Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session G15: Physics in Polymer Recycling and Upcycling IFocus
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Sponsoring Units: DPOLY Chair: Wenlin Zhang, Dartmouth College Room: Room 207 |
Tuesday, March 7, 2023 11:30AM - 12:06PM |
G15.00001: Upcycling of Polyolefins Invited Speaker: Ramanan Krishnamoorti Upcycling of polyolefins through chemical methods offers a promising path to a sustainable plastic waste solution. Low temperature thermal pyrolysis of polyolefins has been tuned to selectively yield a solid residue with controlled molecular weight. High temperature pyrolysis yields low molecular weight polymers with functional terminal vinylidene end groups; however, the resulting functionalization from mild degradation is low. We have identified the coupling of mechanical forces, in our case sonochemistry, in tandem with mild degradation result in increased substitution of functional end groups and control of polymer molecular weight and dispersity. We further explore post-functionalization of degraded polyolefin residue with useful chemical groups such as maleic anhydride or carboxylic acid groups. Here, we describe the independent control over molecular weight and end group functionality achieved by the coupled sonochemistry and low temperature pyrolysis. This functionalized polyolefin can be used as a unit for polymerizations of other useful materials and serves as a foundation for the design of a new class of sustainable polymers. |
Tuesday, March 7, 2023 12:06PM - 12:18PM |
G15.00002: Upcycling Commodity Plastics toward Reversible Smart Responsive Materials through Dynamic Crosslinking Md Anisur Rahman, Alexei P Sokolov, Tomonori Saito Plastics have become an indispensable part of our daily life, but the management of their waste presents a global challenge. Plastic upcycling can be an alternative way to address challenges related to waste plastics and property degradation of current recycling methods. Adaptive polymeric materials through dynamic (reversible) bonds have the potential unique properties to create various revolutionary future technologies. Dynamic bonds can selectively undergo reversible bond breaking and reformation in specific conditions that enable structural rearrangements in polymer networks, strongly improve the toughness, and provide recyclability, self-heal ability, as well as smart response behavior. In contrast, permanently crosslinked polymers (e.g. thermosets), which comprise 15-20% of all produced polymers, are not able to show those dynamic features due to their unpliable nature. Incorporating dynamic covalent bonds into a crosslinked polymeric network provides outstanding mechanical properties due to their crosslinked nature and malleability, thus repeated recyclability. In a recent study we upcycled a commodity thermoplastic elastomer, polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) toward higher value materials. The incorporation of dynamic covalent and noncovalent bonds into the polymer and the interface enable mechanically robust, processable, and smart responsive thermoset materials, where bonding and debonding at the interfaces dictate smart response behavior. Crosslinking with fast-exchangeable boronic ester showed enhanced malleability, reprocessability, and healability upon heating. This crosslinked polymer also exhibits excellent chemical, and thermal stability, and reversible smart responses such as stretch-induced reversible transparency. This presentation will discuss the design, synthesis, recycling, and mechanistic investigation of stretch-induced reversible smart responses of SEBS-based-novel dynamic crosslinked polymers. |
Tuesday, March 7, 2023 12:18PM - 12:30PM |
G15.00003: Vitrimers from Unentangled Polypropylene Zhe Qiang, Mikaela Sadri, Shiwang Cheng Polypropylene (PP) is extremely ubiquitous and widely used in numerous applications, such as single-use plastic bags, food packaging, automotive, and medical supplies. For single-stream PP waste, mechanical recycling allows their reuse into new products. However, after multiple reprocessing events PP often exhibits very low viscosity and brittle mechanical properties, as a result of a large number of chain scission events. The recycled use of low molecular weight PP waste toward circular economy is a great challenge. This talk will discuss the ability to upcycle these water materials to vitrimers, allowing their further use with significantly improved thermal and mechanical properties. We will focus PP resins that contain maleic anhydride (MA) functional groups, which can be dynamically crosslinked with epoxide-functionalized polyethylene glycol (PEG) molecules through epoxy-anhydride curing chemistry with the presence of Zn-based catalyst. The impact of crosslinker chemistry and molecular weight on the resulting vitrimer properties will be discussed, including degree of crystallinity, crosslinking density, and mechanical performance. Building upon these results, we further investigate the use of vitrimers from low-molecular weight PP as post-consumable recyclates (PCR), blended with virgin PP plastics for product manufacturing, following state legislatures which mandate PCR content. |
Tuesday, March 7, 2023 12:30PM - 12:42PM |
G15.00004: Upcycling Polyethylene to Reprocessable Dynamic Covalent Networks via Free-Radical Grafting of Dialkylamino Disulfide Bonds Logan Fenimore, Boran Chen, Mohammed A Bin Rusayyis, John M Torkelson Current methods for recycling polyolefins result in property degradation over time and downcycling to lower value use. Thermoplastic polyethylene (PE) can be permanently cross-linked into thermoset PE, but permanent cross-links prevent the thermosets from being melt-state reprocessed. An emerging avenue to mitigate such sustainability issues involves enriching waste plastic with dynamic covalent bonds as cross-links. By modifying thermoplastics with dynamic covalent cross-links, the resulting covalent adaptable networks (CANs) exhibit robust mechanical properties characteristic of thermosets yet maintain reprocessability. Using melt-state, free-radical reactive processing, we upcycled polyethylene (PE) into covalent adaptable networks (CANs) using a dynamic cross-linker containing dialkylamino disulfide bonds. Importantly, the PE CANs recover their thermomechanical properties after reprocessing. We demonstrated that creep behavior of the PE CANs above their melt transition is dominated by the exclusively dissociative reversible dynamic chemistry of the cross-linker. We also demonstrated the utility of the high activation energy of the dissociative dynamic chemistry for predicting creep in CANs with different viscoelastic behavior. |
Tuesday, March 7, 2023 12:42PM - 12:54PM |
G15.00005: Effect of Polymer Species and Reactive Processing Conditions on Upcycling of Thermoplastic Polyolefins into Reprocessable Polymer Networks Boran Chen, Logan Fenimore, Stephanie Barbon, Hayley Brown, Evelyn Auyeung, Colin Li Pi Shan, John M Torkelson Permanent chemical cross-linking of polyolefins is practiced commercially at major scales. Cross-linked polyolefins made from thermoplastics exhibit upcycling of properties, e.g., improved impact strength. However, thermosets with permanent cross-links cannot be mechanically recycled because the cross-links prevent melt flow. In related work, we upcycled thermoplastic polyethylene into covalent adaptable networks (CANs) with dynamic covalent dialkylamino disulfide cross-links using a melt-state, free-radical grafting method. Here, we extend our method to a series of commodity polyolefins, with resulting CANs being recyclable multiple times without loss of cross-link density. Our method's utility is a function of repeat unit structure, chain architecture, and melt flow index, the latter related to molecular weight (MW). Most tested polyolefins were upcycled into reprocessable CANs, with polypropylene and very low MW polymer being exceptions. We also studied gel fraction and dynamic cross-linking characteristics as functions of initiator and dynamic cross-linker concentrations and processing temperature. Understanding these effects on dynamic cross-linking via reactive processing with a vinyl cross-linker can be an important step in improving the sustainability of plastics. |
Tuesday, March 7, 2023 12:54PM - 1:06PM |
G15.00006: In Situ X-Ray Scattering Methods for the Characterization of Polymers During Recycling Sarah A Hesse, Nicholas A Rorrer, SriBala Gorugantu, Bonnie L Buss, Ana R. C Morais, David G Brandner, Scott R Nicholson, Avantika Singh, Bryon S Donohoe, Jason S DesVeaux, Taylor Uekert, Megan Browning, Jennifer Quigley, Anjani K Maurya, Julia B Curley, Joel Miscall, Christopher J Takacs, Alberta C Carpenter, Robert M Baldwin, Gregg T Beckham, Linda J Broadbelt, Christopher J Tassone, Robert D Allen A fundmanetal understanding of the macromolecular interactions with the catalyst, and how they evolve over the course of the deconstruction is important for designing efficient deconstruction chemistries. We investigated Volatile Catalyst (VolCat), a process for deconstructing polyethylene terephthalate (PET), a semi-crystalline polymer with crystalline regions embedded in an amorphous matrix. Under reaction conditions, PET is in the solid state and there is an interplay between the morphology and the deconstruction kinetics. We monitored the VolCat reaction kinetics by characterizing the structural evolution (crystallinity, polymer conformation) of reactants and products over the course of the reaction without altering the sample or taking aliquots. |
Tuesday, March 7, 2023 1:06PM - 1:18PM |
G15.00007: Connecting Polymerization Physics to Macromolecular Deconstruction Product Distributions and Process Kinetics Zachary R Hinton, LaShanda T Korley, Thomas H Epps Approaches that valorize plastics waste have continued to emerge over recent years. One common strategy is deconstruction, whereby polymers are degraded into smaller molecules by various reaction pathways. The dynamics of these complex systems of molecules, with evolving molecular weights and molecular weight distributions that span the range from monomer up to commodity polymer, are a strong function of process technology. Hence, efficient development of plastics deconstruction technologies will benefit from simple and descriptive models that link process parameters (e.g., reaction time) to physical properties (e.g., kinetic rate, solubility) and product distribution. In this work, we demonstrate a simple mathematical model containing modular components that describes the physical phenomena apparent in experimental results—for instance, a partitioning module was developed to simulate poor mixing between deconstruction products and the input polymer. We use this model in combination with well-described polymerization kinetics and experimentally measured molecular weight distributions to understand catalytic deconstruction more quantitatively. As one example, we highlight the role of polyolefin structure (i.e., branch content) on hydrotreatment product composition. This work demonstrates the ability to parameterize plastics valorization strategies, enabling detailed interpretation of experiments and informing the development of comprehensive models, and it could lead to the potential optimization of industrial deconstruction processes. |
Tuesday, March 7, 2023 1:18PM - 1:30PM |
G15.00008: Thermophysical Properties of Short-Chain Branched Polyethylene Maria Ley-Flores, Riccardo Alessandri, Juan J De Pablo Polyethylene constitutes the major fraction of single-use plastics production. Current recycling efforts focus on mechanical recycling of plastics, often leading to performance losses. Recently, hydrocracking has come up as an attractive chemical recycling technology due to the availability of existing facilities that could accelerate industrial-scale applications. However, an understanding of how linear and branched polyethylene chains behave under hydrocracking conditions and the effect of the cracked products in the dynamics of the melt is still lacking. |
Tuesday, March 7, 2023 1:30PM - 1:42PM |
G15.00009: Structure-Property Relations in Chemically Recyclable Poly(oligocyclobutane) Polymers from Acyclic Diene Metathesis Shawn Maguire, Emily C Davidson, Rodney Priestley, Cherish Nie, R. A Register, Callie W Zheng, Paul J Chirik Single-use plastics are ubiquitous in everyday life due to their low cost, durability, and convenience. However, when sorting, shredding, and melting plastics for reuse, property degradation arises due to chain scission or branching of the material. Materials capable of chemical reversibility back to the monomer form bypasses this limitation by theoretically allowing for closed-loop chemical recycling. Here, we investigate a new class of chemically recyclable polymers derived from butadiene, a commodity monomer. By chain-extending oligocyclobutane building blocks, polymers of tailored molecular weight and architecture are synthesized. Using a combination of thermomechanical analysis techniques, the thermo-oxidative stability, crystalline behavior, and mechanical properties of the polymers are investigated as a function of molecular weight and compared to those of traditional commodity polymers. Exposure of the chain-extended polymers to the metal catalyst used originally for their synthesis results in depolymerization back to the oligocyclobutane building blocks. Importantly, subsequent polymerization-depolymerization cycles result in no discernible change in polymer properties. |
Tuesday, March 7, 2023 1:42PM - 1:54PM |
G15.00010: "Evolution of Chain Structure during the Glycolysis of Poly(ethylene terephthalate)" Shelby Watson, Mark D Dadmun, Shelby Watson Polyethylene Terephthalate (PET) is one of the most used commercial polymers and has the potential to be chemically recycled industrially. The industrial heterogeneous depolymerization of PET via glycolysis is often described as a surface reaction, where reaction rate is dependent on the available surface area of PET flakes. Moreover, the depolymerization is often pushed to formation of monomer, which requires extensive time and energy. Our research seeks to track the evolution of chain structure during the depolymerization process to test the presumption that the depolymerization is a surface reaction and to offer insight into the availability of intermediates in the depolymerization process. Our results show that the heterogenous reaction is governed by the diffusion of the glycol into the polymer, not the PET surface area. We will also present NMR and GPC data that documents the decrease in Mn with little loss in product yield, as well as DSC results that document the isolation of highly crystalline polymer mid depolymerization. This is consistent with the reaction of the glycol with inter-crystalline tie chains in the amorphous phase. Chain scission of tie chains lowers the dispersity of the depolymerized intermediates. This mechanism is also supported by the slow conversion of end groups to two alcohol groups. When all end groups of PET chains are converted to alcohol groups, the PET flakes break apart into highly crystalline and less disperse polymer. This understanding of the evolution of chain structure during the depolymerization process offers pathways to well characterized intermediates that can be used as feedstock for value added materials. |
Tuesday, March 7, 2023 1:54PM - 2:06PM |
G15.00011: Biobased, Non-isocyanate Polythiourethane (NIPTU) Networks: Reprocessability, Enhanced Performance by Inter-chain Disulfide Linkages and End-of-Life Monomer Recovery Yixuan Chen, Boran Chen, Nick Mielke, John M Torkelson Isocyanate-based polyurethanes (PUs) raise concerns about safety, sustainability, and the circular economy. Isocyanates are toxic, and their precursor, phosgene, was a chemical weapon in World War I. Commercial PUs are derived from fossil fuels, a limited resource. Research has yielded biobased PUs, but many biobased PUs are derived from food products needed to feed a hungry world. Most commercial PUs are cross-linked networks, with permanent cross-links preventing melt reprocessing and high-value reuse. Here, we present research on recyclable non-isocyanate polythiourethanes (NIPTUs) derived from non-food biobased sources, e.g., cashew nutshell liquid and glycerol. We address recyclability by designing reprocessable NIPTU networks, with cross-links consisting of dynamic covalent bonds, which yield full recovery of cross-link density and associated properties after multiple melt-recycling steps. We also show that inter-chain disulfide linkages provide NIPTU with enhanced mechanical properties. Finally, using transcarbamoylation dynamic chemistry, we developed a facile solvolysis approach to depolymerize NIPTU to pure monomer with 93% yield. Our work highlights the potential for robust, non-food biobased NIPTU with multiple routes for recyclability. |
Tuesday, March 7, 2023 2:06PM - 2:18PM |
G15.00012: Tunable Methacrylated Chitosan Hydrogels for Dynamic Loading Samuel Wallaert In recent years there has been a tremendous push to seek out more sustainable materials across nearly all fields. As such, materials that were previously classified as waste materials are being reexamined for new uses. Chitin and Chitosan are molecules typically found in the waste products of mushrooms and crustacean shells and demonstrate excellent mechanical properties with a reported Young’s moduli of 126.9 GPa and 191 GPa respectively. Additionally, the absence of acetyl groups in Chitosan allows for greater flexibility regarding chemical modification. In this study, we demonstrate a tunable enhancement of the mechanical properties of hydrogels formed from methacrylated Chitosan. We present a technique to contextualize hydrogel formation in consumer-accessible dynamic light processing 3D printers, with demonstrated resolution up to 50 µm. Curing time, degree of crosslinking, and encapsulating media for the gel have been modified to demonstrate the wide array of applications of this technology. The high versatility of this technology enables its application to a wide array of dynamic loading systems including but not limited to defense and body armor applications. |
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