Effect of injection molding parameters on properties of cross-linked low-density polyethylene/ethylene vinyl acetate/organoclay nanocomposite foams

Injection molding of foam articles has always attracted much interest because of elimination of sink mark, good dimensional stability and reduced production cost. In this study, the nanocomposite samples based on low-density polyethylene/ethylene vinyl acetate/organo montmorillonite were processed into foams by injection molding method. Nanocomposites were prepared by co-rotating a twin-screw extruder. The experimental design was based on Box-Behnken method and parameters such as injection rate, mold temperature and nanolayered silica content were examined in relation to physico-mechanical properties of foams using response surface methodology. Three levels of injection rate (30, 60 and 90 mm/s), nanoclay content (0, 3 and 6 phr) and mold temperature (160, 175 and 190 A degrees C) were chosen. The mathematical model and response surface graphs were employed to illustrate the relationship between the variable parameters and foam properties. The results revealed that the cell size and cell density as the main characteristics of the foams were affected by all parameters. Cell density of samples was affected by mold temperature, injection rate and nanoclay content. At high level of nanocontent the increase of injection rate was accompanied by decreases in density. Tensile strength and specific compression modulus of samples passed through a maximum versus mold temperature due to competition between cross-linking reaction and cell growth. At high mold temperature and injection rate, the cell rupture occurred because of low viscosity of the compounds at these conditions.