Synthesis Of Rare-earth Based Flame Retar-Dant And Its Flame Retardancy And Suppressing "Candlewick Effect" Of PA6/CF Composites

Although the carbon fiber reinforced polyamide 6(PA6/CF)composite is a kind of reinforced material with high performance,the application of PA6/CF composites is greatly limited due to the flammability of PA6 itself and the serious melting drops in the combustion process,coupled with the "candle wick effect" caused by carbon fiber.Therefore,it is necessary to improve the flame retardancy of PA6/CF composites.Aluminum diethylhypophosphate(ADP)is a widely used flame retardant with high flame retardant efficiency for PA6,but it requires a large amount of addition when used alone and causes large smoke because of the vapor phase flame retardant effect,so it is often combined with other flame retardants to improve flame retardant efficiency.Rare earth compounds can be catalyzed into carbon efficiently in the process of polymer combustion,and have good condensed phase flame retardant effect,so they are often used as flame retardant synergies.In this paper,three kinds of rare earth compounds were synthesized to prepare PA6/CF flame retardant composites by compounding with ADP.Firstly,cerium enediamine tetramethylene phosphonate(CeEDTMP)was synthesized by hydrothermal method and then compounded with ADP to prepare PA6/CF flame retardant composites.The results showed that when 1 wt%CeEDTMP and 9 wt%ADP are added,the limiting oxygen index(LOI)of PA6/CF can be increased from 25.5%to 33.8%and pass the UL94 V-1 grade.However,when 10 wt%ADP is added alone,PA6/CF-10ADP had no grade in UL94 test,indicating that CeEDTMP and ADP had good synergistic flame retardancy.Studies on the flame retardant mechanism showed that CeEDTMP could promote the matrix crosslinking into carbon in the agglutinate phase.On the one hand,the carbon layer can cover carbon fiber to weaken its "candle wick effect";on the other hand,it could play the role of oxygen insulation and heat insulation to inhibit the combustion of materials,so as to achieve flame retardant.In addition,the addition of CeEDTMP reduced the tensile strength and elongation at break of PA6/CF composites,but had no significant effect on Young’s modulus.Secondly,in order to further improve the flame retardant properties of PA6/CF and reduce the adverse effects of flame retardants on the mechanical properties of materials,lanthanum phenylphosphonate(LaPP)was synthesized by hydrothermal method,and PA6/CF flame retardant composite was prepared by compounding with ADP.The results showed that LaPP had a layered nanocrystalline structure with excellent thermal stability and charcoal-forming properties.When 3 wt%LaPP and 8 wt%ADP were added,the PA6/CF composite passed the UL-94 V-0 grade with a LOI of 35.5%.What is more,compared with PA6/CF-11ADP,the total heat release(THR)and total smoke release(TSR)of PA6/CF-8ADP-3LaPP were reduced by 8.1%and 17.7%,respectively.The flame retardant mechanism showed that LaPP could play the flame retardant effect in condensed phase by promoting the matrix carbonization,alleviating the "candle wick effect",and had synergistic flame retardant effect with ADP,which could improve the flame retardant performance of PA6/CF composites,and achieve the effect of heat and smoke suppression.However,the interfacial adhesion between LaPP of lamellar structure and PA6 matrix is weak,resulting in stress concentration and a decrease in the elongation at break of PA6/CF composites.Finally,in order to further study the flame retardant effect and mechanism of rare earth phenylphosphonate,layered nanocrystals of cerium phenylphosphonate(CeHPP)were synthesized by hydrothermal method,and PA6/CF flame retardant composites were prepared together with ADP.When CeHPP was added into PA6/CF,the thermal stability and charring property of PA6/CF composites could be improved effectively.At the same time,CeHPP and ADP had excellent synergistic flame retardancy.When 2 wt%CeHPP and 8 wt%ADP were added,the PA6/CF composite could pass the UL-94 V-0 grade with a LOI of 35.6%,and its THR and TSR were reduced compared with PA6/CF-10ADP,especially the TSR decrease by 20.9%,showing better heat and smoke suppression effect.Similar to LaPP,CeHPP of lamellar structure had weak interfacial bonding with PA6,which had an adverse effect on the mechanical properties of PA6/CF composites.