Modified Cellulose Acetate Research Articles

Synthesis, characterization and thermal studies on cellulose acetate membranes with additive

Cellulose acetate (CA) membranes are used in ultrafiltration applications, although they show low chemical, mechanical and thermal resistance. In order to prepare membranes with improved properties, modification of cellulose acetate with polyethelene glycol (PEG 600) has been attempted. In this study, CA has been mixed with PEG 600 as an additive in a polar solvent. The effects of CA composition and additive concentration given by a mixture design of experiments on membrane compaction, pure water flux, water content and membrane hydraulic resistance have been studied and discussed. The efficiency of protein separation by the developed CA membranes have been quantified using model proteins such as pepsin, egg albumin (EA) and bovine serum albumin (BSA). The thermal stability of the developed membranes prepared with PEG 600 additive has also been investigated using thermogravimetric analysis and differential scanning calorimetry.

Zeolites and mesoporous materials at the dawn of the 21st century

The ability of Trametes villosa laccase immobilized on cellulose acetate to reduce/eliminate combustions toxicants was investigated using a model enzyme filter design. In the initial stages, various strategies of grafting laccase onto cellulose acetate polymers including partial deacetylated cellulose acetate followed by generation of reactive groups using either periodate or 2,2,6,6-tetramethylpiperidinyl-1-oxy radical (TEMPO) and the use of different spacer arms [1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDAC); 1,4-butanediol diglycidyl ether (BDGE)] and 3-aminopropyltriethoxysilane was investigated. The best process for effective immobilization of laccase onto both cellulose acetate powders and tows were those involving partial deacetylation, TEMPO activation to generate carboxylic groups, treatment with EDAC as a spacer arm followed by adding the enzyme. This procedure resulted in 45 units/mg laccase activity (28% increase in activity of immobilized enzyme) measured using ABTS as substrate as compared to the other strategies used to immobilize laccase. Further, the immobilized enzyme was able to oxidize > 60% of toxicants resorcinol, hydroquinone and methylcatechol passing through the model enzyme filter. This study therefore demonstrates the great possibility of immobilizing laccase onto modified cellulose acetate and the great potential application of immobilized laccase to remove toxicants during combustion.

CELLULOSE ACETATE AND EPOXY RESIN BLEND ULTRAFILTRATION MEMBRANES: REPARATION, CHARACTERIZATION, AND APPLICATION

ABSTRACT Membranes based on cellulose acetate used in ultrafiltration applications lack good, chemical, mechanical and thermal resistance. In order to prepare membranes with improved properties, modification of cellulose acetate with epoxy resin through solution blending was attempted. In the present work, the membrane casting solutions with different polymer blend compositions of cellulose acetate and diglycidyl ether of bisphenol-A (DGEBA) were prepared at 30±2°C. The maximum percent compatibility of the two polymers, cellulose acetate and diglycidyl ether of bisphenol-A, was estimated to be 60/40%. Ultrafiltration blend membranes based on various blend compositions were prepared, characterized in terms of compaction, pure water flux, water content, membrane hydraulic resistance and molecular weight cut-off. The application of these membranes, in rejection of proteins of various molecular weights, are discussed.

Chemical Modification of Cellulose Acetate with Titanium Isopropoxide

This study describes the chemical modification of cellulose acetate (CA) using titanium isopropoxide (TiP) in a sol-gel process for the formation of an organic/inorganic hybrid (OIH) material. The hydrolysis and condensation reactions that characterize this process result in CA cross-linking and formation of inorganic oxide particles. TiP-modified CA gels and membrane materials are characterized by solubility and swelling measurements, Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy, thermogravimetric analysis, differential scanning calorimetry (DSC) and ultrasonic time-domain reflectometry. Whereas the solubility of the CA significantly decreased with increasing TiP exposure consistent with high levels of cross-linking, unambiguous spectroscopic evidence for cross-linking could not be determined. In addition, DSC measurements indicated no significant change in CA glass-transition temperature as a function of TiP exposure. On the other hand, TiP treatment dramatically improved the creep behavior of treated porous CA membranes, whereby the total compressive strain decreases by as much as 70% relative to the untreated materials. Overall, the results suggest that TiP treatment can be used as a post-fabrication processing step to create OIH-modified CA membranes with improved chemical and mechanical stability.

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.

Characterization of Plasma-Polymerized Thiophene onto Cellulose Acetate Membrane and Its Application to Pervaporation

Surface modification of cellulose acetate (CTA) membranes was achieved by subjecting them to magnetron-enhanced plasma. Plasma polymerization and deposition of thiophene were achieved on these membranes in a nitrogen atmosphere. Such modified membranes were characterized by determining the rate of deposition, angle of contact with water, and IR spectroscopy. The morphology of deposition was studied by SEM, and it was found that the globular particles grow with time to give a honeycomb or platelet structure. The water vapor transmission rates were measured and were found to decrease with an increase in the time of deposition. The pervaporation process of such modified CTA films for the separation of an isopropanol–water mixture was investigated. The water selectivity of the modified membranes was found to be increased.

Enzymatic acylation of cellulose acetate in organic media

Cellulose fatty esters were prepared by acylation of cellulose acetate with various fatty acids catalyzed by immobilized lipase from Candida antarctica (Novozyme) in acetonitrile. The reaction parameters affecting the biocatalytic process such as the role of the nature of the substrates, the concentration of the enzyme and the reactants as well as the agitation speed of the reaction mixture have been investigated. At optimum reaction conditions about 35% of the initial amount of fatty acid were incorporated on the modified cellulose acetate molecule, while an increase of 2% of the ester bonds was observed on the final product.

Permineralized fruits of Diplopanax (Cornaceae, Mastixioideae) from the middle Eocene Princeton chert of British Columbia

Over 80 specimens of a permineralized fruit referable to the Cornaceae (Mastixioideae) have been recovered from the middle Eocene Princeton chert (Allenby Formation) of British Columbia, Canada. Specimens were studied using a modified cellulose acetate peel technique using hydrofluoric acid. Diplopanax eydei Stockey, LePage et Pigg sp. nov. has fruits with endocarps up to 11 mm long and 10 mm in diameter that have a smooth stone surface, a single locule that is U-shaped in cross section, and a germination valve that extends nearly the full length of the fruit. An epicarp (exocarp + mesocarp) composed of thin-walled parenchymatous cells, 1.2–1.5 mm thick, is preserved on one specimen. Remnants of an apical disc with possible perianth scars are seen in three specimens. The endocarp is composed of interlocking fibers with scattered resin ducts and vascular tissue that parallels the edges of the valve. Seed integuments consist of a single external layer of large cells with brown contents and an inner zone of two to four thin-walled cells of smaller diameter lacking contents. Numerous septate fungal hyphae are usually present in the integumentary layers. These fruits represent the first reported fossils of the genus Diplopanax Handel-Mazzetti, and the northernmost known mastixioids in North America. The fruits are compared to those of other living and fossil mastixioids including Mastixicarpum Chandler and add to our knowledge of the diversity and distribution of the North American mastixioids during the Tertiary.

Modification of cellulose acetate: Its characterization and application as an ultrafiltration membrane

The development of cellulose acetate blend membranes using a commercial grade Mycell cellulose acetate and cellulose diacetate with suitable pore structure is discussed. These membranes were characterized in terms of resistance of the mem- brane, pure water flux, the molecular weight cutoff, water content, pore size, and porosity. The removal of copper metal ions by this blend membrane using polyethylene- imine as a chelating agent was studied. The effects of copper ion concentration and casting solution composition on separation are also discussed. A possible correlation between feed and permeate concentration of copper ion is evaluated. q 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 1939-1946, 1998

Modification of cellulose acetate: Its characterization and application as an ultrafiltration membrane

The development of cellulose acetate blend membranes using a commercial grade Mycell cellulose acetate and cellulose diacetate with suitable pore structure is discussed. These membranes were characterized in terms of resistance of the membrane, pure water flux, the molecular weight cutoff, water content, pore size, and porosity. The removal of copper metal ions by this blend membrane using polyethyleneimine as a chelating agent was studied. The effects of copper ion concentration and casting solution composition on separation are also discussed. A possible correlation between feed and permeate concentration of copper ion is evaluated. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1939–1946, 1998

Transport of water vapour and gases in modified cellulose acetate matrices. Influence of the nature of the penetrant on diffusion and relaxation kinetics

AbstractMembranes developed by modification of a cellulose acetate (CA) matrix were studied by means of the flow method CA matrix is modified by poly(4‐vinylpyridine) (PVP), or an interpenetrating network (IPN) agent. The obtained diffusion coefficients, permeability coefficients and relaxation kinetic parameters for oxygen, carbon dioxide and water vapour enabled us to consider not only the transport properties of the membranes but also the influence of the relaxation processes on the membrane permeability and stability. The results show that the interactions between water molecules and polar groups on the polymer chains cause the membrane material to swell. This swelling process provokes an increase in the permeation flux of ca. 20–30%. Oxygen causes a consolidation of unstable membranes of the cellulose acetate matrix modified by IPN but not of blends with PVP. The consolidation process reduces the membrane permeability by ca. 38%, while carbon dioxide has no effects on the membrane properties. Membranes based on a modified cellulose acetate matrix have higher permeability than pure CA membranes.

Internal membranes and laminates for adaptation of amperometric enzyme electrodes to direct biofluid analysis

This study describes the use of discrete, highly selective covering inner membranes in amperometric enzyme electrodes for direct biofluid analysis. Such inner membranes when interposed between the enzyme layer and the electrode working surface has been found to be both selective, as well as biocompatible. Cellulose acetate or detergent (Triton X-100 and Tween 80) modified cellulose acetate and polyethersulphone polymeric membranes, were both found to be highly selective against electroactive solutes normally present in biofluids. The inclusion of such inner perm-selective membranes greatly enhanced the biocompatibility of the enzyme electrode and reduced the passivation of the working electrode on exposure to whole blood or serum. The study indicates that electrode drift in biological solutions may also be due to passivation of the working electrode by small diffusible surface active species.

Vegetative remains of the Magnoliaceae from the Princeton chert (Middle Eocene) of British Columbia

One wood block and many small twigs (up to 1.3 cm diam.) with little secondary growth and showing magnoliaceous characters were identified from the Princeton chert locality (Middle Eocene) of British Columbia, Canada. Specimens were studied with a modified cellulose acetate peel technique and hydrofluoric acid. Well-preserved primary tissues include a chambered pith that distinguishes these twigs from other woods in the chert. Secondary xylem has solitary vessels, radial multiples, and clusters, scalariform perforation plates with 8–27 bars, scalariform, transitional, and opposite intervascular pitting, and tyloses. Imperforate tracheary elements with circular bordered pits, heterocellular and homocellular rays, and marginal parenchyma characterize the twigs. Secondary phloem has dilated rays, alternating bands of fibers and thin-walled cells, and sclerified ray and axial cells. In older wood, opposite intervascular pitting and homocellular rays, suggest affinities with Liriodendron L.; however, the presence of opposite, scalariform, and transitional intervascular pitting and secondary phloem structure necessitate its inclusion in Liriodendroxylon Prakash et al. Liriodendroxylon princetonensis Cevallos-Ferriz et Stockey sp.nov. is distinguished from other species in this genus by the presence of homocellular rays, scalariform intervascular pitting, and well-preserved extraxylary tissues that are unknown for the other fossil species. Liriodendroxylon princetonensis adds to the diversity of extinct magnoliaceous plants during the Eocene and represents the oldest known species of this genus. These plants were probably part of the surrounding forest vegetation in the Princeton basin. Like most extant Magnoliales, L. princetonensis probably lived under subtropical to warm-temperate, moist conditions. Key words: Magnoliaceae, Liriodendroxylon, fossil woods, Eocene.

Studies on diisocyanate-modified cellulose acetate membranes

This paper describes the reaction of the highly reactive NCO group as present in diisocyanate with the basic OH group as present in cellulose acetate in a mixture of dichloromethane and t-butyl alcohol, thereby producing minimally crosslinked cellulose acetate, bearing urethane groups and consequently yielding membranes by using the Kesting [1,2] dry method. Verification of urethane group through infrared spectroscopy, discussion of the transport characteristics of the membrane by means of a reverse osmosis testing system, testing the membrane's tensile strength and observation of the structure of the membrane pores are presented. The results indicated that significant improvements were observed with respect to the salt rejection of the modified cellulose acetate membrane as well as to its tensile strength. However, these improvements were accompanied by a slight decrease in the water flux.

Chemically modified cellulose acetate membrane for biosensor applications

The chemical modification of cellulose acetate by acylation of the C-2 position produces a membrane that is more hydrophobic and biocompatible. The efficacy of this membrane in biosensor applications is compared with the unmodified cellulose acetate membrane.

A PERMINERALIZED FLOWER FROM THE MIDDLE EOCENE OF BRITISH COLUMBIA

A permineralized flower bud, two stamen clusters and one isolated stamen of similar morphology have been found in the black cherts of the Middle Eocene Allenby Formation of Princeton, British Columbia. Specimens were studied using a modified cellulose acetate peel technique and hydrofluoric acid. The single flower specimen, 4.5 mm long and 4.0 mm in diameter, represents half of a relatively mature bud of a bisexual flower with a superior ovary. The two‐loculate pistil is 2.5 mm long with a solid style and a lobed stigmatic surface. No ovules have been observed in attachment. Twenty‐two to 24 stamens are borne in three whorls or a tight helix. Pollen sacs of the anther are elongate with a thin connective while filaments are laminar. Anther walls contain rectangular cells with dark contents that also can be identified in isolated stamens or stamen clusters. Abundant stephanocolpate (pentacolpate), psilate pollen grains 20 μm in diameter have been isolated and examined using scanning and transmission electron microscopy. Grains are tectate, columellate with a broad foot layer that thins near the apertures, and an endexine of small platelets. The remains of four petals are surrounded by one large sepal, suggesting two in the whole flower. Morphological features of this flower are comparable to taxa of the Flacourtiaceae and Papaveraceae, but show closest similarities to the Eschscholziaeae of the Papaveraceae. Difficulties with reconciling the placement of this flower in the Eschscholziaeae and the known environment of deposition of the Princeton chert are discussed. The fossil material represents a new angiospermous taxon: Princetonia allenbyensis Stockey gen. et sp. nov., family Incertae sedis.

Silylcellulose Acetate Membrane for Desalination of Water

Abstract Commercial cellulose acetate (39.9% acetyl) was partially modified with different proportions of Trimethylchlorosilane. The physical properties of modified polymers were studied. The membranes prepared from these polymers were evaluated for desalination of water by reverse osmosis. The thermal stability of modified cellulose acetate was also investigated.

Thermal stability of cellulose acetate urethanes

The thermal degradation of isocyanate modified cellulose acetate has been studied by dynamic thermogravimetric analysis in air. The activation energy of decomposition of these modified polymers has also been determined from differential thermal analysis thermograms. The data indicate that the cellulose acetate urethane polymers are thermally stable.

Selectivity of Isocyanate Modified Cellulose Acetate Membranes to Sugars

Abstract Membrane separation processes are becoming increasingly important for dehydration of liquid food in modem food industry. New membranes with better separation characteristics; improved mechanical, chemical and thermal properties are being developed. In the present work membranes cast from isocyanate modified cellulose acetate polymers have been utilized for the separation/concentration of sugars from their aqueous solutions. Some of the characteristics of the modified polymers and membranes have also been reported.

Selective behaviour of hyperfiltration cellulose acetate membranes: Part II. Streaming potential

Streaming potentials have been measured by the fast pulse method for cellulose acetate membranes cured at 85 and 95°C. Bounding, solutions of Li +, Na +, K +, Cs +, Mg 2+, Sr 2+, Ba 2+ and La 3+ chlorides were used in the concentration of 10 −4-10 −1 M. The streaming potenial was shown to depend on the nature of the cation and to increase with decreasing solution concentration. Rather good consistency was obtained in dilute solutions between the electroosmotic cross coefficients calculated from the streaming potentials and from the electroosmosis measurements for Part I (M.G.A. Khedr, S.M. Abd el Haleem and A. Baraka, J. Electronal. Chem. 182 (1985) 157), according to the Onsager reciprocal relations. The deviation observed at higher concentrations, independent of the cation nature, is attributed to concentration polarization and/or excessive water transport encountered in electroosmosis measurements. Determination of additional phenomenological coefficients of the same system, the hydraulic permeability and the electric resistance enabled the estimation of the effective exchange capacity of modified cellulose acetate membranes. The resulting value of 2.1×10 −3 mol of unit charge/1 of pore liquid is compared to the corresponding values previously reported on a different basis.