We study the changes in adhesive properties of poly(vinyl butyral) (PVB) sheets assigned for safety glass preparation. PVB sheets have been produced by various worldwide manufacturers by simple blending methods such as extrusion, thermo-mechanical mixer processes, etc. Some samples were modified either by magnesium acetate or by oligo-functional organic acid to either reduce the adhesion to glass or to increase it. Adhesive measurements were evaluated on the air side and the tin side of the laminated glass. The study deals with a recognition of causes of the PVB adhesion change as a function of adsorbed water content into the polymer matrix. Results describe the influence of hydroxyl group content and amount of added acidbase reactants for adhesion adjustment of every tested PVB sheet. It also describes typical adhesion fluctuation and specific adhesion bonding of PVB sheets to glass in particular conditions. The analysis evaluates the best and the worst blend combinations and their modification on the adhesion change. We focused on adhesion sensitivity to increasing water content and the amount of added adhesion modifier. This work also evaluated the critical range of water content that provides adhesion fluctuation. The evaluation of various types of PVB sheets was performed and the most stable adhesion adjustment was found. Obtained values and comparisons are very important for the PVB sheets industry and for industry dealing with lamination of laminated glasses. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013