Influence of ultraviolet light on degradation of polyolefin films

Abstract

Three different commercial grade polyolefin films : polypropylene (PP), high density polyethylene (HDPE), and low density polyethylene (LDPE) have been studied. Two methods were carried out simultaneously for comparison between outdoor exposure and simulated condition in Xenotest Beta Lamp machine. The amount of carbonyl group formation (carbonyl index), was used as a key indicator to represent the chemical structure break-down. Mathematical models to express the relationship between exposure time and carbonyl index were proposed in both conditions. It was found that the carbonyl index increased exponentially as the exposure time increased. On the other hand, mechanical properties in terms of elongation at break decreased and hence increasing in initial modulus. Mechanical properties lost indicates the photooxidative degradation time of the films which became brittle. For outdoor exposure condition, it was also observe that the degradation times for PP, HDPE and LDPE were 9, 23 and 24 weeks respectively, while those for accelerated test were 114, 684 and 912 hours respectively.