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21.
Almost all polymer processing operations involve moving and shaping the polymer as a melt and then cooling it, usually quite rapidly, to a solid state. In order to develop models for such processes we have begun systematic studies in non-isothermal rheology; here we interpret the results in the context of melt spinning. Theoretical predictions of stress vs distance from the spinneret were calculated from generalized (non-isothermal) viscoelastic theory and compared with Dees' melt spinning data on high density polyethylene. Despite certain experimental and theoretical difficulties, the agreement is good. Surprisingly, an additional theoretical curve, based on a simple Trouton viscosity, also gave a reasonable approximation over much of the distance, despite the transient nature of the flow. To understand this phenomenon further, a more tractable theoretical problem was studied in detail; the problem, of constant elongational flow (? = constant) in the presence of a constant rate of temperature change (dT/dt = constant). The results depend on two dimensionless groupings; the first is the usual product of a relaxation time and ?; the second involves the ratio of normalized dT/dt to ?. When the second group is large, a quasi-viscous state exists. The melt spinning data for the HDPE may be near this state. 相似文献
22.
Takashi Yamashiki Toshihiko Matsui Keisuke Kowsaka Masayoshi Saitoh Kunihiko Okajima Kenji Kamide 《应用聚合物科学杂志》1992,44(4):691-698
A novel cellulose solution, prepared by dissolving an alkali-soluble cellulose, which was obtained by the steam explosion treatment on almost pure natural cellulose (soft wood pulp), into the aqueous sodium hydroxide solution with specific concentration (9.1 wt %) was employed for the first time to prepare a new class of multifilament-type cellulose fiber. For this purpose a wet spinning system with acid coagulation bath was applied. The mechanical properties and structural characteristics of the resulting cellulose fibers were compared with those of regenerated cellulose fibers such as viscose rayon and cuprammonium rayon commercially available. X-ray analysis shows that the new cellulose fiber is crystallographically cellulose II, and its crystallinity is higher but its crystalline orientation is slightly lower than those of other commercial regenerated fibers. The degree of breakdown of intramolecular hydrogen bond at C3[Xam(C3)] of the cellulose fiber, as determined by solid-state cross-polarization magic-angle sample spinning (CP/MAS) 13C NMR, is much lower than other, and the NMR spectra of its dry and wet state were significantly different from each other, indicating that cellulose molecules in the new cellulose fiber are quite mobile when wet. This phenomenon has not been reported for so-called regenerated cellulose fibers. 相似文献
23.
An acetylene flame was photographed with an SIT camera through optical filters, and the signals were Abel transformed to obtain two-dimensional emission-intensity profiles. It was found that the intensive emissions of CH* and C*2 are localized at the feather boundary, while the OH* emission is localized at the intermediate zone. The structure of the acetylene flame was made clear: it consists of a carbon-radical-rich feather and an oxygen-radical-rich intermediate zone. The carbon-radical concentrations are approximately in equilibrium near the burner exit while they decrease almost linearly via interdiffusion and reactions with the oxygen-radicals in the intermediate zone.Numerical simulations including detailed gaseous and surface reactions reproduced well previous preliminary calculations showing that CH4 is rapidly produced in the boundary layer near the substrate followed by an increase in CH3. This result satisfactorily explains the measured dependence of growth rate on the substrate temperature and
ratio. 相似文献
24.
The dynamic mechanical relaxation of non-crystalline poly(aryl ether-ether-ketone) PEEK and the one irradiated with electron beam were studied. The three distinct γ, β, α′ relaxation maxima were observed in unirradiated PEEK from low to high temperature. It was revealed from the study on the irradiation effects that three different molecular processes are overlapped in γ relaxation peak, i.e., molecular motion of water bound to main chain (peak temperature; at ?100°C), local motion of main chain (at ?80°C), and local mode of the aligned and/or oriented moiety (at ?40°C). The β relaxation connected with the glass transition occurred at 150°C and it shifted to higher temperature by irradiation. The α′ relaxation which can be attributed to rearrangement of molecular chain due to crystallization was observed in unirradiated PEEK ~ 180°C and its magnitude decreased with the increase in irradiation dose. This effect indicates the formation of structures inhibiting crystallization such as crosslinking and/or short branching during irradiation. A new relaxation, β′, appeared in the temperature range of 40° to 100°C by irradiation and its magnitude increased with dose. This relaxation was attributed to rearrangement of molecular chain from loosened packing around chain ends, which were introduced into the non-crystalline region by chain scission under irradiation, to more rigid molecular packing, From these observations, we proposed that deterioration in mechanical properties of non-crystalline PEEK by high energy electron beam was brought about not only by chain scission but structural changes such as crosslinking and/or branching in the main chain. 相似文献
25.
Koji Matsui Kenji Tanaka Takanori Yamakawa Masato Uehara Naoya Enomoto Junichi Hojo 《Journal of the American Ceramic Society》2007,90(2):443-447
The shrinkage behavior of fine zirconia powders containing 2.9 and 7.8 mol% Y2 O3 was investigated to clarify the effect of Y2 O3 concentration on the initial sintering stage. The shrinkage of powder compact was measured under both conditions of constant rates of heating (CRH) and constant temperatures. CRH measurements revealed that when the Y2 O3 concentration of fine zirconia powder increased, the starting temperature of shrinkage shifted to a high temperature. Isothermal shrinkage measurements revealed that the increase in Y2 O3 concentration causes the shrinkage rate to decrease. The values of activation energy ( Q ) and frequency-factor term (β0 ) of diffusion at initial sintering were estimated by applying the sintering-rate equation to the isothermal shrinkage data. When the Y2 O3 concentration increases, both Q and β0 of diffusion increase. It is, therefore, concluded that the increase in Y2 O3 concentration of fine zirconia powder decreases the shrinkage rate because of increasing Q of diffusion at the initial stage of sintering. 相似文献
26.
Fumonisin B1 is a sphingolipid-like compound that enhances the accumulation of yeast sphingolipids and 2-hydroxy fatty acids. These lipids
occur both as freely extractable and cell bound components in yeast fermentations. Both free and bound 2-hydroxy fatty acids
produced byPichia sydowiorum NRRL Y-7130 were increased when fumonisin B1 (50 mg/L) was added to the usual growth medium containing yeast extract/malt extract/peptone/glucose. Fumonisin-treated cultures
contained 38 mg/L more 2-hydroxyhexadecanoic and 15 mg/L more 2-hydroxyoctadecanoic acids than did untreated cultures. By
contrast, fumonisin inhibited the accumulation of free 8,9,13-trihydroxydocosanoic acid inRhodotorula sp. YB-2501 cultures, leading to 240 mg/L lower trihydroxy acid production than by untreated cultures. 相似文献
27.
Tsuneo Okubo 《Polymer Bulletin》1990,23(2):211-218
Summary The adsorption of synthetic polyelectrolytes on the surfaces of monodisperse polystyrene spheres and colloidal silica spheres
is studied by electrophoretic mobility measurements. Electrolytes used are NaCl, CaCl2, LaCl3, Na2SO4, sodium poly(ethylenesulfonate) (NaPES), sodium poly(styrenesulfonate) (NaPSS), polybrene? (PB), poly-4-vinyl-N-ethylpyridinium bromide (C2PVP), poly-4-vinyl-N-benzylpyridinium chloride (BzPVP), and copolymer of
4-vinyl-N-benzylpyridinium chloride (95%) and 4-vinyl-N-n-hexadecylpyridinium bromide (5%) (C16BzPVP). Electrophoretic velocity
(u) and the effective charge number (α) of a colloidal sphere increase in the presence of PB, C2PVP, BzPVP, and C16BzPVP,
and turn to the positive from the negative values in their absence. Addition of NaPES and NaPSS further decreases u and α
values. Adsorption of the polymers on the colloidal spheres are explained by the hydrophobic and/or dipoledipole interactions
in addition to the electrostatic forces. Weak adsorption of simple electrolytes on the colloidal spheres is deduced from the
electrophoretic measurements. 相似文献
28.
α-Tocopherol was reacted with methyl linoleateperoxyl radicals at 37°C. The peroxyl radicals were generated by the reaction
of methyl linoleate with a free radical initiator, 2,2′-azobis(2,4-dimethylvaleronitrile). The primary products of α-tocopherol with methyl linoleate-peroxyl radicals were isolated by
reversephase and normal-phase high performance liquid chromatography (HPLC), and their structures were characterized by ultraviolet
(UV), infrared (IR),1H and13C nuclear magnetic resonance (NMR) and mass spectrometry (MS). There were four stereoisomers of methyl 13-(8a-peroxy-α-tocopherone)-9(Z),11(E)-octadecadienoate and four stereoisomers of methyl9-(8a-peroxy-α-tocopherone)-10(E),12(Z)-octadecadienoate. 相似文献
29.
The reaction of isocyanate in pressure sensitive adhesive (PSA) films adhered on to various adherends having different surface tensions was monitored by depth profiling using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy.In the latter stages of crosslinking reaction, unreacted isocyanate and its derivatives exist more in the bulk of the PSA than in the interfaces between PSA and adherends which are Teflon sheet and PE film having relatively lower surface tensions. In the case of using stainless steel having relatively higher surface tension as adherend, opposite segregation was observed compared to Teflon and PE.From X-ray photoelectron spectroscopy (XPS), it was revealed that N atoms exist more in surface than in bulk when stainless steel is used as adherend. We conclude that polyisocyanates migrate in the PSA film in order to minimize the magnitude of interfacial free energy between the PSA and the adherend, which leads to the change of surface tension of PSA film. 相似文献
30.
Gallium activity in the B2 phase regions of both binary Co–Ga and ternary Co–Ga–Sb systems was measured by EMF method with stabilized zirconia solid electrolyte The temperature range was 1073–1273 K and Sb concentrations were 1, 2 and 3 mol fractions. Ga activity at 1173 and 1273 K increases sharply in Ga rich region and the addition of Sb to the CoGa phase increases Ga activity. Activity change corresponds to the lattice parameter change with Sb addition to the CoGa phase. 相似文献