The future of plastics recycling Garcia, Jeannette M.; Robertson, Megan L.
Science (American Association for the Advancement of Science),
11/2017, Volume:
358, Issue:
6365
Journal Article
Peer reviewed
Chemical advances are increasing the proportion of polymer waste that can be recycled
The environmental consequences of plastic solid waste are visible in the ever-increasing levels of global plastic ...pollution both on land and in the oceans. But although there are important economic and environmental incentives for plastics recycling, end-of-life treatment options for plastic solid waste are in practice quite limited. Presorting of plastics before recycling is costly and time-intensive, recycling requires large amounts of energy and often leads to low-quality polymers, and current technologies cannot be applied to many polymeric materials. Recent research points the way toward chemical recycling methods with lower energy requirements, compatibilization of mixed plastic wastes to avoid the need for sorting, and expanding recycling technologies to traditionally nonrecyclable polymers.
The production of thermoset polymers is increasing globally owing to their advantageous properties, particularly when applied as composite materials. Though these materials are traditionally used in ...more durable, longer-lasting applications, ultimately, they become waste at the end of their usable lifetimes. Current recycling practices are not applicable to traditional thermoset waste, owing to their network structures and lack of processability. Recently, researchers have been developing thermoset polymers with the right functionalities to be chemically degraded under relatively benign conditions postuse, providing a route to future management of thermoset waste. This review presents thermosets containing hydrolytically or solvolytically cleavable bonds, such as esters and acetals. Hydrolysis and solvolysis mechanisms are discussed, and various factors that influence the degradation rates are examined. Degradable thermosets with impressive mechanical, thermal, and adhesion behavior are discussed, illustrating that the design of material end-of-life need not limit material performance.
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•Fatty acid-based triblock copolymers with a transient network were synthesized.•Acrylamide, a hydrogen bonding comonomer, was copolymerized into the midblock.•Mechanical properties ...were significantly improved due to the transient network.•Order-disorder transition temperature decreased, providing enhanced processability.•Negligible impact of acrylamide comonomer on triblock copolymer morphology.
Vegetable oils and their fatty acids are convenient sources for polymers due to their wide availability, ease of functionalization, and lack of toxicity; however, the long alkyl chains of the fatty acids have a large impact on the resulting polymer properties. Polymers with bulky constituents, such as the long alkyl side-chains of fatty acid-derived polymers, typically exhibit poor mechanical performance due to lack of entanglements. In this study, hydrogen bonding moieties were incorporated into the fatty acid-based midblock of a thermoplastic elastomeric triblock copolymer as a means to improve its mechanical behavior. Poly(styrene-b-(lauryl acrylate-co-acrylamide)-b-styrene), containing lauryl acrylate (a derivative of lauric acid) and the hydrogen bonding comonomer acrylamide in the midblock, was synthesized via reversible addition-fragmentation chain transfer polymerization. The chemical and physical properties of triblock copolymers of varying composition were explored. Quantitative FTIR analysis confirmed the formation of a transient network, which exhibited a reduction in crosslink density with increasing temperature, beneficial for high temperature melt processing. The triblock copolymers exhibited spherical morphologies lacking long-range order at room temperature, which were unaffected by the presence of acrylamide. Moreover, the order-disorder transition temperature reduced with increasing acrylamide content, due to a reduction in the Flory-Huggins interaction parameter. Importantly, incorporation of acrylamide into the midblock greatly improved both the tensile strength and strain at break. Incorporation of a transient network into the midblock is therefore an effective method of improving the mechanical properties of triblock copolymer-based thermoplastic elastomers containing bulky constituents.
The mechanical properties of two chemically distinct and complementary thermoset polymers were manipulated through development of thermoset blends. The thermoset blend system was composed of an ...anhydride-cured diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin, contributing high tensile strength and modulus, and polydicyclopentadiene (PDCPD), which has a higher toughness and impact strength as compared to other thermoset polymers. Ultra-small-angle and small-angle X-ray scattering analysis explored the morphology of concurrently cured thermoset blends, revealing a macroscopically phase separated system with a surface fractal structure across blended systems of varying composition. The epoxy resin rich and PDCPD rich phases exhibited distinct glass transitions (T g’s): the T g observed at higher temperature was associated with the epoxy resin rich phase and was largely unaffected by the presence of PDCPD, whereas the PDCPD rich phase T g systematically decreased with increasing epoxy resin content due to inhibition of dicyclopentadiene ring-opening metathesis polymerization. The mechanical properties of these phase-separated blends were in reasonable agreement with predictions by the rule of mixtures for the blend tensile strength, modulus, and fracture toughness. Scanning electron microscopy analysis of the tensile and fracture specimen fracture surfaces showed an increase in energy dissipation mechanisms, such as crazing, shear banding, and surface roughness, as the fraction of the more ductile component, PDPCD, increased. These results present a facile method to tune the mechanical properties of a toughened thermoset network, in which the high modulus and tensile strength of the epoxy resin can be largely retained at high epoxy resin content in the blend, while increasing the fracture toughness.
Mitochondrial fission is sustained through contact with several organelles, including the endoplasmic reticulum, lysosomes, and the actin cytoskeleton. Nagashima et al. (2020) now demonstrate that ...PI(4)P-containing Golgi-derived vesicles also modulate mitochondrial fission, driven by Arf1 and PI(4)KIIIβ activity, identifying a new organelle contact involved in maintaining mitochondrial homeostasis.
Mitochondrial fission is sustained through contact with several organelles, including the endoplasmic reticulum, lysosomes, and the actin cytoskeleton. Nagashima et al. now demonstrate that PI(4)P-containing Golgi-derived vesicles also modulate mitochondrial fission, driven by Arf1 and PI(4)KIIIβ activity, identifying a new organelle contact involved in maintaining mitochondrial homeostasis.
Utilization of biomass for commodity polymers has gained tremendous interest. We report a method to prepare high molecular weight renewable homopolymers and block copolymers derived from natural ...rosin. Monomers with high renewable content (70 wt %) were prepared via a simple esterification reaction between dehydroabietic alcohol and 5-exo-norbornenecarboxylic acid. Living and controlled polymerization of these monomers were achieved by ring-opening metathesis polymerization to obtain polymers with molecular weight up to ∼500 kg/mol. These homopolymers exhibit structure-dependent glass transition temperatures, excellent thermal stabilities, and thermoplastic properties. Chain entanglement molecular weight was determined via rheological assessments for such polymers with bulky side moieties. Using the living ROMP, dehydroabietic-based homopolymer was chain-extended with a soybean oil-derived norbornene monomer to yield triblock copolymers, which showed behaviors of thermoplastic elastomers.
A neglected mechanism for pressure-responsive color change is demonstrated using cellulose acetate composites prepared by direct (solvent) immersion annealing (DIA), with different loadings of ...activated charcoal filler. Namely, compressive plastic deformation of the translucent cellulose acetate leads to a decrease in the optical path length and a concomitant increase in the visibility of the opaque contrasting filler. Composites bearing 1–7 wt% activated charcoal exhibited a linear relationship between applied pressure and resulting pressure mark brightness in the range of 12–56 MPa. Comparison of pressure mark patterns with cross-sectional scanning electron microscopy (SEM) supports the importance of the porous morphology arising from DIA for the tuning of the pressure indicator sensitivity. A simple ball drop test is used to illustrate the robustness and utility of these indicators in optical impact assessment.
Polylactide (PLA), a commercially available thermoplastic derived from plant sugars, finds applications in consumer products, disposable packaging, and textiles, among others. The widespread ...application of this material is limited by its brittleness, as evidenced by low tensile elongation at break, impact strength, and fracture toughness. Herein, a multifunctional vegetable oil, acrylated epoxidized soybean oil (AESO), was investigated as a biodegradable, renewable additive to improve the toughness of PLA. AESO was found to be a highly reactive oil, providing a dispersed phase with tunable properties in which the acrylate groups underwent cross-linking at the elevated temperatures required for processing the blends. Additionally, the presence of hydroxyl groups on AESO provided two routes for compatibilization of PLA/AESO blends: (1) reactive compatibilization through the transesterification of AESO and PLA and (2) synthesis of a PLA star polymer with an AESO core. The morphological, thermal, and mechanical behaviors of PLA/oil blends were investigated, in which the dispersed oil phase consisted of AESO, soybean oil (SYBO), or a 50/50 mixture of AESO/SYBO. The oil additives were found to toughen the PLA matrix, with significant enhancements in the elongation at break and tensile toughness values, while maintaining the glass transition temperature of neat PLA. In particular, the blend containing PLA, AESO, SYBO, and the PLA star polymer was found to exhibit a uniform oil droplet size distribution with small average droplet size and interparticle distance, resulting in the greatest enhancements of PLA tensile properties with no observable plasticization.
Ring-opening bulk polymerization of l-lactide using N-2-hydroxyethylmaleimide (HEMI) as the initiator and tin(II) 2-ethylhexanoate as the catalyst produced a reactive end-functionalized ...poly(l-lactide) (HEMI-PLLA). Melt blends of HEMI-PLLA and conjugated soybean oil (CS) were prepared. HEMI-PLLA underwent a Diels−Alder reaction with the CS to high conversion, coupling the two immiscible components. Up to three HEMI-PLLA molecules reacted with one CS molecule to create products with varying architecture that acted as compatibilizers for the melt blend. Blends of HEMI-PLLA and 5 wt % CS resulted in a greater than 17-fold increase in elongation to break compared to PLLA homopolymer and more than doubled the elongation to break compared to a 5 wt % CS blend with unreactive PLLA. Analysis of the blend morphology indicated that the in situ formation of the compatibilizer decreased the CS droplet diameter compared to unreactive binary blends and that an optimum droplet diameter exists for toughening PLLA with CS.
We investigated the pH-dependent response of flat polyacid brushes of varying length and dispersity in the extended brush regime. Our model system consisted of poly(acrylic acid) brushes, which ...change from hydrophobic and neutral at low pH to hydrophilic and negatively charged at high pH, synthesized on silicon substrates using a grafting-from approach at constant grafting density. We observed three trends in the pH-response: first, the dry brush thickness increased as the pH was increased for brushes above a critical length, and this effect was magnified as the dispersity increased; second, the water contact angle measured at low pH was larger for brushes of greater dispersity; and third, brushes of sufficient dispersity exhibited hysteretic memory behavior in the pH-dependence of the contact angle, in which the contact angle upon increasing and decreasing pH differed. As a consequence, the pKa of the brushes measured upon increasing pH was consistently higher than that measured upon decreasing pH. The observed pH response is consistent with proposed changes in the conformation and charge distribution of the polyelectrolyte brushes that depend on the direction of pH change and the dispersity of the brushes.
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