Surface Preparation: Measurements on Plastics and Composites

Surface Preparation
The cleaning compounds and procedures appropriate for surface preparation of plastics and composites tend to be highly material-specific, and do not lend themselves to broad generalizations. The usual first step in this process, however, is to cleanse the surface with a mild solvent to remove adhering films of oil and grease. Depending on the type of plastic, this may consist of chlorine/fluorine-based solutions, isopropyl alcohol, or even household cleanser or detergent. It is necessary, of course, to ascertain that the chemicals do not react unintentionally with the plastic. Recommendations for suitable solvents can usually be obtained from the supplier of the plastic or from the strain gage manufacturer. * If any doubt exists, the proposed solvent should be tested for cleansing effectiveness and compatibility with the plastic.

Surface abrasion (with abrasive paper, grit blasting, or otherwise) is a common procedure in preparing metals for strain gage bonding. It is also effective for many plastics and composites, but should always be preceded by degreasing to prevent embedment of contaminants in the surface. For some high-performance composites, however, abrasion may not be permitted because of the risk of damage to near-surface fibers. Moreover, abrasion is not always adequate with certain types of plastics (e.g., flourocarbons, polyolefins) for achieving optimum bond strength.

* See, for example, Refs. 11 and 12 , which list recommended solvents and surface-preparation procedures for wide varieties of test materials.

( continued ... )

Page 20 of 32