Influence of relative humidity on surface quality and adhesion strength of coated medium density fiberboard (MDF) panels

The objective of this study is to evaluate surface roughness and adhesion strength of commercially manufactured medium density fiberboard (MDF) panels as function of relative humidity exposure levels. Surface roughness of the samples conditioned at 65%, 75% and 85% relative humidity was measured using a surface profiler. Adhesion strength of the samples coated with polyurethane finish was also determined by employing pull-off type test set up. Roughness values of the panels increased as they are exposed to higher relative humidity levels ranging from 65% to 85%. The highest adhesion strength value was found as 2.20 N/mm2 for the samples made from unrefined fibers exposed to 65% relative humidity. Majority of the failures took place within adhesion line between coating and the substrate with a very limited torn fibers. Overall adhesion strength characteristics of the samples adversely influenced by increased value of relative humidity exposure.