Biomass Thermoplastic (Co)polyamide Elastomers Synthesized from a Fatty Dimer Acid: a Sustainable Route toward a New Era of Uniform and Bimodal Foams

Abstract

Renewable polyamides (PAs) with excellent flexibility and low-temperature foaming capability are of current interest for a wide range of industrial applications. Presently, most commercially available foams are made from fossil-based plastics, and several engineering polymers are not deployed for this, specifically bio-based ones. In this work, a new library of fully bio-based, thermoplastic PAs (denoted as DFA-BDAxHMDAy and DFA-EDAxHMDAy) with low-temperature foaming attributes is synthesized through catalyst-free polycondensation using a renewable fatty dimer acid and different chain length diamines. The resulting PAs showed Mw up to 44,191 g/mol, Td5% over 415 °C, Tm from 63.1 to 103.9 °C, Tg from 14.6 to 23.6 °C, strain from 386.65 ± 0.08 to 832.46 ± 0.03%, and tensile strength up to 18.57 ± 0.02 MPa. The bio-based PA samples were foamed using the scCO2 batch foaming process, and the foam cell structure was investigated with scanning electron microscopy. The results showed that the foaming morphologies could be easily tuned by changing the diamine compositions, indicating the great simplicity and tunability of this method. Consequently, we achieved foams with uniform and bimodal textures with an average diameter range of 18–198 μm for small and large cells, respectively, and the foams with various densities (0.214–0.351 g/cm3) were gained. The creation mechanism of uniform to bimodal foams was proposed and explained by a schematic illustration. All the bio-based PA foams exhibit creep recovery values above 85%. This is the first report on the manufacturing of bio-based PA foams at low foaming temperatures without toxic solvents. These outcomes provide insights into bio-based PA foam research.

Topics & Concepts