Plastics, the greatest invention of the twentieth century, have been developed for almost a century and have successfully infiltrated every aspect of our lives and have brought great convenience to us. However, due to the non-degradability of plastics, plastics waste has deteriorated Our living environment.And to solve the problem of plastic pollution is an effective way to recycle, the formation of plastic recycling system, so that waste plastics can be reused, repeatedly play their own value of plastic.
Waste plastics recycling economy system diagram
As can be seen from the schematic diagram, recycling of waste plastics is roughly divided into several phases: recycling of waste plastics, sorting and crushing, recycling granulation, recycled materials processing products, etc. Here are some links to make an introduction.
Waste plastic recycling
1. Two major sources of waste plastics
① industrial waste plastic
Mainly from the plastic molding processing plant, the thermoplastic resin directly processed or processed into products through the ingredients after mixing inevitably appear scrap scrap scrap scrap test material mixture, etc., China's imports of raw materials can be used along the coast of the waste Plastic, most of them are such items, they are less polluting and are generally available for crushing.
② living source of waste plastics
Mainly from the use of various types of plastic products and consumption process, from the domestic point of view, mainly agricultural plastic packaging plastic daily necessities three major areas, such waste plastic recycling difficult, because of its large amount of use, the use of high frequency, And randomness, most of the mixed with soil waste, composition is complex, white pollution is mainly caused by such waste plastics.
2. Waste plastic treatment
At present, the treatment of waste plastics at home and abroad in the following ways:
① Landfill This is the most direct, simple and economical way, more than 50% of the waste plastic is buried, leaving endless hidden dangers.
② incineration using a professional burner, the use of plastic burning heat energy to generate electricity.
③ chemical recovery. Using cracking or other means, recovery of oil, all kinds of chemical raw materials.
④ physical recovery, that is, we promote the recycling, the current recycling rate of waste plastics is only about 10%.
Waste plastic sorting, crushing, cleaning
1. Waste plastic sorting
Waste plastics recycling must first be sorted.Generally, the recycling station is classified recycling of waste plastics, plastic waste recycling is based on the use of waste plastics and the composition of the difference between the recycling, but because of the composition of waste plastics, coupled with Recycling value, the recycling station is only carried out a rough sorting, therefore, must be refined before processing, in order to remove impurities, raw material classification.
Sorting methods are divided into manual sorting and mechanical sorting. Manual sorting efficiency is low, but flexible; mechanical sorting is now more and more perfect technical development, applications are more and more common. For example, magnetic separation is suitable for the classification of different color quality Shape of waste plastics; wind sorting adapted to the mixed before and after the crushing of waste plastics; there electrostatic separation, density sorting and temperature separation and so on.
2. Broken plastic waste
Due to the wide range of plastic products, different sizes, so the recovery of larger products, it must be some means to break it into a small piece of material of a certain size in order to facilitate the next step of processing.
Because different materials of different qualities of waste plastics, so the choice of broken form will be different, commonly used crushing methods are crushed, crushed, grated and sheared four.
Such as rigid PVC, PS, plexiglass, phenolic resin, urea-formaldehyde resin, polyester resin and other materials are brittle plastics, brittle fragile, subject to compression or impact, easily broken into small pieces, such plastics It is appropriate to use compression or impact crushing equipment; and PE, PP, PA and ABS at room temperature, there is a good toughness of the material, the appropriate use of shear crushing equipment; for some low temperature brittle materials, such as soft PVC , Is suitable for low temperature crushing equipment.
3. Waste plastic cleaning
In order to remove the other substances attached to the surface of waste plastics, so that the final recovery of a higher purity and performance, generally have to waste plastics processing.Most enterprises are using traditional washing method for cleaning, by stirring the method Other substances attached to the surface fall off, if necessary, use hot water or detergent and other methods for cleaning.
At present, the general use of manual cleaning or mechanical cleaning of waste plastic wastes. The manual processing of plastic processing factories with low efficiency and small scale of manual cleaning mainly adopts manual cleaning. The mechanical cleaning has high efficiency and wide adaptability. The waste Plastic and particle oil products, can add some cleaning agents for cleaning.
With the progress of science and technology, some enterprises have developed water-free cleaning equipment suitable for film and packaging plastic waste, and have put into use.Waterless cleaning can save a lot of water, secondary pollution will be greatly reduced, will be Will become an important research direction in the future.
Comparison of anhydrous cleaning and water cleaning
4. Waste plastic dehydration
After washing the plastic fragments need to be dehydrated, dehydration methods are mainly screen dehydration and centrifugal filtration dehydration.Dehydrated plastic fragments can be dried as needed, the drying is usually carried out using hot air dryers or heaters.
Recycled plastic granulation
1. Granulator selection
Currently, the main pelletizers on the market are single-screw extruders, twin-screw extruders and multi-stage pelletizers, etc. The right pelletizer can be chosen according to your needs.
2. Process control
Throughout the extrusion granulation process, strict control of process parameters is necessary. The main process parameters include: processing temperature, processing speed, working pressure, feeding speed and cutting speed. In the production of important processing parameters to be monitored And make a record, in order to ensure the stability of particle quality.
3. Impurities filtration
Waste plastics, even after cleaning, separation, the impurity content is still high, it is necessary before the plastic melt extrusion filtration required to remove residual impurities, to ensure the quality of the particles.
4. Modified plastic waste regeneration
In order to improve the processing performance of waste plastics and to realize the high value of recycled materials, the recycled materials are often modified, the most commonly used are physical modification, including filling modification, blending alloy modification, etc. Sex, can greatly improve the mechanical properties, and broaden the application areas, so that prices have been improved.
Waste plastics processing and utilization of renewable materials
1. The use of recycled materials
The general reuse of waste plastics can be divided into two categories: simple recycling and composite recycling. Simple recycling is the use of a single variety of waste plastics directly recycled or after simple processing; composite recycling is the use of mixed waste plastic Raw materials, and then participate in the use of other ingredients, almost all of the thermoplastic plastic waste, even mixed with a small amount of thermosetting plastic waste can be recycled.
2. Recycled materials processing applications
Waste plastic recycling materials forming methods include: extrusion molding, injection molding, blow molding, compression molding, calendering, casting molding and foam molding.
Extruded products are continuous profiles, such as tubes, rods, wires, plates, films, wire and cable coatings, etc. In addition, it can also be used for plastic mixing, plastic granulation, coloring, blending and so on.
In recent years, injection molding has also been successfully used to form some thermosets. Injection molding has a short molding cycle (seconds to minutes), and the quality of shaped articles can range from a few grams to tens of kilograms , Can form a complex shape, size accuracy, with a metal or non-metallic inserts molded products, therefore, the method adaptability, high production efficiency.
Blow molding is a method of inflating a hot parison closed in a mold by gas pressure into a hollow product or a tubular parison moldless blown into a pipe film.The method is mainly used for various packaging containers and tube type Membrane manufacturing Polyethylene, polyvinyl chloride, polypropylene, polystyrene, thermoplastic polyester, polycarbonate, polyamide, cellulose acetate and polyacetal resin can be used for blow molding, which polyethylene applications Mostly.
Development prospects of waste plastics recycling
In 2016, the total amount of plastic products in our country is more than 77 million tons, and the trend is increasing every year. The amount of plastic waste will grow linearly in the future and will soon reach the stage where the amount of plastic waste to be discarded is larger than that of plastic products. Reuse will be the main way to deal with waste plastics.
If blindly landfill disposal of waste plastics, due to excessive accumulation of contaminated land resources will increase, a serious impediment to water infiltration and groundwater circulation, no harm, but also wasted the available resources; incineration investment, equipment loss And the high cost of maintenance and operation, it is necessary to control the exhaust gas generated by the combustion and prevent the secondary pollutants from affecting the atmospheric environment.
With the ban on the import of waste plastics policy, the accelerated construction of the domestic waste plastics recycling economy system, the help of national policies, and the rapid progress of waste plastics recycling technology, the domestic waste plastics industry will surely receive rapid development. We will wait and see!