Epoxy Adhesive Formulations
Based on a popular course sponsored by the Society of Plastics Engineers, this comprehensive text presents a variety of methods to ensure optimum epoxy performance and reliability.
TABLE OF CONTENTS Epoxy Adhesive Formulations
Chapter 9: Fillers and Extenders
9.1 INTRODUCTION
Fillers and extenders are used in epoxy 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 improvements against property decline. The advantages and disadvantages of filler addition in epoxy formulations are listed in Table 9.1. Common fillers used in epoxy formulations and the properties that they are used to modify are shown in Table 9.2.
| Advantages | Disadvantages | Advantage or disadvantage (depending on application) |
|---|---|---|
| Lower cost of product | Increased weight | Increased viscosity |
| Reduced shrinkage on curing | Increased water absorption (depending on filler) | Increased thermal and electrical conductivity |
| Decreased exothermic temperature on curing | Loss of transparency | Reduced thermal expansion coefficient |
| Improved tensile shear strength | Difficulty in machining hard fillers | |
| Increased surface hardness | ||
| Improved abrasion resistance | ||
| Improved heat-aging properties | ||
| Increased compressive strength | ||
| Increased electrical strength | ||
| Improved toughness if fibrous fillers are used |
| Filler | Function |
|---|---|
| Aluminum | Machineability |
| Alumina | Abrasion resistance, electrical |
| Aluminum silicate | Extender |
| Aluminum trioxide | Flame-retardant |
| Barium sulfate | Extender |
| Calcium carbonate | Extender |
| Calcium sulfate | Extender |
| Carbon black | Pigment, reinforcement |
| Copper | Machineability, electrical conductivity |
| Glass fiber | Reinforcement |
| Graphite | Lubricity |
| Iron | Abrasion resistance |
| Kaolin clay |
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