Optimizing the Mechanical Performance in Semi-Crystalline Polymers: Roles of Melt Temperature and Skin-Core Crystalline Morphology of Nylon

Abstract

Crystalline texture and mechanical (tensile and flexural) properties of injection molded nylon 6 were evaluated to understand the influence of one of the key-processing variable, the melt temperature (T _mlt). We find that mechanical properties are sensitive to T _mlt only below ∼250°C. Rapid quenching of the surface produces a skin with lower crystallinity than the core, which cools more slowly; this difference in the rate of cooling produces γ crystalline form in the skin and α crystalline form in the core. Higher tensile strength at yield, lower elongation at break and higher flexural strength were observed in specimens molded at lower T _mlt. These characteristics are associated with thicker and less ordered skin, and a lower crystallinity core. The role of the T _mlt on micro-structure and mechanical properties of injection molded nylon 6, the development of skin and core morphologies, and the role of the residual stresses in the core are discussed.