Nylon thermo-oxidation

Degradation behaviour of polyamides continues to be the subject of many papers. The degradation of nylon-6 has been examined by hydrolysis,by photolysis, and ultrasonically. Kinetic studies on chain scission by means of e.s.r. spectroscopy showed that the concentration of free radicals originating from broken chains in nylon-6 fibres could be described by a model system in which crystalline and amorphous layers were sandwiched in the fibre direction. Oxyluminescence has also been used in a study of the kinetics of the thermo-oxidative degradation of nylon-6,6. 

The thermo-oxidative cross-linking of nylon 6 and the resistance to oxidation of its graft copolymers with polyacrylonitrile have been studied. The thermal and thermal oxidative degradation of poly(/w-phenylene isophthalamide) and other aromatic polyamide compositions, together with comparative studies on the mechanisms of degradation of poly(p-benzamide) and poIy(p-phenylene terephalamide) have all been reported. 

Pure aromatic structure of given polymers brings them high thermo-oxidation stability and deformation resistance. Mechanical properties of polysulfone allow one to classify them as technical thermoplasts having high durability, rigidity and impact stability. The polymer Astrel 360 is in the same row with carbon steel, polycarbonate and nylon on its durability. 

Figure 3.3 Volatile degradation products in two oxidized polymers monitored by head-space GC. (a) Photo-oxidized LDPE with iron dimethyl dithiocarbamate and carbon black 1 = acetaldehyde 2 = methanol 3 = acetone 4 = 1-butanol 5 = butanol 6 = 3-pentanol. (b) Thermo-oxidized nylon 66 1 = acetaldehyde 2 = Cu-acetate 3 = cyclopentanone 4 = aniline.

The product studied is obtained as a by-product of nylon 6 manufacture and consists of a mixture of epsilon-caprolactam, low-molecular cyclic and linear polyamides and products of their thermo-oxidative degradation and interaction with sodium hydroxide or other neutralising agents. Data are given on the effect of this secondary vulcanising accelerator on the vulcanisation properties and physico-mechanical properties of various mbbers. 3 refs. Articles from this journal can be requested for translation by subscribers to the Rapra produced International Polymer Science and Technology. 

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