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991.
Native corn starch‐ and hydroxypropylated starch (HPS‐) based plastic films were prepared using the short pulp fiber as the reinforcement and the glycerol as the plasticizer. The results of tensile test showed that the strain and stress at break and elastic modulus increased with pulp content. With glycerol content, the strain at break increased considerably, but the breaking stress and elastic modulus decreased. And the stress–strain curves showed that the brittleness problem of films was overcome by the pulp, glycerol, and water content. The hydroxypropyl starch films showed results similar to those of the native starch films. The results of the three‐point bending test showed that maximum deflection, flexural strength, and specific work increased with pulp content, but the flexural modulus was the highest at a pulp content of 20%. And with the glycerol content, the maximum deflection and specific work of rupture increased, but the bending elastic modulus decreased. The hydroxypropyl starch films showed results similar to those of native starch films as far as the maximum deflection and flexural strength were concerned, but the bending elastic modulus and specific work of the hydroxypropyl starch films were considerably lower than those of starch films. So it was concluded that the flexibility of films was improved by the hydroxypropylation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2108–2117, 2003 相似文献
992.
Man-Hee HanJung-Whan Kim Jinwon KimJung Yoon Ko Jules J. MagdaIn Suk Han 《Polymer》2003,44(16):4541-4546
The acrylic comonomers hydroxypropyl methacrylate (HPMA) and N,N-dimethylaminoethyl methacrylate (DMA) have been used in several earlier studies to produce pH-responsive hydrogels. However, these same monomers can also be used to prepare hydrogels that are highly responsive to temperature. One manifestation of this temperature sensitivity is a sharp decrease in hydrogel optical transparency that occurs when the temperature exceeds a critical transition value. For example, a hydrogel that exhibits a swelling transition at the physiological pH value of 7.4 has a transition temperature of about 45 °C when the environmental salt concentration is 0.15 M. The value of the transparency transition temperature is shown to depend on hydrogel synthesis parameters such as comonomer mole ratio, crosslinker mole ratio, and even initiator concentration. By reducing the mole ratio of the crosslinker tetraethylene glycol dimethacrylate (TEGDMA), the transition temperature can be lowered by as much as 15 °C. Environmental salt concentration and solvent polarity are also shown to influence the transition temperature. 相似文献
993.
This study is to investigate the factors influencing the alcohol production byKluyveromyces fragilis using the juice of Jerusalem Artichoke tubers.
The cell growth rate and ethanol production rate were stimulated by aeration and by the addition of unsaturated fatty acids
and the cell mass production and the ethanol production were substantially improved.
It was found that oxygen and unsaturated fatty acids added played a decisive role on the increase of alcohol tolerance of
yeast. 相似文献
994.
Byoung Chul Kim Hyun Woog Kang Young Han Kim 《Korean Journal of Chemical Engineering》2006,23(5):789-794
A crystallization monitoring system using a quartz crystal oscillator was utilized to predict different shapes of crystal
formation by measuring crystal growth rate and to measure supersaturation. Applying different rates of cooling, crystal formation
of different shapes was induced, and the frequency variation of the oscillator and the crystal shape observed with an SEM
were compared to determine how the frequency variation can be interpreted for the prediction of produced crystal shape. The
experimental results obtained from the crystallization of potassium nitrate and cupric sulfate solutions showed that the proposed
frequency measurement technique could be applied in the prediction of crystal shape of cooling crystallization processes.
In addition, supersaturation was determined from the measurements of solution and coolant temperatures. 相似文献
995.
The key to the success of flip‐chip technology lies in the availability of sucessful underfill materials. However, the reliability of flip‐chip technology using current underfill materials is generally found to be lower than that of conventional wire‐bond connection packaging materials such as epoxy molding compound (EMC) because of the high coefficients of thermal expansion (CTE) and moisture absorption of cured underfill material. In this study desbimide (DBMI), which has a low melting point (about 80°C), was used in the underfill materials as a cohardener. As a result, DBMI‐added underfill can show excellent thermal reliability, which is due to the superior properties of the CTE, the elastic modulus, and water resistance. When the properties of a 2 wt % DBMI‐added underfill were compared with those of a typical underfill (epoxy/anhydride), the CTE value was reduced to less than one‐half at the solder reflow temperature (about 200°C), the elastic modulus was reduced to less than one‐half in the temperature region below the glass‐transition temperature, and the water resistance was improved twofold. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2617–2624, 2002 相似文献
996.
Te-Yu Wei Tso-Fu Chang Shih-Yuan Lu Yu-Cheng Chang 《Journal of the American Ceramic Society》2007,90(7):2003-2007
Monolithic silica aerogels with thermal conductivity as low as 0.036 W·(m·K)−1 and porosity as high as 97% were successfully prepared by ambient pressure drying through a multiple modification approach. This approach may replace the more costly and dangerous operation of supercritical drying. The tetraethoxysilane (TEOS)-derived wet gel was made hydrophobic with multiple treatments of trimethylchlorosilane and dried under ambient pressure. The multiple treatments were found to be necessary to achieve sufficient modification of the wet gel for reduction in drying-induced surface tension force to maintain product integrity and high porosity. Comparisons in nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy for surface bonding and contact angle measurement for hydrophobicity between the no, single, and multiple surface modification (MSM) samples were conducted to reveal the difference in the extent of the resulting surface modification. In conclusion, the MSM procedure reduced the volume shrinkage, increased the monolithicity and porosity, and lowered the thermal conductivity of the resulting aerogels. 相似文献
997.
998.
Chang‐Gyu Kim Sung‐Hoon Joo Cheol Hong Cheon Mi‐Yun Jeong Soon‐Wook Cha Byung‐Hee Sohn Jung‐Il Jin 《应用聚合物科学杂志》2006,100(1):307-317
Three new soluble polyconjugated polymers, all of which emitted blue light in photoluminescence and electroluminescence, were synthesized, and their luminescence properties were studied. The polymers were poly{1,1′‐biphenyl‐4,4′‐diyl‐[1‐(4‐t‐butylphenyl)]vinylene}, poly((9,9‐dioctylfluorene‐2,7‐diyl)‐alt‐{1,4‐phenylene‐[1‐(4‐t‐butylphenyl)vinylene‐1,4‐phenylene]}) [P(DOF‐PVP)], and poly([N‐(2‐ethyl) hexylcarbazole‐3,6‐diyl]‐alt‐{1,4‐phenylene‐[1‐(4‐t‐butylphenyl)]vinylene‐1,4‐phenylene}). The last two polymers had alternating sequences of the two structural units. Among the three polymers, P(DOF‐PVP) performed best in the light‐emitting diode devices of indium–tin oxide/poly(ethylenedioxythiophene) doped with poly(styrene sulfonate) (30 nm)/polymer (150 nm)/Li:Al (100 nm). This might have been correlated with the balance in and magnitude of the mobility of the charge carriers, that is, positive holes and electrons, and also the electronic structure, that is, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels, of the polymers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 307–317, 2006 相似文献
999.
An increase in the depolymerization of chitosan was found with an increased concentration of sodium perborate. Acetic anhydride was added to reacetylated chitosan in a molar ratio per gulcosamine unit, and the amide I band of IR spectra changed with the addition of acetic anhydride. Sixteen chitosans with various molecular weights (MWs) and degrees of deacetylation (DODs) were prepared. X‐ray diffraction patterns indicated their amorphous and partially crystalline states. Increases in the chitosan MW and DOD increased the tensile strength (TS). TS of the chitosan films ranged from 22 to 61 MPa. However, the elongation (E) of chitosan films did not show any difference with MW. TS of chitosan films decreased with the reacetylation process. However, E of chitosan films was not dependent on DOD. The water vapor permeabilities (WVPs) of the chitosan films without a plasticizer were between 0.155 and 0.214 ng m/m2 s Pa. As the chitosan MW increased, the chitosan film WVP increased, but the values were not significantly different. Moreover, the WVP values were not different from low DOD to high DOD. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3476–3484, 2003 相似文献
1000.
Chang Dae Han 《应用聚合物科学杂志》1971,15(10):2567-2577
Two slit dies have been designed, having aspect ratios of 10 and 20. Three melt pressure transducers were flush-mounted on the long side of the rectangular slot, along the longitudinal centerline of each die. The dies were then used to measure wall normal stresses along the longitudinal direction of polymer melts flowing through the thin slit. The polymeric materials investigated were high-density polyethylene, low-density polyethylene, polypropylene, and polystyrene. The measurement of wall normal stresses were used to determine the rheological properties of melts, namely, the melt viscosity from the slope of axial pressure profiles and the melt elasticity from exit pressures. The present study shows that the rheological properties determined from the slit rheometer are in good agreement with those from the capillary rheometer reported in the author's earlier papers. Therefore it may be concluded that a slit die also may be used as a means of characterizing polymeric materials by their viscous and elastic properties in the molten state. 相似文献