Investigation of Molding Conditions for CNT Composite Phenolic Resin Bond by Solvent Casting Method

In this paper, we propose a new fabrication method of high concentration carbon nanotube (CNT) composite phenolic resin bond for grinding tools and investigate the molding conditions by solvent casting method. CNT/diamond composite phenolic resin grinding tools with 12.5 vol% Ni-coated diamond grains and 20 vol% CNTs were prepared by the solvent casting method. The novolac phenolic resin with Hexamethylenetetramine as a hardener was used in this study. Partial curing of this resin occurs in the range of 40°C–90°C and harden completely at 180°C. The proposed solvent casting method involves two steps: desolvation and hot press for molding. Methanol or butanol was used as the solvent. When methanol solvent was used, desolvation was performed below 90°C before partial curing of phenol was completed. When butanol solvent was used, desolvation was performed at 100°C after partial curing of phenol. The effect of solvent and desolvation temperature on mechanical strength was determined from four-point bending tests. The porosity of the grinding tools was estimated by X-ray CT analysis, and the relationship between the porosity and mechanical strength was clarified. The effect of addition of CNTs on the phenolic curing process was also clarified by thermogravimetric-differential thermal analysis and Fourier-transform infrared spectroscopy. The mechanical strength of the grinding tools fabricated using methanol solvent and desolvated at room temperature and 40°C was approximately 70 MPa, and twice as high as that desolvated at 70°C. The mechanical strength of the grinding tools fabricated using butanol solvent and desolvated at 100°C was also 70 MPa. There was no difference in the dispersibility of diamond abrasive grains between the methanol and butanol samples; however, the porosity tended to be less in the butanol solvent. This study confirmed that the mechanical strength of CNT/diamond composite phenolic resin is affected by the amount and size of the voids. In particular, it was shown that better strength can be obtained by desolvation to avoid partial curing. The addition of CNTs may inhibit the curing reaction of phenol and hexamine owing to the glycidyl groups, which are functional groups of CNTs.