Adhesion properties of the nanocomposites filled with aluminosilicates and factors affecting them: A review

Use of nanoclays for the adhesives enhancement is being considered in the review as well as adhesive properties of filled adhesives. Both structural and pressure-sensitive adhesives (PSAs) are discussed. Maximum adhesive properties are usually obtained when clay is exfoliated or at least intercalated, which is mostly achieved by using appropriate clay surface modifier, proper mixing techniques or both. In case of structural adhesives, overall improvement of cohesion strength and a decrease in the residual stresses in the system achieved in this case, are usually the main reasons for the adhesion strength growth at low clay content. Further clay addition causes appearance of defects and adhesion strength decrease, thus leading to the adhesion strength vs. modifier content dependencies with a maximum. An increase of 20-40% in lap shear or pull-out adhesion strength is often obtained at 1-2 wt% clay content. For PSAs shear resistance often increases notably with clays incorporation due to the increase in storage modulus (cohesive strength) of the systems, accompanied by a tack decrease because of the worsening in the conditions of adhesion joint formation. To obtain better compromise between tack and shear resistance a uniform clay distribution in the adhesive should be achieved, for this purpose in-situ polymerization techniques of clay incorporation and clay surface modification could be most helpful. Also, a trend to simultaneous increase in the shear and peel strength due to nanofillers incorporation could be observed for clay-filled PSAs. For non-crosslinked PSAs a structure with the elastic network formed by the polymer chains, adsorbed simultaneously at several nanoparticles seem to be most beneficial. An increase of PSA holding time up to 3-4 orders of magnitude could be obtained in this case, with simultaneous growth of peel strength at high clay content (30-40%).