Preparation, characterization and effect of annealing on performance of cellulose acetate/sulfonated polysulfone and cellulose acetate/epoxy resin blend ultrafiltration membranes

Polymeric membranes based on cellulose acetate (CA)--sulfonated polysulfone blends at three different polymer compositions were prepared by solution blending and phase inversion technique, characterized and subjected to annealing at 70, 80 and 90 °C. The permeate water flux, separation of bovine serum albumin and its flux by the blend membranes before and after thermal treatment, have been compared and discussed. Similarly, CA and epoxy resin (diglycidyl ether of bisphenol-A) were blended in various compositions, in the presence and in the absence of polyethyleneglycol 600 as non-solvent additive, using N,N^′-dimethylformamide as solvent, and used for preparing ultraflltration membranes by phase inversion technique. The polymer blend composition, additive concentration, casting and gelation conditions were optimized. Blend membranes were characterized in terms of compaction, pure water flux, water content and membrane resistance. The effects of polymer blend composition and additive concentration on the above parameters were determined and the results are discussed.     

Effect of preparation variables on morphology and pure water permeation flux through asymmetric cellulose acetate membranes

In this study, cellulose acetate (CA) ultrafiltration (UF) membranes were prepared using the phase inversion method. Effects of CA and polyethylene glycol (PEG) concentrations in the casting solution and coagulation bath temperature (CBT) on morphology of the synthesized membranes were investigated. Based on L₉ orthogonal array of Taguchi experimental design 18 membranes were synthesized (with two replications) and pure water permeation flux through them were measured. It was found out that increasing PEG concentration in the casting solution and CBT, accelerate diffusional exchange rate of solvent 1-methyl-2-pyrrolidone (NMP) and nonsolvent (water) and consequently facilitate formation of macrovoids in the membrane structure. Increasing CA concentration, however, slows down the demixing process. This prevents instantaneous growth of nucleuses in the membrane structure. Hence, a large number of small nucleuses are created and distributed throughout the polymer film and denser membranes are synthesized. Rate of water flux through the synthesized membranes is directly dependent on the size and number of macrovoids in the membrane structure. Thus, maximum value of flux is obtained at the highest levels of PEG concentration and CBT (10 wt.% and 23 °C, respectively) and the lowest level of CA concentration (13.5 wt.%). Analysis of variance (ANOVA) showed that all parameters have significant effects on the response. However, CBT is the less influential factor than CA and PEG concentrations on the response (flux).     

Studies on cellulose acetate and sulfonated poly(ether ether ketone) blend ultrafiltration membranes

New ultrafiltration membranes based on chemically and thermally stable arylene main-chain polymers have been prepared by blending the sulfonated poly(ether ether ketone) with cellulose acetate in various compositions in N,N^′-dimethylformamide as solvent by phase inversion technique. Prepared membranes have been subjected to ultrafiltration characterizations such as compaction, pure water flux, water content, and membrane hydraulic resistance. The pore statistics and molecular weight cut-off (MWCO) of the membranes have been estimated using proteins such as trypsin, pepsin, egg albumin and bovine serum albumin. The pore size increased with increasing concentrations of sulfonated poly(ether ether ketone) in the casting solution. Similarly, the MWCOs of the membranes ranged from 20 to 69 kDa, depending on the various polymer compositions. Surface and cross-sectional morphologies of membranes were analyzed using scanning electron microscopy. The effects of polymer compositions on the above parameters were analyzed and the results are compared and discussed with those of pure cellulose acetate membranes.     

Thermal behavior of cellulose acetate produced from homogeneous acetylation of bacterial cellulose

Cellulose acetate (CA) is one of the most important cellulose derivatives and its main applications are its use in membranes, films, fibers, plastics and filters. CAs are produced from cellulose sources such as: cotton, sugar cane bagasse, wood and others. One promissory source of cellulose is bacterial cellulose (BC). In this work, CA was produced from the homogeneous acetylation reaction of bacterial cellulose. Degree of substitution (DS) values can be controlled by the acetylation time. The characterization of CA samples showed the formation of a heterogeneous structure for CA samples submitted to a short acetylation time. A more homogeneous structure was produced for samples prepared with a long acetylation time. This fact changes the thermal behavior of the CA samples. Thermal characterization revealed that samples submitted to longer acetylation times display higher crystallinity and thermal stability than samples submitted to a short acetylation time. The observation of these characteristics is important for the production of cellulose acetate from this alternative source.     

Miscibility studies on blends of cellulose acetate and nylon 6

Miscibility studies on cellulose secondary acetate(CA)/Nylon 6(N6) blends have been carried out in this work. Dilute solution viscometry for the blend solutions using formic acid as the common solvent shows the existence of miscibility window.     

Sisal cellulose whiskers reinforced polyvinyl acetate nanocomposites

Sisal nanowhiskers were used as novel reinforcement to obtain nanocomposites with polyvinyl acetate (PVAc) as matrix phase. They are seen as attractive materials due to the widespread availability and low cost of the sisal source material. Statistical analysis of the sisal whisker length and diameter resulted in average values of 250 nm and 4 nm, respectively, resulting in an average aspect ratio in the upper range of reported cellulose nanowhisker values. The high aspect ratio ensures percolation, with resulting mechanical improvements and thermal stability, at lower fiber loads. Water uptake and thermal behaviour of the sisal whisker–PAVc composites were studied. Whisker addition was found to stabilize the nanocomposites with no benefit seen when increasing the whisker content beyond the percolation threshold: For all whisker contents studied above percolation, the water uptake stays constant, and the Tg does not vary with whisker content at a given relative humidity. The water diffusion rate however increases due to water accumulation at the whisker–PVAc interface. Below whisker percolation, stabilization is only noticed at low relative humidity, whereas high humidity results in disruption of whisker–PVAc interactions. This work shows the potential of cellulose nanowhiskers to stabilize polar polymers even at high humidity conditions with minimal reinforcement addition.     

Formation of cellulose acetate membranes using a supercritical fluid assisted process

Microporous cellulose acetate membranes have been prepared from polymer–acetone solutions using a supercritical fluid phase inversion process in which CO₂ acts as the non-solvent. Series of experiments were performed at various polymer concentrations, temperatures and pressures. The structure of the resulting membranes was analysed using scanning electron microscopy. We operated with polymer concentrations ranging between 5 and 40% (w/w) in acetone obtaining different pore dimensions and membrane structures. Increasing the percentage of polymer in the solution, the structure of the membranes changed from beads-like structure to cellular structure. Polymer concentration also influenced the mean diameter of the pores that ranged from 2 to 50 μm for polymer concentrations from 40 to 5% (w/w). We also tested membrane formation pressures between 100 and 200 bar and at temperature between 45 and 65 °C. Pressure influences the change in membrane structure from cellular to beads-like, whereas temperature has a minor influence on pore size: both the effects can be partially related to CO₂ density. Cellulose acetate membrane formation mechanisms have also been discussed.     

Cellulose acetate and polyetherimide blend ultrafiltration membranes: II. Effect of additive

Ultrafiltration membranes are largely applied in the separation of heavy metal ion and macromolecular solutes from aqueous streams. Studies are presented on ultrafiltration blend membranes, based on cellulose acetate (CA) and polyetherimide (PEI) in various blend compositions. Polyethylene glycol (PEG 600) was employed as a non‐solvent additive in various concentrations to the casting solution to improve the ultrafiltration performance of the resulting membranes. The blend membranes prepared were characterized in terms of compaction time, pure water flux (PWF), water content, membrane resistance, and scanning electron microscopy (SEM). The molecular weight cut‐off (MWCO) obtained from the protein separation studies is also reported. Applications of these membranes for separating toxic metal ions from aqueous streams are discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Miscibility of cellulose acetate with vinyl polymers

Binary blend films of cellulose acetate (CA) with flexible syntheticpolymers including poly(vinyl acetate) (PVAc), poly(N-vinyl pyrrolidone) (PVP),and poly(N-vinyl pyrrolidone-co-vinyl acetate) [P(VP-co-VAc)] were preparedfrommixed polymer solutions by solvent evaporation. Thermal analysis by DSC showedthat CA of any degree of substitution (DS) was not miscible with PVAc, but CAwith DS less than 2.8 was miscible with PVP to form homogeneous blends. Thestate of mixing in CA/P(VP-co-VAc) blends was affected not only by the DS of CAbut also by the VP/VAc copolymer composition. As far as CAs of DS<2.8 andP(VP-co-VAc)s with VP contents more than ca. 25 mol% were used,theCA/copolymer blends mostly showed a miscible behaviour irrespective of themixing ratio. FT-IR measurements for the miscible blends of CA/PVP andCA/P(VP-co-VAc) revealed the presence of hydrogen-bonding interactions betweenresidual hydroxyls of CA and carbonyls of N-vinyl pyrrolidone units, which maybe assumed to largely contribute to the good miscibility.     

Studies on cellulose acetate-carboxylated polysulfone blend ultrafiltration membranes--Part I

Hydrophilic polysulfone ultrafiltration (UF) membranes were prepared from blends of cellulose acetate with carboxylated polysulfone of 0.14 degree of carboxylation. The effects of blend polymer composition on compaction, pure water flux, water content and membrane hydraulic resistance (R_m), have been investigated to evaluate the performance of the membranes. The performance of the blend membranes of various blend polymer compositions were compared with that of membranes prepared from pure cellulose acetate and blends of cellulose acetate and pure polysulfone. The hydrophilic cellulose acetate-carboxylated polysulfone blend UF membranes showed better performance compared to membranes prepared from pure cellulose acetate and blends of cellulose acetate and pure polysulfone.     

Organotin(IV) complexes derived from N-ethyl-N-phenyldithiocarbamate: Synthesis,characterization and thermal studies

Organotin(IV) dithiocarbamate complexes, RSnClL₂ and R₂SnL₂ (R = Me, Bu, Ph, and L = N-ethyl-N-phenyldithiocarbamate), have been synthesized by the reaction of mono- and disubstituted organotin(IV) with ammonium dithiocarbamate. The complexes were characterized by elemental analyses, and spectroscopic techniques (¹H, ¹³C NMR and FTIR). The structures of Me₂SnL₂ and Bu₂SnL₂ were further established by single crystal X-ray diffraction technique. The crystal structure analysis showed that both complexes (Me₂SnL₂ and Bu₂SnL₂) exist as monomers. One of the dithiocarbamate ligands formed a chelate, while the other dithiocarbamate bonded to the central tin atom through one of the sulfur atoms and the second sulfur atom existed as a pendant to form distorted trigonal bipyramidal geometry. The thermal stability of all the complexes was studied using simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC). The TG-DSC results showed that Me₂SnL₂, BuSnClL₂, Bu₂SnL₂, and PhSnClL₂ displayed similar decomposition pathway via isothiocyanate intermediate, while MeSnClL₂ and Ph₂SnL₂ showed decomposition pathways different from the rest of the complexes. All the complexes resulted in SnS as the final product of the thermal decomposition process.     

Preparation and characterization of electrospun fibers based on poly(L-lactic acid)/cellulose acetate

PLLA/CA mixtures of different compositions were successfully electrospun to obtain composite nanofibrous membranes.The microstructures of the membrances changed from homogeneous to heterogeneous with the addition of CA, which was observed by FE-ESEM.The PLLA/CA fabric membranes were characterized by mechanical testing,DSC and contact angle measurements.The tensile stress of the composite fibrous membranes increased obviously with the increase of CA content.DSC results indicated that the CA component was the main factor for the changes of enthalpies in the composite fibers.Contact angle measurements showed the hydrophilicity of the electrospun nanofiber membranes was improved with the addition of CA.     

Homogeneous modification of carbon nanotubes with cellulose acetate

An efficient strategy that comprised shorten,chain extension,active groups introducing and homogeneous reaction tactics,was adopted to modify multiwalled carbon nanotubes(MWNTs) with cellulose acetate(CA).Specially,by utilizing 2,4,6-trichloro- 1,3,5-triazine,a reactive intermediate of the MWNTs(MWNT-triazine) was obtained.Suitable solubility of the MWNT-triazine helps make the homogeneous modification become reality.Detailed characterizations further verified that reaction between chloride atoms in the ...     

Permeation of water as a tool for characterizing the effect of solvent, film thickness and water solubility in cellulose acetate membranes

Cellulose acetate membranes have been used in many applications; of particular interest are reverse osmosis systems, and as a neutral matrix for incorporation of different polymers (e.g., conducting polymers), inorganic ions (e.g., lanthanides) and organic (e.g., pharmaceutical) compounds. The properties of the new polymers derived from cellulose acetate or blends depend on those of cellulose acetate. This work presents an attempt to find links between thermodynamic and kinetic properties of cellulose acetate membranes in equilibrium with water. Water diffusion coefficients in cellulose acetate membranes are reported, measured with a simple water permeation technique. The comparison of these values with the percentage of water uptake and polymer thickness leads to interesting conclusions related with different polymer properties.     

Investigation of melamine and DOPO-derived flame retardants for the bioplastic cellulose acetate

In order to identify suitable flame retardant additives for the eco-friendly polymer cellulose acetate (CA), high-melting derivatives of the known flame retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were combined with the thermoplastic CA and the combustion properties were tested. CA mixtures with bis-phosphonamidates (EDA-DOPO and PIP-DOPO) showed distinct flame retardation effects and a reduction of peak heat release rates (PHRR) by up to 18%. CA mixtures with MDOP, a melamine salt of DOPA (an oxidation product of DOPO), also showed considerable effects and a reduction of PHRR by up to 27%. While producing more smoke than pure CA and CA plus melamine, owing to its aromatic component, MDOP was superior to the CA mixtures with DOPO, EDA-DOPO and PIP-DOPO in this regard. The mixture of CA with melamine gave rise to a distinctly reduced formation of toxic CO and smoke when compared with pure CA. Thus, these additives can be considered for future applications of CA-based polymers with enhanced flame protection.     

Effect of surface morphology on membrane fouling by humic acid with the use of cellulose acetate butyrate hollow fiber membranes

A serious problem faced during the application of membrane filtration in water treatment is membrane fouling by natural organic matter (NOM). The hydrophilicity, zeta potential and morphology of membrane surface mainly influence membrane fouling. The aim of the present study is to reveal the correlation between membrane surface morphology and membrane fouling by use of humic acid solution and to investigate the efficiency of backwashing by water, which is applied to restore membrane flux. Cellulose acetate butyrate (CAB) hollow fiber membranes were used in the present study. To obtain the membranes with various surface structures, membranes were prepared via both thermally induced phase separation (TIPS) and nonsolvent-induced phase separation (NIPS) by changing the preparation conditions such as polymer concentration, air gap distance and coagulation bath composition. Since the membrane material is the same, the effects of hydrophilicity and zeta potential on membrane fouling can be ignored. More significant flux decline was observed in the membrane with lower humic acid rejection. For the membranes with similar water permeability, the lower the porosity at the outer surface, the more serious the membrane fouling. Furthermore, the effect of the membrane morphology on backwashing performance was discussed.     

Evaluation of the permeability of modified cellulose acetate propionate membranes for use in biosensors based on hydrogen peroxide detection

Phase inversion cellulose acetate propionate membranes showed lowpermeability to hydrogen peroxide aqueous solutions. Their permeability wasincreased by alkaline hydrolysis of the ester linking units. However, thepermeability remained lower than that of an unsubstituted cellulose membrane.The inclusion of hydroxypropyl cellulose in the membrane formulation, followedby an alkaline hydrolysis step, increased permeability to hydrogen peroxideaqueous solutions to 29% of that of an unsubstituted cellulose membrane.     

Structural and thermal characterization of sugarcane bagasse cellulose succinates prepared in ionic liquid

The chemical modification of SCB cellulose with succinic anhydride using 1-butyl-3-methylimidazolium chloride ionic liquid/DMSO system as reaction medium was studied. The parameters including the molar ratio of succinic anhydride/anhydroglucose units in cellulose from 1:1 to 12:1, reaction time 5-120 min, and reaction temperature 85-105 °C were investigated. The results showed that the degree substitution of succinylated cellulosic preparations ranged from 0.037 to 0.53. It was found that the treatment of the native cellulose in the ionic liquid/DMSO system under the conditions given significantly degraded the cellulose and completely destroyed the cellulose crystals. FT-IR and solid-state CP/MAS ¹³C NMR spectra produced evidence for succinoylation reaction and the results showed that succinoylation occurred at positions C-6, C-2 and C-3. The thermal stability of the succinylated cellulose decreased upon chemical modification.     

Electrospun cellulose acetate fibers: effect of solvent system on morphology and fiber diameter

This paper reports an investigation of the effects of solvent system, solution concentration, and applied electrostatic field strength (EFS) on the morphological appearance and/or size of as-spun cellulose acetate (CA) products. The single-solvent systems were acetone, chloroform, N,N -dimethylformamide (DMF), dichloromethane (DCM), methanol (MeOH), formic acid, and pyridine. The mixed-solvent systems were acetone–DMAc, chloroform–MeOH, and DCM–MeOH. Chloroform, DMF, DCM, MeOH, formic acid, and pyridine were able to dissolve CA, forming clear solutions (at 5% w/v), but electrospinning of these solutions produced mainly discrete beads. In contrast, electrospinning of the solution of CA in acetone produced short and beaded fibers. At the same solution concentration of 5% (w/v) electrospinning of the CA solutions was improved by addition of MeOH to either chloroform or DCM. For all the solvent systems investigated smooth fibers were obtained from 16% (w/v) CA solutions in 1:1, 2:1, and 3:1 (v/v) acetone–DMAc, 14–20% (w/v) CA solutions in 2:1 (v/v) acetone–DMAc, and 8–12% (w/v) CA solutions in 4:1 (v/v) DCM–MeOH. For the as-spun fibers from CA solutions in acetone–DMAc the average diameter ranged between 0.14 and 0.37 μm whereas for the fibers from solutions in DCM–MeOH it ranged between 0.48 and 1.58 μm. After submersion in distilled water for 24 h the as-spun CA fibers swelled appreciably (i.e. from 620 to 1110%) but the physical integrity of the fibrous structure remained intact.