Soft, fully bio-based poly-hydroxyl thermosets based on catalyst-free transesterification with decent re-processability

Most of the vitrimers based on transesterification (TE) highly rely on the usage of large amounts of catalysts to promote exchange reactions to obtain re-processability, which brings additional concerns on human health or environmental issues. Herein, we demonstrate that TE vitrimers with soft networks (low T-g), though free of catalysts nor any other special design, can be still dynamic enough to be easily re-processed. In this paper, fully bio-based and catalyst-free thermosets from epoxidized soybean oil (ESO) and bio-dicarboxylic acids (DA) were synthesized and found to possess decent re-processability. By means of compressive remolding (10 MPa, 160 degrees C), the ESO-DA thermosets heal visible defects within 30 min and restore the mechanical strength within 3 h. Upon 3 times of mechanical recycling, the mechanical strengths remain nearly unchanged compared with those of pristine thermosets. Stress relaxation experiments confirm the network rearrangement at high temperatures (>= 150 degrees C) as well as vitrimeric flow of the materials. The materials are also capable of being welded without solvents under a small pressure. Lastly, a facile fusion method was employed to tune the mechanical strength of the recycled ESO vitrimers.