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Semicrystalline poly(l-lactide) (PLLA) is a leading biosourced, compostable alternative to conventional plastics but lacks sufficient toughness for many applications. Chain alignment via uniaxial stretching may be used to toughen PLLA but often creates anisotropic materials that are tough in the machine direction (MD) but brittle in the transverse direction (TD). This work reports uniaxially stretched films of PLLA blended with 3 wt % poly(ethylene oxide)-block-poly(butylene oxide) (PEO-PBO), which exhibit as much as a 5-fold increase in toughness in the TD compared to similarly stretched neat PLLA films─and elucidates the impact of PEO–PBO particles on the relationship between stretching, crystallization behavior, and resultant mechanical properties. Faster stretching rates were correlated with higher yield stress and a greater degree of crystallite alignment in the PEO–PBO/PLLA blends. This trend highlights the synergistic relationship between crystallinity and chain alignment and suggests a competing mechanism of heterogeneous crystallite nucleation around PEO–PBO particles. Importantly, PEO–PBO/PLLA exhibited a TD elongation at break of 36%, five times greater than the value of similarly stretched neat PLLA and even greater than the corresponding MD value of either material. Taken together, these findings demonstrate that uniaxial stretching of PEO–PBO/PLLA blends produces biaxially tough films, with the fastest stretching conditions producing the greatest enhancement in TD toughness. 

Additive manufacturing, otherwise known as three-dimensional (3D) printing, is a rapidly growing technique that is increasingly used for the production of polymer products, resulting in an associated increase in plastic waste generation. Waste from a particular class of 3D-printing, known as vat photopolymerization, is of particular concern, as these materials are typically thermosets that cannot be recycled or reused. Here, we report a mechanical recycling process that uses cryomilling to generate a thermoset powder from photocured parts that can be recycled back into the neat liquid monomer resin. Mechanical recycling with three different materials is demonstrated: two commercial resins with characteristic brittle and elastic mechanical properties and a third model material formulated in-house. Studies using photocured films showed that up to 30 wt% of the model material could be recycled producing a toughness of 2.01 ± 0.55 MJ/m3, within error of neat analogues (1.65 ± 0.27 MJ/m3). Using dynamic mechanical analysis and atomic force microscopy-based infrared spectroscopy, it was determined that monomers diffuse into the recycled powder particles, creating interpenetrating networks upon ultraviolet (UV) exposure. This process mechanically adheres the particles to the matrix, preventing them from acting as failure sites under a tensile load. Finally, 3D-printing of the commercial brittle material with 10 wt% recycle content produced high quality parts that were visually similar. The maximum stress (46.7 ± 6.2 MPa) and strain at break (11.6 ± 2.3%) of 3D-printed parts with recycle content were within error the same as neat analogues (52.0 ± 1.7 MPa; 13.4 ± 1.8%). Overall, this work demonstrates mechanical recycling of photopolymerized thermosets and shows promise for the reuse of photopolymerized 3D-printing waste. 

Block copolymers at homopolymer interfaces are poised to play a critical role in the compatibilization of mixed plastic waste, an area of growing importance as the rate of plastic accumulation rapidly increases. Using molecular dynamics simulations of Kremer–Grest polymer chains, we have investigated how the number of blocks and block degree of polymerization in a linear multiblock copolymer impacts the interface thermodynamics of strongly segregated homopolymer blends, which is key to effective compatibilization. The second virial coefficient reveals that interface thermodynamics are more sensitive to block degree of polymerization than to the number of blocks. Moreover, we identify a strong correlation between surface pressure (reduction of interfacial tension) and the spatial uniformity of block junctions on the interface, yielding a morphological framework for interpreting the role of compatibilizer architecture (number of blocks) and block degree of polymerization. These results imply that, especially at high interfacial loading, the choice of architecture of a linear multiblock copolymer compatibilizing surfactant does not greatly affect the modification of interfacial tension. 

Simultaneous ring-opening copolymerization is a powerful strategy for the synthesis of highly functional copolymers from different types of cyclic monomers. Although copolymers are essential to the plastics industry, environmental concerns associated with current fossil-fuel-based synthetic polymers have led to an increasing interest in the use of renewable feedstock for polymer synthesis. Herein, we report a scalable synthetic platform to afford unique polysaccharides with different pendant functional groups from biomass-derived levoglucosan and ε-caprolactone via cationic ring-opening copolymerization (cROCOP). Biocompatible and recyclable bismuth triflate was identified as the optimal catalyst for cROCOP of levoglucosan. Copolymers from tribenzyl levoglucosan and ε-caprolactone, as well as from tribenzyl and triallyl levoglucosan, were successfully synthesized. The tribenzyl levoglucosan monomer composition ranged from 16% to 64% in the copolymers with ε-caprolactone and 22% to 79% in the copolymers with triallyl levoglucosan. The allylic levoglucosan copolymer can be utilized as a renewably derived scaffold to modify copolymer properties and create other polymer architectures via postpolymerization modification. Monomer reactivity ratios were determined to investigate the copolymer microstructure, indicating that levoglucosan-based copolymers have a gradient architecture. Additionally, we demonstrated that the copolymer glass transition temperature (Tg, ranging from −44.3 to 33.8 °C), thermal stability, and crystallization behavior could be tuned based on the copolymer composition. Overall, this work underscores the utility of levoglucosan as a bioderived feedstock for the development of functional sugar-based copolymers with applications ranging from sustainable materials to biomaterials. 

Management of the plastic industry is a momentous challenge, one that pits enormous societal benefits against an accumulating reservoir of nearly indestructible waste. A promising strategy for recycling polyethylene (PE) and isotactic polypropylene ( i PP), constituting roughly half the plastic produced annually worldwide, is melt blending for reformulation into useful products. Unfortunately, such blends are generally brittle and useless due to phase separation and mechanically weak domain interfaces. Recent studies have shown that addition of small amounts of semicrystalline PE- i PP block copolymers (ca. 1 wt%) to mixtures of these polyolefins results in ductility comparable to the pure materials. However, current methods for producing such additives rely on expensive reagents, prohibitively impacting the cost of recycling these inexpensive commodity plastics. Here, we describe an alternative strategy that exploits anionic polymerization of butadiene into block copolymers, with subsequent catalytic hydrogenation, yielding E and X blocks that are individually melt miscible with PE and i PP, where E and X are poly(ethylene- ran -ethylethylene) random copolymers with 6 wt% and 90 wt% ethylethylene repeat units, respectively. Cooling melt blended mixtures of PE and i PP containing 1 wt% of the triblock copolymer EXE of appropriate molecular weight, results in mechanical properties competitive with the component plastics. Blend toughness is obtained through interfacial topological entanglements of the amorphous X polymer and semicrystalline i PP, along with anchoring of the E blocks through cocrystallization with the PE homopolymer. Significantly, EXE can be inexpensively produced using currently practiced industrial scale polymerization methods, offering a practical approach to recycling the world’s top two plastics.