Sandra Rivero

Heat Treatment To Modify the Structural and Physical Properties of Chitosan-Based Films

This work was focused on studying the changes undergone by heat-treated chitosan films with and without tannic acid addition by monitoring both microstructure and physical properties. Once the films were submitted to different heat treatments, they exhibited higher barrier properties as well as lower water uptake, solubility, and moisture content. These results were also confirmed through X-ray patterns, which changed from the hydrated to the anhydrous conformation, sharper FTIR peaks specifically associated with water, and shift of T(g) toward higher temperatures determined by DMA. Moreover, the modifications caused by the curing process at a molecular scale were observed at a structural level by using a TEM technique. FTIR evaluation granted new insights into the interactions between tannic acid and chitosan molecules, before and after the heat curing, especially due to the occurrence of new peaks and changes in the wavenumber region 1550-1750 cm(-1).

Changes induced by UV radiation in the presence of sodium benzoate in films formulated with polyvinyl alcohol and carboxymethyl cellulose

This work was focused on: i) developing single and blend films based on carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVOH) studying their properties, ii) analyzing the interactions between CMC and PVOH and their modifications UV-induced in the presence of sodium benzoate (SB), and iii) evaluating the antimicrobial capacity of blend films containing SB with and without UV treatment. Once the blend films with SB were exposed to UV radiation, they exhibited lower moisture content as well as a greater elongation at break and rougher surfaces compared to those without treatment. Considering oxygen barrier properties, the low values obtained would allow their application as packaging with selective oxygen permeability. Moreover, the characteristics of the amorphous phase of the matrix prevailed with a rearrangement of the structure of the polymer chain, causing a decrease of the crystallinity degree. These results were supported by X-rays and DSC analysis. FT-IR spectra reflected some degree of polymer-polymer interaction at a molecular level in the amorphous regions. The incorporation of sodium benzoate combined with UV treatment in blend films was positive from the microbial point of view because of the growth inhibition of a wide spectrum of microorganisms. From a physicochemical perspective, the UV treatment of films also changed their morphology rendering them more insoluble in water, turning the functionalized blend films into a potential material to be applied as food packaging.

Structural Insight into Chitosan Supports Functionalized with Nanoparticles

The incorporation of suspensions of nanoparticles functionalized with gallic acid (GA) was used as a strategy to obtain nanocomposite active films with different both chitosan : tripolyphosphate (CH : TPP) and nanoparticles:chitosan (N : CH) ratios. The thermal analysis carried out by modulated differential scanning calorimetry (MDSC) allowed observing the shift of an endothermic event towards higher temperatures with a greater N : CH ratio. Analyzing ATR-FTIR spectra through principal component analysis (PCA) can be inferred that the incorporation of the nanoparticles produced a discrimination of the samples into clusters when the region 1400–1700 cm−1 was considered. The decrease in crystalline size with the inclusion of nanoparticles (NA and NB) proved the existence of interactions among CH, TPP, and GA, resulting in a more amorphous structure. The positron annihilation lifetime spectroscopy (PALS) technique was adequate to correlate the glass transition temperatures ( ) obtained by using the MDSC technique with parameters τ2 and I2 ascribed to the annihilation of positrons in the interface. The cross section of nanocomposites obtained by scanning electron microscopy (SEM) clearly showed a homogeneous distribution of the nanoparticles without aggregation, suggesting their compatibility with the CH matrix. By virtue of the obtained results, the nanocomposites with the greatest nanoparticle proportion and the highest TPP concentration attained significant modifications in relation to CH matrices because of the crosslinking of the biopolymer with GA and TPP.