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Recycled rubber

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A rubber that has been processed from vulcanized corner waste in the production of rubber products and has certain plasticity and can be reused. Referred to as recycled rubber. According to the used waste rubber, recycled rubber is divided into outer tires, inner tires, rubber shoes and so on. Recycled rubber can be partially used in rubber products instead of raw rubber to save raw rubber and carbon black. It is also beneficial to improve processing performance and certain properties of rubber products. The regeneration process is a process in which part of the molecular chains and cross-linking points of the vulcanized rubber are broken under the combined effects of plasticizers (softeners and activators), oxygen, heat and mechanical shear.


1 Introduction

Reclaimed rubber

The softening agent plays the role of expansion and plasticization. Commonly used are coal tar, pine tar, petroleum-based softener, and cracked residue. The activator can shorten the regeneration time and reduce the amount of softener. Commonly used activators are aromatic mercaptans and their zinc salts and aromatic disulfides.

The production process of reclaimed rubber includes three steps: crushing, regeneration (desulfurization) and refining.

In addition to this traditional regeneration method, a new method of utilizing waste rubber by freezing and pulverizing the waste rubber to make rubber powder with different particle sizes is directly used as a rubber filler.

2 Development Status

China is a country with relatively scarce raw rubber resources. About 50% of China's annual consumption of recycled rubber needs to be imported. Finding the source of rubber raw materials and their substitute materials is an endless task for China. Therefore, the careful and proper treatment of waste rubber is of far-reaching positive and practical significance for making full use of renewable resources, getting rid of the scarcity of natural resources, reducing environmental pollution, and improving people's living environment. Recycled rubber has always been an important raw material for the world rubber industry. On the one hand, it can replace rubber and alleviate the severe shortage of natural rubber; on the other hand, it enables waste rubber to be recycled and reused, which solves the problem of waste rubber pollution to the environment.

In 2006, China produced 1.65 million tons of recycled rubber, accounting for 85% of the world's total output of recycled rubber. As of November 2007, China has been able to produce more than 30 varieties of recycled rubber products including seven series of tires, rubber shoes, miscellaneous rubber, light-colored, special, special, and export; there are more than 700 recycled rubber companies nationwide, engaged in business The number of people reaches 100,000; several Pingyao, Fenyang, Shanxi Yutian, Cangzhou, Nantong, Jiangsu, Nanzhou, Zhejiang, Wenzhou, Ningbo and other recycled rubber production bases of more than 100,000 tons have been formed; waste tire recycling, dismantling, One-stop industrial chain for processing, regeneration and deep processing.

China's recycled rubber industry has reached the level in terms of production scale, enterprise scale, variety grade, process technology, equipment support, and foreign exchange earnings from exports. After becoming the world's largest producer of recycled rubber in the 1980s, China has joined the ranks of developed countries in the global recycled rubber industry.

From January to December 2005, China's recycled rubber manufacturing industry achieved a cumulative total industrial output value of 5,044,555,000 yuan, an increase of 104.00% over the same period last year; a cumulative product sales income of 4,493,894,000 yuan, an increase of 76.49% over the same period last year; a cumulative Total profit was 172,599,000 yuan, an increase of 66.99% over the same period last year.

From January to December 2006, China's recycled rubber manufacturing industry realized a cumulative total industrial output value of 7,077,772,000 yuan, an increase of 27.09% over the same period last year; realized cumulative product sales income of 7,271,686 thousand yuan, an increase of 45.18% over the same period last year; Total profit was 287,409,000 yuan, an increase of 35.92% over the same period of the previous year.

From January to November 2007, China's recycled rubber manufacturing industry realized a cumulative total industrial output value of 8,579,511,000 yuan, an increase of 34.81% over the same period of the previous year. A cumulative product sales income of 8,165,563 thousand yuan, an increase of 25.69% over the same period of the previous year; The total profit was 430,895 thousand yuan, an increase of 64.90% over the same period last year.

Recycled rubber has become the third largest rubber source in China, and the industry's profitability has grown rapidly and has a good development trend. China's recycled rubber industry has ranked among the developed countries in the global recycled rubber industry. At the end of March 2012, there were 152 recycled rubber manufacturing enterprises above designated size in China, with total industry assets of 5.385 billion yuan, a year-on-year increase of 44.17%. From January to March 2012, China's reclaimed rubber industry enterprises achieved 4.19 billion yuan in revenue from their main operations, an increase of 30.83% year-on-year; total profits reached 251 million yuan, an increase of 44.83% year-on-year.

Waste hazard

The disposal of waste rubber is one of the serious problems people face today. In order to meet the ever-increasing material performance requirements, rubber has developed in the direction of high strength, abrasion resistance, stability and aging resistance, but at the same time caused the problem that the rubber can not be naturally degraded for a long time after waste. Pollution (white pollution) is more difficult to handle with black pollution. On the other hand, valuable rubber resources are wasted.

Millions of tons of waste rubber are produced every year in the world, and the amount is so huge. How to effectively treat it has become a problem of general concern in the whole society. For this reason, in addition to burning waste mountain rubber products as fuel, since 1910, scientists from various countries have studied more effective waste rubber regeneration treatment technologies. Recycled rubber refers to waste vulcanized rubber that undergoes physical and chemical processes such as pulverization, heating, and mechanical treatment to change it from an elastic state to a plastic and viscous rubber that can be revulcanized. The essence of the regeneration process is the destruction of the vulcanizate network under the combined effects of heat, oxygen, mechanical action, and chemical and physical action of the regenerant. The fracture site has both cross-links and macromolecules between cross-links. key.

Regeneration method

Physical regeneration

Physical regeneration uses external energy, such as force, heat-force, cold-force, microwave, and ultrasound, to break the three-dimensional network of crosslinked rubber into low-molecular fragments. Except that microwave and ultrasonic energy can cause real rubber regeneration, the other physical method can only be a pulverization technique, that is, making rubber powder. When these rubber powders are used in the rubber industry, they can only be used as non-reinforcing fillers. The use of microwave, ultrasound and other physical energy can achieve a satisfactory rubber regeneration effect, but the equipment requirements are high and the energy consumption is large.

Normal temperature crushing method

The normal temperature pulverization method generally refers to a pulverization method in which the processing temperature is at 50 ± 5 ° C or a slightly higher temperature by pulverizing rubber by mechanical action to make rubber powder.

Cryogenic pulverization

The low-temperature pulverization method is an effective method for pulverizing the rubber at a low temperature by refrigerating the medium, mainly using liquid nitrogen to freeze the rubber below the glass transition temperature.

Solution pulverization

Wet method or solution pulverization method is a method of pulverizing in a medium such as a solvent or a solution to produce rubber powder.

Microwave regeneration

The microwave regeneration method is a non-chemical, non-mechanical one-step desulfurization regeneration method.

Ultrasonic regeneration

The University of Akron invented the ultrasonic regeneration method in 1993. This method uses high-density energy fields to destroy cross-links and retain the molecular backbone, thereby achieving the purpose of regeneration. The ultrasonic field can generate high-frequency stretching stress in a variety of media. High-amplitude oscillating waves can cause solid fragmentation and liquid cavitation. The theoretical explanation is: it may be that the acoustic wave cavitation mechanism causes the ultrasonic energy to be concentrated at the local position of the molecular bond, so that the ultrasonic field with a lower energy density is transformed into a high energy density at the location of the damaged cavity.

Electron beam regeneration

The electron beam regeneration method mainly uses the unique radiation sensitivity of IIR, and uses the high-energy electron beam of the electron accelerator to produce a chemical depolymerization effect on it.

Chemical regeneration

Chemical regeneration is the use of chemical auxiliaries, such as organic disulfide thiols, alkali metals, etc., under elevated temperature conditions, the use of mechanical forces to break the rubber cross-linking, to achieve the purpose of regeneration. In the chemical regeneration process, a large number of chemicals are used, and these chemicals are almost all unpleasant and harmful at high temperatures and pressures.

The De-link regenerant that has appeared on the market in recent years can be said to open up completely new concepts and methods for the regeneration of rubber. This is a new recycled rubber technology jointly developed by Malaysian scientist Dr. Sekhar and Russian scientist Dr. Kormer. The basic principle is to use a regeneration agent De-link to make it react with the SS bond without destroying the CC bond, thereby maintaining the rubber main Chain macromolecules only break the sulfur network.

RV regeneration agent method

The RV regeneration agent method is to make the RV rubber regeneration agent uniformly wrapped on the surface of the waste rubber powder particles through mechanical shearing, and infiltrate into the rubber powder particles through the infiltration to reduce the bond energy of the SS crosslinks, which can effectively be used in a short time The SS cross-linking bond is released internally without destroying the SC and CC bonds, so that the waste rubber powder is restored to activity, transformed into a recycling state similar to plastic, and the extremely high physical properties of the original rubber are maintained.

TCR regeneration method

This method is to mix a small amount of plasticizer and regenerant into the low-temperature pulverized rubber powder, and then send it to the powder mixer for short-term treatment at room temperature or slightly higher temperature. The advantages of this method are less environmental pollution, energy saving and energy saving, so it is a more promising regeneration method.

Microbial desulfurization

The microbial desulfurization method has been reported in Japan and Germany. This method is to crush the waste rubber to a certain particle size and put it into a solution containing sulfur-phage bacteria to make it biochemically react in the air. Under the action of sulfur-phagizing bacteria, the sulfur bonds on the surface of the rubber particles are broken, showing the performance of recycled rubber.

Mechanochemical regeneration

This kind of waste rubber regeneration method called "shear flow field reaction control technology" is characterized in that it does not use chemical agents and consumes electricity and water to regenerate waste rubber. By giving waste rubber heat, pressure, The shearing force causes the sulfur bonds (crosslinking points) of the vulcanizate to break and become a new type of elastic rubber with stable performance and elasticity.

Other regeneration methods

The oil method is to add a regenerant to the crushed waste rubber powder, put it into a vulcanization tank, and desulfurize under the conditions of 150MPa × 4 ~ 5h, and then crush, knead, refine, filter gel, and produce tablets. product. The water-oil method uses the property that the rubber powder can swell quickly under high temperature and pressure conditions, and the degree of swelling is much larger under lower pressure conditions. The difference between the water-oil method and the oil method is mainly the difference in the desulfurization stage. The high-temperature and high-pressure dynamic desulfurization method is a new regeneration process that appeared in the late 1980s and early 1990s in China. It takes the advantages of the water oil method and the oil method and discards them. The high-temperature and high-pressure dynamic desulfurization method completes the desulfurization process by the transfer of energy and heat under the action of high-temperature and high-pressure and regenerant. This method not only has a high desulfurization temperature, but also the material is always in a moving state during the desulfurization process.

3 production process

Steam method

1. Oil method

The rubber powder and the regenerant are mixed uniformly, put into an iron pan, sent to a horizontal desulfurization tank, and heated by direct steam. The steam pressure is 7MPa (5 ~ 7kgf / cm2), and the desulfurization time is about 10 hours. The process equipment is simple.

2. Superheated steam method

Mix the rubber powder and the regenerant evenly, put it into a desulfurization tank with an electric heater, pass direct steam, and use an electric heater to increase the temperature to 220 ~ 250 ° C to destroy the fibers in the rubber powder. The steam pressure is 0. 4MPa (4kgf / 2).

3. High pressure method

Mix the rubber powder and the regenerant evenly, put it into a closed high-pressure container, and pass 4.9 ~ 69MPa (50-70kgf / cm2) direct steam for desulfurization and regeneration. This method requires high equipment and requires a large investment.

4. Acid method

The rubber powder is first soaked with dilute sulfuric acid to destroy the fibrous material, and then the acid is neutralized and washed with alkali, and then direct steam is passed for desulfurization and regeneration. This method requires corrosion-resistant equipment, consumes a large amount of acid and alkali, has complicated processes and equipment, high costs, and the product is easy to age.

Cooking

1. Water and oil method

The desulfurization device of this method is a vertical desulfurization tank with agitation. Steam in the jacket is passed through 0.9 ~ 0.9MPa (9 ~ 10kgf / cm2). Fill the tank with warm water (80 ° C) as the heat transfer medium. During desulfurization, the rubber powder and the regenerant that have been mechanically removed from the fiber are added to the tank, and the stirring time is about 3 hours. Although there are many equipments in this method, the degree of mechanization is high, and the product quality is excellent and stable.

2. Neutral law

The neutral method is basically similar to the water and oil method, the difference is that the neutral method does not remove the fibers in advance, and a zinc chloride solution is added to remove the fibers during the desulfurization process. The effect is not as good as the water and oil method.

3. Alkaline method

Use sodium hydroxide (5-10% concentration) to destroy the fibers in the rubber powder, then neutralize and clean with acid, and then desulfurize and regenerate by direct steam heating. The equipment is easily corroded, the quality of the product is poor, and the method is backward.

Mechanical method

1. Mixer method

The internal mixer used is a super-strength structure, and the surface of the rotor is plated with hard chrome or surfacing wear-resistant alloy. The rotation speed is 60 ~ 80r / min, the pressure of the upper plug is 1.24MPa (12.6kgf / cm2), the operating temperature is controlled at 230 ~ 280 ℃, and the time is 7 ~ 15 minutes. This method has short production cycle and high efficiency.

2. Screw extrusion

The main machine is a screw extruder (similar to a rubber extruder), with screw diameters of 6, 8, and 12in. There is a jacket in the casing, and the temperature is controlled by steam or oil (about 200 ° C). During operation, the rubber powder and the regenerant are mixed and fed into the machine in advance, and the rubber compound can be discharged from the discharge port after 3 to 6 minutes under the action of shearing and extruding of the screw. This method is continuous production, with short cycle, high efficiency, and excellent product quality. However, due to the large wear of the screw and the inner sleeve, the material requirements of the equipment are high.

3. Rapid desulfurization

The main machine is a mixer with a special structure (similar to a plasticizer). There is a material blocking device in the tank. The stirring speed is adjustable and driven by a DC motor. The speed is divided into two gears. The low speed is controlled at 720 r / min and the high speed is 1440 r / min. After stirring for 10 minutes, the isolated air is gradually cooled. This method has a short production cycle, fast mixing speed, difficult to control process, and insufficient product quality, which is more suitable for recycling waste synthetic rubber.

4. Rotational dynamics

After mixing the rubber powder and the regenerant evenly, put it into the equipment with a pair of hollow screws, heat it with an oil bath, and control the temperature at 240-260 ° C for continuous desulfurization. The rubber can be desulfurized and regenerated after 15 minutes. .

Chemical method

1. Dissolution method

Put the rubber powder and softener into an electrically heated stirring tank, and add 40-50% of the softener (with rubber powder as 100%). Generally, heavy oil or residual oil is used. The temperature is controlled at 200-220 ° C and stirred for 2 to 3 hours. The product after the reaction was a semi-liquid viscous substance. The product can be directly used in rubber products, instead of some softeners, and can also be used as waterproof and anticorrosive materials in the construction industry.

2. Grafting

In the rubber and sulfur process, some monomers with special properties (such as styrene, acrylate, etc.) are added, and the monomers are reacted with the rubber compound under the high temperature of 200-230 ° C. After mechanical treatment, The monomer polymer performance recycled rubber (such as abrasion resistance, oil resistance, etc.). The reaction process of this method is difficult to control.

3. Dispersion method

Add rubber powder and emulsifier, softener, activator, etc. to the kneader, mix and press, and then slowly add a dilute alkali solution to make the rubber powder into a paste. Then dilute with water and scrape it from the rubber mixer. Add 1% concentration of acetic acid to make it solidify, and then dry and tablet, it is the finished product. This method has simple equipment and difficult process control, and is batch production.

4. Low temperature plasticizing

Mix the rubber powder with organic amines or low-molecular polyamides, metal naphthenates, aliphatic acids and softeners, activators, etc., and place them at a temperature of 80 to 100 ° C for a certain period of time. The oxidation-reduction reaction achieves the purpose of regeneration. This method saves energy, the equipment is simple, but the product has low plasticity.

Physical law

The high-temperature continuous desulfurization method mixes the rubber powder and the regenerant as required, and then sends it into a horizontal multi-layer screw conveyor. The conveyor has a jacket and a far-infrared heating device. The rubber is subjected to far-infrared during the transportation process. The uniform heating can achieve the purpose of regeneration. This method is continuous production, with shorter cycle, better quality, and less complicated equipment. It is a new method being explored.

Microwave method

Crush the polar waste vulcanizate to 9.5mm size rubber particles, add a certain amount of dispersant, and transfer it to a pipe made of glass or ceramics to make the rubber particles advance at a certain speed and receive energy from a microwave generator . The energy of the microwave generator is adjusted to cause the C-S and S-S bonds in the rubber powder molecules to be broken to achieve the purpose of regeneration.

References

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