Study On Preparation And Properties Of Polydimethylsiloxane Composite Pervaporation Membrane At High Crosslinking Temperature

The research work of the dissertation had certain guiding significance for the preparation of polydimethylsiloxane (PDMS) pervaporaion membranes at high crosslinking temperature.The research results of the dissertation also had certain reference value for the application of composite pervaporaion membranes in the fermentation system. In order to reduce the crosslinking time, n-heptane was chosen as solvent to prepare PDMS homogeneous membranes. The crosslinking temperature was 65, 70, 75, 85 and 90?. The structure of the homogeneous membranes was characterized by scanning electron microscope. In the dissertation, the effects of crosslinker content, catalyst content and crosslinking temperature on the tensile modulus of the homogeneous membranes were studied. The contact angle of water and ethanol at the surface of the membranes and the swelling degree of the membranes in water and ethanol were measured, the homogeneous performance of the membranes was researched.Two composite membranes were prepared by using polyethersulfone (PES) and polyvinylidene fluoride (PVDF) micro-filtration membranes as support layer. The structure of the composite membranes was characterized by SEM and the molecular chain structure of the composite membranes was determined by X-ray diffraction. The effect of PDMS mass fraction on the properties of the composite membranes was studied. The effect of PDMS mass fraction and feed ethanol concentration on the separation performance of the composite membranes was also measured with ethanol aqueous solution as the feed liquid.It was found that the increase in crosslinker content resulted in the increase of the tensile strength of the membranes. With the increase of the swelling degree of membrane in water, the swelling degree in ethanol decreased. No obvious effect of the crosslinker content on the contact angel was observed. The mechanical strength of the membranes slightly increased with the catalyst content. The change in the catalyst content showed no obvious effect on the contact angel and swelling degree. The increase in crosslinking temperature resulted in the deterioration of the tensile strength of the membranes. Compared with the swelling degree in water, the swelling degree in ethanol was large. Both the crosslinking temperature and catalyst content exerted nearly no influence on the hydrophobic property of the membranes. For the pervaporation experiment, the separation factor decreased but the permeation flux increased with the feed temperature increasing and the maximum separation factor reached 8.The surface of the PDMS/PES and PDMS/PVDF composite membranes was dense, flat and smooth. No obvious layer was observed at the cross section. Therefore, the separation layer was tightly combined with the outer surface of the support layer. For each kind of the composite membrane, compared with its support layer, a diffraction peak existed at the XRD picture of the composite membrane. The influence of mass fraction of PDMS on 20 is different for appearing a highest diffraction peak, when the 2? was changed from 11° to 13°. The results of contact angle experiments showed the value of water contact angle was maximum and the value of ethanol contact angle was minimum when the mass fraction of PDMS was 15wt%.Both of PDMS/PES and PDMS/PVDF composite membranes had the best hydrophobic property and ethanol affinity. In the separation experiment of PDMS/PES composite membrane,for the change of PDMS mass fraction, opposite trends existed for the permeation flux and separation factor. The maximum permeate flux of PDMS/PES composite membrane was 11101 g·m-2·h-1 and the separation factor was 4.6. The separation index had a maximum value of 47483 when the mass fraction of PDMS was 15wt%. Therefore, the comprehensive performance of PDMS/PES composite membrane was the best at this mass fraction. For PDMS/PVDF composite membrane, with the change of PDMS mass fraction, the change trend of permeation flux and separation factor was irregular. The maximum permeate flux of PDMS/PVDF composite membrane was 4930 g·m-2·h-1. The separation factor of was 7.1 and separation index had a maximum value of 32297. Therefore, when the mass fraction of PDMS was 30wt%, the comprehensive performance of PDMS/PVDF composite membrane was the best.