Waste plastic recycling technology

The melt regeneration method for plastics includes the following processes: collection, sorting, cleaning, and drying of waste plastics

one. Sorting of used plastics

The source of waste plastic is complex, often mixed with metal, rubber, fabrics, mud yarn and other impurities, and different types of plastics are often mixed together. This will not only cause difficulties in the processing of recycled plastic waste, but also the quality of products produced. Affected, and mixed with metal impurities will also damage the processing equipment, so when using waste plastics to produce products, not only to remove all kinds of impurities in the waste plastic, but also to separate different varieties of plastic, only in this way, In order to obtain high-quality recycled products.
Sorting methods for waste plastics include manual sorting, magnetic separation, density sorting, electrostatic sorting, flotation, differential temperature selection, and wind screen sorting.

1. Manual sorting manual sorting steps are as follows:
(1) Remove metal and non-metallic impurities and remove severely degraded waste plastics.
(2) According to products, such as film (agricultural film, natural packaging film), bottles (mineral water bottles, carbonated beverage bottles), cups and boxes, shoe soles, sandals, foams, scraps, etc., are classified according to the above section. The law categorizes different plastic varieties such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyester, etc.
(3) The waste plastic products classified above are further sorted according to the color depth and quality. The color can be divided into the following categories: black, red, brown, yellow, blue, green and transparent.
2. Magnetic Separation The main purpose of magnetic separation is to remove iron and steel swarf contaminants that are incorporated in waste plastics. Because these finely divided steel scraps are not easily removed by manual sorting, they must be removed by magnetic separation.

3. Density sorting Density sorting is a method of sorting using the properties of different plastics with different densities. There are usually solution sorting, hydraulic sorting, centrifugal density sorting, etc. The solution sorting method is to put the mixed waste plastic on Into a certain solution with a certain density, and then sorting according to the ups and downs of waste plastics in the solution.
The advantage of the solution sorting method is that it is simple and feasible. As long as one or several solutions are selected, large-scale sorting can be performed, and cumbersome manual sorting can be avoided. The disadvantage is that the density of some kinds of plastics is very close. Therefore, It is difficult to obtain high-purity isolates.
Hydraulic separators are commonly used in hydraulic sorters. In order to improve the sorting efficiency, it is often necessary to perform cleaning before and after solution separation. Centrifugal density separation using a centrifugal density separator.

4. Electrostatic Separation Electrostatic Separation is a method of sorting using various types of plastic electrostatic suction. The procedure is to crush the plastic into small pieces with an area of ​​about 10 mm2. After drying, the high-voltage electrode is used for sorting. For a variety of waste plastics that are mixed together, multiple sorting is required. This is because each pre-selection The high voltage electrode of Po voltage can only sort out a kind of plastic. The electrostatic separation method is particularly suitable for polyvinyl chloride with polarity, and the separation purity can reach 100%.

5. Flotation sorting flotation is the use of wetting agents to change the wettability of water on the plastic surface, causing some plastics to change from hydrophobic to hydrophilic, while the hydrophobic plastic surface adheres to bubbles and floats. , so as to achieve the purpose of separation. Flotation separation of different types of plastics, regardless of the density, shape, size, etc., of plastics, it is the use of water on the wettability of the plastic surface for different sorting.

6. Differential temperature differential temperature selection, also known as low temperature separation, is a method of sorting using various plastics with different embrittlement temperatures. The specific method is as follows: The mixed waste plastics are crushed once and then placed in a cooler with a temperature of -50C to be cooled and crushed. Plastics with embrittlement temperatures below -50C are crushed and separated after screening. The uncrushed plastic is then placed in a cooler with a temperature of -100 degrees, cooled and crushed, and the embrittled plastic is screened. The coolant is liquid nitrogen and can be cooled to -140 degrees.