Preparation and characterization of cellulose acetate/polysiloxane composites

Composites of cellulose acetate and polysiloxane were prepared using 3-isocyanatepropyltriethoxysilane, as a coupling agent. The structure, the thermal and dynamic-mechanical behaviors, and the morphology of the obtained composites were investigated. The composites showed phase separation which was confirmed by the presence of siloxane micro- and nano-domains dispersed in the cellulose acetate matrix, with good interfacial adhesion between the phases. The results demonstrated that the incorporation of a polysiloxane phase on a cellulose acetate matrix caused a decrease in the glass transition temperature, storage modulus and hardness. The proposed methodology was seen to be convenient for the preparation of cellulose acetate/polysiloxane composites with useful properties.     

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.     

Synthesis and characterization of carboxylate waterborne cellulose emulsion based on cellulose acetate

With cellulose acetate (CA) as a base material, a novel environmentally friendly carboxylate waterborne cellulose acetate (CWCA) emulsion was synthesized via the method of self-emulsification. Taking advantage of acrylic acid, hydroxyethyl acrylate as a modifier, and isophorone diisocyanate as a bridging agent, the molecular structural design of CWCA dispersion was completed successfully, and the structure was confirmed by Fourier transform infrared spectroscopy (FTIR). In this work, the particle size and distribution of the stable CWCA dispersion with solid content of 22.6% are 115.6 and 0.158 nm, respectively. It was found that the microstructure of emulsion particles is a core-shell structure containing a hydrophilic carboxylate group as the shell and hydrophobic cellulose acetate molecular as the core. In addition, the hydrophobic behavior of CWCA film is presented as a contact angle of 109.9°. Furthermore, CWCA film provided a higher thermal decomposition temperature of 345.42 °C than that of CA film at the largest mass loss rate.     

Dioxouranium (VI) complexes with cellulose acetate

Dioxouranium [UO₂(VI)] complexes with three degrees of substitution of cellulose acetate, prepared from viscose pulp (DS = 2.2, 2.45 and 2.86), have been synthesis and characterized. Degree of substitution (DS) is defined as the average number of CH groups substituted on each anhydrocellulose repeat unit. Probable structures of the cellulose acetate complexes were inferred from the elemental analysis data, conductance measurements, IR, electronic and ¹H NMR spectra. The results obtained show that the formula of UO₂(VI) complex with cellulose acetate of DS = 2.2 and 2.45 [(CA)₄.UO₂] is more probable than [(CA)₂.UO₂].2(CH₃COO), while the reverse is true for the case of a UO₂ complex with CA of DS = 2.86. For the former formula, cellulose acetate acts as a uni-negatively charged bidentate ligand and reacts with UO₂²⁺ through the ether-carbon-oxygen of the secondary acetylated hydroxyl group of the anhydroglucose unit and the oxygen atom of the residual secondary unacetylated hydroxyl group, forming a five-membered chelate ring. For the later formula, cellulose acetate of DS = 2.86 acts as a neutral bidentate chelating agent through the two ether oxygen atoms of the vicinal ester groups of secondary acetylated hydroxyl groups in anhydroglucose units also forming a five-membered chelate ring. The uranium atom in these complexes is 8-coordinate. The thermal behaviour of cellulose diacetate (DS = 2.2) and cellulose triacetate (DS = 2.86) and their complexes with uranyl acetate in nitrogen atmosphere has been also studied by differential thermal analysis from room temperature to 600 °C. The obtained DTA curves were analyzed using the Prout-Tompkins law. The method of least squares was applied to estimate the appropriate order of the reaction (n), and consequently the thermodynamic parameters. The results revealed that chelation of cellulose acetate with uranyl acetate led to increased thermal stability.     

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.     

Preparation and characterization of cellulose microspheres

The aim of this work was to synthesize and characterize cellulose microspheres with a particle size below 5 μm and narrow size distribution. After activation and functionalization with antibodies, these particles shall be applied as adsorbents in suspension-based extracorporeal blood purification systems, such as the Microspheres-Based Detoxification System. In the frame of this work such microspheres were developed and synthesized with reproducible properties. Besides using well-established methods for characterization of this kind of bead cellulose, additional procedures for the examination of its properties were developed and applied.     

Sorption and permeation behaviour of metal thiocyanate complexes on cellulose acetate polymers

Various metal thiocyanate complexes in aqueous solution were sorbed on solid cellulose acetate polymers. The sorption selectivity increased in the order Zn(2+) > Fe(3+) > Cu(2+) > Co(2+) > Ni(2+). The sorption behaviour followed a Langmuir-type adsorption isotherm, and the maximum adsorption capacity was 6.1 x 10(-5) mole of complex per g of polymer under optimum conditions. The zinc species sorbed appear to be NH(4)Zn(H(2)O)(SCN)(3) or (NH(4))(2)Zn(SCN)(4) according to analysis of the sorption equilibrium. The ion-association species formed by the complex zinc anion and the ammonium ion was supposed to be sorbed (or "extracted") onto the polymer matrix. As an application of sorption of metal complexes, a new hyperfiltration process was proposed for selective separation of metal ions. Thus, a mixture of metal thiocyanate complexes was hyperfiltered through cellulose acetate membranes. Permeation of certain metal complexes was preferred, and the selectivity was found to be similar to the sorption selectivity. These findings lead to a generalized idea that hyperfiltration separation of ionic species, particularly anionic metal complexes, can be attained by using polymer membranes which selectively adsorb or extract such ionic species as ion-association complexes onto the polymer matrix.     

聚醋酸乙烯类梳型分散剂的制备与表征

颜料在工业生产和人们的日常生活中起着重要的作用.由于颜料颗粒具有较大的比表面积和较高的比表面能,是热力学不稳定体系,当分散在介质中时容易发生团聚,影响其特性的发挥[1],因此需加入分散剂使其在分散介质中稳定分散.     

Development and characterization of electrospun cellulose acetate nanofibers modified by cationic surfactant

Polymeric electrospun nanofibers have been gaining notoriety in the same way as their industrial applications, since the manufacturing of this type of material is simple and low-costed. In order to obtain fibrous polymeric material with small diameters and with reduced beads formation, a 2⁴ factorial experiment with triplicate at center point was performed. Cellulose acetate (CA) and cationic cetylpyridinium bromide (CPB) surfactant nanofibers were made using a homemade electrospinning apparatus. The assessed inputs were as follows: CA%, CPB%, flow rate, and applied voltage. From the analysis of the response surface methodology and scanning electron microscope (SEM), the optimal concentrations of CA and CPB for producing nanofibers were 21 w/v-% and 0.5 w/v-%, respectively, using a flow rate of 0.7 mL h⁻¹ and applied voltage of 18 kV. Fibers mats morphology shows average diameter of 0.2 μm and 7 nm pore size, as well as it was found that the single fiber unit presented nanoheterogeneity. Mechanical resistance of 2.70 MPa was obtained in the tensile strength test. The modification of CA by the addition of surfactant attributed better thermal and mechanical resistances to the nanofibers without, however, affecting their biodegradability and water resistance properties. The morphological characteristics of the newly obtained CA/CPB nanofibers combined with mechanical resistance provided subsidies to suggest that the as-obtained material presents potential to be applied as an air filter.     

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.     

Controlled grafting of MMA onto cellulose and cellulose acetate

Homogeneous graft copolymerization of methyl methacrylate onto cellulose and cellulose acetate was carried out in various solvents and solvent systems taking ceric ammonium nitrate, tin (II) 2-ethyl hexanoate [Sn(Oct)₂] and benzoyl peroxide as initiators. The effect of solvents, initiators, initiator and monomer concentration, on graft yield, grafting efficiency and total conversion of monomer to polymer were studied. Formation of Ce³⁺ ion during grafting in presence of CAN enhances the grafting efficiency. Methylene blue was used as a homopolymer inhibitor and controlled the molecular weight of the grafted polymer and its effect on grafting was also studied. In presence of MB, amount of PMMA homopolymer formation reduced and consequently grafting efficiency increased. The number average molecular weights and polydispersity indices of the grafted PMMA were found out by gel permeation chromatography. The products were characterized by FTIR and ¹H-NMR analyses and possible reaction mechanisms were deduced. Finally, thermal degradation of the grafted products was also studied by thermo-gravimetric and differential thermo-gravimetric analyses.     

Synthesis and characterization of photosensitive cinnamate-modified cellulose acetate butyrate spin-coated or network derivatives

The photochemical behavior of photosensitive materials obtained by spin-coating or network synthesis of a cellulosic polymer bearing photo-cross-linkable cinnamate groups was investigated. First, cinnamate groups were grafted on a cellulose acetate butyrate polymer, with different grafting densities. The photochemical properties of the polymers were studied in solution by UV–visible and ¹H NMR spectroscopy. Then spin-coated films and networks were prepared and characterized as a function of the number of cinnamate groups per cellulosic unit. The water-wetting properties of both surfaces were studied by dynamic contact angle measurements, before and after photoirradiation, and subsequent heating. The surfaces obtained by the two methods have significantly different behaviors that can be assigned to the distinct photochemical pathways of the cinnamate groups upon irradiation depending on the sample preparation. Indeed, dimerization reaction is evidenced as the main process in the spin-coated films while the expected isomerization is predominant at the surface of the polymer networks.     

Preparation and characterization of new cycloplatinated carbene complexes

Reaction of iodotrimethylplatinum(IV) tetramer with bis(1,3-diphenyl-2-imidazolidinylidene) [(Hdpim)₂] gave a new dinuclear carbene complex, [{Pt(dpim)I}₂](dpim  1,3-diphenyl-2-imidazolidinylidenato-2-C,2′-C), III, in 84% yield, which contains a cycloplatinated carbene structure. Some mononuclear derivatives, [Pt(dpim)(acac)], [Pt(dpim)I{P(OCHMe₂)₃}], [Pt(dpim)-(NCCH₃)₂]ClO₄, and [Pt(dpim)(COD)]ClO₄ were prepared from III and characterized by means of elemental analysis, IR and NMR spectroscopy, and molar conductivity. An intermediate species, [{PtMeI(Hdpim)}₂], leading to III is discussed also.     

Preparation and characterization of the bacterial cellulose/polyurethane nanocomposites

New nanocomposites based on bacterial cellulose nanofibers (BCN) and polyurethane (PU) prepolymer were prepared and characterized by SEM, FT-IR, XRD, and TG/DTG analyses. An improvement of the interface reaction between the BCN and the PU prepolymer was obtained by a solvent exchange process. FT-IR results showed the main urethane band at 2,270 cm^?1 to PU prepolymer; however, in nanocomposites new bands appear as disubstituted urea at 1,650 and 1,550 cm^?1. In addition, the observed decrease in the intensity of the hydroxyl band (3,500 cm^?1) suggests an interaction between BCN hydroxyls and NCO-free groups. The nanocomposites presented a non-crystalline character, significant thermal stability (up to 230 °C) and low water absorption when compared to pristine BCN.     

Preparation and characterization of water-redispersible nanofibrillated cellulose in powder form

Water-redispersible, nanofibrillated cellulose (NFC) in powder form was prepared from refined, bleached beech pulp (RBP) by carboxymethylation (c) and mechanical disintegration (m). Two routes were examined by altering the sequence of the chemical and mechanical treatment, leading to four different products: RBP-m and RBP-mc (route 1), and RBP-c and RBP-cm (route 2). The occurrence of the carboxymethylation reaction was confirmed by FT-IR spectrometry and ¹³C solid state NMR (¹³C CP-MAS) spectroscopy with the appearance of characteristic signals for the carboxylate group at 1,595 cm⁻¹ and 180 ppm, respectively. The chemical modification reduced the crystallinity of the products, especially for those of route 2, as shown by XRD experiments. Also, TGA showed a decrease in the thermal stability of the carboxymethylated products. However, sedimentation tests revealed that carboxymethylation was critical to obtain water-redispersible powders: the products of route 2 were easier to redisperse in water and their aqueous suspensions were more stable and transparent than those from route 1. SEM images of freeze-dried suspensions from redispersed RBP powders confirmed that carboxymethylation prevented irreversible agglomeration of cellulose fibrils during drying. These results suggest that carboxymethylated and mechanically disintegrated RBP in dry form is a very attractive alternative to conventional NFC aqueous suspensions as starting material for derivatization and compounding with (bio)polymers.     

纤维素醋酸酯的均相合成

纤维素的非均相反应取代不均匀、产率低。本文用纤维素在LiCl／DMAc溶液中的均相反应。制得了纤维素三醋酸酯(CTA)、纤维素二醋酸酯(CDA)、纤维素—醋酸酯(CMA),并对产品结构性能进行了表征。     

Photodegradation of cellulose acetate fibers

The photodegradation of cellulose acetate fibers by ultraviolet light in vacuo at 77°K and at ambient temperature was studied. Three kinds of light sources with different wavelengths between 2353 and 6000 Å were employed. ESR studies at 77°K show that several kinds of free radicals are produced from cellulose diacetate (CDA) and cellulose triacetate (CTA) fibers when irradiated with light of wavelength shorter than 2800 Å. Among these methyl radicals formed decayed within 210 min at 77°K. When the temperature was raised above 77°K, radical transformation occurred at 87°K and most of the free radicals decayed at 193°K, whereas the cellulosic radicals were stable at this and even at higher temperatures. Ultraviolet spectroscopy studies revealed that the main chromophores are the carbonyl function of the acetyl group and acetal groups in the polymer. The photodegradation of the polymers at ambient temperature resulted in the formation of gaseous products (mainly CO, CO₂, and CH₄), together with the loss of bound acetic acid content and sample weight. Decreases in viscosity and reduction of tensile strength and elongation were also observed in the irradiated samples, revealing that the overt effects of ultraviolet light on cellulose acetate fibers are interpreted in terms of free-radical reactions ultimately leading to main-chain and side-group scissions, unsaturation, and the formation of small molecule fragments. Among these, main-chain scission took place predominantly in CDA fiber and side-group scission in CTA fiber. The mechanism of the fundamental photochemical degradation processes of cellulose acetate fibers is elucidated.     

Preparation and characterization of cellulose nanocomposite films with two different organo-micas

The mechanical properties, morphologies, and gas barriers of hybrid films of cellulose with two different organoclays are compared. Dodecyltriphenyl-phosphonium-mica (C₁₂PPh-mica) and hexadecyl-mica (C₁₆-mica) were used as reinforcing fillers in the fabrication of the cellulose hybrid films. The cellulose hybrid films were synthesized from N-methyl-morpholine-N-oxide (NMMO) solutions with the two organo-micas, and solvent-cast at room temperature under vacuum, yielding 15–20 μm thick films of cellulose hybrids with various clay contents. We found that the addition of only a small amount of organoclay is sufficient to improve the mechanical properties and gas barriers of the cellulose hybrid films. Even polymers with low organoclay contents (1–7 wt %) were found to exhibit much higher strength and modulus values than pure cellulose. The addition of C₁₂PPh-mica was more effective than that of C₁₆-mica with regards to the initial tensile modulus, whereas the addition of C₁₆-mica was more effective than that of C₁₂PPh-mica with regards to the gas barrier of the cellulose matrix. The intercalations of the polymer chains in the clays were examined with wide-angle X-ray diffraction (XRD) and electron microscopy (SEM and TEM).