Natural fiber modification

The utilization of enzymes in the natural fiber modification field is rapidly increasing. This trend may be due to the environmentally-friendly nature of enzyme treatments as the catalyzed reactions are very specific and the performance is very focused [3]. Several enzymes have been used in order to enhance the effectiveness of extracting fibers from the agro-residue or fine-tune the properties of extracted fibers such as lowering their diameter. Xylanases, cellulases, pectinases are the enzyme types that have found more use in agro-residual fiber modification [12,13,38]. 

The improvement of the properties of biocomposites can also be attained by polymer matrix modification as well as by natural fiber modification. A right combination of natural fiber and polymer matrix modifications may give rise to a synergetic effect. For instance, the incorporation of organic-inorganic hybrid polymer matrix, nanostructured polymer matrix, blended polymer matrix, or chemically or physically modified polymer matrix into natural fiber reinforcement may be considered. 

Textile finishing includes various efforts to improve the properties of textile fabrics, whether for apparel, home, or other end uses. In particular, these processes are directed toward modifying either the fiber characteristics themselves or the gross textile end properties. Such modifications may be chemical or mechanical in nature. One modification that is not covered in this article relates to the dyeing of textiles and the dyestuffs employed for fibers however, areas that involve chemical finishing designed to modify the normal dye receptivity and the growing use of enzyme treatments are included. 

Treatments with Chemicals or Resins. Resin treatments are divided into topical or chemical modifications of the fiber itself. Most chemical treatments of synthetic fibers are topical because of the inert character of the fiber itself and the general resistance of the fiber to penetration by reagents. By contrast, ceUulosics and wool possess chemical functionality that makes them reactive with reagents containing groups designed for such purchases. Natural fibers also provide a better substrate for nonreactive topical treatments because they permit better penetration of the reagents. 

The quality of the fiber matrix interface is significant for the application of natural fibers as reinforcement fibers for plastics. Physical and chemical methods can be used to optimize this interface. These modification methods are of different efficiency for the adhesion between matrix and fiber. 

An older method of cellulose fiber modification is mercerization [22,33-36], which has been widely used on cotton textiles. Mercerization is an alkali treatment of cellulose fibers. It depends on the type and concentration of the alkalic solution, its temperature, time of treatment, tension of the material, and the additives used [33,36]. At present there is a tendency to use mercerization for natural fibers as well. Optimal conditions of mercerization ensure the improvement of the tensile properties [33-35,37] and absorption characteristics [33-35], which are important in the composing process. 

Analog-to-glass fibers silanes are used as coupling agents for natural fiber polymer composites. For example, the treatment of wood fibers with product A-175 improves wood dimensional stability [53]. In contrast, a decrease of mechanical properties was observed for coir-UP composites after a fiber modification with di-chloromethylvinyl silane [54]. The treatment of mercer-... 

The mechanical properties of composites are mainly influenced by the adhesion between matrix and fibers of the composite. As it is known from glass fibers, the adhesion properties could be changed by pretreatments of fibers. So special process, chemical and physical modification methods were developed. Moisture repel-lency, resistance to environmental effects, and, not at least, the mechanical properties are improved by these treatments. Various applications for natural fibers as reinforcement in plastics are encouraged. 

Yet, the development of processing and modification methods is not finished. Further improvements need to be expected so that it might be possible to substitute technical fibers in composites even more widely. Natural fibers are reusing raw materials and they are recyclable. When recognizing the need for recycling and preserving natural resources, such a substitution is very important. 

Strategies to induce chirality in a prochiral substrate included modification of existing heterogeneous catalysts by addition of a naturally occurring chiral molecules, such as tartaric acid, natural amino acids, or alkaloids, and the implementation of chiral supports, which include quartz or natural fibers, for metallic catalysts. Both strategies have been successful on a limited basis. 

Chemical modification reactions continue to play a dominant role in improving the overall utilization of lignocellulosic materials [1,2]. The nature of modification may vary from mild pretreatment of wood with alkali or sulfite as used in the production of mechanical pulp fibers [3] to a variety of etherification, esterification, or copolymerization processes applied in the preparation of wood- [4], cellulose- [5] or lignin- [6] based materials. Since the modification of wood polymers is generally conducted in a heterogeneous system, the apparent reactivity would be influenced by both the chemical and the physical nature of the substrate as well as of the reactant molecules involved. 

The methods of apphcation of dyes in textile dyeing and printing have undergone several modifications to meet the requirements of the new synthetic fibers and their blends with the natural fibers and new classes of dyes. However, the basic operations of dyeing remain the same and include the following ... 

Antimicrobial Edible films were prepared from natural fiber of pectin and other food hydrocolloids for food packaging or wrapping by extrusion followed by compression or blown film method. Microscopic analysis revealed a well mixed integrated structure of extruded pellets and an even distribution of the synthetic hydrocolloid in the biopolymers. The resultant composite films possess the mechanical properties that are comparable to films cast from most natural hydrocolloids that consumed as foods or components in processed foods. The inclusion of polyethylene oxide) alters the textures of the resultant composite films and therefore, demonstrating a new technique for the modification of film properties. The composite films were produced in mild processing conditions, thus, the films are able to protect the bioactivity of the incorporated nisin, as shown by the inhibition of Listeria monocytogenes bacterial growth by a liquid incubation method. 

A. K. Bledzki, S. Reihmane, and J. Gassan, Properties and modification methods for vegetable fibers for natural fiber composites, J. Appl. Polym. Sci., 59 (1998) 1329-1336. 

Native cellulose are commonly modified by physical, chemical, enzymic, or genetic means in order to obtain specific functional properties, and to improve some of the inherent properties that limit their utility in certain application. Physical/surface modification of cellulose are performed in order to clean the fiber surface, chemically modify the surface, stop the moisture absorption process, and increase the surface roughness. " Among the various pretreatment techniques, silylation, mercerization, peroxide, benzoylation, graft copolymerization, and bacterial cellulose treatment are the best methods for surface modification of natural fibers. 

Pommet, M. Juntaro, J. Heng, J.Y.Y. Athanasios, M. AdamF.L. Karen, W. Gerhard, K. Milo, S.P.S. Bismarck, A. Surface modification of natural fibers using bacteria Depositing bacterial cellulose onto natural fibers to create hierarchical fiber reinforced nanocomposites. Biomacromolecules 2008, 9 (6), 1643-1651. 

Three parts are covered in the chapter. First, the synthesis and properties of PLA are described. The modification and process of PLA are also discussed. Then, the composites with PLA as matrix and natural fiber or nanoparticles as reinforcement are reported in the second part. The processing and the properties of the composites are also given. The interface between PLA and the reinforcement and the surface treatment methods are discussed. Finally, the application and the development of PLA and PLA-based composites in the future are proposed. 

Hokens, D. Mohanty, A.K. Misra, M. Drzal, L.T. The influence of surface modification and compatibilization on the performance of natural fiber reinforced biodegradabale thermoplastic composite. Polymer Preprints, 43(1), 482-483 (2002). 

Identification of fibers is complicated by the presenee of many generie types and modifications of both man-made fibers and common natural fibers. The major generic types of manmade fibers are summarized in Table 12.29. Visual and microseopie examination together with simple manual tests remain the primary methods of fiber identification, though many new sophisticated instrumental methods are available that are based on the chemical and physical property differences among the fibers. These methods are able to distinguish between closely related fibers that differ only in chemical composition or morphology. 

J. George, M.S. Sreekala, S. Thomas, A review on interfaee modification and characterization of natural fiber reinforced plastic composites. Polym. Eng. Sei. 41(9), 1471-1485 (2001)... 

Nagele, H., Pfitzer, J., Nagele, E. et al. (2002) ARBOFORM - A thermoplastic, processable material from lignin and natural fibers, in Chemical Modification, Properties, and Usages of Lignin (ed. Th.Q. Hu), Kluwer Academic / Plenum Publisher, New York, pp. 101-120. 

Adekunle, K., Aakesson, D. and Skrifvars, M. (2008) Synthetic modification of reactive soybean oils for use as biobased thermoset resins in stmctural natural fiber composites. Polymer Preprints (American Chemical Society, Division of Polymer Chemistry), 49(1), 279-280. 

In the 1970 s in this context,the extensive researches on natural fibers, in particular, silk, wool,its yarns, and textiles, have made remarkable progresses further reseaches on properties of fiber assemblies and analyses of their hands have made a considerable progress, and then these seriese of researches have led to silk-like and wool-like modifications. 

Modification of natural protein through grafting have become in a widely used path and some works have carry out studies with acrylic monomers as ethylacrylate, acrylic acid, methacrylic acid and methyl methacrylate (Mostafa, 1995 Athawale and Rathi, 1997 Jia and Yong, 2006 Zampano, et al 2009), which carried out graft of natural fibers and proteins. However, just few of works report grafting of hydroxyethyl methacrylate onto naturals fibers (Joshi and Sinha, 2006) (Martinez et al., 2003, 2005). 

---