Poly(vinyl alcohol) stabilisation in thermoplastic processing

Besides casting from water solutions, PVA processing from the melt seems to be more suitable, particularly for water-soluble films. Processing at high temperatures is very sensitive to PVA degradation and problems with stability of the melt result in a search for suitable additives. Silica is frequently used as an antiblock agent and only a little is known about its effect on PVA melt stability. The study was focused on PVA thermal and processing stability. and an evaluation of low molecular products released as by-products of PVA degradation. It was found that the thermal stability of PVA is strongly influenced by the pH of the environment before drying in the production process. Processing stability of PVA blends with and without glycerol used as plasticiser were evaluated from the torque increase during processing. Regarding the effect of the antiblock agents, silica had a strong negative effect on processing stability of PVA. In contrast, talc did not accelerate degradation up to a relatively high concentration level. To explain these effects, the changes in chemical structure of PVA blown films during thermal loading were studied using IR spectroscopy. It was confirmed that silica accelerates thermal degradation of PVA films due to its acidic character. (C) 2002 Elsevier Science Ltd. All rights reserved.