Preparation And Properties Of Flame Retardant Bio-based And Semi-aromatic Polyamides Modified By Synergetic Aluminum Diethylphosphinate

As the main varieties of engineering plastics,aliphatic and semi-aromatic polyamides with excellent comprehensive properties have been applied in aerospace,transportation,electronic appliances and other fields which require strict flame retardant properties.Aluminum diethyl hypophosphite(ADP)is always used as an efficient flame retardant component adding to polycaprolactam(PA6)and polyhexamethylene adipamide(PA66).When it comes to flame retardant research of aliphatic bio-based polyamides and semi-aromatic polyamides,the synergistic system and its mechanism still need to be further studied.Therefore,this dissertation investigated the flame retardant effect of ADP when used to modified some varieties of aliphatic bio-based polyamides and semi-aromatic polyamides by melt blending.In addition,melamine cyanurate(MCA),organic montmorillonite(OMMT)or nano-silicon dioxide(Si O₂)were selected as synergistic components to improve the flame retardant performance.And the mechanism of synergetic flame retardant was analyzed.(1)When using ADP as the flame retardant and MCA as a synergistic component to modified polypentamyl adipamide(PA56)and poly sebacate decanediamide(PA1010),PA56/7ADP/1MCA and PA1010/12ADP/2MCA could achieve a V-0 rating with the limiting oxygen index(LOI)of30.5%and 30.6%,respectively.When only using ADP as the flame retardant,the optimized composition was PA56/8ADP and PA1010/14ADP,indicating that the synergistic effect of ADP and MCA in PA56 and PA1010 was not obvious.The study on the flame retardant mechanism showed that the ADP/MCA system took effects both in the condensed phase and gas phase.On the one hand,the higher residual carbon content,denser carbon layer,reduced spline damage length and smoke emission when heating suggested the condensed phase.On the other hand,due to the existence of small molecules in the gas phase released form the decomposition of MCA,the surface of the combustion carbon layer was uneven and the A_D:A_G value in Raman spectrum increased with the diluting oxygen and flammable gases.In case of structural properties,the introduction of ADP and MCA resulted in an increase in the crystallization temperature of PA56 and PA1010 and a decrease in tensile strength and elongation at break.(2)When using ADP as the flame retardant,OMMT and Si O₂ as synergistic components to modified poly(hexamethylene terephthalamide)-co-polycaprolactam(PA6T/6),polynonyl terephthalamide(PA9T),polydecyl terephthalamide(PA10T)and poly-m-xylylene adipamide(PAMXD6),PA6T/6-8ADP/1OMMT/0.5Si O₂,PA9T/14ADP/2OMMT/0.5Si O₂,PA10T/12ADP/2OMMT/0.5Si O₂ and PAMXD6/1ADP/1OMMT ADP could achieve a V-0 rating with the LOI of35.2%,46.8%,43.4%and 29.5%,respectively.When only using ADP as the flame retardant,the optimized composition was PA6T/6-10ADP,PA9T/28ADP,PA10T/28ADP and PAMXD6/4ADP,indicating OMMT,Si O₂ and ADP had a good synergistic flame retardant effect.The study on the flame retardant mechanism showed that the ADP/OMMT/Si O₂ system took effects mainly in the condensed phase,causing increased amount of residual carbon and improved strength of carbon layer after heating.At the same time,the introduction of ADP/OMMT/Si O₂resulted in a decrease in melting point and crystallization temperature of PA6T/6,PA9T and PA10T,while the introduction of ADP/OMMT resulted in exothermic crystallization when heating because of the changing of the crystal form of PAMXD6 and increased elongation at break.