Mechanism of action of phosphorus-based flame retardants in nylon 6. I: Ammonium polyphosphate

Comparison of oxygen and nitrous oxide indices indicates that ammonium polyphosphate (APP) should act in the condensed phase when added to nylon 6 (PA-6). A detailed study of the thermal degradation mechanism of PA-6/APP mixtures is carried out. A polyphosphate ester is formed on heating, which is the precursor of an intumescent char. Evidence is given of the thermal insulating action of the intumescent char which slows down the rate of combustion of the polyme

Mechanism of action of phosphorus-based flame retardants in nylon 6. III: Ammonium polyphosphate / manganese dioxide

Partial substitution of ammonium polyphosphate (APP) by manganese dioxide (MnO2) in polyamide 6 (PA-6) fire retarded with 20% of APP strongly increases the fire retardant effect. ‘Linear pyrolysis’ experiments, which are modified cone calorimeter tests, show an increase in the amount and an improvement of the shielding properties of the intumescent char formed on the surface of burning polymer. The enhancement of the yield of aliphatic–aromatic char stable to oxidation was observed in thermogravimetry under air. The fire retardant action of an APP/MnO2 mixture in PA-6 is twofold. On the one hand, this additive promotes involvement of the polymer in the charring and, on the other, the formed manganese phosphate glasses improve the thermo-insulating properties of the intumescent char on the surface of burning PA-6

Thermal degradation of cross-linked polyisoprene and polychloroprene

Polyisoprene and polychloroprene have been cross-linked either in solution or in solid state using free radical initiators. In the comparable experimental conditions higher cross-linking density was observed in the solid state process. Independent of the cross-linking method, polychloroprene tended to give a higher gel content and cross-link density than does polyisoprene. Infrared characterization of the cross-linked materials showed cis-trans isomerization occurred in the polyisoprene initiated by benzoyl peroxide, whereas no isomerization was found in the samples initiated by dicumyl peroxide. Polyisoprene does not cross-link by heating in a thermal analyzer, whereas polychloroprene easily undergoes cross-linking in such conditions. Infrared spectroscopy showed that in the case of polyisoprene, rearrangements occur upon heating which lead to the formation of terminal double bonds, while polychloroprene loses hydrogen chlorine which leads to a conjugated structure. There is apparently some enhancement of the thermal and thermal oxidative stability of polyisoprene because of the cross-linking. Cross-linked polychloroprene is less thermally stable than the virgin polymer. Cross-linking promotes polymers charring in the main step of weight loss in air, which leads to enhanced transitory char

The thermal stability of cross-linked polymers: methyl methacrylate with divinylbenzene and styrene with dimethacrylates

Cross-linking of polymers is frequently presumed to enhance the thermal stability of polymer systems. Methyl methacrylate has been reacted with divinylbenzene and styrene with various dimethacrylates. These systems have been characterized by gel content, swelling ratio, infrared spectroscopy, thermal analysis, TGA/FT-IR, and solid state NMR. Both systems show enhanced thermal stability and char formation. This is most pronounced in the cases of methyl methacrylate with divinylbenzene and styrene with bisphenol A dimethacrylate