Plastic bags are indispensable in life, but they are harmful to human body and seriously pollute the environment. So there are composite food packaging bags to replace ordinary plastic bags. It is not only safe and environmental protection, but also has the function of preserving food. Why are composite food packaging bags so much better than ordinary plastic bags? Let's answer them from the perspective of raw materials

The common food packaging materials are PE polyethylene, PP polypropylene, PS polystyrene and so on. Different materials have different characteristics and should be selected according to the characteristics of food itself.
1、 PE polyethylene
The main component is polyethylene resin, with a small amount of lubricant, aging agent and other additives. Polyethylene is a waxy solid with odorless, nontoxic and milky white appearance. Polyethylene can be divided into high density polyethylene, low density polyethylene and linear low density polyethylene according to different polymerization methods, molecular weight and chain structure.
Low density polyethylene (LDPE), commonly known as high-pressure polyethylene, is mainly used in plastic bags, food, clothing, medicine, fertilizer, industrial products packaging materials and agricultural films, due to its low density and softest material.
Compared with LDPE and LLDPE, high density polyethylene (HDPE) has higher temperature resistance, oil resistance, steam permeability resistance and environmental stress cracking resistance. In addition, it has good electrical insulation, impact resistance and cold resistance. It is mainly used in the production of hollow products (such as milk bottles, detergent bottles), blow molding, injection molding and other fields.
Linear low density polyethylene (LLDPE) is a copolymer of ethylene and a small amount of higher olefins in the presence of catalyst. LLDPE has the advantages of low temperature toughness, high modulus, bending and stress cracking resistance, and better impact strength at low temperature.
It is mainly used in the production of films, daily necessities, pipes, wires and cables by injection molding, extrusion, blow molding and other molding methods.
2、 PP polypropylene
The main component is polypropylene resin, which has high gloss and transparency. Its heat sealing property is worse than that of PE, but better than other plastic materials.
1. Barrier performance is better than PE, strength, hardness and rigidity are higher than PE;
2. Health safety is higher than PE
3. It has excellent high temperature resistance and can be used for a long time at the temperature of 100 ~ 200 ℃. However, its low temperature resistance is worse than that of PE, and the performance becomes brittle when it reaches - 17 ℃.
Polypropylene is mainly made into food packaging bag with film material. It has better water resistance and moisture resistance than Pt. The material is transparent and tear resistant. However, it has poor printability and low cost. It can be used for kink packaging of candy and snacks. It can also be made into heat shrinkable film for food heat shrinkable packaging, such as food vacuum packaging bag and other composite packaging bags.
3、 PS polystyrene
The main component of the polymer is styrene monomer. The material is transparent and glossy.
1. The moisture resistance of PE is worse than that of PE, the chemical stability is general, and the rigidity is high, but the brittleness is big.
2. Good low temperature resistance, but poor high temperature resistance, not higher than 60 ~ 80 ℃.
3. The safety factor is good.
It is mainly made into food box, fruit plate, tableware, cold drink cup, etc.
In addition, food packaging bag materials are commonly made of PE polyethylene, PP polypropylene, PS polystyrene, melamine and other different types of plastic composite film, multi-layer, laminated film and other composite materials. According to different characteristics and processing technology, different kinds of packaging bags can be made, such as rice vacuum packaging bag and dog food self-supporting zipper Bags, condiment plastic bags, tea bags, etc.
Colorants are usually used in the production of color plastic bags. The colorants usually contain benzopyrene, which is a kind of polycyclic aromatic hydrocarbons (PAHs). Polycyclic aromatic hydrocarbons (PAHs) are harmful to human health.
Plasticizers added to improve the properties of plastics will also migrate to hot food during use. Plasticizer is a kind of polymer material additive and PAEs phthalates in environmental estrogens. There are many kinds of plasticizers, the most common one is DEHP (commercial name DOP). DEHP is a colorless, odorless liquid, widely used in industry. It may play an estrogen like role in the human body, interfere with endocrine, cause male reproductive dysfunction, and increase the risk of breast cancer in women.
At present, the common plastic bags are classified according to the production raw materials:
(1) High pressure polyethylene plastic bag
(2) Low pressure polyethylene plastic bag
(3) Polypropylene plastic bag
(4) PVC plastic bag
(5) Vinyl acetate (EVA)
(6) Polyethylene + vinyl acetate (PE + EVA mixture)
(7) Polyethylene coated polypropylene (PE / PP)
(8) Polyethylene coated vinyl acetate (PE / EVA)
(9) Polyethylene coated polyvinyl chloride (PE / PVC)
(10) PE / nylon (PE / PA)
(11) Polyethylene coated polyethylene terephthalate (PE / PET)
(12) Polypropylene coated polypropylene (PP / PP)