PC transparent plastic to share basic knowledge of plastic: flame retardant modification of the basic principles

Plastic combustion process

To understand the principle of plastic flame retardant, we must first understand the plastic combustion process.

The combustion process of plastics is an extremely complex thermal oxidation reaction, which leads to the basic elements of combustion, heat, oxygen and combustible gas.

It is generally believed that the combustion of plastics has gone through three stages.

The first phase, the thermal initiation process. The heat from an external source of heat or fire causes a change in the plastic phase (i.e., from solid state to liquid state) and chemical change.

Second stage, thermal degradation process. This process is endothermic reaction, when the heat absorbed by the plastic is enough to overcome some of the weak bond between atoms in the molecule, the plastic began to take place. The essence of this reaction is a free radical chain reaction in the presence of oxygen in the air, the result of the reaction to produce combustible gas phase objects, such as a variety of flammable hydrocarbons monomer.

The third stage, the ignition process. When the concentration of combustible matter in the second stage of thermal degradation reaches the ignition limit, it meets with the oxygen in the atmosphere.

Two, flame retardant mechanism

The flame retardant can be increased by adding flame retardant to a certain proportion, and the flame retardant effect is obvious. Of course, the oxygen index is only to indicate the flammability of the material and the flame retardant, but also a series of parameters, such as the critical parameters of thermal ignition, the ignition energy, the spontaneous combustion temperature, etc.. In general, when the flame retardant plastics containing flame retardant, the flame retardant is in different reaction areas (gas phase, condensed phase) in many ways. For different materials, the role of flame retardants may be different.

The mechanism of flame retardants is complex. But the aim is to cut off the combustion cycle in physical and chemical ways. The effect of flame retardant on combustion reaction is shown in the following aspects:

(1) in the condensed phase flame retardant endothermic decomposition, so that the condensed relative temperature rise within the slow phase, in order to delay the thermal decomposition temperature of plastics, flame retardant heat generated by the decomposition of incombustible gas to reduce the temperature of heat of vaporization.

(2) flame retardant thermal decomposition, releasing trapped in the combustion reaction OH (Qiang Ji) flame retardant free radicals, the combustion process is carried out according to the free radical chain reaction termination of chain reaction.

(3) under the action of heat, the flame retardant has endothermic phase change, which can prevent the increase of the temperature in the condensed phase.

(4) the thermal decomposition of the catalytic condensation phase, resulting in a solid phase (coking) or foam layer, blocking the heat transfer. This results in a lower temperature of the condensed phase, which results in a decrease in the formation rate of the gas phase reaction material (the decomposition product of the combustible gas).