Ordinary polyester is generally formed by esterification and polycondensation of terephthalic acid (PTA) and ethylene glycol (EG), and belongs to crystalline polymer (strictly speaking, the polymer exists in the crystallization zone and amorphous region). Generally, it is milky white or light yellow, highly crystalline polymer with smooth and shiny surface, and the product can remain transparent even at low temperature without adding filler. It can maintain excellent physical and mechanical properties in a wide temperature range, and the long-term use temperature can reach 120 degrees. Good electrical insulation performance. Creep resistance, friction resistance and fatigue resistance. It has good dimensional stability. However, due to its high glass transition temperature, low crystallization rate, difficult processing and molding, high molding temperature, long production cycle and poor impact resistance. Therefore, it is necessary to improve its processability through reinforcement, filling and * * * mixing. The use of PET can be divided into two parts: fiber (70% was used for synthetic fiber in the early days) and non-fiber. The latter includes well-known packaging materials (food and beverage containers, vacuum packaging, etc. ), insulating materials, tape substrates, films and photographic films. The so-called * * polymerization modification is to introduce a third or even a fourth component to participate in the * * * polymerization in addition to the two main components of terephthalic acid (PTA) and ethylene glycol (EG), so as to make it form an asymmetric molecular structure and form an amorphous PET*** polymer. For example, when dicarboxylic acid (acidic) is used for polymerization modification, the prepared PET polymer is called APET. Compared with PET, the low temperature toughness (impact resistance and tear resistance) and heat resistance of APET are improved. The product appearance transparency is high; If the polymer is modified by ethylene glycol, it is called PETG. The hardness, stiffness and toughness of PETG are better than those of PET homopolymer, and it also maintains its due toughness at low temperature. The product is more transparent and even colorless. In actual processing, PET is provided in the form of particles, while both APET and PETG can be provided in the form of amorphous materials. 1, 2, 3, 4, 5, 6 and 7 in the environmental label correspond to different polymers, that is, 1 stands for PET；; 2 stands for HDPE, high density polyethylene; 3 stands for PVC and polyvinyl chloride; 4 represents LDPE and low density polyethylene; 5 stands for PP and polypropylene; 6 represents PS, polystyrene; 7 stands for other polymers.