Preparation and characterization of cellulose acetate propionate membrane (original) (raw)
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A technique for postsynthesis modification of a cellulose acetate ultrafiltration membrane with possible application in water and wastewater treatment is studied. The technique used an oxidizing agent (persulfate) to develop free radicals on the membrane surface, and that was expected to promote grafting of hydrophilic macromolecules (polyethylene glycol). A chaintransfer agent (2-mercaptoethanol) was tested to control the grafting process, avoiding the formation of long chains that usually lead to high permeability losses in other graft techniques. The modifications aimed at the decrease of the fouling susceptibility of the membrane studied. The possibility of an increase in rejection was also investigated. The membrane was characterized before and after modification, by attenuated total reflectance-Fourier transform-infrared spectroscopy, scanning electron microscopy, atomic force microscopy, and in terms of the rejection of neutral reference solutes. The information given by the different techniques of characterization provided strong evidences of the occurrence of modification, although permeation of (real) foulants was the decisive test. To obtain information about the fouling tendency of the nonmodified and modified membranes, two different kinds of foulants were used: a humic acid (usually found in surface waters) and textile auxiliaries (representing one of the most important industries in Portugal). The results showed an increase in the rejections of the humic acid, and significant improvements in the performance of the membrane with respect to fouling tendency in the case of the textile auxiliaries.
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The most common reverse osmosis (RO) membranes that achieved economic water desalination applications are made of cellulose acetate (CA). Cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) have been blended with CA as innovative combinations to produce RO membranes through phase inversion technique. The relation between membranes compositions, structure, morphology, hydrophilicity and applicability were examined. Scanning electron microscope and Fourier transform infrared were used to evaluate the microstructure of these membranes. Hydrophilicity, strength, salt rejection and flow permeates were tested using a cross-flow reverse osmosis system and contact angle calculations. The contact angle measurements showed an increase from 56°for CA membrane to 71°f or CAP membrane and 74°for CAB membrane. The hydro-phobicity of such membranes increased as CAP and CAB loadings increased. The salt rejection of pristine RO membranes increased from 93.2% with permeate of 1.4 L/m 2 h for CA membrane to 96.8% with permeate of 1.07 L/m 2 h for CAB membrane and 97.8% with permeate of 18.62 L/m 2 hr for CAP membrane. The salt rejection of supported membranes onto a nonwoven polyester fabric decreased from 92.8% with permeate of 3.78 L/m 2 h for CA/0.5 wt% CAP to 91.4% with permeate of 6.05 L/m 2 h for CA/ 0.5 wt% CAB and 88.5% with permeate of 5.84 L/m 2 h for CA/0.1 wt% CAP/0.1 wt% CAB.
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Evaluation of cellulose and carboxymethyl cellulose/poly(vinyl alcohol) membranes
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Cellulose was isolated from rice straw and converted to carboxymethyl cellulose (CMC). Both polymers were crosslinked with poly(vinyl alcholo) (PVA). The physical properties of the resulting membranes were characterized by FT-IR, TGA, DSC and SEM. The cellulose and CMC were first prepared from bleached rice straw pulp. The infrared spectroscopy of the resulting polymer membranes indicated a decrease in the absorbance of the OH group at 3300-3400 cm −1 , which is due to bond formation with either the cellulose or CMC with the PVA. The thermal stability of PVA/cellulose and PVA/CMC membranes was lower than PVA membrane. The surface of the resulting polymer membranes showed smooth surface in case of the PVA/CMC membrane and rough surface in case of the PVA/cellulose membrane. Desalination test, using 0.2% NaCl, showed that pure PVA membranes had no effect while membranes containing either cellulose or CMC as filler were able to decrease the content of the NaCl from the solution by 25% and 15%, respectively. Transport properties, including water and chloroform vapor were studied. The moisture transport was reduced by the presence of both cellulose and CMC. Moreover, the membranes containing cellulose and CMC showed significantly reduced flux compared to the pure PVA. The water sorption, solubility and soaking period at different pH solutions were also studied and showed that the presence of both cellulose and CMC influences the properties.
DESALINATION AND WATER TREATMENT, 2020
In this study, cellulose acetate (CA) membranes were prepared by the dry-wet phase inversion technique for desalination application. The effect of evaporation time on the properties of the prepared cellulose acetate membrane has been investigated. Different evaporation time was selected such as (30, 60, 90 and 120 s). The membrane characterization was carried out by using Fourier transform infrared (FTIR) analysis, scanning electron microscopy (SEM), contact angle measurements. Brackish water was used as a feed solution in a cross flow unit to evaluate the membrane performance. The effect of the evaporation time on the membrane's water flux and salt rejection was tested. The results showed that the different evaporation time has affected the structure as deduced by the FTIR analysis. The SEM analysis showed the asymmetric CA membranes structure, where a thin dense selective barrier layer was deposited (in a finger-like structure) on the surface of the prepared membranes. As the evaporation time increased, the thickness of this layer has increased and the value of the contact angle has decreased. The highest rejection, obtained from the membrane that was prepared with the evaporation time 60 s, reached 96.5% salt rejection with a relatively low flux of 1.0234 L/m 2 h.