The structural characteristics of flame retardants can be described based on different classification categories:
Structural characteristics based on application method
Additive type: Incorporated into the matrix via physical blending; they do not participate in the matrix polymerization reaction, remain structurally independent of the resin molecular chains, and offer high compatibility.
Reactive type: Contain reactive groups within the molecule; they act as monomers participating in the polymerization reaction and are chemically bonded into the polymer molecular chains, resulting in minimal impact on material properties.
Structural characteristics based on chemical properties
Halogen-based: Molecules contain bromine or chlorine; carbon-halogen bonds readily cleave at high temperatures, releasing halogen free radicals that interrupt the combustion chain reaction.
Phosphorus-based: Contain a phosphorus core; phosphazenes, for instance, feature an alternating phosphorus-nitrogen backbone. Upon heating, they readily yield phosphoric acid-type dehydration products, promoting char formation to create a protective barrier.
Inorganic type: Represented by metal hydroxides such as aluminum hydroxide and magnesium hydroxide; their structures contain bound water, which absorbs significant heat and releases water vapor upon thermal decomposition.
Silicon-based: Molecules contain silicon; at high temperatures, they readily migrate to the material surface to form a protective silicate layer, delaying the escape of combustible gases.
