How To Improve The CTI Value of Modified Engineering Plastics?

How To Improve The CTI Value of Modified Engineering Plastics?

Polycarbonate, nylon and PBT are chosen by manufacturers of low-voltage electrical appliances as the materials of choice due to their excellent mechanical, thermal and processing properties.

For safety reasons, plastic products used in electrical and electronic appliances need to be flame retardant. Nowadays, the flame retardants for engineering plastics mainly adopt halogenated bromine-based flame retardant systems, halogen-free phosphorus and nitrogen systems and compound flame retardant systems, which are designed according to different requirements.

• Effect of Brominated Flame Retardants on CTI Values of PA Materials

At present, the largest material used in electrical products is polyamide (PA), and the CTI value of pure PA is generally greater than 600V or more, but after the addition of brominated flame retardants, the CTI value drops to less than 250V. Due to the advantages of high flame retardant efficiency and excellent mechanical properties of brominated flame retardants, they are still widely used in PA flame retardant materials, so it is necessary to improve the CTI value of brominated flame retardant fuels for modification measures.

The thermal decomposition temperature of brominated flame retardants added to flame retardant plastics is generally lower than the decomposition temperature of plastics, so the flame retardants in plastics are more likely to decompose and form carbonization under the action of electric field, leading to leakage and tracing. The CTI value of flame retardant engineering plastics prepared from different bromine flame retardants increases with the improvement of thermal stability.

It has been found that the CTI value of PA can be increased by adding synergistic flame retardants. Currently available halogenated environmentally friendly flame retardants are decabromodiphenyl ethane, brominated polystyrene, brominated epoxy, BC-58 (Phenoxytetrabromobisphenol A carbonate zwitterion) and so on.

The most effective co-efficient of bromine flame retardant system is antimony trioxide, adding antimony trioxide in PA, the flame retardant properties of PA have been significantly improved, but the amount of antimony trioxide on the CTI value of the impact is also relatively large in this system need to be added to the other components suitable for the further improvement of the CTI value of the material.

It is found that the elected bromine flame retardant is polybrominated styrene, and the compounding co-effect flame retardant is composed of antimony trioxide, magnesium hypophosphite and talc, which can effectively improve the GWIT and CTI values of the composite materials, and it is also helpful to improve the GWIT and CTI values by adding appropriate amount of toughening agent.

• Effect of nitrogen-based flame retardants on CTI values of PA materials

Nitrogen-based flame retardant mainly refers to melamine and its derivatives, such as melamine cyanuronate (MCA), whose main advantage is that the flame retardant itself and the decomposition products are low toxicity and low corrosion, which is environmentally friendly, and it has almost no effect on the electrical insulation properties of the material. In addition, because it is a white powder itself, it can be made in various colors.

In non-reinforced PA plastics, MCA is an excellent flame retardant, adding 8~10 parts can reach V0 level, and the CTI value remains above 600V. However, in reinforced PA plastics, the flame retardancy of MCA is greatly reduced, and the flame retardant system must be adjusted.

• Effect of phosphorus-based flame retardants on CTI values of PA materials

The most effective phosphorus-based flame retardant is red phosphorus, which is popular for its low additive amount, good flame retardant effect, and small effect on the mechanical properties of PA and high CTI value. However, the most difficult to accept its color can only be used in red-brown or black products, and black is difficult to achieve the effect of pure black.

At present, red phosphorus masterbatch is basically used in modified plastics, and the safety and dispersion properties have been greatly improved. Adding red phosphorus masterbatch to flame retardant reinforced PA66 can make the product reach flame retardant V0 level, and its CTI value is generally between 350~450V. To obtain products with higher CTI value, it is also necessary to match with suitable metal oxides and lubricants, through which materials comparable to similar foreign products can be made.

Due to the limitation of red phosphorus, it has been banned in many occasions, so there is no way to use red phosphorus in many PA modified materials, and the use of other highly efficient phosphorus-containing flame retardant has been the mainstream of the current modification.

Used in the PA in the most phosphorus-based flame retardant is aluminum diethyl hypophosphite (ADP), because of its own white, can be done in a variety of colors, so in the modified flame-retardant nylon materials are widely used. In addition, ammonium polyphosphate (APP) and melamine polyphosphate (MPP) are also a kind of more common phosphorus-based flame retardant, but their dosage is not large due to the low CTI value and difficult to control the processing technology.

Tests have shown that the use of nano-silica and nano-montmorillonite as nucleating agents in PA materials, and the addition of compounded halogen-free flame retardants MCA, MPP and hypophosphite can improve the CTI value.

• Effect of Compounding Flame Retardant Systems on the Properties of PBT Materials

In the flame-retardant PBT modified materials, the flame retardant brominated epoxy resin (BEO), antimony trioxide, hypophosphite, stannate and other compounding and blending modification, after the preparation of samples to test the performance, to test the compound flame retardant system on the material's burning wire, flame retardant and CTI effect.

The test results show that stannate and antimony have little effect on the burning wire performance, and as the content of hypophosphite added is larger, the burning wire performance is more excellent, up to 850 ℃, which is due to the brominated flame retardant and halogen-free flame retardant compounding, flame retardant effect of diversified, more complete isolation of oxygen. The compounding of flame retardant styrene bromide, magnesium hypophosphite and talcum powder has obvious effect on improving CTI value.

In addition, the effect of antimony trioxide on CTI is quite large, adding the flame retardant into the CTI performance are not too high; if the antimony is replaced by stannate, CTI performance is greatly improved, up to 425V; at the same time, hypophosphite to improve the performance of the CTI also has a certain degree of help, the addition of a large amount of CTI performance is also very obvious.

This is mainly because reducing the amount of antimony added will significantly reduce the carbonization effect on the surface of the material, which leads to an increase in the surface resistivity of the material. This compounded flame retardant system is suitable for the preparation of high-end PBT modifiers.

In the field of engineering plastics, CTI value is a key indicator, which is directly related to the safety and reliability of materials in electrical applications. A high CTI value means that the material has a stronger ability to resist leakage traces and galvanic corrosion caused by electric arcs under the action of electric fields, thus effectively reducing the risk of short circuits and fires.

YINSU Flame Retardant has succeeded in improving the CTI values of engineering plastics by developing products such as highly effective red phosphorus flame retardants and expandable graphite. These flame retardants not only improve the flame retardancy of materials to meet higher safety standards, but also enhance their resistance to electrical traces without sacrificing other properties of the materials. Therefore, YINSU Flame Retardant's innovative flame retardant solutions are of great significance in improving the safe application of engineering plastics in electrical and electronic products, helping to drive the industry in the direction of greater safety and environmental protection.