Çıkarma tarihi ile LEE- Polimer Bilim ve Teknolojisi-Yüksek Lisans'a göz atma
Sayfa başına sonuç
ÖgeHigh internal phase emulsion template method for fast and selective mercury adsorption(Graduate School, 2022-01-06) Yıldırım, Melis Şeval ; Yavuz, Erdem ; 515171009 ; Polymer Science and Technology ; Polimer Bilim ve TeknolojisiThere are many template methods for designing porous polymers. Porous polymers have become highly preferred in the industry due to their easy processability and properties. In this study, it was polymerized using a high internal phase emulsion template (HIPE). HIPE is named by looking at the ratio of the external phase volume to the total volume. If this ratio is greater than 0.74, it can be called HIPE.Macroporous polymers prepared by the HIPE method were used. The main disadvantage of PolyHIPE polymers is that they have a low high area (SBET ~9 m2g-1). To overcome this disadvantage, a hypercrosslinking reaction was performed. High surface area polymers were obtained with the Fiedel Crafts reaction (SBET ~ 594 m2g-1). After the hypercrosslinked polymer was obtained, three different functionalization steps were applied. These are respectively; aldehyde, carboxylic acid and amide functionalization. The main purpose of this study is to obtain a selective, fast adsorbent on mercury. It is amide groups that provide selectivity to mercury. The -CONR2 group was obtained from the -Cl groups. In this study, amide group was obtained from carboxylic acid by using four different amides as propylamine, ethanolamine, aniline, diethylamine and DIC/NHS. With the emulsion templating strategy, hypercrosslinking polymers with different hyper-crosslinking times (15 minutes, 30 minutes, 60 minutes, 22 hours) were obtained, increased to amide groups and adsorption studies were carried out. While the main product, HXL-30min-PHP-CONR2, adsorbs 28 mg/g mercury in the first 2 minutes, it is 40.5 mg/g in the 180th minute when it reaches equilibrium. For these studies, different pH ranges were tried (pH 3, pH 4, pH 5, pH 6, pH 7) and the optimum pH was found to be 7.Isotherm (Langmuir, Freundlich, Dubinin- Radushkevich) and kinetic (pseudo-first order, pseudo-second order, intra-particle diffusion) models were made for HXL-30min-PHP-CONR2. Window and void diameter were calculated by using SEM images with Imagej program. Reuse studies were performed for HXL-PHP-CONR2 using 0.1 M HNO3, and 90% capacity was observed up to the 5th cycle.
ÖgeProduction of special resins for use in polyurethane(Graduate School, 2022-01-18) Hüten, Tibet ; Kızılcan, Nilgün ; 515191015 ; Polymer Science and Technology ; Polimer Bilim ve TeknolojisiPolyurethane prepolymers, generally reaction products of diols and diisocyanates, are considered an important part of polyurethane chemistry due to their direct contribution to final properties. Isocyanate and polyol react and form a strong, reinforcing urethane bond. Prepolymers are generally prepared with a 2/1 ratio of isocyanates to polyols to ensure an NCO (isocyanate) terminated structure. NCO terminated structure later reacts with chain extenders and crosslinkers to produce polyurethane structure with larger molecular weight. In prepolymer chemistry, isocyanate is considered a reactive component of the reaction medium. Apart from their role as a reactive component, they also arrange the mechanical properties of polyurethane. Therefore, a proper type of isocyanate should be considered for its application. In microcellular elastomeric shoe sole polyurethane chemistry, diphenylmethane diisocyanate (MDI) has high consumption. Crude 4,4'- MDI has been chosen as the core of formulation for its highly reactive para-positioned NCO groups to form more reinforcing urethane bonds. However, a phenomenon called dimerization creates a dilemma on its high consumption in prepolymers. The reactivity of isocyanate is proportional to its rate of dimerization. Since crude MDI is a highly reactive material it has more tendency for dimerization. Dimerization is a phenomenon occupying a reaction between two isocyanates. The formation of dimers in the reaction medium reduces the free isocyanate components to react with polyols, creating a different reaction profile. Remaining free isocyanates in the reaction medium will react with a polyol to form a polyurethane structure with less frequent reinforcing urethane bonds. Therefore, fewer urethane bonds result in weaker mechanical properties. Changes in mechanical properties and reaction profiles are known symptoms of dimerization. Apart from these symptoms, dimers are known for their high melting and freezing points. According to this phenomenon, optimal operation and storage temperature of prepolymer will be in a more narrow spectrum. Prepolymer with a higher melting point will take a longer time to melt. Therefore, a more complicated pathway of processing should be considered. Storage conditions of prepolymers are also affected by dimerization. Dimerization rate is faster in 5 to 40 °C and above 50 °C . Therefore, prepolymers should be stored under 0 °C to evade dimerization. When the freezing point of a prepolymer is high and closer to the dimerization area, its stability during storage will dropdown. Freezing temperature is a key element to observing the storage stability of prepolymers. Isomers of crude MDI (2,4'- MDI and 2,2'- MDI) can be mixed with crude MDI to lower its melting and freezing temperatures for better operation and storage temperatures. Today, two forms of isocyanates named OP50 (50% - 50% mixture of 2,4'- and 4,4'- MDI) and carbodiimide modified MDI used for storage stabilization and improvement on melting of the prepolymer. Isomers of crude MDI have orto positioned NCO groups with low reactivity due to steric hindrance and show less tendency to dimerization. In literature, there is no concise study on the effect of OP50 and carbodiimide modified MDI in both melting and freezing points of prepolymers. Our study aims to investigate the effects of change in isocyanate and polyol components on freezing and melting points of prepolymers while preventing a dramatic change in mechanical properties. Prepolymers with carbodiimide modified MDI in 7-12 % show the lowest freezing temperature, the starting point of freezing, melting temperature, the starting point of melting. Its projections on mechanical properties in polyurethane (PU2) show improvement on elongation at break, tensile strength. Modulus shows a decrease due to loss of crystallinity. Besides from the best formulation, the mechanical properties of polyurethanes made from the other two best prepolymers are also investigated. PU3 which was made from PREP5 did not show a significant loss in mechanical properties same as the PU2. However, PU4 where PREP6 was used, show losses in compression set and tear resistance due to a lower amount of hydrogen and urethane bonding. It has the highest elongation at break value for its low level of crystalline hydrogen bonds. From shelf life observations in jars at 21 °C, found formula withstand freezing for 38 days while reference formula withstands for 19 days. Freezing showed a faster propagation in PREP1 than PREP4. At the end of 150 days, PREP1 completely frozen while PREP4 stayed in liquid form. For this reason, the formulation was found successful to be used in standard polyurethane applications and increasing the shelf life of prepolymers.