Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Payne Cell Gravimetric Measurements in Polymer-Solvent Systems for Diffusion Coefficients and Isotherm Data(Wiley, 2021) Zielinski, John M.; Garcia, Armando R.; Alsoy Altınkaya, SacideThe discussion focuses on the application of a Payne cell to the measurement of diffusion and solubility coefficients in polymer/solvent systems. Payne cells have, thus far, been used exclusively to measure steady-state permeation rates of solvents. An analytical model has been developed to describe transient gravimetric sorption and desorption measurements performed with a Payne cell. The model has been validated by a complementary numerical simulation and has been applied to evaluate diffusion and solubility coefficients in two different toluene-silicone rubber systems. The data measured using the Payne cell are found to compare very well with diffusion coefficient and isotherm data measured by traditional gravimetric sorption experiments.Article Citation - WoS: 10Citation - Scopus: 10Multi-Zone Drying Schemes for Lowering the Residual Solvent Content During Multi-Component Drying of Semicrystalline Polymers(Taylor and Francis Ltd., 2007) Wong, Sim-Siong; Alsoy Altınkaya, Sacide; Mallapragada, Surya K.The development of a glassy skin in multicomponent semicrystalline polymer systems limits the diffusion of solvents out of the system and increases residual solvent levels. Based on the results of a mathematical model that we had previously developed, we have proposed a multi-zone drying scheme aimed at lowering the residual solvent levels by taking into account the effect of interactions between the various solvents as predicted by the model. This article focuses on the application of this model to develop optimal drying schemes and to verify the effectiveness of these predictions using experimental techniques. The mathematical model developed previously to study the diffusion of multiple solvents and changes in the crystallinity of semicrystalline polymer systems during drying incorporates many features including Vrentas-Duda diffusion theory, solvent-induced crystallization kinetics, as well as glass transition effects and skinning of the film. The multi-zone drying system was developed by varying the drying temperature in each zone as well as changing the partial pressure of individual solvents during the drying process. The effectiveness of the multi-zone drying schemes predicted by the model was validated experimentally using thermogravimetric methods. The polymer-solvent system chosen was a poly(vinyl alcohol)-water-methanol system. Our experimental data suggested that the multi-zone drying schemes were superior to a single-zone drying system through direct comparison. Further examination of the mathematical model yielded individual solvent profiles and these data reaffirmed our conclusions that a multi-zone drying scheme has the ability to reduce the effect of solvent trapping and thus lower the overall residual solvent content.Article Citation - WoS: 187Citation - Scopus: 208Synergistic Effect of Natural Zeolites on Flame Retardant Additives(Elsevier Ltd., 2005) Demir, Hasan; Arkış, Esen; Balköse, Devrim; Ülkü, SemraThe thermal degradation and flammability of intumescent fire-retardant polypropylene matrix composites consisting of ammonium polyphosphate (APP) as an acid source and blowing agent, pentaerythritol (PER) as a carbonisation agent and natural zeolite (clinoptilolite rich, Gördes II) as a synergistic agent were examined. APP and PER combinations were examined at different ratios (0.25, 0.33, 0.5, 1, 2, 3, and 4) for optimisation of the formulation for flame retardancy. The zeolite was incorporated into flame retardant formulation at four different concentrations (1, 2, 5, and 10 wt%) to investigate the synergism between the flame retardant materials. The thermal degradation and flammability of composites were characterized by thermogravimetric analysis (TGA) and by limiting oxygen index (LOI) measurement and horizontal burning (HB) tests. A synergistic effect in flame retardancy was observed when natural zeolites were used in combination with APP and PER.Article Citation - WoS: 76Citation - Scopus: 84Characterization of Pure and Silver Exchanged Natural Zeolite Filled Polypropylene Composite Films(Elsevier Ltd., 2005) Pehlivan, Hilal; Balköse, Devrim; Ülkü, Semra; Tıhmınlıoğlu, FundaIn the present study, untreated and silver exchanged natural zeolite-polypropylene (PP) composites were prepared and characterized by means of different techniques (TGA, DSC, mechanical tests, density measurements, optical microscopy and colorometer). The effects of zeolite loading and silver concentration on the composite properties were investigated. The thermal characterization studies showed that the addition of the zeolite increased the crystallinity of the composites acting as a nucleating agent in PP crystallization and retarded the degradation of PP. At low silver concentrations, the zeolite behaved as a decelerating agent in PP degradation, however at higher silver concentrations, the composites degraded at a faster rate than pure PP. The experimental densities of the composites were found to be lower than the theoretical densities. When the tensile tested samples are considered, the densities were even lower indicating porous structure of the films. From the optical micrographs of the tensile tested films, it was clearly seen that the stretching along the machine direction caused hole formation around the particles. The optimum conditions obtained in this study for the PP-silver zeolite composite film production are in the range of 2-4 wt% zeolite treated with 4.36 mg Ag+/g zeolite. At higher zeolite loadings, the film becomes brittle and at higher Ag+ concentrations, the film produced was discolored.