Influence of early thermal-oxidative ageing on the structure and properties of polyoxymethylene copolymer

Thermal-oxidative ageing of polyoxymethylene (POM) copolymer in oven at
100 °C for 1, 2, 3, 5, 7, 10, 14 and 21 days and the influence of early
thermal-oxidative on POM structure and properties were studied by
means of wide-angle X-ray diffraction (WAXD), Fourier transform infrared
spectroscopy (FTIR), differential scanning calorimetry (DSC) and
tensile test. Based on the results, we found that the early
thermal-oxidative ageing of POM copolymer can be divided into
three regions. The first region is the initial three days. In
this region, some molecular chains
rearranged, resulting in internal stress
relaxation, increased of crystallinity degree and grain size due
to the perfection of crystal structure; both extended chain
crystal (ECC) and folded chain crystal (FCC) increased
and ECC grew faster than FCC. The second region is from 3 days to 10 days
and in this region chain scission took place in amorphous region and led
to chemi-crystallization. The last region is after 10 days. In this
region, the structure and performance of POM copolymer reached a stable
situation at this stage. In this work, the difference between skin and
core were also analyzed.