Study of the degradation in an ultisol of alginate-chitosan complex and its stability and applicability as a soil conditioner.

The present work describes the process of degradation of a polyelectrolytic complex (PEC) based on sodium alginate (ALG) and chitosan (CHI), buried for different time intervals, in a clayey soil (ultisol) collected from the municipality of Campos dos Goytacazes, in the northern region of the state of Rio de Janeiro, Brazil. The influence of PEC on soil moisture was also investigated. The results showed that soil moisture increased with the presence of PEC after 7 days of testing, and remained high until the end of the study. FTIR and Raman spectra showed that the breaking of the glycosidic bond (C-O-C) was responsible for the PEC degradation. Thermogravimetry results revealed that alginate was possibly degraded faster than chitosan. Microscopic analysis of the PEC revealed a fragile and fragmented surface of the samples that were buried, in comparison with those not buried. The microbiological assays of the soil confirmed the biodegradation of the polysaccharides. Chemical analysis of soil indicated that PEC did not significantly influence soil fertility. Therefore, we conclude that the PEC (ALG: CHI), formed only by electrostatic interaction, buried in clayey soil, even being biodegraded, can be a promising soil conditioner for agricultural applications.

Effect of pH variation and crosslinker absence on the gelling mechanism of high acyl gellan: Morphological, thermal and mechanical approaches.

This article describes the preparation of superabsorbent hydrogels made of high acyl gellan without the addition of a crosslinker . Variations of the pH of the medium and different gellan solution concentrations were evaluated. The samples produced were investigated regarding their morphology by scanning electron microscopy, thermal resistance by thermogravimetry, and compressive strength by mechanical testing. Rheological tests were also performed and the swelling decree of the hydrogels was calculated. The results showed that the morphology of the samples could be modified by varying the preparation conditions, ranging from a foliaceous structure to a brittle structure, containing voids with different sizes. The hydrogels prepared with acidic pH presented less compressive strength than those prepared with basic pH. Although all the samples had swelling degree greater than 1000 %, the highest values were obtained with the samples prepared at pH 4, regardless of the concentration of the gellan solution.

Evaluation of different methods to prepare superabsorbent hydrogels based on deacetylated gellan.

This study stands out for analyzing distinct ways of preparing hydrogels from deacetylated gellan gum that have high swelling capacity and good thermal resistance. We carried out a thorough investigation, applying various combinations of different experimental parameters. Two preparation methods were evaluated, in which the pH was adjusted before or after thermal treatment of the gellan solution, with subsequent addition of the crosslinking agent, to assess the influence of preparation method on the conformation of the gellan chains regarding formation of double helices. The pH range tested varied from acid (2, 3 or 4) to basic (8, 9 or 10). Gellan solution was prepared in different concentrations. Both pure gellan and hydrogel samples were characterized by Fourier-transform infrared spectroscopy and thermogravimetry. Pure gellan was also characterized by atomic absorption spectroscopy. The swelling degree of the hydrogels was analyzed. The results showed that all the hydrogels had high swelling capacity (>400%), so they can be considered superabsorbent materials. Hydrogels prepared with acid pH in general had lower thermal resistance than samples prepared in alkaline pH, regardless of the preparation method. Samples prepared with alkaline pH tended to have initial decomposition temperature similar to that of pure gellan.

New polyelectrolyte complex from pectin/chitosan and montmorillonite clay.

A new nanocomposite hydrogel was prepared by forming a crosslinked hybrid polymer network based on chitosan and pectin in the presence of montmorillonite clay. The influence of clay concentration (0.5 and 2% wt) as well as polymer ratios (1:1, 1:2 and 2:1) was investigated carefully. The samples were characterized by different techniques: transmission and scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, swelling degree and compression test. Most samples presented swelling degree above 1000%, which permits characterizing them as superabsorbent material. Images obtained by transmission electron microscopy showed the presence of clay nanoparticles into hydrogel. The hydrogels' morphological properties were evaluated by scanning electron microscope in high and low-vacuum. The micrographs showed that the samples presented porous. The incorporation of clay produced hydrogels with differentiated morphology. Thermogravimetric analysis results revealed that the incorporation of clay in the samples provided greater thermal stability to the hydrogels. The compression resistance also increased with addition of clay.