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 K15: Physics in Polymer Recycling and Upcycling IIFocus
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Sponsoring Units: DPOLY Chair: Zhe Qiang, University of Southern Mississippi Room: Room 207 |
Tuesday, March 7, 2023 3:00PM - 3:36PM |
K15.00001: Break
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Tuesday, March 7, 2023 3:36PM - 3:48PM |
K15.00002: Towards Quantitative Structure-Property Relationships for Polymer Biodegradability Bradley D Olsen, Katharina Fransen, Sarah Av-Ron Group contribution theories and more recent machine learning methods provide powerful methods to elucidate quantitative structure-property relationships (QSPR) by which the physical properties of polymers may be predicted based on their chemical structure. The increasing focus on sustainability has motivated a desire to incorporate end-of-life considerations into polymer design, necessitating QSPR for polymer biodegradation. However, the extremely limited data available has made this task difficult. Here, we report the synthesis of a large library of polyesters and polycarbonates and the development of a high-throughput biodegradation assay based on the classic clear zone assay. Using these methods, we were able to successfully screen over 640 polyesters for biodegradability, producing a large data set. Analyzing the data for chemical trends reveals key effects of chain length, ring structures, side groups, and heteroatom substitutions within the polyesters. We then applied both logistic regression and random forest classifiers to predict the biodegradation of polyesters, showing a predictive accuracy of up to 82%. Including information on molar mass and the physical state of the polymer did not improve predictions beyond those obtained with chemical structural information alone. |
Tuesday, March 7, 2023 3:48PM - 4:00PM |
K15.00003: Time-gated Raman spectroscopy for characterizing recovered plastics Anthony P Kotula, Sara Orski, Kayla Brignac, Jennifer Lynch, Bryan Heilala, Celeste Copay Raman spectroscopy is a powerful non-destructive tool for the identifying and characterizing polymers, but a major limitation of Raman spectroscopy using continuous wave excitation is that environmental weathering, dyes, and additives in the material can generate a strong fluorescence background that overwhelms the Raman signal. Here, we employ time-gated Raman spectroscopy to successfully reduce the fluorescence signal and measure Raman spectra of recovered plastics. Time-gating removes a significant amount of background signal from the Raman spectra such that the polymers and color additives can be identified using similar measurement times compared to continuous-wave Raman spectroscopy. Examples of this are shown for a small subset of samples recovered from Hawaiian marine environments and e-waste materials. Time-gated Raman spectroscopy can also be used to characterize samples that are black in color due to carbon-based additives that are challenging or impossible to characterize using conventional techniques. |
Tuesday, March 7, 2023 4:00PM - 4:12PM |
K15.00004: Photoinduced Phase Transition in Microstructured Ionic End-functionalized Polymer Blends Shuyi Xie, Rachel A Segalman, Kai-Chieh Yang, Kseniia Karnaukh, Javier Read de Alaniz Compatibilization of immiscible polymer blends is critical to increasing the fraction of industrial plastics that are recycled. We demonstrate that the simple functionalization of the chain ends of incompatible polymers with oppositely charged groups leads to electrostatically stabilized microdomains and suppressed macroscopic phase separation. A functionalized polydimethylsiloxane with a photochromic diarylethene end-group (PDMS-ω-DAE) is blended with a sulfonic acid end-functionalized polystyrene (PS-ω-SO3H). The proton transfer between the acid and base units in the melt state yields contact ion pairs that self-assemble into a cylindrical microstructure. Further, due to the light sensitivity of the DAE, irradiation of the blend triggers isomerization from the ring-opened (DAE-O) to the ring-closed (DAE-C) form. The more localized positive charge on DAE-C leads to stronger ionic bonds and induces a phase transition to a lamellar microstructure. |
Tuesday, March 7, 2023 4:12PM - 4:24PM |
K15.00005: Hydroxy Telechelic Polyethylene Additives as Compatibilizers for Mechanical Recycling Polyethylene Terephthalate/Polyethylene Mixed Waste Aristotle Zervoudakis Mechanical recycling takes plastic waste and melt reprocesses it into new products; however, this process relies on physical sorting methods that can often be imperfect, resulting in polymer blends that are brittle and unsuited for most applications. Mechanical properties can be recovered through the presence of premade or in situ formed block copolymers that can localize at polymer-polymer interfaces and “stitch” the two phases together. In this work, we provide new insight into the mechanisms that hold these “stitches” in place, specifically in cases where compatibilizers can form a loop in a homopolymer phase. We compatibilized blends of polyethylene terephthalate (PET) and polyethylene (PE) using hydroxy telechelic PE (HOPEOH) reactive additives that we believe undergo transesterification reactions with PET homopolymer to form PET-PE-PET triblock copolymers during melt mixing. We observed increased mechanical properties and decreased dispersed phase sizes at additive loadings of only 0.5 wt% for HOPEOH with molar masses ranging from 1-20 kg/mol, indicating the bulk critical entanglement molar mass of PE is unimportant. This goes against conventional wisdom regarding necessary features of compatibilizers demonstrated to date. Comparison to blends containing monohydroxy additives of the same molar mass show the need for reaction of both chain ends to form a loop in the PE phase that can trap PE homopolymer chains via a “hook and clasp” mechanism to anchor the formed compatibilizer in the PE phase. |
Tuesday, March 7, 2023 4:24PM - 4:36PM |
K15.00006: Compatibilization of HDPE and iPP blends with hydrogenated polybutadiene block copolymers Liyang Shen, Gabriela I Diaz, Christopher J Ellison, Frank S Bates Aiming at the global plastic waste crisis, we have investigated the performance of a series of polybutadiene (PB)-derived saturated hydrocarbon block copolymers for HDPE/iPP compatibilization. EX diblock and EXE triblock copolymers were prepared by anionic polymerization of butadiene followed by catalytic hydrogenation, where X refers to an iPP melt miscible poly(ethylene–ran-ethylethylene) random copolymer and E is hydrogenated 1,4-PB. Whereas blends of commercial HDPE (70%) and iPP (30%) exhibit a strain at break of ε = 10%, addition of just 1 wt% of a Mn = 2.2x105 g/mol EXE triblock during melt blending resulted in ε = 600%. This behavior is attributed to the threading of iPP chains through the X loops at the interfaces in the melt state, leading to topological constraints upon iPP crystallization, along with the cocrystallization of the E blocks with HDPE homopolymer. This “threading the needle” mechanism is supported by relatively poor ductility (ε = 30%) with comparable molecular weight EX diblock copolymer, which does not form X-block loops at the domain interfaces. This work exposes an economically viable approach to recycling polyethylene and polypropylene. |
Tuesday, March 7, 2023 4:36PM - 4:48PM |
K15.00007: Atomistic simulations and theory of composition-dependent crystal nucleation in polymer blends Wenlin Zhang, Lingyi Zou We apply united-atom molecular dynamics (MD) simulations to quantify the composition-dependent crystal nucleation in polymer blends. We blend high-density polyethylene oligomers (PE) with small amounts of impurity polymers. By quenching polymer melts to 300K, we allow polymer blends to undergo isothermal crystallization. We show that in strongly phase-separated blends, crystal nucleation occurs in the PE domain with a rate identical to that in pure samples. In well-mixed blends, however, impurity polymers with weak nematic interactions, such as isotactic polypropylene (iPP) and cis-1,4-polybutadiene, impede the formation of nematic precursors and result in a PE nucleation rate that decreases with increasing impurity volume fraction. To quantify the role of impurity polymers in nematic precursor formation, we employ a mean-field theory to compute the nucleation barrier of nematic order in polymer blends. We predict that a mismatch in nematic coupling parameters can drive the impurity polymers out of the critical nematic nucleus, and in turn, enhance the free energy barrier for nucleating nematic precursors. The theoretical prediction agrees well with the composition-dependent nucleation rates in our MD simulations. |
Tuesday, March 7, 2023 4:48PM - 5:00PM |
K15.00008: Block copolymer compatibilizers for improved polymer upcycling Robert J Ivancic, Debra J Audus Block copolymers increase the toughness of incompatible blends by stitching phase-separated polymer domains together. These materials could reduce the price of polymer upcycling by eliminating the need to sort mixed plastic waste. While experiments demonstrate that tetrablock copolymer compatibilizers increase incompatible blend toughness significantly, diblock copolymers do not. How do we optimize copolymer sequence to maximize blend toughness? Here, we investigate this question using coarse-grained molecular dynamics simulations in which we add various sequences of block copolymers to an incompatible polymer blend. We equilibrate, cool, and strain our simulations to failure in analogy to experiments. Our approach provides both rapid iteration of new compatibilizer sequences and access to microscopic data to reveal how toughness increases occur. This research will likely yield enhanced recycling techniques for a more sustainable future. |
Tuesday, March 7, 2023 5:00PM - 5:12PM |
K15.00009: Molecular Weight Determination of Polyolefin Deconstruction Products by Thermal Analysis Alex Balzer, Thomas H Epps, LaShanda T Korley Plastics are an indispensable class of materials found in countless consumer products. Yet, their growing use and limited recycling strategies have led to a rapid accumulation of plastics waste and devastating environmental impacts. Thus, efforts to improve the end-of-life strategies to address plastics pollution are expanding. Polyolefins, which comprise over half of new plastic production, can be chemically recycled into more valuable carbon feedstocks, such as oils and lubricants. This deconstruction process is not trivial and requires fundamental understanding of the physical principles that correlate to the molecular weights, molecular weight distributions, and architectures assigned to the vast array of polyolefin feedstocks. High temperature gel permeation chromatography is the standard approach to determine the molecular weight distribution of these products, but accessibility to this technique is a challenge. To address this accessibility gap, we propose a method to determine the molecular weight distribution of polyolefin deconstruction products using differential scanning calorimetry (DSC). The molecular weight decreases during polyolefin deconstruction correlates to a change in the melting temperature, leading to identification of molecular weight dependent chain lengths and enabling thermal fractionation. For example, longer polymer chains exhibit minimal melting point dependence, however, their entanglement and diffusion behavior reduce their crystallization kinetics, which can be identified using DSC. It is envisioned that expanding the accessibility of techniques to probe deconstruction products will enable tailored identification that, although not as precise as chromatographic techniques, is tolerant to a range of molecular weights, architectures, and additives. |
Tuesday, March 7, 2023 5:12PM - 5:24PM |
K15.00010: Tunable Functionalization and Upcycling of Polyolefins to Polyurethanes Ronard Herrera, Megan L Robertson, Ramanan Krishnamoorti By 2050 the accumulation of plastic waste is projected to reach 12,000 Mt, where 18% are recycled, 24% incinerated, and the remaining 58% are either landfilled or enters the natural environment (In the US, only 9% is recycled). The main contributors to this waste are polyolefins, which constitute roughly 45% of all plastic waste (76% at the U.S. level). Momentum has shifted towards looking for a solution for polyolefin waste and moving to a circular economy. Post-polymerization modification has shown promising results to upcycle polyolefins, removing the limitation of inertness, and improving the final physical properties of the material. Subsequently, this modified polyolefin can be repurposed in a wide variety of applications including polyurethanes, foams, coatings, and films, among others. In this work, polypropylene (PP) was functionalized and upcycled to polyurethanes. First, hydroxylated PP (PPOH) was synthesized through the hydroxylation of maleic anhydride-grafted PP. Then, the polyurethane (PU) was synthesized by the reaction of PPOH with a diisocyanate in solution and in the melt. Melt processing was enabled by using a blocked isocyanate that delayed the crosslinking reaction for easy processability. The presence of PU crosslinks and PP strands in the network were confirmed with spectroscopy. At a low level of maleation and hydroxylation, the PP thermal properties (glass transition, melting, and crystallization temperatures) were unaffected by functionalization, PP crystallization was still observed in the PU network that contained PP segments. |
Tuesday, March 7, 2023 5:24PM - 5:36PM |
K15.00011: Interfacial activity of hydrogenated polybutadiene block copolymers with HDPE and iPP Gabriela I Diaz, Liyang Shen, Christopher J Ellison, Frank S Bates Blending poly(ethylene) and poly(propylene) is an attractive recycling strategy. However, phase separation and poor interfacial strength result in inferior mechanical integrity. Several EX and EXE diblock and triblock copolymers were blended at 1 to 5 wt.% in mixtures of commercial HDPE and iPP, where X denotes an iPP melt-miscible poly(ethylene-ran-ethylethylene) random copolymer and E represents hydrogenated 1,4-poly(butadiene). Micelle formation in the homopolymers, and morphology in HDPE/iPP blends, was probed using atomic force microscopy. Localization of high molecular weight EXE at domain interfaces resulted in exceptional blend ductility, while lower molecular weight EXE, and all EX diblocks, produced mechanically inferior plastics. The associated interfacial adhesion was measured directly using PE/EX/iPP and PE/EXE/iPP trilayer peel tests, and the results correlated closely with the blend tensile toughness. These findings support an interfacial strengthening mechanism that combines co-crystallization of HDPE and the E blocks, thereby anchoring the amorphous X blocks, which are topologically entrained with semicrystalline iPP. |
Tuesday, March 7, 2023 5:36PM - 5:48PM |
K15.00012: Tunable Hydration Properties of Charge Modified Phytoglycogen Nanoparticles Carley Miki, Michael Grossutti, John R Dutcher Phytoglycogen (PG) is a natural and sustainable nanoparticle with unique physical properties that make it ideal for applications in personal care, nutrition, and biomedicine. To tailor the physical and chemical properties of PG to specific functions, the particles can be chemically modified. The covalent attachment of charged groups provides a means of tuning the properties of PG through the introduction of electrostatic interactions. We have investigated the effects of charge modification on the hydration properties of PG that is anionically modified by carboxymethylation (CM-PG). The addition of monovalent (Na+) and divalent (Ca2+) ions through counterion exchange was found to result in dramatic differences in the swelling and network water structuring in CM-PG thin films, as measured using ellipsometry and attenuated total reflectance infrared (ATR-IR) spectroscopy. These studies demonstrate how charge modification of PG nanoparticles can be used to tune their properties for enhanced applications. |
Tuesday, March 7, 2023 5:48PM - 6:00PM |
K15.00013: Reconfiguration of star block copolymer at homopolymer interfaces Zhan Chen, Christian Steinmetz, Mingqiu Hu, Jan-Michael Carrillo, Bryan Coughlin, Thomas P Russell Recycling and upcycling of plastic waste is important to address the rapid increase of plastic waste problems. Star block copolymers (s-BCPs), formed by joining multiple linear diblock copolymers into single junction point, can be unimolecularly dispersed in the corona-miscible polymer, regard less nature of core blocks, giving minimal effects on the mechanical properties of polymer matrix. Consequently, these s-BCPs are stealth until introduction of second phase that is core-miscible, where s-BCPs will first assemble at interface and then deliver the core blocks into second phase while remaining corona blocks in the first phase. We synthesized two molecular weight of 4 arm (deuterated) polystyrene-block-poly(2-vinyl pyridine) ((D)-S-b-V)4, where (D)-PS and P2VP forming core and corona block, respectively. By directly placing s-BCPs at interface between PS and P2VP homopolymer, neutron reflectometry showed that s-BCPs can efficiently broaden interfacial width between homopolymer interface, where smaller MW of s-BCPs has larger interfacial width, even though the asymmetric double cantilever beam (ADCB) tests showed that larger MW has stronger adhesion due to the formation of entanglement with homopolymer. Segmental density distribution of homopolymer and block was solved by selective contrast of deuterium, probing more information on interfacial assembly of s-BCPs. By first mixing s-BCPs with P2VP homopolymer and then adding PS, the interfacial width first increases, then decreases and further increases until reaching equilibrium over longer annealing times, indicating an unusual interfacial behavior of s-BCPs due to a reconfiguration. |
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