The effect of comonomer concentration and distribution on the photo-oxidative degradation of linear low density polyethylene films. (16th June 2017)

• Record Type: Journal Article
• Authors: Hsu, Yu-Chieh; Truss, Rowan W.; Laycock, Bronwyn; Weir, Michael P.; Nicholson, Timothy M.; Garvey, Christopher J.; Halley, Peter J.
• Is Part Of: Polymer. Volume 119(2017)
• Page Start: 66
• Page End: 75
• Publication Date: 2017-06-16
• Subjects: Degradation -- Polyethylene -- Photo-oxidation -- LLDPE -- Short chain branching; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; 547.7
• DOI: 10.1016/j.polymer.2017.05.020
• Languages: English
• ISSNs: 0032-3861

Abstract

Abstract: The photo-oxidative degradation of two complementary linear low density polyethylene (LLDPE) films has been studied: a Ziegler-Natta catalysed 1-octene copolymer (ZN-LLDPE) and a 1-octene copolymer produced by a single site constrained catalyst (m-LLDPE). The degradation processes were followed using a range of characterisation techniques including tensile testing, GPC, MAS-NMR, FTIR, WAXS and SAXS. The chemical species formed on degradation were similar for both polymers. Both also showed an increase in crystallinity and modulus with UV ageing time and a decrease in the long spacing of the lamella. However, the m-LLDPE showed a significantly shorter time to embrittlement than the ZN-LLDPE, which correlated in both polymers with the disappearance of the second yield point. The major observed difference in crystalline structure was a significantly higher interfacial thickness between the crystalline lamellae and the amorphous regions for the ZN-LLDPE, which decreased rapidly on UV ageing. This difference in behaviour was attributed to the nature of the branching in the ZN-LLDPE, which was presumed to sit in blocks along the chain and thus to reside in the interfacial regions. Cleavage of the tertiary carbons in these interfacial regions was less damaging to the mechanical properties than for the m-LLDPE, where chain scission broke more of the tie molecules, thus limiting the ability of the polymer to draw. . This work advances our understanding of polymer microstructural evolution during degradation and the implications of initial polymerisation route and molecular structure on the degradation mechanisms. Graphical abstract: Highlights: A metallocene type LLDPE embrittled faster than a comparable Ziegler-Natta-LLDPE. Embrittlement coincided with the disappearance of the second yield point. The ZN-LLDPE was found to have a thicker interfacial region. More chain branches of the ZN-LLDPE are likely to reside in this interfacial region. Chain cleavage in ZN-LLDPE was less damaging due to its location in the interface.