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As a kind of polymer synthesis material, plastic has been rapidly developed and used in a large amount in the packaging field because of its advantages in variety, excellent performance, low technical content, and low price. However, due to the defects in plastic materials and the environmental pollution caused by waste plastics, the application fields of plastic packaging materials are limited. In particular, the rapid development of the food industry has brought higher requirements to the plastics industry, leading to plastic packaging. Manufacturers of materials have turned to various auxiliaries that can improve their performance. The following describes the application and development of auxiliaries in packaging materials.
1 Plastic additives
Plastic additives, also known as plastic additives, are some of the compounds that must be added in order to improve processing performance or to improve the performance of the resin itself. Plastic additives are gradually developed after the industrialization of PVC, which is currently an important auxiliary material for the plastics industry. Together with resin and processing machinery, it constitutes the three basic elements of today's plastics industry [1].
Plastic additives can be divided into: stabilizing additives, processing system additives and functional additives according to their different functions and roles. Stabilization aids include antioxidants, heat stabilizers, light stabilizers, etc., accounting for about 11% of the total consumption; processing system additives including lubricants, release agents, processing modified additives, etc., accounting for about consumption The total amount of 9%; functional additives, including plasticizers, flame retardants, antistatic agents, foaming agents, cross-linking agents, anti-fogging agents, nucleating agents, accounting for 80% of total consumption. Among them, plasticizers are plastics additives with the largest productivity and the largest consumption in plastics processing; flame retardants are second only to plasticizers; the proportion of various stabilizers is also larger; impact modification Additives and foaming agents are closely followed; some new functional additives such as antistatic agents and anti-fogging agents also have a certain amount of applications [2].
2 plastic additives in the role of packaging materials
2.1 Plasticizers
Plasticizers are a group of low-volatile organic compounds that can be miscible with polymers to a certain extent. They can reduce the viscosity of the polymer melt, the glass transition temperature and the elastic modulus of the product, and thus increase the plasticity of the polymer resin. The flexibility of the product is imparted; its mechanism of action is based on the weakening of the molecular attraction of the polymer molecular chains by the plasticizer molecules. The main products are phthalates, terephthalates, dibasic esters, alkyl sulfonates, epoxy esters, chlorinated paraffins, and phosphate esters. Plasticizers were the earliest plastic additives used. Among them, phthalates were the main plasticizers. Their output accounted for about 80% of the total output of plasticizers, including dioctyl phthalate (DOP for short). ) is the most important species. Some types can be used for food packaging materials, but their use is limited as people attach importance to food safety issues. The new guidelines for phthalates promulgated by the European Union impose strict rules on the use of children's toys, clothing and skin care products, and on all items that may be placed in the mouth. The quality limit must not exceed 0. 1%. A new series of plasticizers based on gemini sorbitol has established a new platform for phthalate substitutes due to its non-toxicity. Secondly, the Hexamoll DINCH phthalate-free plasticizer successfully developed by BASF in 2002 is based on a diester-based cyclohexanedicarboxylic acid. Its toxicity is very low, and its solubility in water and ethanol is extremely low. Outperforms traditional phthalate ester plasticizers and is particularly suitable for sensitive PVC applications such as toys and medical facilities. Since the product was introduced to the market in 2002, it has been exposed to food products. Close attention has been paid to manufacturers of packaging films, pipes and seals, as affirmed by the European Food Safety Authority [3].
2.2 flame retardants
Flame retardants are a class of functional auxiliaries that improve the flammability, self-extinguishing, or smoke-reducing properties of flammable or combustible materials. Most of them are compounds of the group V, VII and III elements of the periodic table, and particularly compounds of phosphorus, bromine, chlorine, gallium, and aluminum. There are two types of flame retardants, additive and reactive. Additive flame retardants are mainly phosphate esters, halogenated phosphate esters, halogenated hydrocarbons, antimony oxides and aluminum hydroxides. They are easy to use and have good adaptability. However, due to the addition of 10% to 30%, they often affect plastics. performance. Reactive flame retardants are monomers containing flame-retardant elements and have little effect on plastic properties. Commonly used are halogenated anhydrides for flame retarding polyesters, tetrabromobisphenol A for flame retarding epoxy resins, and Polyurethane flame-retardant phosphorus-containing polyols. Brominated flame retardants are recognized as high-efficiency organic flame retardants, and they are also the main flame retardant market in the world. Phosphorous flame retardants are mainly phosphate esters and halophosphate esters. In recent years, they have also been coated with red phosphorus. New types of polyphosphates and NP intumescent flame retardants are available; In addition, inorganic flame retardants have high flame retardancy, low smoke, and low harmful properties, which have attracted people’s attention in our country, among which are composite flame retardants and smoke suppressants. Variety has been put on the market. As global environmental protection and safety requirements for flame retardants are increasing, the use of halogen-based flame retardants has been limited. Melamine flame retardants are plasticizers with relatively good safety performance. Currently, their market share is still very small, only 1%, but their consumption growth rate is expected to be higher than the average level of flame retardants, mainly used in plastics and Coatings industry [3]. Tetrabromobisphenol A is a kind of flame retardant with low toxicity and good compatibility with the environment.
2·3 Antioxidants
Antioxidants are chemical additives that can suppress or delay the autoxidation reaction of plastic products to prevent plastic aging during processing, storage, and use. Antioxidants are used in a small amount in plastics, generally 0.1% to 1.0%, but they are important additives for polyolefins, styrene resins, polyvinyl chloride, polyamides, and polyacetals. In the rubber industry, antioxidants are used as anti-aging agents. Antioxidants for plastics are classified into phenolic primary antioxidants and auxiliary antioxidants such as thiodipropionates and phosphites. The main antioxidant is also called chain terminator. Its function is to capture the active free radicals produced by oxidative degradation and interrupt the chain degradation reaction. Its representative species is 2,6-di-tert-butyl-4-methylphenol ( The antioxidant 264) and tetrakis[methyl-[beta]-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester (referred to as antioxidant 1010 for short). An auxiliary antioxidant, also known as a peroxide decomposer, functions to decompose the oxidatively decomposed intermediate product into a non-radical product; dilauryl thiodipropionate and phenyl diisooctyl phosphite are the most commonly used auxiliary agents. Antioxidants. Main and auxiliary antioxidants are usually used together to exert a synergistic effect. The main antioxidant is the main body of plastic antioxidants, and most of them are hindered phenols. Since hindered phenols have the characteristics of non-toxic, non-coloring, and good coupling effect with polymers, it will become a new hot spot in the research of polymeric antioxidants. . As auxiliary antioxidants are mostly phosphites, the improvement of the processing stability and hydrolysis stability of such antioxidants is the direction of their development. Phosphite antioxidants are the main varieties of auxiliary antioxidants for polyolefin processing. Their use together with hindered phenol antioxidants can effectively improve the processing stability, heat stability and color improvement of polyolefin resins. And weather resistance and so on. Due to the low volatility and resistance to extraction, especially the higher processing temperatures, the use of increasing the molar mass of antioxidants to increase their thermal stability is a recent trend in the study of antioxidants. 4].
2.4 Thermal Stabilizers
The heat stabilizer is an auxiliary agent that eliminates or slows down the unsaturated bond in the resin, undergoes a self-addition reaction or is oxidized at a certain temperature, thereby preventing structural and performance changes. The main function is to prevent thermal degradation during resin processing and to prevent aging of the product during long-term use. The amount of thermal stabilizer used in soft products is about 2%, while that in rigid products is 3% to 5%. Polyvinyl chloride and vinyl chloride copolymer in a larger amount. According to the different chemical structures, they can be divided into five categories: lead salts, metal soaps, organic tin compounds, organic stabilizers, and composite stabilizers.
Lead salts have long played a major role in heat stabilizers, but their production has declined in recent years due to their toxicity. Relatively complex metal soaps, organic tin, organic lanthanum, rare earth stabilizers and organic auxiliary stabilizers and other high-efficiency, low-toxicity varieties have been put on the market. Calcium/zinc compound stabilizers are ideal environmental protection heat stabilizers, becoming the most important direction for the development of heat stabilizers. The development of heat stabilizers industry has become an overall trend toward high efficiency, non-toxicity, compound type and harmlessness. [5].
2.5 light stabilizers
Light stabilizer is a kind of stabilizer used to inhibit photo-oxygen degradation of polymer resin and improve the weatherability of plastics. It is an essential additive in agricultural films. Can be divided into the following categories: light shielding agent, mainly refers to the ability to shield the emission of ultraviolet light (carbon black, zinc oxide, etc.), UV absorbers, quenchers (mainly divalent organic nickel chelate), free radicals Capture agent [mainly hindered amine (HALS) light stabilizer].
The consumption structure of China's light stabilizers is still dominated by hindered amines and UV absorbers, accounting for more than 90% of total consumption. Nickel quenchers have been declining year by year due to the toxicity of heavy metal ions in organic nickel complexes. Because HALS has the advantages of high efficiency, multifunction, and non-toxicity, it has become the development direction of light stabilizers in the 21st century. The elimination of hindered amines with low relative molecular mass has turned to the development of high molecular weight, multi-functional, non-alkaline and reactive species [5].
2·6 blowing agent
The foaming agent refers to a substance that can release gas to obtain a polymer product having a micropore structure and reduce the apparent density of the product. Can be divided into physical foaming agents and chemical foaming agents. As the traditional physical foaming agent HCFC has a destructive effect on the atmospheric ozone layer, it is gradually being replaced by a chemical foaming agent. The main chemical foaming agent is azodicarbonamide (AC). Blowing agents are mainly used in the preparation of cushioning packaging materials.
2·7 Antistatic agent
The usual antistatic agents are surfactant compounds, which are cationic, anionic, amphoteric and nonionic, and can be surface-coated and can be directly added to a resin compounding system. Among them, the coating type antistatic agents are mostly ionic surfactants, and the additive type antistatic agents are mainly nonionic surfactants.
Antistatic agents have developed rapidly with the development of electronic products and medical devices. In particular, permanent antistatic agents have important applications and significance in eliminating static electricity in electrical appliances or electronic products. Polyolefin (PE) and Polypropylene (PP), which are commonly used for packaging, have strong electrical insulation and cause difficulties in film processing. During use, static electricity easily generates dust adsorption, which affects the appearance and hygiene of the product. Causes damage to electronic products. Currently, antistatic agents are commonly used to eliminate static electricity on the surface of polyolefins.
2·8 Anti-fogging agent
Anti-fogging agent, also known as dripping agent, is an additive that can effectively prevent the generation of fog on the surface of non-hydrophilic objects. According to the way they are added, they can be divided into two kinds: inner additive type and outer coating type. The use of anti-fogging agent will not affect the light transmission performance and performance of the film. Anti-fogging agents are also an additive developed with the research of agricultural films. However, in recent years, it has also been used in refrigerated foods and fruit and vegetable packaging plastics, and has a positive effect on reducing moisture condensation in the packaging film and increasing the transparency and visibility of the contents.
2·9 Deoxidizer and UV Blocker
Deoxidizers and UV blockers are new types of additives that have emerged in recent years. Oxygen absorber can absorb oxygen in the package, reduce environmental oxygen damage to the contents and prolong food storage time; UV blocker can block ultraviolet rays, avoid UV damage to the contents, and extend product storage stability period. These two types of additives are mainly used for packaging products in the fields of food, medicines, health products and cosmetics.
2·10 Antibacterial agents
Antibacterial agents are new types of auxiliaries that have the ability to inhibit and kill bacteria. The addition of one or more specific antibacterial agents to polymeric materials can produce functional new materials, such as antimicrobial plastics, antibacterial fibers, and the like. Antimicrobial agents are increasingly used in plastics, with an annual growth rate of 3.5% to 4%. Therefore, antibacterial agents have become one of the new plastic additives that have received much attention.
Due to the stringent and expensive registration procedures for new antibacterial agents, many manufacturers are focusing on the development of new applications for existing varieties. In terms of organic antimicrobials, AdekaPalmarole introduced Royalguard BC-250 for polyolefins; Ciba Specialty Chemicals introduced anti-algae agent Irgaguard A2000 for low density polyethylene (LDPE), high density polyethylene (HDPE), PP Polyurethane (PU), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC) and other plastic products on the surface of anti-algae. In terms of inorganic antimicrobial agents, the silver or zinc system is the most widely used, and the silver-based antibacterial Irgaguard B series products introduced by Ciba Specialty Chemicals are particularly suitable for transparent products such as PET; the active ingredients in the antibacterial masterbatch PolybatchAbact introduced by Schuiman Resistant to temperatures up to 1 000°C, the masterbatch can be used in film, injection molding and blow-molded packaging products [2].
2.11 Nucleating agent
The nucleating agent is suitable for incompletely crystalline resins such as polyethylene and polypropylene, and aims to shorten the molding cycle and improve the transparency of the product by changing the crystallization behavior of the resin, accelerating the crystallization speed, increasing the crystal density and promoting the refinement of the crystal grain size. Such nucleating agents are also known as transparent agents, surface gloss, tensile strength, rigidity, thermal deformation and other physical and mechanical properties of the new functional additives. According to the crystal form, α-crystal nucleating agents and β-crystal nucleating agents can be classified. At present, the global nucleating agent consumption is about 5kt/a, 80% of which is diphenylmethylene sorbitol (DBS) nucleating agent. Due to its ability to improve the mechanical properties and toughness of PP, β-crystalline nucleating agents have become a hotspot in the research and development of nucleating agents.
The clearing agent is a branch of the nucleating agent and about 90% of the clearing agent is used for the production of transparent polypropylene (C-PP). The transparent agent gives the original opaque PP with good transparency, so that the very low cost C-PP can not only replace the more expensive poly(ethylene terephthalate) (PET), polystyrene (PS), and poly in many aspects. Transparent plastic such as polycarbonate (PC), and can improve PP's mechanical properties such as rigidity, impact strength, heat distortion temperature.
3 Development Prospects of Plastic Additives
3.1 The use of additives in packaging materials is essential
Stabilizers (including antioxidants, heat stabilizers, and light stabilizers) are of great importance to the processing of plastics. The application of antioxidants involves almost all plastic products and is of great significance for improving the service life of plastics. 80% of the total amount of antioxidants are used in three major categories of polymers: polypropylene, polyethylene, and polystyrene. Among them, both PE and PP are plastic packaging materials that consume a great deal of energy. The two-way stretching and various functional films developed based on these two have shown a strong momentum in the development of packaging materials. The combination of polystyrene and carton for internal packaging has good impact resistance, easy molding, low density and light weight. It is also an excellent sheet for producing various plastic containers. Biaxially oriented polystyrene (BOPS) meets the hygienic requirements of food packaging, has good transparency, good ductility, is suitable for producing various containers, has good printability, and has a broad market prospect. Polyvinyl chloride is a heat-sensitive resin that can easily release hydrogen chloride by heat processing, and then cause thermal aging degradation reaction. PP, PE, PS and PC materials are also susceptible to thermal oxidation when they are heated, and they must be added with heat stabilizer during processing. Light stabilizers have been developed with the development of agricultural films. For agricultural PP and PE films, light stabilizers play an important role.
Plasticizers are plastics auxiliaries with the largest productivity and largest consumption in plastics processing. They are mainly used for soft PVC products and consume about 85% of the total. They are also used in vinyl acetates and other plastics. Base resins, polyvinylidene chlorides, polyvinyl alcohols, celluloses, polyamides, etc. are very versatile.
Foams prepared using foaming agents have important applications in packaging. Foam plastics used as packaging materials can be divided into shock-proof packaging (such as egg packaging bags, cushioning packaging liners, etc.) and general packaging. Its main varieties are polystyrene foam, polyurethane foam and polyethylene high foam materials. Foam plastics are not only important for buffer packaging, fresh packaging, and thermal insulation, but also reduce the quality of packaging materials and packaging.
3.2 functional film promotes the development and application of plastic additives
Antistatic agents are used most in polyethylene and polypropylene. In recent years, as people have continuously improved the quality and performance requirements of polypropylene products, the demand for antistatic agents is increasing. In the production of BOPP film called "Packaging Queen", antistatic agent is one of the largest additives. In addition, antistatic agents are also used in LDPE film, PE, PVC and other plastic packaging materials. Antistatic films are usually made by adding antistatic agents or coating processing technology. They are suitable for packaging electronic products with integrated circuits to prevent external electromagnetic radiation during transportation; or for packaging of powdered goods such as detergent powders to prevent static electricity from being caused by objects. Adsorption at the inlet of the packaging container is not conducive to sealing.
The development of high-barrier films has not only promoted the composite process of plastic films with aluminum foil or paper, but also promoted the development of plated SiOx materials and nano-SiO2. Coating a thin layer of silicon oxide on substrates such as PET, nylon (PA), and PP not only provides better barrier properties, but also has excellent atmospheric environment adaptability, and its barrier properties are almost independent of environmental humidity and temperature. Impact of change. SiOx coating has high barrier property, high microwave permeability and transparency, and can be used for soft packaging such as high-temperature cooking and microwave processing, and can also be used as a packaging container for beverages and edible oils [6].
Nano-plastics are inorganic nano-particles, such as silicate, calcium carbonate, SiO2, TiO2, etc., which are uniformly dispersed in the plastic matrix resin in the nanometer size, and have high strength, high heat resistance, high barrier property, and high flame retardancy. The advantages of good thermal stability and electrical conductivity are one of the most advanced products in the development of composite materials. Currently, nano-packaging materials developed abroad, such as nylon 6-nanometer composites, nano-polyolefins, and nano-polyesters, are mainly used in high barrier packaging for food and beer beverages. Nano-film can also be used for special packaging, such as anti-static, anti-electromagnetic, explosion-proof and invisible, dangerous goods packaging, etc. It will promote a tremendous transformation of traditional packaging materials [7].
Antibacterial film packaging of fresh fruits and vegetables has great practical significance. The application of antibacterial materials and antibacterial technology can prevent mold and other microorganisms from invading the fruits and vegetables and achieve better preservation effect. Antibacterial and anti-mold packaging can also be used for weapons, export clothing, optical equipment and other products. In addition, a film made from a master batch containing 1% of silver ions or a container coated with a layer of such a film on the surface can completely kill fungi that cause food poisoning within 1 to 2 days in the absence of a nutrient source. This antibacterial film is widely used for deli meat, aquatic products and liquid food packaging [7]. In addition, in recent years, anti-fogging agents have been added to the packaging films of frozen meats, cold cooked foods and fruit and vegetables to reduce the condensation of water vapor on the packaging in the environment and increase the transparency and visibility of packaging. The use of deoxidizers and UV-blocking agents reduces the damage of oxygen and ultraviolet rays to the packaging and prolongs the packaging and shelf life of foods and pharmaceuticals. The development of nucleating agents enhances the transparency and impact resistance of polypropylene packaging materials.
4 Conclusion
Plastic additives are companions in the petrochemical and synthetic resin industries. Rapidly growing plastic products market has boosted the rapid growth of China's plastics additives industry; but at present, China's plastics additives industry still has low product quality, high environmental pressure, and new products. Slow development, small-scale production, lack of sustainable development and other weaknesses; the current development of international plastics additives industry presents a trend of green, composite, high-efficiency, and specialization [8], so the domestic plastics additives industry should follow the international trend. , As soon as possible to integrate into the international market, at the same time with the advantages of domestic resources to strengthen the industry's internal research and development and mutual communication, in order to ensure the healthy and sustainable development of plastic additives industry in China. On the other hand, the use of plastics additives industry to promote the development of functional packaging materials in China's development and application of speed, so that China's packaging industry has risen to a new level.
1 Plastic additives
Plastic additives, also known as plastic additives, are some of the compounds that must be added in order to improve processing performance or to improve the performance of the resin itself. Plastic additives are gradually developed after the industrialization of PVC, which is currently an important auxiliary material for the plastics industry. Together with resin and processing machinery, it constitutes the three basic elements of today's plastics industry [1].
Plastic additives can be divided into: stabilizing additives, processing system additives and functional additives according to their different functions and roles. Stabilization aids include antioxidants, heat stabilizers, light stabilizers, etc., accounting for about 11% of the total consumption; processing system additives including lubricants, release agents, processing modified additives, etc., accounting for about consumption The total amount of 9%; functional additives, including plasticizers, flame retardants, antistatic agents, foaming agents, cross-linking agents, anti-fogging agents, nucleating agents, accounting for 80% of total consumption. Among them, plasticizers are plastics additives with the largest productivity and the largest consumption in plastics processing; flame retardants are second only to plasticizers; the proportion of various stabilizers is also larger; impact modification Additives and foaming agents are closely followed; some new functional additives such as antistatic agents and anti-fogging agents also have a certain amount of applications [2].
2 plastic additives in the role of packaging materials
2.1 Plasticizers
Plasticizers are a group of low-volatile organic compounds that can be miscible with polymers to a certain extent. They can reduce the viscosity of the polymer melt, the glass transition temperature and the elastic modulus of the product, and thus increase the plasticity of the polymer resin. The flexibility of the product is imparted; its mechanism of action is based on the weakening of the molecular attraction of the polymer molecular chains by the plasticizer molecules. The main products are phthalates, terephthalates, dibasic esters, alkyl sulfonates, epoxy esters, chlorinated paraffins, and phosphate esters. Plasticizers were the earliest plastic additives used. Among them, phthalates were the main plasticizers. Their output accounted for about 80% of the total output of plasticizers, including dioctyl phthalate (DOP for short). ) is the most important species. Some types can be used for food packaging materials, but their use is limited as people attach importance to food safety issues. The new guidelines for phthalates promulgated by the European Union impose strict rules on the use of children's toys, clothing and skin care products, and on all items that may be placed in the mouth. The quality limit must not exceed 0. 1%. A new series of plasticizers based on gemini sorbitol has established a new platform for phthalate substitutes due to its non-toxicity. Secondly, the Hexamoll DINCH phthalate-free plasticizer successfully developed by BASF in 2002 is based on a diester-based cyclohexanedicarboxylic acid. Its toxicity is very low, and its solubility in water and ethanol is extremely low. Outperforms traditional phthalate ester plasticizers and is particularly suitable for sensitive PVC applications such as toys and medical facilities. Since the product was introduced to the market in 2002, it has been exposed to food products. Close attention has been paid to manufacturers of packaging films, pipes and seals, as affirmed by the European Food Safety Authority [3].
2.2 flame retardants
Flame retardants are a class of functional auxiliaries that improve the flammability, self-extinguishing, or smoke-reducing properties of flammable or combustible materials. Most of them are compounds of the group V, VII and III elements of the periodic table, and particularly compounds of phosphorus, bromine, chlorine, gallium, and aluminum. There are two types of flame retardants, additive and reactive. Additive flame retardants are mainly phosphate esters, halogenated phosphate esters, halogenated hydrocarbons, antimony oxides and aluminum hydroxides. They are easy to use and have good adaptability. However, due to the addition of 10% to 30%, they often affect plastics. performance. Reactive flame retardants are monomers containing flame-retardant elements and have little effect on plastic properties. Commonly used are halogenated anhydrides for flame retarding polyesters, tetrabromobisphenol A for flame retarding epoxy resins, and Polyurethane flame-retardant phosphorus-containing polyols. Brominated flame retardants are recognized as high-efficiency organic flame retardants, and they are also the main flame retardant market in the world. Phosphorous flame retardants are mainly phosphate esters and halophosphate esters. In recent years, they have also been coated with red phosphorus. New types of polyphosphates and NP intumescent flame retardants are available; In addition, inorganic flame retardants have high flame retardancy, low smoke, and low harmful properties, which have attracted people’s attention in our country, among which are composite flame retardants and smoke suppressants. Variety has been put on the market. As global environmental protection and safety requirements for flame retardants are increasing, the use of halogen-based flame retardants has been limited. Melamine flame retardants are plasticizers with relatively good safety performance. Currently, their market share is still very small, only 1%, but their consumption growth rate is expected to be higher than the average level of flame retardants, mainly used in plastics and Coatings industry [3]. Tetrabromobisphenol A is a kind of flame retardant with low toxicity and good compatibility with the environment.
2·3 Antioxidants
Antioxidants are chemical additives that can suppress or delay the autoxidation reaction of plastic products to prevent plastic aging during processing, storage, and use. Antioxidants are used in a small amount in plastics, generally 0.1% to 1.0%, but they are important additives for polyolefins, styrene resins, polyvinyl chloride, polyamides, and polyacetals. In the rubber industry, antioxidants are used as anti-aging agents. Antioxidants for plastics are classified into phenolic primary antioxidants and auxiliary antioxidants such as thiodipropionates and phosphites. The main antioxidant is also called chain terminator. Its function is to capture the active free radicals produced by oxidative degradation and interrupt the chain degradation reaction. Its representative species is 2,6-di-tert-butyl-4-methylphenol ( The antioxidant 264) and tetrakis[methyl-[beta]-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester (referred to as antioxidant 1010 for short). An auxiliary antioxidant, also known as a peroxide decomposer, functions to decompose the oxidatively decomposed intermediate product into a non-radical product; dilauryl thiodipropionate and phenyl diisooctyl phosphite are the most commonly used auxiliary agents. Antioxidants. Main and auxiliary antioxidants are usually used together to exert a synergistic effect. The main antioxidant is the main body of plastic antioxidants, and most of them are hindered phenols. Since hindered phenols have the characteristics of non-toxic, non-coloring, and good coupling effect with polymers, it will become a new hot spot in the research of polymeric antioxidants. . As auxiliary antioxidants are mostly phosphites, the improvement of the processing stability and hydrolysis stability of such antioxidants is the direction of their development. Phosphite antioxidants are the main varieties of auxiliary antioxidants for polyolefin processing. Their use together with hindered phenol antioxidants can effectively improve the processing stability, heat stability and color improvement of polyolefin resins. And weather resistance and so on. Due to the low volatility and resistance to extraction, especially the higher processing temperatures, the use of increasing the molar mass of antioxidants to increase their thermal stability is a recent trend in the study of antioxidants. 4].
2.4 Thermal Stabilizers
The heat stabilizer is an auxiliary agent that eliminates or slows down the unsaturated bond in the resin, undergoes a self-addition reaction or is oxidized at a certain temperature, thereby preventing structural and performance changes. The main function is to prevent thermal degradation during resin processing and to prevent aging of the product during long-term use. The amount of thermal stabilizer used in soft products is about 2%, while that in rigid products is 3% to 5%. Polyvinyl chloride and vinyl chloride copolymer in a larger amount. According to the different chemical structures, they can be divided into five categories: lead salts, metal soaps, organic tin compounds, organic stabilizers, and composite stabilizers.
Lead salts have long played a major role in heat stabilizers, but their production has declined in recent years due to their toxicity. Relatively complex metal soaps, organic tin, organic lanthanum, rare earth stabilizers and organic auxiliary stabilizers and other high-efficiency, low-toxicity varieties have been put on the market. Calcium/zinc compound stabilizers are ideal environmental protection heat stabilizers, becoming the most important direction for the development of heat stabilizers. The development of heat stabilizers industry has become an overall trend toward high efficiency, non-toxicity, compound type and harmlessness. [5].
2.5 light stabilizers
Light stabilizer is a kind of stabilizer used to inhibit photo-oxygen degradation of polymer resin and improve the weatherability of plastics. It is an essential additive in agricultural films. Can be divided into the following categories: light shielding agent, mainly refers to the ability to shield the emission of ultraviolet light (carbon black, zinc oxide, etc.), UV absorbers, quenchers (mainly divalent organic nickel chelate), free radicals Capture agent [mainly hindered amine (HALS) light stabilizer].
The consumption structure of China's light stabilizers is still dominated by hindered amines and UV absorbers, accounting for more than 90% of total consumption. Nickel quenchers have been declining year by year due to the toxicity of heavy metal ions in organic nickel complexes. Because HALS has the advantages of high efficiency, multifunction, and non-toxicity, it has become the development direction of light stabilizers in the 21st century. The elimination of hindered amines with low relative molecular mass has turned to the development of high molecular weight, multi-functional, non-alkaline and reactive species [5].
2·6 blowing agent
The foaming agent refers to a substance that can release gas to obtain a polymer product having a micropore structure and reduce the apparent density of the product. Can be divided into physical foaming agents and chemical foaming agents. As the traditional physical foaming agent HCFC has a destructive effect on the atmospheric ozone layer, it is gradually being replaced by a chemical foaming agent. The main chemical foaming agent is azodicarbonamide (AC). Blowing agents are mainly used in the preparation of cushioning packaging materials.
2·7 Antistatic agent
The usual antistatic agents are surfactant compounds, which are cationic, anionic, amphoteric and nonionic, and can be surface-coated and can be directly added to a resin compounding system. Among them, the coating type antistatic agents are mostly ionic surfactants, and the additive type antistatic agents are mainly nonionic surfactants.
Antistatic agents have developed rapidly with the development of electronic products and medical devices. In particular, permanent antistatic agents have important applications and significance in eliminating static electricity in electrical appliances or electronic products. Polyolefin (PE) and Polypropylene (PP), which are commonly used for packaging, have strong electrical insulation and cause difficulties in film processing. During use, static electricity easily generates dust adsorption, which affects the appearance and hygiene of the product. Causes damage to electronic products. Currently, antistatic agents are commonly used to eliminate static electricity on the surface of polyolefins.
2·8 Anti-fogging agent
Anti-fogging agent, also known as dripping agent, is an additive that can effectively prevent the generation of fog on the surface of non-hydrophilic objects. According to the way they are added, they can be divided into two kinds: inner additive type and outer coating type. The use of anti-fogging agent will not affect the light transmission performance and performance of the film. Anti-fogging agents are also an additive developed with the research of agricultural films. However, in recent years, it has also been used in refrigerated foods and fruit and vegetable packaging plastics, and has a positive effect on reducing moisture condensation in the packaging film and increasing the transparency and visibility of the contents.
2·9 Deoxidizer and UV Blocker
Deoxidizers and UV blockers are new types of additives that have emerged in recent years. Oxygen absorber can absorb oxygen in the package, reduce environmental oxygen damage to the contents and prolong food storage time; UV blocker can block ultraviolet rays, avoid UV damage to the contents, and extend product storage stability period. These two types of additives are mainly used for packaging products in the fields of food, medicines, health products and cosmetics.
2·10 Antibacterial agents
Antibacterial agents are new types of auxiliaries that have the ability to inhibit and kill bacteria. The addition of one or more specific antibacterial agents to polymeric materials can produce functional new materials, such as antimicrobial plastics, antibacterial fibers, and the like. Antimicrobial agents are increasingly used in plastics, with an annual growth rate of 3.5% to 4%. Therefore, antibacterial agents have become one of the new plastic additives that have received much attention.
Due to the stringent and expensive registration procedures for new antibacterial agents, many manufacturers are focusing on the development of new applications for existing varieties. In terms of organic antimicrobials, AdekaPalmarole introduced Royalguard BC-250 for polyolefins; Ciba Specialty Chemicals introduced anti-algae agent Irgaguard A2000 for low density polyethylene (LDPE), high density polyethylene (HDPE), PP Polyurethane (PU), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC) and other plastic products on the surface of anti-algae. In terms of inorganic antimicrobial agents, the silver or zinc system is the most widely used, and the silver-based antibacterial Irgaguard B series products introduced by Ciba Specialty Chemicals are particularly suitable for transparent products such as PET; the active ingredients in the antibacterial masterbatch PolybatchAbact introduced by Schuiman Resistant to temperatures up to 1 000°C, the masterbatch can be used in film, injection molding and blow-molded packaging products [2].
2.11 Nucleating agent
The nucleating agent is suitable for incompletely crystalline resins such as polyethylene and polypropylene, and aims to shorten the molding cycle and improve the transparency of the product by changing the crystallization behavior of the resin, accelerating the crystallization speed, increasing the crystal density and promoting the refinement of the crystal grain size. Such nucleating agents are also known as transparent agents, surface gloss, tensile strength, rigidity, thermal deformation and other physical and mechanical properties of the new functional additives. According to the crystal form, α-crystal nucleating agents and β-crystal nucleating agents can be classified. At present, the global nucleating agent consumption is about 5kt/a, 80% of which is diphenylmethylene sorbitol (DBS) nucleating agent. Due to its ability to improve the mechanical properties and toughness of PP, β-crystalline nucleating agents have become a hotspot in the research and development of nucleating agents.
The clearing agent is a branch of the nucleating agent and about 90% of the clearing agent is used for the production of transparent polypropylene (C-PP). The transparent agent gives the original opaque PP with good transparency, so that the very low cost C-PP can not only replace the more expensive poly(ethylene terephthalate) (PET), polystyrene (PS), and poly in many aspects. Transparent plastic such as polycarbonate (PC), and can improve PP's mechanical properties such as rigidity, impact strength, heat distortion temperature.
3 Development Prospects of Plastic Additives
3.1 The use of additives in packaging materials is essential
Stabilizers (including antioxidants, heat stabilizers, and light stabilizers) are of great importance to the processing of plastics. The application of antioxidants involves almost all plastic products and is of great significance for improving the service life of plastics. 80% of the total amount of antioxidants are used in three major categories of polymers: polypropylene, polyethylene, and polystyrene. Among them, both PE and PP are plastic packaging materials that consume a great deal of energy. The two-way stretching and various functional films developed based on these two have shown a strong momentum in the development of packaging materials. The combination of polystyrene and carton for internal packaging has good impact resistance, easy molding, low density and light weight. It is also an excellent sheet for producing various plastic containers. Biaxially oriented polystyrene (BOPS) meets the hygienic requirements of food packaging, has good transparency, good ductility, is suitable for producing various containers, has good printability, and has a broad market prospect. Polyvinyl chloride is a heat-sensitive resin that can easily release hydrogen chloride by heat processing, and then cause thermal aging degradation reaction. PP, PE, PS and PC materials are also susceptible to thermal oxidation when they are heated, and they must be added with heat stabilizer during processing. Light stabilizers have been developed with the development of agricultural films. For agricultural PP and PE films, light stabilizers play an important role.
Plasticizers are plastics auxiliaries with the largest productivity and largest consumption in plastics processing. They are mainly used for soft PVC products and consume about 85% of the total. They are also used in vinyl acetates and other plastics. Base resins, polyvinylidene chlorides, polyvinyl alcohols, celluloses, polyamides, etc. are very versatile.
Foams prepared using foaming agents have important applications in packaging. Foam plastics used as packaging materials can be divided into shock-proof packaging (such as egg packaging bags, cushioning packaging liners, etc.) and general packaging. Its main varieties are polystyrene foam, polyurethane foam and polyethylene high foam materials. Foam plastics are not only important for buffer packaging, fresh packaging, and thermal insulation, but also reduce the quality of packaging materials and packaging.
3.2 functional film promotes the development and application of plastic additives
Antistatic agents are used most in polyethylene and polypropylene. In recent years, as people have continuously improved the quality and performance requirements of polypropylene products, the demand for antistatic agents is increasing. In the production of BOPP film called "Packaging Queen", antistatic agent is one of the largest additives. In addition, antistatic agents are also used in LDPE film, PE, PVC and other plastic packaging materials. Antistatic films are usually made by adding antistatic agents or coating processing technology. They are suitable for packaging electronic products with integrated circuits to prevent external electromagnetic radiation during transportation; or for packaging of powdered goods such as detergent powders to prevent static electricity from being caused by objects. Adsorption at the inlet of the packaging container is not conducive to sealing.
The development of high-barrier films has not only promoted the composite process of plastic films with aluminum foil or paper, but also promoted the development of plated SiOx materials and nano-SiO2. Coating a thin layer of silicon oxide on substrates such as PET, nylon (PA), and PP not only provides better barrier properties, but also has excellent atmospheric environment adaptability, and its barrier properties are almost independent of environmental humidity and temperature. Impact of change. SiOx coating has high barrier property, high microwave permeability and transparency, and can be used for soft packaging such as high-temperature cooking and microwave processing, and can also be used as a packaging container for beverages and edible oils [6].
Nano-plastics are inorganic nano-particles, such as silicate, calcium carbonate, SiO2, TiO2, etc., which are uniformly dispersed in the plastic matrix resin in the nanometer size, and have high strength, high heat resistance, high barrier property, and high flame retardancy. The advantages of good thermal stability and electrical conductivity are one of the most advanced products in the development of composite materials. Currently, nano-packaging materials developed abroad, such as nylon 6-nanometer composites, nano-polyolefins, and nano-polyesters, are mainly used in high barrier packaging for food and beer beverages. Nano-film can also be used for special packaging, such as anti-static, anti-electromagnetic, explosion-proof and invisible, dangerous goods packaging, etc. It will promote a tremendous transformation of traditional packaging materials [7].
Antibacterial film packaging of fresh fruits and vegetables has great practical significance. The application of antibacterial materials and antibacterial technology can prevent mold and other microorganisms from invading the fruits and vegetables and achieve better preservation effect. Antibacterial and anti-mold packaging can also be used for weapons, export clothing, optical equipment and other products. In addition, a film made from a master batch containing 1% of silver ions or a container coated with a layer of such a film on the surface can completely kill fungi that cause food poisoning within 1 to 2 days in the absence of a nutrient source. This antibacterial film is widely used for deli meat, aquatic products and liquid food packaging [7]. In addition, in recent years, anti-fogging agents have been added to the packaging films of frozen meats, cold cooked foods and fruit and vegetables to reduce the condensation of water vapor on the packaging in the environment and increase the transparency and visibility of packaging. The use of deoxidizers and UV-blocking agents reduces the damage of oxygen and ultraviolet rays to the packaging and prolongs the packaging and shelf life of foods and pharmaceuticals. The development of nucleating agents enhances the transparency and impact resistance of polypropylene packaging materials.
4 Conclusion
Plastic additives are companions in the petrochemical and synthetic resin industries. Rapidly growing plastic products market has boosted the rapid growth of China's plastics additives industry; but at present, China's plastics additives industry still has low product quality, high environmental pressure, and new products. Slow development, small-scale production, lack of sustainable development and other weaknesses; the current development of international plastics additives industry presents a trend of green, composite, high-efficiency, and specialization [8], so the domestic plastics additives industry should follow the international trend. , As soon as possible to integrate into the international market, at the same time with the advantages of domestic resources to strengthen the industry's internal research and development and mutual communication, in order to ensure the healthy and sustainable development of plastic additives industry in China. On the other hand, the use of plastics additives industry to promote the development of functional packaging materials in China's development and application of speed, so that China's packaging industry has risen to a new level.