Development of Lightweight, Recyclable, and Degradable Foams Based on an Environmentally Friendly Polyamide Elastomer System via Supercritical Carbon Dioxide Foaming

In efforts to resolve problems of depletion of earth’s resources and disposal of solid waste caused by traditional petrochemical polyamide systems, biobased and degradable polyamides and their foamed products have received considerable attention. However, the practical development of such sustainable and foamable materials is still challenging. Herein, we designed an environmentally friendly polyamide elastomer system using biobased polyamide 1010 (PA1010) as the hard segment and degradable polycaprolactone (PCL) diol as the soft segment. By increasing PCL diol content, the melting temperature was gradually suppressed from 205 to 173 °C, and the stretchability was progressively enhanced from 18 to 770%. Notably, the polyamide elastomers with high PCL contents were beneficial to the production of lightweight foams with expansion ratios higher than 3.8 via supercritical carbon dioxide (CO2) foaming, effectively overcoming the major difficulties in manufacturing polyamide foams caused by the intrinsic issues of high crystallinity, low extensibility, and insufficient melt strength. Moreover, controlling PCL content at the optimal value of 37 wt % allowed the system to achieve a good balance between foaming performance and shrinkage resistance. Additionally, the polyamide elastomer foams could be easily recycled and remanufactured to form renewed foam products because no reactive cross-linkers or chemical blowing agents were used. The compressive stress could be restored to at least 70% of the original level. Furthermore, the degradable PCL soft segment gave the system favorable degradability. The foamed sample with the highest PCL content showed a mass loss value of approximately 24.65% after 12 weeks in an alkaline medium. Such effective degradability was conducive to resolving the problems of solid waste accumulation from landfilling and greenhouse gas emissions from incineration. We believe that these findings provide a constructive way to design advanced sustainable polyamide materials.