Polycarbonate (PC) is a thermoplastic engineering plastic with excellent mechanical properties, good heat resistance and low temperature resistance, stable electrical properties and good dimensional stability. However, PC has poor processing fluidity, is sensitive to notches, is prone to stress cracking, has poor chemical resistance, and is expensive, which limits its application range. Compatible toughener ST-1 can solve the problem. ABS is also a thermoplastic resin with good chemical resistance and good processability. PC and ABS are blended and extruded to prepare PC/ABS alloy, which can combine the excellent properties of the two. On the one hand, it can improve the heat resistance and tensile strength of ABS; on the other hand, it can reduce the melt viscosity of PC. Improve processability, reduce product sensitivity to stress and reduce costs. Therefore, PC/ABS alloys have been widely used in automobiles, machinery, home appliances, computers, communication tools, office equipment and other industries.
In recent years, in order to meet the special requirements of fire safety, the flame retardant technology of PC/ABS alloy has become a research hotspot. In particular, the promulgation of EU RoHS and WEEE directives restricts the application of halogen-based flame retardant PC/ABS alloys in many industries. Therefore, the research and development of high-efficiency and environmentally friendly halogen-free flame retardants for PC/ABS alloys has become the focus of research in the field of flame retardant.
In this paper, the research progress of halogen-free flame retardant of PC/ABS alloys in recent years is reviewed, and a simple evaluation of each flame retardant system is made based on my own work experience.
1. Inorganic flame retardants
Flame retardants can be divided into two categories: inorganic and organic. Among them, inorganic flame retardants include metal oxides, borates, inorganic phosphorus, etc., and have the advantages of low toxicity, low smoke, and low cost.
(1) Metal oxides
Metal oxide flame retardants are mainly magnesium hydroxide and aluminum hydroxide), both of which exert their flame retardant effect by decomposing and endothermic, generating water vapor to dilute the combustible gas. Aluminum hydroxide is the earliest and the most widely used inorganic flame retardant in China. Aluminum hydroxide has the characteristics of good stability, non-toxicity, no corrosive gas, lasting flame retardant effect, etc., and the product has high whiteness. However, aluminum hydroxide begins to dehydrate at around 230. With the increase of the processing temperature of the polymer, the aluminum hydroxide decomposes and the flame retardant effect decreases. The dehydration reaction of magnesium hydroxide occurs when the temperature is above 350, and its thermal stability and smoke suppression performance are significantly better than those of aluminum hydroxide, and the heat absorption of magnesium hydroxide is 17% higher than that of aluminum hydroxide.
Whether it is aluminum hydroxide or magnesium hydroxide, the dehydration temperature and the maximum endothermic peak will be slightly different due to the particle size and distribution, heating conditions and impurity content. Therefore, when selecting this type of flame retardant, the appropriate flame retardant and its physical properties should be selected according to the processing temperature of the polymer matrix material.
This kind of flame retardant has low flame retardant efficiency, large amount of addition, poor compatibility with materials, and has a great impact on the mechanical properties and heat resistance of materials. Studies have shown that the smaller the particle size, the better the flame retardant effect and the smaller the impact on the mechanical properties. Surface modification of powder can also improve the compatibility of powder and resin. Therefore, nanotechnology and surface modification technology are the main directions of its research.
(2) Inorganic phosphorus flame retardants
Inorganic phosphorus flame retardants mainly include red phosphorus, phosphate and ammonium polyphosphate. Red phosphorus has good flame retardant effect, but it is easy to absorb moisture, oxidize, and dust is easy to explode. Microencapsulation surface treatment of red phosphorus is the most effective solution at present. Red phosphorus can only be used for flame retardant dark or black products, and cannot be used for intrinsic flame retardant, which limits the scope of use.
The combustion behavior of red phosphorus flame retardant PC/ABS alloy was studied by cone calorimeter. The results show that the addition of red phosphorus can reduce the average heat release rate and average effective combustion heat of PC/ABS alloy.
2. Organic flame retardants
The organic flame retardants used in PC/ABS alloys mainly include organic phosphorus flame retardants and silicone flame retardants.
(1) Organophosphorus flame retardants
Organophosphorus flame retardants mainly refer to phosphate ester flame retardants, which are one of the most important varieties of PC/ABS alloy halogen-free flame retardants, with dual effects of flame retardant and plasticization. Its flame retardant mechanism is: on the one hand, it is thermally decomposed to generate phosphoric acid, metaphosphoric acid, etc., which can catalyze the endothermic dehydration of hydroxyl-containing compounds into carbon reaction, so that a dense carbon layer is formed on the surface of the polymer; on the other hand, it is heated to generate PO, which can be captured H, HO, play a role in inhibiting the combustion reaction.
It has important application value. The most representative phosphates are triphenyl phosphate (TPP), resorcinol-bis (diphenyl phosphate) (RDP) and bisphenol A-bis (diphenyl phosphate) ( BDP). Among them, TPP is a flaky solid, but its melting point is low, and the feeding port will be bridged. It is necessary to strictly control the processing temperature during extrusion, otherwise the loss will be large. RDP and BDP are liquids, and they need to be pumped in by a metering pump during processing. Especially, the viscosity of BDP is high, which brings difficulties to processing. Experimenters believe that for PC/ABS alloys, TPP plays a flame retardant role in the gas phase, and RDP mainly plays a flame retardant role in the gas phase and also has a solidification phase resistance.
