Microstructure, physical, and mechanical properties of LDPE/UHMWPE blend foams

Abstract

An investigation was reported on the effect of foaming parameters on the microstructure, mechanical properties, and thermal conductivity of low-density polyethylene (LDPE) foams containing various amount of ultrahigh-molecular-weight-polyethylene (UHMWPE) as a reducer of chemical cross-linking. Azodicarbonamide (ADCA) and dicumyl peroxide (DCP) were used as foaming agent and cross-linking agent, respectively. The LDPE/UHMWPE blends were prepared in an internal mixer and foamed using a single-stage compression molding technique. Considering various parameters and their levels, optimization of Taguchi experimental design was carried out, an L9 orthogonal standard array was selected and the efficient levels for different variables were calculated using analysis of variance (ANOVA) of the results. Also due to different objective functions investigated in this process, optimization of overall evaluation criteria (OEC) method was used. The results revealed that addition of UHMWPE leads to a significant increase in the storage modulus and complex viscosity of melt as well as a considerable decrease in gel content of blend foams compared to neat LDPE foam containing the same amount of DCP was observed. Also in presence of UHMWPE, the foam cell size was decreased compared to previous studies in the same condition. A linear relationship between relative density and thermal conductivity as well as cell size and thermal conductivity was observed. ANOVA results revealed that foaming temperature is the most effective parameter on foam properties and OEC results suggested 10 phr ADCA, 0.6 phr DCP, foaming temperature of 180°C, and 4 min soak time at foaming temperature are the optimum levels of parameters.