Photooxidative effects on properties and structure of high‐density polyethylene

Abstract

SYNOPSISThe environmental degradation of high-density polyethylene (HDPE ) has been studied, in addition to that of HDPE blends, containing various concentrations of ethylene carbon monoxide copolymer. Extruded sheets of each material were exposed to natural Arizona sunlight for times up to 6 months. Exposed samples were then analyzed with respect to molecular weight, density, thermal behavior, mechanical properties, and infrared absorption. Additional samples were exposed to laboratory weathering conditions, evaluated in terms of property changes, melted, reformed, and then reevaluated without further weathering exposure. Results indicate that sunlight exposure causes decreased elongation to break, increased embrittlement, decreased molecular weight, and increased crystallinity. Environmental oxidative degradation is elucidated by the measurement of specific infrared bands, sensitive to the formation of carbonyl and vinyl end groups. As environmental degradation causes reductions of molecular weight, polymer chain mobility increases, leading to a higher degree of crystallinity. This increased crystallinity, along with the decreased molecular weight, accounts for the loss of ductility, indicated by a sharp decrease in ultimate elongation. The presence of carbon monoxide copolymer in the blended samples accelerates the process of environmental degradation, however, the degradation mechanisms appear to be similar to those observed for nonblended HDPE.

Microplastics Generation: Onset of Fragmentation of Polyethylene Films in Marine Environment Mesocosms

“…However, the FTIR results can only be used qualitatively. Jabarin and Lofgren (1994), using FTIR to measure crystallinity were able to deduce that absorbance bands tended to be wider with higher peaks with exposure time, in a similar manner to Tidjani (2000). Increasing ratios of oxidized to non-oxidized carbon, associated with surface oxidation of polymers exposed to natural sunlight, can be related to polymer chain scission reactions, leading to polymer deterioration (Stark and Matuana, 2004).…”

“…Similarly, from our results the ultimate elongation appears to decrease in a statistically significant manner only when all measurements were considered together or at the very end of the weathering period when fragmentation has already begun. Essentially, at this degree of weathering no measurement is possible due to sample breakage (Andrady et al, 1993;Jabarin and Lofgren, 1994;Tidjani, 2000).…”

“…Jabarin and Lofgren (1994) reported that the molecular weight of HDPE decreased from 147,000 in the original sample to 34,100 after 6 months of exposure to artificial UV light. Both increase and decrease of molecular weight have been observed in PE biodegradation experiments.…”

“…Several studies have shown changes in mechanical properties, although their results are often contradicting. Structural modifications and brittleness, although a usual observation, do not always correspond to mechanical strength and molecular weight changes (Andrady, 1990;Jabarin and Lofgren, 1994;Tidjani, 2000;Carrasco et al, 2001). O'Brine and Thompson (2010) observed statistically significant decreases of tensile strength for four different types of plastic carrier bags in marine conditions.…”

Effects of Carbon Black and Titanium Dioxide on Ultraviolet Weathering of Wood Flour-HDPE/Lumber Composites Using Multi-phase Co-extrusion Technology

“…This was because the scissions of the molecular chain of HDPE occurred immediately due to a photo-degradation reaction, which resulted in a decrease in density of the amorphous regions of HDPE. In addition, short-chain hydrocarbons migrate to the surface and lignin photo-bleaching leads to the change of lightness (Jabarin and Lofgren 1994;Muasher and Sain 2006). The lightness of the Ctrl, WPC-U, and WPC-T increased, while the lightness of WPC-C and WPC-T-C decreased.…”