Degradation Processes in Production of Vidlon Polycaproamide Cord Thread

Abstract

In spinning fibres on type PP-1000 IM machines, complex changes take place in polycaproamide, caused by the occurrence of thermal oxidation and thermal degradation processes. The content of carbonyl compounds increases with an increase in the temperature and draw ratio of the fibres in the polymer. Thermal degradation processes decrease with an increase in the drawing temperature.The sensitivity of polycaproamide (PCA) to thermooxidative degradation is well known [1]. As a result of oxidation, the chemical composition and physicochemical properties of PCA change [2]. During oxidation that takes place according to a radical chain mechanism [3], stable chemical crosslinks are formed [4], which worsens the quality indexes of the polymer and correspondingly the fibres made from it.In preparation of the polymer for spinning at the polyamide fibre plant in Vidin, PCA crumb is oxidized immediately after the molten polymer flows out of the pouring unit of the polymerization apparatus and in drying at 160°C in nitrogen medium in fluidized bed driers (FBD plants own design [5,6]). In addition to thermooxidative processes, thermal degradation also takes place in the polymer during drying, primarily because of the severe temperature conditions and design flaws in the FBD, since these driers have dead zones. Further thermal oxidation and thermal degradation of PCA are observed in melting of the polymer crumb during spinning.We know [7,8] that terminal oxygen-containing groups accumulate in PCA in a mechanical stress field in orientation drawing as a result of cleavage of macromolecules.The degradation processes in PCA that take place during spinning, drawing, and twisting of Vidlon cord thread are examined in the present article. We note that degradation processes in production of PCA fibres have been studied very little.Thermooxidative degradation of PCA was evaluated based on the carbonyl compound (CC) content and thermal degradation was judged by the amount of 1,11-diamino-6-ketoundecane (DAKU) in the hydrolysis product of PCA in hydrochloric acid, determined by polarographic methods [9,10]. Data on the change in the CC and DAKU content in the polymer in process changeovers were collected for 7 days. The results of these studies are presented below:Process changeover CC content, meq/g