Synthesis Of A Phosphorus-silicon-Boron Based Flame-Retardant And Its Application In Polyamide6

Polyamide6(PA6) is widely used in all economic sectors with its excellent mechanicalproperties, wear resistance, heat resistance, electrical insulation and weather resistance. ButPA6is a flammable material of which the flames can spread rapidly because of its meltingdrops. Therefore, it is of important significance to develop flame-retarded PA6with excellentcomprehensive properties.9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO) is a novel phosphorscontaining reaction intermediate, DOPO and its derivatives which have less halogen andtoxins and are less likely to divert have been widely used in a variety of polymer as flameretardants in recent years. Organic polysiloxane has the dual performance of organic polymerand inorganic silicon compounds. In recent years, it increasingly arouses concern as a highefficient, non-toxic, low smoke, and environment-friendly flame-retardant. It is also foundthat organic polysiloxane can react with DOPO or boric acid (B(OH)3) to get a better asynergistic flame-retardant.In this paper, a novel Phosphorus-Silicon-Boron based flame-retardant was designed andsynthesized by a two-step reaction: DOPO and vinyl trimethoxy silane (A171) throughaddition reaction to get PSi intermediates, which then reacted with B(OH)3to produce PSiB.We studied the influence of reaction temperature, reaction time and material confect on thereaction yield and thermostability of PSiB，and concluded that the best reaction conditionswas: reaction material confect was DOPO: A171: B (OH)3=1:1:1; the second step reactiontemperature was150℃; the second step reaction time was5h. With these conditions, thePSiB was obtained in90.3%yield as a white solid. The chemical structure of PSiB wascharacterized by FTIR,1H NMR,31P NMR,29Si NMR and11B NMR. The thermal stability ofPSiB was investigated by TG，the results showed that the initial decomposition temperature ofPSiB in nitrogen and air were respectively364.0℃and353.3℃, far higher than theprocessing temperature of PA6, and the residue in800℃were respectively50.7wt%and55.9wt%. With these properties, PSiB meets the basic requirements of PA6asflame-retardants.The PSiB was incorporated into PA6to improve its flame-retardance, flame-retardancy gradually increased with increasing amount of PSiB. When20wt%PSiB was added in PA6,the flammability achieved UL94V-0rating, and cone calorimeter tests also showed a goodflame-retardancy of PA6. The structures of the char formed after cone calorimeter tests wereinvestigated by SEM, and the results showed that PSiB flame-retarded PA6formed thecontinuous and close outer surface of char layer, which protected the underlying materialsfrom further burning. We conjectured that the condensed phase flame-retardant mechanismwas the main. With the adding of PSiB, PSiB flame retarded PA6can maintain goodmechanical properties of PA6and improve the processing properties of PA6at the same time.We also found that PSiB can reduce the crystallization temperature, crystallization rate anddegree of crystallinity of PA6，while improving the glass transition temperature and internalenergy loss of PA6.PA6fleme-retarded by the combination of PSiB and magnesium hydroxide (MH)showed evident synergistic flame-retardancy. When the amount of MH was60wt%, theflammability of PA6achieved UL94V-0rating, while combining45wt%MH and5wt%PSiB imparts a LOI of42.1%and UL94V-0rating to PA6. Compared to the PA6/MH series,the heat release rate and total heat release of PA6/MH/PSiB series declined, and the structureof the carbon residue after the cone calorimeter test were more continuous and closer. TGresults showed that PA6/MH/PSiB series have higher thermal stability than PA6/MH series.The adding of PSiB, improved the compatibility of PA6and MH obviously, thus improvingthe mechanical properties, processing properties, crystal properties of flame-retardant PA6.PSiB also reduced MH’s obstructive effect on the movement of PA6carbon chain, whichmade the dynamic mechanical behavior of flame-retarded PA6close to pure PA6and reducethe impact of adding flame-retardants.