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What are the additives in PET film?

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! Hygiene of plastics and their products
(I recommend PE fresh-keeping film)
(the following is some relevant information)
plastic is a kind of high molecular compound. Plastic products are processed under certain plasticizing conditions with synthetic resin as the main raw material and an appropriate amount of plasticizers, stabilizers, antioxidants and other additives. At present, polyethylene, polypropylene, polyvinyl chloride, vinylidene chloride, polycarbonate, polyethylene terephthalate, nylon, unsaturated polyester resin, acrylonitrile styrene copolymer resin, renitrile styrene copolymer resin, acrylonitrile butadiene styrene copolymer resin, etc. are allowed to be used in food containers, packaging materials and thermoplastics used in the manufacture of food tools and equipment in China; Thermosetting plastics include melamine formaldehyde resin, etc. ?
(I) polyethylene (, PE) and polypropylene (, PP)?
1. Physical and chemical properties: polyethylene and polypropylene plastics are polymeric compounds with ethylene and propylene as monomers respectively
molecular formula of polyethylene:?
molecular weight:?
molecular formula of polypropylene:?
molecular weight: about 100000 ~ 500000?
according to the pressure during polymerization, polyethylene plastics are divided into high-pressure polyethylene or low-density polyethylene (LDPE) and low-pressure polyethylene or high-density polyethylene (HDPE). High pressure polyethylene is mainly used to manufacture food plastic bags, fresh-keeping films, etc; Low pressure polyethylene is mainly used to manufacture food plastic containers, pipes, cutting boards, etc. Polypropylene plastic film can change its mechanical properties and increase its strength and transparency through longitudinal and transverse stretching. According to the stretching direction, polypropylene plastic film is mainly used to manufacture food plastic bags, especially composite plastic bags; Polypropylene can also be processed into both low-temperature and high-temperature food containers, such as fresh-keeping boxes and containers for microwave ovens. ?
2. Main health problems: polyethylene and polypropylene resins have very low toxicity, and kd50 is greater than the maximum possible gavage. Due to the low acute and chronic carcinogenic activity of saturated alkanes, the biological stability of saturated alkanes is not obvious. The content of ethylene and propylene monomer in polyethylene and polypropylene resin is very small, and the toxicity of ethylene and propylene itself is also low. In the production of polyethylene and polypropylene resins and molded products, agents are generally rarely used. Therefore, polyethylene and polypropylene plastics are relatively safe plastics and can be widely used as food containers and packaging materials. However, low molecular weight polyethylene is easy to dissolve in oil, so polyethylene tableware should not always contain edible oil to avoid the taste of oil. According to GB 9691-88 hygienic standard for polyethylene resin for food packaging, GB9687-88 hygienic standard for polyethylene molded products for food packaging, gb9693-88 hygienic standard for polypropylene resin for food packaging and gb9688-88 hygienic standard for polypropylene molded products for food packaging, free monomers need to be controlled for both resin and molded products. ?
(II) polyvinyl chloride (PVC)?
1. Physical and chemical properties: polyvinyl chloride is polymerized with vinyl chloride as monomer.
molecular formula:
molecular weight: about 50000 ~ 120000
according to the amount of plasticizer added to PVC, it can be divided into hard, semi hard and soft PVC. Plasticizers added to rigid PVC are generally & lt; 10%, 10 ~ 30% for semi-rigid and 30 ~ 50% for soft. Its physical and mechanical properties also vary with its components. Generally speaking, PVC has the characteristics of good chemical resistance, high mechanical strength, good insulation and low price. PVC semi-rigid sheet can be processed into plastic box by blistering; Soft PVC can be used as the gasket of beverage cap and four screw bottle cap (commonly known as drop plastic); Rigid PVC can be processed into plastic pipes, plates, etc. ?
2. Main health problems: PVC itself is non-toxic, but its monomer and degradation products are highly toxic, and the content of plasticizer in PVC is high. ?
(1) toxicity of vinyl chloride monomer and degradation products: polyvinyl chloride resin and molded products often contain a certain amount of vinyl chloride monomer, which can migrate to food when in contact with food. After vinyl chloride is absorbed through the gastrointestinal tract, part of it is discharged through the respiratory tract, and the other part is decomposed into chloroethanol and monochloroacetic acid. It can also bind to deoxyribonucleic acid (DNA) in vivo. It mainly has toxic effects on nervous system, bone and liver. The results show that vinyl chloride monomer and its decomposition products have carcinogenic effect. There are epidemiological investigation reports of human angiosarcoma. Therefore, various countries have made regulations on the residue of vinyl chloride monomer in PVC resin, such as Japan, the United States, the United Kingdom, France, the Netherlands, Italy, Switzerland and other countries, which should be less than 1mg /kg; France, Italy and Switzerland also stipulate that the migration amount in food shall not be greater than 0.05mg/kg. China’s gb4803-94 hygienic standard for polyvinyl chloride resin for food containers and packaging materials and gb9681-88 hygienic standard for polyvinyl chloride molded products for food packaging stipulate that the content of vinyl chloride monomer in polyvinyl chloride resin and molded products for food packaging shall be controlled below 5mg /kg and 1mg /1 respectively. ?
(2) toxicity of halogenated hydrocarbons: according to the preparation method of vinyl chloride monomer, polyvinyl chloride is divided into acetylene polyvinyl chloride and ethylene polyvinyl chloride. Due to different synthetic processes, the halogenated hydrocarbons contained in PVC are also different. Acetylene PVC contains 1,1-dichloroethane, while ethylene PVC contains 1,2-dichloroethane. The toxicity of the latter is 10 times that of the former. Therefore, gb4803-94 hygienic standard for vinyl chloride resin for food containers and packaging materials stipulates that the residual amount of 1,1-dichloroethane in vinyl chloride resin by acetylene method shall be less than 150mg /kg; The residual amount of 1,2-dichloroethane in vinyl polyvinyl chloride resin shall be less than 2mg /kg. ?
(3) migration of plasticizers: a large number of plasticizers are used in PVC molded products, especially semi-rigid and soft PVC, some of which are highly toxic (see table 5.1). In addition to plasticizers, additives such as stabilizers and UV absorbers are added to the production of PVC molded products, which will also migrate to food. Therefore, great attention must also be paid to the toxicity of additives. It shall comply with the provisions of gb9685-94 hygienic standard for the use of additives for food containers and packaging materials. ?
(III) polystyrene (, PS)
1. Rational characteristics: polystyrene is polymerized from styrene monomer.
molecular formula: molecular weight: about 200000
Universal polystyrene is colorless and transparent, resistant to oil, acid, alkali and alcohol, but brittle and poor impact resistance; High impact polystyrene (HIPS) with high impact strength can be prepared after modification, which can be used to make fruit and vegetable boxes in refrigerators and household food processing machinery; EPS can also be prepared by adding a certain amount of foaming agent (i.e. pentane, hexane, freon and other foaming agents) to the polystyrene polymerized by suspension method, and then the fast-food lunch box can be prepared by secondary processing. ?
2. Main health problems: Polystyrene itself is non-toxic. It is mixed
with feed to feed animals, and there is no toxicity. However, polystyrene contains free styrene monomer and volatile substances such as toluene, ethylbenzene and cumene. These volatile substances have great toxicity. The LD50 (oral) of styrene monomer on rats is 1 ~ 1.2g/kg body weight. Chronic toxicity test shows that growth retardation and weight loss of liver and kidney; Benzene series compounds such as toluene, ethylbenzene and cumene have toxic effects on the nervous system (see table 5.2). Therefore, the residues of styrene and ethylbenzene in GB9692-88 alkene resin should be controlled below 0.5% and 0.3% respectively.
the foaming agent freon in EPS is highly toxic, and the residue in EPS can be as high as tens to hundreds of mg /kg. Pentane and butane have little toxicity and have been listed in the hygienic standard for the use of additives for food containers and packaging materials. Degradable EPS includes biodegradation, photodegradation and mixed degradation. Biodegradation generally adds 10 ~ 30% starch and /or cellulose to EPS; Generally, photosensitive catalyst must be added to EPS for photodegradation. The hygienic standard for the use of additives for food containers and packaging materials stipulates that the photosensitive catalysts that can be used include ferrocene derivatives: photosensitive catalysts must be added to EPS for mixed degradation. At present, China has not formulated the hygienic standard of EPS for food containers and packaging materials. ?
(IV) melamine formaldehyde resin (MF)?
1. Physical and chemical properties: melamine formaldehyde resin is formed by polycondensation of melamine and formaldehyde.
molecular formula: molecular weight: & gt; 300
melamine formaldehyde resin is a thermosetting plastic (melamine). Heat resistant (120 ℃), oil resistant, alcohol resistant and pollution resistant. It can be made into tableware and tableware of various colors and imitation porcelain. ?
2. Main health problems: melamine formaldehyde resin itself is non-toxic. However, melamine formaldehyde resin contains a certain amount of free formaldehyde, especially in phenolic resin (commonly known as bakelite) polycondensated with phenol and formaldehyde and urea formaldehyde resin (commonly known as Dianyu) polycondensated with urea and formaldehyde. Formaldehyde is a kind of protoplasm poison of cells. When animals ingest formaldehyde orally, hepatocyte necrosis and lymphocyte infiltration can occur. Therefore, phenolic resin and urea formaldehyde resin shall not be used in food containers and packaging materials. The migration amount of formaldehyde in melamine formaldehyde resin decreases with the extension of the thermosetting pressing time of melamine formaldehyde resin, the storage time after thermosetting molding and the increase of thermosetting pressing temperature. According to gb9690-88 hygienic standard for melamine molded products for food packaging, the content of free formaldehyde in the finished products of melamine formaldehyde resin for food packaging shall be controlled below 10mg /L. ?
(V) polycarbonate resin (, PC)?
1. Physical and chemical properties: polycarbonate resin is the general name of a class of high molecular compounds containing carbonate in the molecular chain. Polycarbonates can be divided into aliphatic, alicyclic, aromatic and aliphatic aromatic polycarbonates according to the types of R-groups. At present, there is only bisphenol A aromatic polycarbonate resin, which is made from bisphenol A and diphenyl carbonate by transesterification and polycondensation. Its molecular formula is: polycarbonate tree ester is a thermoplastic engineering plastic with heat resistance, cold resistance and good mechanical properties. Due to the characteristics of tasteless, oil resistant and not easy to pollute, polycarbonate resin is mainly used to manufacture and process horizontal tools of food (such as biscuits, Kongli molds, etc.), baby bottles, food processing machinery and other food containers and food processing equipment with impact resistance and certain transparency requirements. ?
2. Main health problems: polycarbonate resin is non-toxic, and the oral LD50 is & gt; 10g /kg body weight, negative mutagenicity test (a, ES test, micronucleus test and sperm malformation test). However, when bisphenol A is exchanged with diphenyl carbonate, phenol, an intermediate, is produced. Phenol not only has certain toxicity, but also produces strange smell and affects the sensory properties of food. The weight and tensile strength of polycarbonate resin soaked in 50% and 100% ethylene glycol solution for 30 days decreased significantly. Therefore, according to gb13116-9 1 hygienic standard for polycarbonate molded products for food containers and packaging materials, polycarbonate resin for food containers and packaging materials and free benzene in molded products

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