摘要:

AbstractThe powders ofBombyx morisilk fibroin were prepared from aqueous solutions of silk fibroin by several kinds of the insolubilization methods, some of which used methanol. The insolubilization appeared to be effected by the conformational transition of silk fibroin from the random coil to antiparallel β‐sheet form, which was monitored with IR spectroscopy. In order to characterize the structure of the power in the swollen state in water, a spin‐labeled silk fibroin powder was prepared and the ESR spectra were observed, as well as13C‐NMR. The heterogeneous structure was analyzed quantitatively in terms of the fraction of fast, slow, and very slow components in the ESR spectra. Finally, an enzyme, invertase, was immobilized with the silk fibroin powder. The thermal stability of the enzyme was much improved by the immobili

ISSN:0021-8995    

DOI:10.1002/app.1990.070400111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractIt is well known that the glass transition temperature of polydimethylsiloxane elastomers lies close to −120°C. According to the time temperature superposition principle, we may state that these materials keep their caoutchoutic state when they are excited by a 10 MHz mechanical wave. This is an important point particularly for acoustooptic applications. Thus, in the range of 1–10 MHz, materials with good efficiency are missed; low acoustic wave velocity is needed to give the best conditions, which means to be in a caoutchoutic state for polymeric materials. With this work, we show that three polysiloxanes, polymerized under different conditions, do not fulfill this condition. Thus the shift ofTgwith frequency is very large and these polymers reach their glassy state at relatively low frequency. The acoustic wave velocity is in good agreement with mechanical predictions provided by master curves of the Young mod

ISSN:0021-8995    

DOI:10.1002/app.1990.070400112

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractPlasma polymerization of 1,3‐ditrifluoromethylbenzene (DTFMB)/CF4mixture was investigated by means of elemental analysis and infrared spectroscopy and the permeation properties of the formed plasma polymer films were examined. The plasma polymerization deposited films containing fluorine atoms, of which the concentration depended on the starting composition of the DTFMB/CF4mixture. The films were composed of fluorinated alkyl moieties with a small amount of fluorinated aromatic moieties and carbonyl moieties. The CF4addition to DTFMB caused the breaking down of aromatic rings. Permeation properties of the plasma polymer films depended on the starting composition of the DTFMB/CF4mixture, the discharge current, and the thickness of the deposited films. The permselectivity was enhanced by adding CF4and increasing the discharge current. Plasma polymer films prepared from DTFMB/CF4mixture containing 75 mol % CF4at a discharge current of 150 mA had a permselectivity of 5.0 and an oxygen permeation coefficient of 3.5×10‐10cm3(STP) cm/cm2s c

ISSN:0021-8995    

DOI:10.1002/app.1990.070400113

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractA series of thermotropic liquid crystalline copolyesters were prepared by melt polymerization usingp‐hydroxybenzoic acid (HBA) and terephthalic acid (TPA) as mesogenic monomers, poly(ethylene terephthalate) (PET) to give a flexible linkage, and 1,4‐dihydroxynaphthalene (1,4‐DHN) as a dissymmetrical monomer. The composition of these monomers was varied as a means of manipulating processing temperature, morphology, and properties. Copolyesters with inherent viscosities near 0.7 that were melt processible in the temperature range of 200–300°C were obtained. The glass transition, thermal degradation, and melting temperatures, and crystal size all increased with increasing mesogenic unit content. The heterogeneous structure consisting of a PET‐rich phase and a phase rich in mesogenic units was observed by SEM after chemical etching and by X‐ray diffraction analysis. Highly anisotropic melts were observed indicating the presence of a nematic mesophase. The thermotropic LC copolyesters exhibit unusually well developed and highly oriented fibrillar structure at the neck area when injection molded. The orientation developed during processing is very similar to those of short‐fiber‐filled polymer composites. The LC copolyesters commonly have three relaxations in the temperature range of −100–200°C. By dynamic mechanical thermal analysis at 10 Hz, the relaxation temperatures were found to increase with increasing content of mesogenic units and of 1,4‐DHN. For the temperature range of 25–120°C, the storage modulus of one of the members of this series were compared with Vectra (Celanese) and with Eastman PHB80, which have almost the same mesogenic contents. This new copolyester maintained its modulus until 80°C, while the modulus of Vectra decreased in two steps; a small depression at 40°C and then a large reduction at 85°C. PHB80 shows a la

ISSN:0021-8995    

DOI:10.1002/app.1990.070400114

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractStyrene/maleic anhydride (SMA) copolymers were toughened by blending with a styrene/acrylonitrile (SAN) grafted rubber. The AN content of the SAN graft was fixed at 22.5% and the MA content of the SMA matrix was varied from 8 to 25%. The maximum impact strength was observed for blends based on SMA copolymers containing 14–17% MA (depending on the rubber content). These compositions are near the boundary of miscibility between the SMA matrix and SAN graft since miscibility of SMA and SAN occurs when the MA and AN contents are about the same in each Dilatational processes were shown to be the major mechanism of defor‐mation for these blends. Scanning electron microscopy was used to observe fracture surfaces as the miscibility between SMA and SAN or as the rubber content was changed. Toughening of miscible SMA/SAN matrices by this impact modifier was also examined. The results are discussed in terms of a variety of possible contributing factors including the coupling of the rubber to the matrix via miscibility of the latter with the SAN gr

ISSN:0021-8995    

DOI:10.1002/app.1990.070400115

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractDifferential scanning calorimetry has been used to follow the cure behavior of mica filled epoxy system using an aromatic diamine (4,4′‐diaminodiphenylmethane) as a crosslinking agent. Both dynamic and isothermal methods have been adopted. The effect of mica on the kinetic parameters and theTgof the cured system has been studied. It was found that mica accelerates the curing process, and decreases theTgof the fully cured system to some ext

ISSN:0021-8995    

DOI:10.1002/app.1990.070400116

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractA new kind of polymer composite membrane, which we refer as hydrophilic–hydrophobic composite membrane, is prepared by the concentrated emulsion polymerization method6,7and employed to separate permselectively ethanol–water mixtures. This composite contains polyacrylamide as the dispersed phase and crosslinked polystyrene as the continuous phase. The swelling in water of this composite membrane is around 4 g water/g polymer and its swelling in ethanol is negligible. The permeation of the composite membrane by pervaporation decreases with increasing ethanol concentration in the feed and increases with increasing polyacrylamide fraction in the composite. The rate of permeation is in the range of 30–103g/m2h. The selectivity of the membrane ranges between 2 and 50 and increases with increasing ethanol concentration in the feed and increasing polyacrylamide fraction in the composite. The permeation increases and the selectivity decreases with increasing feed temperature. The activation energy of permeation varies between 1.8 and 4.9 kcal/mol, depending upon the compositions of the feed and mem

ISSN:0021-8995    

DOI:10.1002/app.1990.070400117

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe stress‐optical coefficients (SOCs) of miscible polystyrene (PS)/poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PRO) blends were measured in the melt state over a wide range of compositions. The flow birefringence measurements were performed with a slit die rheometer using a simplified procedure which eliminates the need to specify the distribution of extinction angles in the flow space. The SOC of the PS/PPO system at ∼Tg+ 110°C follows a linear blending law and full optical compensation (SOC = 0) is observed at ∼61 wt% PS. This value is lower by ∼10% relative to values obtained by film stretching techniques. Measurements of SOC in the glassy state also yield linear dependence of SOC on composition but no compensation is obtained in this case because of the sign reversal in the SOC of PS in the glass tr

ISSN:0021-8995    

DOI:10.1002/app.1990.070400118

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractA new type of polymer support for immobilizing glucose oxidase was investigated. The starting copolymer was acrvlic‐acid‐grafted polyethylene (PE‐g‐AA). The copolymer was prepared with gamma ray irradiation induced grafting under controlled conditions utilizing post‐irradiation procedures. A number of factors were examined. They were: (1) the effect of the hydrophilic/hydrophobic nature of the support on the enzyme membrane activity; (2) the Michaelis constant (km); (3) the thermal stability, the rate constant for the thermal denaturation, and the activation energies for the denaturation of immobilized and soluble enzyme; and (4) the physical properties of the support affecting the immobilized enzyme activity. An attempt was made to immobilize the enzymeutilizing carbodiimide (CMC) as the coupling agent. This immobilization method resolves in a high enzyme activity. The hydrophilicity of the support and the activity of the enzyme membrane were proportional to the degree of grafting. When the temperature was higher than 60°C, the immobilized glucose oxidase was less sensitive to thermal inactivation than the native enzyme. Various polyethylene was studied; the LLDPE was preferred. The type of polyethylene, the thickness, kind of grafting monomers, and the degree of grafting would influence the activity of the enzym

ISSN:0021-8995    

DOI:10.1002/app.1990.070400119

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe contributions of the changes in porosity and free volume to the differences in the properties of dry and wet heat set fibers are analyzed. Nylon 6 fibers heat set in wet atmosphere (autoclave and Superba process) show a significantly higher small‐angle X‐ray scattering intensity between 0.5° and 1.5° (Cu Kα) relative to corresponding non‐heat‐set fibers, whereas the fibers heat set in dry atmosphere (Suessen process) do not. This scattering arises from the electron density contrast due to pores and free volume which lower the elctron density between the fibrils. The average diameter of the crystalline fibrils, as calculated from the Guinier analysis of diffuse scattering, increases from ca. 50 to 65 Å in all fibers upon heat setting. Additional scattering at much lower angles is attributed to aggregates of fibrils. Transmission electron microscopic studies of fibers stained by AgI, through I2/methanol/AgNO3treatment, suggest that as AgI crystallizes in a dendritic network along the paths opened up by the diffusion of iodine, it brings about large structural changes in the polymer; this process reveals defects and latent diffusion paths in the fiber. The dendritic structures of AgI are more extensive in wet heat set fibers than in dry heat set and non‐heat‐set fibers. The ordering within the crystalline domains, the interlamellar spacing, and the density of the fiber increase during both wet and dry processes. The role of these changes in the structure and the morphology of the fibers on the dyeing and ozone fading behavior, and on the strength and the modulus of the fibers

ISSN:0021-8995    

DOI:10.1002/app.1990.070400120

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY