Waste tire rubber is an important renewable resource. It is of great significance to make waste tires into recycled materials and recycle them into new tires to eliminate the black pollution of waste tires and reduce the dependence of rubber resources on foreign countries. However, the existing tire recycling technology has the problems of high pollution, low efficiency and poor quality, so it is urgent to develop green, resource-based and high-value tire recycling technology. The "10,000-ton waste tire rubber material Green self-recycling and Application Technology Demonstration" project jointly developed by Zhongce Rubber Group Co., LTD., Nanjing Green Golden Rubber & Plastic High-tech Co., LTD., Beijing University of Chemical Technology has broken through the green high-value reuse technology of waste tires, and built a tire green self-recycling application demonstration. And recently won the 2023 China Petroleum and Chemical Industry Federation Science and Technology Award Science and Technology progress first prize.
At present, waste tires in China have formed a recycling pattern based on the preparation of recycled rubber, the preparation of rubber powder, tire retreading and thermal cracking. Among them, waste truck tire rubber is generally prepared by high temperature and high pressure dynamic desulfurization tank technology solid recycled rubber. This technology has some problems, such as uncontrollable decrosslinking, high energy consumption caused by long time high temperature and high pressure, and difficult treatment of waste gas and waste water in the production process. The key to solve these problems is to realize controlled decrosslinking regeneration of waste rubber.
"The molecular structure of tire rubber is linear, in order to achieve its performance, it is usually necessary to add sulfur to vulcanize, so that it forms a three-dimensional network structure of thermosetting materials." This structure causes the waste rubber material to be insoluble and difficult to be applied to new tires after simple processing, so the first step in recycling waste tire rubber is to decrosslink the sulfur cross-linking bonds in the rubber, destroy its three-dimensional network structure, and make it reprocessable." Dr. Shi Jinwei, general manager of Nanjing Green Gold Rubber & Plastic High-tech Co., LTD., explained that it is not easy to control selective cross-linking, and the cross-linking bond in waste truck tire rubber is less than 2%, and there are a variety of cross-linking bond types. At the beginning of the research, there were no precedents for the decrosslinking mechanism with excellent and stable regeneration performance and the equipment for green regeneration of waste rubber.
In addition, waste tires through thermal cracking technology to recover cracked oil, cracked carbon black, the general use of "local oil refining" due to pollution is banned by the state, and through environmental protection high temperature thermal cracking technology to recover waste passenger tires, there are large equipment investment, low product yield, poor product quality and other problems.
This is because the reinforcing system of waste passenger car tires is complex, especially because of the requirements of 'green tires', the amount of silica reinforcing agent in the formula is getting higher and higher, and after high temperature pyrolysis above 450℃, carbon black, silica and other reinforcing agents are inactivated, poor performance, and difficult to separate, difficult to modify, and the economic added value of the product is low." Shi Jinwei explained that there is an urgent need to create a new recycled rubber material, which can achieve decrosslinking without damaging the reinforcing system, and achieve high yield and high added value.
"In addition, the application of recycled materials in tires is disjointed due to the lack of systematic theoretical research, and the high performance of tires after application can not be maintained, can not be stable, and can only be mixed in a small amount, which seriously hinders the development of the industry." Shi Jinwei added that how to accurately combine the performance requirements of different parts of the tire to achieve high-performance and stable reuse of recycled materials, and scientific formula design is also a major problem.
After more than ten years of research, the research team developed green self-recycling technology for waste tire rubber materials, and finally solved the above problems. The technology has the following innovative points: First, the mechanism of waste rubber decrosslinking regeneration and the structure and performance evolution of recycled materials are clarified, and the design and manufacture of special equipment that meets the necessary regeneration conditions are guided. Second, the first to establish the friction transfer mechanism of waste rubber powder, developed a series of twin screw extruder core equipment with different functions such as desulfurization, refining, moderate pyrolysis, cooling exhaust, etc., and has realized the recovery of 10,000 tons of waste truck tires and 5,000 tons of waste passenger tires in a single line. Third, combined with the simulation design of shear field and temperature field in twin-screw extruder, the screw combination structure and process control technology are developed. Fourth, the application formula and process of solid/liquid recycled rubber in tire tread, tire side, tire body and other components are designed to realize the alternative application of petrochemical products such as resin, oil, carbon black, synthetic rubber and natural rubber, which ensures the performance and reduces the material cost.
The project has formed a full-cycle self-cycle model of tire production, sales, recycling, disposal and reuse, which provides a demonstration for the standardized recycling and system improvement of domestic waste tires, provides a green, resource-based and high-value Chinese solution for the recycling and reuse of waste truck tires and waste passenger tires, and reduces the dependence of China's rubber resources on foreign countries. Conducive to the sustainable development of the rubber industry.
At present, the technology has been applied and has produced good economic benefits. Zhongce Rubber Recycling Technology Co., Ltd. has initially built a waste tire recycling system, forming a scale of annual treatment of 50,000 tons of waste tires, the cumulative treatment of about 80,000 tons of waste tires in the past three years, the carbon emission reduction of about 23,000 tons, the application of recycled rubber materials tire sales revenue reached 20.84 billion yuan, saving about 60 million yuan.
