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21.
In this paper, the model based on melt diffusion and Flory-Huggins free energy theory for predicting the weld-line strength of injection molded amorphous polymers and polymer blends parts were modified by considering the diffusion thickness in the interface as a function of contact time. The modified model for weld-line strength prediction of homopolymers and polymer blends were, respectively, used to evaluate the weld-line strength of Polystyrene (PS) and Poly(methylmethacrylate) (PMMA), and that of PS/PMMA blends. The model predictions show that the theoretic predictions as a function of temperature and contact time for PS, PMMA and PS/PMMA (80/20, 70/30) are in good agreements with corresponding experimental results. However, the model predictions for PS/PMMA (20/80, 30/70) blends are much higher than experimental results. The morphology in weld-line regions for PS/PMMA (20/80, 30/70) shows lack of dispersed PS phase. Near the weld-line regions, dispersed PS phase is highly oriented along the weld-line. In theoretic prediction for polymer blends, three kinds of diffusion: Polymer A-Polymer A and Polymer B-Polymer B self-diffusions and Polymer A-Polymer B mutual diffusion were considered. This is why model predictions for PS/PMMA (20/80, 30/70) blends are higher than experimental results. 相似文献
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The effect of the in situ compatibilization on the mechanical properties of PP/PS blends was investigated. The application of Friedel-Crafts alkylation reaction to the PP/PS-blend compatibilization was assessed. Styrene/AlCl3 was used as catalyst system. The graft copolymer (PP-g-PS) formed at the interphase showed relatively high emulsifying strength. Scission reactions, occurring in parallel with grafting, were verified for PP and PS at high catalyst concentration, but no crosslinking reactions were detected. Tensile tests were performed on dog-bone specimens of the blends. Both elongation at break and toughness increased with catalyst concentration. At 0.7% AlCl3, a maximum was reached, which amounted to five times the value of the property for the uncompatibilized blend. At higher catalyst concentrations these properties decreased along with the PP molecular weight due to chain-scission reactions. On the other hand, the tensile strength did not change with the catalyst concentration. The in situ compatibilized blends showed considerable improvement in mechanical properties, but were adversely affected by chain scissions at high catalyst contents. 相似文献
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A series of well‐defined and property‐controlled polystyrene (PS)‐b‐poly(ethylene oxide) (PEO)‐b‐polystyrene (PS) triblock copolymers were synthesized by atom‐transfer radical polymerization, using 2‐bromo‐propionate‐end‐group PEO 2000 as macroinitiatators. The structure of triblock copolymers was confirmed by 1H‐NMR and GPC. The relationship between some properties and molecular weight of copolymers was studied. It was found that glass‐transition temperature (Tg) of copolymers gradually rose and crystallinity of copolymers regularly dropped when molecular weight of copolymers increased. The copolymers showed to be amphiphilic. Stable emulsions could form in water layer of copolymer–toluene–water system and the emulsifying abilities of copolymers slightly decreased when molecular weight of copolymers increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 727–730, 2006 相似文献
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以苯乙烯(St)为单体,偶氮二异丁腈(AIBN)为引发剂,聚乙烯毗咯烷酮(PVP)为分散稳定剂,在甲醇(MeOH)反应介质,使用分散聚合法制备了窄分散的聚苯乙烯微球.分别采用红外(IR)、扫描电镜(sEM)、粒度分析(SPAN)等手段,表征了聚苯乙烯(PS)微球的组成成分、表面形貌、粒径及其分布.并讨论了个各个因素对所制备微球的粒径及其分布的影响.当St质量分数为溶剂量的10%,AIBN质量分数为单体量的0.15%,PVP质量分数为单体量的1.5%时,该条件下制备的微球粒径为1.38μm,SPAN值为0.77,微球形貌及其分散性最佳. 相似文献
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HaiLing Zhu JunYing Zhang TianMin Wang LiuGang Wang Xiang Lan BaiBiao Huang 《中国科学E辑(英文版)》2009,52(8):2175-2179
Aiming at reducing the recombination of photo-induced carriers in semiconductor photocatalytic process, we prepared TiO2 thin film with its surface modified by a connected Cu micro-grid via a microsphere lithography strategy, which showed higher
photocatalytic activity than the pure TiO2 film. The improvement of photocatalytic activity of Cu micro-grid to the TiO2 film is due to the charge carrier separation and electron transfer by the conducting metal grid. The photocatalytic activity
was improved as metal loading increased, which obtained the best performance at a certain loading amount, and then decreased
at higher loading amount. This phenomenon was attributed to the metal’s bulk effect which could be explained by the relationship
between the energetic positions and the metal cluster size.
Supported by the National Natural Science Foundation of China (Grant Nos. 50672003, 50872005) and the National Basic Research
Program of China (“973” Project) (Grant No. 2007CB613302) and the Fok Ying Tong Education Foundation (Grant No. 111050) 相似文献
27.
Mahmoud A.‐Halim Abdel‐Goad 《应用聚合物科学杂志》2004,93(1):37-40
Agricultural residues (cotton straw) were added as very small particles to polystyrene (PS) at different weight ratios by using a melt‐mixing technique. The dynamic mechanical tests were performed over a wide range of temperatures and frequencies by using an ARES rheometer (Rheometrics Scientific) operated in the dynamic mode. The dynamic mechanical properties in terms of the storage modulus (G′), loss modulus (G″), compliance moduli, loss tangent, and dynamic viscosity were studied and compared for PS and PS composite. The results showed that the dynamic mechanical moduli and viscosity were found to increase with the addition of cotton straw and rise further with its loading increasing. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 37–40, 2004 相似文献
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SG3525是一种应用非常广泛的脉宽调制芯片,在开关电源设计中得到了非常广泛的应用。本文以其为研究对象,对其功能详细研究,并根据资料手册在PSIM中对其各个模块进行建模。最后,将所搭建的各个模块相结合并利用PSIM现有的模块封装功能将其封装起来,用于控制一个全桥DC—DC变换,并通过仿真来验证其功能。 相似文献