Plastic bags are indispensable in life, but they are harmful to the human body and are very polluting to the environment. Then there is a composite food packaging to replace the ordinary plastic bag. It is safe, environmentally friendly, and aesthetically pleasing, with the ability to preserve food. Why is the composite food packaging bag so much better than the ordinary plastic bag? We will answer all the questions from the raw materials:
Commonly used food packaging materials are PE polyethylene, PP polypropylene, PS polystyrene and the like. Different materials have different characteristics, and they should be selected according to the characteristics of the food itself.
First, PE polyethylene
The main component is a polyethylene resin, a small amount of a lubricant, an additive such as an aging agent. Polyethylene is a odorless, non-toxic, milky white waxy solid. Polyethylene is classified into high density polyethylene, low density polyethylene and linear low density polyethylene depending on the polymerization method, molecular weight and chain structure.
Low-density polyethylene (LOWEENSITY POLYETHYLENE, LDPE) is commonly known as high-pressure polyethylene. Due to its low density and softest material, it is mainly used in plastic bags, food, clothing, medicine, fertilizer, industrial packaging materials and agricultural films.
High-density polyethylene (HIGH DENSITY POLYETHYLENE, HDPE) is commonly known as low-pressure polyethylene. Compared with LDPE and LLDPE, it has high temperature resistance, oil resistance, vapor permeability and environmental stress crack resistance. In addition, electrical insulation and resistance Good impact and cold resistance, mainly used in the production of hollow products (such as milk bottles, detergent bottles) and blow molding, injection molding and other fields.
LINEAR LOW DENSITY POLYETHYLENE (LLDPE) is a copolymer of ethylene and a small amount of higher-olefin polymerized in the presence of a catalyst. The appearance of LLDPE is similar to that of LDPE, and its transparency is poor. However, it has good surface gloss, low temperature toughness, high modulus, resistance to bending and stress cracking, and good impact strength at low temperatures.
It is mainly used in the production of film, daily necessities, pipes, wires and cables by molding methods such as injection molding, extrusion and blow molding.
Second, PP polypropylene
The main component is polypropylene resin, which has high gloss and transparency, and the heat sealability is worse than that of PE, but it is superior to other plastic materials.
1. The barrier performance is better than PE, and the strength, hardness and rigidity are higher than PE;
2. Health safety is higher than PE
3. Excellent high temperature resistance, can be used for a long time at a temperature of 100~200 degrees Celsius, but the low temperature resistance is worse than PE, and the performance becomes brittle when it reaches -17 degrees Celsius.
Polypropylene is mainly made into film food packaging bags. It is better in water and moisture resistance than PT. The material is transparent and tear resistant. However, the printing property is lower than PT and the cost is low. It can be used for twisting and packaging of candy and snacks. It can also be made into heat-shrinkable film for food shrink packaging, such as food vacuum packaging bags and other composite bags.
Third, PS polystyrene
The main component is a polymer of styrene monomer. The material is transparent and the gloss is good.
1. The moisture resistance is worse than that of PE, the chemical stability is general, and it has high rigidity, but it is brittle.
2. Good low temperature resistance, but the high temperature resistance is poor, not higher than 60~80 degrees Celsius.
3. The safety factor is good.
Mainly made into food boxes, fruit bowls, tableware, cold drinks cups, etc.
In addition, food packaging materials commonly include composite films of different types of plastics such as PE polyethylene, PP polypropylene, PS polystyrene, and melamine, composite packaging bags made of composite materials such as multilayers and laminated films, etc. Different characteristics and different processing techniques can produce different kinds of packaging bags such as rice vacuum packaging bags, dog food self-supporting zipper bags, condiment plastic packaging bags, tea packaging bags and the like.
Color plastic bags generally use colorants in the production process. Colorants usually contain benzopyrene. Benzopyrene is a kind of polycyclic aromatic hydrocarbons. Polycyclic aromatic hydrocarbons cause many harms to human health.
Plasticizers added to improve the properties of plastics also migrate to hot foods during use. Plasticizers are a high-molecular auxiliaries and are also known as PAEs phthalates in environmental estrogens. The most common variety is DEHP (trade name DOP). DEHP chemical name di(2-ethylhexyl) phthalate is a colorless, odorless liquid that is widely used in industry. It may play an estrogen-like role in the human body, interfere with endocrine, cause male reproductive disorders, and increase the risk of breast cancer in women.
The current common plastic bags are classified according to the raw materials for production:
(1) High pressure polyethylene plastic bag
(2) Low pressure polyethylene plastic bag
(3) Polypropylene plastic bag
(4) PVC plastic bags
(5) Vinyl acetate (EVA)
(6) Polyethylene + vinyl acetate (PE + EVA mixture)
(7) Polyethylene-coated polypropylene (PE/PP)
(8) Polyethylene-clad vinyl acetate (PE/EVA)
(9) Polyethylene-clad polyvinyl chloride (PE/PVC)
(10) Polyethylene-coated nylon (PE/Nylon) (PE/PA)
(11) Polyethylene-coated polyethylene terephthalate (PE/PET).
(12) Polypropylene covered polypropylene (PP/PP)