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、合成樹脂

1. Synthetic resin

合成樹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，而且樹脂的性質常常決定了塑料的性質，所以人們常把樹脂看成是塑料的同義詞。例如把聚氯乙烯樹脂與聚氯乙烯塑料、酚醛樹脂與酚醛塑料混為一談。其實樹脂與塑料是兩個不同的概念。樹脂是一種未加工的原始聚合物，它不僅用于制造塑料，而且還是涂料、膠粘劑以及合成纖維的原料。而塑料除了極少一部分含100％的樹脂外，絕大多數的塑料，除了主要組分樹脂外，還需要加入其他物質。

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

填料又叫填充劑，它可以提高塑料的強度和耐熱性能，并降低成本。例如酚醛樹脂中加入木粉后可大大降低成本，使酚醛塑料成為更廉價的塑料之一，同時還能顯著提高機械強度。填料可分為有機填料和無機填料兩類，前者如木粉、碎布、紙張和各種織物纖維等，后者如玻璃纖維、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、增塑劑

3. Plasticizer

增塑劑可增加塑料的可塑性和柔軟性，降低脆性，使塑料易于加工成型。增塑劑一般是能與樹脂混溶，無毒、無臭，對光、熱穩定的高沸點有機化合物，更常用的是鄰苯二甲酸酯類。例如生產聚氯乙烯塑料時，若加入較多的增塑劑便可得到軟質聚氯乙烯塑料，若不加或少加增塑劑(用量<10％)，則得硬質聚氯乙烯塑料。

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、穩定劑

4. Stabilizer

為了防止合成樹脂在加工和使用過程中受光和熱的作用分解和破壞，延長使用壽命，要在塑料中加入穩定劑。常用的有硬脂酸鹽、環氧樹脂等。

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、著色劑

5. Colorants

著色劑可使塑料具有各種鮮艷、美觀的顏色。常用有機染料和無機顏料作為著色劑。

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

6、潤滑劑

6. Lubricants

潤滑劑的作用是防止塑料在成型時不粘在金屬模具上，同時可使塑料的表面光滑美觀。常用的潤滑劑有硬脂酸及其鈣鎂鹽等。

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.

除了上述助劑外，塑料中還可加入阻燃劑、發泡劑、抗靜電劑等，以滿足不同的使用要求。

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