Comparison of cell morphology and mechanical properties of wheat straw powder/HDPE parts molded by supercritical fluid foamed injection with and without gas counter pressure technology

Composites were fabricated using maleic anhydride‐grafted high‐density polyethylene as the matrix material and wheat straw as the filler. Differential scanning calorimetry and rheological properties of these composites were investigated to determine the processing parameters for supercritical fluid (SCF) microcellular injection with and without gas counter pressure (GCP) technology. The impacts of different proportions and dimensions of wheat straw, along with process parameters related to GCP, were determined on both the cellular structure and mechanical characteristics of foamed injection molded components. Experimental results revealed that an increase in the ratio of wheat straw and a reduction in its size led to enhancements in both storage modulus and complex viscosity of the composites, while also improving their cell structure when foamed with SCF. By adjusting GCP process parameters, it was possible to regulate both cell morphology and mechanical properties of foamed injection molded parts. Higher GCP or longer GCP holding time resulted in increased skin thickness and tensile strength but decreased notched Izod impact strength.Highlights Built relations between GCP technology parameters and cell morphologies. Compared the influence of wheat straw powder and GCP parameters quantitatively. Explored the correlation between cellular morphology and mechanical properties. The regulatory mechanism of cell morphology, size ratio, and distribution. GCP effectively modulates cell morphologies and mechanical properties.