Stretching the applications of biomass: Development of lignin based thermoplastic elastomers and composite materials

Bio-based plastics and composites have seen increased industry adoption in recent years due to growing demand for materials with a low carbon footprint. The use of lignin as a feedstock for polymers has seen growing interest as the concept of an integrated cellulosic biorefinery gains traction and advances the need to use all components of separated biomass for value-added applications. Historically, use of lignin in thermoplastic and elastomeric copolymers and blends has been bottlenecked by the inability to introduce lignin content above 30 weight percent due to difficulties with interfacial adhesion of lignin with other soft segments. Efforts to overcome this have typically involved solvent-based chemical modification of lignin, requiring energy intensive solvent separation, and generating waste. In this document, we demonstrate a solvent-free, reactive compounding method to produce lignin-based thermoplastic elastomers with lignin contents as high as 70 weight percent. Our ability to control the dispersion of nano-sized domains of lignin in synthetic elastomers with enhanced interfacial adhesion has resulted in thermoplastic elastomers with tunable mechanical properties, with tensile strengths as high as 45 MPa [megapascals] in some variations, rivaling some engineering thermoplastics like nylon and ABS [acrylonitrile butadiene styrene]. We found that by varying lignin content, type, and additives, the ultimate tensile strength and toughness of the materials could be controlled. Lignins displayed the ability to participate in free-radical based crosslinking, both in the presence of an initiator and spontaneously. Additionally we demonstrated that lignin-based elastomers could be used to create fiber reinforced composites using bio-based fibers such as kenaf and hemp that demonstrate flexibility while maintaining significant tensile strengths. The demonstration of bio-based, flexible thermoplastic elastomers and elastomeric composites that make use of lignin, without the need for solvent-based chemical modification, presents significant promise for the future of renewable materials in durable goods.

Submission with edits and corrections from both my committee and from the last TRACE review. Submission on 4/27 per the extension offered by Abby Sherman. My committee is completing the signature form as well.