Elvan Yilmaz

Gelcasting of alumina and zirconia using chitosan gels

Abstract A new gelcasting system has been analysed. The gel forming system is based on a solution of 1% chitosan in diluted acetic acid and reaction with glutaraldehyde. An Al 2 O 3 powder-loading rate of 50 vol.% was achieved under optimised conditions. Advantages of this new system include the use of a biopolymer (chitosan), possibility of air drying of green parts, possibility of gelcasting at ambient temperature, and versatility of the process by changing process parameters leading to well specified reaction times. The effect of process parameters on reaction time, slurry properties, and green part properties are presented. Slurries prepared from ZrO 2 powders were not fluid. However, dense green parts could still be obtained by transferring these slurries to a mould and drying.

Oxidation and pyrolysis of chitosan as a route for carbon fiber derivation

The oxidation and pyrolysis of chitosan were studied with the aim of obtaining carbon fibers from chitosan fibers. The effect of heat treatment temperature and time as well as pretreatment with ammonium chloride on the conversion process was analyzed. The mechanism for the conversion of chitosan to carbon during oxidation, suggested by FTIR analysis, is one where degradation takes place together with decomposition of the pyranose ring with partial dehydration and deamination. Pretreatment of chitosan improved the carbon yield significantly in the end product. Improved tensile strengths were observed upon pyrolysis. Although the heat treatment temperatures were considerably low, a higher C yield was obtained with chitosan fibers compared to rayon fibers (>20 vs. 15%, respectively). It is concluded that pyrolysis of chitosan fibers in an inert atmosphere can be an alternative method for the production of carbon fibers with regard to pyrolysis of cellulose (rayon) fibers.

Chitosan: A Versatile Biomaterial

Chitosan is an amino polysaccharide with a wide range of biomedical applications in addition to various other uses in food and nutrition, textile and paper industries, cosmetics, photography and water engineering.

Preparation and characterization of physical gels and beads from chitin solutions

Abstract A detailed account of physical bulk gel and bead formation from various chitin solutions and nonsolvents is given. Instant gel formation occurs upon contact of chitin solutions in dimethylacetamide (DMAc)/lithium chloride (LiCl) or N -methyl-pyrrolidinone (NMP)/LiCl solvents and nonsolvents such as water, ethanol, or acetone. Ethanol was found to be the optimal nonsolvent for homogeneous spherical bead formation from chitin solutions. Similarly, DMAc-based chitin solutions proved to yield higher quality beads compared to NMP-based solutions. The differences in bead morphology, crystallinity, and thermal degradation are explained in light of the attainment of a balance between attractive hydrogen bonding in the chitin gel network and segment–nonsolvent interactions. The dependence of swelling of chitin gels on pH indicated a maximum of swelling ratio value of 4.3 at pH 11 in aqueous solutions while the equilibrium swelling ratio value of chitin beads formed with ethanol reached a maximum of 2.4. Bulk gels formed under favorable conditions were demonstrated to be recyclable after solvent separation and drying.

Miscibility of Chitosan and Poly(Ethylene Oxide) in Dilute Solution

Miscibility of chitosan (CHI) with poly(ethylene oxide) (PEO) was studied in dilute solution by viscometry. Blends with CHI/PEO compositions of 0.1/0.9, 0.2/0.8, and 0.3/0.7 were studied at 25°, 30°, and 35°C, in a buffer solution of 0.1 M acetic acid/0.2 M sodium acetate. Starting with the classical Huggins equation, the results of the viscosity behavior of each parent polymer and their blends were interpreted in terms of miscibility parameters, j k, f , and j b. Miscibility between CHI and PEO was found to increase with weight fraction of PEO and polymer concentration. The existence of H-bonding interaction between CHI and PEO was demonstrated by FTIR spectroscopy.

Preparation and Characterization of Maleic Acid Grafted Chitosan

Abstract Modification of chitosan (CHI) with maleic acid (MA) via maleic anhydride (MAn) was investigated in acetic acid solution, in the presence of cerium ammonium nitrate (CAN) as the initiator. The effects of reaction time, temperature, and CAN and MA concentrations on the grafting percentage were studied. The products were characterized by Fourier-transform infrared, differential scanning calorimetry, and 13C NMR, in addition to gravimetric evidence to grafting. A maximum of 105% grafting was achieved under the reaction conditions of 0.12 M CHI, 2.0 M MA, and 0.091 M CAN by stirring for 3 h at 70°C. Dissolution and swelling properties of grafted products were tested in the pH range 3–11. Products up to 36.5% grafting were found to be soluble in aqueous solution, while those with higher grafting percentages (48–81%) were partly soluble in the pH range studied. The product with maximum grafting percentage (105%) swelled and acted as a polyampholyte gel.

Miscibility studies on polystyrene/poly(ethylene oxide) and polybutadiene-graft-polystyrene/poly(ethylene oxide) blends by dilute solution viscometry

Miscibility of polyethylene oxide (PEO) with polystyrene (PS) or polybutadiene-graft-polystyrene (PBS) was investigated by dilute solution viscometry. Miscibility parameters derived from the classical Huggins equation were used to estimate the miscibility of these polymer pairs. The results, which indicated immiscibility between PS and PEO, were compared with findings in bulk reported in the literature. PBS was also found to be immiscible with PEO. The effect of temperature on miscibility was studied by the same method for a blend of PBS with 83% PEO. All miscibility parameters were observed to decrease with increasing temperature.

Synthesis and Characterization of Aliphatic Tri-functional Oligomeric Urethane Methacrylate used for UV-Curable Aluminum Pigmented Coatings

A new UV-curable coating with aluminum pigments was developed as part of an effort to replace chromium coatings, which raise health and environmental concerns. For achieving this, aliphatic tri-functional oligomeric urethane methacrylate (ATOUA) was synthesized using trimethylol propane (TMP), isophorone diisocyanate (IPDI), hydroxyethyl methacrylate (HEMA) and dibutyltin dilaurate (DBTDL) as a catalyst. In order to obtain a metallic shine effect, leafing and non-leafing aluminum pigments were formulated with ATOUA to obtain a series of coatings. The UV-curable aluminum pigmented coatings were prepared by blending ATOUA, 1,6-hexanediol diacrylate (HDDA) and trimethylol propane triacrylate (TMPTA) as reactive diluents, benzophenone as photoinitiator, N-methyl diethanolamine as co-initiator, aluminum pigments, and wetting and dispersing agent (OA 10EO). Surface morphology of the coatings was investigated through SEM. FTIR; 1H-NMR and 13C-NMR spectroscopes were used to characterize composition of the synthesized oligomer. Physical, chemical and mechanical properties of surface coatings have been determined using König hardness, cross cut, impact, gloss, mandrel, cupping and salt spray test. Thermal properties of the cured coating were also investigated by means of DSC and TGA.

Photoinduced Graft Copolymerization onto Chitosan Under Heterogeneous Conditions

Photoinitiated graft copolymerization of acrylamide onto chitosan under heterogeneous conditions and in the absence of a photo initiator was investigated. The effect of irradiation time, the amount of chitosan and monomer concentration on the extent of grafting was examined. The maximum grafting percentage obtained was 294%. The copolymer was characterized using carbon-13 nuclear magnetic resonance (13C-NMR) spectroscopy, X-ray diffraction analysis (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The system designed allows synthesis of grafted chitosan with free amine groups which are otherwise possible only by chemical protection. The swelling properties of copolymer were followed in aqueous solution.

Miscibility Study of Chitosan/Poly(Vinyl Pyrrolidone) Blends in Dilute Solution

Abstract Miscibility of chitosan (CHI) with two poly(vinyl pyrrolidone) samples (PVP-1 and PVP-2) of different molecular weights was studied in dilute solution by viscometry. Blends with chitosan weight fraction in the range 0.10–0.90 were studied at 30°C in a buffer solution of 0.1 M acetic acid/0.2 M sodium acetate. Starting with the classical Huggins equation, the results of the viscosity behavior of each parent polymer and their blends were interpreted in terms of miscibility parameters, Δk, α, and Δb. CHI (Mv = 3.3 × 105) and PVP-1 (Mv = 2.5 × 104) were found to be miscible at a blend composition of CHI/PVP 0.90/0.10. PVP-2 (Mv = 1.1 × 106) and CHI were miscible in the full range of blend compositions studied. The existence of favorable secondary interaction between CHI and PVP leading to miscibility was demonstrated by FTIR spectroscopy.