All birch bark suberin/lignin composite vitrimer elastomer

This research investigates the potential of the utilisation of lignin residue from the extraction process of suberin monomers from birch bark as a filler in birch suberin vitrimer composites. The study focuses on the mechanical performance, recyclability and thermal properties of these composites. The Klason method was applied for lignin extraction. The obtained Klason lignin particles had a broad size distribution with a mean diameter of 4.5 μm. Chemical analysis revealed the presence of both hydroxyl and carboxyl groups that could react with suberin monomers. Composites were synthesised with varying lignin content (5-20 %), demonstrating that the optimal performance was achieved at 10 %, where both elongation and stress at break increased by approximately 30 %. However, increasing the lignin content to 20 % resulted in the aggregation of lignin particles, limiting further improvement in mechanical properties. Importantly, the resulting composites retained the properties of vitrimer; the addition of 20 % lignin, however, increased the relaxation time from 750 to 1800 s at 190 °C The results confirm that the use of Klason lignin as a filler for suberin-based polymers is an easily applicable approach to utilise birch bark for the synthesis of sustainable polymers.