Air plasma treatments of aluminium trihydrate filled poly(methyl methacrylate) polymer (PMMA) composites were carried out in a dielectric barrier discharge. X-ray photoelectron spectroscopy (XPS) and attenuated total reflection - infrared spectroscopy have been employed to analyse the changes in chemical composition. Confocal laser-scanning microscopy and atomic force microscopy yielded the impact on surface structure and morphology. Surface free energy (SFE) measurements and adhesive bond strength tests were used to correlate the results to possible applications like gluing and lacquering. The plasma treatments resulted mainly in an etching of the matrix polymer and a minor chemical modification. An apparent contradiction of XPS, ATR and SFE results was attributed to a re-polymerization and re-deposition of the etched PMMA material as debris back onto the surface. This effect, which is seldom taken into account, annihilated the positive impact of the plasma treatment due to the debris acting as rated break point.