The Effect of Microstructure on the Slow Crack Growth Resistance in Polyethylene Resins

The slow crack growth (SCG) in high density polyethylene (HDPE) is a phenomenon dominated by crazing. In this work, the crazing was analyzed from a microstructural point of view. PENT (Pennsylvania Edge Notched Tensile) test was chosen to study the evolution of the craze with time for different resins from PE-80 up to PE-100 grades. Two different geometries, the standard and an alternative named CDNT (Circumferentially Deep Notched Tensile), were employed. Failure times were correlated with intercrystalline parameters like tie molecules and the molecular weight between entanglements. Experimental results showed good correlations using both direct SCG test (standard PENT and CDNT geometries). Finally, the strain hardening modulus was correlated with PENT failure times. The results disclosed an outstanding correlation for several polyethylene grades from blow molding up to PE-80, PE-100, and higher resistant to crack grades. These results permitted an easy-classifying and ranking method as much to the old polyethylene grades as to the new generation of HDPE resins with a very high SCG resistance. POLYM. ENG. SCI., 55:1018-1023, 2015. (c) 2014 Society of Plastics Engineers