Properties and application research progress in silicone rubber
1, the heat resistance of silicone rubber
Silicone rubber is a high molecular weight poly-siloxane reinforcement, curing processes and made of silicone elastomer, whose chain is based on the SI-o bond alternately connected, as the SI-o bond bond energy much higher than c-c bond bond energy, thus the silicone rubber with high thermal stability. However, with the development of science and technology, heat resistance of silicone rubber has been unable to meet the requirements in harsh conditions of use. Therefore, improving the heat resistance of silicone rubber is a current hot topic in the field of silicone rubber.
Starting from the mechanism of silicone rubber vulcanizate heat aging, improve its thermal ageing methods include: (1) change the structure of Silicon rubber side-chain groups, introduction of phenyl, to prevent the silicone side-chain groups in main-chain cross-linking or degradation caused by oxidation and decomposition. Because phenyl easily oxidation, in Silicon oxygen chain Shang formed bit resistance, makes Silicon oxygen chain difficult to into ring degradation, and due to its conjugate effect, block effect more big, hot decomposition temperature more high; (2) in silicone rubber molecular main chain Shang introduced big volume chain segment, as Asia phenyl and ring II Silicon nitrogen alkyl,, makes sulfide glue AC Alliance key hot stability improve; (3) in glue material in the joined heat additives, as Fe2O3, and CeO2,, to prevent side chain oxidation AC Alliance and main chain ring of degradation. Present method (3) most commonly used and the most effective and the least costly and relatively easy to implement. Heat-resistant additives are commonly used oxide, antioxidant, three main types of silicon and nitrogen additives and silicone.
2, cold tolerance of silicone rubber
Development of the aerospace industry put forward higher requirements for rubber products, such as requiring its at extreme low temperatures maintaining elasticity and sealing performance, resistance to high and low temperature cycle impact vacuum particles and UV-resistance and other properties. Silicone rubber are considered to be the most suitable space requirements of the rubber varieties. Russia of the amorphous silica gel prepared at-60 ° c,-90,-100 degrees centigrade-120 degrees centigrade temperatures, air, inert gases and vacuum environment, long-term use of rubber products. -70 ¡æ ~35 ¡æ 2101, 2103 and phenyl silicone rubber using phenyl silicone rubber using ethyl silicone rubber parts manufactured at-90 ° c and-120 ℃ long-term use. Silicone rubber is suitable for low-temperature seal, but it must be reinforced with glass cloth, space applications, to provide necessary strength. Diethyl silicone rubber can be used for cryogenic sealing system, at-110 ° c cold resistance coefficient of 0.2 per cent. Silicone heat-shrinkable tubing in industrial cables Terminal and junction of the movable parts of the pneumatic system of the insulation can be used.
3, the thermal conductivity of silicone rubber
With Al2O3 layer of thermal conductivity of silicone rubber can be made from electronic components, while Al2O3 are polymers of 3 times when the material's coefficient of thermal conductivity of up to 2.72W/(m · K), with plenty of Al2O3, also for high heat and flame resistance. In the rubber filling silver, BN, and platinum based flame retardants can prepare both fire resistance and thermal conductivity of silicone rubber material in a certain ratio, the material can be equipped with 14 W/(m · K) and thermal conductivity of V-l (UL-94), levels of flame retardant. Silicone rubber filled with metal powder (Al,BN,AlN) and stearic acid surface of AI (OH) 3 powder can be prepared with high thermal conductivity and good flame retardant silicone rubber, flame retardant at the V-0 level (UL-94), 1.09 thermal conductivity w/(m · K), can be made to prevent sliding LCD gaskets. Add lots of BN,Al2O3 in the silicone, quartz powder and the amount of coupling agent, curing agent, then dissolved in xylene solution, to coated glass cloth, drying and curing, and fabric coating has a good appearance, heat and flame resistance. Added to the liquid silicone rubber surface treatment SiC,Ba2SO4, Al, and this liquid mixture in between 2 electrodes, plus the electric fields cause thermal conductive filler orientation, which produced very good thermal conductivity of rubber materials used on electronic components, electronic components and heat sink thermal layer is formed between. AlN powders by Al2O3 vapor coating and then join in silicone rubber, the higher thermal conductivity, high thermal radiation of heat-resistant materials can be used for sheeting.
Thermally conductive silicone rubber studies abroad are fully developed, home is still in the development stage. Thermally conductive silicone rubber application needs to be developed further, can solve its integrated performance and technological unification problem, thermally conductive silicone rubber will undoubtedly have a good prospect. In short, not only has good thermal conductivity thermal conductivity silicone rubber, but also has traditional materials such as metals are immeasurably more comprehensive performance, will become more and more attention, and its development prospects are considerable, will become increasingly wide range of applications.
4, silicone rubber insulation
Silicone rubber with excellent resistance to high and low temperature, weathering, ozone, Corona resistance, electrical insulation, surface hydrophobicity, low compression rate, is the unique properties of rubber varieties. It is ideal for use as organic insulating materials in electrical industry in recent years has been widely used in electrical insulation systems. Most domestic and foreign manufacturers of composite insulators are filled with more aluminium hydroxide (Al2O3 · 3H2O) methyl vinyl silicone rubber (silicone) outdoor insulation material, also is used as a composite surge arresters, circuit breakers, transformers, high-voltage switchgear and coat of insulating materials such as wall bushing and so on. According to incomplete statistics, in 2001 run at higher voltage lines of Silicon rubber composite insulators in China has reached 1.9 million, and to grow at a rate of more than 25% a year.
Since in the 1960 of the 20th century, many of the world's developed countries, such as Germany, the United States, Britain, France, Japan and others had already begun studying the use of organic polymers manufactured outside of composite insulators. First used of insulated material main has fat ring family epoxy, and II Yuan b c rubber, and ternary b c rubber, and PTFE and at room temperature sulfide silicone rubber,, but by these material manufacturing of composite insulated child in using run must time Hou are appeared has some such as of problem, as epoxy easy aging, and cracking, and hate waterborne lost, and surface produced leakage up marks; b c rubber using years Hou appeared hate waterborne declined, and faded, and crack, and produced leakage up marks; PTFE no hate waterborne migration characteristics, Prone to corrosion and other problems after the surface contamination, and expensive, processing difficulty RTV silicone resistance to tracking and erosion resistance and mechanical strength is not ideal, there is mechanical damage and corrosion and cracking of the surface. But HTV silicone rubber effect is better, not aging, resistance to tracking and erosion resistance is relatively good, especially after its surface pollution still have good hydrophobicity, making outdoor composite insulator material of choice.
5, silicone rubber in biomedicine
Silicone rubber with heat, cold, non-toxic, resistant to biological age and physiological inertia, minimal tissue reaction, implantation of human tissue does not cause a foreign body reaction, not cause inflammation to the surrounding tissue and better mechanical performance advantages, and meets the requirements of medical polymer materials; medical and health, medicine has been widely used. Now, application of silicone rubber in the medical, pharmaceutical and health industry can be broadly grouped as follows: long-term indwelling substitutes for the organ or tissue in the human body, short term indwelling medical devices in the human body, plastic surgery, in vitro medical devices, drug delivery systems and other aspects.
Silicone rubber has occupied an important position in the field of medicine, but would like to make more progress, still has to resolve technical problems: the hydrophobicity of silicone rubber, its products into the human body still has a slight sensation. Can used surface modified sex solution, as in Silicon rubber products surface coated reply hydrophilic material, or with radiation, and plasma processing, or through total mixed modified sex, improve silicone rubber of hydrophilic; II is on skin Xia contraceptive buried planting system,, to silicone rubber for carrier of long-term skin Xia buried planting agent in placed effective expires Hou must removed, increased has using who of pain and spent, and difficult to guarantee all using who are can regular removed, thus increased has contraceptive failed of dangerous. Thus triggering a biodegradable subdermal contraceptive implant research, namely a biodegradable and steroidal drugs permeability of silicone rubber as releasing progestogen replacement carrier; progesterone released after the carrier absorbed in the body without having to take out. Single-type implants, bio-degradable implants are the main directions of research and development. Third, with the development of biomedical engineering, tissue engineering, materials technology, performance increasing demand; how to make silicone full application in Bioengineering and tissue engineering will be the main direction of research work, such as bio-sensor is the centrepiece of a bio-technology. Bio-sensor miniaturization, and the adaptability of organisms and so on, will become an important issue associated with artificial organs. In short, medical silicone rubber in the life sciences, medical devices, drugs and other areas have been extensive and important application, but its potential has yet to be dug up; with the development of science and technology, it will make a greater contribution to mankind.