Chitosan nanocoatings N-acylated with decanoic anhydride: Hydrophobic, hygroscopic and structural properties

Thin (ca. 340 nm) chitosan coatings were deposited onto glass substrates via dip-coating, then modified with the methanol solution of decanoic anhydride (0.17-56 mM). NMR, FTIR and XPS measurements confirmed that the acylation degree increased from 18 % to 45 %, and at the highest degree, the whole layer was acylated homogeneously by the reagent molecules. The coating thickness increased (up to 60 %), and the refractive index decreased (from 1.541 to 1.532) due to the acylation, that was determined by UV-visible spectroscopy. The AFM did not reveal morphological changes, but wetting tests showed that the acylation rendered the coating hydrophobic (water contact angle increased from ca. 75° to 100°). The contact angle, however, decreased to 85° due to the development of a second molecular layer of the decanoic acid by-product at the highest (over 25 mM) reagent concentrations. XRD studies showed a self-assembling structuring of the alkyl-chains in the bulk phase, which occurred in the case of the highest degree of acylation. This also manifested itself in a significant decrease of the layer hygroscopicity: the swelling degree decreased from 40 % to 8 % in a saturated water atmosphere monitored by spectroscopic ellipsometry.

Structure, the energy, sorption and biological properties of chiral salts of chitosan with l- and d-ascorbic acid

The influence of l- and d-ascorbic acid diastereomers on the structure, supramolecular ordering, energy, sorption and biological properties of heterochiral (D-L) and homochiral (D-D) salt complexes of chitosan (d-glucan)-acid was studied. The thermal effect of dissolving chitosan in l-ascorbic acid and the protonation degree of (D-L)-salts were lower than those in the medium of the d-isomer. Homochiral (D-D) salts, in contrast to heterochiral (D-L) ones, are distinguished by a more developed system of intermolecular and intramolecular contacts, a more ordered and equilibrium supramolecular organization of macrochains, a higher crystallinity degree, and a smaller amount of crystallization water. The sorption isotherms of chiral salts were approximated by the thermal equation of sorption and the superposition of the Langmuir and Flory-Huggins isotherms. Significant differences were found in the limiting value and energy of sorption, the constant of adsorption equilibrium, the limiting sorption capacity of the localized mode of water, and the Gibbs mixing energy. Biotesting on non-vascular (Scenedesmus quadricauda) and vascular eukaryotes (Linum usitatissimum) revealed the growth-stimulating effect of the D-D salts. The obtained results confirm our hypothesis of the homochiral salt complexes d-glucan-d-ascorbic acid best corresponding to the principles of the functional organization of biological objects.

Free Volume and Water Sorption by Cellulose Esters

The results ofthe sorption properties of cellulose acetate (CA) with different degrees of substitution (SD) are summarised. It has been shown that the sorption capacity of CA in water vapour decreases naturally with increasing content of acetate groups in monomeric units of cellulose ethers. The experimental isotherms are analysed according to the double sorption model. Hydrate numbers of hydroxyl and acetate groups were determined. The paired parameters of the Flory–Huggins interaction were calculated. It is shown that the decrease of the Langmuir component is due to the replacement of hydroxyl groups by ester groups, whose local sorption capacity by water vapour is lower than the sorption capacity of OH groups. In the area of high humidity, there is an increase in vacancy sizes due to plasticisation of the sorbents.

Formation of Liesegang Structures under the Conditions of the Spatiotemporal Reaction of Polymer-Analogous Transformation (Salt → Base) of Chitosan

This paper presents the results of our study of the diffusion front progression of OH^- ions in the bulk of a flat layer of the salt chitosan form during the course of the chemical reaction of the polymer-analogous salt → base transformation, accompanied by the formation of a water-insoluble polymeric phase as a gel film with its structure of concentric rings or tangential bands. Using scanning electron microscopy and polarization microscopy, structural and morphological features of these periodic formations were visualized. Physicochemical parameters and spatiotemporal mass transfer characteristics were obtained. The process under study is shown to obey the classical laws of ion-exchange reactions, and the formation kinetics and the ratio of the positions of periodic structures are described by the laws characteristic of the Liesegang phenomenon. The average diffusion coefficients of hydroxide ions in the periodic formations calculated, considering the protonation degree of amino groups, were found to be no more than a decimal order of magnitude lower than those in an aqueous solution. This confirms the fact of swelling of the formed chitosan base and the existence of a gel film, in whose liquid phase diffusion occurs.

Chitin increases drying survival of encapsulated Metarhizium pemphigi blastospores for Ixodes ricinus control

Ticks, like Ixodes ricinus, have negative impacts on human and animal health in Germany and worldwide, with almost no specific scientifically proven biological control agent commercially available. Biological control agents containing entomopathogenic fungi present many advantages over chemical acaricides but usually high doses of aerial conidia (10¹³-10¹⁴ conidia/ha) are required to control arthropod pests in the field. A suitable formulation containing nutrients not only makes sensitive blastospores applicable but also functions as a microfermenter to multiply the biomass and thus significantly reduce the required application dosage. For this approach, Metarhizium pemphigi X1c blastospores were encapsulated in calcium alginate beads with granular corn starch or chitin powder as nutrients to ensure formation of aerial conidia on the surface and were then dried. The highest concentration was obtained with moist beads containing chitin (4.68 ± 0.71∙10⁷ conidia∙bead^-1). The highest drying survival was also obtained with chitin as the additive (14.7 ± 2.18%). Newly formed aerial conidia of all formulations showed high virulence and caused 100% mortality of I. ricinus nymphs. Altogether, this study paves the way for a lower dose and cost-effective application of blastospores for the control of above ground arthropod pests.

Influence of Genipin Crosslinking on the Properties of Chitosan-Based Films

Chitosan is a promising environment friendly active polymer packaging material due to its biodegradability, exceptional film forming capacity, great mechanical strength, appropriate barrier property along with intrinsic antioxidant and antimicrobial features. Bifunctional reagent was used for producing water insoluble chitosan films. Biopolymeric films crosslinked by Genipin (Gp), which is a reagent of natural origin, should have high potential in food packaging. The influence of the ratio of functional groups in the chitosan-Gp system on film absorption in the visible and ultraviolet regions of the spectrum, sorption, physical, and mechanical properties of the films has been studied. The degree of chitosan crosslinking in the films obtained from solutions containing Gp was estimated using the experimental data on film swelling and water vapor sorption isotherms. It is demonstrated that crosslinking with genipin improves swelling, water resistance, and mechanical properties of the films.

Sorption, diffusivity, permeability and mechanical properties of chitosan, potassium sorbate, or nisin incorporated active polymer films

The active multilayer packaging films were formed from low-density polyethylene (LDPE) and polyamide containing a 2% antimicrobial agent in one of the LDPE sides of the film (LDPE/polyamide/LDPE-2% antimicrobial agent). The antimicrobial agents used were potassium sorbate (PS-film), nisin (N-film), or chitosan (CTS-film). The effects of antimicrobial incorporation on water vapor permeability (P), diffusivity (D _eff ), and solubility (S _o and S _H ) of the active and control films (LDPE/polyamide/LDPE) were investigated. A dynamic vapor sorption analyzer (DVS) was used to estimate the sorption isotherms of the films at 25 °C. Peleg was found to be the best equation to describe sorption behaviors. The addition of PS and nisin into the film matrix resulted in a lower P than that of the control film. The D _eff values of the active films were lower than those of control films, except for the CTS-film. The high water-holding capacity of PS and nisin might limit the D _eff of the respective films. It was found that Henry's law was applicable to relate P, D _eff , and S _o and S _H values of the multilayer film [correlation coefficient (r) = 0.909-0.971]. The mechanical and thermal properties of the active films were not significantly affected by the incorporation of PS and nisin (p > 0.05). However, the impact of stress and elongation (transverse direction) on the CTS-film was lower than on other films, which indicated that chitosan improved the mechanical properties of the film.