EFFECT OF PLASTICIZERS ON MOISTURE ABSORPTION AND MECHANICAL PROPERTIES OF AGAR FILMS

摘要

Introduction. Polysaccharlde-based polymers have a great potential of using in pharmaceutical industry and biotechnology. The advantages of agar versus other gelling agents are its higher stability at low phi values and elevated temperatures. Plasticizers increase the flexibility of the film and prevent its crack during processing and storage.Objective: to investigate the effects of different types of plasticizers and their concentration on the kinetic and static absorption of moisture and on the mechanical properties of agar films.Methods. The effect of plasticizers (glycerol sorbitol, citric acid, sodium citrate, and mixtures thereof) and their mixtures on the absorption of moisture and the mechanical properties of agar films was investigated when the plasticizers were used at various concentrations according to the experiment design.Results. Addition of glycerol to the films increased the rate of absorption and the amount of absorbed moisture when stored under conditions of higher relative humidity. At the same time, the films containing citric acid and sodium citrate absorbed moisture more slowly and in smaller quantities, especially at a lower relative humidity. There was the thinnest water monolayer (0.035-0.036 g water/g film) on the films containing citric acid and sodium citrate as a plastlcizer. When 3.6 wt.-% glycerol and 0.6 wt.-% sorbitol were added to the films, the monolayer thickness increased to 0.065 g water/g film. The highest thickness of the water monolayer (0.158 g water/g film) was observed when 4 wt.-% sorbitol was added. The addition of citric acid to the agar films lowered their strength. While the higher levels of glycerol (up to 5 wt.-%) and sodium citrate (up to 2.5 wt.-%) increased the strength of the films. The strength of agar films with sodium citrate increased by adding of citric acid.Conclusion. The results of the investigation can be used in the pharmaceutical and biotechnological industries when manufacturing agar capsules or an agar-agar pack.