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Characteristics of plastic packaging

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What are the characteristics of plastic packaging?

common plastic varieties have the following meanings:

1: pet (polyethylene terephthalate), a container made of this material, is a common plastic bottle for soda, also known as “Baote bottle”

2: HDPE (high density polyethylene) is mostly used to make containers for detergents, shampoos, bath milk, edible oil, pesticides, etc. The container is mostly opaque and feels like wax

3: PVC (polyvinyl chloride) is mainly used to make water pipes, raincoats, schoolbags, building materials, plastic films, plastic boxes and other utensils

4: LDPE (low density polyethylene), the plastic bags that can be seen everywhere are mostly made of LDPE

5: PP (polypropylene) is mostly used to make buckets, garbage cans, baskets, baskets and food containers for microwave ovens

6: PS (polystyrene), due to its low water absorption, is mostly used to make building materials, toys, stationery and rollers, as well as cup boxes or disposable tableware for drinks in fast food restaurants

7: others

PC is the abbreviation of polycarbonate (). Since polycarbonate does not belong to the material range of 1-6 above, the number marked in the middle of the triangle of the cycle sign is 7. At the same time, in order to facilitate the sorting during the cycle, the material name PC is marked next to the cycle sign.

composition of plastic
the plastic we usually use is not a pure substance. It is made of many materials. Among them, high molecular polymer (or synthetic resin) is the main component of plastics. In addition, in order to improve the performance of plastics, it is necessary to add various auxiliary materials, such as fillers, plasticizers, lubricants, stabilizers and colorants, so as to become plastics with good performance
1. Synthetic resin
synthetic resin is the main component of plastics, and its content in plastics is generally 40% ~ 100%. Because of its high content and the nature of resin often determines the nature of plastics, people often regard resin as a synonym for plastics. For example, PVC resin and PVC plastic, phenolic resin and phenolic plastic are confused. In fact, resin and plastic are two different concepts. Resin is an unprocessed original polymer. It is not only used to make plastics, but also used as raw material for coatings, adhesives and synthetic fibers. In addition to a small part of plastics containing 100% resin, the vast majority of plastics need to add other substances in addition to the main component resin
2. Filler
filler is also called filler, which can improve the strength and heat resistance of plastics and reduce the cost. For example, adding wood powder to phenolic resin can greatly reduce the cost, make phenolic plastic one of the cheapest plastics, and significantly improve the mechanical strength. Fillers can be divided into organic fillers and inorganic fillers, the former such as wood powder, rags, paper and various fabric fibers, and the latter such as glass fiber, diatomite, asbestos, carbon black, etc
3. Plasticizer
plasticizer can increase the plasticity and softness of plastics, reduce brittleness and make plastics easy to process and shape. Plasticizers are generally high boiling organic compounds that are miscible with resin, non-toxic, odorless and stable to light and heat. Phthalates are the most commonly used. For example, in the production of PVC plastics, if more plasticizers are added, soft PVC plastics can be obtained, and if no or less plasticizers are added (dosage & lt; 10%), rigid PVC plastics can be obtained
4. Stabilizer
in order to prevent the decomposition and damage of synthetic resin by light and heat during processing and use and prolong its service life, stabilizer should be added to plastics. Commonly used are stearate, epoxy resin, etc
5. Colorant
colorant can make plastics have various bright and beautiful colors. Organic dyes and inorganic pigments are commonly used as colorants
6. Lubricant
the function of lubricant is to prevent the plastic from sticking to the metal mold during molding, and make the plastic surface smooth and beautiful. Common lubricants include stearic acid and its calcium magnesium salts
in addition to the above additives, flame retardants, foaming agents and antistatic agents can also be added to plastics to meet different application requirements
classification of plastics
I. classification by use characteristics
according to the different use characteristics of famous plastics, plastics are usually divided into three types: general plastics, engineering plastics and special plastics
① general purpose plastics
generally refer to plastics with large output, wide use, good formability and low price. There are five varieties of general plastics, namely polyethylene, polypropylene, polyvinyl chloride, polystyrene and ABS. They are all thermoplastics
② engineering plastics
generally refer to plastics that can bear certain external force, have good mechanical properties, high and low temperature resistance and good dimensional stability, and can be used as engineering structures, such as polyamide, polysulfone, etc
in engineering plastics, they are divided into general engineering plastics and special engineering plastics
general engineering plastics include polyamide, polyoxymethylene, polycarbonate, modified polyphenylene ether, thermoplastic polyester, ultra-high molecular weight polyethylene, methylpentene polymer, vinyl alcohol copolymer, etc
special engineering plastics can be divided into crosslinked and non crosslinked types. Crosslinking types include: polyamine bismaleamide, polytriazine, crosslinked polyimide, heat-resistant epoxy tree finger, etc. Non crosslinked types include polysulfone, polyethersulfone, polyphenylene sulfide, polyimide, polyetherketone (PEEK) and so on
③ special plastics
generally refer to plastics with special functions and can be used in special application fields such as aviation and aerospace. For example, fluoroplastics and organosilicon have outstanding special functions such as high temperature resistance, self lubrication and so on. Reinforced plastics and foam plastics have high strength, high cushioning and other special properties. These plastics belong to the category of special plastics. Br> A. strong plastics: the raw materials of reinforced plastics can be divided into granular (such as calcium plastic reinforced plastics), fibrous (such as glass fiber or glass cloth reinforced plastics) and flake (such as mica reinforced plastics). According to the material, it can be divided into cloth based reinforced plastics (such as rag reinforced or asbestos reinforced plastics), inorganic mineral filled plastics (such as quartz or mica filled plastics) and fiber reinforced plastics (such as carbon fiber reinforced plastics)
B. foam plastics: foam plastics can be divided into three types: hard, semi hard and soft foam plastics. Rigid foam has no flexibility and high compression hardness. Only when it reaches a certain stress value can it produce deformation. Flexible foams are flexible and have very little compression hardness. They are easy to deform. They can be restored to original state after stress relieving, and the residual deformation is small. The flexibility and other properties of semi rigid foams are between hard rigid foam plastics. Br> II. Classification by physical and chemical properties
according to different physical and chemical properties of various plastics, plastics can be divided into thermosetting plastics and thermoplastics
⑴ thermosetting plastics
thermosetting plastics refer to plastics that can cure or have insoluble (melting) characteristics under heating or other conditions, such as phenolic plastics, epoxy plastics, etc. Thermosetting plastics are divided into formaldehyde crosslinking type and other crosslinking types. It softens when heated and hardens when cooled. It can soften an
d harden repeatedly and maintain a certain shape. Soluble in certain solvents, with fusible and soluble properties. Thermoplastics have excellent electrical insulation, especially polytetrafluoroethylene (PTFE), polystyrene (PS), polyethylene (PE) and polypropylene (PP) have very low dielectric constant and dielectric loss, and are suitable for high frequency and high voltage insulation materials. Thermoplastics are easy to form and process, but they have low heat resistance and are easy to creep. Their creep degree changes with load, ambient temperature, solvent and humidity. In order to overcome these weaknesses of thermoplastics and meet the needs of applications in space technology, new energy development and other fields, all countries are developing melt forming heat-resistant resins, such as polyether ether ketone (PEEK), polyether sulfone (PES), polyarylene sulfone (pASU), polyphenylene sulfide (PPS), etc. The composites with them as matrix resin have high mechanical properties and chemical corrosion resistance, can be thermoformed and welded, and the interlaminar shear strength is better than that of epoxy resin. If peek is used as matrix resin and carbon fiber is made into composite, the fatigue resistance is better than that of epoxy /carbon fiber. It has good impact resistance, good creep resistance at room temperature and good processability. It can be used continuously at 240 ~ 270 ℃. It is a very ideal high temperature resistant insulating material. The composites made of polyethersulfone as matrix resin and carbon fiber have high strength and hardness at 200 ℃ and good impact resistance at – 100 ℃; It is non-toxic, non combustible, with the least smoke and good radiation resistance. It is expected to be used as a key component of spaceship, and can also be molded into radar radome
formaldehyde crosslinked plastics include phenolic plastics and amino plastics (such as urea formaldehyde melamine formaldehyde, etc.)
other cross-linked plastics include unsaturated polyester, epoxy resin, phthalate diallyl resin, etc
⑵ thermoplastics
thermoplastics refer to plastics that can be repeatedly heated, softened, cooled and hardened within a specific temperature range, such as polyethylene, polytetrafluoroethylene, etc. Thermoplastics are divided into hydrocarbons, vinyl containing polar genes, engineering, cellulose and other types. After hot working and forming, an insoluble cured product is formed, and its resin molecules are crosslinked into a network structure by a linear structure. Further heat will decompose and destroy. Typical thermosetting plastics include phenolic, epoxy, amino, unsaturated polyester, furan, polysilicate ether and other materials, as well as newer polyphenylene dicarboxylate plastics. They have the advantages of high heat resistance and not easy to deform when heated. The disadvantage is that the mechanical strength is generally not high, but its mechanical strength can be improved by adding fillers to make laminated materials or molding materials
thermosetting plastics made of phenolic resin as the main raw material, such as phenolic molded plastics (commonly known as bakelite), have the characteristics of durability, dimensional stability and resistance to the action of other chemicals except strong alkali. Various fillers and additives can be added according to different uses and requirements. For varieties requiring high insulation performance, mica or glass fiber can be used as filler; For heat-resistant varieties, asbestos or other heat-resistant fillers can be used; For varieties requiring earthquake resistance, various appropriate fibers or rubber can be used as fillers and some toughening agents to make high toughness materials. In addition, aniline, epoxy, polyvinyl chloride, polyamide, polyvinyl acetal and other modified phenolic resins can also be used to meet the requirements of different applications. Phenolic resin can also be made into phenolic laminate, which is characterized by high mechanical strength, good electrical properties, corrosion resistance and easy processing. It is widely used in low-voltage electrical equipment
amino plastics include urea formaldehyde, melamine
formaldehyde, urea melamine formaldehyde, etc. They have the advantages of hard texture, scratch resistance, colorless and translucent. They can be made into colorful products by adding color materials, commonly known as electric jade. Because it is oil resistant and not affected by weak alkali and organic solvent (but not acid resistant), it can be used for a long time at 70 ℃ and 110 ~ 120 ℃ in a short time. It can be used for electrical products. Melamine formaldehyde plastic has higher hardness than urea formaldehyde plastic, has better water resistance, heat resistance and arc resistance, and can be used as arc resistant insulating material
epoxy resin is the main raw material

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