Adhesion of hydroxypropyl cellulose films to low energy solid substrates.

The adhesion of hydroxypropyl cellulose (HPC) to well-defined solid substrates was measured as a function of dry film thickness. A well-controlled butt adhesion test, providing a constant slow rate of film detachment, was used to keep the viscoelastic contribution of the film to the adhesion measurement constant. Films were cast or sprayed from solution in either triply distilled water or absolute ethanol onto relatively smooth surfaces of poly(methyl methacrylate), poly(ethylene terephthalate), and polyethylene. A linear relationship of increasing adhesion with decreasing dry film thickness was obtained for thin films (less than 20-microns thick) on all three surfaces. An adhesion value, A0, determined by extrapolating the adhesion data to zero film thickness, was shown to be proportional to the calculated thermodynamic work of adhesion, Wa, at the film-substrate interface. No significant effect of the method of film preparation, cast or sprayed, on the adhesion measurement was noted. Adhesion for a given film thickness was greater for films prepared from solutions having a higher initial polymer concentration or when using ethanol as opposed to water as the solvent.