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Application of plastic packaging in fresh-keeping packaging of agricultural products (Part 1)


plastic packaging materials and containers are the most used materials and containers for fresh-keeping packaging of agricultural products. Fresh agricultural products are accompanied by the respiration of tissues and the metabolism of enzymes Generally speaking, metabolism slows down due to the decline of temperature, and increases proportionally with the life of goods. However, the vitality of fresh agricultural products is related to their own characteristics and environmental factors. This related factor and characteristic is that plastic packaging materials can be kept fresh by applying certain technical treatment. There are many kinds of fresh-keeping technologies for plastic packaging materials

1. moisturizing and fresh keeping

any fresh agricultural products will have water evaporation after picking, which will affect their quality. Therefore, many plastic packaging films can prevent or reduce water evaporation to achieve fresh-keeping effect. In the design of different material systems, plastic films of hardware module type and thickness should be used as much as possible to have different moisturizing effects. Polyvinylidene chloride is the plastic packaging film with the best moisturizing and sealing effect. Generally, the plastic packaging film used for fruit or vegetable packaging is polyethylene. This is a kind of fresh-keeping material for fresh agricultural products that was first accepted and popularized

2. Anti atomization, condensation and fresh keeping

the moisture preservation mentioned above depends on the sealing and barrier properties of plastic packaging materials, but the water content of fresh agricultural products is very high, and the sealed package is in a high humidity water vapor supersaturation state. The inner surface of plastic packaging film is easy to condense into water droplets. This condensation or atomization not only reduces the transparency, but also accelerates the decay and deterioration of agricultural products. In order to avoid this phenomenon from automobile, lightweight steel to small 5 gold, kitchenware, electric tools, etc., when developing packaging plastic materials, change their processes and add a variety of components, such as glycerol, polyoxide, etc., so as to achieve anti atomization and condensation

an existing anti fog and anti condensation "ethylene vinyl alcohol copolymer (EVOH) packaging film" can achieve the purpose of anti fog and anti condensation and fresh-keeping. After two days of packaging leeks and spinach with this material, it will not shrink, its color will not change, it will not decay, and the inner wall of the film will not condense

3. porous and breathable fresh-keeping

many agricultural products can be sealed to extend their fresh-keeping period, but after the packaging is sealed, fresh agricultural products will produce a lot of respiratory gas, which will make the packaging swell and burst after reaching a certain degree. The porous and breathable polyolefin film can achieve breathable and fresh-keeping. After the package is sealed, the permeability of oxygen or air is increased, while the permeability of water and C02 is reduced. This porous breathable film is partially perforated on its material by discharge method, and the specific perforation is made by high-energy electronic light. The number of holes per square meter can reach 1.1 × 106. Any fresh-keeping packaging of raw fish and other agricultural products has a problem of excluding a certain amount of oxygen or air. We hope to use breathable film to make the air pressure inside and outside the packaging relatively balanced. In particular, the retention of carbon dioxide gas is more conducive to preservation

4. Water permeable and impermeable film preservation

many agricultural products need to be compatible with a certain amount of water in the fresh-keeping packaging, but in the storage process after packaging, gas will be generated to form water vapor, which will expand the packaging bag. At this time, water permeable and impermeable film preservation is needed

the moisture permeable and impermeable fresh-keeping film is usually made by using polyethylene as the base material and adding different components through special processes. The principle of water vapor impermeability is that liquid water has strong intermolecular hydrogen bonding, so the molecular formula of its associated molecule is close to (H20) 8 at room temperature, while the gaseous water structure is smaller, and its molecular formula is h. This is a major theme 20 of the three-day China International Engineering Plastics Industry Innovation conference, but it cannot pass through the large liquid associated molecule (H20) 8. The water vapor transmission rate of this plastic packaging film is 1.5E/100cra2 h。

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