Browsing by Subject "Polybenzoxazine"
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Item Open Access Crosslinked PolyCyclodextrin/PolyBenzoxazine electrospun microfibers for selective removal of methylene blue from an aqueous system(Elsevier, 2019) Doğan, Yelda Ertaş; Satılmış, Bekir; Uyar, TamerIn this study, a blend solution of hydroxypropyl-β-cyclodextrin (HPβCD) and benzoxazine monomer (BA-a) was prepared in dimethylformamide to obtain HPβCD/BA-a microfibers by electrospinning technique. The electrospun HPβCD/BA-a microfibers were then thermally cured to obtain crosslinked PolyHPβCD/PolyBA-a microfibers. The compositions of HPβCD (120%, w/v) and BA-a (25%, w/v) were determined as an optimum concentration for producing bead-free and uniform microfibers from blend of HPβCD and BA-a (HPβCD/BA-a). Afterwards, the HPβCD/BA-a microfibers were thermally cured using step-wise curing method to obtain water-insoluble crosslinked PolyHPβCD/PolyBA-a fibrous membrane (FM). However, the fibrous structure of PolyHPβCD/PolyBA-a membrane was subjected to some morphological deformation during thermal curing. Therefore, citric acid (CTR, 5% and 15%, w/v) was incorporated into blend of HPβCD15/BA-a and it was named as HPβCDx/BA-a where x represents the amount of CTR (w/v) in the system. Blend solution of HPβCD15/BA-a was electrospun into microfibers to facilitate the crosslinking and to improve thermal resistance of the crosslinked fibrous membrane (PolyHPβCD15/PolyBA-a). Structural changes and thermal properties of the microfibers before and after curing were studied. Scanning electron microscopy was further used to monitor the morphology and stability of crosslinked PolyHPβCD/PolyBA-a microfibers in water and organic solvents. Consequently, PolyHPβCD15/PolyBA-a microfibers showed an enhanced structural stability in water and organic solvents along with thermal resistance, indicating successful crosslinking. Afterwards, the molecular separation ability of self-standing PolyHPβCD15/PolyBA-a FM was evaluated using dye mixture of Methylene Blue (MB) and Methyl Orange (MO). While both dye molecules are able to form a host-guest interaction between cyclodextrin molecules, crosslinked PolyHPβCD15/PolyBA-a FM showed sorption selectivity against cationic MB dye due to favorable electrostatic attractions between MB and HPβCD compared to anionic MO dye and HPβCD. In addition to selective sorption behavior of MB dye over MO dye, crosslinked PolyHPβCD15/PolyBA-a FM exhibited a decent adsorption capacity for MB in water.Item Open Access Fabrication of cellulose acetate/polybenzoxazine cross-linked electrospun nanofibrous membrane for water treatment(Elsevier, 2017-12) Ertaş, Yelda; Uyar, TamerHerein, polybenzoxazine based cross-linked cellulose acetate nanofibrous membrane exhibiting enhanced thermal/mechanical properties and improved adsorption efficiency was successfully produced via electrospinning and thermal curing. Initially, suitable solution composition was determined by varying the amount of the benzoxazine (BA-a) resin, cellulose acetate (CA) and citric acid (CTR) to obtain uniform nanofibrous membrane via electrospinning. Subsequently, thermal curing was performed by step-wise at 150, 175, 200 and 225 °C to obtain cross-linked composite nanofibrous membranes. SEM images and solubility experiments demonstrated that most favorable result was obtained from the 10% (w/v) CA, 5% (w/v) BA-a and 1% (w/v) CTR composition and cross-linked nanofibrous membrane (CA10/PolyBA-a5/CTR1) was obtained after the thermal curing. Chemical structural changes (ring opening) occurred by thermal curing revealed successful cross-linking of BA-a in the composite nanofibrous membrane. Thermal, mechanical and adsorption performance of pristine CA and CA10/PolyBA-a5/CTR1 nanofibrous membranes were studied. Char yield of the pristine CA nanofibrous membrane has increased notably from 12 to 24.7% for composite CA10/PolyBA-a5/CTR1 membrane. When compared to pristine CA membrane, CA10/PolyBA-a5/CTR1 nanofibrous membrane has shown superior mechanical properties having tensile strength and Young's modulus of 8.64 ± 0.63 MPa and 213.87 ± 30.79 MPa, respectively. Finally, adsorption performance of pristine CA and CA10/PolyBA-a5/CTR1 nanofibrous membranes was examined by a model polycyclic aromatic hydrocarbon (PAH) compound (i.e. phenanthrene) in aqueous solution, in which CA10/PolyBA-a5/CTR1 nanofibrous membrane has shown better removal efficiency (98.5%) and adsorption capacity (592 μg/g).Item Open Access Investigation of polymerization of benzoxazines and thermal degradation characteristics of polybenzoxazines via direct pyrolysis mass spectrometry(Wiley, 2012-10) Bagherifarm, S. B.; Uyar, Tamer; Ishida, H.; Hacaloglu, J.Polymerization of benzoxazines and thermal degradation mechanisms of polybenzoxazines were investigated using the direct pyrolysis mass spectrometry (DP-MS) technique. The benzoxazine structures were based on phenol and aniline and on bisphenol-A and methylamine or aniline. Polymerizations of the benzoxazines were carried out by curing them at elevated temperatures without addition of initiator or catalyst. DP-MS data showed the presence of chains generated by opposing polymerization reaction pathways indicating quite complex structures for the polybenzoxazines under investigation. Thermal decomposition of polybenzoxazines was started by the cleavage of methylamine or aniline linkages. It was determined that polybenzoxazines based on phenol were more stable than the corresponding bisphenol-A-based polybenzoxazines, while those based on methylamine were more stable than the corresponding polybenzoxazines incorporating aniline. Thus, it can be concluded that the presence of bulky groups decreased the extent of crosslinking which in return decreased the thermal stability. © 2012 Society of Chemical Industry.Item Open Access Synthesis of polybenzoxazine/clay nanocomposites by in situ thermal ring-opening polymerization using intercalated monomer(2011) Demir, K.D.; Tasdelen, M.A.; Uyar, T.; Kawaguchi, A.W.; Sudo, A.; Endo, T.; Yagci, Y.A new class of polybenzoxazine/montmorillonite (PBz/MMT) nanocomposites has been prepared by the in situ polymerization of the typical fluid benzoxazine monomer, 3-pentyl-5-ol-3,4-dihydro-1,3-benzoxazine, with intercalated benzoxazine MMT clay. A pyridine-substituted benzoxazine was first synthesized and quaternized by 11-bromo-1-undecanol and then used for ion exchange reaction with sodium ions in MMT to obtain intercalated benzoxazine clay. Finally, this organomodified clay was dispersed in the fluid benzoxazine monomers at different loading degrees to conduct the in situ thermal ring-opening polymerization. Polymerization through the interlayer galleries of the clay led to the PBz/MMT nanocomposite formation. The morphologies of the nanocomposites were investigated by both X-ray diffraction and transmission electron microscopic techniques, which suggested the partially exfoliated/intercalated structures in the PBz matrix. Results of thermogravimetric analysis confirmed that the thermal stability and char yield of PBz nanocomposites increased with the increase of clay content. © 2011 Wiley Periodicals, Inc.