Defining the Macromolecules of Tomorrow through Synergistic Sustainable Polymer Research.

Transforming how plastics are made, unmade, and remade through innovative research and diverse partnerships that together foster environmental stewardship is critically important to a sustainable future. Designing, preparing, and implementing polymers derived from renewable resources for a wide range of advanced applications that promote future economic development, energy efficiency, and environmental sustainability are all central to these efforts. In this Chemical Reviews contribution, we take a comprehensive, integrated approach to summarize important and impactful contributions to this broad research arena. The Review highlights signature accomplishments across a broad research portfolio and is organized into four wide-ranging research themes that address the topic in a comprehensive manner: Feedstocks, Polymerization Processes and Techniques, Intended Use, and End of Use. We emphasize those successes that benefitted from collaborative engagements across disciplinary lines.

Recent advances and progress in the detection of bisphenol A.

Bisphenol A (BPA) is an important industrial chemical used as a plasticizer in polycarbonate and epoxy resins in the plastic and paper industries. Because of its estrogenic properties, BPA has attracted increasing attention from many researchers. This review focuses primarily on analytical methods for BPA detection that have emerged in recent years. We present and discuss the advantages and disadvantages of sample preparation techniques (e.g., solvent extraction, solid-phase extraction, molecularly imprinted polymer solid-phase extraction, and micro-extraction techniques) and analytical methods (e.g., liquid chromatography, liquid chromatography-mass spectrometry, gas chromatography-mass spectrometry, capillary electrophoresis, immunoassay, and several novel sensors). We also discuss expected future developments for the detection of BPA. Graphical Abstract This review focuses primarily on the recent development in the detection of bisphenol A including sample pre-treatment and analytical methods.

Dihydroxy Polyethylene Additives for Compatibilization and Mechanical Recycling of Polyethylene Terephthalate/Polyethylene Mixed Plastic Waste.

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.

Linear, Graft, and Beyond: Multiblock Copolymers as Next-Generation Compatibilizers.

Properly addressing the global issue of unsustainable plastic waste generation and accumulation will require a confluence of technological breakthroughs on various fronts. Mechanical recycling of plastic waste into polymer blends is one method expected to contribute to a solution. Due to phase separation of individual components, mechanical recycling of mixed polymer waste streams generally results in an unsuitable material with substantially reduced performance. However, when an appropriately designed compatibilizer is used, the recycled blend can have competitive properties to virgin materials. In its current state, polymer blend compatibilization is usually not cost-effective compared to traditional waste management, but further technical development and optimization will be essential for driving future cost competitiveness. Historically, effective compatibilizers have been diblock copolymers or in situ generated graft copolymers, but recent progress shows there is great potential for multiblock copolymer compatibilizers. In this perspective, we lay out recent advances in synthesis and understanding for two types of multiblock copolymers currently being developed as blend compatibilizers: linear and graft. Importantly, studies of appropriately designed copolymers have shown them to efficiently compatibilize model binary blends at concentrations as low as ∼0.2 wt %. These investigations pave the way for studies on more complex (ternary or higher) mixed waste streams that will require novel compatibilizer architectures. Given the progress outlined here, we believe that multiblock copolymers offer a practical and promising solution to help close the loop on plastic waste. While a complete discussion of the implementation of this technology would entail infrastructural, policy, and social developments, they are outside the scope of this perspective which instead focuses on material design considerations and the technical advancements of block copolymer compatibilizers.

Blend Miscibility of Poly(ethylene terephthalate) and Aromatic Polyesters from Salicylic Acid.

Poly(ethylene terephthalate) (PET) is one of the most prevalent polymers in the world due to its combined thermal, mechanical, and gas barrier attributes. Blending PET with other polymers is an appealing strategy to further tailor properties to meet the needs of an even more diverse range of applications. Most blends with PET are macrophase-separated; only a few miscible systems have been reported. Here, the miscibility of the aromatic polyesters poly(salicylic glycolide) (PSG) and poly(salicylic methyl glycolide) (PSMG) with PET is described. Both PSG and PSMG have similar chemical structures to PET but are derived from sustainable resources and readily degradable. This study suggests that they are fully miscible with PET over the entire composition range, which is attributed to favorable interactions with PET. Negative polymer-polymer interaction parameters (χ) were determined using Flory-Huggins theory to describe melting temperature variations in the blends. In addition, the PET blends showed mechanical properties that are intermediate between the two homopolymers.

In vitro culture of sheep lamb ovarian cortical tissue in a sequential culture medium.

PURPOSE: This study evaluates the effect of a sequential culture system on the follicular development of sheep lamb ovaries, aiming to establish an available in vitro culture system for ovarian culture. METHODS: Lamb ovarian cortical fragments were cultured on a steel mesh with a nitrocellulose membrane pre-coated by type 1 collagen. Several culture media were used for the determinations, specifically, a control medium (alpha-MEM), a constant medium (control medium supplemented with 75 ng/mL human recombinant EGF, 200 mIU/mL sheep FSH, 100 ng/mL human recombinant GDF-9, and 100 ng/mL human recombinant bFGF), and a sequential medium (control medium supplemented with sequential growth factors added on different days). Ovarian tissues, both fresh and cultured, were processed for histological and apoptotic assays, while spent culture media were processed for hormone assays. RESULTS: It was found that the growth of lamb primordial follicles can be initiated during culture in vitro. Compared to the control medium, sequential culture medium significantly increased the percentage of secondary follicles in cultures, while the follicle and oocyte diameters of primary and secondary follicles were also observed to increase in this medium. The constant medium was found to increase the number and diameter of secondary follicles only 18 days after culture. After this same period of time, some normal antral follicles were found in the sequential medium, while a few abnormal antral-like follicles were found in the control medium. Moreover, sequential medium appeared to significantly increase estradiol and inhibin production, especially 10-18 days after culture. The highest percentage of normal follicles and the lowest apoptotic cell rates were observed in the sequential medium, suggesting that a sequential addition style of culture can improve follicle and tissue viability. CONCLUSIONS: The sequential addition of FSH, EGF, GDF-9,and bFGF can stimulate primordial follicle transmittal into the later development stages, even as far as the antral stage, improve the survival rate of follicles, and maintain follicular viability.

Compatibilization of iPP/HDPE Blends with PE-g-iPP Graft Copolymers.

The compatibilization of polyethylene (PE) and isotactic polypropylene (iPP) blends is of particular interest due to the challenges associated with recycling these plastics from mixed waste streams. Polyethylene-graft-iPP copolymers (PE-g-iPP) were prepared using a grafting-through strategy by copolymerization of ethylene with allyl-terminated iPP macromonomers in the presence of a hafnium pyridylamido catalyst. Graft copolymers with a variety of graft lengths (Mn = 6-28 kg/mol), graft numbers, and graft spacings were prepared. These graft copolymers were melt-blended with high-density polyethylene (HDPE) and iPP (iPP/HDPE = 30/70 w/w), and the blend properties were evaluated by tensile testing. The blends showed enhanced tensile strength at 5 and 1 wt % loading, with higher tensile strength observed for larger block numbers and graft lengths. These results indicate that graft copolymers are efficient compatibilizers for blends of HDPE and iPP.

Multiblock Copolymers for Recycling Polyethylene-Poly(ethylene terephthalate) Mixed Waste.

Plastic pollution is one of the most pressing global environmental issues we face today, in part due to the continued rise in production and use of disposable plastic products. Polyolefins and polyesters are two of the most prevalent polymers in the world accounting for ∼80% of total nonfiber plastic production. Recycling, despite being intrinsically environmentally friendly and sometimes economically viable, remains at a surprisingly low level (<9% in the U.S.) with most plastic waste ending up in landfills. One reason for this low rate of recycling stems from the challenge of recycling mixed waste streams and multicomponent plastics. In mixed waste streams, physical presorting of components prior to recycling requires significant effort, which translates to added cost. For multicomponent plastics (e.g., multilayer films such as food wrappers), the individual plastic components cannot be efficiently physically separated, and they are immiscible with poor interfacial adhesion when melt reprocessed. Thus, direct recycling of mixed plastics by melt reprocessing results in products that lack desired end-use properties. In this study, we describe the synthesis of novel poly(ethylene terephthalate)-polyethylene multiblock copolymers (PET-PE MBCPs) and evaluate their utility as adhesive tie layers in multilayer films and compatibilizer additives for melt reprocessed blends. PET and PE are targeted because they are two of the most prevalent commercial polymers in the world and are high volume waste streams. The work described here demonstrates two key findings. First, the PET-PE MBCPs serve as effective adhesive tie layers between neat PET/PE films with adhesive strength comparable to that of commercially available adhesives. Second, PET/PE (80/20 wt %) blends containing ∼0.5 wt % PET-PE MBCP were melt mixed to mimic recycling mixed plastic waste, and they were found to exhibit mechanical properties better than neat PET. Overall, this study demonstrates that PET-PE MBCPs could significantly enhance the ability to recycle PET/PE mixed waste streams by serving the role as both an adhesive promoting layer and a compatibilizer additive.

[Effect of ascorbic acid, epidermal growth factor and follicle stimulating hormone on in vitro culture of sheep ovarian cortical tissue].

In this study, we evaluated the effects of ascorbic acid (VC), epidermal growth factor (EGF) and follicle stimulating hormone (FSH) on in vitro culture of sheep ovarian cortical tissue. Using 2 x 2 x 2 factor experimental design, we cultured sheep ovarian cortex fragments in 8 media with MEM (control), MEM+VC (50 microg/mL), MEM +EGF (100 ng/mL), MEM+FSH (50 ng/mL), MEM+VC+EGF, MEM+VC+FSH, MEM+EGF+FSH, MEM+VC+EGF+FSH. After 0 (non-cultured control), 2, 6, 12 days of culture, the pieces of ovarian cortex were proceed to histological and proliferating cell nuclear antigen (PCNA) examination, or observed by transmission electron microscopy (TEM). The percentages of developing follicles were increased (P < 0.05) and the percentages of healthy follicles were reduced (P < 0.05). When compared to the MEM group, the addition of FSH with VC or EGF promoted a significant increase of follicles diameter and follicles survival rate (P < 0.05), and stimulated the proliferation of granulosa cells. After 12 days of culture, medium supplemented with MEM+VC+EGF resulted the lowest proportion of developing follicles (49.3% +/- 3.2%), follicles diameter((32.3 +/- 2.3) microm), follicles survival rate (41.6% +/- 3.1%) and the proportion of PCNA stained follicles (26.4% +/- 1.2%, P < 0.05). In contrast, MEM+VC+EGF+FSH resulted the highest follicles diameter ((42.5 +/- 5.1) microm), follicles survival rate (59.7% +/- 6.1%) and proportion of PCNA stained follicles (43.5% +/- 4.1%, P < 0.05). Ultrastructural analysis confirmed the integrity of follicles cultured in VC+EGF+FSH group, while follicles cultured in MEM+VC+EGF groups showed more degeneration characters. In conclusion, the addition of VC and EGF to culture medium inhibited follicular development, VC+EGF+FSH was the most effective treatment to maintain follicular integrity and promote sheep primordial follicular activation and growth during in vitro culture.