Early detection of degradation in a semi-crystalline polyolefin by a successive self-nucleation and annealing technique

Samples taken from a black pipeline liner that became fragile while in service were analyzed by a Successive Self-Nucleation and Annealing (SSA) technique. Two types of polyethylene, Low-Density Polyethylene (LDPE) and Linear Low-Density Polyethylene (LLDPE) were aged in air, at several temperatures, and changes in the molecular structure were followed simultaneously by infrared and calorimetric techniques. Samples with and without antioxidants were prepared, aged, and evaluated for the same oxidative treatments. The LDPE type was chosen to be identical to the black LDPE originally used for making the pipeline liner. Oxidative reactions of LDPE and LLDPE were quantified via carbonyl group concentrations measured by FTIR. Changes in the crystallization behavior of the original and aged polymers, and of the black pipeline liner, were monitored via the SSA technique. Changes of the fraction of lamellae of specific thickness in the crystallized polymer could be correlated linearly with the formation of carbonyls, and thus this calorimetric method is proposed to be suitable as a tool for early quantitative monitoring of LDPE degradation.