Investigation of the microstructural and mechanical properties of phenol–formaldehyde resin-impregnated polyurethane foam using response surface methodology

Abstract Polyurethane foam (PUF) is widely used in structural and energy-absorbing applications; however, the relationship between its microstructural characteristics and mechanical properties under varying pore densities, strain rates, and solvent used during sample manufacturing is still insufficiently understood. This study investigates the microstructure and mechanical properties of phenol–formaldehyde resin-impregnated polyurethane foam (PFRI-PUF). The main morphological parameters of foam, including pore area and equivalent pore diameter, as well as shape descriptors such as circularity, pore shape anisotropy, and pore anisotropy angle were extracted and compared across foams with different pore densities (20, 40, and 60 PPI) and solvents (acetone, ethanol, and methanol). Mechanical properties including densification strain, plateau stress, energy absorbed, mean crushing stress, peak stress and elastic modulus were analyzed under varying pore densities, strain rates, and solvent conditions. Furthermore, non-linear regression modeling was performed to predict mechanical properties responses for different pore densities, strain rates and solvents. Finally, the effects of pore density, strain rate and solvent on mechanical properties of PFRI-PUF were assessed using two-way ANOVA. The results indicate that pore density is the dominant factor influencing the mechanical properties of PFRI-PUF than both strain rate and solvent type. Furthermore, the multi-response optimization shows that the 60 PPI foam, combined with a strain rate of 3.24 × 10 −4 s −1 and ethanol as the solvent, yields the most optimal overall mechanical performance.