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.

Automated summary

This paper demonstrates the re-processability and mechanical strength recovery of low T-g TE vitrimers without the use of catalysts or special designs. Through compressive remolding, the vitrimers can repair defects and restore mechanical strength within a short period of time. Mechanical recycling does not significantly affect the mechanical properties of the vitrimers. Stress relaxation experiments confirm the network rearrangement and vitrimeric flow of the materials at high temperatures.