Properties of polyurethane adhesives containing natural calcium carbonate plus fumed silica mixtures

Natural ultramicronized calcium carbonate and mixtures of fumed silica + natural ultramicronized calcium carbonate are proposed as a filler for solvent-based polyurethane (PU) adhesives. The PU adhesive containing only calcium carbonate showed similar thermal, mechanical, surface, and adhesion properties to those of the PU adhesive without a filler. The addition of 90 wt%; fumed silica + 10 wt% calcium carbonate mixture to the PU adhesive produced a performance similar to or improved over that of the PU adhesive containing only fumed silica. The increase in the amount of natural calcium carbonate with respect to fumed silica in the filler mixture had a detrimental effect on the theological and mechanical properties of the PU adhesives, although the surface and final adhesion properties were not noticeably modified. The immediate adhesion (35 min after joint formation) was noticeably increased in the joints produced with the PU adhesives containing fillers. mainly in those with a higher fumed silica content: a cohesive failure in the adhesive was produced in those joints and the mechanical and rheological properties of the PU adhesives determined the immediate adhesion. The failure in the joints peeled 72 h after joint formation was adhesional and the adhesion properties were mainly determined by the surface properties of the PU adhesives. All the adhesive joints showed a similar final adhesion because they have similar surface properties.