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 Many well-known halogen-based fire retardants, regardless of their chemical structures and modes of action, have been withdrawn from built environments in the European Union, USA, and Canada.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 effects of covalently bound phosphorus (P-) and nitrogen (N-) bearing groups on the thermal and combustion attributes of polystyrene have been investigated. The necessary chemical modifications were achieved through co- and ter-polymerisation reactions, in a suitable solvent, under radical initiation conditions. The influence of P–N cooperative interactions on the combustion properties of styrenic polymers was studied. The co-monomers of interest included: diethyl(acryloyloxymethyl)phosphonate (DEAMP), diethyl-p-vinylbenzylphosphonate (DEpVBP), acrylic acid-2-[(diethoxyphosphoryl)methyl amino]ethyl ester (ADEPMAE) and maleimide (MI). For the first time, the ter-polymers of styrene containing both P- groups, DEAMP or DEpVBP, and N- groups, MI, were prepared via solution polymerisation. It was found that the thermal stability and combustion characteristics of polystyrene were significantly altered by the presence of nominal amounts of P- and N- containing groups, and, in certain cases, cooperative interactions of these groups were also evident. For instance, the extents of char formation post-degradation of the prepared ter-polymers, as revealed by thermogravimetric investigations in an inert atmosphere (nitrogen), were found to be enhanced by more than 20%, as compared to the unmodified polystyrene. The heat release rates and heat release capacities of the ter-polymers, as measured using the pyrolysis combustion flow calorimetric (PCFC) technique, were reduced by almost 50% in comparison to the same parameters obtained for the unmodified counterpart.
There is a piqued interest in development of biobased sorbents for water treatment. Here in we reported, the fabrication of mechanically strong nanopapers by mixed dimensional assembly of 1D Cellulose nanofibers and 2D amino functionalized graphene oxide for water treatment. The fabricated amino functionalized GO/ cellulose nanofiber (AMGO-CNF) nanopaper showed superior antibacterial resistance towards Escherichia coli MTCC 1610 and Klebsiella due to the enhanced surface roughness which was confirmed from SEM and AFM studies. The amino group present in the AMGO enhanced the adsorption efficiency of the nanopaper towards methyl orange dye. The fabricated nanopaper showed an adsorption of 11.05 mg/gm 30 mg/L concentration at pH 2. Maximum adsorption was observed at pH 2 which was due to protonation of amine group. Moreover, the fabricated membrane showed excellent hydrolytic stability which can be corroborated to the surface roughness and reduced hydrophilicity. The investigation into the surface chemistries of cellulose nanofibers beyond the adoption of toxic solvents can enhance the economic usefulness of the process and yield a new eco-friendly adsorbent material that is agreeable to adsorbing various toxic pollutants.
Polystyrene (PS) was modified by covalently binding P-, P-N- and/or N- containing fire-retardant moieties through co- or ter-polymerization reactions of styrene with diethyl(acryloyloxymethyl)phosphonate (DEAMP), diethyl-p-vinylbenzyl phosphonate (DEpVBP), acrylic acid-2-[(diethoxyphosphoryl)methylamino]ethyl ester (ADEPMAE) and maleimide (MI). In the present study, the condensed-phase and the gaseous-phase activities of the abovementioned fire retardants within the prepared co- and ter-polymers were evaluated for the first time. Pyrolysis–Gas Chromatography/Mass Spectrometry was employed to identify the volatile products formed during the thermal decomposition of the modified polymers. Benzaldehyde, α-methylstyrene, acetophenone, triethyl phosphate and styrene (monomer, dimer and trimer) were detected in the gaseous phase following the thermal cracking of fire-retardant groups and through main chain scissions. In the case of PS modified with ADEPMAE, the evolution of pyrolysis gases was suppressed by possible inhibitory actions of triethyl phosphate in the gaseous phase. The reactive modification of PS by simultaneously incorporating P- (DEAMP or DEpVBP) and N- (MI) monomeric units, in the chains of ter-polymers, resulted in a predominantly condensed-phase mode of action owing to synergistic P and N interactions. The solid-state 31P NMR spectroscopy, Scanning Electron Microscopy/Energy Dispersive Spectroscopy, Inductively-Coupled Plasma/Optical Emission Spectroscopy and X-ray Photoelectron Spectroscopy of char residues, obtained from ter-polymers, confirmed the retention of the phosphorus species in their structures.
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