Birch tree barks are regarded as waste in the pulp and papermaking industry and used primarily as fuel. However, this material presents a source that contains many bio-derived molecules suitable for applications ranging from pharmaceuticals, plastics and composites, coatings, and antifeedants. Among the mixture of bio-derived molecules in birch barks, triterpenoids, such as betulin, betulinic acid, and lupeol, can be present up to 30% by weight of dry bark mass. They are highly valued for their anti-tumor, HIV, and inflammatory responses. Furthermore, birch barks also contain various other useful bio-derived molecules and derivative thereof, such as but not limited to, lignin, holocellulose, and suberin. In our presented work, birch bark extracts were produced from locally sourced river birch trees (Betula nigra) with an average yield of 10.6% (dry bark mass) and characterized via spectroscopy, chromatography, and hydroxyl number titration techniques. The extracts were directly used to synthesize bio-based thermoset polyesters with promising thermal and mechanical properties using minimal processing steps. Furthermore, thermoplastic polyesters containing betulin were synthesized using a melt polycondensation procedure with succinic acid, adipic acid, 1,12-dodecanedioic acid, 1,18-octadecanedioic acid, and itaconic acid. Additionally, glycerol was used for the formation of crosslinked betulin-based thermosets. All created bio-based polyesters were characterized via thermo-mechanical, mechanical, thermogravimetric, and chromatography (where appropriate) techniques to gain a fundamental understanding of the processing-structure-property relationships of these unique bio-based polymers. In addition to the lab-scale synthesis of these bio-based polyesters, we have also studied the economic viability and process scalability of value-added materials from birch bark. All-in-all, this work demonstrates the technical and commercial viability of utilizing birch bark derived molecules to prepare polyesters with potentially 100% bio-based content for a variety of applications.

Awesome polymers from birch bark

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