Chemical Modification of Fibers

The most common fibers in biocomposites come from linen, hemp, cotton, jute, coconut, banana, and leaves of various kinds of agave. The basic problem with the proper application of natural fibers is their great variation in quality and mechanical properties. Synthetic fibers such as glass fiber and carbon fiber have very specific physical characteristics, but the features of natural fiber depend on many factors, such as their origin, the age of the plant, whether the material comes from leaves or stem, and on the process of obtaining the fiber and its preparation. 

Natural fibers should be subject to certain preparatory operations and modifications of their surface. After this process, they should display the following features  

The chemical makeup and structure of a fiber depends on numerous factors such as climatic and cultivation conditions, age, and whether the fiber comes from leaves or stems. Natural fibers consist of more or less desirable components such as cellulose, hemicelluloses, pectin, hgnin, wax, and water-dissolvable substances, all of which affect the fibers physical characteristics. 

The results in Table 10.1 show considerable differences in the chemical makeup of different fibers. The lowest cellulose content and highest hgnin content is observed in coconut fiber. The quantity of lignin and cellulose depends in the first place on the age and species of plants that provided the fiber [9]. 

Hemicellulose is a hydrophihc polymer it therefore largely determines the water absorption by vegetable fibers [6]. 

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Plasma treatment AKD Chemical modification of fiber surface Entire hydrophobization followed by selective dehydrophobization... 

Further, this chapter provides a survey about the formation of a transciystalline layer in the composite system. The occurrence of transcrystallization was found to strongly depend on the type of chemical treatment of the fiber surface. 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... 

Effect of fiber treatment Chemical modification of fibers decreased the dielectric constant of OPF-sisal fiber-NR hybrid composites [59]. This was due to the decrease in orientation polarization of the composites upon treatment. Chemical treatment results in reduction of hydrophilicity of the fibers leading to lowering of orientation polarization and subsequently dielectric constant. Alkali treatment yielded higher dielectric constant comparing to silane treatment. However, higher concentration of alkali... 

Mitra, B. C., Basak, R. K., and Sarkar, M. (1998). Studies on Jute-Reinforced Composites, Its Limitation, and Some Solutions through Chemical Modifications of Fibers. Journal of Applied Polymer Science 67, 1093-1100. 

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. 

Chemical modification of the cotton fiber must be achieved within the physical framework of this rather compHcated architecture. Uniformity of reaction and distribution of reaction products are iaevitably iafiuenced by rates of diffusion, swelling and shrinking of the whole fiber, and by distension or contraction of the fiber s iadividual stmctural elements duting finishing processes. 

When used as substitutes for asbestos fibers, plant fibers and manmade cellulose fibers show comparable characteristic values in a cement matrix, but at lower costs. As with plastic composites, these values are essentially dependent on the properties of the fiber and the adhesion between fiber and matrix. Distinctly higher values for strength and. stiffness of the composites can be achieved by a chemical modification of the fiber surface (acrylic and polystyrene treatment [74]), usually produced by the Hatschek-process 75-77J. Tests by Coutts et al. [76] and Coutts [77,78] on wood fiber cement (soft-, and hardwood fibers) show that already at a fiber content of 8-10 wt%, a maximum of strengthening is achieved (Fig. 22). 

Impact strength also increased if the adhesion between the polymer and fiber is increased [240, 249]. The most promising method of modification of fiber-filled compositions is by pre-treating the fibers or adding to the matrix of specific depressants or modifiers with the aim of creating a chemical bond at the interphase. This improves the composition service lifetime, strength and thermal stability [250],... 

Munkholm C., Walt D.R., Milanovich F.P., Klainer S.M., Polymer modification of fiber optic chemical sensors as a method of enhancing fluorescence signal for pEl measurement, Analytical Chemistry 1986 58 1427-1430. 

Chemical extractants, 10 750 Chemical fiber modification, 16 14 Chemical finishing, of fibers, 11 180-181 Chemical fluid deposition (CFD), of metals, 24 22... 

Surface Modification of Cellulose and PVA Films. Cellulose, as well as PVA,is known to be a typical non-ionic, hydrophilic polymer possessing hydroxyl groups. As this group has a high reactivity,chemical modification of these polymers is relatively easy and, in fact, has been the subject of extensive research. However, so far as we know, no work has been reported concerned with reactions occurring only at the surface of films or fibers from these polymers. 

Kumar, S. (1994). Chemical modification of wood. Wood and Fiber Science, 26(2), 270-280. 

Mahlberg, R., Paajanen, L., Nurmi, A., Kivisto, A., Koskela, K. and Rowell, R.M. (2001). Effect of chemical modification of wood on the mechanical and adhesion properties of wood fiber/polypropylene fiber and polypropylene/veneer composites. Holz als Roh- und Werkstoff, 59(5), 319-326. 

Rowell, R.M. and Ellis, W.D. (1984). Effects of moisture on the chemical modification of wood with epoxides and isocyanates. Wood and Fiber Science, 16(2), 257-267. 

Rowell, R.M., Cleary, B.A., Rowell, J.S., Clemons, C. and Young, R.A. (1993b). Results of chemical modification of lignocellulosic fibers for use in composites. In Wood Fiber/Polymer Composites Fundamental Concepts, Processes, and Material Options, Wolcott, M.P. (Ed.). Eorest Products Society, Madison, Wiseconsin, USA, pp. 121-127. 

In recent years it has become increasingly apparent that the compositional heterogeneity of the chromatin fiber through histone variants, histone post-translational modifications and chemical modifications of DNA (methylation) [9] play an important role in all these processes. The different sources of compositional heterogeneity are described in Sections 2-4 of this review. 

Also, local changes in the structural and chemical variation of DNA may have important effects on the overall extent of chromatin folding. For instance, transitions from the B to the Z form of DNA will result in nucleosome dissolution (as discussed earlier) and this could affect the folding of the fiber. As well, chemical modifications of the bases such as methylation have been shown to increase the folding of the chromatin fiber when linker histones are present [250] although the mechanism involved in this later case remains to be elucidated. 

Chemical Modification of Lignocellulosic Fibers To Produce High-Performance Composites... 

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