| Polyamide,as one of the five most important synthetic materials,has the advantages of high strength,good abrasion resistance,good corrosion resistance,etc.It plays an extremely important role in military,automotive materials,civil textiles and other fields.Polyamide 6(PA6)is the first product to realize industrialization among many polyamide materials,and it is also a widely used market product.However,in actual production and application,as the limiting oxygen index of PA6 is only 22%,the vertical combustion grade is UL-94 V-2,and molten droplets are easy to appear in the combustion process,it is a flammable material,so it needs to be flame retardant modified.Among many modification methods,blending modification is widely used because of its simple operation,good effect and low cost.Among many flame retardants of polyamide,melamine and its derivative flame retardants can reduce the chain degradation rate of the system by decomposing at high temperatures to form cross-linked polycondensates,self sublimation endothermic,and decomposing inert gases,which attracts people’s attention.In addition,the triazine ring structure unit is rich in tertiary nitrogen structure and has excellent carbon formation effect.When burning,it releases nitrogen and other incombustible gases,which can promote the formation of an expansion structure of the carbon layer,so that the modified resin can both block the flammable gas and heat conduction and diffusion.There is also a stable conjugated structure in the triazine ring,which makes it have high thermal stability.Some triazine derivatives have good hydrogen bond assembly ability,which can form hydrogen bonds with carbonyl,imino and other groups in the PA6 molecular chain between molecules or within molecules.The two have potential structural compatibility,which is conducive to improving the overall performance of flame retardant polymers.Therefore,the triazine ring structure can provide functional structural units for flame retardant PA6.In this paper,the flame retardant structure with molecular structure matching was introduced into PA6 resin through blending to prepare a PA6 functional material with high expansion and carbonization efficiency.At the same time,the high-temperature gas phase micro changes and condensed phase reaction of flame retardant PA6 were tracked and studied to clarify its flame retardant and droplet resistant mechanism.1.The flame retardant PA6 was modified by the expansion charring property of the triazine flame retardant(CFA).The structure of the triazine flame retardant was studied by FTIR and NMR,and its good charring property was studied.The carbon residue reached 28.3% in nitrogen atmosphere.The effect of triazine ring flame retardant on the flame retardancy and charring property of PA6 resin was studied,and the mechanism of CFA flame retardant was explained.The results showed that the LOI of PA6 resin increased from 24.5% to 33.4%,the vertical combustion grade increased from UL-94 V-2 to UL-94 V-0,the ignition time(TTI)in cone calorimetry increased by 13 seconds,and the total smoke release(TSR)decreased by 13.3%after adding CFA flame retardant.In the air atmosphere,the carbon yield of the modified resin was more than doubled,from 1.87% to 4.84%.In the Raman test,the peak area ratio(ID/IG)of D and G peaks was increased from 3.54 to 3.78.After adding flame retardant CFA,the mechanical properties of the modified resin not only did not decline,but increased by 28.8% when the mass fraction was 8%.The flame retardant mechanism shows that the dilution effect of incombustible gas in the gas phase and the barrier effect of carbon layer in the condensed phase play a role in the combustion process.2.In order to make the modified resin have anti dripping property,the triazine ring and Schiff base flame retardant(DPTAA)were obtained by combining the triazine ring structure with the irreversible cross-linking Schiff base structure at high temperature through aldehyde amine condensation reaction.The study on the structure and properties of DPTAA shows that DPTAA still has good charring property and expansion charring property.The effect of DPTAA on the flame retardancy and charring performance of PA6 resin showed that after adding DPTAA flame retardant,LOI of PA6 resin increased from 24.5% to 30.0%,and the vertical combustion grade increased from UL-94 V-2 to UL-94 V-0.When the addition amount was 8%,no molten droplets appeared in the combustion process,so as to solve the secondary combustion problem caused by molten droplets.In the conical calorimetry,TTI increased for 14 seconds,PHRR decreased by10.4%,and TSR decreased by 2.9%.In the air atmosphere,the carbon yield of the modified resin increased nearly twice,from 2.89% to 5.64%.In Raman test,ID/IG is increased from 2.86 to 3.07.After adding flame retardant DPTAA,the mechanical properties of the modified resin not only did not decline,but increased by 14.2% when the mass fraction was 8%.3.Although DPTAA can improve the anti dripping property of PA6,its limiting oxygen index is not high,nor does it improve the total heat release of PA6.Therefore,we use phosphorus nitrogen synergistic flame retardant method to mix DPTAA and aluminum hypophosphite(ALHP)and blend them into PA6 with twin-screw for modification,so as to prepare PA6 composite resin with excellent anti dripping,limiting oxygen index and total heat release properties.The effect of DPTAA-ALHP on the flame retardancy and charring of PA6 resin was studied.The results showed that the LOI of PA6 resin increased from 24.5% to 30.9% after adding DPTAA-ALHP flame retardant,and the vertical combustion grade increased from UL-94 V-2 to UL-94 V-0.The peak value of heat release decreased by 4.3%,and the total heat release decreased by 9.23%.In the air atmosphere,the carbon yield of the modified resin was more than 3 times higher,from 5.41% to18.77%.In Raman test,ID/IG is increased from 1.81 to 3.40.Finally,the flame retardant fiber was obtained by melt spinning.The breaking strength of the fiber decreased from 2.53 c N/dtex to 1.45 c N/dtex with the addition of flame retardant. |
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