The demand for polyvinyl chloride (PVC) in China is increasing at a rate of 10% per year. The recycling of PVC can not only solve environmental problems, but also alleviate the pressure of this shortage of resources. Especially when the price of PVC raw materials continues to rise, its recycling is of great significance. The use of PVC in the construction industry is very large. If the waste products can be recycled, the environmental pollution of PVC can be greatly reduced. Recycled plastics create the "Magic Cube" facade of the World Expo In fact, PVC waste is often mixed with other plastic materials. Generally it is necessary to sort plastics first, and then use physical or chemical means to make comprehensive use. PVC sorting Sorting is a difficult part in the process of plastic waste disposal, and it is also one of the key factors that determine the treatment results. Common plastics include polyvinyl chloride, polystyrene, polypropylene, low (high) density polyethylene, polyamine, and polyurethane. There are many disadvantages of manual sorting: low efficiency; workers are in a harmful environment; the error of material classification is large, etc. In industrial production, automated sorting systems have been mostly used, and developed countries in the world have done more research in this area. A German chemical technology association once invented the technology of screening PVC from waste plastics using infrared rays, but the objects are limited to transparent bottles, which has the problems of low screening accuracy and high cost. Recently, Japan has successfully developed a technology for high-precision screening of polyvinyl chloride resin (PVC) from waste plastics. This technology uses the difference between the heating characteristics (within 50 ° C) and the charging characteristics of PVC and other plastics. The detected PVC is marked with red light, which is easy to be screened by the operator. This method has higher precision than near infrared technology, and the cost is only 1/2 of it. The US Rubber Recycling Center (CPRR) invented a method to separate PVC bottles from other waste containers. The key to this process is the use of an X-ray fluorescence detector developed by Asoma Instruments. CPRR researchers have developed a computer system. It uses an X-ray from a radioactive isotope to excite all the electrons in the compound. Upon exposure to chlorine-containing molecules, it emits an X-ray reflection image easily displayed by an X-ray fluorescence analyzer. The separation work is completed by a set of mechanical devices. It can remove all bottles containing chlorine atoms through the conveyor belt, as well as bottles without chlorine atoms. [next] PVC recycling technology At present, there are three main technologies for recycling PVC: one is physical recycling; the second is the comprehensive utilization of chemical recycling; the third is the recovery and utilization of energy by burning PVC materials. Among them, the comprehensive utilization of physical method and chemical method is a method worthy of admiration, they can recycle waste products again, and give full play to the performance of materials. Physical recycling Physical recycling means that the recycling process of PVC waste is only mechanically processed, mainly through procedures such as chopping, sieving, and grinding, to finally obtain films, powders, granules, or other forms of recycled materials. These recycled materials can be used to produce heavy packaging bags, agricultural water pipes and shoe soles. PVC plastic products are divided into soft products and hard products. Soft products mainly include films, cable sheaths, plastic shoes and leather products; hard products mainly include bottles, pipes, profiled materials, and sheet materials. Among the soft products, agricultural films are the most widely used type. Agricultural film manufacturing materials include PVC, PE, EVA and other materials. When recycling, the PVC film should be distinguished from other materials. Agricultural films often contain soil, sand, grass roots, iron nails, etc., to remove these impurities and clean, and then through drying, shredding and other processes to make fragments or pellets, and then into agricultural product packaging film, agricultural reclaimed water pipes And soles. Due to repeated heating and processing and mechanical action of the repeatedly recycled PVC film for waste agriculture, it will inevitably cause partial degradation and the strength will be reduced accordingly. In order to ensure the quality of the product, some new PVC resin and corresponding additives need to be added. If the recycled materials are to be made into secondary plastic film through the mixing, two-roller, and four-roller rewinding, and different colors are added during the mixing process, the rolled film produced will also show different colors. In addition, about 30% of the plasticizers (mainly DOP) remaining in the waste agricultural PVC film can be recovered and can be reused after refining. PVC bottles in hard products are also used in a very large amount, and the waste can be processed into molding materials, pipes and folding plates. In a plastic processing plant, first clean the PVC fragments, remove the caps and labels, dry them, and then crush them into small pieces less than 0.5mm. One of the major PVC manufacturers in the United States, BF Goodrich, conducted a test using new PVC and recycled PVC for co-extrusion. The results show that recycled PVC retains the excellent properties of the new material and can be used in applications with lower performance requirements. . For the physical recycling method, the quality of the PVC recycled matter has a greater relationship with the degree of pollution and the composition of the selected material. The quality of the recycled materials determines the extent to which the original materials can be replaced by recycled materials: "high-quality" recycled materials can be reused in the same type of PVC applications, but "low-quality" recycled materials from mixed waste parts can only "Low-level recycling" into products usually made from other materials. Of course, the quality of the final product is inseparable from the recycling equipment itself. At present, the equipment and processes for recycling and processing PVC waste in Germany have reached a very high level. Among them, the content of pollutants is less than 1%, and the obtained secondary pulverized PVC can be processed into many products by various methods. The American Plastics Industry Association Polyvinyl Chloride Association also strongly encourages the recycling of PVC. It is planned to start the recycling of PVC bottles to drive the recycling of other PVC products. [next] Chemical recycling Chemical recycling refers to the use of the chemical properties of polymers to convert polymers into small molecular compounds or simple compounds. The chemical decomposition method has a high utilization rate of resources, but the process is complicated and the cost is high, thus affecting the recycling of plastic products. For PVC, in addition to the broken polymer chain, the chlorine atoms connected to the chain are also released in the form of HCI. HCI must be reused after purification, or it must be neutralized to form different products, some can be reused, and some must be disposed of, which is determined by the technology used in the processing process. All countries in the world have strengthened research in this field. The waste plastic recycling technology developed by China can recover PVC waste mulch film and shed film to produce oil products, paraffin, building materials, etc. In the case of continuous production with this technology, the daily treatment of waste agricultural film is strong, the oil output rate can reach 40% to 80%, and the conversion rate of gasoline and diesel is high, which meets the standards of vehicle fuel and environmental emission standards. In addition, since the PVC film contains 30% to 37% of dioctyl phthalate, the DOP technology of solvent extraction at room temperature can be adopted to recover the solvent at a temperature lower than 800 ° C. DOP is a plasticizer with a wide range of uses. At present, the market price is 7000 yuan to 8000 yuan / ton. Recycling 1 ton of waste PVC film can make more than 2,000 yuan and eliminate environmental pollution. There are also two more advanced solvent recovery PVC processes in Europe. Belgium Solvay invested 10.6 million euros to build the world's first soft PVC resin recycling device in Italy. The device uses the VinyLoop batch process, which can regenerate 8500 tons of PVC from 10,000 tons of waste plastic (mostly composed of PVC) every year. The technology uses a mixture of methyl ethyl ketone as a solvent, and selectively dissolves PVC and additives at 100 ° C ~ 140 ° C under pressurized conditions. The solution can be precipitated to obtain soft PVC with additives. The cost of recycling PVC produced by this process is equivalent to the production of new PVC, and the resulting PVC contains additives, so the resin price is higher. The VinyLcop process can reduce the impact of PVC, especially soft PVC, on the environment. The second VinyLoop unit will be put into operation in France in 2004 and is designed to recycle PVC-coated varnished fabrics and fabrics. Another new European process for recovering PVC by the solvent method is to recover PVC from the entire automotive wiring board. This process was jointly developed by automobile manufacturers located in Wuppertal and Delphi, Germany, and Wuppertal University. It has been industrialized by Wiefek GmbH, an automotive parts recycler in Nohfelden-Fisen, Germany, three years ago. The cost of recycling PVC using this process is nearly 20% lower than the price of new PVC. The process uses esters and ketones as solvents, but the amount of solvent is much less than the Vinyloop process. The solvent does not completely dissolve the waste PVC, but only softens it to make it easier to separate from the copper wire, and the resulting copper wire can be used to pay for the PVC recycling process. Wiefek has invented a process that uses centrifugal separation of plastics and solvents, and has obtained a patent. The recycling PVC production line established by the company according to this process can recycle 225 tons of reusable PVC every year. [next] Heat recovery method At present, obtaining energy by burning PVC products is also one of the methods of PVC recycling. But this method tends to be eliminated. During the incineration process, PVC waste produces hydrochloric acid (hydrogen chloride) and is released with the flue gas, which needs to be neutralized. The method is to add a neutral substance to the incinerator, the most commonly used is limestone, so that the acid component of the incineration gas can be neutralized. Since the chlorine gas released during the burning of PVC has a strong erosive and destructive power, and is the culprit that causes dioxins, environmental groups in various countries strongly oppose the use of incineration to recover heat energy. The recycling of PVC plastic generally refers to the use of PVC, after crushing, cleaning, drying, heating and plasticizing, wire drawing, cooling, granulation, after processing, the material pellet PVC is generated for the production of PVC related products. Especially as a larger amount of raw materials. Because PVC is widely used in pipes and tools, and it can only be used once for hygienic reasons, the equipment for recycling PVC has always been a concern. Generally, PE and pp are separated from PVC, and they can also be processed and recycled for granulation (PP, PE, ABS, etc. are made with DY plastic recycling granulator). Recycling of various waste plastics has attracted much attention. Generally speaking, plastic crushers are common. Other equipment is the same as PVC recycling equipment. The configuration of recycling equipment is different, and the quality of recycled plastics is also different. The quality of the grain.
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