Preparation and characterization of cellulose acetate complexes

Summary Metal chelates of secondary cellulose acetate (SCA) with chromium(III), copper(II), cobalt(II), nickel(II) and UO ₂ ²⁺ were prepared and characterized by elemental analyses, magnetic moments and spectral studies. SCA acts as a uninegatively charged bidentate ligand and reacts with the metal ion via the oxygen atom of the secondary unacetylated hydroxyl group in the glucose subunit of the polymer, plus the oxygen atom of the vicinal ester group, to form a five-membered chelate ring.     

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.     

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 of modified sodium acetate trihydrate and the thermodynamic analysis

This paper had carried out the optimization screening experiment for the nucleating agent and thickening agent of sodium acetate trihydrate (SAT) targeting its problems of supercooling and phase separation. Our results verified that the addition of 2 mass% disodium hydrogen phosphate dodecahydrate in SAT could effectively suppress the SAT supercooling and control the degree of supercooling within 2 K. Besides, the addition of 1–1.5 mass% xanthan gum in SAT could effectively suppress its phase separation during melting/freezing cycle and could evenly disperse the nucleating agent in SAT. Moreover, comparative test analysis on the modified SAT suggested that the thickening agent in the additive had great influence on the SAT physical property parameters. Additionally, to improve the comprehensive utilization quality of the modified SAT, the modified SAT thermodynamic analysis was performed, which discovered that the initial charging temperature had little influence on the exergy efficiency of the modified SAT, while the final charging temperature had great influence on the exergy efficiency. Typically, the optimal final charging temperature of the modified SAT was 72 °C.

     

Preparation and characterization of plutonium/IV/ phenyl acetate and plutonium/IV/ α-naphthyl acetate

Plutonium/IV/ compounds obtained in the reactions with phenylacetic acid and -naphthyl acetic acid in the pH range of 3.5–5.0 have been isolated and studied. Carbon, hydrogen and plutonium analyses have shown that plutonium/IV/ phenyl acetate and plutonium/IV/ -naphthyl acetate have the composition Pu/OH/₃/C₁₀H₇CH₂COO/, respectively. Infra-red and ultra-violet absorption spectral studies and thermogravimetric analysis have corroborated these chemical formulas.     

Preparation and biodegradation of sugar-containing poly(vinyl acetate) emulsions

To accelerate the biodegradability of poly(vinyl acetate)-based emulsions, emulsion copolymerizations of vinyl sugars, including triacetylated N-acetyl-D-glucosamine (GlcNAc)-substituted 2-hydroxyethyl methacrylate (GlcNAc(Ac)3-substituted HEMA), glucose-substituted HEMA (GEMA) and 6-O-vinyladipoyl-D-glucose (6-O-VAG) with vinyl acetate (VAc), were carried out using poly(vinyl alcohol) as an emulsifying agent in the presence of poly[(butylene succinate)-co-(butylene adipate)] [poly(BS-co-BA)]. Copolymerization with GEMA produced a stable emulsion and that with 6-O-VAG also produced a homogeneous emulsion. Their biodegradation tests indicated that PVAc main chain scission was accelerated by copolymerization with vinyl sugars.     

Preparation of block copolymers from occluded vinyl acetate macroradicals

Stable vinyl acetate macroradicals were produced by polymerization in a nonviscous poor solvent, a viscous good solvent and a viscous poor solvent. These macroradicals were then allowed to react with a second vinyl monomer to produce block copolymers. The formation of block copolymers was monitored for rate and yield data. The block copolymers produced were poly(vinyl acetate-b-methyl methacrylate), poly(vinyl acetate-b-acrylic acid), poly(vinyl acetate-b-vinylpyrrolidone), poly(vinyl acetate-b-acrylonitrile), poly(vinyl acetate-b-styrene), and poly(vinyl acetate-b-methyl acrylate). The block copolymers were characterized by yield, precipitation in selected solvents, pyrolysis gas chromatography, and differential scanning calorimetry.     

Preparation and characterization of aluminum phthalocyanine acetate, propionate, and benzoate

Aluminum phthalocyanine acetate, propionate and benzoate were prepared by the reaction of hydroxy aluminum phthalocyanine and the corresponding acetic, propionic, and benzoic anhydrides. The reaction products were characterized by ¹H and ¹³C NMR spectroscopy and mass spectrometry. The thermal behavior of the products was determined by thermal analysis of particular samples.     

Preparation of cyclic boramides from salicylaldehydes,ammonium acetate and sodium borohydride

Borohydride reduction of salicylaldehyde imines yields surprisingly a cyclic boramide. This is a fairly stable compound, and X-ray analysis shows it has a tetrahedral boron atom. Mechanistic studies show a reaction pathway through an oxazaborinane intermediate. The reaction also works with halogen substituted salicylaldehydes and for the preparation of non-symmetrical boramides.     

Preparation,catalytical activity and crystal structure of a heptanuclear zinc acetate cluster

Reaction of [Zn₄(µ₄-O)(O₂CCH₃)₆] with one equivalent of 4-tertiary-butylpyridine leads to a nearly quantitative formation of the heptanuclear cluster [Zn₇O₂(O₂CCH₃)₁₀(^tbupy)₂] (1). Here, we present the crystal structure of 1 and first results of the examination of its catalytic activity in transesterification reactions and polymerization of lactide compared to the activity of [Zn₄(µ₄-O)(O₂CCH₃)₆] in the presence of 4-tertiary-butylpyridine.     

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.     

ZnMn2O4纳米催化剂制备及催化合成乙酸正丁酯

本文以共沉淀法制备了四方晶系锌锰复合氧化物ZnMn2O4纳米催化剂。采用X射线粉末衍射(XRD)和透射电子显微镜(TEM)测试技术对样品进行了分析表征,结果表明所合成的催化剂为粒径均匀的纳米粒子,平均粒径在20-50 nm,具有较好的分散性。实验考察了所制备的ZnMn2O4纳米催化剂对乙酸和正丁醇酯化反应的催化活性,表明ZnMn2O4对乙酸正丁酯的合成有较高的催化活性;探讨了催化剂焙烧温度、催化剂用量、酸醇摩尔比以及反应时间对酯化率的影响,确定了适宜的酯化反应条件,以焙烧温度为300 ℃制备的ZnMn2O4为催化剂,在催化剂用量为0.3%(以反应物总质量计)、酸醇摩尔比n(酸):n(醇)=1.8:1、反应时间为4 h、酯化反应温度120 ℃的条件下,酯化率可达92.53%。     

Preparation of hydrogenated nitrile rubber using palladium acetate catalyst: Its characterization and kinetics

Hydrogenated nitrile rubber was prepared by using palladium acetate as the homogeneous catalyst system. The effect of different reaction parameters on the level of hydrogenation was studied. The extent of hydrogenation increased with increase in reaction time, temperature, pressure, and catalyst concentration. A maximum conversion of 96% could be achieved. The degree of hydrogenation was estimated from IR and NMR spectroscopy. The selectivity of the catalyst in reducing ? C?C? in presence of ? C?N was supported by IR and ¹³C-NMR spectra. ESCA studies further confirmed this observation. Properties of hydrogenated nitrile rubber were investigated by various techniques such as gel permeation chromatography (GPC), glass transition temperature (T_g), stress-strain behavior and rheological measurements. GPC studies showed no significant change in molecular weights of the products after the reaction. T_g value decreased with an increase in the level of hydrogenation. The ultimate stress improved significantly with the increase in the extent of hydrogenation. The die swell decreased with hydrogenation at a particular shear rate. The kinetics of the NBR hydrogenation were investigated. With the increase of the hydrogen pressure and catalyst concentration, the rate of the reaction increased. The reaction was apparently first order with respect to olefinic substrate at higher hydrogen pressure. The apparent activation energy, enthalpy, and entropy of the reaction were calculated as 29.9 kJ/mol, 27.42 kJ/mol, and –0.20 kJ mol^?1 K^?1, respectively.     

Cellulose acetate and polyethersulfone blend ultrafiltration membranes. Part I: Preparation and characterizations

The overall objective of this investigation is to achieve high‐performance membranes with respect to flux and rejection characteristics, with an interplay of blending polymers having desired qualities. Thus, cellulose diacetate and polyethersulfone as candidate materials, in the presence of polyethylene glycol 600 as a pore forming agent, were blended in 100/0, 95/5, 90/10, 85/15, 80,20 and 75/25% compositions using N,N′‐dimethylformamide as solvent and membranes were prepared by the phase inversion technique. Polymer blend composition, additive concentration, and casting and gelation conditions were standardized for the preparation of asymmetric membranes with various pore statistics and morphology. These blend membranes were characterized for compaction in ultrafiltration experiments at 414 kPa pressure in order to attain steady state flux and is reached within 4–5 hr. The pure water flux was measured at 345 kPa pressure and is determined largely by the composition of polyethersulfone and additive concentration. The flux was found to reach the highest values of 66.5 and 275 1/(cm² hr) at 0 and 10 wt% additive concentrations respectively, at 25% SPS content of the blend. Membrane hydraulic resistance derived by measuring water flux at various transmembrane pressure and by using an algorithm was found to be inversely proportional to pure water flux. Water content is estimated by simple drying and weighing procedures and found proportional to pure water flux for all the membranes. The molecular weight cut‐offs (MWCOs) of different membranes were determined with proteins of different molecular weights and found to vary from 20–69 kDa (globular proteins) depending on the PEG and SPS content in the casting dope. Skin surface porosity of the membranes were analyzed by scanning the frozen membrane samples using scanning electron microscopy (SEM) at different magnifications. The surface porosity is in direct correlation to the MWCO derived from solute retention experiments. Copyright © 2004 John Wiley & Sons, Ltd.     

原位聚合法制备聚醋酸乙烯酯/纳米SiO2复合乳液

采用原位乳液聚合法制备了聚醋酸乙烯酯／纳米二氧化硅复合浮液。用红外光谱、原子力显微镜以及透射电镜等现代测试手段对复合材料进行了表征．考察了纳米二氧化硅在聚醋酸乙烯酯乳液中的分散状况及纳米二氧化硅用量对复合浮液性能的影响。结果表明：随纳米二氧化硅用量增加,复合乳液的干态,湿态粘接强度均而明显提高;乳液的粘度减小;复合乳液的胶膜耐热性提高。     

Preparation of DNA-loaded polysulfone microspheres by liquid-liquid phase separation and its functional utilization

DNA-loaded polysulfone (PSf) microspheres were fabricated by means of a liquid-liquid phase separation technique. The porous microspheres were then used to remove DNA-binding intercalating materials--ethidium bromide, acridine orange, and endocrine disruptors. The DNA-loaded PSf microspheres are stable in water. The stability of the DNA-loaded microspheres and/or the release rate of DNA from the microspheres can be controlled by manipulating the microsphere structure. Increasing the polymer concentration, which causes lower porosity and smaller pores on the outer surface of the microspheres, led to increased stability of the microspheres and decreased release rate of DNA. Additionally, the drying temperature also affected the stability of the microspheres. The DNA-loaded PSf microspheres could effectively accumulate harmful DNA-intercalating pollutants and endocrine disruptors, such as ethidium bromide, acridine orange, biphenyl, dibenzofuran, and dibenzo-p-dioxin. The amount of pollutants removed by the microspheres is dependent on the amount of incorporated DNA and on the microsphere structure. The DNA-loaded microspheres have the potential to be used in environmental applications.     

Preparation of Stable Miniemulsions of Poly(2-ethyl hexyl acrylate-co-vinyl acetate)

Summary: This paper presents the results of the preparation of miniemulsions as well as the subsequent copolymerizations of 2-ethyl hexyl acrylate and vinyl acetate. The miniemulsions were prepared using a mixture of an anionic and a non-ionic surfactant. Sodium dodecyl sulfate (SDS) was used as the anionic surfactant and two non-ionic surfactants were studied: Triton X-405 and Disponil A3065. The miniemulsions prepared with a 90/10 mol.-% Disponil A3065 were able to reach a kinetically-stable state to yield latexes with 43 wt.-% solids content with a maximum change in the number of particles (N_p) with respect to the number of droplets (N_d) of ∼6%. A 2³ factorial design was then used to discern the influence of monomer, chain transfer agent and surfactant concentration on the droplet size distribution (DSD) and particle size distribution (PSD). Pressure-sensitive adhesive (PSA) properties were also examined.     

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 of high catalyst utilization electrodes for polymer electrolyte fuel cells

We have developed a novel preparation procedure for an electrocatalyst layer with high utilization of catalyst for polymer electrolyte fuel cells. A commercial Pt catalyst supported on high surface area carbon black (Pt/CB) and Nafion ionomer solution was heated in an autoclave at 200 degrees C, followed by quenching to form the ink of the mixture. It was found that the cathode prepared with the new catalyst ink exhibited very high performance, i.e., high catalyst utilization and improved gas diffusivity. The microstructure analysis indicated that the autoclave treatment promoted an effective introduction of Nafion ionomer into primary pores of Pt/CB agglomerates, in which ca. 90% of Pt catalysts were supported. It was clearly observed by scanning transmission electron microscopy that Nafion ionomer was distributed more uniformly inside Pt/CB agglomerates, compared with those simply mixed with a ball mill in a conventional manner.