Waste plastics - other sorting methods

For mixed plastic materials, temperature differential selection, electrostatic separation, and magnetic separation can also be used.

Differential temperature separation, also known as low temperature sorting, is a method of sorting using various plastics having 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 -50 DEG C., cooled and crushed. The plastics with embrittlement temperatures above -50 DEG C. are crushed, and are separated after screening. The uncrushed plastic is then placed in a chiller at a temperature of 100° C., cooled and crushed, and the embrittled plastic is then sieved. The coolant is liquid nitrogen and can be cooled to -140°C. Such as PVC and PE, the former's glass transition temperature is about -40 °C, the latter glass transition temperature is less than -100 °C, the use of liquid nitrogen heat absorption cooling materials to -50 °C, the mixture into the pulverizer PVC embrittlement It becomes a lump and the PE is not crushed, and then it is separated, but this method is too costly, as shown by the cryogenic smashing device.

It is also possible to sort waste plastics for differences in temperature sensitivity (such as heat shrinkage temperature, softening and melting temperature). The first shrinkage is separated and the first softened resin is separated from the polymer through the filter mesh, but Thermosetting plastics are not suitable for this method, and polymers with softening points and melting points are difficult to use. 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 constant voltage high voltage electrode can only sort out one kind of plastic. The electrostatic separation method is particularly suitable for polyvinyl chloride with polarity and the separation purity can reach 100%.

Magnetic separation is an effective method for removing metal debris using magnets. Metal scraps in scrap plastic need to be magnetized before and after crushing to ensure the thoroughness of removing metallic impurities in plastics.