Polymeric materials polyamides

Both woven and nonwoven geotextiles are made from four polymeric materials (polyamide, polyester, polyethylene, and polypropylene) and natural materials. Woven geotextiles may be fabricated with monofilament yams, muldfilament yams, or a combination of each. Nonwoven geotextiles are bonded by one of the several methods thermal, mechanical, or chemical. With the many combinations of materials and processes, it is not difficult to see that the physical properties of geotextiles will vary greatiy among products (Yeo, 2008). 

Membranes used for the pressure driven separation processes, microfiltration (MF), ultrafiltration (UF) and reverse osmosis (RO), as well as those used for dialysis, are most commonly made of polymeric materials. Initially most such membranes were cellulosic in nature. These ate now being replaced by polyamide, polysulphone, polycarbonate and several other advanced polymers. These synthetic polymers have improved chemical stability and better resistance to microbial degradation. Membranes have most commonly been produced by a form of phase inversion known as immersion precipitation.11 This process has four main steps ... 

Various polymeric materials were tested statically with both gaseous and liquefied mixtures of fluorine and oxygen containing from 50 to 100% of the former. The materials which burned or reacted violently were phenol-formaldehyde resins (Bakelite) polyacrylonitrile-butadiene (Buna N) polyamides (Nylon) polychloroprene (Neoprene) polyethylene polytriflu-oropropylmethylsiloxane (LS63) polyvinyl chloride-vinyl acetate (Tygan) polyvinylidene fluoride-hexafluoropropylene (Viton) polyurethane foam. Under dynamic conditions of flow and pressure, the more resistant materials which binned were chlorinated polyethylenes, polymethyl methacrylate (Perspex) polytetraflu-oroethylene (Teflon). 

Due to the importance of polymer chemistry for the chemical industry, considerable effort has been devoted to the smdy of the effects of light on polymeric materials. The photochemistry of polymers is complex. However, it is well established that PFR occurs in some aromatic polyesters [211-222] and polyamides [223,224]. This process can take place either in the main chain of the polyester or in the pendant groups. 

Wallace Carothers and coworkers at DuPont synthesized aliphatic polyesters in the 1930s [Furukawa, 1998 Hounshell and Smith, 1988]. These had melting points below 100°C, which made them unsuitable for firber use. Carothers then turned successfully to polyamides, based on the theoretical consideration that amides melt higher than esters. Polyamides were the first synthetic fibers to be produced commercially. The polyester and polyamide research at DuPont had a major impact on all of polymer science. Carothers laid the foundation for much of our understanding of how to synthesize polymeric materials. Out of that work came other discoveries in the late 1930s, including neoprene, an elastomer produced from chloro-prene, and Teflon, produced from tetrafluoroethylene. The initial commercial application for nylon 6/6 was women s hosiery, but this was short-lived with the intrusion of World War II. The entire nylon 6/6 production was allocated to the war effort in applications for parachutes, tire cord, sewing thread, and rope. The civilian applications for nylon products burst forth and expanded rapidly after the war. 

Amino-1,2,4-thiadiazoles79 and their 3-alkoxy-, 3-alkylmercapto-, and 3-dialkylamino derivatives84 have been claimed to be useful intermediates in the manufacture of dyes,84 pharmaceuticals,84 and materials valuable in pest control.79 Mono-azo dyes derived from diazotized 5-amino-l,2,4-thiadiazoles and coupling components of the benzene series are especially suitable for dyeing polymeric materials such as acetate rayon, polyamides, polyurethanes, polyesters, and... 

As already mentioned, there has been renewed interest for using carbohydrates as a source of chemicals since the 1980s with the development of the chemistry of furanic compounds, particularly for the preparation of nonpetroleum derived polymeric materials, such as polyesters, polyamides and polyurethanes.[17,19]... 

Membrane polymeric materials for separation applications are made of polyamide, polypropylene, polyvinylidene fluoride, polysulfone, polyethersulfone, cellulose acetate, cellulose diacetate, polystyrene resins cross-linked with divinylbenzene, and others (see Section 2.9) [59-61], The use of polyamide membrane filters is suggested for particle-removing filtration of water, aqueous solutions and solvents, as well as for the sterile filtration of liquids. The polysulfone and polyethersulfone membranes are widely applied in the biotechnological and pharmaceutical industries for the purification of enzymes and peptides. Cellulose acetate membrane filters are hydrophilic, and consequently, are suitable as a filtering membrane for aqueous and alcoholic media. 

Pyrazinetetracarboxylic acid forms a dianhydride on treatment with acetic anhydride,234 which is useful in the preparation of polyamides and polyimides.235-236 For example, polymeric material is obtained by reaction of the dianhydride with 4,4 -diaminodiphenyl ether. 

Microporous membranes are used to effect the separation by MF and UF processes. These microporous membranes differ from polyamide composite RO membranes in that they are not composites of two different polymeric materials they are usually constructed using a single membrane polymeric material. In simple terms, both UF and MF technologies rely on size as the primary factor determining which... 

The crosslinking of polymeric materials by Mannich reaction includes the polycondensation of acetone with oligomeric polyalkyleneamines and aldehydes (see also 480, Chap. IV) and, more relevantly, polyamides (430, Chap. Ill) crosslinked with benzidine and formaldehyde. Macromolecular materials such as cellophane and polyglucosamine (Fig. 183), deriving from natural substances, are also subjected to the reaction. 

Plastics. Plastics are the polymeric materials with properties intermediate between elastomers and fibers. In spite of the possible differences in chemical structure, the demarcation between fibers and plastics may sometimes be blurred. Polymers such as polypropylene and polyamides can be used as fibers and plastics by a proper choice of processing conditions. Plastics can be extruded as sheets or pipes, painted on surfaces, or molded to form countless objects. A typical commercial plastic resin may contain two or more polymers in addition to various additives and fillers. Additives and fillers are used to improve some property such as the processability, thermal or environmental stability, and mechanical properties of the final product. 

The first widespread use of polymeric membranes for separation applications dates back to the 1960-70S when cellulose acetate was cast for desalination of sea and brackish waters. Since then many new polymeric membranes came to the market for applications extended to ultrafiltration, miciofiltration, dialysis, electrodialysis and gas separations. So far ultrafiltration has been used in more diverse applications than any other membrane processes. The choice of membrane materials is dictated by the application environments, the separation mechanisms by which they operate and economic considerations. Table 1.4 lists some of the common organic polymeric materials for various membrane processes. They include, in addition to cellulose acetate, polyamides. 

Pearce, E.M., Shalaby, S.W. and Baker, P.M., Chapter 6, "Retardation of Combustion of Polyamides", in Flame Retardant Polymeric Materials, (M. Lewin, S.M. Atlas and E.M. Pearce, eds). Plenum Press, New York (1974). 

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