Page 366 - Handbook of Adhesives and Sealants
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322   Chapter Nine


              An ingredient added to an adhesive to reduce the concentration of
            base resin or binder is called a diluent. Diluents are principally used
            to lower the viscosity and modify the processing conditions of some
            adhesives. The degree of viscosity reduction caused by various diluent
            additions to a conventional epoxy adhesive is shown in Fig. 9.1. Dil-
            uents do not evaporate as do solvents, but they become part of the
            final adhesive. Reactive diluents react with the resin base during cure,
            so that the final adhesive characteristics are determined by the reac-
            tion product of the binder and diluent. Nonreactive diluents do not
            react with the resin or curing agent and, therefore, generally dilute
            the final physical properties. Coal and pine tar are common nonreac-
            tive diluents.
              Extenders are substances which usually have some adhesive prop-
            erties and are added to reduce the concentration of other adhesive
            components and the cost of the overall formulation. Extenders also
            have positive value in modifying the physical properties of the adhe-
            sive. Common extenders are flours, soluble lignin, and pulverized
            partly cured synthetic resins.
              Fillers are relatively non-adhesive substances added to the adhesive
            formulation to improve its working properties, strength, permanence,
            or other qualities. The improvements resulting from the use of com-
            mon fillers are listed in Table 9.1. Fillers are also used to reduce ma-
            terial cost. By selective use of fillers, the properties of an adhesive can





























            Figure 9.1 Reduction of diglycidyl ether of bisphenol A (DGEPA) epoxy
            resin by reactive diluents. 1
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