Fibers, chemical constituents

The low electrical conductivity of PET fibers depends essentially on their chemical constituency, but also to the same extent on the fiber s fine structure. In one study [58], an attempt was made to elucidate the influence of some basic fine structure parameters on the electrical resistivity of PET fibers. The influence of crystallinity (jc) the average lateral crystallite size (A), the mean long period (L), and the overall orientation function (fo) have been considered. The results obtained are presented in the form of plots in Figs. 9-12. 

How much a mammal eats of a given plant often depends on the levels of different classes of chemical constituent, notably nutrients and plant secondary metabolites. As in birds, it is not the plant defense compounds alone, but rather complex balances between nitrogen and carbohydrate contents, levels of defense compounds, and fiber that determine palatability. 

As we know, from earliest times up to the present days, the substances used as vehicles for writing have been numerous. The papers of one hundred years ago were basically made from rags of cotton and linters. The principal chemical constituent of these sources is cellulose, a polymeric carbohydrate composed of long linear chains of /3-linked anhydroglucopyranose. The chains in cellulose are composed of as many as ten thousand glucose units (degree of polymerization). The composition of wood fibers is quite different from that of cotton, as can be seen from Table I. The chemical constituents of modern papers are compli-... 

Table II. Chemical Constituents of Wood and Pulp Fibers...

Chemical Characteristics of Paper Documents. From the earliest times up to the present day, the substances used as vehicles for writing have been numerous. Ancient paper documents were basically made from rags of cotton and linters cellulose is the major chemical constituent (I). Modern papers, however, are made of wood fibers, which usually are composed of cellulose, hemicelluloses, and lignin (I). In addition, for most of the modern papers, fillers, sizing agents, and other additives are used to improve paper properties (I). 

Research on the chemical nature of hardwood xylem has revealed that the walls of fibers and ray cells contain lignin of one type, syringyl, while vessel walls together with the surrounding middle lamella are rich in lignin of a second type, guaiacyl, which is the same type found in softwood xylem (9, 10). This basic chemical difference between hardwoods and softwoods could, in some instances, potentially influence phenomena that depend on the chemical nature or reactivity of wood tissue at the cellular level. Further details on the nature and distribution of wood chemical constituents are found in Chapter 2. 

As mentioned earlier, UV-curable resin formulations are very attractive for fiber coating because of the rapid cross-linking rates that are achievable. Most commonly, epoxy- or urethane-acrylate resins are employed (18-22), and viscosity and cross-link density are controlled through the addition of reactive diluents. With these systems work has focused on producing low modulus, low T properties (20-22) through the incorporation of appropriate chemical constituents to enhance higher chain flexibility, for example, ether linkages. 

Figure 1. The effect of gamma irradiation of hemlock sawdust on certain of its chemical constituents and on its susceptibility to rumen microbial action in vitro. ADF = acid-detergent fiber ADL = acid-detergent lignin CD = cellulose digestion DMD = dry matter disappearance...

Retted fibers such as jute and kenaf have three principal chemical constituents, namely, a-cellulose, hemicelluloses, and lignin. The lignin can be almost completely removed by chlorination methods in which a soluble chloro-lignin complex is formed, and the hemicelluloses are then dissolved out of the remaining holocellulose by treatment with dilute alkali. The final insoluble residue is the a-cellulose constituent, which invariably contains traces of sugar residues other than glucose. 

Manzoor-i-Khuda et al. [17] have studied the variation in chemical constituents of jute fiber taken from different grades of both white and tossa and concluded that certain correlations exist between the analytical results and the commercial grade. Thus, it is claimed that the lignin content increases as the grades go from higher to lower, and that the ash content and copper number show similar negative correlations. 

This chapter includes introduction of fibers from different agro-residual sources, extraction methods, chemical constituents and properties of fibers and physical and chemical treatments applied to fibers to provide higher quahty reinforcement elements of biocomposites. Due to the broadness of the scope, this chapter will undoubtedly be unfinished, but it will hopefully provide guidance to researchers who want to contribute to the environment and to the rural society, together with the composite industry. 

Coir fibers are obtained from the husk of the coconut. Coir fiber is generally extracted by mechanical means from the plant [52]. Manilal et al. [52] extracted coir fibers by a closed retting process in an aerobic retting reactor. Bakri and Eichhorn [53] mechanically extracted coir and celery fibers and studied their tensile behaviors in terms of micromechanics. Mothe and Miranda [45] studied the thermal stability and chemical constituent analyses of coir fibers. Khan and Alam [54] investigated the effects of several chemical treatments on the thermal and meachanical properties of coir fibers. Mahato et al. [55] studied the effect of alkalization on the thermal degradation of coir fibers. 

The major chemical constituents of natural fibers contain hydroxyl and other oxygen containing groups that attract moisture through hydrogen bonding [16]. The... 

Due to their low thermal stability, natural fibers are generally processed with plastics where high temperatures are not required (less than about 200 °C). Above these temperatures, many of the polymeric constituents in natural fibers begin to decompose. Since cellulose is more thermally stable than other chemical constituents, highly pulped fibers that are nearly all cellulose have been used to extend this processing window ]11, 17]. 

Table 2. Chemical constituents of maize stalk fiber (Reddy and Yang, 2(X)5a).

Harun J, Labosky P Jr 1985 Chemical constituents of five northeastern barks. Wood Fiber Sci 17 274-280... 

Composition of the huiis—The fibrous hulls have only a small percentage of oil and crude protein and contain about 50% crude fiber. Chemically, the hulls are largely lignin, pentosans, and cellulosic constituents. 

Wood-thermoplastic composites usually consist of wood flour, thermoplastic, and various additives. The wood used in WPCs mostly refers to wood flour or wood fibers. Apart from woody materials, the agricultural plant residues, such as stems, stalks, leave, and seed hairs could also be used as a filler to manufacture WPCs. Generally, wood fiber is the most abundantly used plant fiber due to their extensive use in pulp and paper industries. Commercial composite products typically contain approximately 50 % wood. In some cases, some products only contain little wood, while others contain as much as 70 %. It has been proved that material compositions is highly related to the weathering of WPCs. Therefore, it is imperative to understand the chemical constituents and physical properties of wood. 

What are main differences between insoluble and soluble dietary fibers Give at least two examples of chemical constituents of each type of fiber. 

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