Weld lines in nylon 6 melt-blended nanocomposites

Abstract

The effects of weld lines in injection moldings of nylon 6 and nylon 6 nanocomposite samples were investigated by comparing single-end-gated and double-end-gated tensile samples. The single-gated samples have no weld line, whereas the double-end-gated configuration produces a weld line at the center of the gauge length. Nylon 6 shows little variation in tensile properties for samples with or without weld lines, remaining ductile and tough, even with weld lines present. However, nylon 6 nanocomposites containing organically modified montmorillonite (organoclay), produced by a melt blending technique, exhibits rigid and brittle behavior for both single (no weld line) and double-end-gated (with weld line) samples. The organoclay increases the tensile strength but reduces the strain-to-failure significantly in both cases. A modified L16 orthogonal array based on the Taguchi approach with three levels was designed to run injection-molding experiments to allow production of a modest number of samples to identify the most important process factors. The results were analyzed using the statistical tools signal-to-noise (S/N) ratio and analysis of variance (ANOVA), in particular showing that the principal process factors for the double-end-gated nylon 6 nanocomposite samples are mold and melt temperatures. POLYM. ENG. SCI., 45:1606–1614, 2005. © 2005 Society of Plastics Engineers