Open Access Publications - Center for Research in Soft matter & Polymers
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Open access publications by faculty, staff, postdocs, and graduate students from the Center for Research in Soft matter & Polymers (CRiSP).
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Item Conversion of Compositionally Diverse Plastic Waste over Earth-Abundant Sulfides(Journal of the American Chemical Society, 2025-04-02) Selvam, Esun; Schyns, Zoé O. G.; Sun, Jessie A.; Kots, Pavel A.; Kwak, Yeonsu; Korley, LaShanda T. J.; Lobo, Raul F.; Vlachos, Dionisios G.Chemical deconstruction of polyolefin plastic wastes via hydroconversion is promising for mitigating plastic accumulation in landfills and the environment. However, hydroconversion catalysts cannot handle complex feedstocks containing multiple polymers, additives, and heteroatom impurities. Here, we report a single-step strategy using earth-abundant metal sulfide catalysts to deconstruct these wastes. We show that NiMoSx/HY catalysts deconstruct polyolefin feedstocks, achieving ∼81–94% selectivity to liquid products. Postsynthetic zeolite modification enhances the catalyst’s activity by >2.5 times, achieving over 95% selectivity to liquid fuels with controllable product distribution in the naphtha, jet fuel, and diesel range. The catalyst is resilient to increasingly complex feedstocks, such as additive-containing polymers and mixed plastics composed of polyolefins and heteroatom-containing polymers, including poly(vinyl chloride). We extend the strategy to single-use polyolefin wastes that can generate toxic byproducts, such as HCl and NH3, and eliminate their emissions by integrating reaction and sorption in a one-step process.Item Toward Sustainable Materials: From Lignocellulosic Biomass to High-Performance Polymers(Accounts of Materials Research, 2025-02-21) Mahajan, Jignesh S.; Gottlieb, Eric R.; Kim, Jung Min; Epps, Thomas H., IIIConspectus Lignocellulosic biomass is an ideal feedstock for the next generation of sustainable, high-performance, polymeric materials. Although lignin is a highly available and low-cost source of natural aromatics, it is commonly burned for heat or disposed of as waste. The use of lignin for new materials introduces both challenges and opportunities with respect to incumbent petrochemical-based compounds. These considerations are derived from two fundamental aspects of lignin: its recalcitrant/heterogeneous nature and aromatic methoxy substituents. This Account highlights four key efforts from the Epps group and collaborators that established innovative methods/processes to synthesize polymers from lignin deconstruction products to unlock application potential, with a particular focus on the polymerization of biobased monomer mixtures, development of structure–property–processing relationships for diverse feedstocks, functional benefits of methoxy substituents, and scalability of lignin deconstruction. First, lignin-derivable polymethacrylate systems were probed to investigate the polymerization behavior of methacrylate monomers and predict thermomechanical properties of polymers from monomer mixtures. Notably, the glass transition temperatures (Tgs) of lignin-derivable polymethacrylates (∼100–200 °C) were comparable to, or significantly above, those of petroleum-based analogues, such as polystyrene (∼100 °C), and the Tgs of the complex, biobased copolymers could be predicted by the Fox equation prior to biomass deconstruction. Second, an understanding of structure–property relationships in polymethacrylates was applied to create performance-advantaged pressure-sensitive adhesives (PSAs) using phenolic-rich bio-oil obtained from the reductive catalytic fractionation of poplar wood. The use of actual lignin-derived monomers as the starting material was an important step because it underscored that nanostructure-forming, multiblock polymers could be readily made despite the complexity of real lignin deconstruction products. This work also highlighted that lignin-based phenolics could be used to make colorless/odorless PSAs, without complex separations/purifications, and still perform as well as commercial adhesives. Third, an intensified reductive catalytic deconstruction (RCD) process was developed to deconstruct lignin at ambient conditions, and the deconstructed products were successfully employed in 3D printing. The reactive distillation-RCD process operated at ambient pressure using a low-volatility and biobased solvent (glycerin) as a hydrogen donor, which reduced capital/operating costs, energy use, and safety hazards associated with conventional RCD. Technoeconomic analysis showed that such optimization could lead to a 60% reduction in cost to make the PSAs described above. Fourth, lignin-derivable bisguaiacols/bissyringols were explored as potential alternatives to petroleum-derived bisphenol A (BPA) in diamine-cured epoxy resins. A distinguishing feature of the lignin monomers (vs. BPA/bisphenol F [BPF]) was the presence of methoxy groups on the aromatic rings, and these methoxy moieties enabled tuning of application-specific properties, such as Tg, degradation temperature (Td), and glassy storage modulus (E′), to achieve improved processing and performance. The lignin-derivable thermosets exhibited Tgs above 100 °C, Tds above 300 °C, and E′s above 2 GPa, all values that were comparable to those of BPA-/BPF-based analogues. Moreover, the methoxy groups on these lignin-derivable compounds sterically hindered hormone receptor binding and could mitigate many of the toxicity concerns associated with BPA/BPF. This Account concludes with suggestions on future research needed to advance lignin-derived materials as sustainable and performance-advantaged alternatives by leveraging recycling/upcycling strategies and scaling-up/commercializing biomass waste.Item A nonequilibrium statistical mechanics derivation of the hydrodynamic equations of simple fluids using a noncanonical form of the Poisson bracket(Physics of Fluids, 2024-10-07) Edwards, Brian J.; Beris, Antony N.The continuum level hydrodynamic equations of a simple fluid were derived by Irving and Kirkwood directly from discrete particle dynamics using statistical mechanics almost 75 years ago. Their elegant derivation demonstrated the fundamental molecular basis of macroscopic fluid flow and culminated in molecular expressions for the stress tensor and heat current density that have since been employed in countless molecular simulations to date. In this article, an alternative derivation is presented, which leads to more general expressions for the fundamental transport relationships and which arrives at them in a more straightforward chain of consistency that ensues directly from the Principle of Least Action. The main point of departure from the Irving–Kirkwood derivation is the application of a transformation mapping of the total momentum of each individual particle onto the sum of its peculiar momentum and its momentum relative to the local velocity field. This mapping provides a phase-space distribution function applicable in the space of particle positions and peculiar momentum, from which a noncanonical Poisson bracket can be derived in terms of the same set of microscopic variables. For a given dynamic variable, expressed in terms of particle positions and peculiar momenta, the expectation value of the noncanonical Poisson bracket of the dynamic variable is shown to correspond to the evolution equation of the expectation value of the dynamic variable. This allows for a direct derivation of all macroscopic density evolution equations (mass, momentum, and energy density fields) using a systematic procedure free of assumptions concerning the macroscopic state of the system. Furthermore, an explicit expression of the time evolution of the entropy density at the hydrodynamic level is derived following the same procedure. Finally, in the limit of short-range interparticle interactions, a molecular-based expression for the local stress tensor as properly defined from continuum mechanics is developed at the hydrodynamic level that elucidates the continuum mechanics connection of the general stress expression of Irving and Kirkwood.Item Increased hydrophilicity of lignin-derivable vs. bisphenol-based polysulfones for potential water filtration applications(RSC Sustainability, 2024-09-18) Mahajan, Jignesh S.; Shokrollahzadeh Behbahani, Hoda; Green, Matthew D.; Korley, LaShanda T. J.; Epps, Thomas H., IIIThe functionality inherent in lignin-derivable aromatics (e.g., polar methoxy groups) can provide a potential opportunity to improve the hydrophilicity of polysulfones (PSfs) without the need for the additional processing steps and harsh reagents/conditions that are typically used in conventional PSf modifications. As determined herein, lignin-derivable PSfs without any post-polymerization modification exhibited higher hydrophilicity than comparable petroleum-based PSfs (commercial/laboratory-synthesized) and also demonstrated similar hydrophilicity to functionalized BPA-PSfs reported in the literature. Importantly, the lignin-derivable PSfs displayed improved thermal properties relative to functionalized BPA-PSfs in the literature, and the thermal properties of these bio-derivable PSfs were close to those of common non-functionalized PSfs. In particular, the glass transition temperature (Tg) and degradation temperature of 5% weight loss (Td5%) of lignin-derivable PSfs (Tg ∼165–170 °C, Td5% ∼400–425 °C) were significantly higher than those of typical functionalized BPA-PSfs in the literature (Tg ∼110–160 °C, Td5% ∼240–260 °C) and close to those of unmodified, commercial/laboratory-synthesized BPA-/bisphenol F-PSfs (Tg ∼180–185 °C, Td5% ∼420–510 °C). Sustainability spotlight Commercial bisphenol A-polysulfones (BPA-PSfs) are hydrophobic in nature, and post-polymerization modification is often required to increase the hydrophilicity of commercial PSfs for water filtration applications. Such PSf modification adds extra processing steps and often requires harsh reaction conditions/reagents, and these extra functionalization steps also have a detrimental effect on application-specific thermal properties. Herein, bio-derivable PSfs were synthesized using potentially safer, lignin-derivable bisguaiacols. Notably, the lignin-derivable PSfs, without any post-polymerization modification, demonstrated similar hydrophilicity to functionalized BPA-PSfs reported in the literature, and they also exhibited improved thermal properties relative to functionalized BPA-PSfs. Moreover, the thermal properties of bio-derivable PSfs remained close to those of commercial BPA-PSfs. Overall, this work is aligned with the UN's Sustainable Development Goal 12 (responsible consumption and production of chemicals).Item Tracking Chain Populations and Branching Structure during Polyethylene Deconstruction Processes(ACS Central Science, 2024-08-21) Balzer, Alex H.; Hinton, Zachary R.; Vance, Brandon C.; Vlachos, Dionisios G.; Korley, LaShanda T. J.; Epps, Thomas H., IIICatalytic deconstruction has emerged as a promising solution to valorize polyethylene (PE) waste into valuable products, such as oils, fuels, surfactants, and lubricants. Unfortunately, commercialization has been hampered by inadequate optimization of PE deconstruction due to an inability to either truly characterize the polymer transformations or adjust catalytic conditions to match the ever-evolving product distribution and associated property changes. To address these challenges, a detailed analysis of molar mass distributions and thermal characterization was developed herein and applied to low-density polyethylene (LDPE) deconstruction to enable more thorough identification of polymer chain characteristics within the solids (e.g., changes in molar mass or branching structure). For example, LDPE hydrocracking exhibited comparable rates of polymer chain isomerization and C–C bond scission, and the solids generated possessed a broadened molar mass distribution with a disappearance of a significant fraction of highly linear segments, indicating polymer-structure-dependent interactions with the catalyst. Solids analysis from pyrolysis yielded starkly different results, as the resulting solids were devoid of unreacted polymer chains and had a narrowed molar mass distribution even at short times (e.g., 0.2 h). By tracking the polymeric deconstruction behavior as a function of reaction type, time, and catalyst design, we mapped critical pathways toward PE valorization. Synopsis A comprehensive approach to track polymer chain evolution during deconstruction was developed and revealed the influence of deconstruction method and polymer architecture on product distributions.Item Lignin-derivable, thermoplastic, non-isocyanate polyurethanes with increased hydrogen-bonding content and toughness vs. petroleum-derived analogues(Materials Advances, 2024-04-02) Mahajan, Jignesh S.; Hinton, Zachary R.; Nombera Bueno, Eduardo; Epps, Thomas H. III; Korley, LaShanda T. J.The functionality inherent in lignin-derivable bisguaiacols/bissyringols can improve the processability and performance of the resulting polymers. Herein, non-isocyanate polyurethanes (NIPUs) were synthesized from bisguaiacols/bissyringols with varying degrees of methoxy substitution and differing bridging groups. Notably, the presence of increasing numbers of methoxy groups (0, 2, and 4) in bisphenol F (BPF)-, bisguaiacol F (BGF)-, and bissyringol F (BSF)-NIPUs led to higher percentages of hydrogen-bonded –OH/–NH groups (i.e., ∼65%, ∼85%, ∼95%, respectively). Increased hydrogen bonding between chains improved the elongation-at-break (εbreak) and toughness of lignin-derivable NIPUs over their petroleum counterparts without a reduction in Young's moduli and tensile strengths. For example, BSF-NIPU exhibited the highest εbreak ∼210% and toughness ∼62 MJ m−3, followed by BGF-NIPU (εbreak ∼185% and toughness ∼58 MJ m−3), and then BPF-NIPU (εbreak ∼140% and toughness ∼42 MJ m−3). Similar trends were found in the dimethyl-substituted analogues, particularly for the bisphenol A-NIPU and bisguaiacol A-NIPU. Importantly, the melt rheology of the lignin-derivable NIPUs was comparable to that of the petroleum-derived analogues, with a slightly lower viscosity (i.e., improved melt flow) for the bio-derivable NIPUs. These findings suggested that the added functionalities (methoxy groups) derived from lignin precursors improved thermomechanical stability while also offering increased processability. Altogether, the structure–property-processing relationships described in this work can help facilitate the development of sustainable, performance-advantaged polymers.Item A polydisperse model for thixotropic elasto-viscoplastic suspensions of aggregating particles using population balances(AIChE Journal, 2023-09-18) Jariwala, Soham; Song, Rong; Hipp, Julie B.; Diemer, R. Bertrum; Wagner, Norman J.; Beris, Antony N.An improved population balance-based rheological constitutive framework for polydisperse aggregating suspensions is derived by incorporating detailed models for orthokinetic and perikinetic aggregation and shear breakage processes. The framework accounts for critical properties such as dynamic arrest, viscoelasticity, kinematic hardening, thixotropy, and yield stress to generate a full range of thixotropic elasto-viscoplastic (TEVP) response. Additionally, the model is thermodynamically consistent because the dynamics and timescales are completely determined by internal structural and kinetic variables. The model connects the rheological response to the structural descriptors such as the size distribution of agglomerates, mean sizes, fractal dimension, and agglomerate volume fraction. Predictions are compared against a wide range of shear rheology measurements data for model thixotropic suspensions of fumed silica and carbon black, including large amplitude oscillatory shear (LAOS), as well as ultra-small angle neutron scattering under steady shear (Rheo-uSANS).Item Unlocking Circularity Through the Chemical Recycling and Upcycling of Lignin-Derivable Polymethacrylates(Macromolecules, 2023-11-22) Christoff-Tempesta, Ty; O’Dea, Robert M.; Epps, Thomas H. IIIThe synthesis of polymers from lignin-derivable compounds can replace petrochemical building blocks with a renewable feedstock. However, the end-of-life management of bioderivable, nonbiodegradable polymers remains an outstanding challenge. Herein, the chemical recycling and upcycling of two higher-glass-transition temperature (>100 °C), lignin-derivable polymethacrylates, poly(syringyl methacrylate) (PSM) and poly(guaiacyl methacrylate) (PGM), is reported. Neat PSM and PGM were thermally depolymerized to quantitative conversions, producing their constituent monomers at high yields and purity. The deconstruction atmosphere influenced the depolymerization reaction order, and depolymerization was thermodynamically favored in air over N2. Further, monomer bulkiness and volatility impacted depolymerization activation energies. Notably, bulk depolymerization of PSM and PGM was performed without solvent or catalyst to high polymer conversions (89–90 wt %) and monomer yields (86–90 mol %) without byproduct formation. The resultant monomers were then upcycled to narrow-dispersity polymers and phase-separated block polymers. The findings herein offer a pathway to material circularity for higher-performance, lignin-derivable polymethacrylates.Item A Life Cycle Greenhouse Gas Model of a Yellow Poplar Forest Residue Reductive Catalytic Fractionation Biorefinery(Environmental Engineering Science, 2022-09-13) Luo, Yuqing; O’Dea, Robert M.; Gupta, Yagya; Chang, Jeffrey; Sadula, Sunitha; Soh, Li Pei; Robbins, Allison M.; Levia, Delphis F.; Vlachos, Dionisios G.; Epps, Thomas H. III; Ierapetritou, MarianthiThe incentive to reduce greenhouse gas (GHG) emissions has motivated the development of lignocellulosic biomass conversion technologies, especially those associated with the carbohydrate fraction. However, improving the overall biomass valorization necessitates using lignin and understanding the impact of different tree parts (leaves, bark, twigs/branchlets) on the deconstruction of lignin, cellulose, and hemicellulose toward value-added products. In this work, we explore the production of chemicals from a yellow poplar-based integrated biorefinery. Yellow poplar (Liriodendron tulipifera L.) is an ideal candidate as a second-generation biomass feedstock, given that it is relatively widespread in the eastern United States. Herein, we evaluate and compare how the different proportions of cellulose, hemicellulose (xylan), and lignin among leaves, bark, and twigs/branchlets of yellow poplar, both individually and as a composite mix, influence the life-cycle GHG model of a yellow poplar biorefinery. For example, the processing GHG emissions were reduced by 1,110 kg carbon dioxide (CO2)-eq, 654 kg CO2-eq, and 849 kg CO2-eq per metric ton of twigs/branchlets, leaves, and bark, respectively. Finally, a sensitivity analysis illustrates the robustness of this biorefinery to uncertainties of the feedstock xylan/glucan ratio and carbon content.Item Estrogenic activity of lignin-derivable alternatives to bisphenol A assessed via molecular docking simulations(RSC Advances, 2021-06-23) Amitrano, Alice; Mahajan, Jignesh S.; Korley, LaShanda T. J.; Epps, Thomas H. IIILignin-derivable bisphenols are potential alternatives to bisphenol A (BPA), a suspected endocrine disruptor; however, a greater understanding of structure–activity relationships (SARs) associated with such lignin-derivable building blocks is necessary to move replacement efforts forward. This study focuses on the prediction of bisphenol estrogenic activity (EA) to inform the design of potentially safer BPA alternatives. To achieve this goal, the binding affinities to estrogen receptor alpha (ERα) of lignin-derivable bisphenols were calculated via molecular docking simulations and correlated to median effective concentration (EC50) values using an empirical correlation curve created from known EC50 values and binding affinities of commercial (bis)phenols. Based on the correlation curve, lignin-derivable bisphenols with binding affinities weaker than ∼−6.0 kcal mol−1 were expected to exhibit no EA, and further analysis suggested that having two methoxy groups on an aromatic ring of the bio-derivable bisphenol was largely responsible for the reduction in binding to ERα. Such dimethoxy aromatics are readily sourced from the depolymerization of hardwood biomass. Additionally, bulkier substituents on the bridging carbon of lignin-bisphenols, like diethyl or dimethoxy, were shown to weaken binding to ERα. And, as the bio-derivable aromatics maintain major structural similarities to BPA, the resultant polymeric materials should possess comparable/equivalent thermal (e.g., glass transition temperatures, thermal decomposition temperatures) and mechanical (e.g., tensile strength, modulus) properties to those of polymers derived from BPA. Hence, the SARs established in this work can facilitate the development of sustainable polymers that maintain the performance of existing BPA-based materials while simultaneously reducing estrogenic potential.