Relationship between structure, properties and UV/Heat protection behavior of two different types of polyethylene manufactured in Qatar

Abstract

Accelerated (artificial) weathering and thermal ageing tests were performed to investigate the effectiveness of different UV/HALS formulations in reducing the UV/heat degradation effect for two different low-density polyethylene grades with different structures because of production through two different production methods (autoclave and tubular reactors). Combinations of two commercial-grade HALS (Chimassorb 944 and Sabostab 119) and two UV absorbers (Chimasorb 81 and Tinuvin 1577) were introduced to both the LDPE grades at different loadings. The morphologies, as well as thermal and mechanical properties, of the investigated samples were determined through tensile and impact testing, gel permeation chromatography (GPC), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). All the results from the different characterization techniques showed a significant degradation for the unstabilized neat samples of both LDPEs, while little or no degradation was observed for the stabilized ones, confirming the effectiveness of the selected UV/HALS systems in improving the weathering resistance of the two LDPE grades and enhancing their useful lifetime. The GPC results showed that the LDPE-A contained significantly more long-chain branching (LCB) than the LDPE-T, implying that the LDPE-A was much more compact than the LDPE-T. Young’s modulus values for LDPE-T were much higher than those of LDPE-A, indicating a higher crystallinity of the LDPE-T samples. For the heat exposed samples, more brittle behaviour was observed for the LDPE-T samples. There was very little difference in the maximum tensile stress values of LDPE-A and LDPE-T, except for LDPE-T/UV3 where the σ value increased by about 9% after 12 months. LDPE-T was found to be thermally more stable than LDPE-A, even after long UV exposure times. For stabilized formulations, LDPE-A/UV8 seems to be the best formulation in terms of thermal stability whereas LDPE-T/UV8 was the least promising formulation. Generally, the UV/heat stabilized LDPE-A samples were thermally more stable than LDPE-T The carbonyl indices were similar for the two polymers, which means that the differences in polymer structure had little influence on the formation of carbonyl groups during the oxidative degradation process