In recent years, polypropylene foam materials with excellent comprehensive performance, recyclable and easily degradable have become the "new darling" in the foam plastic family, and are the fastest growing varieties of polymer foam materials. Supercritical carbon dioxide (CO2) foaming polymer technology is the key core technology for the preparation of polypropylene microcellular foaming materials. Recently, the team of Professor Zhao Ling of School of Chemical Engineering, East China University of Science and Technology has made a substantial breakthrough in this technical field and successfully developed high performance Optimization and strengthening technology of green preparation process of polypropylene microcellular foaming material.
There are two main types of polymer foaming agents, physical foaming agents and chemical foaming agents. Chemical blowing agents have the disadvantages of chemical residues, difficult control of the foaming process and difficulty in obtaining high expansion ratios. The chlorofluorocarbons in physical blowing agents have a destructive effect on the ozone layer and have been gradually banned and restricted; and some new types The global warming potential of fluorocarbons is still relatively high, and alkanes foaming agents are easy to burn and unsafe. Compared with these traditional blowing agents, supercritical CO2 foaming polymer technology, as a green manufacturing technology, has been listed by the Ministry of Industry and Information Technology as a key common technology in China's priority development, and CO2 will cause melting point, surface tension and viscosity after entering the polymer. A series of changes such as descent and changes in crystallization behavior can prepare microporous or even nanocellular materials.
Polypropylene is a crystalline polymer. Low-temperature solid-state foaming is limited by crystallization, making it difficult to prepare products with high expansion ratios. High-temperature foaming polymers have insufficient melt strength to maintain intact cells and a narrow operable window. Therefore, it is difficult to produce high-expansion-ratio microcellular materials with stable and uniform cell morphology and external dimensions on a large scale.
In order to overcome this problem, the Zhao Ling team, together with Wuxi Huitong, Sinopec Beihua Institute, Zhejiang Xinhengtai, Zhenhai Refinery and other units, carried out supercritical CO2 in suitable material systems, controllable processes and efficient industrial equipment. A series of work such as the optimization, strengthening and engineering of foamed polypropylene have formed "special materials for polypropylene suitable for supercritical CO2 foaming" "new step-by-step/segment foaming process" "optimized construction of flow field structure to achieve efficient scale Three major technological innovations in preparation.
Zhao Ling introduced that foaming in the deformable area below the flow temperature can not only break through the limitation of crystallization, but also ensure the stable formation of the microcellular structure and external dimensions of the foamed material. Based on this foaming mechanism, they have developed a polypropylene foaming material with both a wide foaming temperature window and a strong CO2 dissolution and diffusion capability, as well as new functional additives that can improve the cell structure and apparent morphology/ additive. CO2 pressure-saturation improves the process efficiency and foaming ratio, and the staged implementation of bubble nucleation and growth reduces the volume of high-pressure equipment; meanwhile, the structure optimization of high-pressure equipment such as autoclave foaming and molded foam and polymer preforms are optimized The design ensures uniform pressure field, temperature field and velocity field, and realizes the large-scale manufacturing and flexible production of low-density polypropylene microcellular foamed materials.
Using the above-mentioned innovative technologies, the project team built 2 sets of 30,000 cubic meters of molded foaming equipment, which has achieved world-leading manufacturing of low-density polypropylene microporous thick plates; 4 sets were newly built, and 3 sets were optimized and transformed. 10,000~60,000 cubic meters of autoclave foaming equipment, production efficiency increased by 25%, finished product rate increased to more than 99%, special foaming material has been produced in Zhenhai Refining and Chemical, 2016-2018 new output value of 331 million yuan, profits and taxes 1.009 billion yuan. In addition, the team has obtained 8 authorized invention patents and 8 utility model patents; related research results have published 46 SCI/EI papers.
Zhao Ling said that supercritical CO2 molding foaming technology has strong versatility. In addition to polypropylene, it can also be used for the production of polyurethane elastomer microcellular foaming materials. Pilot tests of various thermoplastic polymers and their composite materials have been completed. The polypropylene foam special material produced by this technology can be applied to traditional fields such as auto parts and interior decoration, cushioning packaging, etc., and can also meet the demand for green materials in the fields of children's toys, food, medical treatment, household goods, etc. Because micropores give polypropylene unique properties, polypropylene microcellular foam materials can also be used in more emerging fields, such as new energy vehicle power battery gaskets, 5G communication microwave relay radomes, and high-end car audio diaphragms. , Backboard of body armor, etc.