What benefits does scrap silicone rubber products bring to silicone?silicone plate custom

　　With the development of industrial production, transportation, urban construction and the increase of population density, the problems of noise pollution, air pollution, water pollution and solid waste discharge are becoming more and more serious, and it has been listed as the four major pollutants in the world. Silicone rubber is a synthetic rubber with a silicon-oxygen bond as the main chain. It has properties such as high and low temperature resistance, radiation resistance, high pressure resistance, physiological inertia, ozone aging resistance, weather resistance, and high air permeability. Demonstrates excellent chemical inertness. The production and consumption of high-temperature silicone rubber in my country has experienced rapid growth in recent years. It is expected that the consumption of high-temperature silicone rubber in various fields will maintain a growth rate of 8% in the next five years. By 2022, the output of high-temperature silicone rubber in my country will reach 703,000 tons.

　　my country's high temperature silicone rubber production capacity and output in recent years and forecast

　　Analysis and forecast of my country's high temperature silicone rubber supply and demand and product self-sufficiency rate in recent years

　　It is estimated that by 2022, the market demand for high-temperature silicone rubber in my country will reach about 675,000 tons. The consumption proportion of high temperature silicone rubber in various fields in 2017 is shown in Figure 3.

　　What follows is a rapid increase in the amount of waste secondary silicone rubber raw rubber produced in production, silicone products and scraps formed in vulcanization molding, and waste silicone rubber products formed in the application process. According to an annual elimination rate of 10%, the amount of waste silicone rubber products produced will exceed 40,000 tons per year, which is a problem that cannot be ignored.

　　Organosilicon compounds cannot be decomposed naturally, so landfill cannot decompose waste silicone rubber. The process of converting waste silicone rubber into silica through combustion is very energy-intensive. The price of silicone rubber raw materials is relatively high, and the production and accumulation of waste silicone rubber will not only occupy a large number of workshops and pollute the environment, but also lead to rising costs and cause great economic pressure on enterprises. Therefore, recycling waste silicone rubber is of great significance to reducing environmental pollution and improving economic benefits. At present, the recycling of silicone rubber mainly includes physical crushing method and chemical cracking method.

　　01

　　physical crushing

　　The physical crushing method refers to the physical crushing of waste silicone rubber by shearing machines, double-rollers, ball mills and other equipment, and then directly used as filler after classification and screening, or used after modification treatment (activation). According to the different temperature and mode of action, the physical crushing method can be divided into four types: low temperature crushing method, kneading method, polishing method and elastic deformation method, and the obtained particle surface morphology, shape and size are different.

　　1. After crushing, it can be directly used as filler

　　Silicone rubber is chemically inert. After simple physical crushing, there are few active functional groups on the surface of the particles, and it is difficult to react with the new base rubber. Therefore, the products prepared by this method are mainly used as modified fillers for rubber and plastics to achieve the purpose of reducing product cost, power consumption and modification. The silicone rubber particles prepared by the physical crushing method can be mixed with the silicone rubber compound in any proportion.

　　2. Modification treatment after crushing

　　Ordinary rubber such as natural rubber, styrene-butadiene rubber, butadiene rubber, nitrile rubber, etc., the molecular structure is C—C C—C, its bond energy is low, its chemical activity is high, and it is easy to react with sulfur and oxygen. easy. The molecular structure of silicone rubber is Si-O-Si, which has high bond energy, good heat resistance and aging resistance, and is not easy to be oxidized.

　　In the 1980s, the former Soviet Union carried out the first physical crushing of waste silicone rubber into particles, and then the particles were treated with tetraethyl orthosilicate to form active silicone rubber powder, which was mixed into new silicone rubber compounds and vulcanized into products. , found that the activated silicone rubber powder can improve the low temperature resistance, electrical strength and physical and mechanical properties of the vulcanizate.

　　my country has also carried out research on the modification of waste silicone rubber. For example, Wu Shaoyin and others adopted the methods of all-weather aging degradation, effective crushing and classification, and surface stearic acid activation treatment to process waste silicone rubber into a suitable particle size ( 40. The active regenerated silicone rubber powder can be used as silicone rubber filler with good processing performance and reinforcing effect; Zhang Weiying et al. used a mixture of hexamethylenetetramine and ferric chloride/ferrous chloride to treat waste silicon The rubber was activated and modified and used as a filler to prepare EPDM rubber. It was found that this type of activator can effectively activate waste silicone rubber.

　　02

　　chemical cracking method

　　Although the polysiloxane molecular chains in waste silicone rubber have been cross-linked, the cross-linking density is not large. By adding appropriate catalysts (acids, bases, salts, etc.) to cleavage the silicon-silicon chain, waste silicone rubber can be decomposed into dimethylcyclosiloxane mixture (DMC) and small molecular chain polysiloxane, and Can be re-applied to silicone rubber raw rubber preparation. The above method is the chemical cracking method, which has become the main way to recycle waste silicone rubber. Chemical cracking methods mainly include base catalysis, acid catalysis, water, thermal and ultrasonic cracking methods. Europe and the United States started early in the pyrolysis and recycling of silicone rubber, and has now formed a complete set of silicone rubber pyrolysis and recycling technologies with mature technology and standardized management. Mainly focus on high temperature pyrolysis, catalytic pyrolysis, vacuum pyrolysis recovery and so on.

　　1. Alkali catalytic cracking method

　　Since both alkali and silicone rubber are solid powders, solvents are often used to improve their contact effect, which will cause solvent loss and environmental pollution. Although the quality of DMC prepared by this process is high and the equipment corrosion is small, there are still the following problems: First, the consumption of catalyst is large, and 700-750 kg KOH is needed to produce 1 t of crude DMC; High risk, local violent reactions are prone to occur in the kettle, which may cause combustion and explosion accidents; Third, the product composition is complex and difficult to use; Fourth, the scope of application is small, only suitable for depolymerization of button scraps and mold glue, not applicable on glass glue.

　　2. Acid catalytic cracking method

　　Acid catalytic cracking is a commonly used process in China in recent years, and the catalyst used is mainly concentrated sulfuric acid. Compared with the strong base catalytic degradation method, the biggest advantage of the concentrated sulfuric acid catalytic degradation method is that the safety factor is high, and the possibility of combustion and explosion is small. However, there are still many deficiencies in this method, mainly in four aspects: First, the corrosion resistance of the equipment is required to be high, and the equipment is replaced frequently in actual production, which increases the cost; Second, the recovery rate of DMC is unstable, even if the For the same waste silicone rubber, the DMC recovery rate can fluctuate within a range of ±15%; third, the DMC recovery rate is relatively low. 40% to 50%; Fourth, a large amount of acidic waste liquid and waste residue will cause secondary pollution and further increase the cost. The following figure shows the general process flow of the concentrated sulfuric acid catalytic cracking method used by domestic enterprises.

　　Although the acid-catalyzed cracking of silicone rubber has been significantly improved compared to the alkali-catalyzed cracking of silicone rubber. However, when the silicone rubber formulation contains basic substances such as aluminum hydroxide and calcium carbonate, the acid used as a catalyst can react with these basic substances, resulting in a large amount of catalyst consumption and a large amount of side reaction residues. Therefore, the types of silicone rubbers that can be treated by acids as catalysts are limited.

　　3. Ultrasonic cracking method

　　The high-energy ultrasonic method has been successfully applied to the recovery of vulcanized silicone rubber, and the filler in the silicone rubber plays a key role in its recovery possibility. Although DMC cannot be obtained by this method, linear oligomeric dimethylsiloxane can be obtained, which can be used again in the production of silicone rubber. S. E. Shim et al. found that ultrasonic waves can break the strong hydrogen bonds between filler and matrix in silica filled silicone rubber, and recovered the silicone rubber in an extruder with additional high-energy ultrasonic waves.

　　4. Thermal cracking method

　　The thermal cracking method has harsh reaction conditions, high energy consumption, many side reactions, low recovery rate, and the reactor is small in size and low in safety, making it difficult to carry out mass production. However, this method also has the advantages of relatively pure cracked products and no introduction of other chemical impurities. At present, there are very few [ ] adopting this process at home and abroad.

　　5. Water splitting method

　　When vulcanized silicone rubber is exposed to high pressure water vapor, its silicon-oxygen-silicon bond can be broken and depolymerized into siloxane oligomers. Depolymerization is more likely to occur especially in the presence of small amounts of alkali metal hydroxides. However, this method has high energy consumption and low efficiency

　　03

　　Catalytic cracking method

　　The physical crushing method is simple in process, simple in operation, non-toxic and pollution-free, and has low requirements for equipment. By selecting a reasonable regeneration process and processing aids, the silicone rubber can be regenerated in a short time, which is suitable for the direct utilization of silicone rubber scraps. However, the scope of application is limited, and the multiple recycling of silicone rubber cannot be realized. Chemical cracking methods mainly include alkali catalytic cracking, acid catalytic cracking, water cracking, thermal cracking and ultrasonic cracking. The content of D4 in the product of the alkali-catalyzed cracking method is low, and the addition of solvent can improve the yield, but the solvent added in this method will bring new pollution, and it is not suitable for decarboxylated silicone sealant. The acid catalytic cracking method has mature technology, good effect, and high content of D4 in the product, but the equipment is seriously corroded, the utilization rate is low, and the waste acid is difficult to handle. It will also react with fillers such as aluminum hydroxide and calcium carbonate in silicone rubber. Scope is limited. However, the water cracking method, thermal cracking method and ultrasonic cracking method have a relatively small application range and require high equipment, so they cannot be widely used. The catalytic cracking method of siloxane halogenation agent is a new method with low energy consumption and high yield, and has relatively significant technical advantages and economic prospects. However, due to the short time when this method was proposed, the relevant research is not deep enough, and there is still a lot of room for exploration and development. Further development is needed in the aspects of production process optimization, regulation of the proportion of siloxane mixed rings, exhaust gas and waste residue treatment, etc. Related work and production process standards still need to be further formulated.

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