Compared with metallic materials and inorganic non-metallic materials, plastic materials have the advantages of low cost, convenient production and variety of materials, and are widely used in many fields. In recent years, with the development of electrical equipment in the direction of lightweight, miniaturization and refinement, the application of flame retardant plastics in the electrical field has become a hot spot.
However, some plastic materials contain more carbon, hydrogen and other elements, and the heat resistance needs to be improved, and it is easy to cause secondary combustion in the event of a fire. Usually, the flame retardant properties of plastic materials are improved by using material modification to further expand the application scope of plastic materials in the field of electrical equipment.
In this paper, taking flame retardant plastics as the research object, the current application of flame retardant plastics, such as polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), acrylonitrile-butadiene-styrene copolymer (ABS), polyurethane (PU), polycarbonate (PC) and other materials as examples, discusses the application status and development trend of different types of flame retardant plastics in the field of electrical equipment, and provides a reference for the research and development of new flame retardant plastics in the future.
1. Overview of flame retardant plastics
Flame retardant plastics have good flame retardant properties, chemical resistance, mechanical properties, insulation properties, and have the advantages of low cost and low density, which can meet different production and processing needs and reduce the cost of material use.
Common flame retardant plastics include PVC, PE, PP, etc., of which PVC flame retardant performance is better, can be directly used as a flame retardant material, and PE, PP, etc. need to add flame retardant agents to improve flame retardant heat resistance. The flame retardant properties, mechanical properties and electrical insulation properties of composite flame retardant plastics have been improved, and they have a wider application potential than pure flame retardant plastics.
Common flame retardants used in plastics include brominated flame retardants, phosphorus-nitrogen flame retardants, phosphorus flame retardants, aluminum hydroxide (ATH) and magnesium hydroxide (MH) flame retardants.
2 The application status of flame retardant plastics in electrical equipment
2.1 PVC plastic flame retardant
PVC pipe is a widely used new synthetic material, with good heat resistance and flame retardant performance, high insulation, high elasticity, etc., so it has a wide range of applications in the field of building electrical, electrical automation systems, and distribution systems.
With the continuous improvement of the requirements of application scenarios, in order to improve the flame retardant properties and mechanical properties of PVC, researchers have conducted a lot of research on the types, additions and processing technology of PVC flame retardants. PVC flame retardant plastics can be divided into hard flame retardant type and semi-hard flame retardant type.
To improve the flame retardant performance of hard flame retardant PVC. Lin Yalian takes the hard PVC plastic of the electrical pipeline of the construction project as the research object, and uses organic montmorillonite, MH, ammonium polyphosphate and other flame retardants to modify the PVC plastic.
The results show that the MH modified PVC plastic has the best flame retardant performance, and the limiting oxygen index (LOI) is 28% when the MH content is 30 parts, which further shows that the MH modified PVC has an endothermic and dehydrating reaction during combustion, which then plays a flame retardant role, and the mechanical properties of the modified PVC are improved.
Sun Yingjuan et al. explored the formation of new flame retardants and modified soft PVC in microcapsules of red phosphorus (MRP), zinc borate (ZnBO3), ATH and MH under different ratios.
The results show that when the mass ratio of PVC/MRP/ZnBO3/ATH/MH is 100:3:1:20:20, the PVC composite has good flame retardant properties, its LOI value can reach 35.9%, and the smoke release is less and the thermal stability is stronger, which provides a reference for building electrical pipeline applications.
PVC composite materials can be applied to scenarios below 80 °C and below 600V voltage, and are commonly used materials in electrical automatic control systems. Ma Wanli et al. use silicone resin to modify PVC plastics to improve the flame retardant properties and corrosion resistance of materials, and apply modified materials to the field of cables.
The results show that the mechanical properties of the modified PVC plastic are better, the tensile strength is above 15MPa, and the LOI value is up to 27.3%, indicating that the flame retardant performance of the modified material is significantly improved, and after a period of aging corrosion, the flame retardant performance is still relatively stable.
2.2 PE plastic
PE has the advantages of good chemical stability, low cost and low density, and is used in the field of electrical equipment, but due to the poor heat resistance of PE, it is easy to dissipate heat in a fire environment, resulting in the spread of fire, so the scope of use of PE is limited.
Pe properties are usually modified by materials such as halogen flame retardants, phosphorus flame retardants, and metal hydroxide flame retardants. In order to improve the flame retardant properties of PE, scholars have carried out many studies on the types and modification conditions of PE plastic modifiers.
Jiang Xiaojuan et al. studied the application of PE plastics in cables in high-voltage electrical equipment, selected flame retardant additives such as decabromodiphenylethane (DODPE), Sb2O3, ATH, MH, and red phosphorus masterbatch as modifiers, and measured the electrical properties of modified PE plastics.
The results show that the electrical properties of MH-modified PE plastics are the most stable under water immersion conditions, while the electrical properties of red phosphorus masterbatch modified flame retardant PE after immersion in water are significantly reduced, which provides a reference for the application environment of flame retardant PE plastics.
Liu Ying et al. used hexahydroxymethyl melamine (HMM) and benzophosphonyl dichloride (PPD) as raw materials to make flame retardants, reacted with PE plastics, and determined the flame retardant properties of PE composites under different flame retardant content.
The results show that when the phosphorus content of the flame retardant is 6.22%, the LOI value of the PE composite material reaches 29.3%, which has good mechanical properties and the maximum impact strength is 16.9 kJ/m2. The study provides direction for the selection of flame retardants for PE materials.
Zhou Cheng et al. studied the PE material for wire and cable in electrical equipment, and selected modified MH as a flame retardant to modify PE flame retardant to determine flame retardant performance and electrical performance.
The results show that the flame retardant content increases, the carbon layer of pe composite material is denser, and the flame retardant performance is better, but the electrical properties and mechanical properties of the material are slightly reduced, and when the modifier content is added to 70 parts, the comprehensive performance of PE composite material is the best. PE is also an important material for the shell of electronic equipment such as telephones and alarms, and improving the flame retardant and antistatic properties of the shell of electronic equipment can effectively reduce the risk of use.
2.3 PP plastic
PP has good electrical insulation properties, tear resistance and low cost, and is currently used in electrical equipment such as switches, electrical boxes, cable clamps, TVs, etc., but because the LOI value of PP is only 18%, it is prone to droplets during combustion, so the flame retardant modification of PP has important application value.
At present, there are many studies on the modification of PP flame retardant performance, mainly focusing on the types of flame retardants and modification conditions. Shi Yanshan et al. used PP as raw material and modified PP by using halogen-free P-N expansion flame retardants.
The results show that the SMOKE density of PP composite material is low at 6 min and reaches UL94 V-0 level. Cai Hao et al. used shuangspirocycloschfu alkali as raw materials to make pentaerythritol phosphate (SPDEB) flame retardant, and modified PP. The results show that the LOI value of PP composite material is up to 35%, which passes the UL94 V-0 rating, and compared with pure PP, it forms a dense carbon layer during combustion, which can play a flame retardant role.
Lin Zhidan et al. selected Decabromodiphenylethane/Sb2O3, nitrogen and phosphorus flame retardant AP752/pentaerythritol and PP melt blending, and measured the flame retardant properties, mechanical properties and insulation properties of PP composites.
The results show that the modified PP composite material passes through UL94 V-0 grade, the LOI value is 30%, and the electrical strength is 57.14 kV/mm. The PP flame retardant plastic is environmentally friendly and in line with future trends.
2.4 Other flame retardant plastics
Flame retardant plastics are widely used in the field of electronic equipment packaging, including ABS, PU, PC and so on.
Wang Liang et al. modified ABS, which is widely used in the field of electronic and electrical equipment, added wollastonite and made flame retardant ABS composite materials by melting and blending, and measured the mechanical properties, dimensional stability and flame retardant properties of the materials.
The results show that when the mass fraction of wollastonite is 10%, the flame retardant grade of ABS composite material reaches UL 94 V-0, and the dimensional stability and mechanical properties are better. In terms of research on the modification of the flame retardant properties of PU plastics, Xue Zhulin et al. [34] used phosphorus-containing polyols (DMMP-EG) and ammonium polyphosphate (APP) as composite flame retardants to modify PU plastics. The results show that when the ratio of DMMP-EG and APP is 1:2, the mechanical properties of PU composites are significantly improved, the impact strength is increased by 101.53%, and the LOI value is as high as 21.7%.
3. The development trend of flame retardant plastics in electrical equipment
The use of flame retardant plastics in the field of electrical equipment can meet the development trend of lightweight and convenience, and halogen-containing flame retardants can effectively improve the flame retardant properties of plastics, and are widely used in the early stage of flame retardant plastics. However, halogen flame retardants are easy to release toxic gases and corrosive gases, so in the context of increasing environmental protection requirements, flame retardant plastics have transformed into environmentally friendly, non-toxic and harmless directions, and the preparation of flame retardant plastics with low toxicity, low smoke and no halogen has become a research hotspot.
In order to study environmentally friendly and high-performance flame retardant plastics, many researchers are actively exploring.
Huang Xinbing et al. synthesized a new composite environmentally friendly flame retardant with dimethyl trimethiomethylphosphonate, melamine cyanurate, red phosphorus and ATH as raw materials, and prepared HDPE composite flame retardant plastics by melting and mixing with HDPE, and determined the flame retardant properties and mechanical properties of the material.
The results show that when the mass fraction of flame retardant is 30%, the LOI value of HDPE composite flame retardant plastic can reach 33.4%, while the LOI value of unmodified HDPE flame retardant plastic is only 17.5%, indicating that the flame retardant performance of HDPE plastic is significantly improved after modification.
4. Conclusion
Plastic materials have good chemical resistance, mechanical properties and insulation properties, and convenient processing, low cost, low material density, has a good application in the field of electrical equipment. By adding flame retardant modifiers, the flame retardant properties of plastic materials can be improved.
In the future, with the continuous improvement of environmental protection requirements and electrical equipment requirements, flame retardant plastics need to develop in the direction of environmental protection, low toxicity and degradable recycling, and new flame retardant plastic materials and efficient and environmentally friendly flame retardants will become future research hotspots.
Source: New Materials Research Society
References: Cangzhou Transportation College Ning YaBoron, Liu Xinwei, Zhou Meiling
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