Preparation and characterization of polymer monolith

Polyethylene glycol (PEG) 20000 (PEG20000) monoliths were prepared by thermally induced phase separation method (TIPS). Toluene, ethanol, and DMSO solvents and EtOH:DMSO (1,1), EtOH:hexane (2,1), and EtOH:hexane (1,1) solvent mixtures were successful in performing phase separation for the formation of monoliths. Hexane was chosen as the non-solvent for the preparation of M5, M6 and M7 monoliths. Porosity of the prepared monoliths, which ranged up to 81% was measured by the gravimetric method. The morphology of PEG monoliths was examined by scanning electron microscope (SEM) and the presence of continuous pores was observed. Pore sizes of the prepared monoliths can be controlled by changing the polymer concentration and non-solvent ratio. The prepared monoliths had average pore areas of 0.59-1.62 µm2, skeleton of 0.30-0.97 µm2, with corresponding average pore and skeleton ranging from 1.57-2.29 µm and 1.65-2.50 µm, respectively. Nitrogen adsorption-desorption isotherms showed that M5 monolith had a large surface area of 53 m2. In the Fourier infrared spectroscopy (FTIR) spectra of the monoliths, changes in the wavenumber and intensities of the peaks were observed compared to pure PEG20000. Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) methods were used in the thermal characterization of the monoliths. The melting point of the products was found to be close to the melting point of pure PEG material, which is 69 °C. X-ray diffraction (XRD) analysis was performed to investigate the crystallization of the prepared monoliths during the phase separation process. Crystallite sizes of the monoliths were calculated. The cloud points which determine phase separation were found by the visual turbidity method and varied between 25-35 °C. The 'D distance', which determines the quality of solvent and solvent mixtures for the polymer, was calculated using Hansen solubility parameters. Monoliths showed good absorption behavior against organic liquids such as gasoline, sunflower oil, and oleic acid. As a result of absorption tests, swelling and retentions of the monoliths were found. Some monoliths (M1, M3, and M5) were able to effectively absorb 3-3.5 times their own weight of these organic liquids.