Preparation And Performance Of Flame-retardant Polyamide 6 And 6,6 Fibers Based On Metal Salts Of Alkylphosphinate

Polycaprolactam(PA6)and poly(hexamethylene adipamide)(PA66)(collectively known as polyamides,PA)have excellent properties,such as high strength,wear-resisting,high resilience and so on.But their limit oxygen index(LOI)value is only 21-22%,burning in the air and generating a number of flaming molten drops,which easily result to spot fire.In this paper,Aluminum diethylphosphinate(ADP),Zinc diethylphosphinate(ZDP),Melamine cyanurate(MCA),N,N'-ethylene-bis(tetrabromophthalimide)(EPT)and Antimony trioxide(ATO)were selected to modify flame retardancy of PA and improve their anti-dropping and self-extinguishing-away-fire.And a series of flame-retardant PA fibers were produced by blending in twin screw and melt spinning.Their flame-retardant mechanism and properties were signified and analyzed by UL-94,LOI,SEM,Py-GC/MS,FT-IR,TG,DSC,Tensile strength of single fiber and multifilament and so on.(1)Flame-retardent sections of PA/ADP/MCA were prepared.And PA6/8ADP and PA66/6ADP reached to V-0 about UL-94,and their LOI values were 28.6%and 30.6%.Moreover,PA6/7ADP/2MCA and PA66/5ADP/1MCA also reached to UL-94 V-0 with 28.9%and 29.7%LOI values,which implied that adding MCA could decrease the price of raw material,favorable to market.The flame-retardent mechanism of PA/ADP/MCA was gas phase and condensed phase flame retardant synergism:In gas phase,phosphinic radical,generated during splitting decomposition of ADP,could cancellate flammable small molecular substances(FSMS),while CO₂,H₂O and NH₃,produced from decomposition of MCA,could play a diluting FSMS role.In condensed phase,curing reaction between PA and ADP was not happened before decomposition of PA,but Al⁺³ could combine with splitting carbon bone in the form of Al-O,forming cross-linked carbon layer.In addition,inert gases,generated by composition of MCA,played a swelling char layer role during foaming.And compared with PA,the high-temperature residue mass of PA/ADP increased,which implied that ADP had excellent carbon formation effect.And adding MCA into PA/ADP,compared to PA/ADP,the residues mass had improved more or less.What's more ADP and MCA had a little effect on melt behavior of PA,but crystallization temperature(T_c)and degree of crystallinity of PA were reduced by increasing ADP contents.And Owning to hydrogen-bond interaction between MCA and PA,the contents of?crystal-form of PA decreased,even disappeared.T_c and degree of crystallinity were increased by adding more MCA.(2)Flame-retardent sections of PA/ZDP/EPT/ATO were prepaered.And, PA6/6ZDP/4EPT/2ATO and PA66/6ZDP/4EPT/2ATO got to V-0 and V-2 level about UL-94with LOI values of 29.4%and 29.1%,and self-extinguishing-away-fire and anti-dropping of PA were obviously improved.The flame-retardent mechanism of PA/ZDP/EPT/ATO was also gas phase and condensed phase flame retardant synergism:In gas phase,phosphinic radical,Br·,benzodiazepines residues of EPT was detected during splitting of ZDP and EPT.Phosphinic radical and Br·could react with FSMS,decreasing the number of FSMS radicals and retarding combustion.The difficult-flammble benzodiazepines residues of EPT could combine with-NH₂radicals,playing a role of capturing free radical and diluting combustible gases.In condensed phase,before decomposition of PA,curing reaction was not happened between PA and ZDP/EPT/ATO,while metal ion could combine with splitting carbon bone in the form of M-O,forming cross-linked char layer and promoting char form.And ATO made the cross-linked char layer stronger and more,improving residue mass.The decomposition temperature of PA would be decreased by adding EPT/ATO,while adding ZDP could improve the decomposition temperature of PA.ZDP had a little effect on crystallization and melting behaviors of PA.However,owning to hydrogen-bond interaction between imide bond of EPT and amido bond of PA,the contents of?crystal-form of PA decreased,even dispeared.And T_c and degree of crystallinity increased first and then decreased.(3)Flame-retardent fibers of PA/ADP/MCA and PA/ZDP/EPT/ATO were prepared.The single fiber tensile strength of PA6/10ADP,PA67ADP/2MCA,PA6/6ZDP/4EPT/2ATO and PA66/6ADP fibers was 2.9,2.8,3.9 and 2.9 c N/dtex,and their LOI value was 27.1,25.1,27.5 and27.4%,possessing relatively good self-extinguishing-away-fire and anti-dropping properties.ZDP/EPT/ATO was more suitable to modify the flame retardancy of PA6 fiber,owning to its more contents and better mechanical strength and flame retardancy,while ADP was more appropriate for modifying the flame retardancy of PA66 fiber.The degree of orientation and crystallinity first increased and then decreased with increasing ADP contents.But the degree of orientation and crystallinity decreased,when EPT and MCA were added In addition,adding flame retardant could make the moisture rate and water absorption of flame-retardant PA slightly lower.