1. © Rheological Investigation Of The Influence Of Molecular Structure On Natural And Accelerated UV Degradation Of Linear Low Density Polyethylene Hussein, IA ELSEVIER SCI LTD, POLYMER DEGRADATION AND STABILITY; pp: 2026-2032; Vol: 92 King Fahd University of Petroleum & Minerals http://www.kfupm.edu.sa Summary Metallocene and Ziegler-Natta (ZN) linear low density polyethylenes (LLDPEs) of different branch types and contents as well as linear high density polyethylene (HDPE) were exposed to natural and accelerated weather conditions. The degree of UV degradation of exposed samples was measured by theological techniques and results were compared with unexposed polymers. Dynamic shear measurements were performed in an ARES rheometer in the linear viscoelastic range. The degree of enhancement or reduction in viscosity and elasticity was used as a measure of the degree of cross-linking or chain scission, respectively. The degradation results of LLDPE suggest that both cross-linking and chain scission are taking place. Chain scission dominated the degradation at high levels of short chain branching (SCB) and long exposure times. The degradation mechanism of m-LLDPE and ZN-LLDPE is similar; however, m-LLDPE showed a higher degradation rate than ZN-LLDPE of similar M, and average SCB. ZN-LLDPE was found to be more stable than a similar m-LLDPE. Comonomer type had little influence on degradation. Dynamic shear rheology was very useful in revealing the influence of different molecular parameters and it exposed the degradation mechanism. (c) 2007 Elsevier Ltd. All rights reserved. Copyright: King Fahd University of Petroleum & Minerals; http://www.kfupm.edu.sa

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3. 43. 44. © UZOMAH TC, 1998, J APPL POLYM SCI, V69, P2533 UZOMAH TC, 1998, J APPL POLYM SCI, V69, P667 For pre-prints please write to: ihussein@kfupm.edu.sa Copyright: King Fahd University of Petroleum & Minerals; http://www.kfupm.edu.sa