Temperate UV-Accelerated Weathering Cycle Combined with HT-GPC Analysis and Drop Point Testing for Determining the Environmental Instability of Polyethylene Films

Abstract

Polyethylene films are one of the most frequently used packaging materials in our society, due to their combination of strength and flexibility. An unintended consequence of this high use has been the ever-increasing accumulation of polyethylene films in the natural environment. Previous attempts to understand their deterioration have either focused on their durability using polymer analysis; or they have focused on changes occurring during outdoor exposure. Herein, this study combines those strategies into one, by studying the chemical and physical changes in the polyethylene structure in a laboratory using molecular weight and IR spectroscopic mapping analysis, combined with temperate UV-accelerated weathering cycles. This approach has been correlated to real-world outdoor exposure timeframes by parallel testing of the sample polyethylene films in Florida and France. The formation of polyethylene microparticles or polyethylene waxes is elucidated through comparison of drop point testing and molecular weight analysis.

The performance and environmental impact of pro-oxidant additive containing plastics in the open unmanaged environment—a review of the evidence

“…All films containing the additive met this requirement after weathering, whereas the films without the additive showed a drop point above 140°C. This is consistent with the presence of the additive accelerating film degradation and conversion into a wax [ 39 ]. This is evidence that the PAS 9017 : 2020 accelerated test standard does predict aspects of the degradation of PAC plastics in the South of France and Florida.…”

“…In the second study [ 39 ], the control sample tested in the South of France showed a 67% M w loss, which exceeded the 27% M w reduction observed for the same control sample in laboratory weathering test using PAS 9017; thus the correlation between artificial and outdoor weathering is less clear in this case. 1.b) The control sample for the Florida test was not included in the second study [ 39 ], so a comparison/correlation between samples cannot be made. 1.c) For the purpose of PAS 9017 more than one replicate is required.…”

“…Outdoor weathering was performed at the Q Lab Corporation testing site in Miami, Florida, according to ASTM D1435, for 90 days. In the second study [ 39 ], a film consisting of 52% LLDPE, 40% mLLDPE, 5% VLLDPE and 3% Green MB by weight was used as a control. For films containing 2% of PAC MB additive the LLDPE component was reduced to 50%.…”

“…This value should be greater than 1.0 after artificial or outdoor weathering, as specified in PAS 9017, for a film sample to be qualified for soil-biodegradability. In the second study [ 39 ], the CI measured for the 17 µm films containing the PAC additive after 120 days of outdoor exposure in the South of France was 0.62, significantly below the 1.0 threshold required by PAS 9017. However, the same film met the required molecular weight criteria of PAS 9017 after 120 days.…”

“… M n (Da) M w (Da) M z (Da) PDI a article 1 [ 38 ] 87.5 µm films (75% LDPE, 25% LLDPE) control without PAC additive 32 280 219 680 1 263 734 6.8 sample with PAC additive 20 963 239 603 845 366 11.4 article 2 [ 39 ] 17 µm films (52% LLDPE, 40% mL LDPE, 5% VLLDPE, 3% green MB) control without PAC additive 37 616 110 118 251 393 2.9 sample with PAC additive 21 554 151 588 495 400 7.0 a PDI = polydispersity index = M w / M n. …”