Aluminum hypophosphite(ALHP&AHP) has a high phosphorus content and exhibits some flame retardant effect in ABS. However, the mechanical properties of the flame-retarded ABS material do not meet requirements. Ammonium polyphosphate (APP) is an inexpensive P,N halogen-free flame retardant. Its drawbacks are significant when used alone; large addition amounts can significantly impact the mechanical properties of ABS. The flame retardant mechanisms of AHP and APP in ABS differ considerably, which we will briefly discuss below.

1. During combustion, the polyphosphoric acid generated by the decomposition of AHP removes water molecules from the system, causing charring of the burning surface and thus providing solid-phase flame retardancy.

2. The combined effect of AHP and a carbon source significantly increases the char residue rate. Under high temperatures, aluminum hypophosphite and ammonium polyphosphate react chemically to form a dense carbon layer, similar to the glassy structure of inorganic phosphates, covering the surface of the burning material and isolating it from oxygen and heat.

3. When ABS material is heated to above 250-300℃, the ammonia released from the decomposition of APP and the nitrogen and ammonia released from the decomposition of melamine, among other non-combustible gases, cause the composite material to expand. This generates viscous liquid acids such as polyphosphoric acid or metaphosphoric acid, which have strong dehydrating properties. The generated polyphosphoric acid/metaphosphoric acid is a strong acid and an excellent dehydrating agent; it reacts chemically with ABS, dehydrating and carbonizing the ABS material's molecular chains, transforming the reaction pathway that originally produced combustible small molecules into the formation of a carbon-rich carbon layer. Under the catalysis of the acid, the carbon source reacts with the dehydrating agent to form a viscous melt. Non-combustible gases fill this melt, causing it to foam and expand.

To mitigate the impact of using aluminum hypophosphite and ammonium polyphosphate (APP) alone on ABS materials, the following formulation can be used, achieving the following flame-retardant effect: AHP: 2.5%, APP: 17.5%, and an appropriate amount of charring agent. This formulation flame-retardant ABS showed a char residue rate of 6.9% at 700℃, a LOI of 30%, and a flame-retardant rating of V-0.

The flame-retardant mechanisms of aluminum hypophosphite and ammonium polyphosphate on ABS may involve more than just these two aspects. Different carbon source types can lead to completely different charring mechanisms, effects, and charring chemical reaction processes.