Katarzyna Lewandowska

The Huggins viscosity coefficient of aqueous solution of poly(vinyl alcohol)

Abstract Although water at room temperature is not a poor solvent for poly(vinyl alcohol) (PVA), the values of the Huggins viscosity coefficient k H are typically higher than 1/2. This is attributed to association. Based on the model put forward by Peterlin, the k H values reported in the literature for aqueous solutions of PVA were examined and the equilibrium constant K * was estimated. It turned out that it increases with increasing molecular weight and depends on the content of residual acetate units. The effect of temperature seems to be weak. Based on the theory of phase equilibria in solutions of crystalline polymers, the values of the Flory–Huggins interaction parameter χ , necessary for molecular dissolution in water of semicrystalline samples, were estimated and compared with the experimental data for samples of PVA with different content of vinyl acetate units. Differences in stability (aging) of PVA solutions can be explained on this basis. Existing experimental data on the viscosity of fresh dilute solutions of PVA in water are interpreted in terms of a model, where the association is due to intermolecular hydrogen bonds between the OH groups of polymer chains. On the contrary, aging phenomena may be attributed to an increase in size and amount of semicrystalline domains acting as multifunctional cross-linking agents.

Characterization of chitosan composites with various clays

The structural properties, thermal behaviour and mechanical properties of composites of chitosan (Ch) with nanoclay (montmorillonite, MMT) and/or nanoclays after surface modification have been characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA) and a tensile tests. The microstructure obtained by SEM and AFM microscopy for unmodified chitosan and its composites showed that particles are relatively well dispersed in the chitosan matrix. However, the increasing concentration of the chitosan solution from 1% to 2% decreases the homogeneity of the surface of the composites. In the case of chitosan composite with modified nanoclay (contains 25-30 wt.% of octadecylamine), the lack of particles aggregates in polymer matrix independent of the concentration of chitosan solution was observed. Generally, addition of nanoclay after its surface modification improved the mechanical and thermal properties of the composite much more than montmorillonite without modification.

3D composites based on the blends of chitosan and collagen with the addition of hyaluronic acid

3D porous composites based on blends of chitosan, collagen and hyaluronic acid were obtained through the lyophilization process. Mechanical properties, swelling behavior and thermal stability of the blends were studied. Moreover, SEM images were taken and the structure of the blends was studied. Biological properties of the materials obtained were investigated by analyzing of proliferation rate of fibroblast cells incubated with biomaterial extract using MTT assay (3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide). The results showed that the properties of 3D composites based on the blends of chitosan and collagen were altered after the addition 1%, 2% and 5% of hyaluronic acid. Mechanical properties and thermal stability of chitosan/collagen blends were improved in the presence of hyaluronic acid in the composite. New 3D materials based on the blends of chitosan, collagen and hyaluronic acid were non-toxic and did not significantly affect cell morphology.

The influence of UV-irradiation on thermal and mechanical properties of chitosan and silk fibroin mixtures.

In the present paper the results regarding the influence of UV-irradiation with 254 nm wavelength on the thermal and mechanical properties and the intrinsic viscosity of chitosan/silk fibroin mixtures are presented. The mixture of chitosan and silk fibroin in solution and thin films made of chitosan/silk fibroin mixture obtained by solvent evaporation were submitted to the treatment with UV irradiation (wavelength 254 nm) for different time intervals. Mechanical properties of thin films made of chitosan/silk fibroin blends before and after UV-irradiation have been investigated by mechanical testing machine and compared with mechanical properties of chitosan films. The changes in such mechanical properties as ultimate breaking strength, percentage of elongation at break and Young Modulus have been investigated. The results have shown, that the mechanical properties of the blends were greatly affected by time of exposure to UV irradiation. Ultimate tensile strength and ultimate percentage of elongation decreased after UV irradiation of the blend. Increasing UV irradiation led to the decrease in Youngs Modulus of the chitosan/silk fibroin blend. Viscosity of chitosan/silk fibroin mixtures decreased after UV-irradiation. Thermal properties of the mixtures have been only slightly altered by UV-irradiation.

Characterization of chitosan composites with synthetic polymers and inorganic additives

In the present study, the results from thermogravimetric analysis (TGA), contact angle measurements, tensile tests, scanning electron microscopy (SEM) and atomic force microscopy (AFM) of polymer composites containing chitosan (Ch) and montmorillonite (MMT) with and without poly(vinyl alcohol) (PVA) are presented. Measurements of the contact angles for diiodomethane (D) and glycerol (G) on the surfaces of chitosan films, Ch/MMT and Ch/PVA/MMT, were made and surface free energies were calculated. It was found that the wettability of the chitosan/MMT or Ch/PVA/MMT composite films decreased relative to the wettability of chitosan. The microstructure of unmodified polymers and their composites, as observed by SEM and AFM, showed particles that are relatively well dispersed in the polymer matrix. The TGA thermograms and mass loss percentages at different decomposition temperatures showed that the thermal stability of the binary composite slightly decreases upon the addition of PVA. The film mechanical properties such as tensile strength, Youngs modulus and tensile strain at break depend on the composition and varied non-uniformly. Both composites possessed a tensile strength and Youngs modulus of 27.6-94.3MPa and 1.5-3.5GPa, respectively. The addition of PVA to the composite led to a reduction in tensile strength by approximately 40%.

Mechanical and Morphological Studies of Chitosan/Clay Composites

In the present paper, the results of mechanical properties and atomic force microscopy studies of chitosan (Ch) with montmorillonite (MMT) or nano-clay are presented. The blends composed of chitosan (Ch) with montmorillonite (MMT) have been prepared as material designed for cosmetic industries and/or biomedical applications. Mechanical properties such as the ultimate tensile strength, percentage elongation and Youngs modulus of films have been determined and compared. Addition of nanoclay after surface modification improved the mechanical properties more than montmorillonite without modification. The surface properties of the chitosan and montmorillonite films and their composites have been studied by tapping-mode atomic force microscopy (AFM). The changes of topography images were considered by determining the root mean square (Rms) deviation in the image data. AFM images show differences in surface properties of chitosan films, chitosan/MMT films, and chitosan/nanoclay films. Surface roughness decreased with addition of MMT and/or nanoclay into chitosan matrix. The obtained results suggest that the properties of chitosan and montmorillonite composites depend on the blend composition and on the way of surface modification of nano-clay.

Characterization of Thin Chitosan/Polyacrylamide Blend Films

The structure and surface properties of blends containing chitosan (Ch) and partially hydrolyzed polyacrylamide (HPAM) were analyzed by contact angle measurements and atomic force microscopy (AFM). The results of contact angle and the surface free energy revealed that HPAM films are more polar than chitosan films. In the case of Ch/HPAM blends, the values of surface free energy and polar component are reduced significantly compared with pure polymers. This behavior indicates rather hydrophobic character of this surface. The roughness of the blends increases with the increase of Ch content. This may indicates a strong interaction between the polymeric components.

Surface and thermal properties of collagen/hyaluronic acid blends containing chitosan

The structure and surface properties of binary and ternary blends containing collagen (Coll), hyaluronic acid (HA) and chitosan (Ch) were investigated by contact angle measurements, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Thin films of Coll/HA and Coll/HA/Ch blends have been formed by casting methods from aqueous acid solutions. The surface roughness, hydrophobic/hydrophilic character and thermal stability of Coll/HA were changed after addition of chitosan. Thermal stability of binary blends increase upon the addition of chitosan. The results of contact angle and the surface free energy revealed that hyaluronic acid films are more polar than collagen and chitosan films. The surface energy and its polar and dispersive components of binary and ternary blends were calculated and more hydrophilic films were produced by the addition of HA and chitosan, also resulting in more thermally stabile materials. These results demonstrate that collagen interacts with hyaluronic acid and chitosan changing the surface properties of polymer films.

Physico-chemical properties of three-component mixtures based on chitosan, hyaluronic acid and collagen

ABSTRACT The aim of this work was preparation of biopolymer materials based on blends of chitosan, hyaluronic acid and collagen. The properties of blend films have been investigated by contact angle measurements and atomic force microscopy. The contact angle measurements showed that chitosan films are more polar after addition of hyaluronic acid and collagen. The AFM results showed that the addition of chitosan to hyaluronic acid led to the increase of surface roughness. Moreover, miscibility studies of biopolymeric blends were also done using the viscometric method. Viscometric studies indicated that two-component and three-component blends are partially miscible.

Structure and Interactions in Chitosan Composites

In the present study, the results of Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) studies of chitosan (Ch) with montmorillonite (MMT) or nanoclay are presented. MMT samples have been used without modification and after nanoclay surface modification. Composites of chitosan with montmorillonite samples were obtained by drop casting suspensions of montmorillonite (3% relative to chitosan) and polymer (2wt%) in 1% acetic acid. The FTIR spectra of film composites in the amide I, amide II bands and the hydroxyl stretching bands of chitosan have been analyzed. The homogeneity and morphology of chitosan composites were ascertained from tapping-mode atomic force microscopy. The obtained results suggested that there were interactions between chitosan and montmorillonite. The microstructure obtained by AFM microscopy for chitosan and its composites showed that particles are relatively well dispersed in the chitosan matrix.