Synergistic effect of phosphorus and nitrogen-containing groups in fire retardancy of polystyrene

Abstract

The relative high flammability of polystyrene (PS) often restricts its wider applicability as an insulation material in the building and construction sector. The primary strategies to improve the fire retardance of styrene-based polymers are largely reliant on the use of halogenated fire retardants, which are considered hazardous to public health and the environment. Hence, many halogen-based fire retardants have already been withdrawn from the products used as construction elements in built environments. Amongst the possible halogen-free alternatives,phosphorus(P)-containing compounds have gained great attention owing to their excellent fire retarding efficiencies and environmentally benign attributes. In other previous studies, several organic phosphonates were found to be effective in inhibiting the ignition propensities and suppressing the combustion of styrene-based polymers. These effects were thought to arise from both gaseous- and condensed-phase inhibitory actions of the P-bearing groups.

In the current study, the primary focus is to chemically modify polystyrene with P-containing moieties. The selected P-containing monomers include diethyl (acryloyloxymethyl) phosphonate (DEAMP), diethyl-p-vinylbezyl phosphonate (DEpVBP), and acrylic acid-2-[(diethoxyphosphoryl) methyl amino] ethyl ester (ADEPMAE). Meanwhile, different nitrogen-containing compounds such as imides, amides and nitrile are selected to prepare styrenic copolymers. The modified styrenic polymers were prepared by solution polymerisation techniques. With a view to further improve the fire retardance of PS, tried to chemically bindthe above-mentioned phosphorus- and nitrogen-containing groups for the first time, via a terpolymerization route, thus exploring possible P-N synergism. The characterisation of the modified materials with regard to their thermal degradation characteristics and combustion attributes is studied. Furthermore, the influence of the chemical environments of P and N atoms within the FR groups on the thermal behaviours and combustion characteristics of the modifiedpolymers is also discussed. The comparison of thermal and combustion behaviours of polymers confirmed that the ter-polymers are more efficient in enhancing the thermal stability and combustion inhibition of polymer rather than the corresponding co-polymers. In addition, the use of N-containing monomers alone cannot exert a notable fire-retardant effect. However, the use of N compounds in combination with P-containing monomers, in nominal amounts, exerted synergistic actions and imparted a significant reduction of the thermal degradation and combustion characteristics of polymers.

Date of Award	Mar 2024
Original language	English
Supervisor	Jianping Zhang (Supervisor) & Seng-Kwan Choi (Supervisor)