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Do you know the waste plastic granulation process and precautions

Do you know the waste plastic granulation process and precautions?

With the development of industry, all kinds of plastic products have entered thousands of households, and the consequent plastic waste is also increasingly waste plastic granulation process and precautions. Do you know? many. A variety of plastic packaging, plastic containers, plastic toys and stationery, plastic shoes, plastic appliances shells, vehicle bumpers, plastic pipes, industrial waste, etc., can be seen everywhere, causing great environmental pollution. The recycling of waste plastics is conducive to environmental protection and saves resources. They can be recycled and granulated, or granulated by modification, and can be used again to produce plastic products.

First, the characteristics of waste plastics

Waste plastics can be divided into three types according to their origin:

1. Corner scraps produced during the production process, which are relatively clean, less polluting and contain impurities, such as substandard film, trimming, pipe, or part of the profile production or defective products in the production of the film, injection Unfilled parts in production, etc.;

2. Used plastic waste with single material system, such as dismantled pipes, doors and windows, packaging materials or other waste plastic products that are sorted according to the type of resin;

3. Mixed waste plastics that are difficult to distinguish or cannot be separated at all, such as multi-layer co-extruded composite films, coated plastic products, composite products of plastics and other materials.

Different types of waste plastics have different characteristics. Do you know the process and precautions for waste plastic granulation? In terms of the factory production of corner scrap impurities containing waste plastic granulation process and precautions, do you know? Less than 0.1%, stacking scraps for a certain period of time and other used product impurities including waste plastic granulation process and precautions Do you know? It is 0.1% to 0.5%. Do you know that the composite waste plastics mixed with aluminum, cloth and paper contain waste plastic granulation process and precautions? Often greater than 10%.

For used plastic products, depending on the conditions of use, it will include the effects of ultraviolet radiation, heat and oxygen aging, and the effects of pollutants. Different shapes of waste plastics have a large difference in the bulk density of the materials after crushing, and the bulk density of the broken materials of film, sheet and flat yarn is small, which must be considered in the process of adding waste plastic granulation. problem.
Second, the pretreatment of waste plastics

Waste plastics from waste packaging, such as bags, shopping bags, bottles, cans, boxes and used agricultural film, are pretreated before granulation. The pretreatment process mainly includes classification, washing, crushing and drying.

The classification work is to classify a variety of waste plastic products according to the type of raw materials and the shape of the products. Sorting by raw material type requires the operator to have a good knowledge of plastic varieties. The purpose of sorting is to avoid inferior performance of recycled materials due to the mixing of different kinds of polymers; the classification according to the shape of the product is to facilitate the waste. The plastics crushing process can be carried out smoothly, because the crushing equipment used for the film, the flat yarn and the fabric thereof and the crushing equipment of some thick-walled and hard products are often not mutually replaceable.

There are three processes as follows for cleaning and crushing before granulation.

1. First cleaning and crushing process

For large-scale waste plastic products with less serious pollution and uncomplicated structure, it is advisable to adopt the first cleaning and crushing process, such as automobile bumpers, instrument panels, turnover boxes and plates.

First, dip with water with detergent, then rinse with water, remove and air dry. Large parts that cannot be placed in the crusher hopper due to their large volume should be crushed and then finely crushed for feeding by the extrusion granulator. Do you know the process and precautions to ensure the quality of waste plastic granulation of recycled pellets? Drying should be carried out after fine crushing. Rotary dryers with heating interlayers are often used. Superheated steam is introduced into the interlayer and rotated while being heated. The drying efficiency is high.

2. Rough washing-crushing-finishing-drying process

For contaminated profiles, used agricultural film, and packaging bags, coarse washing should be carried out first to remove foreign matter such as sand, stones and metal to prevent damage to the crusher. The waste plastic products are subjected to coarse washing, centrifugally dehydrated, and then sent to a crusher for crushing. After crushing, it is further washed to remove the impurities contained therein. If the waste plastic contains oil, can you use the waste plastic granulation process and precautions? Do you know? Immerse in the concentration of alkaline water or warm washing liquid, then stir and make friction and collision between the waste plastic blocks (sheets), remove the dirt, rinse and dehydrate, and dry.

3. Mechanized cleaning

Before the waste plastic enters the cleaning equipment, it is crushed in a dry or wet crushing equipment. After drying, it is blown into a storage bin, and then the screw feeder will waste the plastic waste granulation process and precautions. Do you know? ? Enter into the cleaning tank. The two counter-rotating paddle shafts slowly transport material through the cleaning tank, and the resulting eddy current rinses off the dirt on the plastic. The dirt sinks to the bottom of the tank and is removed at the bottom of the tank at regular intervals. The cleaned waste floats and is discharged by a screw conveyor. Most of the water was removed. Spiral input device will crush the material waste plastic granulation process and precautions Do you know? Feed into the drying system. The drying system consists of a rotary dryer and a hot air dryer. The residual moisture of the material output from the drying system accounts for 1% to 2%. The cleaned material is sent to the storage bin, which is then sent to the extrusion granulator to produce pellets.

Third, the extrusion granulation process of waste plastics

Waste plastics differ in performance from new resins in that they undergo the thermal history and shear history of the forming process and experience the effects of heat, oxygen, light, weather and various media during use. Therefore, the mechanical properties of the recycled materials, including tensile strength and impact properties are lower than the original resin, the surface structure changes caused by cracks, the appearance of waste plastic granulation process and precautions do you know? It is also worse than before, the color is yellow and the transparency is reduced. The performance variations of various materials are different. The change in polyolefin material is relatively small. Do you know the processing and precautions of the relative molecular waste plastic granulation process caused by processing, especially multiple processing? The reduction can be compensated by the crosslinking reaction, and thus, the processability can be kept constant to some extent; the styrene copolymer is different, and the tensile properties are lowered once per process. After about four processes, the toughness reduction is very serious. Moreover, the effect of the rubber phase impact modifier is also lowered due to cross-linking. Although it is high-impact polystyrene, the impact toughness is not better than that of general-purpose polystyrene.

The performance of waste plastics can be improved by blending new materials or adding specific stabilizers and additives. For example, adding antioxidants and heat stabilizers can reduce the adverse effects of heat and oxygen during the granulation process of waste plastics. In some mixed waste plastics, a compatibilizer may also be appropriately added, such as EP D M or E V A in the waste plastic mixed with polyethylene and polypropylene. Filling modification can also be carried out in waste plastics recycling granulation, such as adding 10% to 35% filler, 3% to 6% lubricant, and 2% to 4% masterbatch in the PP waste film. The recycled material prepared by using CaC O 3 as a filler is used for injection products, which can effectively shorten the molding cycle, improve the rigidity of the product, increase the heat distortion temperature, and reduce the shrinkage rate.

The lubricant improves the fluidity of the melt. In the recycling of some engineering plastics, you can also carry out the filling, waste plastic granulation process and precautions. Do you know? Strong and alloyed. For some moisture-absorbing materials, such as PA, PET, etc., during processing, water will cause degradation, so that the relative molecular plastic waste plastic granulation process and precautions do you know? Decrease, melt viscosity decreases, and physical properties decrease. Do you know the process of removing the moisture in the waste plastic before processing and drying it thoroughly to ensure the quality of the waste plastic granulation process and precautions? .

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