Nine common plastic additives

Plastics need to be added with different kinds of additives during processing to meet different processing and application requirements. Additives refer to chemical substances that are dispersed in the molecular structure of plastics and will not seriously affect the molecular structure of plastics, but can improve its properties or reduce costs. The addition of additives can promote the plastic to improve the processability, physical properties, chemical properties and other functions of the substrate and increase the physical and chemical properties of the substrate. Today, we briefly introduce the classification and characteristics of these additives.

Additives are known by many different names depending on the difference in their ability to improve plastics. Specifically, from the perspective of increasing the processing characteristics of the substrate, the additives include:

① Mobility: lubricant;

② Thermal stability: thermal stabilizer, antioxidant;

③Dispersibility: processing aids, dispersants;

④ Compatibility: compatibilizer, coupling agent;

⑤ Melt strength: cross-linking agent, tackifier.

From the analysis of increasing the physical and chemical properties of the substrate, the additives include:

①Rigidity, strength: filler, nucleating agent;

②Impact: impact modifier;

③ Heat resistance: filler, nucleating agent;

④Flammability: flame retardant;

⑤ Weather resistance: stabilizer, UV stabilizer;

⑥Conductivity: antistatic agent, conductive filler;

⑦Color: pigment;

⑧ hardness: plasticizer;

⑨ Density: foaming agent;

⑩ Transparency: nucleating agent;

⑪ Hygiene: Antibacterial agent.

Additives are mainly classified into the following categories:

1. Antioxidant

Unsaturated double bonds in plastics are attacked by oxygen atoms, heat and light, causing them to break and generate free radicals, thereby causing chain reactions, breaking molecular chains or forming chain cross-links, resulting in reduced strength or brittle plastic products. The function of antioxidants is to delay the decomposition of plastics due to oxidation and prolong the life of plastic products.

Antioxidants used in the plastics industry can be classified according to their function as:

(1) Oxidative chain reaction inhibitors: such as Alkyl phenol, Butylated hydroxytoluene (BHT), Aromaticamines, Phenyl-B-Naphtylamine, Alkyl quinone, Alkylene bisphenol, Alkyl phenolthioether, Phenyl salicylate, etc.

(2) Peroxide decomposers: such as alcohol thioether series, Thio propionate ester, Organic phosphites, dithiosulfonate series, etc.

(3) Heavy metal inactivator: such as amidate, hydrazine, aromatic amine compounds, etc.

2. Antistatic agent

The main function of the antistatic agent is to impart electrical conductivity to the plastic so that it avoids the accumulation of static electricity caused by friction. Commonly used antistatic agents are quaternary ammonium salt, ethoxylated amines, fatty acid esters and sulfonated wax.

3. Blowingagent

There are three main types of foaming agents for plastics:

①Nitrogen, carbon dioxide, and air are directly pressed into the plastic melt to foam;

② Volatile liquids such as butane, pentane, petroleum ether, difluorodichloromethane, etc., will volatilize and expand after heating up, and the plastic body will foam. Common polystyrene foam belongs to this type;

③ Decomposable chemical foaming agents, such foaming agents are generally solid powders, which decompose and release gas (usually nitrogen or carbon dioxide) when heated, which makes plastics have cell-like structures and reduce weight.

Most of these foaming agents are organic azo compounds, such as azobiscarbonamide and azobisisobutyro-nitrile (AIBN for short). The foamed plastics mainly include: ABS, PS, PVC, PU, EVA, PE, PP, etc.

4. Flameretardant

When the flame retardant-added plastic is exposed to the flame, it can suppress the spread of the flame by itself, preventing the formation of smoke, and the combustion will stop when the flame is removed.

The principles of flame retardants used in plastics can be roughly divided into three types:

(1) Reactive type flame retardants can react with oxygen to form an inert gas, which surrounds the combustion material and reduces the oxygen content of the combustion material to achieve the purpose of terminating combustion. This method is used for all products that can produce CO, CO2, NH3 and halogen compounds during combustion, such as PVC, PU foam, polyester or epoxy resin.

(2) Non-Reactive type flame retardants are compounds containing halogen, phosphorus, nitrogen or boron. When combustion occurs, an inert substance can be decomposed and covered on the surface of the plastic combustion material to form a flame retardant. A layer of obstacles to isolate the oxygen from the outside world and achieve the purpose of fire resistance.

(3) When the flame retardant containing water oxides such as alumina is burned, it can release water vapor, absorb the heat of the combustion process, reduce the temperature around the combustion object, inhibit the spread of the flame, and prevent the formation of smoke.

5. Lubricant

Lubricants can be divided into internal lubricants and external lubricants. The main function of internal lubricants is to improve the internal fluidity of the resin and reduce the internal friction between the resin molecular chains, such as fatty acid lipids (monoglycerol stearate); External lubricants reduce resin adhesion to processing machinery and improve product surface smoothness and ease of mold release, such as HoechstWax.

6. Impactmodifier

Impact modifiers are usually added with special resins by compounding to improve the impact resistance of plastics. Impact modifiers often affect the heat resistance, fluidity or processability of plastics and must be selected carefully.

7. Plasticizer

Most synthetic resins have plasticity, but the size of plasticity is different. In order to make the resin easy to plasticize and give the product softness, some low-molecular substances are generally added to the resin. These low-molecular substances are called plasticizers. Plasticizers are liquid or low-melting substances, and should have good miscibility with resins. Commonly used plasticizers are phthalates, aliphatic dibasic acid esters, phosphate esters, chlorinated paraffins, etc.

8. Coloring agent

It is a colorant-containing additive added to the material to beautify and decorate the plastic called colorant.

9. Filling material

It is added to the batch of plastics to reduce costs, and sometimes can also improve the physical properties of plastics, such as hardness, stiffness and impact strength. Relatively inert substances are called fillers. The most commonly used fillers are clay, silicate, talc, carbonate, etc.