Spinning aliphatic polyamides

While W. Carothers with DuPont developed the idea of spinning aliphatic polyamides, it was not until J.T. Dickson with Calico Printers polymerized polyethylene terephthalate (PET) from terephthalic acid in the 1950s that this application really started to grow commercially. Both DuPont and ICI expanded this technology. 

Flexible chain molecules can be spun by the melt, dry- or wet-spinning processes from the melt or from sufficiently concentrated solutions. Examples are poly(ethylene), it-poly(propylene), poly(acrylonitrile), poly(oxymethyl-ene), and aliphatic polyamides. All of these chain molecules have only low potential energy barriers for conformation transitions in addition, they crystallize readily to lamellar structures with chain folding. Crystallization, however, is not a precondition for filament formation since, for example. 

Section 14.6) and hence the attempts to overcome the network constraints in nylon 6,6 fibres cannot be rated as successful the same applies to nylon 6 and PET. In contrast, the superdrawing of melt-spun polyethylene and polypropylene fibres is well established. In the case of polyethylene it was possible, by optimization of polymer molecular weight and spinning as well as drawing conditions, to obtain a fibre with a tenacity of 1.75Ntex and extension at break of 3.9% i.e sg over 1.8 N tex It appears that, due to weaker intermolecular interactions in polyalkenes compared with aliphatic polyamides and PET, it is much easier to overcome the network constraints. 

N.N-Dimethylformamide [68-12-2] (DMF) [14.276] is miscible with water and organic solvents except aliphatic hydrocarbons. It is a good high-boiling solvent for cellulose esters, cellulose ethers, poly(vinyl chloride), vinyl chloride copolymers, poly(vinyl acetate), polyacrylonitrile, polystyrene, chlorinated rubber, polyacrylates, ketone resins, and phenolic resins. Alkyd resins and resin esters are partially soluble. Dimethylformamide does not dissolve polyethylene, polypropylene, urea-formaldehyde resins, rubber, and polyamides. It is used as a solvent in printing inks, for polyacrylonitrile spinning solutions [14.277], and as a solvent in the synthesis of acetylene. 

Vinyl polymers and condensation polymers were studied for the production of synthetic fiber. In 1932, Carothers and Hill of Du Pont studied linear aliphatic polyester and showed that fibers of sufficiently good mechanical properties are obtained by melt-spinning and colddrawing [8]. Polyester fiber was considered unsuitable as a commercial fiber because it has a low melting point and hydrolyzes easily with water. Carothers therefore turned his investigation from polyester to polyamide, and, in 1938, Du Pont announced the success of a new fiber called nylon. In Japan, studies to produce textile fibers from PVA began in 1938 and were intensively promoted. 

Aramids The term aramid is used to describe aromatic and partially aromatic polyamides, which constitute a class of materials that are analogous to the aliphatic nylons . The fully aromatic polymers in this category are linear, but not thermoplastic, as they decompose before they flow sufficiently to allow shaping. However, wet spinning of fibres is possible and such materials have many technical applications besides being used as reinforcement. 

In recent years, aliphatic/aromatic and aromatic polyamides have been developed. For example, the polymer obtained from HMD and terephthalic acid (Nylon 6,T) has a heat distortion temperature of 200°C. However because the is 370 °C, melt processing and spinning is not possible (decomposition results) and solution spinning from strong acids (H2SO4) must be used. Also interfacial polymerization (from the terephthaloyl acid chloride) is necessary to achieve high MWs. 

Hancock, T., SpmieU, J. and White J. (1997), Wet spinning of aliphatic and aromatic polyamides ,/oMmflZ of Applied Polymer Science, 21,1227-1247. 

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