For mixed plastic materials, temperature differential selection, electrostatic separation, and magnetic separation can also be used.
Temperature differential selection, also known as low temperature sorting, is a method of sorting using various plastics with different embrittlement temperatures. The specific method is as follows: the mixed waste plastic is once pulverized and then placed in a cooler at a temperature of -50 ° C to be cooled and pulverized, and the plastic having an embrittlement temperature of -50 ° C or higher is pulverized, and sieved and separated. The unpulverized plastic is then cooled and pulverized in a cooler at a temperature of 100 ° C, and then the embrittled plastic is sieved. The coolant is cooled to -140 ° C using liquid nitrogen. For example, PVC and PE, the former has a glass transition temperature of about -40 ° C, and the latter has a glass transition temperature of -100 ° C or less. The liquefied nitrogen is used to heat-cool the material to about -50 ° C, and the mixture is sent to a crusher for PVC embrittlement. It becomes a fine block and the PE is not broken, and then it is separated, but the cost of this method is too high, as shown in the low-temperature pulverizing device.
It is also possible to sort the difference between the temperature sensitivity of the waste plastic (such as heat shrinkage temperature, softening and melting temperature), and the first shrinkage is separated, and the softened resin can be separated from the polymer through the filter, but Thermosetting plastics are not suitable for this method, and polymers having similar softening points and melting points are difficult to use. Electrostatic sorting is a method of sorting using various electrostatic suctions of various plastics. The step is to first pulverize the plastic into small pieces with an area of ​​about 10 mm2. After drying, the high-pressure electrodes are used for sorting. For a variety of mixed waste plastics, multiple sorting is required, because each time a pre-selection is passed. A fixed voltage high voltage electrode can only sort one plastic. The electrostatic separation method is especially suitable for polyvinyl chloride with polarity, and the separation purity can reach 100%.
The magnetic separation method is an effective method for removing metal debris by using a magnet. The mixed metal debris in the waste plastic needs magnet magnetization before and after the crushing to ensure the thoroughness of the metal debris in the plastic.
1—plastic feeding port; 2—screw precooler; 3—grinder; 4—liquid nitrogen storage tank; 5—liquid nitrogen; 6—nitrogen discharge
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