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91.
This study analyzed the effects of polyurethane (PU) resin treatments on surface homogeneity, dimensional stability, and finishing performances of medium‐ and small‐diameter softwoods produced in Taiwan. Two‐pack PU resins were prepared by combing short castor oil‐modified alkyd resin serving as a polyol with polymeric 4,4′‐diphenymethane diisocyanate (PMDI) serving as a hardener, by the molar ratio of NCO/OH+COOH of 1.2. Four types of short oil‐modified alkyd resins with different polyhydric alcohols (glycerin and pentaerythritol) and polybasic acids (phthalic anhydride and isophthalic acid) were synthesized. Three kinds of medium‐ and small‐diameter softwoods, including China fir, Taiwanina, and Japanese fir with a diameter of 10–15 cm were obtained from Hui‐Sun Forest Station, Taiwan. The wood coating of nitrocellulose (NC) lacquer including sanding sealer and top clear was used. Results show that the surface hardness, homogeneity, moisture excluding efficiency, and antiswelling efficiency of woods were enhanced by PU resin treatments. Among all the PU resins, the isophthalic acid and pentaerythritol‐containing PU resin (IPA‐P‐MDI) achieved the best improved efficiency on dimensional stability of woods. Results of two types of finishing procedure, i.e. NC lacquer sanding sealer plus top clear and top clear only, applied onto the PU‐treated woods revealed that the hardness, adhesion, and durability of NC lacquer films on the PU‐treated wood were superior to those of untreated one, especially for top clear finishing alone. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
92.
The effect of end groups (2NH2) of poly(ethylene glycol) (PEG) on the miscibility and crystallization behaviors of binary crystalline blends of PEG/poly(L ‐lactic acid) (PLLA) were investigated. The results of conductivity meter and dielectric analyzer (DEA) implied the existence of ions, which could be explained by the amine groups of PEG gaining the protons from the carboxylic acid groups of PLLA. The miscibility of PEG(2NH2)/PLLA blends was the best because of the ionic interaction as compared with PEG(2OH, 1OH‐1CH3, and 2CH3)/PLLA blends. Since the ionic interaction formed only at the chain ends of PEG(2NH2) and PLLA, unlike hydrogen bonds forming at various sites along the chains in the other PEG/PLLA blend systems, the folding of PLLA blended with PEG(2NH2) was affected in a different manner. Thus the fold surface free energy played an important role on the crystallization rate of PLLA for the PEG(2NH2)/PLLA blend system. PLLA had the least fold surface free energy and the fast crystallization rate in the PEG(2NH2)/PLLA blend system, among all the PEG/PLLA systems studied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
93.
94.
对不同温度及不同搅拌工艺下得到的材料的显微组织的比较,确定了合理的半固态温度和搅拌工艺,即半固态温度为590℃,震荡电流为500A。随后对单个线圈电磁搅拌过程进行建模及电磁场和流速场的耦合模拟得到了电磁场和流速场分布,此结果与电磁搅拌的原理及实验结果相一致。计算出在该温度和工艺下熔体内部的平均流动速度为3.2cm/s,将该结果作为能否得到半固态浆料的判据。 相似文献
95.
96.
97.
Aluminum–boron carbide particle reinforced composite is an advanced material which can be used in applications such as neutron-shielding
components, aircraft, and aerospace structures. In the microstructural characterization of an Al–7%Si–10%B4C die casting, attention is particularly focused on particle distribution and interface reaction products between B4C particles and the aluminum matrix. The quantitative analysis results show that, in a cross-section of the cast part, more
particles concentrate in the center and fewer particles are present in the wall regions. Moreover, some particle segregation
bands have been observed. The mechanisms of the particle migration are proposed to describe the phenomenon. However, the average
particle fraction in any cross-section of the cast part is almost the same. A barrier layer consisting of several sublayers
was detected on the surface of B4C particles. Using electron diffraction in selected areas, it is found that these sublayers are composed of Al3BC crystals, TiB2 crystals, Si crystals, and coarse stick-shaped TiB2 particles. In addition, it is observed that Si plays an important role in the formation of a dense barrier layer. The barrier
layer can limit B4C decomposition and improve B4C stability in the aluminum melt. 相似文献
98.
Stock market forecasting has been a challenging financial research topic for decades. In the literature, there are numerous
results based on point methods. However, poor forecasting quality has been a continuous problem. Motivated by the fact that
financial data varies within intervals, we apply interval methods on a well known stock pricing model [3] to predict stock
market variability as intervals. Empirical results obtained with a few different approaches in this paper consistently suggest
that interval forecasts have better overall quality than traditional point forecasts. 相似文献
99.
100.
通过把迁移率的实测值与影响HgCdTe晶体电子迁移率的主要散射机构进行对比,得出结论:位错是HgCdTe晶体低温电子迁移率降低的主要原因。 相似文献