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Abstract
Lignin is a promising bio-based feedstock for aromatic platform chemicals. Of particular interest to polymer chemist are the various hydroxycinnamic acid
derivatives that can be obtained from lignin depolymerization. The valorization of
these derivatives and their subsequent polymerizations are well described in the
literature, but robust mechanical and degradation properties of these materials is
lacking. The systematic study of the thermal, mechanical, and degradation
properties of both novel and previously reported lignopolyesters is described. The
properties of polyesters functionalized with alkyl linkers at the phenolic moiety were
investigated by conventional techniques. These polymers exhibited excellent
thermal stability, allowing for extrusion and injection molding. These semi-aromatic
polymers show a wide array of mechanical properties, including a highly ductile
thermoplastic, a strong and rigid thermoplastic, and an elastomer. Composting
biodegradation tests showed both degradable and nondegradable polymers can
be achieved in this class. Of the polymers synthesized, one exhibited shape
memory characteristic of thermoplastic polyester elastomers (TPEEs). TPEEs are
unique in that they behave like elastomers but lack any crosslinking. To improve
its mechanical properties, reactive extrusion with epoxide chain extenders was
used to induce branching. The degree of branching can be controlled by epoxide
loading, allowing for tuning of the elastic modulus and ductility. Elastic modulus
was increased by up to 3 orders of magnitude and shape memory was retained.
The rheological properties of the branched TPEE were also significantly enhanced.
These materials were blended with commercial biopolymers to further probe their
applications. Formulations with PBS and PHA were melt compounded with and
without compatibilizers. Generally, all blends showed increased toughness. PHA’s
elongation at break of 18% was dramatically increased, with its ultimate elongation
with and without compatibilizers increasing to 136% and 247% respectively.
Further applications and melt rheology of the blends is described. Optimization of
high melting polymers derived from lignin is also described. The conventional
synthesis was substantially improved in terms of molecular weight and
sustainability. The scalability and extensive characterization of lignopolyesters
demonstrates their potential to replace petrol polymers. Further investigation into
the structure-property relationships of these structures could aid in developing new
generations of lignopolyesters.