Dissolution Processing of Nanostructured Polymers Tailored for Effective Utilization of Cellulosics

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Intellectual Merit: The proposed research addresses the outstanding need for an integrated approach to dissolve cellulosics, an abundant and renewable resource, as an essential step for their processing into functional polymers, specialty chemicals, and biofuels. While several approaches have proven useful for activation of crystalline cellulose, the search is still on for solvents that can effectively dissolve cellulose. The few known solvents that are capable of dissolving cellulose do so under strict and often conflicting composition and temperature conditions, and fundamental understanding is lacking. The project team bases the proposed research program on the premise that fundamental understanding of cellulose-solvent molecular interactions (nanoscale), coupled with knowledge of the dissolution mechanism of semicrystalline cellulosic (microscopic) particles, can lead to the rational selection and (macroscopic) optimization of solvent processing conditions for cellulosic biomass. To this end, the team aims to (1) advance fundamental understanding of intermolecular interactions acting in select solvent systems that appear promising for dissolving cellulose, and express these interactions in terms of appropriate parameters, (2) identify and quantify the transport phenomena and kinetics governing the dissolution of solid cellulose, e.g., solvent penetration, transformation from crystalline to amorphous domains, specimen swelling, and polymer chain untangling, and (3) guide scale-up from the lab to industrial production by modeling the dissolution of polydisperse cellulose particulates (employing parameters determined in 1 and 2), exploring synergisms in mixtures of solvents and additives, and testing the dissolution of biomass specimens. In the above the team will target aqueous NaOH-based and ionic liquid solvent systems that exhibit a potential for process integration and are compatible with cellulose functionalization chemistry and biocatalysis. A main novelty of the proposed research resides in the team's concerted effort to rationally integrate cellulose dissolution information from the fundamental, (supra)molecular level to the practical, large-scale. This would have a transformative effect on what is mostly an empirical approach. Further novel aspects include (i) a unified approach for understanding molecular interactions in different solvent systems, including testing a recent hypothesis on the importance of hydrophobic effects which defies current wisdom; (ii) quantification of the dissolution mechanism, based on real-time monitoring of cellulose swelling and mass loss coupled with phenomenological modeling; (iii) characterization of cellulosic biomass structural evolution during dissolution; and (iv) experiments and population balance modeling on dissolution of polydisperse cellulose particulates. Each of these research topics will be new in the literature, and addressing all in tandem should prove powerful. Broader Impacts: In summary, this research will have a positive and timely impact on efforts directed toward the utilization of cellulosics as starting material for the synthesis of high value-added functional polymers and chemicals and also for biofuel production. The team's findings will be beneficial to nano/bio-applications where well-defined cellulose surfaces or nanoparticles are desired, and for the analytical characterization of cellulose and its derivatives; also to the solvent processing of difficult-to-dissolve liquid crystalline polymers and carbon nanotubes. Collaborations will be pursued with researchers in industry and in Europe. This project will integrate research and education by incorporating lectures and projects related to biomass, solvent selection, and dissolution modeling in the various courses that the PIs teach at both the undergraduate and graduate levels. Several students will contribute to this research, resulting in U.S.-based scientists who have both advanced technical training and sensitivity toward efficient resource utilization. The team will work with the AIChE student club to develop and offer outreach activities geared toward middle-school and 1st year college students.