Sandpaper, solvent, and composite.

Introduction

 

Solvent wiping and sanding procedures can greatly affect the surface energy of a substrate. To investigate the surface energy differences following different preparation procedures of an epoxy composite laminate, researchers created several different surface conditions utilizing different cleaning techniques. For this experiment, a BTG Labs Surface Analyst™ obtained measurements.

The Surface Analyst is a fast, easy, accurate and nondestructive instrument that measures the contact angle of water  applied to the surface in a precise, controlled manner. This contact angle is determined by how strongly the surface energy of the substrate and the liquid deposited interact. The relationship between this contact angle and surface energy is complex, but well understood. More importantly, this relationship correlates with the adhesive strength of a paint, coating, print or adhesive to the substrate.

Experimental


Effect of Solvent Wiping

To examine the surface energy differences due to solvent wiping techniques, the epoxy composite laminate substrates were contaminated with MIL-PRF-32014 grease and subjected to either a “proper” or “improper” acetone wipe. A “proper” wipe consists of an unidirectional wipe with a solvent-soaked lint-free wiper, followed immediately by a dry wipe with a lint-free wiper.  An “improper” wipe consists of a non-unidirectional wipe pattern and lacks the final dry wipe.


Effect of Sanding Procedure

To investigate the surface energy differences due to sanding procedures, the epoxy composite laminate substrates were contaminated with MIL-PRF-32014 grease, subjected to a “proper” acetone wipe at different steps in the procedure and sanded using 150 grit sandpaper. One substrate took contamination with MIL-PRF-32014 grease, and then received a sanding, proper wipe and then evaluation. A second substrate received contaminated, a proper wipe, a sanding, a second proper wipe, then an evaluation.  Finally, an uncontaminated substrate received a proper wipe, sanding, and then proper wipe prior to evaluation.

To read about results and how these processes effected surface energy, click here.