Obtenção de amidos termoplásticos para a extrusão de pós cerâmicos

Evaluation of dual modification by high hydrostatic pressure and annealing on the physicochemical properties of bean starch

This study investigated the physical modifications by high hydrostatic pressure (HHP) at 600 MPa for 30 min/30 °C, annealing (AN) at 50 °C/24 h and the combination of both (HHP + AN and AN + HHP) applied to yellow bean starch to verify changes in morphology, X-ray diffraction, molecular order, thermal properties and pasting properties of native (NS) and modified starches. Morphological analysis showed loss of sphericity and increase in diameter with the appearance of pores on the surface after application of treatments. The AN starch showed lower values of syneresis, degree of double helix (DD), order (DO), and viscosity of the paste obtained by RVA. It exhibited a Vh-type classification with the appearance of the amylose-lipid complex. However, the gelatinization temperatures, as well as the enthalpy of gelatinization, were significantly higher. On the other hand, the starch treated with HHP showed a higher Setback (SB) value. The greatest modifications were found for the starches subjected to the combined treatments (AN + HHP) and (HHP + AN), where the order of the treatments was significant for the morpho-structural changes of yellow bean starch. According to the micrographs, the surface aspect was altered, with AN + HHP showing greater irregularities and flat yet irregular faces, as well as a larger granule diameter (147.05). The X-ray diffractogram showed a reduction in crystallinity from 28.14 % (NS) to 18.09 % (AN + HHP) and classified the starch as type "A". The double modification (HHP + AN and AN + HHP) reduced the gelatinization temperature and the enthalpy of gelatinization but had no effect on the bands of the FT-IR spectrum. There was only a reduction in the degree of order and the double helix. Finally, the treatment with AN + HHP is more effective as the gelatinization with AN facilitates the application of HHP. Both methods used are classified as physical (thermal and non-thermal), aiming to minimize environmental impacts and achieve faster and safer morpho-structural modification without leaving chemical residues in the products.

Influence of Glycerol and SISAL Microfiber Contents on the Thermal and Tensile Properties of Thermoplastic Starch Composites

The increasing use of petroleum plastics has caused environmental damage due to the degradation time of these materials. An alternative to petroleum plastics could be thermoplastic starch (TPS). However, thermoplastic starch does not exhibit satisfactory tensile properties. The mechanical properties of thermoplastic starch can be improved by adding sisal microfibers. Thus, the objective of this study was to evaluate the influence of different levels of glycerol and sisal microfibers on the thermal and tensile properties of thermoplastic corn starch composites. The microfibers were obtained via mechanical treatment followed by chemical treatment (alkaline treatment and bleaching). The films were obtained by the casting method using commercial corn starch and glycerol as a plasticizing agent, reinforced with sisal microfibers. Fourier transform infrared spectroscopy (FTIR) results revealed that the addition of microfibers did not change the chemical structure of the TPS matrix. The films from the samples with 18% glycerol and 10% microfibers had the highest value for the maximum tension, equal to 4.78 MPa. The thermal decomposition profile of TPS was not altered by the addition of microfibers. Our findings demonstrated the profound influence of glycerol and microfiber contents on the tensile properties of thermoplastic starch composites.

Films composed of white angico gum and chitosan containing chlorhexidine as an antimicrobial agent

Anadenanthera colubrina, popularly known as white angico, is a species extensively cultivated in Brazil, mainly in the cerrado region, including the state of Piauí. This study examines the development of films composed of white angico gum (WAG) and chitosan (CHI) and containing chlorhexidine (CHX), an antimicrobial agent. The solvent casting method was used to prepare films. Different combinations and concentrations of WAG and CHI were used to obtain films with good physicochemical characteristics. Properties such as the in vitro swelling ratio, the disintegration time, folding endurance, and the drug content were determined. The selected formulations were characterised by scanning electron microscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and X-ray diffraction, and the CHX release time and antimicrobial activity were evaluated. CHX showed a homogenous distribution in all CHI/WAG film formulations. The optimised films showed good physicochemical properties with 80% CHX release over 26 h, which is considered promising for local treatment of severe lesions in the mouth. Cytotoxicity tests of the films did not show toxicity. The antimicrobial and antifungal effects were very effective against the tested microorganisms.