Effects of Knit Lines on the Creep and Fatigue Performance Properties of Modified Poly(phenylene ether)

Based on their viscoelastic nature, plastics exhibit both long-term and short-term mechanical properties. Plastics are highly sensitive to static and cyclic loading, and typically have much lower creep strength and fatigue strength relative to their measured tensile strength. Despite this, creep and fatigue testing are often overlooked as part of the material selection process. Poly(phenylene ether) / High impact polystyrene (PPE+HIPS) samples were injected molded using single and dual gate configurations to investigate the impact of production artifacts, using knit lines as a representative imperfection. Tensile testing showed that modulus was unaffected by the knit line and ultimate tensile strength was only marginally affected. However, both creep and fatigue testing showed a notable difference in strength between the samples, with substantial reduction in creep performance and fatigue resistance associated with the presence of the knit line.