Study On Preparation, Solidification And Properties Of Benzoxazine Modified With Lignin

In this paper, lignin, which is a kind of rich, cheap and renewable resource, was used to partly substitute phenol from petrochemical products to synthesize a new type of lignin modified polybenzoxazine. The conditions of desulfonation reaction of sulfonate lignin to prepare lignin, the synthesis and changes in structure and nature of modified precursors, and the interfacial properties and thermal stability of the product which was directional cured in silicone oil were studied. According to the product cured in silicone oil which was used as a kind of dispersion medium, we discussed the self-assembly mechanism of spherical polybenzoxazine resin. Fourier transform infrared spectroscopy(FT-IR) was used to characterize the effect of desulfonation; FT-IR, mini-rotary viscometer(MRV), thermal gravimetric analysis(TGA), differential scanning calorimeter(DSC), contact angle measurement(CAA), upright fluorescence microscopy(UFM), electronic universal testing machine(EUTM) were used to characterize the structure and properties of polybenzoxazine modified with lignin.The results showed:the infrared absorption peak of sulfonic group in sulfonate lignin disappeared, and the major structure units of desulfonated resultant are hydroxyphenyl propane unit and p-guaiacyl unit, which indicated that the desulfonated product can be used to partially replace phenol to synthesize the modified benzoxazine precursors; Oxazine group can be introduced into the structure of lignin to prepare modified precursors by Mannich reaction, the best solvent for synthesis is ethanol/water (V:V=50:50) mixed solvent and the maximum amount of lignin is 15%; viscosity of modified precursors increased with the amount of lignin; the lignin modified polybenzoxazine resin, which was obtained by the directional curing of modified precursors on glass substrate in the medium of silicone oil, showed the maximum degree of polymerization when cured at 180℃; the interface between directionally cured product and silicone oil was hydrophobic, while the interface between glass and product was hydrophilic, showing a controlled polymerization behaviour; compared with that of polybenzoxazine resin, the surface crack of lignin modified resin significantly reduced and toughness enhanced, contact angle of water decreased with increasing lignin content, but the interface still was hydrophobic; the thermal stability reduced, although 10% lignin modified resin showed the best thermal stability; modified precursors could not obtain spherical resin in the dispersion medium of silicone oil, which proved the self-assembly mechanisms of spherical resin preparation.Currently, the utilization rate of lignin is low and most are discharged into the river with waste water as byproduct of paper-products industries, which causes environment pollution and waste of resources. How to achieve the development and utilization of lignin is now a hot research topic. Based on its structure and properties, lignin is used to modify benzoxazine and other polymer to improve material performance, and this will realize the comprehensive utilization of lignin.