The composition of plastic bags is mainly plastic. The plastic we usually use is not a pure substance, it is made of many materials. In addition, in order to improve the properties of plastics, various auxiliary materials, such as fillers, plasticizers, lubricants, stabilizers and colorants, should be added to the polymers in order to become good plastics.

1、合成树脂

1. Synthetic resin

合成树脂是塑料的更主要成分，其在塑料中的含量一般在40％～100％。由于含量大，而且树脂的性质常常决定了塑料的性质，所以人们常把树脂看成是塑料的同义词。例如把聚氯乙烯树脂与聚氯乙烯塑料、酚醛树脂与酚醛塑料混为一谈。其实树脂与塑料是两个不同的概念。树脂是一种未加工的原始聚合物，它不仅用于制造塑料，而且还是涂料、胶粘剂以及合成纤维的原料。而塑料除了极少一部分含100％的树脂外，绝大多数的塑料，除了主要组分树脂外，还需要加入其他物质。

Synthetic resin is the main component of plastics, and its content in plastics is generally 40% - 100%. Because of its high content, and the nature of resin often determines the nature of plastic, so people often regard resin as a synonym for plastic. For example, PVC resin and PVC plastic, phenolic resin and phenolic plastic are confused. In fact, resin and plastic are two different concepts. Resin is a kind of raw polymer, which is not only used in the manufacture of plastics, but also the raw material of coatings, adhesives and synthetic fibers. In addition to a small part of plastics containing 100% resin, the vast majority of plastics, in addition to the main component resin, also need to add other substances.

2、填料

2. Filler

填料又叫填充剂，它可以提高塑料的强度和耐热性能，并降低成本。例如酚醛树脂中加入木粉后可大大降低成本，使酚醛塑料成为更廉价的塑料之一，同时还能显著提高机械强度。填料可分为有机填料和无机填料两类，前者如木粉、碎布、纸张和各种织物纤维等，后者如玻璃纤维、硅藻土、石棉、炭黑等。

Filler also known as filler, it can improve the strength and heat resistance of plastics, and reduce the cost. For example, the cost of phenolic resin can be greatly reduced by adding wood powder, which makes phenolic resin one of the cheapest plastics, and can significantly improve the mechanical strength. The fillers can be divided into organic fillers and inorganic fillers, the former such as wood flour, rags, paper and various fabric fibers, and the latter such as glass fiber, diatomite, asbestos, carbon black, etc.

3、增塑剂

3. Plasticizer

增塑剂可增加塑料的可塑性和柔软性，降低脆性，使塑料易于加工成型。增塑剂一般是能与树脂混溶，、无臭，对光、热稳定的高沸点有机化合物，更常用的是邻苯二甲酸酯类。例如生产聚氯乙烯塑料时，若加入较多的增塑剂便可得到软质聚氯乙烯塑料，若不加或少加增塑剂(用量<10％)，则得硬质聚氯乙烯塑料。

Plasticizers can increase the plasticity and softness of plastics, reduce brittleness, and make plastics easy to process. Plasticizers are usually organic compounds with high boiling point, which are miscible with resin, nontoxic, odorless, light and heat stable, and phthalate esters are the most commonly used. For example, in the production of PVC plastics, soft PVC plastics can be obtained by adding more plasticizers, while rigid PVC plastics can be obtained without or less plasticizer (dosage < 10%).

4、稳定剂

4. Stabilizer

为了防止合成树脂在加工和使用过程中受光和热的作用分解和破坏，延长使用寿命，要在塑料中加入稳定剂。常用的有硬脂酸盐、环氧树脂等。

In order to prevent the decomposition and destruction of synthetic resin by light and heat in the process of processing and using, and prolong the service life, stabilizers should be added into the plastics. Commonly used are stearate, epoxy resin and so on.

5、着色剂

5. Colorants

着色剂可使塑料具有各种鲜艳、美观的颜色。常用有机染料和无机颜料作为着色剂。

Colorants can make plastics have a variety of bright and beautiful colors. Organic dyes and inorganic pigments are commonly used as colorants.

6、润滑剂

6. Lubricants

润滑剂的作用是防止塑料在成型时不粘在金属模具上，同时可使塑料的表面光滑美观。常用的润滑剂有硬脂酸及其钙镁盐等。

The function of the lubricant is to prevent the plastic from sticking to the metal mold during molding, and to make the surface of the plastic smooth and beautiful. Commonly used lubricants are stearic acid and its calcium magnesium salt.

除了上述助剂外，塑料中还可加入阻燃剂、发泡剂、抗静电剂等，以满足不同的使用要求。

In addition to the additives mentioned above, flame retardant, foaming agent and antistatic agent can be added to the plastics to meet different requirements.