified by the normal specific sound absorption coefficient and the sound barriers are quantified by the sound transmission loss properties. These values vary with frequency. Thus for effective noise control in a particular frequency the acoustical properties of the noise control material at that frequency need to be known.

Case studies from various applications made by the authors research group in using jute derivatives for noise control has been reported. Noise reduction using jute derivatives have been achieved in home appliances like domestic vacuum cleaner, clothes dryer and a refrigerator. Jute derivatives have been used for building acous­tics to improve the reverberation time and in to reduce the transmission loss in office partitions. Jute has excellent fire retardant properties and has a high temperature stability, thus can be used in lining of machinery enclosures, HVAC ducts, breakout noise reduction in engine silencers. Jute derivatives in various forms can be used at different locations in an automobile for noise reduction, as well.

Research is progressing on the engineering of these materials for use in the transportation sectors of aviation and rail for noise reduction. In the materials front, materials researchers are working on improving the bonding strength of the fibers by suitable chemical pretreatment to the fibers. Research is being done on using the properties of these derivatives in the numerical prediction of the noise produced by different products where these materials are being used for noise control.

KEYWORDS

Acoustic Properties Biocomposites

Environmental Friendly Materials Jute

Natural Fibers Noise Control Sound Absorption

PHA is a member of biopolyesters that is obtained by a broad variety of microor­ganisms. These microorganisms consume PHA as carbon and energy sources.8-20’44 More than 159 different types of PHAs, that is, homopolymers and copolymers can be produced by using various bacterial species and growth conditions.20 The most popular polymers of the PHA family are polyhydroxybutyrate (PHB) and poly(hydroxybutyrate-cohydroxyvalerate) (PHBV). These polymers are synthe­sized when bacteria are exposed to carbon source while all other necessary nutri­ents are limited.2045 The properties of PHBV alter by varying the valerate content. PHAs are renewable, biodegradable and biocompatible. However, they possess a narrow processing window and are sensitive to processing conditions as well high temperature and shears. Therefore, additives, blends, and composites are potential techniques that can be employed to resolve these shortcomings of PHA.20

DIENE NDIAYE, MAMADOU GUEYE, COUMBA THIANDOUME, ANSOU MALANG BADJI, and ADAMS TIDJANI

ABSTRACT

Wood polymer composites (WPC) have attracted a lot of researchers, mainly due to their low densities, low cost, high filling levels, renewable and none toxic organic fibers to the glass or carbon, biodegradability and above all their availability from renewable sources. They present considerable commercial interest due to these po­tential opportunities. WPCs are used in a variety of innovative applications, such as the automotive sector, construction products or packaging industries. The product has the esthetic appearance of wood and the processing capability of thermoplastics and its performance in mechanical properties.

12.1 INTRODUCTION

The incorporation of various types of fillers into polymer matrices is an interest­ing route to produce polymer composites with different properties. Considerable researches have been focused extensively in the use of natural fibers as reinforce­ment material in a thermoplastic matrix. The utilization of vegetable fibers is driven by growing market trends in terms of environmental impact. The most common composites with natural fibers are made with polyolefin (polyethylene PE and poly­propylene PP) and polyvinyl chloride (PVC) matrices and wood fibers as reinforce­ment.

In last few years, the utilization of fibers and powders derived from agricultural sources has attracted attention of many researchers mainly due to their low den­sities, low cost, none abrasiveness, high filling levels, renewable and none toxic

organic fibers to the glass or carbon, biodegradability, and above all the availability from renewable sources.1-5

The acronym ‘WPC’ covers an extremely wide range of composite materials that use plastics ranging from PP to PVC and binders/fillers ranging from wood flour to natural fibers (e. g., flax)6. Wood polymer composites (WPC) are experi­encing a growing market demand; hence it is logical to study ways to enhance the performance attributes of WPCs.

The use of various reinforcing fillers in the composites and their effect has to be typified. This will augment the industry with better understanding of proper­ties and consequently delivering better products. Extensive research and product development has been done to reinforce polyolefin and other none biodegradable plastics, but research on reinforcing biodegradable polymers is limited because of the incompatibility between the two entities. The application of biodegradable poly­mers has primarily focused on the medical, agricultural, and consumer packaging industries78. The lignocelluloses’ fibers used in polyolefins include cellulose fibers, wood fiber, flax, cannabis sativa (hemp), jute fiber, pine, sisal, rice husk, sawdust, wheat straw paper, mud, coir, kenaf, cotton, pineapple leaf fiber, bamboo fiber and palm tree9.

Reinforcements such as wood have been successfully used to improve the me­chanical properties of thermoplastic composites. Extensive efforts are being made to develop biodegradable composites using renewable resources in an attempt to replace the nonbiodegradable synthetic polymers used for composites10. Composites made from blends of thermoplastics and natural fibers have gained popularity in a variety of applications because they combine the desirable durability of plastics with the cost effectiveness of natural fibers as fillers or reinforcing agents11. The product has the esthetic appearance of wood and the processing capability of ther­moplastics and its performance in humid area.

Another attraction is the fact that these materials are obtained easily from natural wastes. Because of these attributes, WPCs are used in a variety of innovative ap­plications, such as the automotive (door panels or trims, door trims, trunk liners), construction products (decking, fencing, siding, windows, door frames, interior pan­eling or decorative trim), or packaging industries. Natural fibers possess excellent sound absorbing efficiency and are more shatter resistant and have better energy management characteristics than glass fiber reinforced composites. The incorpora­tion of natural fibers into polycaprolactone (PCL) has been shown to enhance the biodegradability of the resulting composites12. However, the biodegradability of the resulting product is limited if all polymers are not biodegradable13.

Properties of WPCs depend on the characteristics of matrix and fillers, chemical interaction between wood fibers and polymer, humidity absorption and processing condition. However, the use of wood-fibers shows some drawbacks such as fiber- polymer incompatibility and their low temperature of thermal degradation due to the presence of cellulose and hemicelluloses. The presence of hemicellulose, lignin and other impurities in these organic reinforcements causes a lack of adhesion between fibers and polymers. The low thermal degradation limits the allowed processing temperature to less than 200 °C. The compatibility between the wood fibers and polymeric matrix constitutes one important factor in the production of WPCs with improved mechanical properties14,15,16.

These disadvantages of wood led some researchers to use other materials as reinforcements instead of wood. In resents years, natural fillers such as jute, kenaf, hemp, sisal, pineapple, rice husk, have been successfully used to improve the me­chanical properties of thermoplastic composites17. The hydrophobic nature of PP poses a potential problem in achieving good fiber/matrix adhesion in these systems however, as cellulose is an inherently hydrophilic polymer because of the numerous hydroxyl groups contained within it. To alleviate this obstacle, chemical compati — bilizers or coupling agents have been developed which alter the surface of the hy­drophilic cellulose fiber in order to improve the dispersion and interfacial adhesion between the fiber and matrix. The most popular coupling agent that is being used by many researchers is maleic anhydride grafted polyolefin, such as polyethylene (MAPE) and polypropylene (MAPP)18,19. Many in-depth studies have elucidated the mechanisms of adhesion between MAPP treated wood fibers and the PP matrix that cause the improvement by the formation of linkages between the OH groups of wood and maleic anhydride20,18. It was found that coupling agent can form chemical bonds on the surface of wood and the interface between wood and polymer and it can well infiltrate the surface of wood, which finally result in lower surface tension of wood material21,22,23. One such compatibilizer is maleic anhydride grafted poly­propylene (MAPP), a waxy polymer system that has been proven useful in the pro­cessing and production of cellulose reinforced PP composites24,25. MAPP is formed by reacting maleic anhydride (MA) with PP in the presence of an initiator to produce PP chains with pendant MA groups (Fig. 12.1).

The PP portion of MAPP can entangle and co crystallize with the unmodified PP, while the maleic anhydride groups can bond to the hydroxyl (-OH) groups on the fibers. When mixed with cellulose, the hydroxyl group of the cellulose breaks one of the C-O bonds in the MA group and forms a new bond between one of the carbons from the MAPP group and the oxygen from the cellulose (Fig. 12.2).

The resulting chemical bond between the oxygen of MAPP26,27 is also able to compensate for insufficient breakup forces during processing, such as low shear stress, by reducing the interfacial tension between PP and the cellulose, which leads to finer dispersion of the fiber throughout the system28. Addition of MAPP also re­duced the degree of water absorption (>20%), making these materials more suitable for using in damp environments.

There are some studies on using other coupling agents such as silane29,30 and iso­cyanates31,32. In all cases, with the coupling agents used, there is usually a significant improvement of the mechanical properties of the final composites.

Our study is inspired by the principle of ecological replacement of inorganic pol­luting substances by agricultural products (wood fibers, rice straw and Dried Distill­ers Grain with Soluble (DDGS) as reinforcements in polymer matrices. DDGS is a coproduct of the dry grind corn process that is used to produce fuel ethanol from corn. Considerable efforts have been made to use the coproducts obtained during the processing of corn, wheat and soybeans, wheat gluten and soy proteins, respectively for composite applications33.

Usually Rice husk is a coating or protective layer formed during the growth of grains of rice. Removed during the refining of rice, these shells have low commer­cial value, because the SiO2 and the fibers contained have poor nutritional value and are used in few quantities in animal ration. Rice Husk (RH) has been a problem for rice farmers due to its resistance to decomposition in the ground, difficult digestion and low nutritional value for animals34. Therefore, the development of new polymer composites filled with RH turns out to be a very interesting approach.

Another problem in our country, ethanol industry has grown exponentially in recent years, and the supply of distillers dried grains with solubles (DDGS) has subsequently increased dramatically. Currently, the ethanol industry’s only outlet for DDGS is animal feed ingredients35,36.

The voluminous production rate of DDGS is exceeding its consumption rate as animal feed. Most research publications about DDGS focus on its feed applica­tion37. Successfully making the separated DDGS fiber-based WPC would benefit the dry grind plants, wood composites manufacturers and the rural economies in which these production facilities are largely located by increasing their revenues. As technology develops towards the utilization of natural by products, classical wood fibers have shown strong potential as reinforcement in polymer matrix composites.

Composites were prepared by extruding DDGS with polypropylene and phe­nolic resin38. The need for materials with environmentally friendly characteristics has increased due to limited natural resources and increasing environmental regula­tion39,40,41. It is interesting to note that natural fibers such as jute, rice husk, DDGS, banana, sisal, etc., are abundantly available in developing countries in Africa but are not optimally used.

In this study, polypropylene was reinforced with pine wood, rice husk and dis­tillers dried grains with soluble, byproducts of the ethanol process. The objectives of this study were to develop composites with PP matrix and three different rein­forcing fillers: pinewood, rice husk and DDGS and to explore the performances and limitations of these reinforcing fillers on the mechanical, thermal and morphologi­cal properties of the composites. The results obtained in these tests, are discussed. We also discuss how to provide competitive alternative materials to natural wood, which becomes increasingly expensive and is diminishing in supply.

As mentioned above, the lignocellulosic materials in the wood are arranged in the form of complex matrix following a natural organization of these constituents. The cellulose polymer is composed of glucose monomers containing three free hydroxyl groups in positions 2, 3 and 6. These hydroxyls are responsible for interactions intra and intermolecular (Fig. 14.9). These interactions result in the formation of poly­mers beams that are arranged in organized crystalline regions and in disorganized amorphous regions, resulting in the formation of the successive structures such as nanofibrils, microfibrils, fibrils and finally the cell wall (Fig. 14.3). Therefore, the deconstruction of the cell wall to obtain individuals materials for different applica­tions, either by chemical, thermal or physical methods originates materials with different size and surface charge, and morphology that may influence the formation of composites.

According to Samir et al.,21 nanocrystalline cellulose regions grow under con­trolled conditions, which enable the formation of individual nanocrystals with high purity. These nanocrystals exhibit highly ordered structure with different dimen­sions and morphology that can confer significant change in strength, electrical, opti­cal, magnetic, ferromagnetic, conductive, and dielectric materials properties.

The surface characteristics of the nanocrystalline cellulose and also of the nano- fibrillated cellulose are related to methods for isolating these nanomaterials. Con­sidering the nanocrystalline cellulose the main isolation processes use strong acids such as sulfuric acid and hydrochloric acid. According Araki et al.,65 nanocrystalline cellulose obtained with the use of sulfuric acid have a net surface negative charge due to sulfate groups present on the surface of these particles. Moreover, the use of hydrochloric acid gives the neutral net charge of the nanocrystal surface. According to these authors, the aqueous dispersion of the nanocrystals insulated with sulfuric acid provides more stable than the dispersion of the isolated nanocrystals with hy­drochloric acid. Also, the morphological characteristics of these nanomaterials are related to the raw material source and to the conditions used in the isolation meth­ods. For example, Elazzouzi-Hafraoui et al.66 using the same conditions of tempera­ture, type of acid, acid concentration and hydrolysis time, found close dimensions to nanocrystalline celluloses for cotton fiber and microcrystalline cellulose. For cotton, the length was between 105 and 141 nm and a width between 21 and 27 nm, and for microcrystalline cellulose, 105 nm and 12 nm for the length and the width param­eters, respectively. On the other hand, cotton fibers treated with different conditions of temperature was found that there was a reduction in the size of nanocrystalline cellulose by increasing the hydrolysis temperature, and, no clear correlation was found between the effects of temperature and diameter of these nanoparticles. Also the effect of the cotton fiber hydrolysis conditions with sulfuric acid was studied by

Dong et al.67 These authors observed a negative correlation of the nanocrystalline cellulose particles length and positive surface charge of these nanoparticles with increasing time of hydrolysis.

Owing to its abundance, renewability, biodegradability, biocompatibility (low cy­totoxicity), antimicrobial activity and chemical and physical functionalities, chitin/ chitosan is being explored as potential candidate for packaging and biomedical ap­plications. Due to their poor thermal processability and low solubility in neutral media, the applications of chitin/chitosan alone are still underexplored. Through chemical modification (esterification, etherification, N-acylation, and grafting), blending with other biopolymers, reinforcement by nanoscale particles, chitosan is being explored as potential candidates for these applications. With aid of nano­science of nanotechnology, chitosan based nanocomposites are being explored for packaging including smart active and antimicrobial packaging for food, meat and dairy products, antimicrobial sanitary products and biomedical applications includ­ing wound dressing, drug-delivery and tissue engineering. This chapter reviewed the recent developments on the nanocomposites of chitosan using nano-cellulose, which is also bio-renewable. They are usually processed using acidic media or in water after specific chemical modification. The nanocomposites of chitosan/cellu- lose exhibited remarkable improvement mechanical properties, reduction in water absorption/uptake, decrease in permeability coefficient for water vapor and oxy­gen and retained transparency and antimicrobial or microbicidal activity, making them suitable candidates for packaging and applications. These improvements have been attributed to the property of highly crystalline individual nanocrystals and their strong interactions with the chitosan matrix. This hetero-phasic domains phenom­enon was also observed when the chitosan and cellulose blended by dissolution. The approach of covalent conjugation has been demonstrated to increase the higher loading of nanocellulose, to improve compatibility and to decrease the water uptake/ permeability. The approach of layer-by-layer assembly for preparing nanocomposite films or coating can be explored for high barrier coatings, and packaging without compromising the transparency. Superabsorbent materials for sanitary applications or antimicrobial applications can also be prepared via in-situ grafting of chitosan in presence of cellulose nanocrystals. Biological applications such as drug deliv­ery, antimicrobial nonwoven materials for wound dressing are also accessible via multicomponent nanomaterials based on chitosan and cellulose. It is observed that the technological advancements on the chitosan-based nanocomposites are still be­ing explored. For larger scale commercialization, the industrial scale production of these nanocomposites is still to be demonstrated. By portraying the recent develop­ments in this area, this chapter may stimulate further research activities on the in­novative nanomaterials based on chitosan and nanocellulose at favorable production cost/performance ratio.

16.3 ACKNOWLEDGEMENT

Authors are acknowledging the financial support from Queensland Government un­der Smart Futures Research Partnerships Program (2012-2014).