Modification of Cellulose Acetate by Aliphatic Isocyanates for Reverse Osmosis Studies

Abstract

In the present study an emphasis has been given to modify the commercially available cellulose acetate (CA) (39.9% acetyl) by aliphatic isocyanates to increase the mechanical resistance of the polymer. The transport properties of the cast membranes from these modified CA polymers have been studied. The work has been further extended to study the thermo oxidative degradation of these modified cellulose acetate polymers in dry state in air.     

Laccase functionalized cellulose acetate for the removal of toxic combustion products

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.     

Influence of Structure-Physical Properties of Polymer Matrix on Kinetics of Inside Cell Radical Reactions

Abstract

In polymethylmethacrylate and cellulose acetate the kinetics of triplet cyclohexadienone carbenes decay by 77–135 K including a hydrogen atom transfer from C[sbnd]H bonds of macromolecules with the radical pair formation was examined. The kinetics of this process reflects the influence of peculiarities on a level of cells. The influence of external magnetic field on the decay of carbenes was established. The character of the magnetic is different in two polymers. It's determined by the cell recombination efficiency of radicals and the exchanged energy in radical pairs depending on mutual radical configurations. The structure-physical modification of polymers by aerosil filling connected with the formation of interfaces influences strong on the rate of carbenes conversions.     

IR and Dielectric Analysis of Cellulose and Its Derivatives

Abstract

Infrared (IR) spectra of cellulose, cellulose carbamide, cyanoethyl cellulose, cellulose acetate, and acetylated cyanoethyl cellulose from 400 to 4000 cm^?1 were studied. All cellulose derivatives have lower crystallinity index than cellulose except cellulose carbamide, which is attributed to hydrogen bond strength. Dielectric properties of these derivatives were measured in the range of frequency (0.1–100 kHz). The results showed that cellulose derivatives have lower values and cellulose carbamide has the lowest value. AC conductivity and resistivity values were calculated, and the conduction mechanism beside relaxation was discussed.     

Aromatic Polyamide Hydrazide Membranes for Reverse Osmosis Separations

Abstract

Wholly aromatic polyamide hydrazide (PAH) polymers were synthesized by low temperature polycondensation from freshly prepared m-amino benzhydrazide, p-amino benzhydrazide, isophthaloyl chloride, and terephthaloyl chlorides in dimethyl acetamide solvent. A series of film-forming polymers prepared by altering the molar ratios of the reacting monomers was characterized in terms of % moisture regain, η_inh, and x-rays. Asymmetric membranes prepared from selected polymer samples were tested in reverse osmosis test cells, and the pure water permeability and the membrane constant were determined. An optimum meta: para molar ratio of the reacting monomers has been identified for the best performance under reverse osmosis which gave solute separation close to 98% for a feed concentration in the range of seawater. The PAH membranes appear to be potential barrier candidates for treatment of effluents containing ammonium, nitrates, etc. and radioisotopes. Separation data for a few other solute systems were also evaluated and compared with those obtained from cellulose acetate membranes.     

Physical ageing in rigid chain polymers

Torsional and tensile creep properties of a cellulose acetate butyrate ester and the polyimide Kapton-H were studied in order to reveal physical ageing in these rigid chain polymers. The measured shift rates, μ, were 0.75 and 0.5 for cellulose and polyimide respectively, which indicates that physical ageing also occurs in polymers with stiff chains. These values, compared with those already known for most thermoplastics (μ ～ 1), suggest that physical ageing is slowed down by the rigidity of the main chain.     

Modification of precipitated calcium carbonate with cellulose esters and use as filler in papermaking

New hybrid materials of precipitated calcium carbonate (PCC) and cellulose esters (cellulose acetate and cellulose acetate butyrate) were prepared aiming to obtain new modified fillers for papermaking. A novel simple procedure based on the mixing of an aqueous suspension of PCC with an organic solution of the cellulose derivative, followed by the addition of the resultant mixture to hot water, was followed. The hybrids were characterized by several analytical and spectroscopic techniques. The organics content in the hybrids determined based on the carbon elemental analysis or by thermogravimetry, was found to be of ca. 10 wt%. Due to the presence of the organics the average size of the particles increased slightly in comparison to the unmodified PCC. Results of the modified PCCs as fillers in papermaking showed a slight improvement of some paper strength properties, whereas the structural and optical properties were not affected.     

The pyrolysis of cellulose derivatives

The thermal degradation in vacuo of ethyl cellulose and cellulose acetate in the form of very thin films or bulk material between 230° and 320°C has been studied. With the ethyl cellulose films, volatilization (as measured by weight loss) was a first-order process up to about 50% reaction, with an activation energy of 208 kJ/mole. This is about the same as that associated with the initial drop in intrinsic viscosity of the solid during bulk pyrolysis, in which very high molecular weight material, probably crosslinked, was formed at a later stage. The volatile products from ethyl cellulose included H₂O, CO, CO₂, C₂H₄, C₂H₆, C₂H₅OH, CH₃CHO, unsaturated aliphatic compounds, and furan derivatives. Acetic acid and acetyl derivatives of D -glucose were produced from cellulose acetate. It is suggested that the polymers degrade by radical chain mechanisms, and a number of possible elementary steps are proposed.     

Modified cellulose acetate membranes for desalination

Residual hydroxyl groups of commercially available cellulose acetate (39.9% acetyl) have been reacted partially with phenyl isocyanate. The characteristics of these modified polymers have been studied. Membranes have been cast from these polymers to study their potentiality as reverse osmosis membranes. The work has been further extended to investigated the stability of these modified CA under the influence of high temperature and γ irradiation.     

Plasma modification of cellulose derivatives as biomaterials

A film of cellulose acetate was submitted to a cold plasma of tetrafluoromethane or of sulfur hexafluoride. The interactions of these cold plasmas and cellulose acetate lead to a material whose surface has been modified by fluorination. Comparison of CF₄ or SF₆ plasma treatment shows that fluorine atoms provided by each kind of plasma induce degradation and grafting of fluorocarbon radicals on the surface. As a consequence, the surface energy decreases and offers the possibility of a better response of plasma-modified cellulose derivatives used as biomaterials (e.g. hemodialysis membrane).     

Micro- and macroscopic aspects of polymer bonded paper

The bonding of polymers was examined using analogues of commercial adhesive which were selected so that they could be readily detected by surface microanalytical techniques including scanning electron microscopy, X-ray photoelectron spectroscopy and secondary ion mass spectrometry. When reagents were added to the pulp prior to handsheet preparation, epoxides but not isocyanates, were found to adhere to cellulose and wood fibers by polymerizing with themselves. That is, epoxides polymerized to form gels, which then adhered to the fibers. To test this hypothesis, handsheets were treated subsequently with solutions of pre-formed polymers. In the case of both polyvinylchloride and cellulose acetate, the tensile breaking length and burst index of treated handsheets increased significantly compared with the controls. No surface analytical, or bulk property data was found in this study to demonstrate covalent bonding of adhesives to cellulose or wood fibers. This means that adhesives should be readily extracted from recycled paper with appropriate organic solvents.¹     

Hydrophobic cellulose fibers via ATRP and their performance in the removal of pyrene from water

In the present work, cellulose fibers were modified by grafting with poly(lauryl acrylate) and poly(octadecyl acrylate). The grafted materials were prepared by polymerization of the corresponding monomers via surface initiated atom transfer radical polymerization, starting from cellulose papers previously modified with 2‐bromoisobutyryl groups. The polymerizations were carried out in the presence of ethyl‐2‐bromoisobutyrate, as a sacrificial initiator, added to control the molecular weight of the anchored segments, and polymerization kinetics. The grafting of both polymers was confirmed by infrared spectroscopy and elemental analysis. The effect of grafting these polymers on the thermal stability, morphology, and surface properties of cellulose fibers was studied using thermogravimetric analysis, scanning electron microscopy, and measuring water contact angle, respectively. The results reveal that grafting poly(lauryl acrylate) and poly(octadecyl acrylate) to cellulose confers the filter paper a hydrophobic character, and increases its affinity with pyrene, allowing the removal of this pollutant from water. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44482.     

Synthesis and characterization of the novel cellulose derivative dansyl cellulose

Summary Novel, soluble 5-dimethylamino-1-naphthalenesulfonyl esters of cellulose (2) with a degree of substitution from 0.67 to 1.59 were prepared by esterification of cellulose dissolved in N,N-dimethylacetamide/LiCl solvent system and characterized by means of FTIR-as well as ¹H and ¹³C NMR-spectroscopy. The remaining OH groups of 2 can be fully acetylated in pyridine using N,N-dimethylaminopyridine as a catalyst. The polymers show typical fluorescence and absorption spectra with absorptions at 217, 250 and 317 nm which are in good agreement with quantum chemical calculations.     

Dynamic deposition of polyacids on porous membrane supports

Poly(acrylic acids), poly(styrenesulfonic acid), and their block and random copolymers were tested for their ability to form dynamic membranes on partially cured asymmetric cellulose acetate. Chemically modified porous polypropylene (Celgard) was also used as a support for poly(acrylic acid). Salt rejections, water fluxes, and streaming potentials of membranes were tested under hyperfiltration conditions. Sorption of the polyelectrolytes by the cellulose acetate supports was studied using spectrophotometric, ²²Na tracer, and electron microscopy techniques. The dynamic membrane formation was noted only for poly(acrylic acid) and for its 1:4:1 block copolymer with poly(styrenesulfonic acid). The uneffectiveness of other polyelectrolytes was discussed in terms of a negative zeta potential of cellulose acetate. The increase in salt rejection (R) due to the polyelectrolyte is strongly dependent on the initial R_i of the support. Sharp maxima in the ΔR -versus-R_i curves have been noted for R_i in the range of 40–55%. The most significant improvement in the hyperfiltration characteristics of cellulose acetate was attained with the 1:4:1 block copolymer. Flux of 17 gfd at 350 psi and R = 93% was obtained in short-term tests for a 0.1N feed solution. Long-term tests did not reveal any flux or salt rejection decline for membranes in which poly(acrylic acid) was complexed with phosphoramidic groups grafted onto Celgard.     

增塑性光固化醋酸丁酸纤维素酯的合成与应用

采用"两步法"合成了醋酸丁酸纤维素(CAB)与丙烯酸羟乙酯/己内酯加合物(PCLA)的接枝共聚物。首先,丙烯酸羟乙酯/己内酯加合物(PCLA)与异佛尔酮二异氰酸酯(IPDI)反应,得到端异氰酸酯预聚物(NCOPCLA),接着用该预聚物与CAB反应得到接枝共聚物(CAB-g-PCLA)。比较了改性前后CAB性能的变化。实验结果表明:引入长链线性基团,提高了醋酸丁酸纤维素的柔韧性;预聚物按取代CAB中的90%羟基投料反应时,接枝共聚物涂膜的综合性能优良。     

Permeation of Gas Mixtures in Cellulose Acetate Membranes Practical Approach to Predict the Permeation Rate Co2/Ch4 Mixture

Abstract

Dry cellulose acetate reverse osmosis membranes of different porosities are prepared by using the solvent exchange method and then shrunk at various temperatures.     

Novel aprotic polar polymers 3. Synthesis and properties of poly(phenyl vinyl sulfoxide)

Summary Poly(phenyl vinyl sulfoxide) 1 was prepared by anionic polymerization and its properties as a polymer homolog of dimethyl sulfoxide (DMSO) were examined. Polysulfoxide 1 was found to have good miscibility with poly(vinyl acetate) as well as poly(2-methyl-2-oxazoline) and poly(N-vinylpyrrolidone) by comparing glass transition temperature(s) (T_gs) of the mixture of these polymers with T_gs of the original polymers by differential scanning calorimetry. Received: 4 March 1998/Accepted: 23 March 1998     

Surface Force-Pore Flow Model in Predicting Separation and Concentration of Polyhydric Alcohols in Aqueous Solutions Using Cellulose Acetate Membranes

Abstract

The reverse osmosis separation and concentration of polyhydric alcohols were experimentally tested by using cellulose acetate membranes of different average pore sizes. An attempt was made to predict membrane performance data, such as the solute separation and the product permeation rate, on the basis of the surface force-pore flow model, and the results were tested by experimental values. The processing capacities of the membranes were also calculated.     

Surface modifications of polymers with fluorine-containing plasmas: Deposition versus replacement reactions

Surfaces of polyethylene; poly(vinyl fluoride), poly(vinylidene fluoride), poly(tetrafluoroethylene), cellulose acetate butyrate, and polyoxymethylene were modified in various cold plasma reactions; feed gases to the plasma reactor were trifluoromethane, hexafluoroethane, and tetrafluoromethane. Using X-ray photoelectron spectroscopy (ESCA) to characterize the surfaces, it was established that the plasma reactions lead to fluorinated surfaces containing ? CF₃, ? CF₂, and ? CF groups, All of these fluorinated surfaces exhibit advancing contact angles (with water) larger than 900. However, differences in the ESCA spectra, weight-gain/-loss measurements and scanning-electron-microscopy (SEM) photographs reveal that the mechanisms of fluorination in the various plasma environments are markedly different. The CF₃H gas polymerizes in the gas phase of the plasma and deposits a smooth, fluorinated film on polymers and other substrates. The C₂F₆ plasma simultaneously etches polymers and polymerizes onto polymer surfaces. The CF₄ plasma etches and reacts with the polymer surface but does not polymerize. For polyoxymethylene, the combined roughening (by etching) and fluorination of the surfaces lead to completely non-wettable surfaces (water contact angle approximately 180°). The highly non-wettable surfaces of these two polymers are believed to result from the physical etching and roughening at a very fine scale (approximately five micrometers) while the outermost surfaces are reacting to become highly fluorinated.     

Separation of Lindane from Its Aqueous Solutions by Reverse Osmosis System

Abstract

The separation characteristics of cellulose acetate/reverse osmosis (RO) membranes toward trace levels of lindane in water were investigated. A large fraction of this pesticide readily traversed the membrane; another portion, although tenaciously sorbed in or on the membrane, was slowly released into the product water. The implications of these observations on RO systems for municipal, domestic, and hospital use are discussed.