Engineering Plastics Flame Retardant Systems Roundup!

—Part I Flame Retardants

Engineering plastics have good mechanical properties and dimensional stability, in the high temperature, low temperature environment can still maintain its excellent performance, usually used as instrumentation parts, equipment shells and a variety of insulating parts and other engineering structures. With the continuous progress of polymer synthesis and processing technology, engineering plastics have penetrated into all areas of people's lives, in some often contact with high-temperature environment in the field, engineering plastics flame retardant to measure its comprehensive performance of an important indicator.

The flame retardancy of plastics can be evaluated by combustion test method, which is divided into horizontal and vertical methods. The vertical method evaluates the flame retardancy of materials by measuring the duration of afterflame and afterglow, the range of combustion and the drop of particles. According to the behavior of the specimen, the materials are classified into V-0, V-1, and V-2 levels according to the criteria shown in Table 1 (V means vertical combustion).

Different plastics have different combustion properties, such as PC itself has a certain degree of flame retardancy and can reach V-2 grade in the vertical combustion test, while ABS itself is flammable and cannot be graded. Flame retardant modification of plastics through the addition of flame retardants can delay combustion and reduce the intensity of combustion. However, plastic in the combustion process, in addition to their own combustion, but also produce droplets ignite other combustible materials, resulting in the spread of fire, resulting in serious consequences. Therefore, flame retardant plastics, often also need to add anti-dripping agent to prevent the melt from dripping during the combustion process.

Engineering plastics flame retardant system

The flame retardant system for engineering plastics includes flame retardants, base resins and anti-drip agents.

01 Flame Retardant

The flame retardants used in engineering plastics are mainly halogenated flame retardants and phosphorus flame retardants.

(1) Halogenated flame retardants

Halogenated flame retardants are divided into chlorine flame retardants and bromine flame retardants. Chlorine flame retardant is cheap, but it has poor thermal stability and is only suitable for products with processing temperature below 200℃.

Brominated flame retardants have high flame retardant efficiency, which is twice as much as chlorinated flame retardants, so the relative dosage is small, and because of its good mutual compatibility with the base resin, it has less influence on the mechanical properties of the material, and has an important position in the flame retardant field. Halogenated flame retardants are one of the main flame retardants used in plastics, with high flame retardant efficiency, good weather resistance and thermal stability, and small influence on the mechanical properties of materials.

Halogenated flame retardants mainly play a flame retardant role in the gas phase, which liberates flame retardant hydrogen halide gas when heated, which can dilute the concentration of oxygen and flammable gases in the air, and can eliminate or reduce the reactive free radicals generated in the combustion process of polymers, thus terminating or slowing down the chain reaction in the combustion process in the gas phase, and playing the purpose of flame retardant.

At the same time, in the condensed phase halogenated flame retardants can also form a carbonized layer through dehydration reaction, covering the surface of the polymer to isolate the air, so as to play a flame retardant role in the condensed phase. Halogenated flame retardants and metal oxides, phosphorus-containing compounds and other synergistic agents used in conjunction with the flame retardant effect is better, so in practical applications, halogenated flame retardants are often used in conjunction with antimony trioxide (Sb2O3).

Halogen flame retardants in the combustion process will produce smoke and corrosive gases, etc., to human health and the environment to bring serious secondary disasters, so low-halogen or halogen-free environmentally friendly flame retardants are concerned.

(2) Phosphorus flame retardants

Phosphorus flame retardants have formed a wide range of varieties, including inorganic phosphates, phosphate esters, phosphorus heterophenols, phosphorus nitrile and red phosphorus.

Phosphorus flame retardants in the combustion process of decomposition of the formation of high boiling point oxygen-containing acid can promote polymer dehydration and carbonization, and the formation of carbonized residue protective layer, so that the polymer and air isolation.

At the same time, the dehydrated water absorbs a large amount of heat, which can also reduce the surface temperature of the polymer, thus achieving the effect of flame retardant. The advantages of phosphorus-based flame retardants are low toxicity and corrosiveness, good thermal stability and long-lasting effect. The European Union has banned the use of halogenated flame retardants such as polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) in the manufacture of electronic equipment.

Phosphate ester-based phosphorus flame retardant bisphenol A-bisphosphoric acid diphenyl ester (BDP) is compatible with PC/ABS and other engineering plastics, and has the advantages of good environmental performance, high thermal stability, and a small impact on the performance of the material, so it has been widely used in cell phones, laptops, and electronic and electrical equipment such as televisions.