Volume 17, Issue 6 (November 1989)
A Technique to Evaluate the Bonding Reactivity of Thermosetting Adhesives
The rate at which thermosetting adhesive bonds develop strength critically effects the economic viability of many manufacturing processes. Bonds between the constituents of laminated and particulate panel products, overlays, and moldings must, for example, attain a certain minimum strength before the hot press used in their manufacture may be opened. A technique is reported that will prove useful to adhesive technologists endeavoring to develop resins with reactivities tailored to the specific conditions occurring within products during their manufacture. With the technique, many small lap-shear bonds pressed under controlled conditions of temperature and load are pulled after a range of curing times for measurement of their accumulated shear strength. This enables a family of shear-strength development curves to be constructed for a range of nearly constant temperature conditions. The effect of temperature on the bonding kinetics of the adhesive-adherend combination may thereby be evaluated. The technique lends itself to standardization for use in commercial laboratories, requiring much simpler sample preparation and apparatus than previously reported methods in which bonds are tested in tension perpendicular to the glueline. Wood adherends and a liquid phenol formaldehyde adhesive are used in a candidate system demonstrating the technique.