Mechanical properties of edible starch based films

BERTUZZI, MARÍA ALEJANDRA; CASTRO VIDAURRE, ELZA FANI; ARMADA, MARGARITA; GOTTIFREDI, JUAN CARLOS

Cancún, México

Congreso; XIII International Materials Research Congress 2004; 2004

Academia Mexicana de Ciencias de Materiales

The mechanical properties (tensile strength, TS and percentage of elongation at break, %E) of high amylose corn starch films plasticized with glycerol were evaluated using tension tests. The effect of different variables, such as composition, film thickness and storing conditions were studied. Films exhibited negative exponential dependence on plasticizer concentration for TS, while they showed linear dependence on plasticizer concentration for %E. TS decreased from 26.84 MPa to 1.52 MPa when glycerol content increased from 0 to 42% (dry starch) and %E increased from 4.10% to 42.62% when glycerol content increased from 0 to 42%. Starch based films were hydrophilic and mechanical properties of these films were strongly dependent on the water content. Sorption isotherms showed the equilibrium moisture content of films increased sharply for relative humidity higher than 60%. The effect on TS of moisture sorption is similar to plasticization of glycerol. TS decreased from 14.2 MPa to 0.9 MPa when relative humidity increased from 11% to 89%. This effect could be explained by a dependence of the molecular mobility on the water content. %E suffer a different effect, maximum value were reached for 45% relative humidity. TS and %E increased linearly when film thickness increased over the range of thickness studied (35 to 100 mm). Results suggested that to prepared starch based film plasticizer concentration of 30% was sufficient to provide films with flexibility as well as strength. Furthermore, these films were more suitable for applications where relative humidity ranged from 30 to 60%.