Before reusing waste plastics using various recycling methods, sorting is often necessary. Due to the diverse and complex channels of plastic consumption, and the difficulty in easily distinguishing post-consumer plastics by appearance, it is best to label plastic products with their material type. China has developed GB/T16288-1996 "Recycling Marking for Plastic Packaging Products," referencing the material type marking proposed and implemented by the Society of Plastics Engineers (SPE) in the United States. While this marking method facilitates sorting, the large number of unmarked plastic products in China still presents sorting difficulties. To separate different types of plastics for recycling, it is essential to first understand how to identify different plastics. The following is a simple method for plastic identification:
Appearance: By observing the appearance of the plastic, one can initially identify its category: thermoplastic, thermosetting, or elastomer. Generally, thermoplastics are divided into crystalline and amorphous types. Crystalline plastics appear translucent, milky, or opaque, only becoming transparent in a thin film state, with hardness ranging from soft to horny. Amorphous plastics are generally colorless and completely transparent without additives, with a hardness ranging from harder than horn-like rubber (in which case plasticizers and other additives are often added). Thermosetting plastics usually contain fillers and are opaque; they are transparent if they do not contain fillers. Elastomers have a rubbery feel and a certain degree of elongation.
Heating Characteristics: The heating characteristics of the above three types of plastics are also different and can be identified by heating. Thermoplastics soften when heated, melt easily, and become transparent when molten, often able to be drawn into threads from the melt, and are generally easy to heat-seal. Thermosetting plastics maintain their original hardness and do not soften before chemical decomposition, remaining relatively dimensionally stable until carbonization at the decomposition temperature. Elastomers do not flow when heated until their chemical decomposition temperature, at which point the material decomposes and carbonizes.
