A MODEL SYSTEM FOR DIFFERENTIATING BETWEEN WATER ACTIVITY AND GLASS-TRANSITION EFFECTS ON SOLID-STATE CHEMICAL-REACTIONS

Recent debates have emerged on whether water activity (a(w)) or the st ate of the system as dictated by the glass transition temperature (T-g ) controls the rates of chemical reactions in reduced-moisture solid s ystems. Previously, model systems in which the effects of water activi ty and glass transition on chemical reactions could be evaluated indep endently did not exist, The use of polyvinylpyrrolidone (PVP) of diffe rent molecular weights allows the water activity and moisture content of the systems to be kept virtually constant while the glass transitio n temperature varies. At a given water activity and temperature, the e quilibrium moisture content for any molecular weight of PVP differed b y only 1-2%, while the T-g values differed by 20-30C, Using PVP of dif ferent molecular weights as a model system will allow the effects of w ater activity and glass transition on chemical reactions to be studied independently and at a constant temperature.