Converting Unrefined Birch Suberin Monomers into Vitrimer

Suberin extracted from birch bark, a side product of the wood industry, was used as a resin for the synthesis of a biobased vitrimer utilizing the transesterification reaction. Suberin was extracted by hydrolyzing the outer bark of birch trees under alkaline conditions and used further without refining. The resulting resin, natively rich in hydroxyl and carboxyl groups, was polymerized in the presence of various catalysts and a small-molecule polyol to provide an excess of primary OH groups. The study showed that among the catalysts tested, only dibutyltin dilaurate (DBTDL) promoted the transesterification reaction in the polymer matrix to the extent that the polymer could be recycled at elevated temperatures. Furthermore, a chemical recycling route was successfully tested through alkaline hydrolysis and repolymerization of the obtained vitrimer. The resulting suberin vitrimer showed elastomer-like properties with Tg at approximately −20 °C and a Young's modulus exceeding 1 MPa. It was also demonstrated to be hydrolytically stable under moderately alkaline and acidic conditions.