Thermal conductivity modification of plastics is generally achieved by adding metallic and carbon-based thermal conductive fillers. However, such thermal conductive fillers are also electrically conductive. While improving thermal conductivity, they will simultaneously increase electrical conductivity, thereby impairing insulation performance.
Thermally conductive plastics are widely used in insulation-required applications such as circuit boards, connectors, and packaging materials. For this reason, electrically conductive thermal conductive fillers cannot be used in insulating and thermally conductive formulations; only insulating thermal conductive fillers such as ceramic metal oxides are allowed.
8. Processability of the Formula
The formula shall maintain proper processability to ensure product molding, without causing adverse effects on processing equipment and service environment.
Auxiliaries in composite materials shall feature good heat resistance. They shall not volatilize or decompose at processing temperature (except for crosslinking agents, initiators and foaming agents). The addition of auxiliaries shall have minimal impact on the original processing performance of the resin. The added auxiliaries shall cause as little wear and corrosion to equipment as possible, and shall not release toxic gas during processing to harm operators’ health.
(1) Flowability
Most inorganic fillers deteriorate processability. When added in large dosage, processing modifiers such as lubricants need to be incorporated correspondingly to compensate for the loss of melt flowability.
Organic auxiliaries generally improve processability. For example, flame retardants such as decabromodiphenyl ether and tetrabromobisphenol A can enhance melt flowability, with tetrabromobisphenol A showing a particularly obvious effect.
An appropriate amount of lubricant is usually required in most modified plastic formulas.
(2) Heat Resistance
Auxiliaries must remain stable without decomposition during processing, except for foaming agents, initiators and crosslinking agents which are designed to decompose for functional purposes. The following points should also be noted:
- Due to low decomposition temperature, aluminum hydroxide is not suitable for PP and can only be used in PE.
- Tetrabromobisphenol A is unsuitable for ABS flame retardancy because of its low decomposition temperature.
- Most organic dyes have low decomposition temperatures and are not applicable to engineering plastics processed at high temperature.
- Flavoring agents generally have a decomposition temperature below 150°C, and can only be carried by resins with low processing temperature such as EVA.
Modified plastic formulas are subjected to strong shearing during processing, so antioxidants are indispensable to prevent thermal decomposition and material yellowing.
9. Environmental Friendliness of Plastic Formula Components
Specific requirements: all auxiliaries in the formula shall be harmless to operators, processing equipment, end users and the contacted environment.
In the past, environmental requirements were limited in scope, only requiring non-toxicity for direct human contact scenarios such as food and pharmaceutical packaging. Nowadays standards are much stricter. Materials in indirect human contact are also regulated, and formulas must cause no pollution to soil, water, atmosphere and the overall ecological environment.
