Plastic additives, also known as plastic additives, are compounds added during the molding process of polymers (synthetic resins) to improve their processing performance or to improve the performance of the resin itself. The main function is to improve the process performance of polymers, optimize processing conditions, improve processing efficiency, and improve the performance of products, thereby increasing the use value and lifespan of products. For example, plasticizers are added to reduce the molding temperature of polyvinyl chloride resin and make the product soft; Another example is the foaming agent added to prepare foamed plastics with light weight, shock resistance, heat insulation and sound insulation; The thermal decomposition temperature of some plastics is very close to the molding and processing temperature, and they cannot be formed without the addition of heat stabilizers. Therefore, plastic additives play a particularly important role in plastic molding and processing. The additives used for plastic molding processing include heat stabilizers, plasticizers, antioxidants, light stabilizers, flame retardants, foaming agents, antistatic agents, colorants and brighteners, fillers, coupling agents, lubricants, release agents, etc.

1 Stabilizer

1) Heat stabilizer

Heat stabilizers are mainly used for polyvinyl chloride and its copolymers. During the hot processing of polyvinyl chloride, a small amount of molecular chain breaks before reaching melting flow, releasing hydrogen chloride. Hydrogen chloride is a catalyst that accelerates the chain reaction of molecular chain breaks. Therefore, if the newly decomposed hydrogen chloride is not removed in a timely manner, the polymer chain will continue to crack into low molecular compounds, resulting in plastics such as polyvinyl chloride being unable to be processed and formed. Adding appropriate alkaline substances to polyvinyl chloride can immediately neutralize the decomposed hydrogen chloride, achieving the goal of stabilizing polyvinyl chloride.

The commonly used heat stabilizers are divided into main stabilizers and auxiliary stabilizers:

Main stabilizer: mainly salts and soaps containing heavy metal cations such as lead, calcium, cadmium, zinc, barium, aluminum, lithium, strontium, etc

Among them, lead sulfate and lead stearate are the most widely used.

Auxiliary stability: mainly refers to epoxidized oils and esters, and they also have certain plasticizer functions

2) Antioxidants

Antioxidants are a type of chemical substance that, when present in small amounts in polymer systems, can delay or inhibit the oxidation process of polymers, thereby improving their service life. Commonly used plastic antioxidants are generally divided into five categories based on their molecular structure and mechanism of action: hindered phenols, phosphite esters, thio compounds, composite compounds, and hindered amines (HALS).

3) UV absorber

High polymers undergo photodegradation when exposed to ultraviolet radiation. UV absorbers are a type of chemical substance that can absorb or reduce the transmission of ultraviolet rays. They can convert high-energy ultraviolet light into thermal energy or non-destructive longer light waves to release energy, thereby protecting polymers from UV damage.

UV absorbents can be classified into the following categories based on their chemical structure: salicylates, phenylketones, benzotriazoles, substituted acrylonitrile, triazines, and hindered amines.

4) Light shielding agent

Light shielding agents are a type of substance that can absorb harmful light waves from polymers, then convert light energy into thermal energy to scatter or reflect light waves, thereby providing a shielding effect on polymers. Light shielding agents mainly include black or white substances such as carbon black, zinc oxide, titanium dioxide, and lithopone that can absorb or reflect light waves.

2 Processing aids

Processing aids refer to additives used to improve the rheological and molding properties of plastic processing, usually with low viscosity or surface energy, and have a certain lubricating effect; Mainly including plasticizers and lubricants.

1) Plasticizer

Plasticizers, due to their ability to weaken the van der Waals force between polymer molecules, increase the mobility of polymer molecular chains, reduce their crystallinity, and increase the softness, elongation, and plasticity of plastics. They also reduce the flow temperature and hardness of plastics, which is beneficial for the molding of plastic products. Commonly used plasticizers include phthalates, sebacates, chlorinated paraffin, etc.

Plasticizers can be divided into two categories: main plasticizers and secondary plasticizers:

The characteristics of the main plasticizer are good compatibility with the resin, high plasticization efficiency, migration resistance, low volatility, low oil (water) extraction, and low-temperature flexibility; The compatibility between the secondary plasticizer and the resin is poor, mainly used together with the main plasticizer to reduce costs.

2) Lubricants

Lubricants are additives that can improve the friction and adhesion between plastic particles and between the melt and the metal surface of processing equipment, increase the fluidity of the resin, achieve adjustable resin plasticization time, and maintain continuous production.

Lubricants can be divided into external lubricants and internal lubricants.

The main function of external lubricants is to enable the polymer melt to smoothly leave the hot metal surface of the processing equipment. The solubility of external lubricants with polymers is poor, only forming a thin lubricant layer at the interface between polymers and metals. The most commonly used external lubricants are stearic acid and its metal salts.

Internal lubricants have good solubility with polymers, which can reduce the cohesion between polymer molecules, thereby facilitating the flow of polymers and reducing the temperature rise caused by internal friction heat. The most commonly used internal lubricants are low molecular weight polyethylene, etc.

3) Release agent

Release agent is a functional substance that lies between the mold and the finished product. Release agents have chemical resistance and do not dissolve when in contact with the chemical components of different resins, especially styrene and amines. The release agent also has heat resistance and stress resistance, which is not easy to decompose or wear; The release agent is bonded to the mold without being transferred to the processed parts, without hindering painting or other secondary processing operations. Due to the rapid development of processes such as injection molding, extrusion, rolling, molding, and lamination, the amount of release agent has also significantly increased.

3 Reinforcement materials and fillers

In many plastics, reinforcing materials and fillers account for a considerable proportion, with the main purpose of increasing the strength and rigidity of plastic products or reducing production costs by generally adding various fiber materials or inorganic substances. The most commonly used reinforcement materials include glass fiber, asbestos, quartz, carbon black, silicate, calcium carbonate, metal oxides, etc.

4 Coupling agent

Coupling agents refer to a type of substance that can improve the interfacial properties between fillers and polymer materials. Usually, there are 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. For example; Silane coupling agent, the general formula can be written as RSiX3 (R is an active functional group with affinity and reaction ability with polymer molecules, such as vinyl, chloropropyl, epoxy, methacryl, amino, and thiol; X is an alkoxy group that can be hydrolyzed, such as methoxy, ethoxy, etc.). After being treated 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. Organic silane is the most widely used coupling agent, while organic titanate is a more efficient coupling agent.

5 cross-linking 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, they have low strength, are easy to break, and lack elasticity. The function 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 an accelerator needs to be added. The general crosslinking agent mostly refers to organic peroxides, such as the crosslinking agent for polyethylene, which can use diisopropylbenzene peroxide.

6 foaming agents

Foaming agent is a type of substance that can form a microporous structure of rubber or plastic in a liquid or plastic state within a certain viscosity range. Foaming agents can be divided into physical foaming agents and chemical foaming agents according to their mechanism of action. Physical foaming agent: A type of compound that achieves foaming goals by relying on changes in its physical state during the foaming process; Chemical foaming agent: At a certain temperature, it will undergo thermal decomposition to produce one or more gases that cause polymer foaming.

7 nucleating agents

Nucleating agent is a new functional additive suitable for incomplete crystalline plastics such as polyethylene and polypropylene. By changing the crystallization behavior of the resin, it accelerates the crystallization rate, increases the crystallization density, and promotes the refinement of grain size, thereby shortening the molding cycle, improving the transparency, surface gloss, tensile strength, rigidity, thermal deformation temperature, impact resistance, creep resistance, and other physical and mechanical properties of the product.

8 Stabilizers

Colorants cannot be dissolved in ordinary solvent chemicals, so in order to achieve ideal coloring performance, it is necessary to use mechanical methods to evenly disperse pigments in plastic. Inorganic pigments have excellent thermal and photo stability, low price, but relatively poor coloring power and high relative density; Organic pigments have high coloring power, bright color, complete chromatography, and low relative density, but their disadvantages include inferior properties such as heat resistance, weather resistance, and covering power compared to inorganic pigments. Colorants mainly include color masterbatches and fluorescent brighteners.

1) Color masterbatch

Color masterbatch is an aggregate made by uniformly attaching super constant pigments or dyes to 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.

2) Fluorescent whitening agent

Fluorescent whitening agent is a fluorescent dye, also known as a white dye, and a complex organic compound. Its characteristic is that it can stimulate incident light to produce fluorescence, causing the dyed substance to achieve a sparkling effect similar to fluorite, making the substance visible to the naked eye very white. According to the parent classification of fluorescent whitening agents, they can be roughly divided into nine categories: carbocyclic, triazine aminostilbene, stilbene triazole, benzoxazole, furan, benzofuran and benzimidazole, 1,3-diphenylpyrazoline, coumarin, naphthalimide, and miscellaneous.

9 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 commonly used in antibacterial plastics. Antibacterial agents refer to chemical substances that can maintain the growth or reproduction of certain microorganisms (bacteria, fungi, yeast, algae, viruses, etc.) below the necessary level within a certain period of time. Antibacterial agents are substances with antibacterial and bactericidal properties.

10 Flame retardants

The additives that slow down the combustion performance of plastics are called flame retardants. Most plastics containing flame retardants have self-extinguishing properties or have a slow burning rate effect.

11 Antistatic agents

Any object carries its own static charge, which can be either negative or positive.