Description of degradation influence on the plasticized PVB during its re-working by kneading

Abstract

PVB sheet (type Butacite 3GO) with polymer chains containing butyraldehyde, hydroxyl- and small amount of acetate groups, was tested. These sheets were highly plasticized, with the content of plasticizer 28%. Studied material was tested at different kneading conditions; especially the influence of temperature, oxygen, mechanical energy and created heat of dissipation was studied. PVB sheet was kneaded at their usual humidity oca 0.5%. Because PVB in known as the material with high hydroscopity, next tests were done on PVB sheets macerated in water. By this operation the humidity of sheets increases to the content 8.0%. High humidity influenced all observed properties. Simultaneously, samples of PVB sheets re-worked by calendaring and pressing. At the calendaring the sheets were thermally stressed. The calendaring represents shear stress at low temperature. The degradation was evaluated as the change of optical properties, like the light transmittance through the re-worked material, created haze and yellowing. Next evaluated data were the change of mechanical properties - melt flow index and stress-strain behaviour. Summarized data were used for the choice of the optimal conditons for re-working of PVB sheets. The optimal conditions should bring the lowest energetic costs, minimal shear and thermo-oxidative degradation.