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TESTING: ADHESION

URETHANE ELASTOMERS AND ADHESION Since Techthane spray-applied elastomers are strong, elastic linings that can stand by themselves like a rubber sheet, and the highest likelihood of disbondment is in a peel form, Technical Urethanes reports the adhesion of its products using the 90° peel test, a severe, relevant, accurate, and reliable test for this type of product and adhesion. Technical Urethanes does not typically use vertical pull-off tests, as they are best-suited to measure the adhesion of brittle, thin-film paints and in most cases are not relevant to thick, flexible sheet linings. For more information, see the ASTM adhesion test descriptions. The general method of the 90° peel test is that half of the of piece is prepared and primed as would be done typically in a normal coating operation, and the other half is masked off to prevent adhesion. This creates a 'flap' to which the test device can grip the coating and pull it upward. Strips are cut 1" (25 mm) wide. The 1" (25 mm) wide flap is pulled upward, creating a 90° angle in the coating at the interface. For instance, 75 pli (13.15 kN/m) adhesion indicates that the 1" (25 mm) wide strip required 75 lbs. (34 kg) of force to remove the coating. Products which may appear to have good adhesion in direct pull-off tests often are proven to have low adhesion in the peel test. This is why, with tough, high build, elastomeric coatings such as Techthane, the peel test is the best indicator of adhesion. Additionally, simply reporting that the adhesion of a product exceeds the strength of the elastomer does not indicate good adhesion, and in fact usually indicates a coating with a very low tensile strength that breaks before any disbondment has occured. Additionally, this statement is not acceptable, as if this occurs, the coating should then be made thick enough to be stronger than the bond strength, thus providing an true measure of adhesion. In over 17 years of use by Technical Urethanes, actual field service results have proven peel tests to be a reliable indicator of a material's actual service adhesion performance.

© 1998 Technical Urethanes, Inc.