Polymeric Flame Retardants: a Promising Category for Enhanced Performance

Abstract

The flame retardancy for polymers is very demanding as a lot of polymers are flammable and decompose into small and volatile hydrocarbons upon pyrolysis. In the past, most effective flame retardants for polymers are halogen-based. With the increasing regulatory requirements on safety and environments, halogen-based flame retardants are gradually being replaced with non-halogenated flame retardants. Inorganic metal hydroxides, mainly aluminum hydroxide (ATH) and magnesium hydroxide (MDH), are the largest class of flame retardants by volume. Other non-halogenated flame retardants, such as phosphorus-, nitrogen- and silicon-based, show promises for this property. The up-to-date technique gaps are: (1) for inorganic flame retardants, high loading of 40 - 60 wt% is required, leading to worse mechanical properties and heavy weight, (2) for current non-halogenated ones, most of them are small molecules. Such small flame retardant molecules have relatively poor thermal stability and mechanical strength, and will slowly leach out from the composites surface, leading to performance deterioration and possible environmental pollution. The development of new flame retardants with higher efficacy, lower loading, higher strength and high stability are therefore in need. Targeting this, we have developed new flame retardants with polymeric nature, which theoretically possess the above advantages over the current ones, and demonstrated their effectiveness in various polymers like polypropylene, polyamide. The flame retardant long chains will entangle with polymer matrix chains, stabilizing the whole composites without leaching issues.