Abstract:
Highly filled polybenzoxazine nanocomposites filled with nanosilica particles were investigated for their mechanical and thermal properties as function of filler loading, particle size and surface treatment. The nanocomposites were prepared by high shear mixing followed by compression molding. A very low viscosity of benzoxazine monomer gives it excellent processability having maximum untraeted nanosilica loading as high as 20, 25, 40 and 45 wt% with nanoparticle size of 7, 14, 20 and 40 nm, respectively, while the maximum loading of treated nanosilica was measured to be 30 wt%. In addition, the enhancement in mechanical properties (storage modulus and microhardness) of the nanosilica filled polybenzoxazine composites was found to be significantly higher than that of the recently reported nanosilica filled epoxy composites at maximum loading of each particle size of nanosilica. The dependence of the modulus value of nanocomposite on the nanosilica content is well fitted by the generalized Kerner equation. Furthermore, the microhardness of the nanosilica filled polybenzoxazine composites at maximum loading of nanosilica up to 625 MPa was achieved, which the experimental data agree with Halpin-Tsai model. Moreover, the substantial enhancement in glass transition temperature (Tg) of the nanosilica filled polybenzoxazine composites at maximum loading of nanosilica was observed to be 203 oC, while the Tg of neat polybenzoxazine was mesured to be 185 oC. The degradation temperature at 5 % weight loss (Td,5) of the nanocomposites shifted significantly to higher temperature as a function of the nanosilica contents and smaller size of nanosilica. The nanocomposite shows reduction in specific wear rate by 89% at maximum loading content of nanosilica. Coefficient of friction (COF) of nanosilica filled polybenzoxazine composites was found to increase with nanosilica content. In addition, the mechanical and thermal properties of nanocomposite with untreated nanosilica was better than that of nanocomposite with treated nanosilica, which it was due to nanocomposites filled untreated nanosilica can form chemical bonding between the untreated nanosilica and the polybenzoxazine matrix.
