Preparation and characterization of a PMMA/Ce(OH)3, Pr2O3/graphite nanosheet composite

An easy process for the synthesis of poly(methyl methacrylate)/Ce(OH)₃, Pr₂O₃/graphite nanosheet (PMMA/Ce(OH)₃, Pr₂O₃/NanoG) composite was developed. Graphite nanosheets (NanoG) were prepared by treating the expanded graphite with sonication in aqueous alcohol solution. The PMMA/Ce(OH)₃, Pr₂O₃/NanoG composites were prepared via in situ polymerization of MMA monomer in the presence of graphite nanosheets and Ce(OH)₃, Pr₂O₃ through reverse micelle template, in which the methyl methacrylate was designated as the oily phase. The composites were then dispersed with chloroform and coated on glass slides to form films. Scanning and transmission electron microscopy were used to characterize the structure and dispersion of the graphite nanosheets and the composites. The results showed that the high-aspect-ratio structure of the nanosheets played an important role in forming a conducting network in the PMMA matrix. From thermogravimetric analysis, the introduction of graphite nanosheets and inorganic nanopartices exhibited a beneficial effect on the thermal stability of PMMA.     

锆莫来石材料的反应烧结机制和显微结构特征

研究了用锆英石和工业氧化铝合成锆莫来石材料的反应烧结过程和显微结构。结果表明，添加适量ＭｇＣｌ２·６Ｈ２Ｏ可以促进反应烧结进程。锆英石大颗粒完全分解以后形成ＺｒＯ２聚集体，结构中出现封闭气孔可能与ＺｒＯ２聚集体有密切关系。加入ＭｇＣｌ２·６Ｈ２Ｏ后锆莫来石材料显微结构的主要特征：ＺｒＯ２有聚集体和均匀分布两种赋存形式；封闭气孔一般与ＺｒＯ２聚集体相邻。     

基于Fisher字典学习稀疏表示的高光谱图像分类

近年基于稀疏表示的分类框架(Sparse Representation based Classification,SRC)在计算机视觉和模式识别领域取得了巨大成功,高光谱图像解译也逐渐引入稀疏表示方法。针对基于SRC的高光谱图像分类算法随机抽取训练样本构成字典较难捕获相似类别的相对差异性信息问题,提出采用Fisher字典学习方法增强相似类训练样本的可区分性。此外,考虑到高光谱图像具有较强空间相关性的特点,设计一种简单有效的投票策略进行类别判决。大量实验表明:基于Fisher字典学习的联合投票分类方法能够较好地改善高光谱分类精度。     

Low-pressure CO2 sorption in ammonium-based poly(ionic liquid)s

Ammonium-based ionic liquid monomers and their corresponding polymers [poly(ionic liquid)s] are synthesized and characterized for CO₂ sorption. The polymers have much higher CO₂ sorption capacities than the room-temperature ionic liquids and imidazolium-based poly(ionic liquid)s. For example, P[VBTMA][PF₆] with polystyrene backbone has a CO₂ sorption capacity of 10.67 mol%. The CO₂ sorption is selective over N₂ and O₂. The effects of cation, backbone, substituent, anion and crosslinking on CO₂ sorption are discussed. The sorption mechanism study indicates that CO₂ sorption by the poly(ionic liquid)s is a bulk and surface phenomenon.     

Phase Evolution and Dielectric Properties of MgTiO3–CaTiO3-Based Ceramic Sintered with Lithium Borosilicate Glass for Application to Low Temperature Co-Fired Ceramics

Effects on phase evolution caused by the addition of a new sintering agent, lithium borosilicate, Li₂O·B₂O₃·SiO₂ (LBS) glass to 0.9MgTiO₃–0.1CaTiO₃ ceramic and resultant dielectric properties were investigated. The added LBS glass, a liquid phase sintering agent, significantly lowered the densification temperature from 1300° to about 950°C, while yielding decomposition of MgTiO₃ into MgTi₂O₅ and Mg₂TiO₄. At the same time, the by-products of the decomposition reaction, MgO and TiO₂, were dissolved into the glass network. Such phase evolution partly compensated the influence of deleterious glass addition so that the specimen demonstrated fairly good apparent dielectric properties.     

弹性条缝筛网用聚氨酯弹性体的研制

采用预聚法常压浇注制备煤矿用聚氨酯筛网，考察了聚醚多元醇、甲苯二异氰酸酯异构体种类、预聚体的NCO质量分数、扩链反应温度、后熟化温度及时间等条件对制筛网用的浇注型聚氨酯弹性体体系操作性能及物理性能的影响。实验表明，采用聚四氢呋喃二醇与聚氧化丙烯二醇的混合二醇(质量比为80：20)，制得的预聚体NCO质量分数控制在4．5％左右；再以MOCA和一种三官能度扩链剂的混合扩链剂进行扩链，制得的浇注型聚氨酯弹性体满足洗煤用筛网的性能要求。     

Grafting polymerization of l-lactide on the surface of hydroxyapatite nano-crystals

A novel method of grafting ring-opening polymerization of l-lactide (LLA) onto the surface of hydroxyapatite nano-particles (n-HAP) was developed. PLLA was directly connected onto the HAP surface through a chemical linkage. The PLLA-g-HAP particles could be stably dispersed in organic solvent such as chloroform for several weeks. The n-HAP particles still retained the original dimension and shape after the grafting of PLLA. Compared with the ³¹P MAS-NMR spectrum of pure HAP powders, there appeared a downfield displacement of 1.2 ppm in the spectrum of PLLA-g-HAP. Fourier transformation infrared (FT-IR) spectra further confirmed the existence of PLLA on the surface of PLLA-g-HAP. The amount of grafted polymer determined by thermal gravimetric analysis (TGA) was about 6% in weight. The tensile strength and elongation at break of the PLLA/PLLA-g-HAP composite containing 8 wt% of PLLA-g-HAP were 55 MPa and about 10-13%, respectively, while those of the PLLA/n-HAP composites were 40 MPa and 3-5%, respectively.     

Morphology and characterization of conductive films based on polyaniline‐coated polystyrene latexes

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 (T_g). 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     

汽车尾气用催化剂载体研究现状及展望

汽车尾气催化净化器中，催化剂载体是实现高效尾气净化的一个关键因素。本文综述了对尾气净化催化剂载体的要求和研究现状。并提出导电型复合陶瓷是今后尾气净化载体材料研究和发展的一个新型方向。     

Mechanical properties of poly(lactic acid) and wheat starch blends with methylenediphenyl diisocyanate

Poly(lactic acid) (PLA) and wheat starch are biodegradable polymers derived from renewable sources. A previous study showed that thermally blending starch and PLA in the presence of methylenediphenyl diisocyanate (MDI) enhanced the mechanical properties of the blends. In this work, blends of PLA with various levels of wheat starch and MDI were hot mixed at 180°C then hot‐pressure molded at 175°C to form test specimens. The blends were characterized for mechanical properties, fracture microstructure, and water absorption. Pure PLA had a tensile strength of 62.7 MPa and elongation of 6.5%. The blend with 45% wheat starch and 0.5 wt % MDI gave the highest tensile strength of about 68 MPa with about 5.1% elongation. The blend with 20% starch and 0.5 wt % MDI had the lowest tensile strength of about 58 MPa with about 5.6% elongation. Dynamic mechanical analysis showed that storage modulus increased and tan δ decreased as starch level increased, but almost leveled off when starch level reached 45% or higher. Water absorption of the blends increased significantly with starch content. Yet the blend, if water proofed on its surface, has potential for short‐term disposable applications. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1257–1262, 2002; DOI 10.1002/app.10457