This project belongs to the field of new materials. Supercritical CO2 foamed polymer is a new green and safe technology and a key common technology for my country's priority development. Polypropylene (PP) is a general plastic with large output, rapid growth and wide application fields in the world. The preparation of its high-performance foaming materials has always been a hot spot and difficulty in the field of polymer foaming. The project has carried out a series of innovative research on precise control strategies for multi-scale structures of polypropylene microporous foaming materials, special polypropylene foaming materials, new functional additives/additives, and high-efficiency foaming processes and equipment, providing optimization, strengthening and engineering technologies for low-density microporous PP foaming materials with stable and uniform cell structure and external size. The main technological innovations include: (1) A method was established to determine the foamable temperature window based on the melting behavior of polymers in high-pressure CO2 environment. It was found that foaming PP in the deformable zone below its flowing temperature can not only break through the crystallization constraints but also ensure the stable formation of the microporous structure and shape size of the foamed material; A special PP foaming material with appropriate melt strength was developed, which has a wide foaming temperature window and strong CO2 dissolution and diffusion ability, and the cell morphology was optimized by controlling the aggregation structure of PP in high-pressure CO2 environment. (2) The development of new functional additives/additives has effectively improved the cell structure and apparent morphology of PP microporous foaming materials. As a CO2-friendly additive, medium molecular weight polysiloxanes can reduce the cell size and increase the foaming ratio; the new composite additives reduce the blocking rate and dead particle rate of foamed beads during the autoclave foaming process, and make the cell structure more uniform. (3) The CO2 pressure swing saturation/pre-saturation process is used to form fine holes in the PP matrix to store CO2, shorten the diffusion path, strengthen the saturation process, broaden the foaming window and foaming ratio; transient bubble nucleation and The step-by-step implementation of the cell growth process greatly reduces the volume of high-pressure equipment and is conducive to the controllable preparation of PP foamed products with different cell morphologies. (4) Optimize the design of preformed polymer structures and high-pressure foaming equipment structures, control flow, strengthen mixing and dispersion and heat/mass transfer, and build a uniform CO2 concentration field, temperature field, pressure field and velocity field to improve the efficiency of the foaming process. and ensure the stability and uniformity of the multi-scale structure of PP foam materials. The project scale-up of supercritical CO2 die pressing foaming to prepare high-foaming ratio and large size microporous PP plates has been successfully achieved. Two sets of devices with an annual output of 1,000 tons and one set with an annual output of 500 tons have been built, realizing the world-leading manufacturing of low-density PP microporous thick plates; The optimization and upgrading of the stirring kettle for preparing PP beads by high-pressure CO2 autoclave foaming has been carried out, and 3 sets of devices with an annual output of 1,000 tons have been renovated and 4 sets of devices with an annual output of 1,000 tons have been built. The production efficiency has increased by 25%, the yield has increased by 6%, and energy consumption has been reduced by 13%. The series of PP microporous foaming materials produced have excellent performance, green environmental protection, and high added value. They have been widely used in automotive parts and interiors, children's toys, electronic product packaging and fresh cold chain transportation, and have expanded new applications such as energy vehicle power battery gaskets, communication microwave relay radome, high-end car audio diaphragms, and military packaging materials. It has authorized 8 invention patents and 8 utility model patents in China; and published 46 SCI/EI papers. The scientific and technological novelty search and consultation report pointed out that the relevant technologies of this project are novel at home and abroad and have reached the international advanced level, among which molded foaming is internationally leading. After applying it in Zhejiang Xinhengtai, Wuxi Huitong, Sinopec Zhenhai Refining and Chemical and other enterprises, the cumulative added output value was 331.082 million yuan and the added profits and taxes were 108.981 million yuan from 2016 to 2018. This project has achieved technical advantages and product advantages in the preparation of high-performance PP microporous foamed materials, and led the green manufacturing and high-end application of high-performance PP foamed materials.