Mussel-inspired fabrication of structurally stable chitosan/polyacrylonitrile composite membrane for pervaporation dehydration

Different polydimethylsiloxane (PDMS) nanocomposite membranes were synthesized by incorporating various contents of nanosized silica particles to improve the PDMS pervaporation (PV) performance. A uniform dispersion of silica nanoparticles in the PDMS membranes was obtained. The nanocomposite membranes were characterized morphologically by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results showed that surface roughness increases by incorporating silica, and this decreases absorption of penetrants on the membrane. Swelling studies showed that the presence of silica nanoparticles into the PDMS membranes decreases degree of swelling, which can be attributed to rigidification of the PDMS matrix. Additionally, the results revealed that helium permeability decreases through the nanocomposite membranes, due to the more polymer chains packing. Effects of silica on recovery of isopropanol (IPA) from water mixtures were also investigated. Based on the results, incorporating silica nanoparticles promotes significantly the PDMS membrane selectivity because the polymer chains are rigidified and also the polymer free volume decreases. However, permeation flux decreases as diffusion of the penetrants reduces in the presence of silica nanoparticles within the PDMS membranes. As PV performance depends on operating conditions, effects of feed composition, and temperature were also studied. Moreover, recoveries of IPA, ethanol, and methanol from water mixtures were compared using the PDMS-silica nanocomposite membranes. The results demonstrated that polarity and solubility of alcohols affect permeation flux and selectivity resulting in the higher permeation flux and selectivity for IPA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Recovery of alcohols from water using polydimethylsiloxane–silica nanocomposite membranes: Characterization and pervaporation performance

Studies on the coating layer in a PTFPMS/PEI composite membrane for gaseous separation

Hydrogels prepared from polysiloxane chains by end linking them with trifunctional silanes containing hydrophilic groups

There is a lack of stable and hydrophobic organic solvent nanofiltration (OSN) membranes meaning that their implementation in non-polar solvent nanofiltration remains a challenge, typically in solvent (e.g. hexane) recovery during vegetable oil production (e.g. soybean oil/hexane). Considering this, novel trifluoropropylmethylsiloxane dimethylsiloxane (PDMS–PTFPMS)/polyvinylidene fluoride (PVDF) membranes, with both high hexane permeability of PDMS and excellent hexane stability of PTFPMS, were successfully developed to recover hexane via OSN. Their microstructure and surface properties were characterized by SEM, FTIR, DSC, TGA, XPS and contact angle measurements. We explored the effects of the ratio of the PTFPMS segment in polymer chain and polymer viscosity on membrane performance. With regards to the F50-M membrane, we also conducted a comprehensive study on the OSN performance of the F50-M membrane under different operational conditions. The oil rejection was above 95% with stable hexane permeability of 3.06 kg−1 μm m−2 h−1 bar−1 over a 32-day period. Experimental results confirmed its ability to recover hexane under various operational conditions, showing high oil rejection and excellent long-term operational stability. We attributed its outstanding performance to its unique microstructure and surface properties due to the fluorine-containing PTFPMS segment. This study indicates that fluoropolymer membranes are promising candidates in OSN processes, offering a wider choice of membrane materials and application fields.

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Highly stable PDMS–PTFPMS/PVDF OSN membranes for hexane recovery during vegetable oil production

In this work we have compared and contrasted the pervaporation behaviour (separation factor and flux) of fluorosilicone dense membranes based on poly(trifluoropropylmethylsiloxane) (PTFPMS) with poly(dimethylsiloxane) (PDMS) dense membranes. In particular, pervaporation experiments were carried out at 298 K using lab-made PTFPMS, lab-made PDMS and commercial PDMS membranes in order to remove three different organic liquids pyridine (PY), isopropanol (IPA) and methylethylketone (MEK) from dilute (<10 wt.%) binary aqueous mixtures. All of the silicone membranes studied were found to be successful for the desired separations. The permeation flux of pyridine–water liquid mixtures for the PTFPMS membranes was found to increase with the pyridine concentration in the feed mixtures. The separation factor for PDMS membranes for the removal of pyridine, IPA and MEK from aqueous binary mixtures (1 wt.%) was found to be higher than that of PTFPMS membranes while the normalized flux was higher for PTFPMS membranes under identical test conditions. The effect of crosslink density of the PTFPMS membranes on the separation of pyridine–water mixtures was also studied. For a 1 wt.% feed solution the total flux increased with the molar mass between crosslinks, whereas the separation factor for pyridine–water was highest for a molar mass between crosslinks of 15,320 g mol−1.

Pervaporation of Organic Liquids from Binary Aqueous Mixtures using Poly(trifluoropropylmethylsiloxane) and Poly(dimethylsiloxane) Dense Membranes

Organotin compounds have been used to catalyze the condensation of various α,ω-dihydroxyl terminated organosiloxane diols. This tin catalyzed reaction extends the length of siloxane chains and it also produces narrow molar mass distribution polyorganodisilanols (Mw/Mn = 1.4). The reaction occurs between a variety of siloxanes that are terminated with hydroxyl groups and it does not depend on the organic side groups connected to silicon for the systems studied here. These systems include silicon atoms bearing dimethyl, methylphenyl or methyl 1,1,1 trifluoropropyl substituents. The organotin catalyst in the reaction facilitates the organosilanol condensation releasing water as a byproduct. However it does not appear to facilitate the opening of siloxane bonds nor the redistribution of siloxane bonds under the conditions employed here. Copolymerization of linear oligomeric dimethylsiloxane diol and linear oligomeric methylphenylsiloxanediol was found to give a relatively equal reactivity of homo polymerization and hetro polymerization in the condensation and randomly alternating segmented block copolymers that were formed. The reaction kinetics of the polymerization was used to experimentally verify the fact that there is a chain length dependence of the reacting silanol end-groups. The molar mass values during the polymerizations were determined using gel permeation chromatography. The chromatography, viscosity and FTIR results demonstrate that the reactivity of the hydroxyl end-groups in the polycondensation reaction decreases upon increasing the chain length of the siloxane. It therefore appears that these tin catalyzed siloxane systems deviate from the widely demonstrated hypothesis of Paul Flory on the “equal reactivity of functional groups” for step-growth polymerizations.

Chung Mien Kuo

Papers

Pervaporation of Organic Liquids from Binary Aqueous Mixtures using Poly(trifluoropropylmethylsiloxane) and Poly(dimethylsiloxane) Dense Membranes

On the Role of Tin Catalysts in Step-Growth Polymerization Reactions