Two common flame retardants suitable for polypropylene and their pros and cons

There are many types of flame retardants that can be used for polypropylene, which can be classified into two categories according to their chemical composition: organic flame retardants and inorganic flame retardants; they are further divided into reactive and additive types according to their usage methods. Representative flame retardants include bromine-based, phosphorus-nitrogen-based, phosphorus-based, aluminum hydroxide, magnesium hydroxide, etc.

1. Phosphorus-nitrogen flame retardant

Phosphorus-nitrogen flame retardants are also called intumescent flame retardants. When polymers containing such flame retardants are heated, a uniform carbon foam layer can be formed on the surface to provide heat insulation, oxygen isolation, and smoke suppression. function and prevent the occurrence of droplets, so it has good flame retardant properties. Intumescent flame retardant systems generally consist of three parts: acid source (dehydrating agent), carbon source (carbon-forming agent) and gas source (nitrogen source, foaming source). Intumescent flame retardants mainly play a flame retardant role in the condensed phase by forming a porous foam carbon layer. Phosphorus-nitrogen flame retardants have the advantages of halogen-free, low smoke and low toxicity.

2. Phosphorus flame retardant

The main reason why phosphorus-based flame retardants can play a flame retardant role is that they can promote dehydration and carbonization during the initial decomposition of polymers. This dehydration and carbonization step must rely on the oxygen-containing groups of the polymer itself. For polymers with oxygen-containing groups in their own structure, their flame retardant effect will be better. For polypropylene, since its molecular structure does not have oxygen-containing groups, the flame retardant effect is not good when using phosphorus-based flame retardants alone. However, if combined with aluminum hydroxide, magnesium hydroxide, etc., it can produce a synergistic effect. , thereby obtaining good flame retardant effect.

Commonly used organophosphorus flame retardants include triphenyl phosphate, tricresyl phosphate, tri(xylene) phosphate, propylbenzene phosphate, butylbenzene phosphate, etc. Phosphate esters are characterized by their dual functions of flame retardancy and plasticization. It can make flame retardants halogen-free, and its plasticizing function can improve the flow and processability of plastics during molding, and can suppress residues after combustion. Its main advantages are higher efficiency; less impact on light stability or light stabilizer action; less corrosive during processing and combustion; hindering re-ignition; little or no increase in the quality of flame retardant materials; It contains less toxic gases and corrosive gases than halogen flame retardants. However, most phosphate ester flame retardants also have some shortcomings, such as poor heat resistance, high volatility, unsatisfactory compatibility, and the production of dripping materials when burning.

The main products of phosphorus-containing inorganic flame retardants include red phosphorus flame retardant, ammonium phosphate salt, ammonium polyphosphate, etc. Phosphorus-containing inorganic flame retardants are widely used because of their good thermal stability, non-volatility, no corrosive gas generation, long-lasting effect, and low toxicity.