The Effect of Clay Content on Bonding Properties of Novolak Adhesives

In this investigation, physical and adhesive properties of phenolic novolak resin based adhesives containing different nano clay (Cloisite 30B) content were studied. A phenolic resin adhesive was prepared by dissolving the novolak resin (61 wt% solid content) in ethanol. Five formulations were prepared by varying the nano clay content (0, 1, 3, 5 and 6.5 wt%). In order to characterize these formulations, their viscosity, drying time, gel time, lap shear and peel strength were measured. The results show that the more content of nano clay, yield the higher viscosity. The viscosity increased from 548 cp to 2187 cp in 5% of nano clay content. The results of drying time tests indicate that as the content of Cloisite 30B increases, the drying time decreases generally but there is an unexpected value at 1 wt% of Cloisite 30B content. Gel time measurements at temperature intervals of 120ºC to 150ºC for different clay content show that the gel time first decreases at 1% of clay content and then increases for the other formulations. This might be attributed to the morphology and the state of dispersion of clay layers. By increasing the nano clay content, the peel strength of novolak resin adhesive decreased from 27.1 of neat adhesive to 13.1 N/m but, this reduction is not significant for more that of 1% clay content. The lap shear strength of novolak resin adhesive containing more Cloisite 30B was lower than of adhesives containing less nano clay. This might be due to the brittle nature of neat phenolic adhesives. All over, the results show that the optimum properties can be achieved at 1% of clay content.

Keywords:

phenolic resin , clay , nanocomposites , adhesive