Precautions for selecting additives for plastic modification

Plastic modification formula is very important when choosing plastic additives. How to obtain a formula with higher performance, low cost and easy processing will introduce the selection of additives from the following six aspects.

01. Select additives according to purpose

Improve processing performance: lubricant, release agent, stabilizer, processing aid, thixotropic agent, plasticizer, PVC stabilizer.

Improve mechanical properties: plasticizers, reinforcing fillers, toughening agents, impact modifiers.

Improve optical properties: pigments, dyes, nucleating agents, optical brighteners.

Improve aging performance: Antioxidant, PVC stabilizer, UV absorber, fungicide, antifungal agent.

Improve surface properties: antistatic agent, slip agent, wear-resistant agent, anti-blocking agent, anti-fogging agent.

Cost reduction: diluents, fillers.

Improve other properties: foaming agent, combustion aid, chemical crosslinking agent, coupling agent, etc.

02. The additive is selective to the resin

Red phosphorus flame retardants are effective for PA, PBT, PET; nitrogen-based flame retardants are effective for oxygen-containing species, such as PA, PBT, PET, etc.;

The heat-resistant modification of glass fiber has a good effect on crystalline plastics and poor effect on amorphous plastics;

Carbon black filled conductive plastic works well in crystalline resins;

The nucleating agent is effective for copolymerized polypropylene.

03. Compatibility of additives and resin

The compatibility between the additive and the resin should be good, so as to ensure that the additive and the resin are dispersed according to the expected structure, to ensure the completion of the design index, to ensure that the effect will be exerted for a long time within the service life, and it is resistant to extraction, migration, and precipitation.

Except for a few additives such as surfactants, good compatibility with the resin is the key to exert its efficacy and increase the amount of addition. Therefore, it is necessary to try to improve or improve its compatibility, such as using a compatibilizer or a coupling agent for surface activation treatment.

04. Shape selection of additives

The reinforcing effect of fibrous additives is good. The degree of fiberization of additives can be expressed by aspect ratio, the larger the aspect ratio, the better the reinforcement effect, which is why we add glass fiber through the vent hole.

The molten state is better than the powder state to maintain the aspect ratio and reduce the probability of fiber breakage.

The spherical additive has good toughening effect and high brightness. Barium sulfate is a typical spherical additive, so barium sulfate is used for filling high-gloss PP, and barium sulfate can also be used for small rigidity and toughening.

05. Particle size selection of additives

Effect 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.

The effect 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 oxide and antimony trioxide, the less the amount of addition to achieve the same flame retardant effect.

The effect of additive particle size on color matching: the smaller the particle size of the colorant, the higher the tinting strength, the stronger the hiding power, and the more uniform the color. However, the particle size of the colorant is not as small as possible, there is a limit value, and the limit value is different for different properties. In terms of tinting strength, the limit particle size of azo colorants is 0.1 μm, and the limit particle size of phthalocyanine colorants is 0.05 μm. For hiding power, the limit particle size of the colorant is about 0.05 μm.

Effect of particle size of additives on electrical conductivity: Take 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 achieve the same conductive effect is reduced. But like the colorant, the particle size also has a limit value, if the particle size is too small, it is easy to aggregate and difficult to disperse, and the effect is not good.

06. The amount of additives added

Appropriate addition of additives is not only to improve the target resin to the appropriate performance, but also based on the economic basis of low cost. The requirements for different additives are different:

(1) For flame retardants, tougheners, magnetic powders, barrier agents, etc., although the more additions, the better from a performance point of view, the cost must also be checked;

(2) Conductive additives, generally forming a circuit path;

(3) Antistatic agent, just form a charge leakage layer on the surface;

(4) Coupling agent, just form a surface coating.

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