Structure-Property Relationships of Bio-Based Thermosets from Birch Bark

Plastic pollution is a pressing issue that threatens ecosystems around the world. Many commonly-used plastics have long lifetimes and are often discarded in the environment. Additionally, plastic manufacturing taxes the environment and diminishes natural resources. Thus, developing bio-based alternatives to petroleum-derived plastics is a promising approach towards lessening the adverse environmental impacts of plastic use. This study focuses on the valorization of betulin, a pentacyclic triterpenol, which can be extracted in high quantities from birch bark. Previously, we incorporated betulin into a series of polyester networks with varying bio-based diacids. The focus of the current study is to develop and characterize the properties of betulin-based thermosets synthesized with two diacid co-monomers in varied ratios and glycerol as the crosslinker. We use dynamic mechanical analysis to examine thermomechanical properties and thermogravimetric analysis to investigate degradative temperatures. Our results show that the storage moduli at room temperature range from 44.6 MPa to 199 MPa depending on the composition and exhibit thermal stability above 296°C in both inert and oxidative environments. This work is part of a larger study to develop and evaluate bio-based plastics at all stages of life, from monomer extraction, to polymer synthesis, to end of life. These results demonstrate that thermosets with promising and tunable properties can be synthesized using betulin and other co-monomers.