Polybenzoxazines are thermoset resins derived from benzoxazine monomers. The advantages of polybenzoxazines include high thermal resistance, chemical resistance, flame retardancy, low-cost starting materials, and an environmentally friendly solventless reaction. Current limitations of polybenzoxazine resins include brittleness, slow cure speed, high melt viscosity, and high curing temperature. These properties make polybenzoxazine a difficult material to use in 3D printing applications. This study aims to create a formulation of epoxy/benzoxazine composite with optimal thermomechanical properties that can be 3D printed reliably at a high resolution. The various composite blends in this study are formulated by altering the benzoxazine monomer and epoxies added and the percentage of benzoxazine monomer in the composite. For this study, three benzoxazine monomers are being incorporated into the different epoxy composites: B-a (0 methyl groups on benzene ring), B-mt (1 methyl group), and B-35x (2 methyl groups). These methyl groups create arylamine linkages in the resin, which enhances thermal stability. Silica nanoparticles are added to each blend to increase the thixotropy and mechanical integrity. Also, an initial curing step is incorporated to cure the epoxy before the benzoxazine cure because benzoxazines cure well above the melting temperature of the blend. Initial observations are that the composite resins are printable at room temperature with a satisfactory resolution. DMA testing has confirmed that increasing the number of methyl groups in the phenol raises the glass transition temperature which proves that thermal stability increases and the multistage curing mechanism is efficiently curing the blends. FT-IR characterization also shows that no degradation is appearing during curing.

Formulation of high performance benzoxazine and epoxy composite blends for direct ink writing applications

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