Photo-induced scission and crosslinking in LDPE, LLDPE, and HDPE

• Published in: Polymer engineering and science Vol. 45; no. 4; pp. 579 - 587
• Main Authors: Craig, I.H., White, J.R., Shyichuk, A.V., Syrotynska, I.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.04.2005; Wiley Subscription Services; Society of Plastics Engineers, Inc; Blackwell Publishing Ltd
• Subjects: Ageing; Applied sciences; Chemical engineering; Crosslinking polymerization; Employee motivation; Exact sciences and technology; Mechanical properties; Monte Carlo method; Oxidation; Physical properties; Polyethylene; Polymer industry, paints, wood; Polypropylene; Properties and testing; Technology of polymers; Ultraviolet radiation; Photochemical crosslinking; Molecular weight distribution; High density ethylene polymer; Competitive reaction; Experimental study; Gel permeation chromatography; Low density ethylene polymer; Crosslinked polymer; Reaction mechanism; Artificial ageing; Olefin polymer; Kinetics; Measurement method; Linear low density ethylene polymer; Photochemical degradation
• ISSN: 0032-3888; 1548-2634
• DOI: 10.1002/pen.20313

The molecular degradation characteristics of three different polyethylenes were determined by deriving chain scission and crosslinking concentrations from gel permeation chromatography molecular weight distributions obtained after 3 weeks and 6 weeks laboratory ultraviolet exposure. Injection‐molded bars (3 mm thick) made from a low‐density polyethylene (LDPE), a linear low‐density polyethylene (LLDPE), and a high‐density polyethylene (HDPE) were used and all showed strong depth variations in degradation. Degradation was rapid near the exposed surfaces but very little change occurred in the bar centers, due to oxygen starvation. The most rapid rises in scission and crosslink concentrations were observed with LDPE, for which the concentrations after 6 weeks exposure were approximately double those measured after 3 weeks. With LLDPE and HDPE the scission and crosslink concentrations after 6 weeks exposure were very much greater than twice those after 3 weeks. Scission dominated over crosslinking at all depths and for all materials the scission/crosslink ratio was always ≥3, with a value of ∼9 recorded for HDPE near the exposed surface after 6 weeks exposure. POLYM. ENG. SCI., 45:579–587, 2005. © 2005 Society of Plastics Engineers