Green Synthesis and Properties of Vanilla-Aldehyde-Based Benzoxazine Resins
To explore the effects of six-membered rings and their quantities on the flame retardancy and thermal properties of benzoxazine resins,vanillin-and sodium-glycinate-based benzoxazine monomer(XG-BOZ,without six-membered ring),vanillin-and nicotinamide-based benzoxazine monomer(XY-BOZ,single six-membered ring),vanillin-and diaminodiphenylmethane-based benzoxazine monomer(XD-BOZ,two six-membered rings),vanillin-and melamine-based benzoxazine monomer(XS-BOZ,three six-membered rings)were synthesized by green solvents.Thermal analysis and combustion performance tests show that the thermal performances and flame retardancy of XY-BOZ are better than those of XG-BOZ,XD-BOZ and XS-BOZ.At 700℃under nitrogen,the carbon residue rate of XY-BOZ is 60.9%,the peak heat release rate is 64.6 W/g,the total heat release is 6.8 kJ/g,and the theoretical limited oxygen index(LOI)is41.8%.The thermal decomposition behaviors of XY-BOZ and XG-BOZ at different heating rates are tested.According to the thermal degradation kinetics calculation method(Flynn-Wall-Ozawa method),when the mass conversion is 5%,the apparent activation energy(Ea)of the degradation reaction of XY-BOZ with single six-membered ring is140 kJ/mol,while that of XG-BOZ without six-membered ring is50.7 kJ/mol.The Ea of XG-BOZ is63.8%lower than that of XY-BOZ.
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