ISSN:0021-8995    

DOI:10.1002/app.1991.070420101

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

年代:1991

数据来源: WILEY

摘要:

AbstractAs predicted by thermodynamic studies of polymer conformation, high molecular weight poly(methyl methacrylate) (PMMA) dissolves cleanly, and at a constant rate, in a 7 : 3 mixture of 1‐butanol and acetonitrile, although neither liquid is a solvent for PMMA by itself. Mixtures of other alcohols with acetonitrile also dissolve PMMA. When mixtures with the same fraction of acetonitrile are compared, methanol dissolves PMMA almost twice as fast, ethanol and hexanol at about the same rate, and 2‐propanol somewhat more slowly than the 1‐butanol mixture with acetonitrile. The measurements of dissolution rate were made using a laser interferometer at

ISSN:0021-8995    

DOI:10.1002/app.1991.070420102

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe crystal orientation in injection molding of talc‐filled polypropylene has been studied by means of polarizing microscopy and X‐ray diffraction measurements. The plate planes of talc particles are aligned parallel to the surface of injection molding. Thec‐anda*‐axes of polypropylene crystals are bimodally oriented to the flow direction, and theb‐axes are oriented to the thickness direction. Namely, the crystals in the injection molding of talc‐filled polypropylene show a kind of uniplanar‐axial orientation according to the classification of Heffelfinger and Burton. The degree of the bimodal orientation ofc‐anda*‐axes decreases toward the interior of the injection molding. Theb‐axis orientation is strong throughout the thickness direction, although it is a little weaker at the surface skin and central regions. This peculiar crystal orientation originates from the flaky shape and crystallization nucleation ability of talc particles. In a mold cavity, talc particles are aligned parallel to the cavity wall by the action of flow, and crystallization progresses, with the (040) plane of polypropylene crystal piling on the plate planes of talc particles and theb‐axis, which is the growth direction of polypropylene crystal, being aligned to the thickness and cooling direction of injection molding. The crystal orientation in injection molding of unfilled polypropylene is basically similar to that of talc‐filled polypropylene, although theb‐axis orientation to the thickness

ISSN:0021-8995    

DOI:10.1002/app.1991.070420103

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

年代:1991

数据来源: WILEY

摘要:

AbstractSignificant progress has been made in recent years regarding the photooxidation of olefin copolymers, but questions still remain. This paper reviews the progress and probes the photooxidative chemistry of ethylene–propylene (EP) and ethylene/propylene/diene monomer (EPDM) copolymers. Both stabilized and unstabilized polymer plaques were irradiated in a xenon are and the surface chemistry followed using infra‐red spectroscopy. Model compounds were used to help elucidate the chemistry caused by unique structural features present in the copolymers. Volatile products evolved during photooxidation were determined giving valuable insight into the degradation chemis

ISSN:0021-8995    

DOI:10.1002/app.1991.070420104

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

年代:1991

数据来源: WILEY

摘要:

AbstractA thermosetting resin consisting of a mixture of vinyl‐terminated oligomeric ethers was prepared by a two‐step synthesis. This required the reaction of 1,4‐bis (chloromethyl) benzene with the potassium salt of bisphenol A, and subsequent vinylation of the chloromethyl end groups by means of a Wittig reaction. The linear vinyl prepolymers were thermally crosslinked through their reactive styryl end groups (without the addition of catalyst) to produce castings and woven glass laminates. A study of the crosslinking process was carried out by differential scanning calorimetry (DSC). The water absorption and the thermooxidative stability of the crosslinked polymer were investigated. A styrene solution of the oligomeric ethers was also crosslinked, using benzoyl peroxide as a catalyst. The moisture absorption characteristics of the crosslinked styrene copolymer were compared with those of the crosslinked homopolymer. Both substances showed hydrophobic char

ISSN:0021-8995    

DOI:10.1002/app.1991.070420105

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

年代:1991

数据来源: WILEY

摘要:

AbstractPreviously, starch‐derived glycol and glycerol glucosides were prepared by batch‐reaction processes and had excellent potential as chemical intermediates for a wide range of products. However, more efficient processes for preparation of these derivatives are needed. In this present work, a modern corotating, intermeshing, twin‐screw extruder with a barrel length/screw diameter (L/D) ratio of 43: 1 was used to study the reaction of starch with ethylene glycol and glycerol in the presence of sulfuric acid catalyst at elevated temperatures. A fully continuous process was used. Variables that were investigated included temperature (140–180°C), glycol or glycerol/starch AGU mol ratio (1.5–4.0), starch feed rate (5–30 lb/h), screw speed (100–475 rpm), residence time, specific energy, and several types of commercial cornstarch and corn flour products. Rates and extents of reaction that occurred in the barrel were determined by analyzing samples that were quenched just prior to extrusion. The major glucosides were quentitated by high‐performance liquid chromatography. Results of this study show that starch can be continuously, rapidly, and efficiently converted to glucosides in 90% yield at high production rates. Such processing is expected to be technically feasible for the reaction of a wide range of polyhydroxy alcohols with various s

ISSN:0021-8995    

DOI:10.1002/app.1991.070420106

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

年代:1991

数据来源: WILEY

摘要:

AbstractSouthern pine samples with different dimensions and bulk densities were impregnated with the multifunctional monomer ethyl α‐hydroxymethylacrylate (EHMA) and 5 mol % of fluorinated or nonfluorinated crosslinking agent. The maximum impregnation yield (105% by weight) was achieved under vacuum with good improvement of water repellency.Impregnation with EHMA plus another multifunctional monomer 2‐vinyl‐4,4‐dimethyl‐2‐oxazolin‐5‐one (vinyl azlactone) was carried out to improve the mechanical properties of wood samples. Water repellency was also improved depending on the amount of vinyl azlactone in the monomer solution. A maximum of 41% antiswell efficiency (ASE) was obtained by impregnation with a 9 : 1 w/w mixture of EHMA and vinyl azlactone. Improvements of 38–54% in impact strength and 27–44% in compression modulus were achieved depending on the relative amount of vinyl azlactone incorporated. FT‐IR and solution or solid‐state NMR spectroscopy were used for chemical characterization of the polymers themselves and the

ISSN:0021-8995    

DOI:10.1002/app.1991.070420107

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe behavior of a highly fluorinated epoxy resin blended with Epon 828 was studied. The two resins are immiscible, resulting in 10–20‐μm spherical domains and a surface layer of fluorinated resin. A B stage for the blend providing for good ply lamination is indicated. The mechanical properties of the blend were commensurate with the Epon p

ISSN:0021-8995    

DOI:10.1002/app.1991.070420108

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

年代:1991

数据来源: WILEY

摘要:

AbstractPolyimide (PI) is an insulating polymer that is finding increased use in the semiconductor industry as an intermetal dielectric, passivation coating, and planarization layer. It has a low dielectric constant (3.5 at audio frequencies) and can be processed at temperatures below 450°C. These features make PI attractive to the integrated circuit industry. One disadvantage of this material is that, like most polymers, it is hygroscopic. Moisture can lead to such reliability problems in integrated circuits as increased insulator conductivity, loss of adhesion, and corrosion. It is important to quantify the moisture uptake in polyimide so that the reliability implications of its use can be fully understood. In this study, the steady‐state moisture uptake of the model PI pyromellitic dianhydride‐oxydianiline (PMDA‐ODA) is reported. The moisture uptake is measured using a Cahn 1000 Microbalance with a 1‐μg resolution. The samples are prepared by spin‐coating one or more layers of the precursor polyamic acid onto 2‐in silicon substrates. The moisture uptake in these polymers is found to be linearly related to ambient relative humidity, and the maximum moisture uptake by weight is 3.2%. The moisture uptake in PI is also shown to be a bulk absorption rather than a surface adsorpti

ISSN:0021-8995    

DOI:10.1002/app.1991.070420109

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

年代:1991

数据来源: WILEY

摘要:

AbstractWater‐insoluble proteases were prepared by immobilizing papain, ficin, and bromelain onto the surface of porous chitosan beads with any length of spacer by covalently fixation. The activity of the immobilized proteases was found to be still high toward small ester substrate,N‐benzyl‐L‐arginine ethyl ester (BAEE), but rather low toward casein, a high‐molecular‐weight substrate. The relative activity of the immobilized proteases with spacer gave an almost constant value for the substrate hydrolysis within the surface concentration region studied. The values of the Michaelis constantKmand the maximum reaction velocityVmfor free and immobilized proteases on the porous chitosan beads are estimated. The apparentKmvalues were larger for immobilized proteases than for the free ones, whileVmvalues were smaller for the immobilized proteases. The pH, thermal, and storage stability of the immobilized proteases were higher than those of the free ones. The initial enzymatic activity of the immobilized protease maintained almost unchanged without any elimination and inactivation of proteases, when the batch enzyme reaction was performed repeatedly, indicating the excellent

ISSN:0021-8995    

DOI:10.1002/app.1991.070420110

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

年代:1991

数据来源: WILEY