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  1. Polymer blend compatibilization is an attractive solution for mechanical recycling of mixed plastic waste because it can result in tough blends. In this work, hydroxy-telechelic polyethylene (HOPEOH) reactive additives were used to compatibilize blends of polyethylene terephthalate (PET) and linear low-density polyethylene (LLDPE). HOPEOH additives were synthesized with molar masses of 1–20 kg/mol by ring-opening metathesis polymerization of cyclooctene followed by catalytic hydrogenation. Melt-compounded blends containing 0.5 wt % HOPEOH displayed reduced dispersed phase LLDPE particle sizes with ductilities comparable to virgin PET and almost seven times greater than neat blends, regardless of additive molar mass. In contrast, analogous blends containing monohydroxy PE additives of comparable molar masses did not result in compatibilization even at 2 wt % loading. The results strongly suggest that both hydroxy ends of HOPEOH undergo transesterification reactions during melt mixing with PET to form predominantly PET–PE–PET triblock copolymers at the interface of the dispersed and matrix phases. We hypothesize that the triblock copolymer compatibilizers localized at the interface form trapped entanglements of the PE midblocks with nearby LLDPE homopolymer chains by a hook-and-clasp mechanism. Finally, HOPEOH compounds were able to efficiently compatibilize blends derived solely from postconsumer PET and PE bottles and film, suggesting their industrial applicability. 
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  2. Chain orientation, a natural consequence of polymer film processing, often leads to enhanced mechanical properties parallel to the machine extrusion direction (MD), while leaving the properties in the transverse direction (TD) unaffected or diminished, as compared to the unoriented material. Here, we report that mixing poly(ethylene oxide)-block-poly(butylene oxide) (PEO-PBO) diblock copolymer that forms dispersed particles in an amorphous polylactide (PLA) matrix produces uniaxially stretched blend films with enhanced toughness in both the MD and TD. Small-angle X-ray scattering experiments and visual observations revealed that the dominant deformation mechanism for blend films transitions from crazing to shear yielding in the MD as the stretching ratio increases, while crazing is the primary deformation mechanism in the TD at all stretching ratios investigated. As the films age at room temperature, crazing becomes more prevalent in the MD without compromising the improved toughness. The stretched blend films were susceptible to some degree of mechanical aging in the TD but remained fivefold tougher than stretched neat PLA films for up to 150 days. This work presents a feasible route to produce uniaxially stretched PEO–PBO/PLA films that are mechanically tough, which provides a more sustainable plastic alternative. 
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  3. Abstract

    In this study, poly(ethylene terephthalate)‐block‐polyethylene (PET‐PE) multiblock copolymers (MBCPs) with block molar masses of ~4 or 7 kg mol−1and either alternating or random block sequencing, and a PE‐PET‐PE triblock copolymer (TBCP) of comparable total molar mass, were synthesized. To explore the effect of molecular architecture on compatibilization, both MBCPs and TBCPs were blended into 80/20 wt/wt mixtures of PET/linear low‐density PE (LLDPE). Compatibilization was remarkably efficient for all MBCP types, with the addition of 0.2 wt% yielding blends nearly as tough as PET homopolymer. Addition of MBCP also significantly decreases LLDPE dispersed phase sizes compared to PET/LLDPE neat blends, as much as 80% in as‐mixed blends and by a factor of 10 in post‐mixing thermally annealed samples. Conversely, the TBCP was less efficient at decreasing domain sizes of the blends and improving the mechanical properties, requiring loadings of 1 wt% to produce comparably tough blends. Peel tests of PET/BCP/LLDPE trilayer films showed that both MBCPs and TBCP all improve interfacial strength over a PET‐PE bilayer film by two orders of magnitude; however, when the BCPs were preloaded into LLDPE, only the MBCP containing films showed strong adhesion highlighting their potential utility as adhesive agents in multilayer films.

     
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