At present, the development direction of the world's si […]
At present, the development direction of the world's silicone material technology is high performance, multi-function and compounding. By cooperating with the progress of technology and adding new additives, and by modifying cross-linking methods, copolymerization, blending and other modification technologies, organic polymerization The compounding of materials and silicone materials is an important direction of the current development of silicone technology. Scientists and technicians design various silicone products with different molecular structures according to their needs in the following ways to meet the needs of high-tech development on different occasions, especially. In recent years, although there have been more and more silicone products, it boils down to three main aspects of new technologies used in the development and application of new silicone materials:
1 Crosslinking method
The traditional preparation method of silicone resin and room temperature vulcanized silicone rubber is to use the condensation reaction of silanol groups and alkoxy groups, and the development of the addition reaction of vinyl groups and hydrogen has brought great technological progress. The addition reaction can control the curing speed, and no by-products are formed, so the electrical properties and heat resistance of the products are improved. In terms of condensation reaction, various crosslinking agents for single-component room temperature vulcanized silicone rubber have also been developed. On the basis of the original acetic acid type, ketoxime type and alcohol type crosslinking agents, amoxygen type and amide type crosslinking agents which can make the silicone rubber have low modulus and large elongation were developed. Furthermore, an acetone-type crosslinking agent with low toxicity, fast curing and no decomposition at high temperature has been developed.
In recent years, the liquid silicone rubber developed by hydrosilicone cross-linking has attracted people's attention. The rubber compound has single-component and two-component. At present, the most used is the two-component. The tensile strength of liquid silicone rubber can reach 8 ~ 9M Pa, it has high production efficiency, each machine can produce 106 parts in one year, and the production of small parts can reduce the cost by 1/4.
2 Chemical modification of polymers
(1) Reinforced plastics Introduce a small amount of PDMS, improve the toughness of engineering plastics (such as nylon, polycarbonate, etc.), improve the impact strength, and also improve the precision of mechanical processing.
(2) Reinforced rubber Introducing a small amount (<20%) of thermoplastic polymers into silicone rubber instead of silica and other inorganic fillers can be made into thermoplastic elastomers (TPE), which can be processed by plastic methods and the strength can also be improved a lot.
(3) Improving surface properties In some polymers (such as epoxy resin, natural rubber, polyimide, etc.), the introduction of PDM S, even if the amount is only 1% ~ 3%, can also improve its surface properties. If it changes from hydrophilic to hydrophobic, it is easy to release the mold during processing, and it can also improve the lubricating performance and reduce the friction coefficient, and it is not easy to be damaged by oxidation during friction.
(4) The separation membrane PDM S has an air permeability that is 1 to 2 orders of magnitude higher than other polymers, but it has poor strength and cannot be used as a membrane alone. The combination with other polymers solves the support problem, and its selection coefficient can also be increased.
(5) Preparation of liquid crystal skeletons. On polyhydrogenmethylsiloxane, various mesogenic groups are connected by hydrosilylation reaction to prepare polymerized liquid crystals, so that the phase transition temperature is widened, and the crystalline state is relatively stable. The chemical effects of some liquid crystals are also obvious.
(6) Lower processing temperature Some polymers, such as polyimide and polyarylate, have high melting points and thermal decomposition during processing. The introduction of PDMS can reduce the processing temperature.
(7) Medical materials Since silicones are widely used in medical materials, they will be discussed separately.
3 Matching technology and new additives
Develop coordination technology, processing technology and add new additives. Increasingly, there are more and more examples of functionality given by technological advancement and the addition of new additives. For example, carbon black was added to develop conductive silicone rubber. At present, advanced processing technologies such as vacuum casting and ultra-high frequency continuous extrusion (UH F) have been developed and applied. At present, at home and abroad, the method of adding different types of additives to improve the thermal stability of silicone rubber has achieved good results. The Beijing Institute of Chemistry, Chinese Academy of Sciences, uses the addition of silicon nitrogen rings or polymers to eliminate the degradation of the main chain caused by the hydroxyl groups and water of the silicone rubber, and can effectively improve the thermal stability of the silicone rubber in the closed system. It adopts the addition of a special polymer compound that is self-innovated and synthesized. Under high temperature (above 250 ℃), it can generate ions and prevent free radical oxidation and reoxidation many times. Finally, a thermally stable product is formed, which effectively prevents the thermal degradation of the side chain of the silicone rubber, and increases the heat resistance time of the silicone rubber (at 250-350 ℃) by 2 to 5 times. After being applied by Beijing Institute of Aeronautical Materials, it was added to dimethyl room temperature vulcanized silicone rubber. In a specific vulcanization system, after 300 hours of hot air assessment at 600 ℃ for a long time, it has not lost its elasticity and has been put into practical use. In addition, we have added a very small amount of silicone anti-yellowing agent to high temperature vulcanized silicone rubber and added a special silicone polymer of no more than 1% to epoxy resin to achieve anti-yellowing and change the surface properties of epoxy resin (Do not stick to other materials and smooth, etc.), to achieve the purpose of internal release.
In general, the development trend of organic silicon material technology is mainly reflected in the realization of the functionalization of organic silicon compounds and organic silicon polymers, specifically including the following micro-technical methods:
(1) Change the molecular structure of siloxane, for example, change the size, shape (linear, branched) and crosslink density of molecules.
(2) Change the organic group bonded to the silicon atom, such as alkyl (methyl, ethyl polycarbon), phenyl, vinyl, hydrogen, polyether, etc.
(3) Choose different curing methods. For example, peroxide curing, dehydrogenation reaction, dehydration reaction, addition reaction, dealcoholization reaction, deketone oxime reaction, ultraviolet light curing, electron beam curing, etc.
(4) Modified by organic resin (copolymerization, mixing). For example, epoxy, alkyd, polyether, acrylic, etc.
(5) Choose different packings. For example, metal soap, silica, carbon black, titanium oxide, etc.
(6) Choose various secondary processing technologies. For example, emulsion, solution fat, rubber compound, adhesive tape, etc.
(7) Adopt various copolymerization technologies, such as bulk polymerization, block polymerization, emulsion polymerization, etc.
Hangzhou Silva New Material Technology Co., Ltd. was established in 2014. It is a young but fast-growing company, specializing in the research, development, production and sales of silicone chemicals Silway specializes in modified silicones and formulation technology. The product line covers agricultural silicone additives, silicone waterproofing agents, cosmetic silicones, sealants and additives, modified silicones for die casting, etc. Welcome to consult and order: https://www.silways.com/