Understanding appropriate ESCR test methods for rotomolding resins

摘要

Environmental stress crack resistance (ESCR) is an important consideration in designing and selecting polyethylene resins for the packaging of surface-active liquids. Resin designers and processors of rotomolding resins can choose from at least two distinctive test methods when comparing ESCR performance of polyethylene resins. Traditional bent strip methods impose a fixed strain on test samples. The subsequent stress experienced by the samples varies with time, and is a function of resin stiffness as well as stress relaxation characteristics. More modern constant tensile load (CTL) techniques, such as developed by the Association of Rotational Molders, apply a fixed stress to test samples, which is held constant throughout the duration of the test. This paper examines the advantages and limitations of both bent strip and CTL tests, and compares the relative ESCR performance of actual rotomolded containers to comparative values from bent strip and CTL methods. Typical CTL values for a range of resin classes are included.