Influence of type and content of chemical foaming agent on the dynamic mechanical properties of high density polyethylene-flax fiber composites

This study aims to evaluate the influence of type and content of chemical foaming agent on the dynamic mechanical properties of high density polyethylene-flax fiber composites. Composites were prepared via melt mixing in an internal mixer, and then foamed using single-stage batch foaming method. Two type of chemical foaming agents including azodicarbonamide (ADC) and sodium bicarbonate (SB) were considered at three levels of 0, 2 and 4 per hundred resins (phr). The amount of flax fiber and coupling agent for all formulations was fixed at 60% and 2 phr, respectively. Static mechanical tests including flexural and tensile were performed on samples. The dynamic mechanical properties such as storage modulus, loss modulus and damping factor of composites were investigated in the temperature range of -60 to 150 0C at a step of 5 0C and frequency of 1 Hz. Morphology of the samples was also evaluated by scanning electron microscopy (SEM). Results indicate that the chemical foaming agent substantially increased cell size and reduced cell density and mechanical strength of composites. Moreover, the lowest mechanical strength was observed in foamed composites with SB. SEM confirmed that the type and content of chemical foaming agent had significant influence on density reduction of foamed composites. Finally, by increase in the chemical foaming agent content, the storage modulus and loss modulus of samples decreased. However, on addition of chemical foaming agent to composites, the damping factor was increased. Foamed composites prepared with ADC exhibited inferior storage modulus compared than the SB.