Converting Birch Bark Extracts into Bio-based Thermosets

Abstract

Birch tree barks are regarded as waste in the pulp and papermaking industry and used as fuel. However, this material presents a source that contains many bio-based chemicals suitable for applications ranging from pharmaceuticals, plastics and composites, coatings, and antifeedants. Among the mixture of bio-derived chemicals in birch barks, triterpenoids, such as betulin, betulinic acid, and lupeol, can be present up to 30% weight of dry bark mass. They are highly valued for their anti-tumor, HIV, and inflammatory responses. In our presented work, triterpenoid mixtures were extracted through a Soxhlet extractor using the barks from locally sourced river birch trees (Betula nigra) with an average yield of 10.6% (dry bark mass). The extracted materials were characterized using the Nuclear Magnetic Resonance (NMR), Advanced Polymer Chromatography (APC), High-Performance Liquid Chromatography (HPLC), and hydroxyl number titration to assess the identity, average molecular weight, triterpenoid content, and the number of reactive sites, respectively. The extracts have been used to synthesize bio-based polymers with promising thermal and mechanical properties using minimal processing steps. Birch bark extract naturally contains many potential reactive sites and thus making it advantageous for synthesizing polymers without requiring multiple purification steps. We demonstrate the potentials for increasing the utility of birch bark, contributing to sustainability challenges in materials science and engineering.