Nitrogen-phosphorus intumescent flame retardants have the following characteristics:
Environmental performance: It does not contain halogens and does not use antimony oxide as a synergist. The amount of smoke and toxic gases produced during combustion is very small, which conforms to the future development trend of flame retardants with less smoke and lower toxicity. It is an environmentally friendly flame retardant.
Flame retardant mechanism: With phosphorus and nitrogen as the main components, an expanded carbon layer is formed through the chemical reactions of dehydrating agents (acid sources), carbonizing agents (carbon sources), foaming agents (gas sources), and part of the polymer itself. At lower temperatures, the acid source releases inorganic acids that can esterify polyols and act as dehydrating agents. At a temperature slightly higher than that of the releasing acid, inorganic acids undergo esterification reactions with polyols, and the amines in the system act as catalysts for the esterification reaction to accelerate it. The system melts before or during the esterification reaction; The water vapor generated during the reaction and the non-flammable gas produced by the gas source cause the already molten system to expand and foam. At the same time, polyols and esters dehydrate and carbonize, forming inorganic substances and carbon residues, and the system further expands and foams. When the reaction is nearly complete, the system gels and cures, eventually forming a porous foam carbon layer, which plays a role in heat insulation, oxygen isolation, smoke suppression, anti-dripping, etc., achieving the purpose of flame retardancy.
Composition:
Acid source: Also known as dehydrating agent or carbonization promoter, it is generally inorganic acid or compound that can generate acid in situ during combustion, such as phosphoric acid, boric acid, sulfuric acid, phosphate esters, and ammonium polyphosphate (APP), etc.
Carbon source: Also known as carbonizing agent, it is the basis for forming the foam carbonized layer. It mainly consists of some polyhydroxy compounds with high carbon content, such as starch, sucrose, dextrin, pentaerythritol, ethylene glycol, phenolic resin, etc.
Gas source: Also known as foaming source, it is a nitrogen-containing compound, such as urea, melamine, polyamide, etc.
Application fields: It can be applied to various fields and materials such as fibers and fabrics, plastics (such as PP, PE, EVA, EPDM, ABS, etc.), rubber, unsaturated resins, coatings, paints, etc., for halogen-free, environmentally friendly and flame retardant purposes. For example, it can be formulated into a finishing solution and finished onto the fabric surface through methods such as coating. It is added to polymers as a copolymer monomer for flame retardancy of synthetic fibers. It can be added to thermoplastic vulcanized rubber and polyvinyl chloride to prepare flame-retardant materials, etc.
Existing problems:
Hygroscopicity: For instance, APP and PER have a certain degree of water absorption and are prone to alcoholysis reactions, ultimately leading to a decline in the water resistance of flame-retardant polymers and their susceptibility to moisture absorption.
Low-molecular issue: Most of the intumescent flame retardants currently in use are low-molecular substances. The degree of polymerization of inorganic polymers is relatively low, resulting in poor thermal stability, easy exudation, poor anti-migration and compatibility with polymers, ultimately leading to very poor mechanical properties and appearance of flame retardant products.
The proportion issue: The proportion among the components of intumescent flame retardants will affect the flame retardant performance.
Compatibility issues with materials: For instance, phosphorus-nitrogen intumescent flame retardant have poor dispersibility and compatibility with ABS, and the processing performance of the blend system of the two is significantly lower than that of pure ABS.
