Reactive and Additive Modifications of Styrenic Polymers with Phosphorus-Containing Compounds and Their Effects on Fire Retardance

Abstract

Polystyrene, despite its high flammability, is widely used as a thermal insulation material for buildings, for food packaging, in electrical and automotive industries, etc. A number of modification routes have been explored to improve the fire retardance and boost the thermal stability of commercially important styrene-based polymeric products. The earlier strategies mostly involved the use of halogenated fire retardants. Nowadays, these compounds are considered to be persistent pollutants that are hazardous to public and environmental health. Many well-known halogen-based fire retardants, regardless of their chemical structures and modes of action, have been withdrawn from built environments in the European Union, USA, and Canada. This had triggered a growing research interest in, and an industrial demand for, halogen-free alternatives, which not only will reduce the flammability but also address toxicity and bioaccumulation issues. Among the possible options, phosphorus-containing compounds have received greater attention due to their excellent fire-retarding efficiencies and environmentally friendly attributes. Numerous reports were also published on reactive and additive modifications of polystyrene in different forms, particularly in the last decade; hence, the current article aims to provide a critical review of these publications. The authors mainly intend to focus on the chemistries of phosphorous compounds, with the P atom being in different chemical environments, used either as reactive, or additive, fire retardants in styrene-based materials. The chemical pathways and possible mechanisms behind the fire retardance are discussed in this review.

The Flame-Retardant Mechanisms and Preparation of Polymer Composites and Their Potential Application in Construction Engineering

“…The heat generated in this process is fed back to the condensed phase of the polymer system to maintain the combustion process. In addition, polymer materials tend to melt and flow, forming pools of flammable degradation products, which may constitute a very serious secondary fire hazard as this usually leads to further fire or the burning of surrounding fuel loads [ 29 , 30 ].…”

The influence of phosphorus- and nitrogen- containing groups on the thermal stability and combustion characteristics of styrenic polymers

“…Among the halogen-free FR options, phosphorus (P-)based compounds are found to be relatively less toxic yet effective [4]. Several studies carried out in recent years have been focused on P-containing compounds acting as FRs for styrenic polymers, including red phosphorus, phosphine oxides, inorganic and organic phosphates, or blends of P-containing compounds with other FRs [5]. However, relatively high loadings (20-40 mass%) of additive FRs are normally required to achieve acceptable levels of fire retardance.…”

“…Thus, as an alternative (i.e. reactive FRs), certain P-containing compounds can be used for the chemical modification of PS via a radical polymerisation technique [5]. Among the various P-containing reactive FRs for PS, unsaturated organophosphorus compounds are considered to be the preferred options, as they can be chemically bonded to the polymeric chains through the chain-growth processes [6].…”

Mode of Action of Condensed- and Gaseous-Phase Fire Retardation in Some Phosphorus-Modified Polymethyl Methacrylate- and Polystyrene-Based Bulk Polymers

“…These flame retardants may be mixed as additives in the polymer matrix by physical means. Another way of improving flame retardancy is to prepare inherently less flammable polymers through the copolymerization with compounds that can impart fire resistance [ 10 , 11 ]. Organohalogen compounds are primarily used for this purpose as they are excellent in reducing the flammability of polymers.…”

“…However, the environmental toxicity of these materials caused a ban on their use for commercial purposes. Therefore, inorganic fillers such as magnesium hydroxide, graphene oxide and modified nanoparticles such as clays and silica, etc., and phosphorus-containing compounds are now more commonly used [ 11 ]. The efficiency of phosphorus-based compounds generally depends on several factors: the chemical environment and oxidation state of the P atom, volatility, and the nature of the decomposition products formed upon thermolysis, etc.…”