What Is Aluminum Diethylphosphinate (AlPi)? CAS 225789-38-8, Uses & Benefits

What Is Aluminum Diethylphosphinate (AlPi)?

Aluminum diethylphosphinate (AlPi), also called aluminum diethylphosphinate salt or DEPAL, is an organophosphorus salt with CAS No. 225789-38-8. It is one of the most widely used halogen-free flame retardants for engineering plastics. As a white, free-flowing crystalline powder, AlPi offers strong flame-retardant efficiency at low loading while preserving the mechanical and electrical properties of the host polymer.

How Does AlPi Work?

AlPi acts through a dual-phase flame-retardant mechanism:

• Gas phase: at high temperature it releases volatile diethylphosphinic acid radicals that trap combustion free radicals and interrupt the flame reaction chain.
• Condensed phase: it forms an aluminum-rich phosphate char layer on the polymer surface, which acts as a physical barrier against heat, oxygen and flammable gas transfer.

This combination gives AlPi excellent performance in glass-fiber-reinforced systems, where conventional halogenated additives often lose efficiency due to the 'wick effect.'

Where Is AlPi Used?

AlPi is mainly applied in:

• Polyamides: PA6 and PA66, especially glass-fiber-reinforced grades
• Polyesters: PBT and PET
• Thermosets: epoxy resins and adhesives
• Electrical & electronics (E&E) parts such as connectors, switches, plugs, PC fans, relay housings and structural components
• Wire & cable sheathing and insulation

At typical loadings, AlPi can reach UL94 V-0 (0.4–1.6 mm) in reinforced PA and PBT compounds.

Key Benefits

• Halogen-free and antimony-free, meeting RoHS and environmental demands
• Good relative tracking index (CTI) and electrical insulation
• Lower smoke density than many brominated systems
• Limited impact on mechanical strength compared with inorganic fillers
• Suitable for recyclable engineering-plastic compounds
• A cost-effective alternative to branded grades such as Exolit OP 1230 / OP 1240

Typical Loading & Handling

Recommended addition levels are usually 10–20 wt% depending on the polymer, glass-fiber content and target UL94 rating. AlPi is commonly masterbatched or direct-fed during compounding. It should be dried before processing and dispersed uniformly to avoid surface blooming.

Summary

Aluminum diethylphosphinate (AlPi, CAS 225789-38-8) is a high-efficiency, halogen-free flame retardant designed for PA, PBT and epoxy applications. Its dual gas-/condensed-phase mechanism, good electrical performance and compliance with halogen-free regulations make it a preferred choice for E&E manufacturers and compounders worldwide.