Performance of various fillers in adhesives applications: a review

Adhesives, which also comprise of terms like bonding agents, glues and gums, are substances which possess the ability to attach to various substrates and hence can be used to join materials. They find use for bonding of various substrates such as wood, metals, plastics and find applications in automotive, construction sectors, electrical or thermal conductivity applications, and dentistry among others. Adhesives are mainly composed of polymers and different additives, of which, one is fillers. Fillers are solid substances which are insoluble in the adhesive, and they are incorporated in adhesives to reduce cost, modify mechanical properties, increase viscosity, improve electrical and/or thermal conductivity, obtain better adhesion, etc. Some types of fillers utilized are bio-based (cellulose nanoparticles, tree bark powders); carbon-based (carbon black, carbon nanotubes, diamond, graphene); ceramics (aluminium oxide, boron nitride, iron carbide, silicon carbide); metallic (aluminium, aluminium oxide, copper, silver, titanium dioxide); silicon-based (layered silicate, silica); or hybrid (consisting of more than one type of filler). Both the type and the amount of filler added will affect the properties of the adhesive. Several adhesives having diverse uses have been considered in this study. The paper reviews in detail the effect of a number of fillers on the properties of the different adhesives.