Cüneyt H. Ünlü

Rheology and structure of aqueous bentonite-polyvinyl alcohol dispersions

The influence of polymer on flow behaviour of Balikesir, Turkey bentonite dispersions (2%, w/w) was studied for non-ionic polymer, polyvinyl alcohol (PVA). In a range of 3.3 × 106 −3.3 × 105 mol/l, PVA was added to the bentonite dispersions in different concentrations and its behaviour was observed on rheology parameters. Thixotropy was detected by a hysteresis loop of the flow curves. The data were interpreted taking into account the interactions of colloidal clay particles, bentonitic clay concentrations, structure, and concentrations of added PVA. The particle size analysis was explained by surface orientation of PVA to the clay particles dispersed in aqueous solution. Zeta potential determination also emphasized that PVA molecules got attached on the face and edge surface of clay particles. The morphology of bentonite dispersions was analysed by scanning electron micrograph (SEM). FTIR studies carried out in parallel to rheology studies showed that hydrogen bonds were formed between surface of the clay, and absorbed PVA molecules and adsorbed water. The presence of PVA did not prevent extensive swelling of bentonite.

Synthesis and characterization of HDA/NaMMT organoclay

In this study, the rheologic and colloidal characterizations of sodium montmorillonite (NaMMT) were examined. Hexadecylamine (CH3(CH2)15NH2, HDA) was added to the bentonite water dispersion (2%, w/w) in different concentrations in the range 5.6 × 10−4−9.4 × 10−3 mmol/l. The rheological and electrokinetic behaviour of aqueous montmorillonite dispersions was investigated as a function of solid content and HDA concentration. The basal spacings of the HDA/NaMMT composites were studied by X-ray diffraction. The FTIR spectra were obtained from the modified bentonite products, which revealed the characteristic absorbances after treatment with HDA.

Synthesis and thermal characterization of xylan-graft-polyacrylonitrile

In this study emulsion polymerization of acrylonitrile using xylan from agricultural waste material (corn cob) and cerium ammonium nitrate was investigated in terms of catalyst acid. Stock ceric solutions were prepared using either nitric or perchloric acid as catalyst. Optimum conditions were determined using different parameters such as reaction time, temperature, and component concentrations. Nitric acid catalyzed reactions resulted in maximum conversion ratio (96%) at 50°C, 1 h where ceric ion, acrylonitrile, xylan, and catalyst concentrations were 21.7 mmol l(-1), 0.5 mol l(-1), 0.2% (w/v), and 0.1 mol l(-1), respectively. However, 83% conversion was obtained with perchloric acid catalysis at 27 °C, 1 h where concentrations were 5.4 mmol l(-1), 0.8 mol l(-1), 0.5% (w/v), and 0.2 mol l(-1), respectively. Copolymer synthesis using perchloric acid was realized at milder conditions than using nitric acid. Thermal analyses of obtained polymers were conducted to characterize copolymers. Results showed that calculated activation energy, maximum degradation temperature, and heat of thermal decomposition changed relying mainly on molecular weight.

Carboxymethylcellulose from recycled newspaper in aqueous medium.

Recycled paper cellulose has some drawbacks, for example loss in mechanical strength, to use in paper industry alone. However, derivatives of cellulose can find applications in other industrial areas. Carboxymethylcellulose (CMC) is one of the most used cellulose derivatives and can be obtained by heterogeneous modification of cellulose. In general carboxymethylation of cellulose achieved in alkaline alcoholic dispersions. In this work modification of cellulose from recycled newspaper in aqueous alkaline solution was aimed. First cellulose was recovered from newspaper under oxidative alkaline conditions. Cellulose recovery was determined as 75-90% (w/w) of starting material. Carboxymethylation reactions were carried out to find optimum conditions for derivatization, changing concentrations of components and reaction temperature. Obtained CMC samples had a DS of 0.3-0.7% and 84-94% CMC content. As a result, carboxymethylation of cellulose from recycled newspaper was achieved in aqueous alkaline dispersion giving commercial grade CMC for industrial use.

Interactions of BDTDACl and DTABr Surfactants with Montmorillonite in Aqueous Systems

In this study, the effect of the two cationic surfactants (benzyldimethyltetradecylammonium chloride (BDTDACl) and dodecyltrimethyl-ammonium bromide (DTABr)) on the electrokinetic and rheologic properties of Na-montmorillonite dispersion (3% w/w) has been investigated at their concentrations between 0 and 10 mmol/L. Experimental results reveal that cationic surfactants are attached on the surface of negatively charged clay particles and also they penetrate into the interlayer of clay particles. The intercalation of surfactants with clay minerals is shown to lead to an increase in the interlayer spacing of montmorillonites by X-ray diffraction. The Fourier transform infrared (FTIR) spectra obtained from the modified bentonite products reveal the characteristic absorption bands. The morphology of bentonite dispersions was analyzed by scanning electron microscopy (SEM). Both X-ray diffraction data and scanning electron micrographs of intercalated montmorillonites indicate that most of the montmorillonites are dispersed randomly in the organo-clay dispersion.

Synthesis, characterization and electrospinning of corn cob cellulose-graft-polyacrylonitrile and their clay nanocomposites.

This study aims at evaluation of cellulose recovered from agricultural waste (corn cob) in terms of synthesis of graft copolymers, polymer/clay nanocomposites, and nanofibers. The copolymers and nanocomposites were synthesized in aqueous solution using Ce(4+) initiator. Conditions (concentrations of the components, reaction temperature, and period) were determined first for copolymer synthesis to obtain the highest conversion ratio. Then found parameters were used to synthesize nanocomposites adding clay mineral to reaction medium. Although there was a decrease in conversion in nanocomposites syntheses, thermal and rheologic measurements indicated enhancements compared to pristine copolymer. Obtained polymeric materials have been successfully electrospun into nanofibers and characterized. Average diameter of the nanofibers was about 650nm and was strongly influenced by NaMMT amount in the nanocomposite sample.

Mannich reaction of polysaccharides: Xylan functionalization in aqueous basic medium.

In this study modification of xylan via Mannich reaction in aqueous basic solution to obtain dimethylaminomethylated products and characterization of modified xylan were examined. Components were xylan (obtained from corn cob and used without modification) as active hydrogen containing compound, formaldehyde as carbonyl compound having no α-hydrogen and dimethylamine. Mannich reaction was used with different parameters such as component concentration, reaction temperature, and time. The highest modification was observed about 35°C with a nitrogen content of 4.6% by weight indicating successive modification. Both 1D and 2D NMR measurements displayed new signals related with aminomethyl groups. Spectral characterizations indicated that aminomethylation took place on oxygen sites. Moreover modified xylan could form film while xylan could not without an auxiliary agent. Antimicrobial activity tests indicated that modified xylan acted as a bacteriostatic material.

Eu(fod)3 binding on the 1H-NMR spectra of bis(2′-ethylbenzoate)ethylene glycol podands†

The complexing and selective binding constants of Eu(fod)3 with bis(2′‐ethylbenzoate)ethylene glycol podands having one to four oxyethylene groups was observed on their 1H‐NMR spectra at 250 MHz and 295 K in CDCl3. The Eu(fod)3 interaction displayed the selective binding role of oxygen on H2C–O–CH2 backbones with referring the 1H chemical shifts.