Paths to sustainable plastic waste recycling

Parameters optimization for decontamination and fine physical regeneration pathways of polypropylene plastics from waste lunchboxes

Due to the development of the food delivery industry, a large amount of waste lunchboxes made of homo polypropylene (PP) plastic have been generated. This study developed a new technological strategy to effectively regenerate PP from waste lunchboxes. Through response surface curve analysis, it was found that under the optimal process conditions of hot alkali washing at 80 ℃, 30 min, and pH 13, the optimal contact angle was 65.55°, indicating a good oil stain removal effect. By identifying and analyzing the characteristics of impurities in waste lunchboxes, a physical sorting and granulation regeneration process was constructed. And through large-scale statistical analysis and data collection, it was further verified that recycled PP plastics maintained their physical stability and excellent processing performance. The quality stability of recycled PP plastics in terms of impurities content was also verified. By designing different formulations specifically, recycled PP was mixed with different virgin PP and antioxidants in appropriate proportions, and extruded into particles under 150-300 mesh filtration conditions to obtain modified recycled PP. Modified recycled PP was applied in textiles, clothing, and injection molded products. In conclusion, we achieve the up-cylcing of waste PP lunchboxes instead of down-cylcing.

Self-evolutionary recycling of flame-retardant polyurethane foam enabled by controllable catalytic cleavage

Polyurethane (PU) foams, pivotal in modern life, face challenges suh as fire hazards and environmental waste burdens. The current reliance of PU on potentially ecotoxic halogen-/phosphorus-based flame retardants impedes large-scale material recycling. Here, our demonstrated controllable catalytic cracking strategy, using cesium salts, enables self-evolving recycling of flame-retardant PU. The incorporation of cesium citrates facilitates efficient urethane bond cleavage at low temperatures (160 °C), promoting effective recycling, while encouraging pyrolytic rearrangement of isocyanates into char at high temperatures (300 °C) for enhanced PU fire safety. Even in the absence of halogen/phosphorus components, this foam exhibits a substantial increase in ignition time (+258.8%) and a significant reduction in total smoke release (-79%). This flame-retardant foam can be easily recycled into high-quality polyol under mild conditions, 60 °C lower than that for the pure foam. Notably, the trace amounts of cesium gathered in recycled polyols stimulate the regenerated PU to undergo self-evolution, improving both flame-retardancy and mechanical properties. Our controllable catalytic cracking strategy paves the way for the self-evolutionary recycling of high-performance firefighting materials.

Toward Heart-Healthy and Sustainable Cities: A Policy Statement From the American Heart Association

Nearly 56% of the global population lives in cities, with this number expected to increase to 6.6 billion or >70% of the world's population by 2050. Given that cardiometabolic diseases are the leading causes of morbidity and mortality in people living in urban areas, transforming cities and urban provisioning systems (or urban systems) toward health, equity, and economic productivity can enable the dual attainment of climate and health goals. Seven urban provisioning systems that provide food, energy, mobility-connectivity, housing, green infrastructure, water management, and waste management lie at the core of human health, well-being, and sustainability. These provisioning systems transcend city boundaries (eg, demand for food, water, or energy is met by transboundary supply); thus, transforming the entire system is a larger construct than local urban environments. Poorly designed urban provisioning systems are starkly evident worldwide, resulting in unprecedented exposures to adverse cardiometabolic risk factors, including limited physical activity, lack of access to heart-healthy diets, and reduced access to greenery and beneficial social interactions. Transforming urban systems with a cardiometabolic health-first approach could be accomplished through integrated spatial planning, along with addressing current gaps in key urban provisioning systems. Such an approach will help mitigate undesirable environmental exposures and improve cardiovascular and metabolic health while improving planetary health. The purposes of this American Heart Association policy statement are to present a conceptual framework, summarize the evidence base, and outline policy principles for transforming key urban provisioning systems to heart-health and sustainability outcomes.

A Tough Monolithic-Integrated Triboelectric Bioplastic Enabled by Dynamic Covalent Chemistry

Electronic waste is a growing threat to the global environment and human health, raising particular concerns. Triboelectric devices synthesized from sustainable and degradable materials are a promising electronic alternative, but the mechanical mismatch at the interface between the polymer substrate and the electrodes remains unresolved in practical applications. This study uses the sulfhydryl silanization reaction and the chemical selectivity and site specificity of the thiol-disulfide exchange reaction in dynamic covalent chemistry to prepare a tough monolithic-integrated triboelectric bioplastic. The stress is dissipated by covalent bond adaptation to the interface interaction, which makes the polymer dielectric layer to the conductive layer have a good interface adhesion effect (220.55 kPa). The interfacial interlocking of the polymer substrate with the conductive layer gives the triboelectric bioplastic excellent tensile strength (87.4 MPa) and fracture toughness (33.3 MJ m-3). Even when subjected to a tension force of 10 000 times its weight, it still maintains a stable triboelectric output with no visible cracks. This study provides new insights into the design of reliable and environmentally friendly self-powered devices, which is significant for the development of flexible wearable electronics.

Chemical Circularity in 3D Printing with Biobased Δ-Valerolactone

Digital Light Processing (DLP) is a vat photopolymerization-based 3D printing technology that fabricates parts typically made of chemically crosslinked polymers. The rapidly growing DLP market has an increasing demand for polymer raw materials, along with growing environmental concerns. Therefore, circular DLP printing with a closed-loop recyclable ink is of great importance for sustainability. The low-ceiling temperature alkyl-substituted δ-valerolactone (VL) is an industrially accessible biorenewable feedstock for developing recyclable polymers. In this work, acrylate-functionalized poly(δ-valerolactone) (PVLA), synthesized through the ring-opening transesterification polymerization of VL, is used as a platform photoprecursor to improve the chemical circularity in DLP printing. A small portion of photocurable reactive diluent (RD) turns the unprintable PVLA into DLP printable ink. Various photocurable monomers can serve as RDs to modulate the properties of printed structures for applications like sacrificial molds, soft actuators, sensors, etc. The intrinsic depolymerizability of PVLA is well preserved, regardless of whether the printed polymer is a thermoplastic or thermoset. The recovery yield of virgin quality VL monomer is 93% through direct bulk thermolysis of the printed structures. This work proposes the utilization of depolymerizable photoprecursors and highlights the feasibility of biorenewable VL as a versatile material platform toward circular DLP printing.

Unraveling the driving factors of the plastic waste trade network formation and dynamics

International trade of plastic waste promotes the global plastic circular economy and improves resource efficiency, but exacerbates the ubiquitous plastic pollution. Understanding the drivers behind the evolution of the global plastic waste trade network (GPWTN) is pivotal for developing new international instruments to end plastic pollution and fostering clean solid-waste trade. Employing social network analysis (SNA) and quadratic assignment procedure (QAP) model, this study structures the GPWTN using bilateral trade data, revealing shifts from highly centralized to cross-layered networks and relevant drivers. It is suggested that Malaysia and Turkey has become the new key recipients of the GPWTN, replacing China, accompanied by the launch of new environmental regulations in some countries. Transportation cost is the most critical factor for the formation of the GPWTN, followed by gaps in resource demand, bio-based resource availability, and transportation accessibility. Trading partners in closer proximity, especially those with contiguous borders, are more likely to trade in waste plastics, while coastal countries play an important role in these partnerships. Economies with more abundant biomaterials, higher incomes, and greater environmental burdens are more likely to be exporters, while economies with scarcer resources and more compelling demands are more likely to import plastic waste. Countries involved in the trade in plastic waste, as either importers or exporters, receive varying degrees of economic benefits but bear potential environmental impacts. Therefore, global plastic pollution control and trade prosperity necessitates necessitate coordinated endeavors from nations and intergovernmental bodies for a mutually advantageous denouement.

Improved Antibacterial Properties of Polylactic Acid-Based Nanofibers Loaded with ZnO-Ag Nanoparticles through Pore Engineering

In the post-epidemic era, bio-based protective fiber materials with active protective functions are of utmost importance, not only to combat the spread of pathogens but also to reduce the environmental impact of petroleum-based protective materials. Here, efficient antibacterial polylactic acid-based (PLA-based) fibers are prepared by solution blow spinning and their pore structures are regulated by controlling the ratio of the solvent components in the spinning solutions. The porous PLA-based fibers exhibit antibacterial efficiencies of over 99% against Escherichia coli and over 98% against Bacillus subtilis, which are significantly higher than that of the nonporous PLA-based fibers. The excellent antibacterial property of the porous PLA-based fibers can be attributed to their high porosity, which allows antibacterial nanoparticles to be released more easily from the fibers, thus effectively killing pathogenic microorganisms. Moreover, pore structure regulation can also enhance the mechanical property of the PLA-based fiber materials. Our approach of regulating the microstructure and properties of the PLA-based fibers through pore engineering can be extended to other polymer fiber materials and is suitable for polymer-based composite systems that require optimal performance through sufficient exposure of doped materials.

Recycling and Processing of Waste Materials

Just a few days ago, the world population, as expected, surpassed 8 billion [...].