Effects of types of heat stabilizers on recycling ability of poly(vinyl chloride) for pipe application

Abstract

Poly(vinyl chloride) or PVC is a well-known commodity plastic because of its versatility, low cost and long life cycle. In Thailand, water pipe is a major product of PVC. However, PVC is known to degrade at elevated temperature. Without the discovery of heat stabilizers, PVC was not an industrially useful polymer. In practice, lead stabilizers are used to improve the decomposition temperature in order to obtain high-quality PVC products. But they are limited as stabilizers because of their toxicity. Initiative of limiting lead consumption has led to the development of alternative stabilizers. Calcium/zinc stabilizers are typical nontoxic heat stabilizers, however, Ca/Zn stabilizers have some disadvantages in their long-term stability. Whereas, organic based stabilizers (OBS) are new technology providing environmentally friendly stabilization for rigid PVC pipe applications. This research aims to suggest suitable organic based stabilizers to substitute conventional lead stabilizer as well as Ca/Zn stabilizer for PVC pipe. In this research, uracil derivative and eugenol compare with commercial heat stabilizer i.e. lead stabilizer, Ca/Zn stabilizer and commercial organic based stabilizer in their efficiency as heat stabilizer or important PVC properties. The PVC samples was processed by two-roll mills and compression molder at 180ºC. From the results, uracil derivative and eugenol were found to be more readily fused with PVC than commercial heat stabilizers. From mechanical testing, PVC stabilized with uracil derivative and eugenol showed higher tensile and flexural properties than other samples. In addition, PVC stabilized with uracil derivative provided relatively low thermal discoloration by maintaining original white color of PVC at temperature of 180°C up to 50 minutes. From recycle ability, PVC stabilized with commercial stabilizers could processed up to at least 5 cycles. However, PVC stabilized with uracil derivative was found to be able to withstand the processing cycle up to 4 cycles. Whereas PVC stabilized with eugenol was able to undergo only one cycle. Thus, it is clearly seen that uracil derivative showed high potential use as a safe and effective organic based heat stabilizer for PVC to substitute lead or Ca/Zn stabilizer. Moreover, Synergistic behavior in thermal stability of PVC was also observed when mixture of eugenol and uracil derivative at 1:1 mass ratio.