The study on aging behaviors and critical stress of cross-linked high-density polyethylene during stress and photo-oxidative aging

In order to study the effects of cross-linking and critical stress during stress and photo-oxidative aging, the aging behaviors were studied by making cross-linked HDPE materials through a self-made stress and photo-oxidative aging apparatus in this paper. The cracking and aging behaviors of cross-linked polyethylene under stress was studied through microscopic observation, strain measurement, determination of gel content, breaking time statistics, fitting of stress-breaking time curves and so on. The critical stress was studied through fitting of stress-breaking time curves. It can be found that the surface morphologies were different under different stresses. The growth rate and strain at break decreased as the degree of cross-linking increasing. The breaking time of specimens were different under different stresses, and showed different trends as time increasing due to UV radiation and the network structure. The critical stresses of all kinds of samples ranged from 6.20 MPa to 7.02 MPa, showing an increasing trend as the degree of cross-linking increasing.