Effects of high nano-SiO2 contents on properties of epoxy-modified polybenzoxazine

Abstract

High-performance nanosilica composites based on epoxy-modified polybenzoxazine matrices are developed. Chemorheological study of benzoxazine–epoxy resin mixtures reveals that processing window of the benzoxazine resin (BA-a) is substantially broadened with an addition of the liquid epoxy. Glass transition temperature (Tg) of the BA-a copolymerized with epoxy resin shows a synergistic behavior with a maximum Tg value (174°C) at the benzoxazine–epoxy mass ratio of 80:20. The copolymer at this composition is also used as a matrix for nano-SiO2 composites. A very low melt viscosity of the benzoxazine–epoxy mixtures promotes good processability with the maximum attainable nano-SiO2 loading up to 35 wt%. From scanning electron microscopy investigation, fracture surface of the 35 wt% nano-SiO2-filled benzoxazine–epoxy composite reveals relatively homogeneous distribution of the nano-SiO2 in the copolymer with good particle wet-out. In addition, very high reinforcing effect was also observed in such high content of the nano-SiO2, i.e., about 2.5 times in modulus improvement. This improvement is attributed to the strong bonding between the copolymer matrix and the nano-SiO2 through ether linkage as confirmed by Fourier-transform infrared investigation. POLYM. COMPOS., 38:2261–2271, 2017. © 2015 Society of Plastics Engineers. © 2015 Society of Plastics Engineers