Noncellulosic polymers

A plot of 6gp vs 3 for several cellulosic and noncellulosic polymers is shown in Figure 10(b) and, for the same polymers, a plot of 6gp vs <5h/ d sp shown in Figure 10(a). The results show that unique correlations exist between the parameters... 

It is important to understand the different types of fibers. Classes are best differentiated based on both the origin of the fiber and its structure. The structure and chemistiy of many of these polymers was discussed earlier in Chapter 14. Table 17.1 contains a list of the three important types of fibers— natural, cellulosic, and noncellulosic— as well as a list of specific polymers as examples of each type. The ones marked with an asterisk are the most important. 

These polymers are distinguished from cellulose by the presence of both/ -(l— 3)- and / -(l— 4)-linked D-glucosyl residues, lower molecular weights (some noncellulosic glucans are water-soluble), and susceptibility to hydrolysis by / -D-glucanases that cannot hydrolyze cellulose. Unlike cellulose, whose microfibrillar structure and structural role in the cell wall has been clearly established, the function of these polymers as structural components of the wall is still a subject of controversy there is some evidence that they are energy-reserve materials.110-201 202... 

During the 1960s and 1970s the Office of Saline Water sponsored development of noncellulosic reverse osmosis membranes. Many polymers were evaluated as Loeb-Sourirajan membranes but few matched the properties of cellulose acetate. Following the development of interfacial composite membranes by Cadotte, this line of research was abandoned by most commercial membrane producers. 

Nonetheless a few commercially successful noncellulosic membrane materials were developed. Polyamide membranes in particular were developed by several groups. Aliphatic polyamides have low rejections and modest fluxes, but aromatic polyamide membranes were successfully developed by Toray [25], Chemstrad (Monsanto) [26] and Permasep (Du Pont) [27], all in hollow fiber form. These membranes have good seawater salt rejections of up to 99.5 %, but the fluxes are low, in the 1 to 3 gal/ft2 day range. The Permasep membrane, in hollow fine fiber form to overcome the low water permeability problems, was produced under the names B-10 and B-15 for seawater desalination plants until the year 2000. The structure of the Permasep B-15 polymer is shown in Figure 5.7. Polyamide membranes, like interfacial composite membranes, are susceptible to degradation by chlorine because of their amide bonds. 

Membrane Limitations Chemical attack, fouling, and compaction are prominent problems with RO and NF membranes. Compaction is the most straightforward. It is the result of creep, slow cold flow of the polymer resulting in a loss of water permeability. It is measured by the slope of log flux versus log time in seconds. It is independent of the flux units used and is reported as a slope, sometimes with the minus sign omitted. A slope of-0.001, typical for noncellulosic membranes, means that for every threefold increase in log(time), 10 seconds, a membrane looses 10 percent of its flux. Since membranes are rated assuming that the dramatic early decline in permeability has already occurred, the further decline after the first few weeks is very slow. Compaction is specific to pressure, temperature, and envi-... 

Among the fibers, all except acrylics and rayon have shown significant growth in production in the 1994-2003 period (Table 21.2). Rayon production in the U.S.A. has declined about 70% since 1984. The American proportion of the world output of modified cellulosic and noncellulosic fibers production is about 3 and 13%, respectively. The preparative details of several of the more important condensation polymers are discussed in the following sections. 

For the purpose of discussion of the chemistry and technology of man-made, fiber-forming polymers, the term "synthetic fiber" will be used to denote all man-made fibers manufactured from noncellulosic raw materials. The term "cellulosics" will apply to those man-made fibers that are manufactured from cellulosic raw materials. The term "man-made fibers" will apply to all fibers except the naturally occurring cellulosic and protein fibers. 

Total production of synthetic polymer fibers is high. In 1978, 3.53 billion kg and 11 billion kg of noncellulosic organic fibers were produced in... 

Lignin is synthesised in plants from monomeric molecnles, whose functionality varies from two to four. Thus, both branched chain and the crosslinked structure may be formed. In plant tissue, the polymer chains of lignin are snrronnded by macromolecules of noncellulosic polysaccharides, with which they form an amorphous lignocarbohydrate matrix. The experimental methods that allow the stndy of the complex topology of macromolecules in a multicomponent solid composite are very limited. Therefore, most of the data are interpreted using theoretical methods developed from polymer chemistry. 

While most of noncellulosic membranes rely on the selectivity of glassy polymers such as polysulfone, the Ube Gas Separation System is based on poly-imide produced by condensation polymerization of biphenyltetracarboxylic di-anhydride and aromatic diamines. The chemical formula of the polymeric ma-... 

Synthetic polymers that are commercially manufactured in the quantity of billions of pounds may be classified in three categories (1) plastics, which include thermosetting resins (e.g., urea resins, polyesters, epoxides) and thermoplastic resins (e.g., low-density as well as high-density polyethylene, polystyrene, polypropylene) (2) synthetic fibers, which include cellulosics (such as rayon and acetate) and noncellulose (such as polyester and nylon) and (3) synthetic rubber (e.g., styrene-butadiene copolymer, polybutadiene, ethylene-propylene copolymer). 

Genetic modification of the lignin biosynthesis by downregulation of the cinnamoyl-coenzyme A reductase in poplar P. tremula x Populus alba) decreased the lignin content and increased breakdown or remodeling of noncellulosic cell wall polymers as supported by FT-IR analysis [105]. 

Noncellulosic Synthetic Membranes In the dialysis field, the term synthetic membrane is used to denote all polymeric membranes that are not cellulose based. Table 19.2 lists the various synthetic membranes that are commercially available. Polymers such as polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), and ethylene vinyl alcohol (EVAL) copolymer were adapted from the textile industry, while polymers such as polysulfone, polycarbonate, and polyurethane were developed as engineering plastics. Synthetic membranes with high water permeability were developed in the 1960s... 

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