Under the background of global advocacy for green development, traditional methods of production and processing are facing a severe test of transformation and upgrading. The development of advanced processing technologies that reduce energy consumption and reduce the emission of harmful pollutants has become the only way for green, healthy and sustainable development. Supercritical carbon dioxide continuous extrusion foaming is a foaming technology that combines green foaming agent and direct extrusion processing. It exhibits green, high-efficiency, and continuous advantages in polymer foaming. At the same time, supercritical carbon dioxide is a green medium that combines the mass transfer of liquids and the diffusion rate of gases. It can reduce the viscosity and processing temperature of polymers, and has the advantages of reduced energy consumption and emission reduction for polymer processing. Recently, the Advanced Polymer Processing Group of the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences has used supercritical carbon dioxide processing platforms to achieve a series of research results in continuous extrusion foaming and polymer processing.
1. The polymer foamed material with a bimodal cell structure exhibits more excellent performance than the uniform cell material in the fields of packaging materials, tissue engineering, sound-absorbing and heat-insulating materials, and thus has a broader application prospect. The Ningbo Institute of Materials Science and Technology advanced processing team researchers through the continuous extrusion of supercritical carbon dioxide foaming, the use of bubbles in the two-phase nucleation ability difference, in the polypropylene / polystyrene blend system to obtain a bimodal cell structure ( Figure 1) is expected to provide a method for the preparation of bimodal cellular materials for other polymer blends (Patent Application No. 6; The Journal of Supercritical Fluids, online).
2. Offshore crude oil leakage and industrial waste oil have become an important cause of disrupting ecological balance. The development of an oil-absorbing material with a large oil absorption rate, good oil-water selectivity, and reusability can provide a solution that satisfies the application requirements. Researchers used supercritical fluid continuous extrusion foaming technology to prepare high open-cell foams with open porosity higher than 90% based on polypropylene composites. The material exhibits superior oleophilic hydrophobicity, oil-water separation, high oil absorption ratio, and repeated use in the oil-absorbing tests of organic solvents, edible oils, and engine oils (Fig. 2). It is expected to be used in oil-water separation, industrial and offshore oils. Processing and other aspects have good application prospects (Patent Application No. 0 and 201510392373.2).
3. Traditional linear polypropylene is difficult to foam due to its low melt strength. In order to improve the foaming behavior, it is usually necessary to prepare high melt strength polypropylene, a common method being reactive extrusion. However, the conventional reactive extrusion processing temperature is high, which easily causes the degradation of polypropylene. Researchers use supercritical fluids as both a reaction medium and a foaming agent. Through continuous extrusion of foaming experimental lines, simultaneous reaction extrusion and foaming are achieved, which not only reduces the reaction temperature and reduces degradation, but also produces high melts. The strength polypropylene also improves its foaming behavior and expands its foaming window (Application No. X; Journal of Materials Science, 2016, 51: 2705-2715).
4. Obtaining good dispersion is the key to improving the performance of blends or composites. A commonly used method is to introduce an interface compatibilizer in the system. Researchers have used supercritical fluids to adjust the viscosity ratio of the two components of the polymer, which has enabled the improvement of Polypropylene/Polystyrene (Polymer Bulletin, online) and Polypropylene/Polyolefin elastomers without the addition of compatibilizers. (Patent Application No. 8) The dispersion state of the blend system, which greatly improved the foaming behavior of the material, and improved the mechanical properties to some extent. In addition, the reaction extrusion directly generated the interface compatibilizer is an effective means to achieve the in-situ compatibilization of the polymer blend system and improve the mechanical properties. However, the conventional reaction extrusion temperature is high, and it is easy to cause side reactions to cause degradation of the polymer. Researchers used supercritical fluids as the green medium for reactive extrusion to achieve in-situ compatibilization of polypropylene/polystyrene systems, reducing the occurrence of side reactions and obtaining better mechanical properties (patent application number .6). .
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