Study of the effect of lactose on the structure of sodium alginate films

The aim of this study was to evaluate the interaction between the film-forming sodium alginate and lactose monohydrate. This combination is used in the co-spray-drying technique for microencapsulation, but no respect on the structure of the film formed has not been published previously. From mechanical tests, positronium lifetime measurements and FT-IR studies on free films containing different ratios of film-former and lactose, we concluded that the mechanical strength of the sodium alginate film decreased with the increasing proportion of lactose. The free volume in the polymer matrix decreased to a minimum as the lactose content was progressively increased to 40%, but subsequently increased at higher lactose contents. The explanation of this phenomenon is the filling of the holes with the sugar. As lactose became predominant component, the structure of the polymer network weakened. These conclusions were supported by the FT-IR findings. The present results permit a clear explanation of the previously reported favourable effects of this film-forming combination on the dissolution of the active agent from the microcapsules. (C) 2009 Elsevier Ltd. All rights reserved.