Esam A. El-Hefian

The Preparation and Characterization of Chitosan / Poly (Vinyl Alcohol) Blended Films

In this study, chitosan and PVA were blended at different proportions (considering chitosan as the main component) in solution forms. The chemical structure and the morphology of the obtained blend films were investigated using FTIR and field emission scanning electron microscope (FESEM). The thermal stability of the blend films were also studied using thermal gravimetric analysis (TGA). Our results showed that chitosan and PVA form a compatible blend and their films displayed homogenous and smooth surface properties compared to their individual pure components. The blending of PVA with chitosan at all proportions was found to highly enhance the swelling of the obtained films compared to that of pure chitosan one.

Preparation and characterization of chitosan/poly(vinyl alcohol) blended films: Mechanical, thermal and surface investigations

In this study, blends of chitosan (CS) and polyvinyl alcohol (PVA) (CS/PVA) having various proportions were prepared and characterized by universal mechanical tester, the differential scanning calorimetry (DSC) and contact angle measurements. Studying the mechanical properties of the films showed that blending improved the tensile strength, which increased with increasing PVA content up to 40% while the elongation% at break of the blends was decreased compared to that of the pure components. The obtained results of DSC suggested that some interaction between chitosan and PVA mostly took place. Static water contact angle measurements showed an improvement in the wettability of the obtained films.

Preparation and Characterization of Chitosan/Agar Blended Films: Part 1. Chemical Structure and Morphology

Chitosan/agar (CS/AG) films were prepared by blending different proportions of chitosan and agar (considering chitosan as the main component) in solution forms. The chemical structure and the morphology of the obtained blended films were investigated using Fourier transform infrared (FTIR) and field emission scanning electron microscope (FESEM). It was revealed that chitosan and agar form a highly compatible blend and their films displayed homogenous and smooth surface properties compared to the individual pure components.

Preparation and characterization of chitosan/agar blended films: Part 2. Thermal, Mechanical, and surface properties

Chitosan/agar (CS/AG) films were prepared by blending different proportions of chitosan and agar (considering chitosan as the major component) in solution forms. The thermal stability of the blended films was studied using thermal gravimetric analysis (TGA). It was revealed that chitosan and agar form a compatible blend. Studying the mechanical properties of the films showed a decrease in the tensile strength and elongation at break with increasing agar content. Blending of agar with chitosan at all proportions was found to form hydrogel films with enhanced swelling compared to the pure chitosan one. Static water contact angle measurements confirmed the increasing affinity of the blended films towards water suggesting that blending of agar with chitosan improves the wettability of the obtained films.

PREPARATION AND CHARACTERIZATION OF CHITOSAN/AGAR BLENDS: RHEOLOGICAL AND THERMAL STUDIES

In this work, a number of mixture aqueous solutions of chitosan/agar (CS/AG) at different ratios (considering chitosan as the main component) were prepared. The rheological properties i.e. shearing viscosity and shear stress of the blend solutions as a function of shear rate as well as the thermal properties of the blend films were investigated. Among the parameters studied were temperature, shearing time and storage time. Results showed that almost Newtonian behavior was observed at temperatures from 40°C to 55°C for the ratios 100/0, 90/10, 80/20 and 70/30. However, the proportions 60/40 and 50/50 showed a clear shear thinning behavior (pseudoplastic non-Newtonian behavior). It was also found that all the blend solutions obeyed the Arrhenius equation. In addition, the effect of shearing time on the shearing viscosity of all blends did not show any significant differences at all shearing times applied in this study except the proportion 50/50 wherein decreasing in shearing viscosity and shear stress was observed as the shearing time increased. Furthermore, different behaviors were observed for the blend solutions when the period of storage was extended to three weeks. The FTIR results and the differential scanning calorimetery (DSC) curves showed that the interaction between chitosan and agar can occur.

Preparation and Characterization of Chitosan/Polyvinyl Alcohol Blends-A Rheological Study

Blends of chitosan (CS) and polyvinyl alcohol (PVA) of different proportions (considering chitosan as the main component) were prepared. The rheological properties of the obtained blend solutions such as the shearing viscosity and the shear stress were investigated as a function of shear rate under various temperatures, shearing times and solution storage times using a digital viscometer. The CS/PVA solutions showed a Newtonian behavior at temperatures in the range of 40-55 °C regardless of the blend composition. This was accompanied by a general decrease in the viscosity with increasing PVA content in the blend. The heat-dependant viscosity changes of the blend solutions were found to follow Arrhenius equation. The shearing time was found to have no significant effect on the shearing viscosity of all blended solutions. However, the variation of solution storage period was found to have a mixed effect when time was extended to 3 weeks.

Preparation and Properties of Non-Crosslinked and Ionically Crosslinked Chitosan/Agar Blended Hydrogel Films

Hydrogel films of chitosan (Cs) and agar blends of various proportions were prepared using physical solution blending. Some of the obtained films were ionically cross-linked by treatment with calcium chloride solution. The obtained films were characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetry analysis (TGA), differential scanning calorimetery (DSC) and universal mechanical tester. The non-crosslinked Cs/agar blended films showed lower water swelling, melting temperature, stiffer and less elastic properties than that of pure Cs films and higher than pure agar films. Crosslinked blended films displayed further reduction in the swelling and melting temperature while maintained more hydrogel stability.

A Preliminary Qualitative Study of Two Common Acacia Species in Sudan

This research is dealing with the analysis of tannins of two common Acacia species of Sudan i.e. Acacia nilotica and Acacia seyal. Bark samples from collections of the two acacia species were extracted with distilled water, 80% methanol and 70% acetone. Two sets of extraction were made, one by boiling, and the other by shaking the samples in the respective solvent for eight hours at room temperature. It was found that the 70% acetone was a more efficient solvent than either water or 80% methanol. In addition, qualitative analysis of the phytochemicals showed that the fruits (garad) contain tannins materials, flavonoids and coumarins.

Mechanical, Thermal and Surface Investigations of Chitosan/Agar/PVA Ternary Blended Films

The mechanical and thermal properties of chitosan/agar/poly vinyl alcohol (CS/AG/PVA) ternary blended films having various proportions considering chitosan as the main component were investigated. The various variables static water contact angle such as contact angle, drop base area, drop volume and drop height was also studied in correlation with the variation of time. Results obtained from mechanical measurements showed a noticeable increase in the tensile strength (TS) coincided with a sharp decrease in elongation percent at break (E%) of blended films with increasing agar and PVA contents. The DSC results prevailed the development of an interaction between chitosan individual components: agar and PVA. Moreover, an enhancement of the wettability of the blends was obtained with increasing agar and PVA contents. It was also found that the pure CS film and the blended films with 90/05/05 and 80/10/10 compositions were more affected by time than blended films with other compositions when the contact angle, the drop height and the drop length were studied as a function of time. In addition, when the drop is initially placed on the substrate, the drop area and the drop volume of all films remained almost constant up to a certain time after which they showed a slight difference with the elapse of time.