Real-time monitoring of the starch cross-linking with citric acid by chemorheological analysis.

Cross-linking has been used as a strategy to improve the mechanical properties of starch films. However, the concentration of the cross-linking agent and the cure time and temperature determine the structure and properties of the modified starch. This article, for the first time, reports the chemorheological study of cross-linked starch films with citric acid (CA) through monitoring the storage modulus as a function of time G'(t). In this study, a CA concentration of 10 phr showed a pronounced increase of G'(t) during the cross-linking of starch, followed by a constant plateau. Analyses of infrared spectroscopy validated the result chemorheological. In addition, the mechanical properties showed a plasticizing effect of the CA at high concentrations. This research demonstrated that chemorheology is a valuable tool in the study of starch cross-linking, which becomes a promising technique to evaluate the cross-linking of other polysaccharides and cross-linking agents.

Oxidized cellulose nanofibers from sugarcane bagasse obtained by microfluidization: Morphology and rheological behavior.

It is advantageous to understand the relationship between cellulose fiber morphology and the rheological behavior of its dispersions so that their application can be optimized. The goal of this study was to produce sugarcane bagasse-sourced cellulose dispersions with different numbers of high-pressure homogenization cycles. Microfluidization produced cellulose nanofibers (between 5 and 80 nm in diameter) with similar surface charge densities and crystallinities (measured on the resulting films). Oscillatory rheology showed that TEMPO-oxidized cellulose dispersions exhibited gel-like behavior. However, not only did the samples with more microfluidization cycles present a lower storage modulus, but the sample with 100 cycles completely lost the gel-like characteristic, presenting a viscous fluid rheological behavior. Thixotropy loop tests revealed the influence of nanofiber length on the dispersion's structure, as evidenced by the decrease in the hysteresis value along with fiber breakage. Therefore, our findings demonstrate that the rheological properties of the dispersion can be tuned according to the length of the nanofibers, allowing for targeted applications.