Investigation of the thermal decomposition properties of polyoxymethylene

By testing the melt index (MI), tensile strength and breaking extension ratio, the thermal ageing rate of polyoxymethylene (POM) was analyzed and compared. The surface morphology and type of function group of POM surface were observed and analyzed by SEM and XPS. The results show that the MI value increases gradually with the ageing time at 120 °C, indicating that the thermal oxidation decomposition occurrs slowly. The effect of 20-day thermal ageing on the tensile strength and breaking extension ratio of POM is not obvious, showing that the ageing of POM is quite a long process. After 105-day, thermal ageing cracking and powdering occurr on the POM surface. XPS determination shows the C1s spectra of samples before and after ageing include two peaks of C-C and C-O, while after ageing the content of C-C decreases and the content of C-O increases, indicating that the thermal ageing of POM is mainly the breaking and decomposing of C-C bond. The O1s/C1s ratio of original samples is 56.98% and after 105-day thermal ageing the ratio is 72.92%.