P. Bergo

Influência do grau de hidrólise do poli(vinil álcool) nas propriedades físicas de filmes à base de blendas de gelatina e poli(vinil álcool) plastificados com glicerol

The aim of this work was to study the effect of the Degree of Hydrolysis (DH) of poly(vinyl alcohol) (PVA) on the properties of films based on blends of pigskin gelatin and PVA with two DH. The films were made with solutions with 2 g macromolecules/100 g solution, containing 23.1 g PVA.100 g-1 macromolecules and 25 g glycerol/100 g macromolecules. The mechanical and thermal properties, color, opacity, moisture and solubility of the films were studied, as well as Fourier Transform Infrared (FTIR) spectra. The solutions were analyzed by dynamic rheometry. The films containing PVA with lower DH were more hygroscopic and more soluble. However, the type of PVA did not affect color, but affected the opacity and the gloss of the films. The PVA of higher DH produced films which were more resistant to puncture and stress, and the PVA of lower DH produced films which were more deformable upon stress, although less deformable upon puncture. The DH of PVA did not affect the first scan glass transition temperature of the films, but did affect this property in the second scan. The results from the FTIR analysis were in conformity with the results of the thermal analysis. The viscoelastic properties of the solutions determined by rheometry were not affected by the DH of PVA, possibly because the solutions studied were diluted.

Physical Properties of Gelatin Films Plasticized with Glycerol, Studied by Spectroscopic Methods

The effect of glycerol content on the physical properties of gelatin-based edible films was studied in this work, on the basis of the interactions between the plasticizer and polymeric matrix. In this work, some non-usual techniques were used to characterize edible films. For dielectric measurements and infrared spectroscopy, these films were conditioned in silica gel in order to minimize the water effect. For other analysis, the films were conditioned in NaBr. Infrared spectroscopy showed no apparent changes in the position peaks, suggesting an absence of new interactions between the plasticizer and film matrix. It seems that the plasticizers only occupy some specific regions between the polymeric matrix, increasing their distance, and thus, affecting their mobility, which results in more flexible films. Dielectric constant of the films increased with plasticizer content, and decreased over silica gel conditioning. The polarizability was found to arise mainly from water molecules present in the film. Microwave response was found to be also sensitive to water content in the films, due to plasticizer hydrophilic nature. According to the diffractograms, gelatin films presented essentially an amorphous nature, independently of the glycerol content. The results suggest, therefore, that the glycerol induces no chemical modifications in the films.

Semi Crystalline Behaviour of Cassava Starch Films Plasticized with Glycerol

In this work, the method of Fourier transform infrared was used to study the recrystallization phenomenon in cassava starch films containing different plasticizers content and type. The films were obtained by conventional casting method and then, conditioned for several periods in desiccators containing saturated water-NaBr solution and also, in desiccators containing silica gel. From the results, the main changes occurred in the fingerprint region, and were attributed to new interactions arising between the polymeric chains and the plasticizer. The changes in the peak amplitude located near 1015 cm-1 were associated to the formation of semi crystalline junctions in the film matrix, as affected by the plasticizer and moisture content in the films. The slight changes in peak positions were attributed to the modifications in the intermolecular forces in the film matrix. The semi crystallinity nature of films was checked by X-ray diffraction. At macroscopic scale, the flexibility of the films increased, which could favor the reorientation of the macromolecules.