Abstract
The combined influence of chemical structure and cellular morphology on the performance of high-density polyurethane foams has received limited attention. In this work, three foams based on a commercial petrochemical polyol (SD441) were compared with three foams produced from a mixture of epoxidized soybean-oil polyol and glycerol at densities ranging from approximately 100 to 300 kg/m³. The biobased foams exhibited substantially lower compressive strength than the petrochemical materials, with longitudinal strength ranging from 0.60 to 4.07 MPa compared with 1.03 to 8.92 MPa for the petrochemical foams. Electron microscopy revealed larger cells, greater anisotropy, and pronounced morphological heterogeneity in the biobased materials, particularly at higher densities. Despite their lower initial storage modulus, the biobased foams exhibited greater resistance to thermally induced softening: at 170 °C, they retained approximately 32–39% of their initial storage modulus, compared with only 6–8% for the petrochemical foams. A second DMA heating run, together with FTIR and DSC results, indicated irreversible structural changes during the first heating cycle. The reduction in residual isocyanate content and changes in the carbonyl and amide II regions were consistent with further network development during heating, suggesting additional post-curing in the biobased foams. DSC identified two exothermic events in the biobased materials: a broad event between 60 and 245 °C, consistent with additional reactions, and a second event between approximately 255 and 300 °C that overlapped with the onset of thermal degradation observed by TGA. In contrast, the type of blowing agent strongly influenced the degradation temperature but had no significant effect on mechanical performance within the investigated density range. Overall, the results demonstrate a distinct trade-off between mechanical and thermomechanical performance in high-density biobased polyurethane foams, highlighting the influence of polyol molecular architecture, network development, and cellular morphology on their behaviour.