Carbon nanotubes stabilize poly(vinyl chloride) against thermal degradation

Abstract

In this study, multiwalled carbon nanotubes (CNT), ball-milled CNT (bmCNT), and acid-treated CNT (CNT-COOH) were assessed as thermal stabilizers in poly(vinyl chloride) (PVC). Films of pure PVC, CNT/PVC, bmCNT/PVC, and CNT-COOH/PVC cast from tetrahydrofuran were subjected to thermal aging in N2 in a test tube submerged in an oil bath maintained at 180 °C for a certain time. FTIR and UV-Vis spectra and discoloration of aged PVC composites were investigated on the formation of conjugated polyene structure in PVC. The results found that all three types of CNT of small amounts (0.1 or 0.3 phr) could stabilize PVC against thermal degradation by retarding the rate of formation of a conjugated polyene structure, with the stabilizing efficacy in the order of bmCNT > CNT > CNT-COOH. Moreover, Congo red and dehydrochlorination (pH measurement) tests were investigated on the degradation of PVC to HCl during the thermal aging as a function of time, CNT type and content. Thermal degradations of PVC to HCl were promoted by all three types of CNT in the initial 30 min of aging but were clearly stabilized against degradation over prolonged aging (for instance, 120 min) by bmCNT followed by CNT-COOH, both exhibiting the optimal stabilizing efficacy at 1 phr. The bmCNT was the most effective thermal stabilizer among the three types of nanotubes studied in PVC to resist both its discoloration and degradation of HCl. This newly-developed PVC composite with CNT as an additive provides an efficient route towards the development of highly thermal-stabilized PVC.