1.Degradation conversion and recycling of polyolefins
Polyolefins (mainly polyethylene and polypropylene) are one of the most widely used organic polymer materials. The widespread use of polyolefins (mainly polyethylene and polypropylene) poses a serious challenge to sustainable human development due to the increasing environmental pollution and the huge resource consumption caused by single-use and very low recycling rates. The challenge is particularly acute in China. Chemical degradation and conversion of polyolefins has unique advantages over physical/mechanical recycling. However, since polyolefins are basically composed of C-H and C-C bonds and are highly chemically inert, it is difficult to achieve efficient and highly selective degradation and recycling through chemical conversion methods. Addressing this challenge is a long-term process that requires broad participation from all areas of society. Some important advances and breakthroughs around this challenge have been made by relevant researchers worldwide in the past few years. Depending on the type of polyolefin degradation and conversion or up-cycling reactions, the focus will be on catalytic reaction products, catalytic efficiency, catalytic selectivity, reaction scale and catalytic tolerance to impurities, and conclude with an outlook on chemical approaches to polyolefin degradation and recycling.
2.New method of upcycling thermosetting resins and their composites
As a kind of renewable resource, the recycling of waste thermosetting resins and their composites has become a hot spot of researchers’ attention. Due to the difficulty of recycling, its disposal methods are mainly based on landfill and incineration at present, which causes serious environmental pollution and resource waste. Among the existing recycling methods for thermosetting resins and their composites, physical recycling is simple, efficient and easy to be promoted industrially, but the performance of the recovered products is poor and the added value is low; chemical recycling can recover monomers, oligomers or value-added chemicals from waste resins, which has the advantages of flexible methods and high development potential, but there are problems such as harsh reaction conditions, complex products, cumbersome post-treatment and poor performance of the recycled products. . Therefore, it is of great importance to propose and establish new strategies and methods for the upcycling of thermoset resins and their composites. The current status of the recycling of thermoset resins and their composites is reviewed, and based on this, the new progress of the authors’ team in the field of thermoset resin upcycling in recent years is highlighted, and the future development of this field is also prospected.
3.Research progress of waste nylon recycling technology
In today’s rapidly changing technology, sustainable development has become the consensus of all countries in the world, and the rational and efficient research and development of renewable resources has become an important research direction and hot spot at home and abroad. As the consumption of nylon, which has an important position in synthetic fibers, is increasing, the recycling of its waste has received wide attention from scholars. The research status of physical recycling and chemical depolymerization processes of waste nylon materials at home and abroad in recent years is reviewed. Several major recycling processes are highlighted, including dissolution/re-precipitation for physical recycling, hydrolysis, alcoholysis, ammonolysis and ionic liquid depolymerization for chemical recycling, and the advantages and disadvantages of these process methods are outlined. Finally, the practical application of waste nylon recycling technology in industrial production is discussed, and the green solvent dissolution/re-precipitation technology, fluid depolymerization technology with sub/supercriticality, solid super acid catalytic depolymerization technology and ionic liquid depolymerization technology are clearly pointed out as the key research directions in the future.
4.The current status of the development of recycling and resource utilization of waste tires
China has a large population, relatively poor resources, fragile ecological environment, with the continuous promotion of industrialization and urbanization, the contradiction between the supply and demand of resources and environmental pressure will become increasingly large, the development of circular economy has become an inevitable choice for China’s social and economic development. Tires and other rubber products are essential bulk products in China’s national economic development process, which will cause serious “black” pollution after disposal. How to turn waste into treasure and realize the resource utilization of waste is an important issue, which is of great significance to achieve “carbon peak” and “carbon neutral”. After years of research and development, China’s waste tire recycling and resource utilization industry has formed four major business segments: tire remanufacturing, recycled rubber, rubber powder and waste tire cracking, which has greatly eased the plight of China’s rubber resource shortage and formed a unique road of waste tire recycling. On this basis, the current situation and development trend of China’s waste tire recycling and resource utilization, as well as the main problems exist, are systematically summarized in the hope of providing reference for the research and development of related fields.
5.New materials based on CO2 copolymers
The synthesis of carbon dioxide copolymers by copolymerization of carbon dioxide and epoxides to produce new polymeric materials such as carbon dioxide based plastics or carbon dioxide based polyurethanes with biodegradable properties is becoming an important part of green polymer chemistry and chemistry, and is a frontier hot spot for polymer academia and industry to implement the national carbon neutral strategy. Among all carbon dioxide copolymers, poly(propylene carbonate) (PPC), a copolymer of carbon dioxide and propylene oxide, has received the most attention and is the most industrially mature species. Based on the work of the author’s group and domestic and international research teams, we summarize the synthesis method, material properties and industrialization process of PPC, focus on the wide application of PPC in the fields of low-cost biodegradable plastics and environmentally friendly polyurethane, and predict its future development trend.
6.Reversible cross-linked polymer materials: remediation, recycling and degradation
While traditional polymer materials have created convenience for human society, they have also caused serious resource waste and environmental pollution problems. The vigorous development of reversible, recyclable and degradable polymer materials can effectively alleviate the problems of resource waste and environmental pollution, which is of great significance for building a sustainable society. The progress of reversible cross-linked polymer systems based on non-covalent interactions and dynamic covalent bonding for the preparation of repairable, recyclable and degradable polymer materials is systematically summarized. Based on the work of the authors’ research group, the synergy of multiple reversible forces and microstructures is highlighted to prepare repairable and recyclable polymeric materials with high strength, high toughness and excellent tear resistance, as well as degradable supramolecular plastics with good environmental stability. The design and preparation of reversible cross-linked polymer systems based on non-covalent interactions and dynamic covalent bonding is an effective idea for the development of repairable, recyclable and degradable polymer materials.
7.Current situation and future development of biodegradable plastics industry
With the rapid development of China’s economy, people’s demand for various plastic products is increasing. However, the imperfect waste disposal technology has led to a large amount of plastics being leaked into the environment, thus leading to serious white pollution. Biodegradable plastics have received attention from scientific and industrial circles due to their environmental friendliness, easy recycling and easy processing. Biodegradable plastics have been widely used in disposable products, agriculture, forestry, fishery and animal husbandry, automotive industry, 3D printing and other fields. Starting from the types and characteristics of biodegradable plastics, the characteristics, life cycle assessment (LCA), current industrial development and applications in various fields of mainstream biodegradable plastics in the market, such as polylactic acid (PLA), polyhydroxy fatty acid esters (PHA), polybutylene terephthalate (PBAT) and polypropylene carbonate (PPC), are reviewed, along with a brief description of national regulations for commercial The future development prospect of biodegradable plastics is analyzed to provide reference for the development of biodegradable plastics industry in China.