A detailed investigation of the effect of calcium crosslinking and glycerol plasticizing on the physical properties of alginate films.

Alginates attract growing interest due to their biocompatible and biodegradable nature. Here, a wide spectrum of glycerol added alginate films (from 0 to 30% w/w, glycerol/alginate) were prepared and crosslinked by four different concentrations of calcium chloride solutions (0.5, 1, 1.5, 2%, w/w). This is the first investigation involving variation of both the plasticizer and crosslinker concentrations in twenty different compositions. It is shown that glycerol and calcium have a synergic effect on the mechanical properties and the behavior of crosslinked and plasticized alginate films cannot be predicted by studies, which vary only one of these, keeping the other constant. Without glycerol, crosslinking had a negligible effect on tensile behavior, but with glycerol addition, the effect of crosslinking became evident in mechanical properties. Calcium and glycerol concentrations exhibited a combined effect, displaying optimum combinations with good strength and fracture strain properties. Crosslinking increased the thermal resistance of all films. Low crosslinked high swelling films and highly crosslinked low swelling films were prepared. Water vapor permeability of films decreased regularly with increasing calcium concentration. The films exhibited high transmittance in the visible region. The results showed that alginate films have an appreciable potential in wound dressing and food packaging applications.

Stress relaxation and humidity dependence in sodium alginate-glycerol films.

The control of viscoelastic properties of alginate biopolymer that mimics the matrix properties of biological substrates plays an important role for the success of its biomedical applications. For this purpose stress relaxation behavior of glycerol plasticized sodium alginate films is characterized at room temperature as a function of the glycerol concentration ranging up to 40%. A series of experiments are thus conducted at relative humidity levels of 38 ±â€¯1% and 51 ±â€¯1%. The glycerol content is demonstrated to amplify the effect of humidity on relaxation profiles. In the case of 30% glycerol, normalized stress at the level of 65% is recorded at the end of the first 30 min at the low humidity level, whereas the corresponding value drops to 8% with increased humidity. Alginate films with no glycerol content exhibit much higher normalized stresses of 89% and 73% at low and high humidity levels, respectively. In addition, stress relaxation is observed to continue well beyond the first 30 min, especially for glycerol concentrations lower than 30%, where 9-hour parameters for a stretched exponential Kohlrausch - Williams - Watts function are reported demonstrating the importance of relaxation time for successful modeling.