Plastic additives, also known as plastic additives, are some compounds that must be added when the polymer (synthetic resin) is molded to improve its processing performance or to improve the performance of the resin itself. For example, in order to reduce the molding temperature of PVC resin and make the product soft, the plasticizer is added. Another example is to add a foaming agent in order to prepare a light,shock-resistant, thermally insulated, and sound-insulating foam plastic. The thermal decomposition temperature of some plastics is very close to the molding processing temperature, and it cannot be molded without the addition of heat stabilizers. Therefore, plastic additives occupy a particularly important position in plastic molding processing.
A large class of additives for plastic molding products, including plasticizers, heat stabilizers, antioxidants, light stabilizers, flame retardants, blowing agents, antistatic agents, antifungal agents, colorants and whitening agents (see pigments), fillers, coupling agents, lubricants, mold release agents, etc. Among them, colorants, brighteners and fillers are not plastic-specific chemicals, but generally used mating materials.
"How to choose an additive?"
Plastic formula design looks very simple on the surface, but in fact contains a lot of internal links, in order to design a high-performance, easy-to-process, low-price formula, there are many factors that need to be considered when choosing additives, according to the purpose to be achieved to choose the right kind of additives, the added additives should be able to give full play to their expected effects, and reach the specified indicators. The specific range of additives to choose from is as follows:
Toughening – selection of elastomers, thermoplastic elastomers and rigid toughening materials;
Reinforcement - selection of glass fiber, carbon fiber, whiskers and organic fibers;
Flame retardant - bromine (ordinary bromine and environmentally friendly bromine), phosphorus, nitrogen, nitrogen/phosphorus composite intumescent flame retardants, antimony trioxide, hydrate metal hydroxides;
Antistatic - all kinds of antistatic agents;
Conductive - carbon (carbon black, graphite, carbon fiber, carbon nanotubes), metal fibers and metal powders, metal oxides;
Magnetic - ferrite magnetic powder, rare earth magnetic powder including samarium cobalt (SmCo5 or Sm2Co17), neodymium NdFeB, samarium ferrous nitrogen (SmFeN), aluminum nickel;
Thermal conductivity – metal fibers and metal powders, metal oxides, nitrides and carbides; carbon materials such as carbon black, carbon fibers, graphite and carbon nanotubes; semiconductor materials such as silicon and boron;
Heat resistance - glass fibers, inorganic fillers, heat resistant agents such as substituted maleimides and β crystalline nucleating agents;
Transparent - nucleating agent, for PP α crystalline nucleating agent sorbitol series of the best effect;
Wear-resistant - graphite, molybdenum disulfide, copper powder and other cobalt magnetic powder three categories
Insulation - calcination of kaolin;
Barriers – mica, montmorillonite, quartz, etc.
"Additives match plastics
Red phosphorus flame retardant is effective against PA, PBT, PET;
Nitrogen flame retardants are effective against oxygen-containing substances, such as PA, PBT, PET, etc.;
Nucleating agent has a good effect on copolymer polypropylene;
The heat resistance modification of glass fiber has a good effect on crystalline plastics and a poor effect on amorphous plastics;
Carbon black filled conductive plastic, which works well in crystalline resins.
Additives of the same ingredient, with different forms, have a great impact on the exertion of the modified effect.
"The shape of the additive
The reinforcing effect of the fibrous additive is good (the degree of fibrosis of the additive can be expressed by the length-to-diameter ratio, the larger the L/D, the better the reinforcement effect, which is why we add glass fiber to be added from the exhaust hole);
The melting state is more conducive to maintaining the length-to-diameter ratio than the powdery state and reducing the probability of fiber breakage;
The toughening effect of the spherical additive is good and the brightness is high;
Barium sulfate is a typical spherical additive, so barium sulfate is used for high-gloss PP filling, with small rigid toughening.
"The particle size of the additive
(1) The influence of additive particle size on mechanical properties:
The smaller the particle size, the more beneficial it is to the tensile strength and impact strength of the filler material;
(2) The influence of additive particle size on flame retardant performance:
The smaller the particle size of the flame retardant, the better the flame retardant effect. For example, the smaller the particle size of hydrated metal oxides and antimony trioxide, the less the amount added to achieve the same flame retardant effect;
(3) The influence of additive particle size on color matching:
The smaller the particle size of the colorant, the higher the coloring force, the stronger the hiding force, and the more uniform the color;
(4) The influence of additive particle size on conductivity:
Taking carbon black as an example, the smaller the particle size, the easier it is to form a network conductive path, and the amount of carbon black added to the same conductive effect is reduced. However, like colorants, the particle size also has a limit value, the particle size is too small to be easy to gather and difficult to disperse, and the effect is not good.
"Surface treatment of additives
After the surface of all inorganic additives is treated, the modification effect is improved. Especially the filler is the most obvious, other glass fibers, inorganic flame retardants and so on.
The surface treatment is mainly based on coupling agents and compatibilizers, coupling agents such as silanes, titanates and aluminates, and the compatibilizer is the maleic anhydride grafting polymer corresponding to the resin.
plasticizer
A class of low volatile organic compounds that can be miscible with polymers to some extent, which can reduce the viscosity of polymer melts as well as the glassing temperature and elastic modulus of the product. Its mechanism of action is based on the weakening of the gravitational attraction between the molecular chains of the polymer by the plasticizer molecules.
Plasticizers were the earliest plastic additives used. In the second half of the 19th century, camphor and phthalates were used as plasticizers for nitrocellulose. After the industrialization of polyvinyl chloride in 1935, plasticizers were widely used. Currently, about 80% is used for POLYH and vinyl chloride copolymers, and the rest are used for cellulose derivatives, polyvinyl acetate, polyvinyl alcohol, natural and synthetic rubber.
Soft PVC adds an average of 45% to 50% (quality, the same below) plasticizer. Due to the rapid development of rigid POLYETHYLENE, which does not require or only add a small amount of plasticizer, the growth rate of plasticizers in many industrially developed countries has been lower than that of PVC. China's PVC soft products still account for a large proportion, so plasticizers will still have a rapid development.
Phthalates are the main body of plasticizers, and their output accounts for about 80% of the total output of plasticizers, of which dioctyl phthalate (DOP for short) is the most important variety.
Smaller plasticizers are: adipic acid and sebacic acid esters (with good cold resistance), phosphate esters (with flame retardant effect), epoxy oils and epoxy esters (with a synergistic effect with heat stabilizers), triphenyl tritilates and pentaerythritol esters (better heat resistance), chlorinated paraffins (auxiliary plasticizers and flame retardant plasticizers), alkyl sulfonate (auxiliary plasticizers).
Heat stabilizer
The main function is to prevent thermal degradation during processing, and also to prevent the aging of products during long-term use. The larger amount used is the heat stabilizer of polyvinyl chloride and vinyl chloride copolymers. The amount of heat stabilizer in soft products is about 2%, while in hard products it is 3% to 5%.
The main categories of heat stabilizers are salt-based lead salts, fatty acid soaps, organotin, organic auxiliary stabilizers and compound stabilizers.
(1) Salt-based lead salts (i.e., basic lead salts) such as tri-salt-based lead carbonate and dihydral-based lead phosphite are the earliest used and are still widely used. Its heat resistance, electrical insulation and weather resistance are good, the price is low, but it is toxic, opaque and poorly dispersed.
(2) Fatty acid soap, mainly cadmium, barium, calcium, zinc and magnesium salts of stearic acid and lauric acid. Cadmium soap is usually used in conjunction with barium soap, calcium soap and zinc soap to create a synergistic effect. Cadmium soap is highly toxic, barium soap also has a certain degree of toxicity, but calcium soap and zinc soap are not toxic.
(3) Organotin, which is the fastest growing category in recent times. With good transparency, many varieties of heat resistance and weather resistance are very prominent, is an indispensable heat stabilizer for hard transparent products. Dithiomer isooctyl acetate and di-n-octyltin are the most widely used non-toxic stabilizers.
(4) Phosphite esters and epoxy compounds, as auxiliary stabilizers are often used as components of composite stabilizers. Compound stabilizers are general-purpose cadmium-barium (zinc), barium-zinc, non-toxic calcium-zinc, and organotin complexes, mostly liquid.
Antioxidant
i.e. antioxidants. At room temperature and higher temperatures, most polymers undergo automatic oxidation reactions of varying speeds, which cause yellowing, degradation and decreased strength of plastics, and substances that can inhibit or delay this reaction can be called antioxidants.
In 1918, phenols began to be used to inhibit the oxidation of rubber. In the 1930s, the first varieties of modern antioxidants such as alkylphenols and p-phenylenediamines came out one after another. Although antioxidants are used in small amounts (0.1% to 1.0%) in plastics, they are important additives for large-tonnage plastics such as polyolefins, styrene resins, polyvinyl chloride, polyamides, and polyacetals. In the rubber industry, antioxidants are still customarily called antioxidants.
Antioxidants for plastics are mainly phenolic main antioxidants and auxiliary antioxidants such as thiodipropionate and phosphite.
The main antioxidant, also known as the chain terminator, its function is to capture the active free radicals produced in oxidative degradation, thereby interrupting the chain degradation reaction, its representative varieties are 2,6-di-tert-butyl-4-methylphenol (antioxidant 264) and tetra [3-(3',5'-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester (antioxidant 1010).
Auxiliary antioxidants, also known as peroxide decomposers, are used to decompose the intermediate products of oxidative degradation into non-free radical products.
Dilauryl thiopropionate and monophenyl diisooctyl phosphite are the most commonly used adjunctive antioxidants.
Primary and secondary antioxidants are often used in combination to exert synergistic effects.
Light stabilizer
Plastics and other polymers absorb ultraviolet light energy, which triggers an automatic oxidation reaction and leads to degradation. This process is called photo-oxidation or photoaging, and substances that can inhibit or delay this process are called light stabilizers.
In the 1940s, phenyl salicylate was first used as a light stabilizer in cellulose acetate. In the early 1950s and early 1960s, benzophenone and benzotriazole appeared, respectively, and in the mid-1970s, hindered amine light stabilizers appeared.
Light stabilizers are mainly used in polyolefins, especially polypropylene. Polyvinyl chloride, polycarbonate, polyester also use a small amount of light stabilizer, the amount of which is about 0.1% to 0.5%.
According to its mechanism of action, light stabilizers are divided into ultraviolet absorbers, quenching agents, and light shielding agents. Ultraviolet absorbers strongly absorb UV light at wavelengths of 290 to 400 nm, and 2-hydroxy-4-octoxybenzophenone (UV-531) and 2-(3′,5′-di-tert-butyl-2′-hydroxyphenyl)-5-chlorobenzotriazole (UV-327) are the two most effective varieties.
Quenching agents are mostly organic complexes of nickel. It quickly and efficiently quenches (returns to equilibrium) energizing excited molecules, thus avoiding photochemical reactions. Light shielding agents can weaken the transmission of ultraviolet rays, usually with carbon black.
The new hindered amine light stabilizers are mainly derivatives of tetramethyl or pentamethylpiperidinol, which have the comprehensive function of capturing free radicals, quenching singleline oxygen and decomposing peroxides, so they are very effective light stabilizers.
Flame retardants
Most plastics are flammable. With the wide application of plastics in construction, furniture, transportation, aviation, aerospace, electrical appliances, etc., improving the flame retardancy of plastics has become a very urgent issue. Flame retardants are a class of additives that inhibit the flammability of polymers, and they are mostly compounds of group V,7., vii,000 and III elements in the periodic table; in particular, compounds of phosphorus, bromine, chlorine, antimony and aluminum.
Flame retardants are divided into two categories: additive type and reactive type. Additive flame retardants are mainly phosphate esters and halophosphate-containing esters, halogenated hydrocarbons, antimony oxide, aluminum hydroxide and the like. The advantage is that it is easy to use and adaptable. However, due to the addition of 10% to 30%, it often affects the performance of plastics. Reactive flame retardants are actually monomers containing flame retardant elements, so they have less impact on the properties of plastics.
Common reactive flame retardants such as halogenic anhydride for polyesters, tetrabromobisphenol A for epoxy resins, and phosphorus-containing polyols for polyurethanes.
Flame retardants were originally used in the United States, and after the 1960s, the dosage increased dramatically, and the current dosage is second only to plasticizers. The plastics that consume the most flame retardants are polyvinyl chloride, polystyrene, polyurethane foam, unsaturated polyester, ABS resin and polypropylene.
Halogen flame retardants are flame retardants that do not contain halogens Both halogen-free and inorganic halogen-free inorganic flame retardants are aluminum hydroxide, magnesium hydroxide, red phosphorus, expandable graphite halogen flame retardants refer to halogen-containing polymers or combinations with halogen-containing flame retardants, mainly antimony trioxide and decabromodiphenyl ether, that is, bromine antimony grade flame retardants, bromine antimony flame retardants have excellent flame retardant properties, has been widely used as a retardant material.
However, in the event of a fire, such materials made of halogen-containing flame retardants are heated to produce large amounts of fumes and toxic corrosive hydrogen halide gas.
Blowing agent
It is divided into two categories: physical blowing agent and chemical blowing agent. Chemical blowing agents are further divided into inorganic blowing agents and organic blowing agents. They are named after the polymer due to the heat gasification or decomposition of the gas, so that the polymer material produces bubble holes.
Physical blowing agents are mainly chlorocarbons or HCFCs, such as trichlorofluoromethane, trichlorotrifluoroethane and the like. It is mainly used in the production of polyurethane foam.
The main varieties of chemical blowing agents are azo diformamide (blowing agent AC) and N, N′-dinitros pentamethylenetetramine (blowing agent H), the former is mostly used in plastics, the latter is often used in rubber.
Antistatic agent
The volume resistivity of the polymer is generally as high as 1010~1020Ω·cm, which is easy to accumulate static electricity and cause danger. Antistatic agent multi-line surfactants, can make the surface of the plastic affinity for moisture, ionic surfactants also have a conductive effect, so that static electricity can be leaked in time.
According to the method of use, the antistatic agent is divided into an external antistatic agent and an internal antistatic agent. An external antistatic agent is a dilute solution of 0.5% to 2.0% to coat the surface of the plastic. The internal antistatic agent is additive, and the dosage varies from 0.1% to 3.0%. Cationic surfactants, such as ammonium salts, quaternary ammonium salts and alkyl imidazoline, are commonly used antistatic agents in plastics.