SELF-CROSS LINKABLE SUPERABSORBENT HYDROGELS BASED ON DIFFERENT VINYLALKOXYSILANES AS CROSSLINKERS
Materials Science and Engineering, M.Sc. Thesis, 2013
Prof. Dr. Yusuf Z. Menceloğlu (Thesis Supervisor), Asst. Prof. Fevzi Çakmak Cebeci, Asst. Prof. Gözde İnce, Assoc. Prof. Selmiye Alkan, Asst. Prof. Murat Çokol
Date &Time: June, 03rd, 2013 - 10.00
Place: FENS G032
Keywords: Superabsorbent, Free Radical Solution Precipitation, Acrylamide, AMPS, Vinylalkoxysilanes, Equilibrium Swelling Ratio, Cross linking
Novel superabsorbent hydrogels were synthesized through the Free Radical Solution Precipitation polymerization technique. The synthesized materials were characterized by Differential Scanning Calorimetry (DCS), Simultaneous Thermal Analysis (STA), FTIR (Fourier Transmittance Infrared) ,1H Nuclear Magnetic Resonance Spectroscopy (NMR), 29Si Nuclear Magnetic Resonance Spectroscopy. Thin film surfaces of polymers were characterized by Drop Shape Analysis (DSA). These characterization methods provide valuable information to understand chemical structure and performance level of water uptake synthesized hydrogels, effect of synthesis parameters; change in cross linker agents, and thermal behavior of polymers.
Equilibrium Swelling ratio (ESR) of synthesized superabsorbent hydrogels were measured gravimetrically and highest ESR value with correspoding polymer structure and concentration were optimized.
Due to chemical structure and reactivity relationship, in terms of hydrolysis and condensation reactions, three different type of cross linking agents reactions were used in polymerization. Based on three different chemical structures of vinylalkoxysilane cross linking agents, namely Triethoxyvinylsilane (TEVS), Vinyltrimethoxysilane(VTMS) and Tris(2-methoxyethoxy)vinylsilane (TMEVS), the ESR value was obtained for each based samples.
According to 1H – NMR analysis, monomer reactivities of AMc and AMPS were found as 1.32 and 1.25 respectively. Based on monomer reactivity results, it is clear to conclude that for the Free radical solution precipitation polymerization of acrylamide and AMPS occurred randomly.
Experimentally three different polar aprotic solvents were used as solvent medium in reactions,1,4-dioxane,Dimethylacetamide and Dimethylformamide. A significant difference result from using these three polar solvents was the comparable change in ESR under same conditions.
Solution viscosity of prepared standard 6 %(wt/ml) of polymers were measured in Brookfield DV-III Rheometer while keeping torque value 15%.
Molecular weight of synthesized polymers based on three different vinylalkoxysilanes were calculated according the results obtained from Dilute Solution Viscometery experiment, while using the constants for polyacrylamide since approximately about 90 % of synthesized polymers are acrylamide.