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21.
S. J. Liao D. Y. Chang H. J. Chen L. S. Tsou J. R. Ho H. T. Yau W. H. Hsieh James T. Wang Y. C. Su 《Polymer Engineering and Science》2004,44(5):917-928
Optimal process conditions of thin‐wall injection molding of a cellular phone cover were investigated with the consideration of interaction effects between process parameters. L27 experimental tests based on Taguchi's method were performed, and then Cyclone Scanner, PolyCAD and PolyWorks were used to measure the shrinkage and warpage of the thin‐wall injected parts to determine the optimal process conditions. Based on the results of the analysis of variables and the F‐test, interaction effects for each observed factor were determined. The results indicated that the packing pressure was the most important process parameter affecting the shrinkage and warpage of the thin‐wall part. The optimal process conditions were different for the shrinkage and the warpage. This was because during the injection process, the mechanisms affecting shrinkage or warpage were different. Compared with the results obtained with simplified thin‐wall parts in the literature, it was found that the geometry of a real commercial part did affect the optimal process conditions and the order of influence of process parameters. The optimal process conditions determined by Taguchi's method for reducing the shrinkage and warpage were verified experimentally in this work. Polym. Eng. Sci. 44:917–928, 2004. © 2004 Society of Plastics Engineers. 相似文献
22.
Different amounts of K2 CO3 were added to (Ba,Sr)TiO3 -based PTCR (positive temperature coefficient of resistance) ceramics to investigate their influence on the microstructural and electrical properties. Experimental results showed that the incorporation of K acted as an A-site acceptor-type dopant. In addition to enhancing discontinuous grain growth, the increase of K2 CO3 was found to raise the room-temperature resistivity which was dominated by grain-boundary resistance rather than grain resistance. By adjusting to a suitable amount of donor dopant, the inherent contamination of K in raw material can be compensated to achieve a high-quality PTC resistor. 相似文献
23.
Summary The diffusion of C.I. direct orange 34(MW=299) and benzoic acid(MW=122) through degraded semicrystalline polyethylene glycol(PEG)/poly(L-lactide)(PLLA) block copolymers with various PEG contents and PEG segment lengths at 37°C was studied by UV-visible spectroscopy, differential scanning calorimetry(DSC), wide angle X-ray diffractometer (WAXS) and scanning electron microscopy(SEM). The influences of the PEG contents, PEG segment lengths and hydrolytic degradation of PEG/PLLA copolymers on the solute diffusion coefficient and mode for transport were investigated. It is concluded that the diffusion rate increases with the increase of PEG contents and PEG segment lengths in PEG/PLLA copolymers. This is understandable that the increase of PEG content and PEG segment length both make the degree of crystallinity decrease. The steady state of mass flux could not be reached at the diffusion times up to 1000 h, because the copolymers underwent hydrolysis reaction during this period. Furthermore, it is understood that the characteristic time of diffusion as defined by the square of film thickness at an instant of time over the diffusion coefficient of solute through polymer decreases with the increasing diffusion time. 相似文献
24.
The isothermal cure of an epoxy-novolac molding compound was studied by means of Fourier-transform infrared spectroscopy (FTIR) and dielectrometry (DE). Results obtained were compared with previous differential scanning calorimetric (DSC) observations. The behavior of epoxide conversion (FTIR) measured via FTIR was found similar to (but not exactly coinciding with) the extent of cure (DSC) determined previously by means of DSC. As for the DE analysis, directly measurable properties such as permittivity () and loss factor () varied in a complicated manner during the course of cure, showing strong dependence on both temperature and frequency. Other dielectric parameters (such as ionic conductivity, relaxed permittivity, and characteristic relaxation time) previously suggested in the literature as suitable for cure monitoring purposes were found difficult to determine within the limited frequency range (100 to 104 Hz) here. With some arbitrariness, the relative drop in log (at 100 Hz) was taken as an index (DE) for the extent of cure. It was observed that DE behaves in a manner similar to FTIR and DSC Comments on the application of these three techniques in the characterization of thermosetting systems were given. 相似文献
25.
The UV‐curable urethane‐acrylates based on 2‐hydroxyethyl methacrylate (HEMA)‐terminated polyurethane (PU) for lithographic and coating applications are investigated in this study. Series of PU prepolymers were made from 4,4‐diphenyl methane diisocyanate (MDI), poly(propylene oxide) glycol (PPG 400), poly(butylene adipate)glycol (PBA 500), or poly(tetramethylene oxide) glycol (PTMO 1000) and are terminated with HEMA. The 2,2‐azobisisobutyronitrile (AIBN) was used as a UV‐initiator under air atmosphere. The curing kinetics of HEMA‐terminated PU film were studied. The curing analysis, using FTIR and reaction kinetics, indicate the reaction rate equation correlates well with the film thickness [T], initiator concentration [I], unreacted double bond concentration [C?C], and exposed energy [E] of the reaction system. The kinetic rate equation for the UV‐curable reaction can be written as © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3162–3166, 2004 相似文献
26.
Wen‐Bin Liau Yu‐Ting Sun Ling‐Yueh Yang Lee‐Yih Wang Wen‐Yen Chiu Kuo‐Huang Hsieh Sheng‐Mao Tseng 《应用聚合物科学杂志》2006,102(6):5406-5413
The polyaniline (PANI)‐coated polystyrene (PS) latexes were synthesized, and the electrically conductive films were prepared thereafter. The weight ratio of PANI was 5%. Thermal analysis of the latices was performed using DSC and TGA. In this study, the electrically conductive films were prepared above the PS glass transition temperature (Tg). During the film formation, the effects of the annealing temperature and atmosphere (air or N2) on the film resistance were investigated. In addition, the film morphology was observed utilizing scanning electron microscopy. The film resistance decreased in the initial heating stage due to the increasing temperature and the compaction of film. Then the film resistance increased with further annealing due to the aging of PANI. Typically, the film resistance was about 6000 Ω/sq, and the conductivity was 0.3 S/cm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5406–5413, 2006 相似文献
27.
Two surface modification methods—plasma surface treatment and chemical agent treatment—were used to investigate their effects on the surface properties of ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers. In the analyses, performed using electron spectroscopy for chemical analysis, changes in weight, and scanning electron microscope observations, demonstrated that the two fiber‐surface‐modified composites formed between UHMWPE fiber and epoxy matrix exhibited improved interfacial adhesion and slight improvements in tensile strengths, but notable decreases in elongation, relative to those properties of the composites reinforced with the untreated UHMWPE fibers. In addition, three kinds of epoxy resins—neat DGEBA, polyurethane‐crosslinked DGEBA, and BHHBP‐DGEBA—were used as resin matrices to examine the tensile and elongation properties of their UHMWPE fiber‐reinforced composites. From stress/strain measurements and scanning electron microscope observations, the resin matrix improved the tensile strength apparently, but did not affect the elongation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 655–665, 2007 相似文献
28.
The electronic portfolio (ePortfolio) is learner-centred, and its effectiveness depends on the learners’ long-term use. Thus, it is proper to conduct the study from the learners’ perspectives. Currently, most research on the use of the ePortfolio is in the form of cross-sectional studies, and it is difficult to find the reasons for the changes in students’ beliefs with regard to the long-term use of the ePortfolio. Based on the longitudinal test, this study explained the students’ continuous use of ePortfolio and the changes in their beliefs. With 122 samplers in the adoption–continuous stage (t 1–t 2) and 117 samplers in the continuous stage (t 2–t 3), this study demonstrates that in continuous use stage (t 2–t 3), perceived ease of use still influences the users’ perceived usefulness (PU) and attitude towards the ePortfolio. Attribution significantly moderates the users’ beliefs from the adoption stage (t 1) to the continuous use stage (t 2). However, the moderating effect of attribution in the continuous use stage (t 2–t 3) is insignificant; satisfaction and attribution are the key factors driving the users’ continuous intention towards the ePortfolio rather than PU and attitude. Meanwhile, satisfaction and attribution will change because of the users’ expectation disconfirmation, and it will influence the users to continue using ePortfolio. 相似文献
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