Attapulgite as a filler for solvent-based polyurethane adhesives

—Different amounts (5-20 wt% with respect to the solids content in the adhesive) of a hydrated magnesium/aluminum silicate (attapulgite) were added to solvent-based polyurethane (PU) adhesive formulations. The rheological, thermal, mechanical, surface, and adhesion properties of the filled PU adhesives obtained were measured. The addition of attapulgite provided an increase in viscosity, imparted thixotropy and pseudoplasticity to the PU adhesive solution, and produced an increase in storage and loss moduli. Increase in the amount of attapulgite enhanced these effects. Some interactions (not well defined in this paper) between the attapulgite, the polyurethane, and/or the solvent seemed to be responsible for the improved properties of the filled PU adhesives. Furthermore, the addition of attapulgite increased the mechanical properties, decreased the glass transition temperature, affected the crystallization rate and melting process, and modified the surface properties of the PU adhesive films (without solvent). On the other hand, the immediate (green) T-peel strength of roughened or (roughened + chlorinated with 1 wt% trichloroisocyanuric acid solutions in 2-butanone) styrene-butadiene rubber (SBR)/PU adhesive joints was greatly improved if the adhesive contained attapulgite. However, similar T-peel strength values in fully cured adhesive joints (measured 72 h after bond formation) were found irrespective of whether the PU adhesives contained attapulgite or not.