Plastics are often sorted before recycling used plastics by various plastic recycling methods. Due to the complexity and complexity of plastic consumption channels, some post-consumer plastics are difficult to distinguish by simple appearance. Therefore, it is best to indicate the variety of materials on plastic products. China has formulated GB/T16288-1996 “Recycling Mark for Plastic Packaging Products” with reference to the material variety label proposed and implemented by the American Plastics Association (SPE). Although the above marking method can be used to facilitate sorting, there are still many unmarked in China. The plastic products bring difficulties to the sorting. In order to separate the different types of plastics for classification and recycling, we must first grasp the knowledge of identifying different plastics. The following describes the simple identification method of plastics:

1. Plastic appearance identification

By observing the appearance of plastics, it is possible to initially identify a large category of plastic products: thermoplastics, thermosets or elastomers. Generally thermoplastics are available in both crystalline and amorphous forms. The appearance of the crystalline plastic is translucent, opaque or opaque, and it is transparent only in the state of the film, and the hardness is soft to horny. Amorphous is generally colorless, completely transparent when no additives are added, and hardness is harder than horny rubber (additives such as plasticizers are often added at this time). Thermoset plastics are usually filled and impervious to materials, such as when they are free of fillers. The elastomer has a rubbery feel and a certain stretch ratio.

2. Plastic heating identification

The heating characteristics of the above three types of plastics are also different, and can be identified by heating. Thermoplastics soften when heated, are easy to melt, and become transparent when melted, often pulling the filaments out of the melt, usually easily heat-sealed. The thermosetting plastic is heated until the material is chemically decomposed, and the original hardness is not softened, the size is relatively stable, and the carbonization is performed at the decomposition temperature. When the elastomer is heated, no flow occurs until the chemical decomposition temperature, and the material is decomposed and charred to the decomposition temperature.

The softening or melting temperature range of common thermoplastics is shown in the table.

3. Plastic solvent treatment

Thermoplastics swell in solvents, but generally do not dissolve in cold solvents. In hot solvents, some thermoplastics will dissolve. For example, polyethylene is soluble in xylene. Thermosetting plastics are insoluble in solvents and generally do not swell or Slightly swell only, the elastomer is insoluble in the solvent, but swelling usually occurs.