Structure and properties of starch - BaSO4 composite obtained using mechanical activation techniques.

The aim of this study is to obtain and characterize starch films structurally modified by in situ precipitation of BaSO4 combined with mechanical activation of casting dispersion in a rotor-stator device. By the rheological method, it was found that the modification causes a decrease in the ability of casting dispersions to structure over time. Composite films with a filler content of 0 %-15 % (w/w) were characterized using optical and SEM microscopy, FT-IR spectroscopy, and tensile and moisture resistance testing data. The maximum increase in strength (by 70 %) and elongation at break (by 870 %) is achieved with a filler content of 5 % and 15 %, respectively. An increase in the filler content to 5 % causes an increase in starch recrystallization rate, but at concentrations above 5 % of BaSO4, it inhibits retrogradation. The films obtained by mechanical activation with optimized parameters were uniformly translucent, had lower water vapor permeability than films made from starch alone, had high flexibility, and did not warp or shrink. The developed high-performance, environmentally friendly method can be recommended for the large-scale production of starch-based composite materials.

The influence of the combined impact of shear stress and cavitation on the structure and properties of starch-natural rubber composite.

In this article, we examined a high-performance, environmentally friendly method for producing composite films based on starch and natural rubber latex (NR). To increase the compatibility of the components, the casting dispersions were subjected to short-term (10 s) mechanical activation in a rotor-stator device. Using the rotational viscosimetry method, it was found that mechanical activation reduces the structuring degree and the effective viscosity of the casting dispersions. The composite films with the NR content of 0-30 % were characterized using optical and SEM microscopy, X-ray diffraction, tensile, and moisture resistance testing data. When the NR content increases from 0 to 30 %, the elongation at break increased by 570 % and 950 % for films obtained using mechanical activation and without it, respectively. The extremely high increase in film tensile strength (on average by 155 %) and the decrease in the NR extractability with toluene due to the use of mechanical activation indicate the possibility of mechanically induced formation of an in situ copolymer at the starch-NR interface. The developed method can be recommended for large-scale production of composite starch-based materials.

Effect of mechanical activation on starch crosslinking with citric acid.

The aim of this research was to investigate the influence of mechanical activation in a rotor-stator device on starch crosslinking with citric acid and the properties of the films obtained by the casting method. Two methods of preparation of the casting hydrogels were used: involving the introduction of chemical reagents before and after the mechanical activation. The films from the initial and mechanically activated hydrogels were characterized using optical and AFM microscopy, X-ray diffraction and FTIR-spectroscopy. The di-esterification degree, opacity, tensile properties and moisture resistance of the films were also studied. Mechanical activation of the starch hydrogels made it possible to make the films smoother and more transparent and to increase their tensile strength and moisture resistance. Pre-activation of the hydrogels without reagents showed better film performance than activation in the presence of citric acid.

Effect of composition and mechanoactivation on the properties of films based on starch and chitosans with high and low deacetylation.

The effect of composition and mechanoactivation in the rotor-stator device on the rheological and film-forming properties of casting blends based on corn starch and chitosans with high (HDC) and low (LDC) deacetylation degree was studied. Films were characterized using optical and atomic force microscopy, X-ray diffraction, FTIR-spectroscopy and by tensile and moisture permeability testing data. An increase in chitosan content was found to result in the blends viscosity increase as well as the tensile strength, elongation and moisture permeability of films. Mechanoactivation was shown to cause an increase in the homogeneity, smoothness and transparency of the films, and an increase in the tensile strength by 1.5 and 2.5 times for the HDC and LDC based films, respectively. It is concluded that the developed eco-friendly and easily implemented method, which allows improving the unsatisfactory properties of starch-chitosan films without the introduction of additional chemicals, can be used on an industrial scale.

Gelation in solutions of low deacetylated chitosan initiated by high shear stresses.

A new process of mechanically initiated formation of chitosan physical hydrogels in aqueous solution, without a cross-linking agent, was studied. Physical hydrogel is formed by mechanical activation of solutions of chitosan with a low deacetylation degree (58%) in situ in a rotor-stator device for 10 s. The formation of 3D gel structure has been proven by rotational viscometry and dynamic rheometry methods. Gelation is caused by the action of high shear stresses initiating the formation of hydrophobic associates from residual chitinous blocks. In comparison with the films from untreated chitosan, the films obtained by drying hydrogel have a lower degree of crystallinity and a higher sorption capacity towards water vapor and Cu2+ ions, as well as the ability to retain up to 5000% of water during re-swelling without destruction.

The influence of the combined impact of shear stress and cavitation on the structure and sorption properties of chitin.

In this work, we studied the structural, morphological and chemical transformations in α- chitin, caused by its mechanical activation in the form of an aqueous suspension in the rotor-stator device for 5-30 s. Mechanically activated chitin (MA-chitin) was characterized using optical and electron scanning microscopy, N2 adsorption/desorption isotherms, X-ray diffraction and FTIR-spectroscopy. It was established that the specific surface area, porosity and the deacetylation degree of chitin increase with increasing processing time, and the decrease in crystallinity and reducing the packing density of macromolecular chains does not correlate with this indicator due to the development of recrystallization. The efficiency of chitin activation was evaluated by studying its ability to adsorb anionic and cationic dyes. It was found that the limiting adsorption capacity of MA-chitin was on average 2-4 times higher, and the time to reach equilibrium was, on average, 3-4 times less compared to raw chitin.

Influence of the composition and high shear stresses on the structure and properties of hybrid materials based on starch and synthetic copolymer.

The method of mechanical activation in the rotor-stator device was used to combine the starch hydrogel and the latex of the synthetic copolymer. The compatibility of the components was found to improve consistently by the preliminary mechanoactivation of the starch gel and the joint activation of the mixturs. The joint activation was shown to promote the crystallization of starch and the amorphous phase ordering of the composite. An increase in the starch content and co-activation were found to result in rise in the Young's modulus and tensile strength, but joint activation ensures an increase in the elasticity of the samples. The kinetic parameters of moisture transfer through composite films were estimated. A distinct compensative effect was found, consisted in a significant increase in the sorption coefficient and a decrease in the diffusion coefficient with increasing starch content.