A film of poly(l-lactic acid) (PLLA) consisting of highly oriented α crystals was uniaxially drawn by tensile force. The effects of the draw ratio (DR), draw temperature (Td), and draw stress on the crystal/crystal transformation from the α- to the β-form crystals were studied. At the initial stage of drawing, the highly oriented α crystals of the starting film transformed into a broader orientation distribution, and significant crystal disorder was introduced. Upon further drawing, the α crystals steadily transformed into β crystals with increasing the DR. For the drawing at a constant Td, the crystal transformation proceeded more efficiently at a higher draw rate and, hence, at a higher draw stress. Furthermore, for the drawing at a constant draw rate, the transformation proceeded with DR most efficiently for the tensile draw at a Td around 140 °C, although the draw stress increased with decreasing the Td. The present result combined with the previous finding in the drawing of PLLA by solid-state extrusion [Macromolecules 36 (2003) 3601] suggests that there is a Td of around 140 °C at which the crystal transformation proceeds most efficiently with DR, suggesting that there are two factors that have opposite effects on the efficiency of the crystal transformation with increasing the Td. However, as a result of the combined effects of the Td and DR on the crystal transformation and the ductility increase with the Td, an oriented film consisting predominantly of β crystals was obtained by tensile drawing at a Td in the range of 140-170 °C to the highest DR achieved at each Td. 相似文献
The steady flow of non-Newtonian polymer solutions on their own and together with air transverse to a bundle of circular rods, has been studied experimentally. In particular, the frictional pressure drop has been measured as a function of non-Newtonian power-law constants, flow rates, voidage of bundles and the input fraction of air over wide ranges of conditions as: power-law flow behaviour index, 0.5 to 1; voidage values of 0.78 and 0.87-0.88; air velocity (superficial), 0.09 to 0.28 m/s and liquid velocity (superficial) 0.018 to 0.5 m/s. While the single phase flow results for power-law liquids are in excellent agreement with an existing equation, the two-phase pressure drop results are also in accordance with the form of the well-known Lockhart-Martinelli correlation. Based on these results, it is suggested that a value of 5-10 for the Reynolds number based on rod diameter marks the limit of the laminar flow in such systems. 相似文献
FemaleMicroplitis croceipes wasps were tested in a wind tunnel for their ability to orient to various concentrations of eight different green leaf volatile
(GLV) substances [hexanal, (E)-2-hexenal, (E)-2-hexen-1-ol, (Z)-3-hexen-1-ol, (E)-2-hexenyl acetate, (Z)-3-hexenyl acetate, (Z)-3-hexenyl propionate, and (Z)-3-hexenyl butyrate]. Overall, the esters elicited the greatest percentage of successful orientation flights, the alcohols
elicited an intermediate response, and the aldehydes elicited a low response. The semilog dose-response curves were generally
hill-shaped with high responses at medium release rates and low responses at high or low release rates. For the aldehydes,
positive responses occurred at all GLV release rates between 0.01 and 100 nl/min. For some alcohols and esters, positive responses
occurred at release rates as low as 1 pl/min and as high as 1μl/min. These data show thatM. croceipes wasps are strongly attracted to GLVs and are capable of orienting to GLV concentrations that would occur in nature when a
caterpillar feeds on a green leaf. Hence, in nature, GLVs may be important clues, enablingM. croceipes to locate their hosts. 相似文献
In previous studies, asphaltenes and resins have been treated as two distinct fractions of a crude oil. The asphaltenes were assumed to be the only self‐associating fraction. However, there is evidence that resins also participate in this self‐association. In this study, molar masses of mixtures of asphaltenes and resins were measured with vapour pressure osmometry. Precipitation from the same mixtures dispersed in solutions of toluene and pentane were also measured. The data were modelled with previously developed self‐association and precipitation models. Model results with asphaltenes and resins characterized as a single distribution and as individual components are compared. The data and the modelling suggest that asphaltenes and resins are better characterized as a single distribution of self‐associating components. 相似文献
Two‐phase decanter olive pomace (TPOP) is the by‐product of a centrifugation system, used to produce olive oil, that separates olive oil and moist pomace. The water content in these olive pomaces is about 70%, while it was 45‐50% in the olive pomace stemming from three‐phase systems (oil, water, and pomace) and 30% in the old press system. The aim of this work is focused on quantification and changes undergone during olive pomace storage in ponds of esters of fatty acids with short‐chain linear alcohols, which can be considered as a refining loss. The results indicate that oil deterioration increases very rapidly, in particular when oil is extracted from the TPOP surface. Special attention should be paid to the storage of TPOP, establishing a maximum of 2 months in all cases. 相似文献
Summary: Non‐Newtonian fluid behavior has significant influence on quantities in chemical engineering like power input, mixing time, heat transfer etc. In the laminar flow region, the concept of effective viscosity by Metzner and Otto is well established. In the transition region between laminar and turbulent flow, the existing concepts use three and even more empirical parameters to determine the specific power input. Here, a unified and general but simple approach is introduced to calculate the power input for shear thinning fluids over the whole flow region using just one empirical parameter. The Metzner‐Otto relation is obtained as a limiting case for the laminar region. The empirical parameter of the new approach is related to the Metzner‐Otto constant. The concept is validated for eight different stirrer systems. Mixing time and maximum shear rate and heat transfer can also be calculated using this approach. The new concept presented should also be applicable for other apparatuses, e.g., static mixers.
Comparison of experimental data and a curve calculated according to the new method (solid line). 相似文献