| Nylon 6(PA6),one of the most important engineering thermoplastics,has been widely used in various fields due to its good overall performances.However,the lower notched impact strength and inflammability limit its application.As a commonly used thermosetting resin,epoxy resin also has the disadvantages of poor toughness and flammability.Therefore,it is important to improve the toughness and flame-retardance of nylon 6 and epoxy resin.Silicone epoxy compounds are used to extend the molecular chains and then to improve the mechanical properties of PA6 by reacting with the terminal amine and carboxyl groups of nylon 6.At the same time,the flame retarded element silicon is introduced into the molecular chains of nylon6,which is expected to improve the flame retardancy.In addition,silicone epoxy compounds are used as reactive modifiers to improve the properties of epoxy resins,and are also used as a kind of new epoxy prepolymer.The introduction of silicone segments is also expected to simultaneously improve the toughness and flame retardancy of epoxy resin.Based on the above research background,in this paper,two novel silicon epoxy compounds were synthesized and used to modify nylon 6 and bisphenol A diglycidyl ether(DGEBA)epoxy resin.(1)Two novel silicone epoxy compounds were synthesized,namely dendritic silicone epoxy compound D1 and Schiff base silicone epoxy compound BDEP.D1 was synthesized from dimethychlorosilane,methyltrimethoxysilane and allyl glycidyl ether by the hydrosilylation reaction.BDEP was synthesized from 3,4-dihydroxybenzaldehyde,1,3-Bis(3-aminopropyl)tetramethyldisiloxane and epichlorohydrin by a two-step process.Fourier infrared transform spectroscopy(FTIR)and hydrogen nuclear magnetic resonance spectroscopy(1H-NMR)were used to characterize the structures of D1 and BDEP,and the results were consistent with the expected ones.The epoxy values of D1 and BDEP were 0.49 mol/100g and 0.56mol/100g,respectively.(2)Both D1 and BDEP were effective chain extenders for PA6.When the addition amount of D1 was 2.0 wt%,the equilibrium melt torque of PA6 was 15.3 N·m,which was 5.9 times as large as that of original PA6.Similarly,that was increased to 11.8 N·m by the same addition amount of BDEP,which was 4.6 times as large as that before modification.(3)The long chain branches were formed along with the chain extension reaction between PA6 and D1,which significantly changed the rheological properties of PA6.When the addition amount of D1 was 2.0 wt%,the zero-shear viscosity of PA6 was increased by 6.8 times compared with that before modification,the relaxation time was increased by 27.2 times,the power law index was reduced by 70.2%,and the shear viscosity was reduced by 52.2%at the shear rate of 1000 s-1.The introduction of D1 is beneficial to improve the industrial production efficiency of PA6,where the high shear rate is often used.Besides,the mechanical properties of PA6 were also improved by the incorporation of D1,especially the toughness.When the addition amount of D1 was 2.0 wt%,the elongation at break of PA6 was increased by 379.5%,and the notched impact strength was also improved by 69.7%,compared with those of original PA6.(4)Due to the low loading of chain extender,D1 or BDEP alone did not significantly improve the flame retardancy of PA6.Compounding diethyl aluminum hypophosphite(Al Pi)with D1 or BDEP significantly improved the flame retardancy of PA6.The addition of 11 wt%Al Pi was necessary to reach the V-0 level in UL-94 test for the flame retarded PA6,while PA6with 9 wt%Al Pi and 1 wt%BDEP also achieved the V-0 rating.The limiting oxygen index(LOI)value of PA6/Al Pi-9/BDEP-1(31.0%)was higher than that of PA6/Al Pi-11(30.4%),indicating a good synergistic flame retarded effect between Al Pi and BDEP.The flame retardancy of the combination of Al Pi and D1 was inferior to that of Al Pi and BDEP,but better than that of Al Pi alone.Compared with original PA6,the tensile strength,flexural strength and notched impact strength of PA6/Al Pi-11 were decreased by 8.8%,5.7%and 8.3%,respectively.The combination of Al Pi and BDEP not only effectively improved the flame retardancy of PA6,but also reduced the adverse effect of Al Pi on the mechanical properties of PA6.Compared with PA6/Al Pi-11,the tensile strength,flexural strength and notched impact strength of PA6/Al Pi-9/BDEP-1 were increased by 6.4%,4.0%and 22.3%,respectively.(5)D1 was used as a reactive modifier to improve the properties of the cured DGEBA/MHHPA(methylhexahydrophthalic anhydride).The addition of D1 improved the hydrophobicity and decreased the dielectric constant of DGEBA/MHHPA.When the addition amount of D1 was 20 wt%,the water contact angle of DGEBA/MHHPA was increased by 6.7°and the dielectric constant(at 100 MHz)was decreased by 11.0%.TG results showed that the T5%of DGEBA/MHHPA was decreased by 7.5°C after adding 20 wt%D1.However,the char residue of DGEBA/MHHPA at 800°C was increased by 77.8%.The addition of D1 could significantly improve the toughness of DGEBA/MHHPA,and the impact strength was increased by 45.4%at the loading of 20 wt%D1.However,the addition of D1 did not significantly improve the flame retardancy of DGEBA/MHHPA due to the low flame retarded efficiency of silicon on epoxy resin.(6)A new cured BDEP/DDM(4,4-diaminodiphenylmrthane)was prepared by curing the Schiff base silicone epoxy compound BDEP with DDM.TG test showed that the T5%of BDEP/DDM was 94.5°C lower than that of DGEBA/DDM,but the char residue of BDEP/DDM at 600°C was 2.34 times than that of DGEBA/DDM.BDEP/DDM reached V-1 rating in UL-94test and had a LOI value of 29.4%.Compared with DGEBA/DDM,the p HRR,THR and p RSR of BDEP/DDM were reduced by 33.2%,40.5%and 64.0%,respectively.The dielectric constant of BDEP/DDM was reduced by 5.7%compared with that of DGEBA/DDM,and the water contact angle is 12.8°higher than that of DGEBA/DDM.Moreover,the toughness of BDEP/DDM was better than that of DGEBA/DDM.The impact strength of BDEP/DDM was22.2 k J/m2,which was 13.8%higher than that of DGEBA/DDM. |
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