Chemical modification, natural fiber

Many factors such as adhesion between components, fiber topography, and kinetic parameters of crystallization of semicrystalline matrix have been reported to influence transciystallinity. The transcrystallinity phenomenon in the natural fibers/polypropylene system is affected by the different type of chemical treatment of lignocellulosic materials. Moreover, the ability of natural filler to induce nucleation in polypropylene matrix is also dependent on the kind of chemical modification of surface fibers. Predominant nucleation ability was found for unmodified fibers. However, chemical modification of fiber surface slightly depressed the nucleation of polypropylene matrixes. 

Mitra BC, Basak RK, Sarkar M (1998) Studies on jute-reinforced composites, its limitations and some solutions through chemical modifications of fibers. J Appl Polym Sci 67 1093-1100 Bhal NS, Singh B (1998) Potential of natural fiber reinforced polymer composites for civil engineering applications in India. In Saadatmanesh H, Ehsani M R (eds) Proceedings of... 

Textile dyes were, until the nineteenth century invention of aniline dyes, derived from biological sources plants or animals, eg, insects or, as in the case of the highly prized classical dyestuff Tyrian purple, a shellfish. Some of these natural dyes are so-caUed vat dyes, eg, indigo and Tyrian purple, in which a chemical modification after binding to the fiber results in the intended color. Some others are direct dyes, eg, walnut sheU and safflower, that can be apphed directly to the fiber. The majority, however, are mordant dyes a metal salt precipitated onto the fiber facUitates the binding of the dyestuff Aluminum, iron, and tin salts ate the most common historical mordants. The color of the dyed textile depends on the mordant used for example, cochineal is crimson when mordanted with aluminum, purple with iron, and scarlet with tin (see Dyes AND DYE INTERMEDIATES). 

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. 

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. 

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. 

Abstract Cellulose is the most important biopolymer in Nature and is used in preparation of new compounds. Molecular structure of cellulose is a repeating unit of p-D-glucopyranose molecules forming a linear chain that can have a crystallographic or an amorphous form. Cellulose is insoluble in water, but can dissolve in ionic liquids. Hemicelluloses are the second most abundant polysaccharides in Nature, in which xylan is one of the major constituents of this polymer. There are several sources of cellulose and hemicelluloses, but the most important source is wood. Typical chemical modifications are esterifications and etherifications of hydroxyl groups. TEMPO-mediated oxidation is a good method to promote oxidation of primary hydroxyl groups to aldehyde and carboxylic acids, selectively. Modified cellulose can be used in the pharmaceutical industry as a metal adsorbent. It is used in the preparation of cellulosic fibers and biocomposites such as nanofibrils and as biofuels. 

Polymer forming began with the chemical modification of natural polymers such as natural rubber vulcanization and cellulose acetylation. The first efforts to shape natural polymers and early synthetic ones into useful products such as textile fibers and films for packaging date from the middle of the 19 century. 

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. 

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. 

The earliest applications of polymer chemistry involved chemical modification designed to improve the physical properties of naturally occurring polymers. In 1839, Charles Goodyear transformed natural rubber, which is brittle when cold and tacky when warm, to a substance that maintains its elasticity over a wider temperature range by heating it with sulfur (vulcanization). The first synthetic fibers— called rayons—were made by chemical modification of cellulose near the end of the nineteenth century. 

Natural saccharides (carbohydrates) are highly important as biomass, food, and raw materials. As a result, their chemical modification has been investigated from early on to develop a variety of industrial products like fibers. Due to their high biocompatibility and biodegradability, carbohydrate-based materials (Fig. 5.17) have also been widely used for pharmaceutical and medical applications. 

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. 

Chemical or synthetic fibers are further classified into regenerated and synthetic fibers. Regenerated or semisynthetic fibers are produced from natural products by a chemical procedure or modification. These fibers can, for example, be rayon, acetate silk, and alginate fibers. In contrast, synthetic fibers are completely synthesized from other raw materials, and may, for example, consist of polyesters, polyamides, poly(acrylonitrile), polyolefins, or glass. 

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