Ammonium Polyphosphate-pentaerythritol Research Articles

Sulfenamides in synergistic combination with halogen free flame retardants in polypropylene

Sulfenamide based radical generators that contain a nitrogen-sulfur (N-S) core, can alone provide flame retardancy in polypropylene (PP), polyethylene and polystyrene, as we have earlier demonstrated. Herein, sulfenamides potential as synergists with conventional halogen free flame retardants has been explored. Thus, five different sulfenamides were individually combined with selected eco-friendly, phosphorus based flame retardants or aluminium trihydroxide (ATH), and their effect on polypropylene flammability was assessed by limiting oxygen index (LOI), vertical flammability (UL 94 V) and cone calorimeter tests. Thermogravimetric analysis (TGA) and nuclear magnetic resonance (NMR) studies were carried out to detect changes in thermal behaviour when such two component FR systems were mixed together at different ratios. TGA-FTIR (thermogravimetric analysis-Fourier transform infrared spectroscopy) was used to investigate the differences in decomposition products of non-flame retarded versus flame retarded PP. Strong synergistic effects were observed, and the UL 94 V-0 rating was reached for PP with a total FR loading of 10 wt% using 8 wt% of phosphonate ester AFLAMMIT®PCO 900 together with 2 wt% of sulfenamide flame retardant. In a ternary mixture of an additional phosphazene additive (SPB-100), the needed total concentration for V-0 rating was further reduced to 9 wt%. In addition, the combination of 4 wt% of aluminum hypophosphite (AHP) with 0.5 wt% of sulfenamide offered a unique halogen free solution for achieving UL 94 V-2 rating in PP. Cone calorimeter studies of an ammonium polyphosphate-pentaerythritol based intumescent system in combination with 0.5 wt% of sulfenamide also showed encouraging results. The char stability was enhanced, the peak of heat release rate (HRR), CO and CO2 production and total smoke generation were all reduced compared to the reference sample without sulfenamide.

3D-map modelling for the melting points prediction of intumescent flame-retardant coatings

The applicability of 3D map modelling for melting point prediction was studied. The melting points in the ammonium polyphosphate–pentaerythritol–melamine chemical system of intumescent flame-retardant coatings over a wide range of concentrations were collected. The ternary diagram (triangle) of the melting points was plotted and an approximated 3D map was built for the range 205–345°C. The present work contains the thermal data for the observed ternary system and provides a new graphic system for making predictions for intumescent flame-retardant coatings. The applicability of the calculated 3D map for obtaining experimental samples of fire-retardant paints with a low melting point for thin steel constructions was shown.

Synthesis and Application in Polypropylene of a Novel of Phosphorus-Containing Intumescent Flame Retardant

A novel phosphorus-containing triazine oligomer poly(2-morpholinyl-4-penta-erythritol phosphate-1,3,5-triazine) (PMPT) was synthesized as a kind of tri-component intumescent flame retardant (IFR). The chemical structure of PMPT was characterized by FTIR, 1H-NMR and 31P-NMR, and the mechanical and flammability properties of FR-PP were measured. The FTIR results showed that the expected chemical reactions had happened at each step. The 1H-NMR and 31P-NMR spectra also agreed with the chemical structure of PMPT. The slight effect of PMPT on the mechanical properties of FR-PP suggested that PMPT and PP are compatible. The high limited oxygen index (LOI) values of FR-PP revealed that PMPT was an efficient IFR and there was the synergistic effect between PMPT and ammonium polyphosphate/ pentaerythritol (APP/PER).

Synergy in intumescence—application to β-cyclodextrin carbonisation agent in intumescent additives for fire retardant polyethylene formulations

The study first compares the FR performances of ammonium pyrophosphate (PY)-xylitol, PY-d-sorbitol and PY-β-cyclodextrin additives systems with the classical ammonium polyphosphate-pentaerythritol intumescent system in low density polyethylene(LDPE)-based formulations. It shows that β-cyclodextrin, a starch derivative, whose thermal degradation leads to high amounts of carbonaceous residue, is not a carbon source of interest in intumescent FR additives for LDPE-based formulations. A comparative study using X-ray diffraction and Raman spectroscopy shows that the absence of the FR property may be connected both to the development of a free radical reaction in the additive system in the temperature range corresponding to processing reactions and to the presence of a crystalline phase in the carbonaceous materials formed from the additive. Secondly, it is shown using the Sheffé procedure for experiments with mixtures that a synergistic effect exists in the ammonium pyrophosphate-d-sorbitol-β-cyclodextrin system. In particular, the method gives the corresponding composition of the additive mixture. The improved performance is explained by the formation of a large amount of carbonaceous residue when the formulation degrades. Moreover, the synergistic effect is discussed as a competition between antagonistic effects related to chemical characteristics of the char: amounts of free radical in carbon, structural organisation of the char and the presence of crystalline phases.

Carbonization mechanisms resulting from intumescence-part II. Association with an ethylene terpolymer and the ammonium polyphosphate-pentaerythritol fire retardant system

In this work we study the carbonization resulting from an intumescence phenomenon of the fire-retardant formulation: ethylene terpolymer-ammonium polyphosphate/pentaerythritol. Characterisation of the intumescent coating is carried out using infrared spectroscopy and MAS-NMR of the solid state. The study shows the formation of organic phosphocarbonaceous esters, which limits depolymerisation or the evolution of gaseous hydrocarbons. These esters prevent the development of condensed polyaromatic structures. These latter are bridged by the polyethylenic links, which provide the mechanical properties of interest in the protective shield.

Carbonization mechanisms resulting from intumescence association with the ammonium polyphosphate-pentaerythritol fire retardant system

In this work we study the thermal behavior of an ammonium polyphosphate-pentaerythritol mixture, fire-retardant additive for polyolefins and most particularly the carbonization process resulting from an intumescent phenomenon. The study has been carried out using Micro-Raman and 13C, 1H, 31P NMR of the solid state spectroscopies. It is shown that the structure consists in phoscarbonaceous and polyaromatic species. These latter form an anisotropic structure above 280°C. This structure grows when the temperature increases. Finally, a reactional scheme of the carbonization of the intumescent system is proposed.

Thermal Behaviours of Ammonium Polyphosphate-Pentaerythritol and Ammonium Pyrophosphate-Pentaerythritol Intumescent Additives in Polypropylene Formulations

The comparative study of the intumescent formulations (poly propylene-ammonium polyphosphate-pentaerythritol) and (polypropylene- ammonium pyrophosphate-pentaerythritol) shows that the highest fire retar dance property of the second system may be related to the existence of a protective carbonaceous coating stable in the temperature range 300-550°C. Comparatively, the stability of the carbonaceous coating on the first system is only observed between 300 and 420°C. A31P N.M.R. study shows the presence (in the carbon-based layers) of acidic phosphate species (Lewis acids) which result from the thermal degradation of the additive mixtures. In the particular case of (PP-PPA-PER), these species degrade at 420 ° C to give phosphorus oxide. The study reveals that, with (PP-PY-PER), an additional protective char (stable in the temperature range 420-550°C) is formed by a reaction between the Lewis acids and the oxidized products of the thermo-oxidative degradation of the polymer.

Study of the mechanism of intumescence in fire retardant polymers: Part VI—Mechanism of ester formation in ammonium polyphosphate-pentaerythritol mixtures

It is shown that, on heating ammonium polyphosphate-pentaerythritol mixtures, phosphoric ester bonds are formed first by alcoholysis of the polyphosphate chain. Further intramolecular alcoholysis and/or esterification leads to cyclic pentaerythritol phosphate structures inserted in the polyphosphate chains. Evidence is also given of intermolecular dehydration of pentaerythritol in mixtures with a large excess of alcoholic hydroxy groups over phosphorus atoms. The intumescent behaviour of the mixtures is discussed in relation to the final structure of the product of reaction which depends on the composition of the original mixture.

Study of the mechanism of intumescence in fire retardant polymers: Part III—Effect of urea on the ammonium polyphosphate-pentaerythritol system

Urea, which is commonly used as a ‘blowing’ co-additive in intumescent coatings, is shown to depress intumescence when it is added to ammonium polyphosphate-pentaerythritol mixtures incorporated into the bulk of polypropylene. Concurrently, the fire retardant properties of the intumescent additive are depressed in the presence of urea although, in this case, a smaller amount of flammable hydrocarbons is evolved in the thermal degradation of the polymer.

Study of the mechanism of intumescence in fire retardant polymers: Part II—Mechanism of action in polypropylene-ammonium polyphosphate-pentaerythritol mixtures

It is shown that, by the addition of a typical intumescent mixture of ammonium polyphosphate and pentaerythritol to polypropylene, the mechanism of intumescence which develops on heating is not significantly affected by dispersion of the intumescent mixture in the polymer. On the other hand, in these mixtures, polypropylene seems to evolve, by thermal degradation, a smaller amount of flammable products than when it is heated alone. The ammonium polyphosphate-pentaerythritol additive is shown to induce fire retardant characteristics in polypropylene by means of a ‘condensed phase’ mechanism.

Study of the mechanism of intumescence in fire retardant polymers: Part IV—Evidence of ester formation in ammonium polyphosphate-pentaerythritol mixtures

Experimental evidence is given of the formation of a phosphate ester as the first step in the heat-induced reaction between ammonium polyphosphate and pentaerythritol. The reaction takes place with elimination of ammonia and water and disruption of the chain structure of the polyphosphate