Plastic additives are compounds which must be added during the molding process of polymers (synthetic resins) to improve their processing performance or to enhance the resin's own properties. For example, plasticizers are used to lower the molding temperature of polyvinyl chloride resin and make the product softer; Another example,in order to prepare foamed plastics with light weight, vibration resistance, heat insulation and sound insulation, foaming agent shall be added; Some plastics have a thermal decomposition temperature very close to the molding processing temperature, and cannot be molded without the addition of heat stabilizers. Therefore, plastic additives play a particularly important role in plastic molding and processing.
1. Plasticizer
Some plastics with high glass transition temperatures require the addition of a certain amount of plasticizer in order to produce soft products at room temperature and improve their melt flow properties during processing. These small molecular weight oily plasticizer have good compatibility with high polymers. They are distributed between polymer chains, reducing the intermolecular forces between them, making it easy for the molecular chains to move under certain temperature and pressure, thus achieving the purpose of processing and molding. Therefore, plasticizers have the effect of reducing the glass transition temperature and minimum molding temperature of plastics. The decrease in glass transition temperature is usually proportional to the volume fraction of plasticizer.
Plasticizer can be divided into two categories: primary plasticizer and secondary plasticizer. The characteristics of primary plasticizer are good compatibility with resins, high plasticizing efficiency, migration resistance, low volatility, low oil (water) extraction, and low-temperature flexibility. The solubility of the secondary plasticizer is poor, mainly used together with the main plasticizer to reduce costs, so it is also known as an additive.
2. Antioxidants and light stabilizers
We all know that plastic products undergo aging phenomena such as fading, brittleness, and cracking under the action of light, heat, and oxygen during processing, storage, and use. To delay and prevent the occurrence of aging, stabilizers must be added. Mainly used to prevent thermal aging, it is called a heat stabilizer; Mainly used to prevent oxidative aging, it is called antioxidant; Mainly used to prevent photo aging, they are called light stabilizers, collectively referred to as stabilizers. The best performing plastic stabilizer today is methyl tin heat stabilizer (abbreviated as 181), which is very effective for the rolling, extrusion, injection molding, and blow molding of rigid polyethylene (PVC). Due to its high safety, it is particularly used for food packaging and high-definition hard polyethylene products. At the same time, it is also widely used in plastic doors and windows, water pipes, and decorative materials to replace other highly toxic plastic heat stabilizers. It has been widely used in the United States, Europe, and Japan. In recent years, 181 methyltin heat stabilizers have been widely used in China.
3. Flame retardants
The additives that slow down the combustion performance of plastics are called flame retardants, which can be divided into four types according to different flame retardant mechanisms:
When combined with the decomposition products of plastics, a flame suffocating gas is produced, such as the reaction between antimony trioxide and hydrogen chloride released during the decomposition of PVC, which produces antimony trichloride with flame extinguishing effect.
Absorbing the heat generated during combustion to cool plastics and slow down the combustion rate, such as aluminum hydroxide, which is the most commonly used type of flame retardant: it acts as a filler, smoke suppressant, and flame retardant. At the same time, it is inexpensive and has little impact on polymer properties, so its growth rate in application is remarkable.
Provide a coating that is isolated from oxygen, such as phosphate esters. The main products include triphenyl phosphate, which is actually a plasticizer with flame retardant properties.
It can generate free radicals that prevent combustion reactions, which can react with plastics to produce products with poor combustion performance.
4. Heat stabilizer
The main function of a heat stabilizer is to prevent or alleviate the decomposition of polyvinyl chloride resin during high-temperature plasticization processing, as well as the chemical changes caused by light and oxygen in the environment during the use of the product after molding, thereby changing the performance of the product and shortening its service life. Heat stabilizers inhibit or prevent resin degradation, prolong product lifespan, and have a certain antioxidant effect by absorbing and neutralizing HCl, displacing unstable allyl chloride atoms in PVC molecules, undergoing addition reactions with polyene structures, capturing free radicals, etc., to prevent plastic products from degrading and discoloring. In addition, heat stabilizers can also absorb ultraviolet radiation or shield the resin from damage caused by ultraviolet radiation. When added to mixtures mainly composed of PVC resin, they should not undergo chemical reactions with other additives and should not affect the performance of the product. These mechanisms of action together ensure the important role of heat stabilizers in plastic processing, especially in the processing and application of PVC resin
5. Impact modifier
The main function of impact modifiers is to improve the low-temperature brittleness of polymer materials and endow them with higher toughness. These chemicals play an important role in the field of engineering technology and are widely used in various plastic products, such as PP plastics, PVC resins, etc. Specifically for PVC materials, impact modifiers can increase the hardness and impact resistance of PVC, thereby improving the toughness, strength, and wear resistance of the material, and enhancing the product's service life and performance stability. For example, Acrylic Impact Modifier (AIM) is a high-quality and environmentally friendly plastic modifier mainly used for PVC hard products, such as pipes and fittings, plastic steel doors and windows, panels, containers, etc. AIM disperses particles in the PVC continuous phase matrix, absorbs impact energy when subjected to external forces, prevents the further development of cracks, and thus improves the impact strength of the material. In addition, impact modifiers can also endow PVC products with good processability and weather resistance, making them particularly suitable for outdoor products
6. Foaming agent
Foaming agent is a kind of organic compound that will decompose and release gases when heated. These gases will remain in the plastic substrate and become foamed plastics with many fine foam structures.
As a good foaming agent, it should have the following conditions: release gas in a short period of time, adjustable release rate, inert gases such as CO ₂ and N ₂ released during decomposition, easy dispersion and decomposition in plastics, appropriate decomposition temperature, low heat generation during decomposition, irreversible decomposition reaction, non-toxic foaming agent, etc. The most widely used foaming agent is azodicarbonamide.
7. Coupling agent
Coupling agent refers to a type of substance that can improve the interfacial properties between fillers and polymer materials. There are usually two functional groups in the molecular structure of coupling agents: one can undergo chemical reactions with the polymer matrix or has good compatibility; Another type can form chemical bonds with inorganic fillers. Like; Silane coupling agent, with the general formula RSiX3 (R is an active functional group that has affinity and reactivity with polymer molecules, such as vinyl, chloropropyl, epoxy, methacryloyl, amino, and thiol groups; X is an alkoxy group that can hydrolyze, such as methoxy, ethoxy, etc.). After treatment with a coupling agent, the surface of the reinforcing agent or filler can be chemically modified, forming a bridge bond between the dispersed inorganic phase and the continuous polymer, becoming a composite material that enhances the effect of the reinforcing agent or filler. Organosilane is the most widely used coupling agent, while organic titanate is a more efficient coupling agent.
8. Crosslinking agent
Crosslinking agents are mainly used in polymer materials (rubber and thermosetting resins). Because the molecular structure of polymer materials is linear, without cross-linking, their strength is low, they are easy to break, and they have no elasticity. The role of cross-linking agents is to create chemical bonds between linear molecules, connecting them together to form a network structure, thereby improving the strength and elasticity of rubber. The cross-linking agent used in rubber is mainly sulfur, and accelerators need to be added. Generally, crosslinking agents refer to organic peroxides, such as diisopropylbenzene peroxide, which can be used as a crosslinking agent for polyethylene.
9. Reinforcing materials and fillers
In many plastics, reinforcing materials and fillers account for a considerable proportion, especially reinforcing plastics and calcium plastic materials. The main purpose is to improve the strength and rigidity of plastic products by adding various fiber materials or inorganic substances. The most commonly used reinforcement materials include glass fiber, asbestos, quartz, carbon black, silicates, calcium carbonate, metal oxides, etc.
10. Lubricants
During the hot processing of polymers, a small amount of lubricant is often added to facilitate demolding. Lubricants can be divided into two types: external lubricants and internal lubricants. The main function of external lubricants is to facilitate the smooth flow of polymer melt away from the hot metal surface of processing equipment. The compatibility between external lubricants and polymers is poor, and only a thin lubricant layer is formed at the interface between polymers and metals. Internal lubricants have good compatibility with polymers, which can reduce the cohesion between polymer molecules, thereby facilitating polymer flow and reducing temperature rise caused by internal friction heat. The most commonly used external lubricants are stearic acid and its metal salts, while internal lubricants are low molecular weight polyethylene, etc.
11. Release agent
Release agent is a functional substance that lies between the mold and the finished product. Release agents have chemical resistance and are not dissolved when in contact with the chemical components of different resins, especially styrene and amines. Release agents also have heat resistance and stress resistance, and are not easily decomposed or worn; The release agent adheres to the mold without transferring to the processed parts, and does not hinder painting or other secondary processing operations. Due to the rapid development of injection molding, extrusion, rolling, compression molding, lamination and other processes, the amount of release agent used has also significantly increased.
12.Coloring agent
Colorants are chemical substances that are insoluble in ordinary solvents, so to achieve ideal coloring performance, it is necessary to use mechanical methods to evenly disperse pigments in plastics. Inorganic pigments have excellent thermal and photostability, low price, but relatively poor coloring power and high relative density; Organic pigments have high coloring power, bright colors, complete chromatography, and low relative density. However, their disadvantages include lower heat resistance, weather resistance, and covering power compared to inorganic pigments. Colorants mainly include color masterbatch and fluorescent whitening agents.
13. Color master batch
Master batch is an aggregate made by uniformly attaching a super constant amount of pigment or dye onto a resin. Its basic components include pigments or dyes, carriers, dispersants, and additives; It has the following advantages: it is conducive to maintaining the chemical and color stability of pigments, improving the dispersibility of pigments, simple operation, easy color conversion, clean environment, saving time and raw materials.
14. Antistatic agent
Antistatic agents play a role in eliminating or reducing static electricity generated on the surface of plastic products. Most anti-static agents are electrolytes, which have limited compatibility with synthetic resins. This allows them to migrate to the surface of plastics, achieving the effects of moisture absorption and eliminating static electricity.
15. Antibacterial agents
With the continuous enhancement of people's safety awareness, more and more people are starting to purchase antibacterial plastic products. Antibacterial agents are used in antibacterial plastics. Antimicrobial agents refer to chemical substances that can maintain the growth or reproduction of certain microorganisms (bacteria, fungi, yeast, algae, viruses, etc.) below necessary levels for a certain period of time. Antimicrobial agents are substances with antibacterial and bactericidal properties.
16. Defoamer
Plastic defoamers, also known as plastic desiccants, plastic defoaming master batch, some plastic raw materials or recycled plastics often contain trace amounts of moisture. If not eliminated, bubbles or water marks will form on the surface of the processed products, which will affect the performance and appearance of the products. The traditional process of using electric drying machinery to eliminate moisture requires early drying of raw materials, which causes inconvenience in production, prolongs product processing time, leads to low production efficiency, consumes electricity, deteriorates processing environment, and increases production costs. Plastic defoamers are a new type of functional master batch developed specifically to solve the problem of water bubbles in plastic products made from PE, PP, ABS, PS, and nylon during processing. This master batch can be molded and processed by adding a small amount and simply mixing it before plastic molding, without going through a drying process. It has the advantages of easy use, improved production efficiency, and reduced energy consumption.
The plastic additive industry in our country has developed with the development of the PVC industry. The proportion of additives in plastic materials is relatively small, but it has a significant impact on the quality of plastic products. High performance green, environmentally friendly, non-toxic, and efficient plastic additives will become the main direction for the development of China's plastic additive industry in the future