Correlation of a Temperate UV-Weathering Cycle to Outdoor Exposure for the Determination of the Environmental Instability of Polyethylene Films Using HT-GPC Analysis

Abstract

Accelerated UV‑weathering cycles are predominately used for evaluating the durability of plastic materials, particularly polyethylene (PE) films. The point of failure for this testing is usually the loss of a physical property, such as the loss of tensile strength over time. For plastics designed to be instable under environmental conditions, the accelerated weathering cycles are yet to be defined and their correlation to outdoor exposure has yet to be made. This study demonstrates the utility of a newly defined temperate accelerated UV‑weathering cycle, recently codified in the British Standard PAS 9017:2020. In addition, the effectiveness of the laboratory weathering cycle has been correlated to real‑world outdoor exposure through simultaneous testing of the same samples at a specialist outdoor exposure site in Florida. The utility of the testing methodology and the performance of the polyethylene samples was demonstrated through the use of High Temperature Gel Permeation Chromatography (HT‑GPC) analysis. The data led to a detailed insight into the physico‑chemical changes occurring in the PE films upon exposure to environmental stimuli. By comparison, and surprisingly, the techniques employed appear to provide an insight into the processes in which secondary micro‑particles of PE are formed from macro‑polyethylene samples. The temperate accelerated UV‑weathering cycle over 14 days demonstrated an approximate correlation to 90 days of outdoor exposure in Florida for the PE film studied.

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

“…All the samples completely dissolved in the TCB, suggesting that no gel or insoluble formations were produced as a result of the QUV or outdoor weathering. As previously reported [ 22 ], the key changes in molecular weight are more clearly observed when the loss and percentage (%) loss of weight-average molecular weight (Mw) and higher weight-average molecular weight (Mz) are compared and plotted ( Table 2 and Figure 4 ). Furthermore, the use of the runtime fraction [ 16 ] allowed for the comparison of temperate laboratory accelerated and outdoor exposure studies to be compared and contrasted ( Figure 4 and Figure 5 ).…”

“…Following on from our previous work [ 22 ], we noted the value in using transmission or reflectance IR spectroscopic analysis for determining the chemical transformations across the surface and through the bulk of the sample. We also noted, however, that single-point analysis limited the ability to observe whether the changes were homogeneous.…”

“…Following on from our previous work [22], we noted the value in using transmission or reflectance IR spectroscopic analysis for determining the chemical transformations…”

“…Likewise, any technologies designed to increase the rate of chemical transformations occurring within the polyethylene chains need to be evaluated by simulated laboratory techniques of relevancy to real-world exposure conditions and timeframes. To that end, we recently published, a novel temperate UV-accelerated weathering cycle for evaluating polyethylene materials, via a laboratory technique that has been correlated to outdoor exposure conditions [ 22 ]. This relative correlation is important in assessing the utility of the Service Life Prediction of materials, to which a defined point of failure is equally critical to define in the analysis [ 11 ].…”

“…In contrast, the same polyethylene sample containing Polymateria’s biotransformation technology was tested alongside this. The chemical changes caused the polyethylene chain structure to significantly decrease to polyethylene waxes containing a high concentration of carbonyl groups, a result in stark difference to the standard polyethylene sample [ 22 ].…”