What are the main ingredients in plastic packaging bags

source： time：2014-11-17

With its excellent performance, plastic has gradually replaced many materials and utensils that have been used for decades and centuries, and has become an indispensable assistant in people"s life. Plastic combines the hardness of metal, the lightness of wood, the transparency of glass, the corrosion resistance of ceramics, and the elasticity and toughness of rubber. Therefore, in addition to daily necessities, plastic is more widely used in aerospace, medical devices, petrochemical industry, machinery manufacturing, national defense, construction and other industries.

There are many kinds of plastics. So far, there are about 300 kinds of plastics put into production in the world. There are many classification methods for plastics, and there are two commonly used:

1. According to the different properties of plastics after heating, they are divided into thermoplastic and thermosetting plastics

Thermoplastic molecular structures are linear structures, which soften or melt when heated, plastic into a certain shape, and then harden after cooling. When heated to a certain extent, it softens again and hardens again after cooling. This process can be repeated many times. Such as PVC, polyethylene, polystyrene, etc. Thermoplastic molding process is relatively simple, can be produced continuously, and has quite high mechanical strength, so it develops rapidly.

The molecular structure of thermosetting plastics is body structure, which also softens when heated and can be molded into a certain shape. However, when heated to a certain degree or a small amount of curing agent is added, it will harden and set, and it will not soften and change its shape when heated again. Thermosetting plastics, such as phenolic plastics, amino plastics and epoxy resins, cannot be recycled because they will not soften after being processed and molded. Thermosetting plastic molding process is more complex, so continuous production has some difficulties, but its heat resistance is good, not easy to deform, and the price is relatively low.

The plastic packaging bag we usually use is not a pure substance. It is made of many materials. Among them, high molecular polymer (or synthetic resin) is the main component of plastic. In addition, in order to improve the performance of plastic, it is necessary to add various auxiliary materials in the polymer, such as fillers, plasticizers, lubricants, stabilizers, colorants, etc., in order to become a plastic with good performance.