Polyamide (PA), commonly known as nylon, is a set of mechanical properties, heat resistance, chemical resistance and self-lubrication of equal to one of the engineering plastics, widely used in automotive, electrical and electronic, mechanical, textile, daily necessities and other fields.
However, the oxygen index of PA is low, and it is easy to burn and cause fire, and the combustion of PA is a process accompanied by oxidative degradation. PA first melts to cause the material to form a viscous flow state, and with the transfer of heat, the molecular chain segments will break to form free radicals, forming gases such as ethane and propane.
PA flame retardant method
1) Reactive type: the flame retardant monomer is grafted onto the PA main chain or copolymerizes with the PA monomer, the composite material obtained by the system is more stable, and the material properties are not greatly affected by the flame retardant, but the operation and processing of the method is more complicated and difficult to industrially produce;
2) Additive type: The method of mechanical blending is used to blend PA with added halogen-free flame retardants (such as phosphorus, nitrogen series flame retardants, inorganic fillers, etc.) to form a uniform composite material. This method is easy to operate and has become the main way of PA flame retardancy at present.
Flame retardant grades are usually judged using vertical combustion test criteria and can be divided into V-0, V-1, V-2 grades, of which V-0 grades have the best flame retardant effect.
Nylon flame retardant
The existing flame retardants can be divided into halogen flame retardants, phosphorus flame retardants, nitrogen flame retardants, metal hydroxide flame retardants and so on according to the varieties. Among them, halogen flame retardants have been banned in many countries due to the easy generation of toxic gases at high temperatures.
For nylon, flame retardants must have good thermal stability to adapt to high processing temperatures, while also having good compatibility.
<h1 class="pgc-h-arrow-right" data-track="22" >1. Brominated styrene polymer</h1>
Advantages: It has extremely superior thermal stability and, since it is meltable and mixable with nylon, it has good flowability during processing. In addition, the flame retardant nylon prepared with it also has superior electrical properties and good physical and mechanical properties.
Disadvantages: Poor light stability, not completely compatible with nylon and high cost
<h1 class="pgc-h-arrow-right" data-track="29" >2</h1>
DCRP is a flame retardant that has been used in nylon for many years, it is a chlorine-containing flame retardant with high flame retardant efficiency and electrical properties, but its limitations in thermal stability make it only suitable for nylon flame retardant systems with lower processing temperatures.
<h1 class="pgc-h-arrow-right" data-track="34" >3.decabromodiphenyl ether</h1>
Advantages: low cost and therefore the most widely used in China, due to its high bromine content and high flame retardant efficiency for nylon.
Disadvantages: It is a filler-type flame retardant, so it has a great negative impact on the processing flow and physical and mechanical properties of the product. And its thermal stability and light stability are also poor.
<h1 class="pgc-h-arrow-right" data-track="40" >4.decabromodiphenoxyethane</h1>
Advantages: The same bromine content and the same high flame retardant efficiency as decabromodiphenyl ether, and as with brominated styrene polymers, there is no DPO problem. It also has good thermal stability and light stability.
Disadvantages: filler type flame retardant, so the compatibility with polymers is poor, processing fluidity and physical and mechanical properties of products are poor. In addition, the cost is higher compared to decabromodiphenyl ether.
<h1 class="pgc-h-arrow-right" data-track="46" >5</h1>
Advantages: high available phosphorus content, under the same flame retardant grade, the amount of addition is lower than other flame retardants, so that nylon can better maintain its own mechanical properties.
Disadvantages: The color of the product can only be red, and the red phosphorus is flammable, which can react with water to generate highly toxic phosphine. Generally only used in nylon 6. (Microencapsulation or mastergrainization of ordinary red phosphorus circumvents its drawbacks.) ）
<h1 class="pgc-h-arrow-right" data-track="53" >6</h1>
Ammonium polyphosphate (APP) participates in the thermal degradation process of nylon by reducing the degradation temperature of nylon and changing the composition of the final gas phase product, while forming a honeycomb carbonization overlay on the polymer matrix, cutting off the heat and material transfer at the two-phase interface, and playing a role in protecting the matrix.
Due to the flow trend of carbon formation, it will lead to the exposure of the substrate under the carbon layer, which increases the risk of combustion. Add some inorganic additives, such as talc,MnO2,ZnCO3,CaCO3,Fe2O3,FeO,Al(OH)3,etc., and increase the flame retardant effect.
In the ammonium polyphosphate (APP) added to the amount of nylon 6 is added to 20% of the above additives (1.5% ~ 3.0%), the LOI value can rise to 35% ~ 47%, reaching the V-0 level.
<h1 class="pgc-h-arrow-right" data-track="62" >7. Nitrogen flame retardants (MCA, MPP, etc.</h1>).
Nitrogen flame retardants suitable for nylon mainly include MCA (melamine cyanurate), MPP (melamine polyphosphate) and so on.
Regarding its flame retardant mechanism, on the one hand, it is the physical flame retardant method of "sublimation heat absorption", that is, the flame retardant reduces the surface temperature of the polymer material and isolates the air through the "sublimation heat absorption" of the flame retardant to achieve the purpose of flame retardancy, on the other hand, the flame retardant and nylon in the condensed phase catalyze the direct carbon expansion mechanism.
Advantages: Nitrogen flame retardant is low toxicity, non-corrosive, stable to heat and ultraviolet rays, flame retardant efficiency and low price.
Disadvantages: its flame retardant plastic processing difficulties, poor dispersion in the substrate, poor thermal stability, and due to the easy moisture absorption and the product in a humid environment the electrical performance is poor.