High-Performance, Biobased, Degradable Polyurethane Thermoset and Its Application in Readily Recyclable Carbon Fiber Composites

Carbon fiber (CF) reinforced polyurethane (PU) composites have attracted increasing attention in recent years. It is still a challenge to recycle the CF reinforced composites, and there is no report on the recycling of CF from PU matrix. In this paper, for the first time, a readily recyclable CF reinforced PU composite was prepared based on a biobased acetal diol, 2-(4-hydroxy-3-methoxyphenyl)-1,3-dioxan-5-ol (HMDO). The acetal diol was synthesized from the lignin derivative vanillin and was used to react with hexamethylene diisocyanate trimer to prepare the PU thermoset (PU-HMDO). On account of the cleavable acetal groups, the PU-HMDO could be decomposed within 40 min in low-concentration acidic solution completely. In addition, the heterocyclic structures of acetal and isocyanurate resulted in excellent mechanical and thermal properties of PU-HMDO. The tensile strength was 68 MPa, the elongation at break was 7.9%, and the glass transition temperature (T-g) was 130 degrees C, which are comparable to those of a PU thermoset (PU-BPA) from commercially available diol bisphenol A (BPA). The thermal stability of PU-HMDO was even higher than that of PU-BPA. The PU-HMDO-based CF composite exhibited similar mechanical properties to the PU-BPA-based CF composite, and CF could be reclaimed with maintained microscale morphology, chemical structures, and mechanical properties under mild acid conditions. This work will open a door to develop readily recyclable PU-based CF composites.