There are many types of plastics, with seven main types being common, each with specific uses and food safety characteristics. The following is an overview based on the classification of common plastic materials, food applicability, and specific uses.

1) PET (polyethylene terephthalate): commonly used in beverage bottles, mineral water bottles, edible oil bottles, etc. This material is lightweight and chemically stable, but has poor heat resistance, with a heat resistance of about 65 ℃. Therefore, it is only suitable for storing warm or cold drinks, and should not be used for hot water or secondary use to avoid the dissolution of harmful substances. ‌

2) HDPE (high-density polyethylene) is commonly used in acidic milk bottles, medicine bottles, cleaning product containers, etc. It can be used for food packaging, but if not cleaned properly, it can easily breed bacteria and is not suitable for long-term circulation as a water cup or water container. ‌

3) LDPE (Low Density Polyethylene): mainly used for cling film, plastic bags, etc. The heat resistance is not strong, and harmful substances may precipitate when heated. Therefore, when wrapping food and heating, the plastic wrap should be removed to avoid contact with oily food. ‌

4) PP (polypropylene): widely used in microwave oven lunch boxes, soybean milk bottles, juice bottles, etc. It is a plastic that can be safely placed in a microwave oven, with a heat resistance of up to 130 ℃. It can be reused after cleaning and is suitable for holding hot food. ‌

5) PS (polystyrene): commonly used in disposable meal boxes, instant noodle boxes, etc. Due to limited heat resistance, harmful substances are easily decomposed when exposed to high temperatures or oils, so it is not suitable for storing hot or high oil foods and cannot be used for microwave heating.

What about the quality of the materials? Here are a few small knowledge points for everyone:

1. First, let's look at the mechanical properties: tensile strength and ductility are the foundation

Tensile strength: The higher the value, the less likely the film is to be pulled apart. For example, the national standard requires that both the vertical and horizontal pressure should not be less than 10MPa, so that it can withstand compression and impact during transportation.

Elongation at break: The higher this indicator, the more resilient the material is and less prone to brittle fracture. The national standard requires a minimum of 120%, so it is not easy to break at low temperatures or under stress.

Recommended testing instrument: ETT-A electronic tensile testing machine

2‌. Gas permeability: There are range requirements for the permeability of oxygen and carbon dioxide, such as oxygen between 7000 and 20000 cm ³/(m ² · 24h · atm), which can affect food preservation if it is too high.

• Recommended testing instrument: GTR-V3 gas permeability (pressure difference method)

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3. Water vapor transmission rate: generally between 50-400 g/(m ² · 24h), too high can easily cause food to become damp.

• Recommended testing instrument: WVTR-RC6 water vapor permeability tester

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4. Application scenarios: Different needs and choices

• Food packaging enterprises: focus on testing the mechanical properties of PE film in cooking, freezing and other scenarios, and optimize packaging design.

• Research institutions: Compare the tensile strength of different formula materials to promote the development of new environmentally friendly packaging.

In short, when choosing PE food packaging film materials, it is necessary to consider both mechanical properties and other physical indicators, as well as reliable equipment for testing. This way of packaging can be both safe and reliable.

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