The most complete knowledge of plastic additives in history

Plastic additives can be explained in both broad and narrow sense. The generalized plastic auxiliaries refer to all the additives added to the resin matrix during the processing of plastic products, which can be used to reduce the cost of the product, improve or impart a certain performance to the product, or improve the processability of the plastic product. Plastic additives. Including organic, inorganic, small molecules and macromolecules. Narrowly defined plastic additives, also known as plastic additives, are specific chemical materials that can improve the processing properties of plastics or improve or impart a certain property to a product. Such as lubricants, antioxidants and flame retardants. Here we mainly introduce plastic additives in a broad sense.

Second, the classification of commonly used plastic additives

At present, commonly used plastic additives are roughly divided into the above three categories. In the narrow sense, the auxiliaries actually refer to the processing aids and functional auxiliaries in the above, and do not include fillers. Next, Jiuzhi Plastics Network Xiaobian will give you a detailed introduction to each type of additives.

1, plastic filler

Fillers can be divided into three categories depending on the application at the time of addition:

(1) Cost reduction: It can be divided into organic fillers and inorganic fillers. Commonly used inorganic fillers are CaCO3, talc, wollastonite, BaSO4, kaolin, Yuanming powder, glass beads, and the like. Commonly used organic fillers are mainly wood powder, bamboo powder, fruit shell powder, shell powder and powder of cotton, hemp and rice agricultural by-products. This type of filler is one of the most widely used and most expensive plastic additives. In addition to reducing costs, it can also improve certain properties of the product. For example, inorganic filling generally improves the rigidity, heat resistance (inorganic filler), dimensional stability, reduction of mold shrinkage and creep resistance of plastic products. Organic filling can reinforce, reduce molding shrinkage, and improve dimensional stability, but the heat resistance is poor.

(2) Reinforced fillers: There are two types of reinforcing fillers most commonly used: fibers and whiskers. Mainly include: inorganic (such as glass fiber, carbon fiber, graphite fiber, whisker, quartz fiber and ceramic fiber); organic (such as PA fiber, aramid fiber, polyester fiber, ultra high molecular weight polyethylene fiber, etc.). These fillers are the most important reinforcement of plastics and can account for more than 90% of the total reinforcement. At present, the most commonly used plastic reinforcement modification is glass fiber and carbon fiber, especially in the light weight of automobiles, and there are many research applications. Whisker is mostly used for reinforcement, and CaCO3 whiskers and CaSO4 whiskers are common.

(3) Toughening filler: The toughness of plastic is usually expressed by the magnitude of its impact strength. The impact strength refers to the work consumed per unit area when the sample is broken by impact damage. It is used to evaluate the ability of a material to resist external shocks or to determine the brittleness or toughness of a material. The higher the impact strength, the better the toughness; on the contrary, the greater the brittleness. Toughened fillers are mainly composed of rubber and thermoplastic elastomers. High impact rubbers are mainly: ethylene propylene rubber (EPR), EPDM, EPBR, styrene butadiene rubber, natural rubber, butadiene rubber, neoprene, polyisobutylene and dibutyl Ethylene and the like. The thermoplastic elastomers are: ethylene-octene copolymer (POE), SBS, SEBS, and the like. Such fillers, while toughening, reduce the strength and rigidity of the article. Therefore, the more popular method is to add the rigid inorganic nano-powder together to the resin matrix for blending and toughening modification.

2, processing additives

Plastic processing additives can be divided into three categories:

(1) Lubricant: The role of lubricant is to reduce the friction between materials and the surface of materials and processing equipment, thereby reducing the flow resistance of the melt, reducing the viscosity of the melt, improving the fluidity of the melt, and avoiding melt and equipment. Adhesion, improve the surface finish of the product, and the like.

Lubricants can be classified into internal lubricants and external lubricants by action. The essence is what we usually call plasticizers and mold release agents. It is only called different in different resins. For example, plasticizers are usually used in the processing of PVC resin, and the essence is also the effect of internal lubrication. The distinction between internal and external lubricants is mainly based on their compatibility with the resin. The internal lubricant has a large affinity with the resin, and its function is to reduce the force between the macromolecules; the external lubricant has a small affinity with the resin, and the effect is to reduce the friction between the resin and the processing machine.

(2) Heat stabilizer: During the processing of plastics, plastics may generate heat due to heating, friction or shearing, or performance deterioration due to heat of plastic products during use. In order to prevent the plastic from degrading and aging due to heat, it is necessary to add a substance which does not cause decomposition and change when the plastic is heated. This substance is called a heat stabilizer. Mainly used for the processing of PVC resin.

Pure PVC resin is extremely sensitive to heat. When the heating temperature reaches above 90 °C, slight thermal decomposition occurs. When the temperature reaches 120 °C, obvious thermal decomposition occurs, and the color of the PVC resin gradually deepens. The thermal degradation mechanism of PVC is very complicated, but the essence of the thermal decomposition reaction of PVC is a series of reactions caused by the dehydrochlorination reaction, which eventually leads to macromolecular cleavage.

(3) Foaming agent: The so-called foaming agent is a substance that makes a target substance pore. It can be divided into three major categories: chemical foaming agent, physical foaming agent and surfactant. The chemical foaming agent is a compound which can decompose two gases such as CO2 and N2 and form fine pores in the polymer composition after being decomposed by heating; the physical foaming agent is a physical form of the foam through a certain substance. The change is formed by the expansion of the compressed gas, the volatilization of the liquid or the dissolution of the solid; the foaming agent has a high surface activity, can effectively reduce the surface tension of the liquid, and is surrounded by the double electron layer on the surface of the liquid film. Air, which forms bubbles, and then consists of a single bubble.

3, functional additives

(1) Anti-aging additives: refers to the inhibition, degradation or loss of macromolecular chains in the process of storage, transportation and use of plastic products due to external factors (light, heat, oxygen, etc., non-mechanical factors). The process of mechanical properties. It has substances which inhibit the breakage of polymer molecular chains and prolong the performance of plastic products, and is collectively referred to as an antioxidant. Including: light / heat stabilizers, antioxidants, anti-UV stabilizers and anti-hydrolysis agents.

1 light stabilizer / antioxidant: plastics usually aging under the action of light, oxygen and heat, resulting in: strength, stiffness and toughness decreased; discoloration; scratches, surface gloss decreased. Affect the performance of plastic products. It is necessary to add a light stabilizer and an antioxidant to inhibit the breakage of the molecular chain and prolong the use property of the product.

2 anti-hydrolysis agent: in a humid, warm environment, water molecules will destroy the polymer's macromolecular chain, causing some polymers to degrade or even lose any performance phenomenon called "hydrolysis." Polyhydrocarbons are relatively stable to moisture, and water content is also small when immersed in an aqueous solution to reach equilibrium. However, a polymer produced by a polycondensation reaction such as nylon (PA), polycarbonate (PC), polyurethane (PU), polyester (PET, PBT), etc., contains a large amount of an amide group, an ester group, a urea group, a biuret group. a highly polar group such as a urethane group. Under the condition of low water content and room temperature, the inhaled moisture forms hydrogen bonds with the polar groups, which weakens the hydrogen bond between the self molecules in the polymer, thus degrading the physical and mechanical properties of the polymer. This effect is reversible and performance can be restored when moisture is removed. However, at higher temperatures and higher relative humidity, water reacts with polar groups of the polymer molecular chain to cause degradation.

In order to effectively prevent the hydrolysis of certain polymers, it is common to add a hydrolysis stabilizer, also known as an anti-hydrolysis agent, to the material. The addition of the hydrolysis stabilizer can effectively capture the carboxyl groups produced by the hydrolysis of the polymer to form a stable and harmless product (such as a ureide derivative), thereby preventing further hydrolysis of the polymer. There are many varieties of hydrolysis stabilizers, generally including mono (poly)carbodiimide, oxazoline compounds, epoxy compounds and other substances which can terminate hydrolysis.

(2) Hygiene and safety additives: The biggest defect of plastic products is flammability, and melt drops will occur during the combustion process, causing secondary fires. In addition, the plastic article has poor conductivity, and a layer of electric charge is accumulated on the surface to generate electrostatic attraction, so that a large amount of dust and bacteria are adsorbed on the surface of the product. Therefore, plastic products generally require the addition of flame retardants, antistatic agents and antibacterial agents. To ensure the hygiene and safety of plastic products during use.

1 Flame Retardant: Flame retardant is a kind of auxiliaries that can prevent plastic from igniting or inhibiting flame propagation. Efficient and safe flame retardant can generally play the role of flame retardant, smoke suppression, heat dissipation and drip prevention. According to its method of use, it can be divided into two types: additive type and reactive type.

Commonly used flame retardants are classified into four categories: halogen flame retardants, phosphorus flame retardants, inorganic flame retardants, and intumescent flame retardants.

2 Antibacterial agent: An antibacterial agent refers to a chemical substance that can keep the growth or reproduction of certain microorganisms (bacteria, fungi, yeasts, algae, viruses, etc.) below a necessary level within a certain period of time. The antibacterial effect of antibacterial agents is generally divided into bactericidal and bacteriostatic effects. The concentration and duration of the antibacterial agent have a great influence on the antibacterial effect. Metal ions such as silver, copper and mercury, strong oxidants mainly play a bactericidal role, and organic antibacterial agents mainly exhibit bacteriostatic action. The same antibacterial agent, low concentration often shows inhibition, and high concentration is sterilization.

3 Antistatic agent: Any object itself has an electrostatic charge. This charge can be either a negative charge or a positive charge. The accumulation of static charge can affect or even harm the life or industrial production, and guide or eliminate the accumulated harmful charge. Chemicals that make them inconvenient or hazardous to production/life are called antistatic agents. Antistatic agents generally have the characteristics of a surfactant, both structurally polar and non-polar. Commonly used polar groups (ie hydrophilic groups) are: anions of carboxylic acids, sulfonic acids, sulfuric acids, phosphoric acid, amine salts, cations of quaternary ammonium salts, and groups such as -OH, -O-, commonly used non-polar The group (i.e., lipophilic group or hydrophobic group) is an alkyl group, an alkylaryl group or the like. Thus, five basic types of ASA commonly used in the fiber industry, namely, derivatives of amines, quaternary ammonium salts, sulfates, phosphates, and derivatives of polyethylene glycol are formed.

4, appearance performance

A variety of plastic products have brought different colors to our lives, all thanks to plastic colorants. Colorants cause plastics to change the inherent absorption and reflection properties of light waves. It can be organic or inorganic and can be natural or synthetic. Pigments are colorants that are insoluble in common solvents, so to achieve the desired coloring properties, it is necessary to mechanically disperse the pigments uniformly in the plastic. Inorganic pigments have excellent thermal stability and light stability, low price, but relatively poor coloring power and high relative density; organic pigments have high tinting strength, bright color, complete chromatogram, and low relative density. The disadvantages are heat resistance, weather resistance and hiding. The force is not as good as inorganic pigments.

5, other performance additives

In addition to these additives, there are many additives for plastics during processing, such as compatibilizers, coupling agents, nucleating agents and anti-fogging agents. These additives have an important role in the performance of plastic products.

1 Compatibilizer: Compatibilizer, also known as compatibilizer, refers to the incorporation of incompatible two polymers by means of the intermolecular bonding force, thereby obtaining a stable blend of additives. It is used more in plastic alloys and wood plastic products.

Taking ABS as an example, directly blending the two materials to get "ABS" is definitely not what you want because its performance is a mess. Why is there such a difference? This involves the key technology of polymer alloys - compatibilization technology. As far as ABS is concerned, you may know that his production method is to first polymerize the obtained PB rubber powder, and then use it as a seed, add acrylonitrile and styrene monomer, and graft it on PB rubber powder. Thus, the surface of the PB rubber powder is actually a polymer of PB-g-AS. This polymer combines two otherwise incompatible polymers to improve the performance of the original system. Compatibilizers are generally graft polymers.

2 Coupling agent: It is a kind of substance with amphiphilic structure. Some of the groups in the molecule can react with chemical groups on the inorganic surface to form chemical bonds; the other part has the property of organic matter, and can be combined with organic molecules. A chemical reaction occurs or a strong intermolecular action is produced, thereby firmly bonding two materials of distinct properties.

Generally used to improve the dispersion state of the inorganic filler in the polymer matrix, improve the mechanical properties and performance of the filled polymer material. Commonly used are silane coupling agents, titanate coupling agents, aluminate coupling agents, and composite coupling agents. The current hyperdispersant is actually this concept.

3 Nucleating agent: The nucleating agent is suitable for incompletely crystallized plastics such as polyethylene and polypropylene. By changing the crystallization behavior of the resin, accelerating the crystallization rate, increasing the crystal density and promoting the grain size, the molding cycle is shortened and the product is improved. Functional additives for physical and mechanical properties such as transparency, surface gloss, tensile strength, rigidity, heat distortion temperature, impact resistance, and creep resistance.

4 Anti-fogging agent: transparent plastic film, sheet or plate. When the humidity reaches below the dew point in the humid environment, a layer of fine water droplets will be condensed on the surface to make the surface foggy and fog, which hinders the transmission of light waves. For example, when a product is packaged by a film, the contents may not be visible due to fogging, and the generated mist may easily cause rot damage of the contents. Therefore, in order to improve the service life of the product, it is necessary to add a certain amount of antifogging agent. Anti-fogging agents are some surfactants with hydrophilic groups, which can be oriented on the surface of plastics. The hydrophobic groups are inward and the hydrophilic groups are outwards, so that water can easily wet the plastic surface, and the condensed fine water droplets can rapidly diffuse to form extremely thin. The water layer or large water droplets flow down the film. In this way, the atomization caused by the light scattering of the small water droplets can be avoided, and the condensed water droplets can be prevented from falling onto the packaged object, thereby damaging the packaged object.