One of the main problems faced by human beings entering the 21st century is the disposal and reuse of waste rubber by waste rubber recycling equipment . At present, waste rubber products are the second-most waste polymer materials except waste plastics. They are mainly derived from industrial products such as waste tires, hoses, tapes, rubber shoes, and backing plates. Among them, the largest number of used tires, in addition to rubber. The scrap produced during the production process. The accumulation of a large number of waste tires not only causes waste of resources, but also is extremely prone to fire. Incomplete combustion of the tires releases hydrocarbons and toxic gases, and the flame is difficult to extinguish. A more serious problem is that waste rubber brings pollution to human living environment such as air, water and soil. Since waste rubber is a thermosetting polymer material, it is difficult to degrade, and the recycling cost is high and the technical difficulty is high. Therefore, in the past, the United Kingdom, the United States and other countries have always regarded them as waste, and only considered how to deal with it. However, after entering the 21st century, with the development of science and technology, people regard the waste rubber as a new type of black gold, which has been studied extensively at home and abroad. The waste rubber is ground into a vulcanized rubber powder, and the vulcanized desulfurization is made into a reclaimed rubber, which is the main way to recycle the waste rubber, and the most research value is obtained by using the rubber powder.
China is the world's largest consumer of rubber. Rubber consumption has ranked first in the world for seven consecutive years: China is also a country with a shortage of rubber resources. More than 75% of natural rubber is imported. China is still the world's largest producer of waste rubber. One of the countries, the problem of pollution of waste rubber products cannot be ignored. With the rapid development of the rubber industry, the output of waste rubber is increasing substantially every year. The utilization of waste rubber will be more severe. Therefore, the correct handling and utilization of waste rubber is an inevitable choice to promote the scientific development of China's rubber industry.
Waste rubber utilization is an industry that recycles, processes, and uses discarded tires, pipe belts, industrial rubber products, rubber shoes, and rubber factory waste. At present, the waste rubber utilization industry has included the recycling and processing of various waste rubber products, tire renovation, reclaimed rubber and rubber powder manufacturing, etc., involving materials recovery and rubber processing. The waste rubber utilization industry is an industry that is related to the continued development of the rubber processing industry and an important part of the environmental protection industry.
There are two main methods for recycling waste rubber: mechanically crushing or grinding waste tires into fine particles, so-called rubber particles and rubber powder; and destroying the chemical network structure of vulcanized rubber by desulfurization technology to produce so-called recycled rubber.
The rubber powder was originally used to produce reclaimed rubber. Later, with the advent of fine rubber powder (FRP), ultra-fine rubber powder (uFRP) and various modified rubber powders, the application field of rubber powder has been continuously expanded. At present, the global recycled recycled rubber production is 10% of the new rubber production. Rubber powder production is regarded as a new industry with high technology content, high market potential and broad prospects.
Pre-processing of waste rubber. Waste rubber products generally have non-rubber skeleton materials such as fiber and metal, plus a wide variety of rubber products. Therefore, pre-processing must be carried out before the waste rubber is crushed, including sorting, removal, cutting, cleaning and so on. Waste rubber should be inspected and classified. The waste rubber and its products from different categories and sources should be classified according to requirements. It is most desirable to adopt a recycling management cycle method and handle it according to the source of the waste rubber. For larger products such as waste tires, the bead is removed, and the tread separator is used to separate the tread from the carcass. The rubber shoes mainly collect the soles, and the inner tubes remove the valve fittings.
Freeze pulverization method. The basic principle of the low-temperature freeze-grinding method is that when a polymer material such as rubber is below the glass transition temperature (Tg), it is embrittled by itself, and at this time, it is easily pulverized into a powdery substance by mechanical action, and the vulcanized rubber powder is pressed. This principle is made.
There are two kinds of freeze pulverization processes: one is the low temperature freeze pulverization process. The other is a combination of low temperature and normal temperature. The former uses liquid nitrogen as the refrigerant. After the waste rubber is cryogenically cooled, it is pulverized by a hammer mill or a roller mill. The fine rubber powder production line is produced by the latter method. Using liquid nitrogen deep cooling technology to process used tires into fine rubber powder of 80 mesh or more, the temperature, speed and overload in the production process are controlled by closed-loop interlocking microcomputer, and there is no pollution to the environment. The production process of the production line adopts a compressed air-powered feeder and closed pipeline transportation. The whole line is closed except for the contact of the waste tires and the product packaging. In addition, since it is produced by the freezing method and has no high-temperature odor, it does not cause secondary pollution. And through the heat exchange process of fine rubber powder and coarse powder, the purpose of fully utilizing energy, reducing energy consumption and reducing product cost is achieved.
The method of simultaneous coarse and fine crushing: the two rolls performing this operation have grooves on one surface and no grooves on the other surface, which is a groove roller machine. Firstly, the washed rubber block is sent into the two rolls through the conveyor belt to break the glue, and then the broken rubber block and the rubber powder are dropped into the reciprocating sieve at the bottom of the device to be sieved, and the particle size requirement is dropped from the screen. Through the conveyor into the warehouse; the required rubber block is not reached, and the crushing is continued by turning the material into the groove roller machine.
The method of coarse and fine crushing on two machines: coarse crushing is carried out on a groove roller machine with grooves on both rolls, and the size of the coarsely crushed rubber is generally 6-8 mm. Then, it is passed into a light roller fine crusher for fine crushing, and its particle size is generally 0.8-1.0 mm (26-32 mesh). The rubber powder factory crushing equipment is different from the traditional recycled rubber crushing equipment, and is a special waste rubber crusher, medium crusher and fine crusher.
Application of rubber powder: The application of rubber powder can be divided into two major areas: one is direct molding or combined with new rubber to make products. For example, when 10 parts of FRP is added to tire tread rubber, its physical properties change little. But can reduce the cost of tread rubber. In the round, this belongs to the rubber industry; the second is in the broad field of the non-rubber industry. Nowadays, more and more manufacturers around the world use rubber powder instead of virgin materials, which is not only beneficial to environmental protection, but more importantly, the use of rubber powder can effectively reduce costs, improve performance, and obtain effects that other materials cannot obtain. It can be widely used as rubber, filler and composite materials in tires, hoses, tapes, rubber shoes, rubber industrial products, wires, cables and building materials. The fineness (90-120 mesh) and dosage of waste tire rubber powder As for the compressive strength of cement mortar, it is found that when the rubber powder content is less than 10%, it has little effect on the early strength of cement mortar; when the dosage is the same, the finer the rubber powder, the higher the mortar strength). The rubber powder can also be used together with plastics, such as polyethylene, polyvinyl chloride, polypropylene (the toughening materials commonly used for the multi-toughening modification of polypropylene are polyethylene, ethylene-vinyl acetate copolymer, rubber, thermoplastic elastomer). And rubber powder, etc., the material modified by rubber powder has the lowest cost. Adding a small amount of uFRP can improve the rigidity, hardness and heat resistance of polypropylene; as a nucleating agent of polypropylene, the impact toughness of polypropylene is improved. ), polyurethane, etc., to improve performance and reduce costs.
The use of rubber powder to modify the asphalt pavement is also widely used. When the asphalt used for pavement is modified with fine rubber powder, the performance of the modified asphalt and the asphalt mixture after the rubber powder is finely ground is good. Roads coated with rubber powder modified asphalt are used in many developed countries in Canada, the United States, Belgium, France, the Netherlands and other countries. Some provinces and cities in China have also entered Jiangxi, Hubei, Guangzhou, Beijing and other places, and successively laid experimental sections. Practice has proved that roads paved with rubber powder modified asphalt can reduce road surface cracking and softening, road surface is not easy to freeze and slip, improve driving safety, and can improve road life, at least improve the service life of ordinary asphalt roads. Doubled.
Recycled rubber refers to the physical and chemical action of waste rubber products through pulverization and re-processing and mechanical processing, so that it can be changed from the original elastic state to the viscoelastic state of processing and can be vulcanized. The production of recycled rubber by recycled rubber is the main method for recycling waste tires in China. The early stage of reclaimed rubber technology is based on the reverse chemical desulfurization technology of natural rubber. The regeneration (desulfurization) chemical reaction process in production will produce more serious exhaust gas. The environmental pollution caused by these acidic waste gases has high cost and complicated technology. Developed countries have stopped producing reclaimed rubber as early as the 1970s and 1980s. Many countries have classified reclaimed rubber as a phase-out product with secondary pollution and high energy consumption. However, due to historical reasons and the lack of rubber resources in China, and the early development of the reclaimed rubber industry, the country has been developing stably and continuously, and has formed a production capacity of nearly one million tons.
Rubber regeneration methods can be broadly classified into three categories: physical regeneration, chemical regeneration, and biological regeneration. Physical regeneration uses external energy, such as force, heat, cold force, microwave, ultrasonic wave, ray energy, etc., to break the three-dimensional network of crosslinked rubber to form a regenerative glue with fluidity. Chemical regeneration is the use of chemical auxiliaries, such as organic disulfides, mercaptans, alkali metals, etc., at a certain temperature, by mechanical force directed catalytic cracking of rubber cross-linking bonds, and the fracture point is stabilized, to achieve the purpose of regeneration. Biological regeneration is the sulphur cross-linking of vulcanizates that breaks or desulfurizes under the action of microorganisms, so that the waste rubber can be reprocessable. Here is a brief introduction to several methods of physical regeneration.
Physical regeneration technology
1.1 Microwave regeneration
Microwave desulfurization is a non-chemical, non-mechanical one-step regeneration method that uses microwave energy to cut off sulfur-sulfur bonds (s-s) and sulfur-carbon bonds (s-C) without destroying carbon-carbon bonds (C - C), thus achieving the purpose of regeneration. Because microwave energy is controllable, the bond energy of various chemical bonds is different, and the energy required for fracture is also different, such as s-s bond (213 kJ/m01), s-C bond (259 kJ/m01), CC bond ( 347 kJ/m01), so the microwave energy breaking button is selective, so the performance of the reclaimed rubber produced by this method is close to that of the original rubber, and there is no need to add any additives during the microwave desulfurization process. Therefore, the microwave desulfurization is basically free from pollution.
1.2 Ultrasonic regeneration
Ultrasonic waves can also be used to destroy the cross-linking bonds and retain the molecular backbone, so that the vulcanized rubber can be regenerated. In addition to destroying the three-dimensional network structure, the ultrasonic desulfurization process of vulcanized rubber also causes the c-C bond of the macromolecular chain to be broken.
Cracking, so further research is needed to improve the selectivity of ultrasonic desulfurization. The performance of the original glue can be maintained to the utmost extent only if the chemical bond is selectively destroyed.
1.3 Electron beam regeneration
The electron beam irradiation regeneration method utilizes the unique radiation sensitivity characteristic of butyl rubber (IIR), and the chemical energy-breaking-depolymerization effect is generated by the high-energy electron beam of the electron accelerator. Make it regenerate. Most rubber elastomers undergo a structured cross-linking reaction under the action of radiation, and only a few types of rubber containing structural units of tertiary carbon atoms, such as IIR and IIR vulcanizates, exhibit degradation reactions. Electron beam radiation regeneration is the use of a high-energy radiation field to exhibit degradation reactions. Electron beam radiation regeneration utilizes the unique radiation chemistry of butyl rubber to form the basis of electron beam radiation regeneration of butyl rubber.
The traditional production process of reclaimed rubber mainly includes oil method (direct steam static method), water oil method (cooking method), high temperature dynamic desulfurization method, extrusion method, chemical treatment method, microwave method and the like. But the principles of application are basically water and oil. The main methods for the production of reclaimed rubber in China are oil method, water oil method and high temperature dynamic desulfurization method. The main process, method characteristics and some equipment are briefly described below.
1) Oil process
Waste rubber - cutting rubber - washing rubber - coarse crushing - screening - fiber separation - mixing oil - desulfurization - kneading - filter rubber - refining film - finished product. The method is characterized by simple process, no special requirements for the plant, low investment in construction, low production cost and no pollution of sewage. However, the regeneration effect is poor, the performance of the reclaimed rubber is low, and the particle size of the rubber powder is small (28~30 mesh), which is suitable for rubber shoes and miscellaneous rubber varieties and small-scale production.
2) Water and oil process
Scrap rubber - cutting glue - washing - coarse crushing - fine crushing - screening - fiber separation - weighing and blending - desulfurization - kneading - filter gel - refining film - finished product. The method is characterized by complicated process, special requirements of factory buildings, many production equipments, large investment in construction, small particle size requirements and high production costs. There is sewage discharge and there should be sewage treatment facilities. However, the regeneration effect is good, and the quality of the reclaimed rubber is high and stable. Especially for the waste rubber containing more natural rubber components, it can produce high quality reclaimed rubber. Applicable to tires, rubber shoes, miscellaneous rubber and other waste rubber varieties and medium and large-scale production.
3) High temperature dynamic desulfurization
The waste rubber does not need to be pulverized too much, generally about 20 mesh. Widely used rubber, natural rubber and synthetic rubber can be desulfurized, and the desulfurization time is short, and the production efficiency is good. The fiber content can reach 10%, and it can be fully carbonized at high temperature. There is no sewage discharge, less environmental pollution, good quality of reclaimed rubber, and simple production process. However, the equipment investment is larger than the oil method, and the desulfurization process conditions are strict. Suitable for a variety of waste rubber varieties and medium and large-scale production.
With the rapid development of the world's modern industry, the use of rubber products will increase. On the one hand, waste rubber is increasing year by year, and waste rubber recycling equipment resources are in short supply; on the other hand, the increase of rubber waste has increased environmental pollution. In today's increasingly environmentally conscious awareness, improving the recycling process of waste rubber is one of the important issues we have to solve. From the development point of view, the recycling of rubber should be based on the original process, and vigorously develop waste rubber products that do not undergo regeneration or only add a small amount of regenerant.