Loss of Curing Agent During Thin Film (Droplet) Curing of Thermoset Material

Recently, it has been reported by our group and others^1.2 that loss of curing agent is encountered during the curing of small droplets or thin films of amine cured epoxies. In our earlier study³ results were reported on loss of curing agent in small droplets used in conducting the rnicrobond, single fiber test for determination of interfacial shear strength (ISS). It was reported that use of a volatile curing agent (meta-phenylene diamine (m-PDA) with DGEBA resin) resulted in increasing amounts of curing agent being lost (as measured by T₈ of the cured droplets) with decreasing droplet size during the processing procedure. Droplets smaller than 150 micrometers were seen to lose up to 40% of the curing agent leading to alteration of the mechanical properties of the droplet and, therefore, causing measured values of ISS to be exceedingly low. Use of a less volatile curing agent (Jeffamine 700, a polyether diamine, Texaco Specialty Chemicals) in combination with DGEBA resin produced results which indicated that loss of curing agent was not occuring. This study was undertaken to show the relationships between film (or droplet) size and the amount of curing agent lost (during the processing) for three different aminecured epoxy systems.     

专用粉末涂料和涂装发展的新展望

新型专用粉末涂料以其涂膜超薄型化、低温固化和高耐候性等优势,并以预裁割坯料新工艺代替预涂装卷材工艺的新特点,将成为粉末涂料新的增长点。还提出了若干建议和意见。     

Factors influencing magnetic polymer microspheres prepared by dispersion polymerization

Magnetic iron oxide (Fe₃O₄) was prepared by a coprecipitation method. Core–shell composite magnetic polymer microspheres with carboxyl groups were synthesized by the dispersion polymerization of styrene and acrylic acid in the presence of magnetic oxide, and dibenzoyl peroxide was used as an initiator. The synthesized magnetic polymer microspheres were characterized with X‐ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and so forth. The results indicated that the product was single‐phase Fe₃O₄, and its average size was about 10 nm. The configuration of the microspheres, which contained carboxyl groups, was spherical, and the average size was about 2 μm. The results of vibrating sample magnetometry tests showed that the magnetic powders produced by different surfactants had different saturation magnetizations. When poly(ethylene glycol) with a weight‐average molecular weight of 4000 was used as a surfactant, the saturation magnetization of the samples reached 69.2 emu/g. The factors that affected the shape, magnetism, size, and distribution of the microspheres were also studied. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Image-based extended finite element modeling of thermal barrier coatings

Further advances in Thermal Barrier Coating (TBC) design are linked with the evolution of numerical models for TBCs. The present paper, therefore, enhances the idea of a currently available FEM package (OOF) that has been designed for microstructural level simulations. The approach of Extended FEM (XFEM) is incorporated in an in-house developed program to account for the existence of cracks in TBCs; both for stress-strain analysis and for heat transfer analysis. The new XFEM program is then employed to carry out the analyses of a YSZ deposit and a multilayered TBC to predict the effective Young's moduli, the overall thermal conductivities, and to assess the fracture behavior of the coating.     

Comparison between Ni-Cr-40vol%TiC wear-resistant plasma sprayed coatings produced from self-propagating high-temperature synthesis and plasma densified powders

Plasma sprayed Ni-Cr-40vol%TiC coatings produced from powders obtained by self-propagating hightemperature synthesis (SHS) and plasma densification (PD) processes are characterized. Chemical composition, microstructure, and mechanical properties, such as microhardness and wear resistance, are evaluated and compared. SHS coatings exhibit good sliding wear performance. The exact stoichiometry of titanium carbide inclusions in the metallic matrix affects the dimension of the crystal lattice parameter and was investigated by examining the shift of x-ray diffraction (XRD) peaks of the TiC. A value of the combined carbon/titanium ratio of about 0.6 was calculated for both powders, thus excluding the influence of the stoichiometry of the carbide inclusions on the wear properties of the coatings.     

Thermal spraying of biomaterials

Osteoconductive hydroxyapatite coatings for metallic endoprostheses for hip and knee joint replacement provide a state-of-the-art template for enhanced in-growth of bone cells. However, the high temperature of the plasma jet leads to large scale dehydroxylation and decomposition of the starting powder. A model is being developed to explain the formation of chemically and mechanically inhomogeneous porous calcium phosphate coatings deposited by atmospheric plasma spraying onto titanium alloy substrates. In addition the biofunctionality is being discussed of titania bond coats and their influence on the in vivo performance of hydroxyapatite-titania duplex coating systems.     

三聚氰胺改性聚氨基环三磷腈对环氧树脂的阻燃作用

通过极限氧指数测定,垂直燃烧试验和锥形量热分析研究了三聚氰胺改性聚氨基环三磷腈(MPHACTPA)对改性脂肪胺固化环氧树脂(E-44/DG593)的阻燃作用,并与聚氨基环三磷腈(PHACTPA)进行了比较。结果表明,PHACTPA和MPHACTPA对E-44/DG593均有较好的阻燃作用。三聚氰胺与六氯环三磷腈的摩尔比对MPHACTPA的阻燃作用有些影响,当两者的摩尔比为1.5∶1(MPHACTPA-2)时,其阻燃作用最好。锥形量热试验残余物分析结果表明:PHACTPA和MPHACTPA在燃烧过程中受热分解成磷酸、偏磷酸、聚磷酸等,这些化合物促使E-44/GD731脱水炭化,并在NH3、N2、CO2等惰性气体的发泡作用下形成膨胀性炭层,因而产生强的凝聚相阻燃作用。MPHACTPA-2促进成炭的能力较强,因而阻燃作用更好。     

环氧季铵盐对明胶的阳离子化改性

碱性条件下,环氧季铵盐1,2-环氧丙基二甲基十二烷基氯化铵(EPQA)与明胶侧链的伯胺基、羟基反应,得到阳离子改性明胶EPQA-GE,核磁共振(~(13)C-NMR、~1H-NMR)及元素分析结果表明,精氨酸、赖氨酸的氨基以及羟脯氨酸的羟基参与了反应,季铵阳离子基团成功引入了明胶结构中。X射线衍射及差示扫描量热分析结果表明,明胶的微观相结构受阳离子含量的影响较大,引入的季铵离子越多,EPQA-GE的近程有序度越高。以水和乙二醇为标准液,测定了阳离子化程度不同的EPQA-GE膜的接触角,并应用Owens-Wendt方程计算了表面自由能,结果显示阳离子基团的引入增加了明胶的亲水性,且随着阳离子化程度增加,膜表面的亲水性增强。抗菌实验结果表明阳离子的引入增加了明胶的抗菌性,EPQA-GE对革兰氏阳性菌的抗菌效果优于对革兰氏阴性菌的抗菌性。     

溶剂微胶囊/环氧树脂复合材料的自修复性能

通过手动修复实验验证了多种溶剂的修复效果,选择可以包裹在微胶囊中的苯乙酸乙酯作为修复剂。采用一步原位聚合法,制备了包裹苯乙酸乙酯的微胶囊,并对微胶囊的表面形貌进行表征与分析。采用手动修复实验,研究了修复时间和修复剂量对修复效果的影响,并将微胶囊加入到环氧树脂基体中实现了材料的原位自修复。研究结果表明,修复时间为24 h,修复剂量为5μL时,手动修复效果可达到最佳。当微胶囊质量分数为5%时,最大修复效率为98%。微胶囊/环氧树脂复合材料具有多次自修复能力。形貌观察结果表明,裂纹在溶剂的溶胀作用下发生了完全修复。