Fillers in adhesives

Fillers may be broadly defined as solid particulates or fibrous materials, substantially inert chemically, incorporated in polymer compositions to modify the properties and/or to reduce cost. Cost reduction is not the primary reason to incorporate fillers in adhesives but they are used to impart specific properties such as flow, improved adhesion, mechanical, thermal, electrical and optical properties, chemical and weather resistance, and rheological behaviour. 

Other mineral additives have been used for many years as functional extenders and fillers in adhesives and sealants. These include kaolin (hydrated aluminum silicate), bentonite (hectorite clay), talc (magnesium silicate), and attapulgite (hydrated magnesium aluminum silicate) additives.1213 Kaolin and talc are considered to be viscosity thickeners whereas attapulgite is more of a conventional thixotrope. They are considered to be very cost-effective rheological additives. 

Most high-quality nanoparticles are stiU produced in experimental quantities at universities or research laboratories and thus are still quite expensive and not widely available for use as fillers in adhesives. 

The effect of fillers in adhesives might be considered as another general effect which may have similar responses for a variety of surface conditions. Bodnar and Wegman(96) have shown the superior resistance to natural weathering of filled polyamide-epoxy adhesive/aluminum joints as compared to the corresponding joints made with nonfilled Epon 828/Versamid 140 combinations. Minford<97) has obtained similar results comparing filled and unfilled Epon 815/Versamid 125 combinations in a variety of accelerated lab tests. Minford ) has also noted durability differences between different fillers in certain exposures. For example, aluminum-powder-filled polyamide/epoxies tested superior in four-year exposures to marine conditions. 

Clays and bentonites are used as fillers in adhesives. Sodium bisulfite, hydrogen peroxide, sodium perborate serve as bleaches. Solvents are added to help wet water-repellent surfaces. Preservatives prevent microbial growth. De-foamers prevent foam during cooking. Colloid stabilizers such as soaps and sodium chloride are often added. 

Other uses - Wollastonite is used as an energy-conserving alternative to limestone and sand in the production of glass and glass fiber and as a white reinforcing filler in adhesives and sealants, where it can be used at high loadings. 

Caldum Carbonate (Tapper, 1992 Kurmner, 1978) - Calcium carbonates are the most widely used fillers in adhesives and sealants. There are two types... 

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