Influence of the addition of lauric acid to films made from gelatin, triacetin and a blend of stearic and palmitic acids

The objective of this research was to verify the influence of adding increasing amounts of lauric acid on the functional properties of homogenized films made from gelatin, triacetin and a blend of palmitic and stearic acids. The films were characterised with respect to their visual aspect, water vapour permeability (WVP), water solubility, mechanical properties (tensile strength and percent elongation), oxygen permeability (O2P), opacity (OP) and melting and glass transitions temperatures. The films produced were malleable and macroscopically homogeneous. The addition of 1% of lauric acid to the film of gelatin, triacetin and blend of palmitic and stearic acids (5.84 +/- 0.31 gmm center dot m(-2) dkPa) caused a slight decrease in WVP. The additions Of 2.5% (5.70 +/- 0.76 gmm center dot m(-2) dkPa), 5% (5.38 +/- 0.64 gmm center dot m(-2) dkPa) and 10% (4.50 +/- 0.55 gmm center dot m(-2) dkPa) of lauric acid were sufficient to make a significant difference in the WVP at the higher levels used. As compared to the gelatin and triacetin film, the addition of lauric acid at all the concentrations studied resulted in a slight increase in the film solubility. The addition of hydrophobic substances to gelatin/triacetin films (15.26 +/- 0.28 cm(3)center dot mu m center dot m(-2) dkPa) favoured an increase in O2P permeability, this effect being greater in the films made from gelatin, triacetin, blend of palmitic and stearic acids and 10% lauric acid (24.48 +/- 0.07 cm(3)center dot mu m center dot m(-2) dkPa). The increasing addition of lauric acid significantly reduced the tensile strength and increased elongation of the films composed of gelatin, triacetin and blend that being more evident at the concentrations Of 5% (67.58 +/- 1.23 MPa and 11.45 +/- 0.57%) and 10% (63.50 +/- 1.56 MPa and 12.90 +/- 0.57%). The addition Of 1% (OP, 27%) and 10% (OP, 28%) of lauric acid induced no visible effect on the opacity of the films. The thermogrammes showed three transitions for the gelatin/triacetin/stearic-palmitic blend/1% lauric acid films (-57.42 degrees C, 23.74 degrees C and 44.11 degrees C) and two for the gelatin/triacetin/stearic-palmitic acids blend/10% lauric acid films (-56.22 degrees C and 17.35 degrees C). As observed by DSC, the addition of fatty acids resulted in the appearance of more than one melting peak for all films in relation to the gelatin and triacetin film.