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Today, the editor of Zekun takes everyone to understand several materials of plastic packaging bags and the differences between these materials.

The plastics commonly used in packaging mainly include polyethylene and polypropylene. Polystyrene, polyvinyl chloride, polyurethane, phenolic resin.

1. polyethylene (PE)

Polyethylene is a high-molecular polymer of ethylene. It is a kind of thermoplastic. According to its industrial production method, there are high-pressure, medium-pressure, and low-pressure polymerization methods. Different production methods have very different molecular structures, and product properties also vary with molecular structures.

Polyethylene is a milky white waxy solid, lighter than water, softer, good water resistance, low temperature resistance, odorless, non-toxic, poor heat resistance, poor film air tightness, and sensitive to ultraviolet rays. It is easy to oxidize and age, and the thermal shrinkage changes greatly, and the printing performance is poor. According to its density. It can be divided into high-density, medium-density, low-density polyethylene, and linear low-density polyethylene. 

2. Polypropylene (PP)

Polypropylene is a by-product propylene from petroleum refining. The refined propylene monomer is polymerized under the catalysis of a catalyst and then separated from the polymer. The molecular weight is 100,000 to 500,000, and the density is very small, which is the smallest among known plastics; non-toxic, odorless, high transparency, mechanical properties, surface strength, friction resistance, chemical corrosion resistance, and moisture resistance are all good; at room temperature Above, the impact resistance value is large, but the low temperature impact resistance value is small; it is prone to static electricity, and the printing performance is not good. Polypropylene has a wide range of raw materials, low price, and wide adaptability of performance. It is widely used in the food industry. It is mostly used to make films and composite films. It has good transparency and surface gloss, and can withstand temperatures of 120 degrees; it can be made into packaging boxes, blow molded into plastic bottles, and certain fillers can be added to make certain machine parts.

3. Polystyrene (PS)

Polystyrene is ethylene and benzene catalyzed by anhydrous aluminum trioxide, undergoes an alkylation reaction to generate ethylbenzene, and then undergoes catalytic dehydrogenation to obtain styrene. Styrene monomer is heated and polymerized into polystyrene in an aqueous suspension of an appropriate amount of initiator (benzoyl peroxide) and dispersant (polyvinyl alcohol). Polystyrene is a colorless, transparent, non-ductile thermoplastic; non-toxic, odorless, odorless, good colorability, moisture permeability is greater than polyethylene, low moisture absorption, dimensional stability, good gloss; processing properties Good, low cost; mechanical properties increase with the increase of molecular weight; low heat resistance, can not be used in boiling water; low temperature resistance, can withstand low temperature of -40 ℃; good indoor aging resistance; to alcoholic organic solvents , Mineral oil has good tolerance, acid and alkali resistance is also very good.

Due to its superior performance, low price, and wide application, polystyrene can be made into films and containers, and is widely used in the food industry; the shrinkage rate can reach 60-70%, and it is a good material for making shrink packaging and has good insulation properties. It can make a variety of telecommunication parts; it can also make various machine parts, toys, daily necessities, etc.; adding foaming agent to polystyrene can make foam plastic, which is a good cushioning packaging material.

4. Polyvinyl chloride (PVC)

“Polyoxyethylene” is a suspension polymerization or emulsion polymerization of vinyl chloride to produce polyvinyl chloride through the action of primers. It is light brown, transparent, good toughness, density 1.4g/cm; it has good chemical stability, is not easy to be corroded by acid and alkali; air tightness, water resistance, heat sealing performance, good printing performance, production energy consumption Less, cheap; mechanical strength, wear resistance, pressure resistance are better than polyethylene and polypropylene. The main disadvantages are poor thermal stability, easy decomposition when heated, and release of hydrogen chloride gas. Due to the different types and quantities of additives, such as plasticizers and stabilizers, polyvinyl chloride can be made into different products and can produce hard products, such as hard pipes, building materials, etc.; it can be used to make artificial leather, wire and cable insulation, Plastic floor, etc. Its main function in packaging is to make a film, which is divided into three types: soft film, hard film, and shrink film. The soft film has a soft texture and good heat-sealability, suitable for high-frequency sealing; low tensile strength, high tear strength; poor sliding properties, and poor processing performance.The tensile strength and tear strength of the hard film are large, the texture is harder, and the elongation is small; the moisture permeability is small, the gas barrier property is good, and the sliding property is good; the printing adaptability is good, but the appropriate ink solvent must be selected; It has poor temperature resistance and becomes brittle at low temperatures. The shrink film has good transparency, low air permeability, shrinks when heated, a wide shrinking temperature range, and a large shrinkage rate. It is a good heat shrinkable packaging material. According to different production processes, it can be divided into dry stretching. Tubular stretching and vertical and horizontal unidirectional stretching and other varieties.

5. Polyester (PET)

“Polyester” is a polycondensation product of terephthalic acid and ethylene glycol. Compared with other plastics, polyester has excellent barrier properties, such as carbon dioxide, oxygen, water and fragrance, etc. It can be well barrier; with excellent mechanical properties, it has high strength, compression resistance and impact resistance.; Good chemical stability, resistance to acid and alkali corrosion; high transparency, good gloss and optical properties; non-toxic, tasteless, in line with food hygiene standards; its structure has ester groups, so the printing performance is good. Polyester is a unique and versatile packaging material. Film can be made into packaging containers such as bottles, cans, cups, etc., and it can also be used as a dual-purpose bakeable tray.

6. Phenolic plastic (PF)

Phenolic resin is formed by polycondensation of phenols (mainly phenol) and aldehydes (mainly formaldehyde). Depending on whether the catalyst is acidic or basic, the ratio of phenol to formaldehyde is different. Thermoplastic resin or thermosetting resin can be obtained. The two can be transformed into each other under suitable conditions. In practice, thermosetting resins are often used. Phenolic resin has good mechanical strength and thermal strength; good moisture resistance and corrosion resistance; easy processing and low price.

After adding different fillers and curing agents to the phenolic resin, different phenolic plastics can be produced. Various sheet fillers are added to thermosetting resin, and laminates with various properties can be obtained after lamination; adding foaming agent can make phenolic foam; when phenolic plastic is used for packaging, phenolic resin is mixed with filler and cured Powder, coloring agent, etc. are made into molding powder, and then molded into bottle caps, machine parts, daily necessities, and some packaging containers.   

Phenolic plastic products have good chemical stability; excellent heat resistance; high mechanical strength and wear resistance; not easy to deform, but poor elasticity; good electrical insulation; monotonous color, mostly dark red or black. Since its main raw materials are phenol and formaldehyde, which are both toxic to a certain extent, it is not suitable for food packaging materials.

7. Polyamide (PA)

Polyamide is commonly known as “nylon”, which can be obtained by polycondensation reaction of dibasic acid and dibasic acid. Polyamide is non-toxic, colorless and transparent; it has good abrasion resistance. Strong impact toughness, excellent mechanical properties; good light resistance, not easy to aging under light; good oil resistance, good chemical stability, but not resistant to alcohols, formic acid and phenol; good air tightness; high temperature adaptability, which can be in -40 Used in the range of ~100 degrees; good printability and decoration; high moisture absorption.
  Polyamide has a wide range of uses, such as bearings, gears, pump blades, and auto parts. Its application in packaging is mainly flexible packaging. It can be made into film for food packaging and can also be used to make packing belts and ropes. Its sturdiness is better than polypropylene packing belts.          

8. Urea-formaldehyde plastic (UF)

Urea-formaldehyde plastic, commonly known as “electric jade”, is made of urea and formaldehyde as raw materials, through polycondensation reaction to obtain urea-formaldehyde resin, and then add fillers, colorants, lubricants, plasticizers, etc., processed into compression molding powder (electric jade powder), and then It is heated and molded into products. It has large surface hardness, certain mechanical strength, not easy to deform, but relatively brittle; it is odorless, tasteless, strong in coloring power, bright in color, and looks like beautiful jade; it has good heat resistance, not easy to burn, acid and alkali resistance, and water resistance. Poor, high water absorption, good electrical insulation. Urea-formaldehyde plastics can be made into a variety of products, such as daily necessities and electrical components. The package can be made into beautiful packaging boxes, packaging trays, bottle caps, etc.; because formaldehyde has a certain toxicity, it is not suitable for food packaging. Adding a foaming agent to the urea-formaldehyde resin and using a mechanical method to make it foam, the urea-formaldehyde foam can be obtained. It is lightweight, inexpensive, good in heat preservation, and corrosion resistant, and is a widely used cushioning packaging material.

9. Melamine plastic (ME)

Melamine plastic and urea-formaldehyde plastic are both amino plastics. It is made of resin obtained by polycondensation reaction of melamine and formaldehyde as the main component, adding fillers, lubricants, coloring agents, hardeners, etc., and is formed by hot pressing. It is also a thermosetting plastic.

Melamine plastic is non-toxic, odorless, tasteless, and has good hygienic properties; it has high mechanical strength, good surface hardness, and is not easy to deform; the surface is smooth and feels like porcelain; it has strong impact resistance and pollution resistance; good chemical stability. Melamine plastic can be used to make packaging containers of various colors including food packaging.

10. Polyvinyl alcohol (PVA)

Polyvinyl alcohol is a hydrolysis product of polyvinyl acetate. It is transparent, non-toxic, and tasteless; it has excellent gas barrier properties, water resistance and oil resistance; good chemical stability; good printability, no static electricity; good mechanical properties.

Polyvinyl alcohol mostly uses its film in packaging, which can be used for food packaging. It has a significant effect on preventing oxidative discoloration, taste change and deterioration of food, and maintaining the freshness of food; it can also package other products, such as chemical products.

11. Polycarbonate (Pc)

“Polycarbonate” is a general term for resins containing carbonate structure in the molecular chain, and usually refers to bisphenol A type polycarbonate. It is colorless and transparent, has good gloss; it has excellent heat resistance and cold resistance, and can be used for pressure sterilization; it has high mechanical strength. It can be side by side with polyester and nylon; it has excellent impact toughness, and the product is not easy to break under impact; it has low water absorption, moisture absorption, and air permeability; it has good chemical resistance and can prevent ultraviolet rays from penetrating non-toxic, odorless, and tasteless; The molding performance is good, and general molding methods can be used. The precision of the molded product is very high. But the heat sealing performance is poor.

Polycarbonate is an engineering plastic with excellent comprehensive properties, which can be used to make various gears, machine parts, etc.; it can be made into films for packaging food and other items. When sealing is required, composite films are often used to improve heat sealing performance. ; Can also be made into various packaging containers.

12. Polyvinylidene chloride (PVDC)

“Polyvinylidene chloride” is a homopolymer of vinylidene oxide. It is non-toxic, tasteless and transparent; it has high mechanical strength. Good toughness; resistance to oil and organic solvents; good heat shrinkability and self-adhesiveness, easy adhesion between films; excellent air tightness and moisture resistance. However, it has poor machinability, poor thermal stability, is not easy to heat seal, and easily decomposes when exposed to ultraviolet rays.

The application of polyvinylidene chloride in packaging is mainly to make food packaging film, which can be used as a sealed package, which can effectively prevent food from absorbing moisture. Oil and fat foods are oxidized to ensure long-term food quality; it can be used as sterilized food packaging because it can be heat sterilized; it can also be used as a packaging material for household daily use.

13. Polyurethane (PVP)

“Polyurethane” is also called polyurethane, which is made by the reaction of isocyanate and hydroxyl compound. The main characteristics of polyurethane are good wear resistance, excellent low temperature resistance, outstanding oil resistance and chemical corrosion resistance. Polyurethane is mainly processed into foam plastics, and foams with different hardness and softness can be obtained by changing the raw materials and the ratio. Soft products have good toughness, good elasticity, and oil resistance. They are the main varieties of polyurethane foam and are widely used in packaging to make cushioning materials such as cushions. Rigid products are heat-resistant, cold-resistant, heat-insulating, and have excellent shock resistance. They are widely used in the packaging of precision instruments and meters. The production of polyurethane foam is simple. Easy to operate, low cost, good shockproof performance, can be prepared at room temperature, especially can be prepared by on-site foaming, which brings great convenience to packaging.

Ok, let’s share common knowledge about packaging bags here. If you want to know more, please follow the website of Hunan Zekun Packaging Technology Co., Ltd.: or /

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