High thermal and mechanical properties enhancement obtained in highly filled polybenzoxazine nanocomposites with fumed silica

Highly filled polybenzoxazine nanocomposites filled with nano-SiO2 particles were investigated for their mechanical and thermal properties as a function of filler loading. The nanocomposites were prepared by high shear mixing followed by compression molding. A very low A-stage viscosity of benzoxazine monomer gives it excellent processability having maximum nano-SiO2 loading as high as 30 wt% (18.8 vol%) with negligible void content. Moreover, thermal analysis of the curing process of the compound of the PBA-a/nano-SiO2 composites was found to be autocatalytic in nature with average activation energy of 79-92 kJ mol−1. Microscopic analysis (SEM) performed on the PBA-a/nano-SiO2 composite fracture surface indicated a nearly homogeneous distribution of the nano-scaled silica in the polybenzoxazine matrix. In addition, the enhancement in storage modulus of the nano-SiO2 filled polybenzoxazine composites was found to be significantly higher than that of the recently reported nano-SiO2 filled epoxy composites. The dependence of the nanocomposites' modulus on the nano-SiO2 particles content is well fitted by the generalized Kerner equation. Furthermore, the relatively high micro-hardness of the PBA-a/nano-SiO2 composites up to about 600 MPa was achieved. Finally, the substantial enhancement in the glass transition temperature (Tg) of the PBA-a/nano-SiO2 composites was also observed with the ΔTg up to 16 °C at the nano-SiO2 loading of 30 wt%. The resulting PBA-a/nano-SiO2 composite is a highly attractive candidate as coating material in electronic packaging or other related applications.