Effect of thermal aging above the glass transition temperature on the mechanical properties of rigid PVC tube

Abstract

Thermal aging of standard samples of rigid PVC (u-PVC) taken from plastic tubes near and above the glass transition temperature (Tg) was used to investigate the effect of elevated temperatures on the mechanical properties of rigid (u-PVC) tubes used in industrial areas. Three aging protocols were used, each lasting 90 days at 80 °C, 100 °C, and 120 °C. Crosslinking and chain scission reactions changed the tensile properties, either increasing them or decreasing them. For all three aging protocols, it was discovered that Young's modulus increased with aging time. Furthermore, the rate of increase of the modulus was observed to increase with aging temperature. The Yield stress showed the same pattern. Their increase in both cases is due to material stiffening caused by a crosslinking process. This last one was revealed by DSC, where Tg increased as a result of the chemical process. The decrease in elongation at break, which occurred progressively in all aging protocols and more precisely at temperatures above Tg, on the other hand, demonstrated the relationship between chain scissions and temperature. The material becomes more brittle as the temperature rises. Brittleness is caused by a high activity of chain scissions on the surface sample, which allows micro-cracks to form. When subjected to tensile forces, cracks propagate from the surface toward the sample's thickness.