Thermosets from Birch Bark: A Holistic Approach Using Green Solvents and Processes

TL;DR

Scientists made eco-friendly thermoset polymers from birch bark waste using green solvents and processes.

Contribution

A holistic green approach for synthesizing polyester thermosets from birch bark using biobased solvents and avoiding energy-intensive purification.

Findings

Betulin-rich extracts (62.2–81.5 wt%) were obtained from birch bark using green solvents.

Polyester thermosets made from extracts had properties comparable to those made from pure betulin.

Solventless polycondensation used 100% biomass-derived materials.

Abstract

Many recent efforts
toward sustainable polymer development use
building blocks from renewable biomass feedstocks. However, issues
arising from the processes used to extract starting materials from
biomass are often overlooked, despite the safety and environmental
hazards associated with energy-intensive separation processes and
solvent utilization. Here, we describe a holistic approach toward
using green solvents and processes to synthesize polyester thermosets
from birch bark, a waste product from the paper and pulp industry.
Betulin, a diol with a pentacyclic ring structure, was extracted from
the bark of silver birch trees via reflux boiling using green solvents
available from biobased sources. Ethanol and 1:1 ethanol:ethyl acetate
mixtures were effective solvents for extraction, with additional selectivity
achieved via antisolvent precipitation. Betulin-rich extracts containing
62.2–81.5 wt % betulin were produced and directly used to prepare
polyester thermosets using one-pot, solventless polycondensations
with 100% of the starting materials available from biomass feedstocks.
The polymers prepared directly from extracts had properties comparable
to those synthesized from pure betulin, suggesting that additional
processing steps required to achieve higher purity betulin may not
be warranted. Overall, we present an approach to polyester development
from betulin-rich birch bark extracts, which incorporate green chemistry
and engineering principles from feedstock to product.

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