Kemal Kesenci

Poly(d,l-cactide/ε-caprolactone)/hydroxyapatite composites

Abstract In this study, elastomeric d , l -lactide and e -caprolactone copolymers with two different molecular weights ( M n : 108.000 and 40.000) were synthesized by ring-opening polymerization of the respective dimers by using stannous octoate as the catalyst, as a potential bone-filling material. The final ratio of d , l -lactide to e -caprolactone obtained by 1 NMR was 60/40 (comparing to the initial ratio of 50/50). Both copolymers were amorphous having T g at around −21°C. Different amounts of hydroxyapatite (HA) powder were loaded within the copolymers. These composites were easily shaped by hand. Mechanical properties of the composites changed with the HA loading and the molecular weight of the copolymer. The percent elongation decreased, while both the Youngs modulus and yield point (stress) increased with the HA content. The copolymers were degraded within the Ringer solutions in about 6 weeks. The molecular weight distribution became broader during degradation. Incorporation of HA reduced the degradation rate.

Dithiocarbamate-incorporated monosize polystyrene microspheres for selective removal of mercury ions

Abstract Dithiocarbamate-incorporated monosize polystyrene based microspheres (2 μm in diameter) were used for selective removal of Hg(II) from aqueous solutions containing different amounts of Hg(II) (10–100 ppm). Adsorption rates were observed as high at the beginning of adsorption and then equilibrium was reached in about 30 min. The maximum Hg(II) adsorption capacity of the dithiocarbamate-incorporated PS microspheres was about 33.2 mg per gram of dry polymer, which was observed at pH 7.0. While non-specific Hg(II) adsorption onto the plain microspheres was 0.85 mg per gram of dry microsphere. The Hg(II) adsorption ability increased with increasing pH, in the range where the solubility of the Hg(II) was not affected by the pH. The preferential (i.e., competitive adsorption) binding of Hg(II) by the microspheres implies that this sorbent system might contain higher-affinity binding sites for Hg(II) than Cu(II), Cd(II) and Pb(II) ions. More than 96% of the adsorbed Hg(II) was desorbed in 15 min by using 0.1 M HNO 3 as an elution agent. The regeneration of the dithiocarbamate-incorporated PS microspheres was also sufficient.

Swellable ethylene glycol dimethacrylate-hydroxyethylmethacrylate copolymer beads

Abstract In this study, Swellable poly(EGDMA/HEMA) beads in the size range of 30–170 μm with different size distributions were produced by suspension copolymerization of ethylene glycol dimethacrylate (EGDMA) and hydroxyethylmethacrylate (HEMA) in aqueous media. Poly(vinyl alcohol) and benzoyl peroxide were used as the stabilizer and the initiator. The diluent, i.e. toluene was included in the recipe of the second group of copolymerizations. The beads were characterized by optical microscopy, FTIR and FTIR-DRS. Crosslinked, transparent, nonporous and Swellable (up to a swelling ratio of 31.2%) poly(EGDMA/HEMA) beads were obtained in which there was no toluene in the recipe. While copolymerizations with toluene provided Swellable (up to a swelling ratio of 57.1%), opaque, porous and crosslinked copolymer beads. In the polymerization (without toluene) HEMA is mainly incorporated on the outer layers (near surface) of the beads. In this case, increase in the EGDMA/HEMA ratio resulted larger beads with wider size distributions, and with lower swellabilities. The porosity of the dry copolymer beads were studied with mercury pycnometric method. Incorporation of toluene within the recipe (in the modified polymerization) caused pronounced effects both on bead size and swellability. Larger beads with broader size distributions, with higher swellabilities were obtained when the relative amount of toluene increased.

Preparation and properties of poly(L-lactide)/hydroxyapatite composites.

In this study, two different viscosity-average molecular weight (η = 4.0 and 7.8) poly(L-lactide) (PLLA) were synthesized by ring-opening polymerization and the poly(L-lactide)/hydroxyapatite composites (PLLA/HA) were prepared by blending HA particles (size range: 25-45 μm and Ca/P = 1.69) with a content of 10, 30, and 50 wt% in PLLA solution with further evaporation of the solvent. The plain PLLA polymers and PLLA/HA composites were compressionmolded and machined to yield 25×3×2 mm3 specimens. The molar mass of resulting specimens was decreased drastically due to the hydrolytic and thermal degradation of ester bonds. Scanning electron microscopy and thermal gravimetric results indicated that the compositions of HA in PLLA were well dispersed. With increasing HA content, the crystallinity of PLLA/HA composites are slightly increased due to the effect of HA as a nucleating agent. The dynamic mechanical analysis is useful in studying the viscoelastic behaviour of the PLLA/HA composites and no secondary relaxation was observed below the glass-to-rubber transition (60°C). The mechanical properties of the PLLA/HA composites were found to vary with HA content. Increased levels of HA resulted in increased bending modulus and strength.

Photon transmission technique for studying film formation from polystyrene latexes prepared by dispersion polymerization using various steric stabilizers

A photon-transmission method was used to monitor the evolution of transparency during film formation from various polystyrene (PS) particles which were produced using different steric stabilizers, that is, poly( acrylic acid) (PAA), poly(vinyl alcohol) (PVA), and polyvinylpyrrolidone (PVP). The latex films were prepared from PS particles at room temperature and annealed at elevated temperatures in various time intervals above the glass transition (Tg). To simulate the latex film-formation process, a Monte Carlo technique was performed for photon transmission through a rectangular lattice. The number of transmitted (N tr ) photons were calculated as a function of particle-particle interfaces that disappeared. The increase in the transmitted photon intensity (( r ) was attributed to the increase in the number of interfaces that disappeared. The Prager-Tirrell (PT) model was employed to interpret the increase in crossing density at the junction surface. The backbone activation energy (AE) was measured and found to be around 120 kcal mol -1 for a diffusing polymer chain across the junction surface for all PS latex films.

Cibacron blue F3GA-incorporated macroporous poly(2-hydroxyethyl methacrylate) affinity membranes for heavy metal removal

Abstract Macroporous poly(2-hydroxyethyl methacrylate), poly(HEMA), membranes were prepared by UV-initiated photopolymerization of HEMA in the presence of an initiator (azobisisobutyronitrile, AIBN). An affinity dye, i.e., Cibacron Blue F3GA was then incorporated covalently. These affinity membranes with a swelling ratio of 58%, and carrying 10.67 mmol Cibacron Blue F3GA/m 2 membrane were used in the adsorption/desorption of some selected heavy metal ions [i.e., As(III), Cd(II) and Pb(II)] from aqueous media. Very high adsorption rates were observed and adsorption equilibria were reached in about 30 min. The maximum adsorptions of heavy metal ions onto the dye-incorporated affinity membranes from their single solutions were 12.6 mmol/m 2 for As(III), 61.0 mol/m 2 for Cd(II) and 79.0 mol/m 2 for Pb(II). However, when the heavy metal ions competed (in the case of the adsorption from their mixture) the amounts of adsorption for As(III), Cd(II) and Pb(II) were quite close. Desorption of heavy metal ions was carried out by using 0.1 M HNO 3 (pH 1.0). Up to 95% of the adsorbed heavy metal ions were desorbed in 60 min. Repeated adsorption/desorption cycles showed the feasibility of this novel affinity membrane for heavy metal removal.

Nonswellable and swellable ethylene glycol dimethacrylate‐acrylic acid copolymer microspheres

In this study, nonswellable and swellable poly(ethylene glycol dimethacrylate/acrylic acid) copolymer microspheres, in the size range of 50–150 μm, were produced by conventional and modified suspension copolymerizations of the respective monomers, i.e., ethyleneglycol dimethacrylate (EGDMA) and acrylic acid (AA) in aqueous media. Poly(vinyl alcohol) and benzoyl peroxide were used as the stabilizer and the initiator. The diluent, i.e., toluene was included in the polymerization recipe of the modified suspension polymerization. The microspheres were characterized by optical microscopy, FTIR, and FTIR-DRS, and potentiometric titrations. Highly crosslinked, transparent, and nonswellable poly(EGDMA/AA) microspheres were obtained with the conventional suspension polymerization procedure. The modified suspension polymerization provided swellable, opaque, and crosslinked copolymer microspheres. Acrylic acid incorporation into the copolymeric microspheres were significantly higher in the modified procedure, relative to the conventional procedure.

Poly(EGDMA/AAm) copolymer beads: a novel carrier for enzyme immobilization

Abstract In this study, we evaluated a new carrier (i.e., the poly(EGDMA/AAm copolymer beads) for enzyme immobilization. Two different types of copolymer beads with different swellabilities with an average diameter of about 200 μm were produced by suspension copolymerization of the respective comonomers, with or without using toluene. BPO and PVA were used as the initiator and the stabilizer. The copolymer beads produced without toluene were nonporous and nonswellable. While porous and swellable (swelling ratio: 14.28%) beads were obtained in which toluene was used as the diluent. Both type of beads were modified by using glutaraldehyde and hexamethylene diamine as the coupling agent and the spacer-arm, respectively. Immobilization of a model enzyme (i.e., glucose oxidase) was studied to show the feasibility of using these beads as an enzyme carrier. More enzyme, but with very low activities, were immobilized on the beads with relatively lower swellabilities. While much higher activities were observed on the beads with relatively higher swellabilities prepared with toluene. Incorporation of the spacer-arm (i.e., hexamethylene diamine) increased the apparent activity of the immobilized enzyme. The optimal glutaraldehyde concentrations to achieve the highest immobilized enzyme activities for the swellable and nonswellable beads were 23.1 and 4.8% (v/v), respectively, while the optimal hexamethylene diamine concentrations to achieve the highest immobilized enzyme activities for these beads were 0.10 and 0.16 mmol/ml, respectively.

Dithiocarbamate-incorporated monodisperse polystyrene microspheres as specific sorbents: Adsorption of cadmium ions

In this study, adsorption of cadmium ions from aqueous solutions by using dithiocarbamate-incorporated monodisperse crosslinked polystyrene (PS)-based sorbents was investigated. Monodisperse PS microspheres with a diameter of 2 μm were produced by dispersion polymerization of styrene in isopropyl alcohol/water by using polyvinylpyrrolidone and azobisisobutyronitrile as stabilizer and initiator, respectively. These microspheres were then crosslinked by using divinylbenzene. In order to incorporate dithiocarbamate functional groups on the PS microsphere, first benzylamine was physically absorbed, then the amine groups were transformed into dithiocarbamate groups by interacting these microspheres with carbon disulphide. These PS-based sorbents carrying physically entrapped benzyl dithiocarbamate were characterized by scanning electron microscopy, optical microscopy, FTIR, and elemental analysis. Adsorption of cadmium ions on the PS-based sorbents were investigated in the batch equilibrium experiments by using atomic absorption spectrophotometer. Adsorption rates were very fast. Adsorption equilibria were achieved within 5-60 min. The highest adsorption capacity achieved was 154.1 mg cadmium/g sorbent. The most suitable pH was 6.0.

Poly(ε-caprolactone-co-D,L-lactide)/silk fibroin composite materials: Preparation and characterization

Poly(ε-caprolactone-co-D,L-lactide) copolymers with 10, 30, and 50% by weight of silk particles (size range: 5-250 μm) derived from Bombyx mori were blended in acetone solution. After evaporation of the solvent, the morphology, thermal behavior, and mechanical properties of the composites were examined. The composites were transparent and the silk fibroin particles were homogeneously distributed within the composite structure. The particles appeared as bright reflected images under the optical microscope, suggesting that they were in a crystalline state. DSC thermograms of the composites revealed that the glass transition of the matrix was at ca. -18°C. Degradation of the silk fibroin occurred beyond 270°C. The decomposition temperatures and degradation rate decreased with increasing silk fibroin content as revealed by TGA analysis. FTIR spectra of the composites showed absorption bands at 1730 and 1088 cm-1 for the copolymer and at 3273 and 1617 cm-1 for the silk fibroin. Although the characteristic lines of poly(ε-caprolactone-coD,L-lactide) were independent of filler concentration, the absorption bands of the β-sheet form of the silk fibroin increased slightly due to the interaction of silk fibroin with the copolymer.