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 r heological, thermal, mechanical, surface, and adhesion properties of t he filled PU adhesives obtained were measured. The addition of attapul gite provided an increase in viscosity, imparted thixotropy and pseudo plasticity to the PU adhesive solution, and produced an increase in st orage and loss moduli. Increase in the amount of attapulgite enhanced these effects. Some interactions (not well defined in this paper) betw een the attapulgite, the polyurethane, and/or the solvent seemed to be responsible for the improved properties of the filled PU adhesives. F urthermore, the addition of attapulgite increased the mechanical prope rties, decreased the glass transition temperature, affected the crysta llization rate and melting process, and modified the surface propertie s of the PU adhesive films (without solvent). On the other hand, the i mmediate (green) T-peel strength of roughened or (roughened + chlorina ted with 1 wt% trichloroisocyanuric acid solutions in 2-butanone) styr ene-butadiene rubber (SBR)/PU adhesive joints was greatly improved if the adhesive contained attapulgite. However, similar T-peel strength v alues in Fully cured adhesive joints (measured 72 h after bond formati on) were found irrespective of whether the PU adhesives contained atta pulgite or not.