Mechanistic Aspects of Condensed- and Gaseous-Phase Activities of Some Phosphorus-Containing Fire Retardants

Abstract

As a part of our ongoing investigations on passively fire protecting polymeric materials, we have been employing both reactive and additive routes involving phosphorus-containing compounds. These included inorganic and organic substances, and in the latter case, the phosphorus-bearing groups differed in terms of the chemical environments (phosphite, phosphate, phosphine, phosphine oxide and phosphonate ester) and oxidation state of the P atom (i.e., III, or V). The overall flammability profiles of wood substrates coated with the phosphorus-containing compounds were obtained through cone calorimetric measurements. The elemental composition, morphology and chemical natures of the char residues, obtained from the cone tests, were analysed through a variety of spectroscopic, chromatographic and spectrometric means. From the complementary information, obtained through these analyses, some probable mechanistic pathways that underpin the condensed- and gaseous-phase activities of the different additives are suggested. It was found that the inorganic solid additive, i.e., (NH4)2HPO4, underwent a two-step degradation, yielding ammonia gas and phosphoric acid. Furthermore, the liquid additives, owing to their volatility as compared to the solid ones, showed a relatively higher presence in the vapour phase than volatile fragments emanating from the latter ones (i.e., from phosphine and the phosphine oxides).

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

“…radicals into the vapour space. The corroborative evidence of this type of bond cleavage can be drawn from the pyrolysis-GC/MS studies of the solid additives [ 18 ]. However, thermal cracking of the ethyl groups (in phosphites, phosphates, and phosphonate/phosphorlaminoester) is quite feasible in producing the corresponding ‘phosphorus’ acid species with ∂ ∼ 0.0 ppm [ 19 ].…”

“…These acidic species can subsequently initiate the chemical pathway used to produce char precursors. In the case of TPP, TPPO and DOPO, it is more likely that they produce phosphorus- and/or oxygenated phosphorus-containing volatiles that can act in the gaseous-phase [ 18 ].…”

“…The detailed procedures for sample preparation, instruments used, operating parameters, and data accusation and processing, relating the various analytical instrumentation and associated techniques were published previously [ 18 ]. These involved the following: the phosphorus contents of aqueous extracts of the test samples were measured in triplicate by using Shimadzu ICPE-9000, and the average values were taken.…”

Passive Fire Protection of Taeda pine Wood by Using Starch-Based Surface Coatings

“…The solid-state NMR ( 31 P with CP/MAS mode) spectrum of the char residue was obtained by employing a 500 MHz Bruker machine at ambient probe conditions, typically at 10 kHz rotor speed, and the signals were calibrated against phosphoric acid as the external calibrant. The raw data were then processed by using a proprietary software from the manufacturer (TopSpin 4.0.6) [26,27].…”

Flame Retardancy of Biobased Composites—Research Development

“…Methods of reducing the flammability of polymers and polymeric materials obtained from petrochemical raw materials have been known for years but are constantly being developed [ 10 ]. The same methods are used for bio-composites [ 11 , 12 ]. Accordingly, in this paper, special attention is devoted to methods of reducing the flammability of composites in which the matrix is made of bio-polymers (produced by living organisms, biotechnological and chemical methods from raw materials of natural origin) and bio-polymer systems with the filler of natural origin in the form of plant fibers, as well as methods used for reducing the flammability of natural origin fibers.…”