Plastic waste has been a concerning topic for the last several decades due to its negative impacts on the environment. It is estimated that plastic production has increased by approximately 6 MMt in 2015 which contributes 15% of greenhouse gas emissions annually. While some types of plastic materials are recycled more than others, overall, less than 15% of produced plastic was recycled in 2018. The upcycling of plastic waste by introducing biodegradable components, such as lignin, is an additional approach to address plastic waste issues. Lignin is a natural biodegradable polymer found in plants and produced abundantly in multiple industries including paper pulping. However, it is generally treated as waste or occasionally used in low-value applications such as burning as a fuel source. The objective of this research is to develop copolymers from lignin and synthetic polymer – yielding a potentially biodegradable polymer. Native lignin biopolymer is nonlinear, and this branching causes the polymer to be too rigid and brittle for many applications. The chemical composition of lignin is complex with the ring structure and functional groups depending on the processing methods. Therefore, several reduced functionality methods were examined on the native lignin – such as amination, esterification, phenolation, hydroxypropylation, and lignin-based azo coupling – to generate a more linear lignin polymer that can be extended through block copolymerization. After functionalization, lignin polymers are used as the macro-initiator to synthesize block copolymer via polymerization of olefin monomer (styrene is used as an initial model for olefin monomer). The copolymers produced from this work were characterized to determine the mechanical, thermal, and rheological properties using FTIR spectroscopy, DSC, TGA, DMA, and rheology measurements. The thermomechanical properties of the formed copolymers were accessed to determine whether they were malleable and thermoformable such that they would be suitable for replacing plastic films in single-use packaging.

Development of biodegradable copolymers from lignin and polyolefins

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