| Summary: | Dissertação (Mestrado) - Universidade Federal de Santa Catarina, Centro de Ciencias Agrarias. Programa de Pós-graduação em Ciência dos Alimentos === Made available in DSpace on 2012-10-23T20:09:42Z (GMT). No. of bitstreams: 1
256323.pdf: 4508922 bytes, checksum: 9073805d484c75a850d3a79c85b7015c (MD5) === The objective of this work was to develop and characterize films made from two natural polymers, chitosan and hydroxypropylmethylcellulose (HPMC). In order to promote an improvement in their properties, sorbitol was added as a plasticizer. The rheological properties of solution-forming films and blends were characterized. Moreover, the mechanical properties (tensile strength, Young's modulus and elasticity), thermal (through thermogravimetric analysis - TGA and differential scanning calorimetry - DSC), structural (difratometry by X-ray) and morphological (through scanning electron microscopy), as well as solubility, color, transparency and interaction with three liquids of different polarities were also studied. The chitosan solution, a low concentration (1.0%), presented a typical Newtonian behavior, while in higher concentrations (1.5% to 3.5%) the solution behaved as a non-Newtonian fluid. The HPMC solutions had a non-Newtonian behavior in all concentrations. The higher the proportion of HPMC in the samples the greater its solubility. The HPMC films had the highest transparency, greater brightness and greater luminosity. The other samples showed a slight yellowness in color, increasing the tone the higher the proportion of chitosan. The transmittance of the samples in the ultraviolet region (210nm) was lower than in the visible region (500nm), indicating that films made with this biopolymers have a good preventive ability against ultraviolet radiation. The chitosan films showed the highest averages for tensile strength and Young's modulus and the lowest for the maximum elongation. The glass transition temperature (Tg) of the chitosan films was 114,06oC, while in the HPMC films this value was 164,5oC. The chitosan and HPMC films had two thermal degradation stages, while the other samples had three stages of degradation. The micrographs of the samples showed up smooth, compact and without pores. In the films made from both biopolymers, the cross section showed some roughness, with the presence of tortuosity the larger the proportion of HPMC. The HPMC films reacted easily with water and formed a smaller contact angle than the angle formed by chitosan films. The opposite occurred with the diiodomethane (highly apolar liquid). With formamide (liquid with an intermediate polarity), measures of the contact angle were between the values found for water and the diiodomethane. The polar surface free energy (ãp) increased its value the larger the proportion of HPMC in the samples and surface free energy dispersive (apolar) (ãd) decreased its value the higher the proportion of HPMC in the samples. The adhesive work (W) of the chitosan films was lower when in contact with
deionized water and higher when in contact with the diiodomethane. For
formamide, the W has a similar behavior to the diiodometane. The chitosan films had four peaks of diffraction, confirming the presence of crystalline domains in its structure, while HPMC films had only two peaks of diffraction, being more amorphous. On the other hand, the films made from both biopolymers had a displacement of their diffraction angles and a change in the peaks intensity, which is indicative of a partial miscibility between the polymers.
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