| Benzoxazine resin as a new class of heat-resistant resin rencently, which is not only can be easily synthesized by certain chemical methods, and ring-opening polymerization reaction can be carried out under heat or catalyst. Benzoxazine resin has some excellent characteristics such as thermal stability, low water absorption, chemical resistance, molecular design flexibility. Benzoxazine resin has simple curing process, small volume shrinkage, no small molecules released in the curing process. Because of excellent heat resistance and flame resistance and mechanical performance, high glass transition temperature, Benzoxazine resin attracted widespread attention, and used in many important areas. However, the high benzoxazine resin curing temperature, low cross-linking density of the cured product, brittle and other defects restrict its application in some special fields. Modified polybenzoxazine is an important research direction to expand its application in the field of high-performance materials. Preparation of nanocomposites is an important aspect of modified polybenzoxazine.In this study, Fe3O4/polybenzoxazine nanocomposites was prepared by uniformly dispersing magnetic nanoparticles (Fe3O4@SiO2@BZS) into the polybenzoxazine matrix. Firstly, well dispersed Fe3O4magnetic nanoparticles was synthesised by solvothermal method. Secondly, Fe3O4magnetic nanoparticles was coated with a layer of dense SiO2by sol-gel method to enhance the oxidation resistance of nanoparticles. Oxazine ring modified Fe3O4@SiO2magnetic nanoparticles (Fe3O4@SiO2@BZS) was prepared by sol-gel method with the hydrolysis reaction of3-(Triethoxysilyl-)n-propyl-3,4-dihydro-2H-1,3-bezoxazine(BZ S). Fe3O4@SiO2@BZS magnetic nanoparticles was dispersed into the benzoxazine monomer, and then cured at high temperature to prepare Fe3O4benzoxazine magnetic nanocomposite. The mechanical properties, heat resistance, and magnetization of nanocomposite were studied.Fe3O4@SiO2@BZS magnetic nanoparticles have good dispersion, and the size of nanoparticles was between200-300nm. Organic coating thickness is about10nm. The proportion of organic mass is about4.2%. Magnetic nanoparticles have good magnetic properties and heat resistance. Magnetization reaches28.7emu/g and the char yield is89.6%at700℃in a nitrogen atmosphere.Tensile properties of composites is studied and the results showed that when the content of the composite Fe3O4@SiO2@BZS magnetic nanoparticles is3%, the mechanical properties of the composites is the best. The tensile strength of64.9MPa Compared to that of the unmodified benzoxazine (46.4MPa), increased by39.9%; elongation at break of2.20%, compared with those of the unmodified polybenzoxazine (1.29%), increased by70.1%. However, when the content of Fe3O4@SiO2@BZS magnetic nanoparticles was4%, the tensile strength and elongation at break decreased. The reason was that agglomeration of excessive magnetic nanoparticles in polybenzoxazine caused defects in nanocomposites. Thermal gravimetric analysis (TGA) showed that Fe3O4@SiO2@BZS magnetic nanoparticles can improve the heat resistance of nanocomposites.5%weight loss temperature,10%weight loss temperature and the weight residue at800℃of nanocomposites, compared with those of unmodified polybenzoxazine, all increased. When the content of the magnetic nanoparticles is4%,5%weight loss temperature (335℃),10%weight loss temperature (360℃), compared with those of unmodified polybenzoxazine, all increased. The weight residue at800℃, compared with that of unmodified polybenzoxazine, increased by13.8%. The results of magnetic analysis showed that nanocomposites have good magnetic properties. |
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