Showing papers by "Donghua University published in 2002"

Direct synthesis with melt polycondensation and microstructure analysis of poly(L-lactic acid-co-glycolic acid)

Abstract: High-molecular-weight poly(L-lactic acid-co-glycolic acid) (PLGA) was prepared through melt polymerization from glycolic acid (GA) and L-lactic acid (L-LA) and then characterized. High resolution 1H and 13C NMR were performed for microstructure analysis of polymer. The solubility in chloroform, compositions, and sequence lengths of PLGA suggest higher reactivity of GA compared with L-LA and shortening GA blocks with reaction time. The racemization of L-LA blocks and transesterification in PLGA are enhanced by increase of GA fractions. PLGA (90/10) samples show crystallization of relatively long L-LA sequences in copolymer chains and the absence of the crystallization of GA blocks. All these results demonstrate the influence of racemization and transesterification on the microstructure of PLGA.

A New Cellulose Based Carbon Fiber from a Lyocell Precursor

Abstract: The structure and properties of lyocell and viscose rayon fibers are compared in this paper. SAXS results show that the rayon precursor has a higher ratio of larger microvoids, WAXD curves show that both fibers have a monoclinic crystalline structure, but lyocell fibers have higher crystallinity and a larger crystal size. The morphology of lyocell and rayon, observed by scanning electron microscopy (SEM), is the same with an average diameter of 10.6 μm, but different distributions. A Gaussian statistical analysis indicates that the single-strand strength of lyocell fibers is twice as high as for rayon precursors, which have a wider strength distribution. Similar TGA curves show the same pyrolysis mechanism, and based on this, lyocell fibers are proposed as high performance carbon fiber precursors. Lyocell fibers are successfully carbonized under conditions identical to those for manufacturing rayon-based carbon fibers. The two kinds of carbon fibers are compared by SEM and a Weibull statistical analysis.

Measuring and Modeling 3D Wrinkles in Fabrics

Abstract: In this paper, we propose a new method for measuring fabric wrinkling based on integrating photometric stereo and image analysis techniques. In the traditional method. wrinkled fabrics are evaluated subjectively according to the grades of replica plates supplied by the American Association of Textile Chemists and Colorists (AATCC). But due to the disadvantages of subjective methods. which are tedious, time-consuming, subjective, and so on. image analysis techniques are used in this work as an objective method. However, serious problem occur when colored and patterned fabrics are tested with conventional images and processing techniques, although they work for tests of solid fabrics. In this paper, a photometric stereo method is used to extract three-dimensional surfaces of fabrics and successfully eliminate the influence of color and pattern. Image analysis techniques are furthered to extract wrinkling features of these reconstructed 3D images, and there is a good linear correlation between objective para...

Synthesis of Boc-protected cis- and trans-4-trifluoromethyl-D-prolines

Abstract: Both Boc-protected trans- and cis-4-trifluoromethyl prolines were synthesized starting from L-serine simultaneously. In our synthetic route, the key intermediate 4 was obtained through the reaction of Garner's aldehyde 1 with ylide 2 followed by trifluoromethylation with FSO2CF2COOMe–CuI. After hydrogenation followed by reduction of 4, the alcohol 5 was obtained in low diastereoselectivity, however, the two diastereoisomers could be separated easily by flash chromatography in the following steps. The bromide 8b obtained from the alcohol 5 in a straightforward fashion could not afford the desired cyclization product because of the strong electron-withdrawing properties of the trifluoromethyl group and the low ability of bromide as a leaving group. Instead, mesylation of alcohols 12a and 12b followed by treatment with potassium bis(trimethylsilyl)amide (KHMDS) afforded the desired cyclization products 13a and 13b respectively, which were transformed into Boc-protected cis- and trans-4-trifluoromethyl-D-prolines in a straightforward fashion.

Wash-and-Wear Finishing of Silk Fabrics with a Water-Soluble Polyurethane

Abstract: A water-soluble bifunctional polyurethane WPU200 is prepared and used for wash-and- wear finishing of silk fabrics. The wet resiliency of the finished silks greatly improves, and dry resiliency drops a little. Anionic and nonionic softeners, which can improve the dry crease recovery angle and handle of finished silk fabrics, can be used in a single bath with WPU200. Factors that have a great influence on the resiliency of the finished fabrics include WPU200 concentration, curing temperature and time, and pH of the finishing bath. All these factors have been optimized. Changes in the physical properties of the finished silk fabrics are reported, such as breaking strength, elongation, moisture regain, whiteness, and stiffness. Finished silk fabrics have good laundry durability after twenty washing cycles.

A comprehensive model for solid-state polycondensation of poly(ethylene terephthalate): Combining kinetics with crystallization and diffusion of acetaldehyde

Abstract: A comprehensive mathematical model was established by considering the main and side reactions for solid-state polycondensation of poly(ethylene terephthalate). The effect of temperature on chain mobility was used to estimate the rate constants of chemical reactions. The polymer crystalline fraction was modeled as containing only repeat units, thus concentrating end groups and condensates in the amorphous fraction. The diffusion coefficient of acetaldehyde was calculated by the model. The simulation results of this comprehensive model were validated by experimental data reported in literature. The model predictions were important clues for further experimental study on poly(ethylene terephthalate) solid-state polycondensation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3133–3144, 2002; DOI 10.1002/app.10113

The glass transition, crystallization, and melting characteristics of a class of polyester ionomers

Abstract: The glass transition temperature (Tg), crystallization, and melting character of a class of random polyester ionomers (polymer containing < 10 mol % ionic groups) were investigated. The nonlinear change of the Tg and crystallization and melting behavior were characterized using differential scanning colorimetry (DSC). The ionomers are derived from polyethylene terephathalate (PET) modified through copolycondensation with a fully neutralized sulfonate moiety (sodiosulfo) isophthalate (Na-SIP). Significant and systematic changes in the glass transition temperature and thermal characteristics upon addition of Na-SIP on the PET backbone were observed, indicating strong association and interaction on the ionic species. At Na-SIP levels ≥ 4 mol %, the turn of the the glass transition temperature was found, and the same results were obtained for the samples treated either by quenching or dissolution, suggesting the presence of reversible crosslink and aggregation of the ionic species within the organic matrix. When crystallized from the healing or cooling the samples during the DSC nonisothermal crystallization run at a 10°C/min, the enthalpy of the cold crystallization and melting showed an obvious decrease with the increase of Na-SIP content, and changes of the crystal temperature had an analogy to those of the Tg. A tune of the crystal temperature was found at Na-SIP levels ≥ 3 mol % (see Figs. 4, 5, and 7). The experimental data were discussed in the context of the restricted mobility model of the aggregation in the ionomers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3660–3666, 2002

Morphology and thermal properties of conductive polyaniline/polyamide composite films

Abstract: Polyaniline (PANI) in an emeraldine-base form, synthesized by chemical oxidation polymerization, was doped with camphor sulfonic acid (CSA). The conducting complex (PANI-CSA) and a matrix, polyamide-66, polyamide-11, or polyamide-1010, were dissolved in a mixed solvent, and the blend solution was dropped onto glass and dried for the preparation of PANI/polyamide composite films. The conductivity of the films ranged from 10(-7) to 10(0) S/cm when the weight fraction of PANI-CSA in the matrices changed from 0.01 to 0.09, and the percolation threshold was about 2 wt %. The morphology of the composite films before and after etching was studied with scanning electron microscopy, and the thermal properties of the composite films were monitored with differential scanning calorimetry. The results indicated that the morphology of the blend systems was in a globular form. The addition of PANI-CSA to the films resulted in a decrease in the melting temperature of the composite films and also affected the crystallinity of the blend systems.

Effect of Mercerization on the Crosslinking of Ramie Fabric Using 1,2,3,4- Butanetetracarboxylic Acid: Physical Properties and Crosslink Distribution

Abstract: Ramie, tension-mercerized ramie, slack-mercerized ramie, and cotton fabrics are treated with 1,2,3,4-butanetetracarboxylic acid (BTCA) to obtain wrinkle-resistant properties, and their physical properties are compared. Tension mercerization slightly enhances the loss of both tensile and tearing strengths of the crosslinked ramie fabric, while slack-mercerized crosslinked ramie fabric has severe mechanical strength loss mainly due to the destruction of fiber orientation during mercerization. Both the tension- and slack-mercerized crosslinked ramie fabrics show increased moisture and water retention, as well as a very rigid handle. Both tension and slack mercerization minimize surface migration of the crosslinking agent.

Preparation and properties of conductive polyaniline/poly‐ω‐aminoundecanoyle fibers

Abstract: Historically, polyaniline (PANI) had been considered an intractable material, but it can be dissolved in some solvents. Therefore, it could be processed into films or fibers. A process of preparing a blend of conductive fibers of PANI/poly-omega-aminoun-decanoyle (PA11) is described in this paper. PANI in the emeraldine base was blended with PA11 in concentrated sulfuric acid (c-H,SO,) to form a spinning dope solution. This solution was used to spin conductive PANI/PA11 fibers by wet-spinning technology. As-spun fibers were obtained by spinning the dopes into coagulation bath water or diluted acid and drawn fibers were obtained by drawing the as-spun fibers in warm drawing bath water. A scanning electron microscope was employed to study the effect of the acid concentration in the coagulation bath on the microstructure of as-spun fibers. The results showed that the coagulating rate of as-spun fibers was reduced and the size of pore shrank with an increase in the acid concentration in the coagulation bath. The weight fraction of PANI in the dope solution also had an influence on the microstructure of as-spun fibers. The microstructure of as-spun fibers had an influence on the drawing process and on the mechanical properties of the drawn fibers. Meanwhile, the electrically conductive property of the drawn fibers with different percentage of PANI was measured.

Oxygen enrichment from air through multilayer thin low-density polyethylene films

Abstract: Several multilayer thin low-density polyethylene (LDPE) films were fabricated by blown thin film having a thickness of 7 μm and an area of 130 cm2. They were characterized for their oxygen-enrichment performance from air by a constant pressure–variable volume method in a round permeate cell with an effective area of 73.9 cm2. The relationship between oxygen-enrichment properties, including oxygen-enriched air (OEA) flux, oxygen concentration, permeability coefficients of OEA, oxygen, nitrogen, as well as separation factor through the multilayer LDPE films, and operating parameters, including transfilm pressure difference, retentate/permeate flux ratio, temperature, as well as layer number, are all discussed in detail. It is found that all of the preceding oxygen-enrichment parameters increase continuously with an increase of transfilm pressure difference from 0.1 to 0.65 MPa, especially for the trilayer and tetralayer LDPE films. The oxygen concentration and separation factor appear to rapidly increase within the retentate/permeate flux ratio below 200, and then become unchangeable beyond that, whereas the OEA flux and the permeability coefficients of OEA, oxygen, and nitrogen seem to remain nearly constant within the whole retentate/permeate flux ratio investigated, especially for the monolayer and bilayer LDPE films. The selectivity becomes inferior, whereas the permeability becomes superior, as the operating temperature increases from 23 to 31°C. The highest oxygen concentration was found to be 44.8% for monolayer LDPE film in a single step with air containing oxygen of 20.9% as a feed gas and operating pressure of 0.5 MPa at a retentate/permeate flux ratio of 340 and 23°C. The results demonstrate a possibility to prepare an oxygen-enriching membrane directly from air, based on the easily obtained thin LDPE films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3013–3021, 2002; DOI 10.1002/app.2331

Reactive blending of poly(ethylene terephthalate)(pet)/ poly(ethylene 2,6-naphthalate)(pen). I: Effect of mixing conditions on chain structure

Abstract: Reactive blending of poly(ethylene terephthalate)/poly(ethylene naphthalene 2,6-dicarboxylate) with addition of 2,2'-bis(1,3-oxazoline) (BOZ) has been studied under various mixing conditions for the different compositions. The transesterification level, the sequence length of both PET and PEN short blocks, and the degree of randomness were estimated using 1 H NMR. The results indicate that both mixing time and temperature are the primary factors controlling the transesterification, while the chain extender BOZ can significantly accelerate the transesterification between PET and PEN at 275°C. The composition also, to some extent, influences the transesterification level as the mixing time is increased. As a consequence of transesterification proceeding, the sequence structures of the reactive blends are also markedly changed, which corresponds to a transfer from an initial block structure to a multiblock structure with higher randomness. The change in the microstructure of the reactive blends has also been analyzed by a Bernoullian statistics model. The effect of the BOZ on the intrinsic viscosity of the reactive blends is discussed.

Classifying Fleece Fabric Appearance by Extended Morphological Fractal Analysis

Abstract: Image analysis techniques have been widely accepted as objective methods for evalu ating fabric appearance. This paper presents the development of a fairly new fractal analysis method (extended morphological fractal analysis) for characterizing polar fleece fabric appearance after abrasion. The digital gray level image is treated as a three- dimensional surface whose fractal dimension is calculated by performing a series of dilations and erosions on this surface and plotting the area of the resulting set of surfaces against the size of the structuring element. In contrast to a single morphological fractal .parameter, which is scale-invariant, extended fractal analysis is able to characterize fabric textures where the roughness of these textures is not necessarily scale-invariant. This approach can be used to physically describe surface roughness and texture regularity with the parameter MFV (multiscale fractal vector) and to classify the appearance grade with the Bayes classification method. Our experimen...

Atomic force microscopy of cellulose membranes prepared from the N‐methylmorpholine‐N‐oxide/water solvent system

Abstract: Cellulose membranes were obtained by solutions of cellulose being cast into a mixture of N-methylmorpholine-N-oxide (NMMO) and water under different processing conditions. Atomic force microscopy (AFM) was used to investigate the surface structures of the membranes. The AFM method provided information on both the size and shape of the pores on the surface, as well as the roughness of the skin, through a computerized analysis of AFM micrographs. The results obtained showed that the surface morphologies were intrinsically associated with the permeation properties. For the cellulose membranes, increasing the NMMO concentration and the temperature of the coagulation bath led to higher fluxes and lower bovine serum albumin rejection. These were always correlated with higher values of the roughness parameters and larger pore sizes of the membrane surfaces. When the cellulose concentration of the casting solution was 11 wt %, the membrane showed a nodular structure with interconnected cavity channels between the agglomerated nodules. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3389–3395, 2002

Molecular weight distribution of polyacrylonitrile produced in supercritical CO2

Abstract: An effectively linear molecular weight calibration curve of polyacrylonitrile (PAN) was obtained using a copolymer standard with a single broad molecular weight distribution. The molecular weights and molecular weight distributions of PAN obtained from precipitation polymerization of acrylonitrile in supercritical CO2 were quantitated by the calibration curve. The effects of monomer concentration, initiator concentration, the CO2 pressure, and the total reaction time on the molecular weight and molecular weight distribution were studied in detail. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2338–2341, 2002

Quantum dynamics of methanol: Hamiltonian, representation and intensity considerations

Abstract: Employing a body-fixed axis system and Jacobi coordinates, a model for the vibration–torsion–rotation Hamiltonian of the CH 3 OH molecule with large-amplitude internal motions has been derived. This Hamiltonian is expressed in terms of Jacobi coordinates and is partitioned in the form H A + H B + H int , where H A and H B are the rovibrational Hamiltonians of methyl group CH 3 and asymmetric rotor OH, and H int represents their interactions. The resulting Hamiltonian is used to carry out a pure quantum mechanical calculation for this kind of molecule or to construct the potential surface using observed data. The detailed discussion of the Hamiltonian is presented for the model with a rigid methyl group and a rigid OH, which describes five lower frequency vibrational modes and pure rotation in the molecule. We discuss the advantages of body-fixed Jacobi form of the Hamiltonian and solution strategies for practical programming. The properties of labels of the energy states, potential function and dipole moments are investigated according to the molecular symmetry group G 6 of methanol. Finally, the developed formulation is used to calculate the energy levels of CO-stretching–torsion–rotation for lower rotational excitation ( J ⩽5). Comparison of the calculated results with experimental ones is presented.

A stochastic nonlinear evolution model of neuronal activity with random amplitude

Abstract: In this paper we propose a new stochastic nonlinear evolution model with the stochastic amplitude in neuronal activities to obtain the average number density, which is used to describe the neurocommunication among population of neurons. The average number density is a function of the amplitude, phase and time. The number density of the diffusion process of neurocommunication is given for the active states of populations of coupled oscillators under perturbation by both periodic stimulation and random noise. Particularly, the evolution model presented in this paper can be used to describe the stochastic evolution process of the amplitudes in activities of multiple interactive neurons.

Study on synthesis and morphology control of poly(4-vinylpyridine-co-butyl acrylate)/poly(styrene-co-butyl acrylate) composite microspheres

Abstract: Monodispersed crosslinked cationic poly(4-vinylpyridine-co-butyl acrylate) [P(4VP-BA)] seed latexes were prepared by soapless emulsion polymerization, using 2,2′-azobismethyl(propionamidine)dihydrochloride (V50) as an initiator and divinylbenzene (DVB) or ethylene glycol dimethacrylate (EGDMA) as a crosslinker. The optimum condition to obtain monodispersed stable latex was investigated. It was found that the colloidal stability of the P4VP latex can be improved by adding an adequate amount of BA (BA/4VP = 1/4, w/w), and adopting a semicontinuous monomer feed mode. Subsequently, poly(4-vinylpyridine-co-butyl acrylate)/Poly(styrene-co-butyl acrylate) [P(4VP-BA)/P(ST-BA)] composite microspheres were synthesized by seeded polymerization, using the above latex as a seed and a mixture of ST and BA as the second-stage monomers. The effects of the type of crosslinker, the degree of crosslinking, and the initiators (AIBN and V50) on the morphology of final composite particles are discussed in detail. It was found that P(4VP-BA)/P(ST-BA) composite microspheres were always surrounded by a PST-rich shell when V50 was used as initiator, while sandwich-like or popcorn-like composite particles were produced when AIBN was employed. This is because the polarity of the polymer chains with AIBN fragments is lower than for the polymer with V50 fragments, hence leading to higher interfacial tension between the second-stage PST-rich polymer and the aqueous phase, and between PST-rich polymer and P4VP-rich seed polymer. As a result, the seed cannot be engulfed by the PST-rich polymer. Furthermore, the decrease of Tg of the second-stage polymer promoted phase separation between the seeds and the PST-rich polymer: sandwich-like particles formed more preferably than popcorn-like particles. It is important knowledge that various morphologies different from PST-rich core/P4VP-rich shell morphology, can be obtained only by changing the initiator, considering P4VP is much more hydrophilic than PST. The zeta potential of composite particles initiated by AIBN in seeded polymerization shifted from a positive to a negative charge. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1190–1203, 2002

Synthesis of 2',3'-Dideoxy-2'-trifluoromethyl- N -azanucleosides

Abstract: The trifluoromethylation of ( Z )/( E )- tert -butyl (4 S )-4-(2'-ethoxycarbonyl-2'-bromoprop-1'-enyl)-2,2-dimethyloxazolidine-3-carboxylate ( 4 ), which is derived from chiral serine aldehyde, yields α-trifluoromethyl-α,β-unsaturated ester 1 . Compound 1 is used as a key intermediate for the synthesis of a number of 2',3'-dideoxy-2'-trifluoromethyl- N -azanucleosides.