| Fillers and extenders are used in structural adhesive formulations to improve properties and to lower cost. Properties that can be selectively improved include both the processing properties of the adhesive as well as its performance properties in a cured joint. However, the use of fillers can also impair certain properties. Typically, the formulator has to balance the expected improvements against possible property decline. Fillers and extenders generally have different functions and are employed for different reasons. However, these functions may overlap, and then fillers and extenders can be thought of as serving the same purpose depending on the application. This article reviews the reasons for using and the types of fillers and extenders that are commonly employed in structural adhesive formulations. Epoxy adhesives are the focus due to their popularity and general use in many industries. However, much of what is presented also extends to structural adhesives in general. Dont hesitate to react about this Article Fillers are relatively non-adhesive substances added to the adhesive formulation to improve its working properties, strength, permanence, or other qualities. The advantages and disadvantages of filler addition in epoxy formulations are listed in Table 1. Common fillers used in epoxy formulations and the properties that they are used to modify are shown in Table 2. Some fillers may act as extenders. This is the case when their primary function is to reduce formulation cost.
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