(4bz) Renewable Polymers and the Design of Sustainable Plastics

To continue benefiting from the incredible utility and value of plastics, there is a critical need to address plastic pollution. A sustainable circular plastics economy is difficult to attain with current technology due to our heavy reliance on fossil fuels for feedstock and the challenges in recycling complex mixtures of polymers, additives, and fillers that make up plastics. I am particularly passionate about (1) developing strategies to utilize renewable biopolymers as feedstock for plastics and (2) developing design strategies and alternatives for fillers that hinder recycling processes or severely limit quality of recycled materials.

Utilization of renewable biopolymers such as protein, lignin, and fatty acids as replacement materials for synthetic polymers has been limited, even when compared to polymers from biomass-derived monomers or platform chemicals (eg. polylactic acid). However, valorization of these biopolymers can have broad impacts on sustainability, as it could be synergistic with biorefinery industries and biofuel production. In addition, biopolymers like proteins are capable of hierarchical self-assembly and can potentially expand the design space for engineering plastics. Developing biopolymer-based materials will require synthetic and processing strategies to achieve competitive performance, which also have to be compatible with the functional group and feedstock diversity common to biomass based materials.

Besides developing materials from renewable sources, moving towards plastics designed for recyclability is also crucial for reducing plastic waste. Plastic formulations typically contain various additives and fillers which are highly optimized for the products’ end use. While the complexity provides handles for tuning material performance, it can pose a huge barrier to recycling. Carbon black, for example, is known to be incompatible with infrared based sorting systems and can lead to recyclate contamination. In addition, as the material goes through use and recycling, changes in polymer-filler interactions that play crucial roles for mechanical reinforcement become difficult to determine, further complicating material design and may limit recycled materials to applications where performance needs are less stringent. The redesign of materials to eliminate problematic additives or fillers without sacrificing performance will therefore be crucial.

My research will first aim to answer two questions: (1) how can we design engineering plastics using underutilized biopolymers and control the structural organization of these biopolymers, and (2) how do we design composites for mechanical recyclability, potentially through better understanding of polymer-filler interactions, and drawing inspiration from hierarchical self-assembly in natural systems and developments in covalent adaptable networks. I will leverage skill sets from my graduate research, which involved developing synthetic and processing methodologies for making use of underutilized agricultural and waste polymer sources, and from my post-doctoral work, where I am using block copolymer self-assembly to prepare nanostructured porous materials.

Research Experience

My graduate research with Prof. Bradley Olsen at Massachusetts Institute of Technology focused on developing sustainable materials from underutilized feedstocks, namely agricultural waste proteins and rubber from used car tires. My work in developing protein-based elastomers entails exploring synthetic strategies to prepare copolymers comprised of stiff protein domains and rubbery polymers, along with processing and compatibilization strategies to expand the scope of monomers for the rubbery block and to address difficulties in thermally processing proteins. Crosslinked protein-based thermosets were prepared by first installing polymerizable groups onto proteins, followed by copolymerization with a (meth)acrylate comonomer that makes up the flexible soft segment. Using whey protein as a model mixture of agricultural proteins, we demonstrated this approach using solution polymerization in water, and showed that it is tolerant to the feedstock diversity and chemical functionalities typical in protein biomass streams. To enable hydrophilic proteins to be copolymerized with non-water soluble monomers, we introduced a surfactant compatibilization strategy, which allowed us to copolymerize the otherwise immiscible protein-comonomer mixture using melt polymerization. We further explored protein charged group modifications to address the undesirable protein hygroscopicity in elastomers. In addition, we demonstrated the preparation of thermally reprocessable protein-based thermoplastic materials using site-selective conjugation chemistry to prepare diblock copolymers. Lastly, I also explored methods to recycle waste rubber from car tires, where I developed expertise in polymer compounding and processing. To use recycled ground rubber particles as partial replacement for virgin rubber in tire formulations, we coated the ground rubber particles with an adhesive layer prior to reblending, and showed that this approach improved mechanical performance of rubber containing recycled particles.

My current post-doctoral work at the University of Minnesota with Prof. Marc Hillmyer is allowing me to expand my skill set in block copolymer self-assembly and polymer chemistry. We are exploring the use of disordered triblock polymers for rationally designing ultrafiltration membranes with tailored pore wall properties. The copolymers are comprised of a short pore-lining midblock flanked by a rigid matrix block and a polyester etchable pore-forming block. Bicontinuous pores with uniform size distributions were formed from selective removal of the etchable domain, which exposes the midblock on the pore surface. To demonstrate the tunability of this triblock copolymer platform, we selected a PEG-based polyacrylate as the midblock for fouling resistant porous materials.

Teaching Interests

I co-lectured the undergraduate thermodynamics course as a graduate student instructor, which enabled me to obtain valuable experience in course development and teaching. I was involved in the course revamp aimed at improving student learning outcomes and at addressing declining interest in chemical engineering among undergraduates. The course was restructured to establish and build upon strong foundational knowledge on molecular origins of thermodynamic properties, and was well received as shown in student feedback and overall course ratings. I learned valuable lessons in identifying points of weak understanding, and strived to emphasize connections between new topics and key basic concepts while providing real world examples for conceptualization in lectures. In addition, I also served as a teaching assistant for an experimental lab course aimed at introducing hands-on design experience to freshmen. I co-developed the bioreactor design module and guided students to build their homemade bioreactor, where I introduced basic concepts in biochemistry and reactor design, and provided students with lab skills for producing polyhydroxyalkanoates from food waste.

Beyond the classroom, I have mentored seven undergraduate student researchers; one of them is a co-author on a publication. I aimed to provide students with an engaging research experience, and learned the importance of providing well-structured research projects and specific feedback. I believe that undergraduate research experience can encourage interest in graduate school particularly for students from underrepresented groups, and have prioritized interest in science instead of prior experience in hiring decisions. I look forward to setting up an inclusive lab environment where students and postdocs will develop critical thinking and interdisciplinary skills to address complex technical challenges.

Selected publications

Calabrese, M. A., Chan, W. Y., Av-Ron, S., Olsen, B. D., Development of a rubber recycling process based on a single component interfacial adhesive. Submitted

Andersen, E.*, Chan, W. Y*., Av-Ron, S., Olsen, B. D., Tuning compatibility and water uptake by protein charge modification in melt-polymerizable protein-based thermosets. Submitted

Chan, W. Y., Av-Ron, S., Olsen, B. D., Synthesis of protein-based thermoplastic elastomers through site-specific protein modification and grafting-from polymerization. In preparation

Chan, W. Y., King, E. J., Olsen, B. D., Hydrophobic and bulk polymerizable protein-based elastomers compatibilized with surfactants. ACS Sustainable Chem. Eng., 2019, 7, 10, 9103-9111, 10.1021/acssuschemeng. 8b03557

Bochenski, T., Chan, W. Y., Olsen, B. D., Schmidt, J. E., Techno-economic analysis for the production of novel, bio-derived elastomers with modified algal proteins as a reinforcing agent. Algal Res 2018, 33, 337-344, 10.1016/j.algal.2018.06.012.

Chan, W. Y., Bochenski, T., Schmidt, J. E., Olsen, B. D., Peptide domains as reinforcement in protein-based elastomers. ACS Sustainable Chem. Eng., 2017, 5, 10, 8568-8578, 10.1021/acssuschemeng.7b00698