Browsing by Subject "Curing"
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Item Open Access Development of an iterative learning controller for polymer based micro-stereolithography prototyping systems(IEEE, 2016) Türeyen, Erkan Buğra; Karpat, Yiğit; Çakmakcı, MelihAdditive manufacturing has become increasingly popular for a wide range of applications in recent years. Micro-stereolithography (μSLA) is a popular method for obtaining polymer-based parts. Systems using the μSLA approach usually consist of a vertical positioning system, a light source and a container where the component is built gradually as the polymer is cured at the locations where the ultraviolet light is projected. It has been noted that the motion of the positioning system and the intensity of the light source is an important factor to achieve high level dimensional precision. In this paper a three dimensional error based learning scheme is presented to improve the time varying process parameters of the system so that the dimensional accuracy of the product is improved. A mathematical model of the curing process is used for developing the error based learning algorithm. The current process parameters as a function of time and the dimensional error obtained at each layer of the production are used for increasing the quality and precision of the same part in the next iteration. Our initial simulation results show significant improvements can be obtained in a few iterations if the correct learning parameters are used based on the target parts dimensional properties.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 Polybenzoxazine-based nanofibers by electrospinning(Elsevier Inc., 2017) Ertaş, Yelda; Uyar, Tamer; Ishida, H.; Froimowicz, P.In this chapter recent progress in the production of polybenzoxazine-based nanofibrous mats by electrospinning is highlighted. The benzoxazine monomers could easily form thermosetting polybenzoxazines by in situ thermally initiated ring-opening polymerization, hence, they are promising materials for both the surface modification of polymeric nanofibrous mats and the production of polybenzoxazine-based composite nanofibers. After curing, polybenzoxazines provide hydrophobic characteristic for the modified polymeric nanofiber surfaces by in situ polymerization of the benzoxazines because of their highly cross-linked structure. Also, they allow for the further functionalization of the surfaces as superhydrophobic and superleophilic by the incorporation of SiO2 nanoparticles into the benzoxazine solution. In addtion, benzoxazine monomers could be directly added into electrospinning solutions and the thermal curing of the obtained nanofibrous mat could yield hydrophobic composite nanofibers. Moreover, because of outstanding properties, such as near-zero volumetric change upon curing, low water absorption, high glass transition temperature, high char yield, and no by-products without any catalysts during curing, polybenzoxazines are good a candidate as a precursor for the production of carbon nanofibers. In addition, the molecular structure of polybenzoxazines facilitates immense design flexibility, which enables the tailoring of the properties of the cured material. Therefore, suitable polybenzoxazines can be synthesized, and cross-linked polybenzoxazine nanofibers, with enhanced thermal and mechanical properties, can be obtained by electrospinning without the blending of other polymers. By combining the unique properties of nanofibers and the facinating properties of polybenzoxazines, highly cross-linked polybenzoxazine-based nanofibrous mats can be obtained and these materials are quite useful, especially in filtration applications. © 2017 Elsevier Inc. All rights reserved.Item Open Access Polymeric waveguide Bragg grating filter using soft lithography(Optical Society of American (OSA), 2006) Kocabas, A.; Aydınlı, AtillaWe use the soft lithography technique to fabricate a polymeric waveguide Bragg grating filter. Master grating structure is patterned by e-beam lithography. Using an elastomeric stamp and capillary action, uniform grating structures with very thin residual layers are transferred to the UV curable polymer without the use of an imprint machine. The waveguide layer based on BCB optical polymer is fabricated by conventional optical lithography. This approach provides processing simplicity to fabricate Bragg grating filters. © 2006 Optical Society of America.