Microstructure and interfacial interaction of polyimide/silica hybrid nanocomposites prepared with 3-aminopropyltriethoxysilane

A series of polyimide (PI)-silica hybrid nanocomposites are prepared from 3,3′,4,4′biphenyltetracarboxylic dianhydride (BPDA)-4,4′-oxydianiline (ODA) polyamic acid (PAA) and tetraethoxysilane (TEOS) or tetramethoxysilane (TMOS) by the sol-gel process. 3-Aminopropyltriethoxysilane (3-APS) is used to enhance the interfacial interaction between polyimide and silica. The morphology, interfacial interaction, and properties of the hybrids are investigated using scanning electron microscope (SEM), UV-vis spectroscopy, atomic force microscope (AFM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). SEM and AFM images indicate that silica particles of ca. 45-55 nm size are uniformly distributed in polyimide matrices and that the interfacial interaction between PI and TEOS is better than that between PI and TMOS. The optical transparencies of the PI/TEOS hybrids are better than that of the PI/TMOS hybrids. FTIR spectra confirm the Si O Si bond as well as the conversion of PAA to polyimide and PI/silica hybrid films. The thermal stability is increased after incorporation of the silicas in the polyimide matrix.     

HLDPE/organic functionalized SiO2 nanocomposites with improved thermal stability and mechanical properties

High-pressure low-density polyethylene (HLDPE)/organic functionalized SiO₂ nanocomposites were synthesized using melt-blending technique in a sigma internal mixer. The properties of the nanocomposites were studied using two different organic functional modifiers: diglycidyl ether of bisphenol-A (DGEBA) and triacetoxyvinylsilane. Reinforcing, thermal stability and toughening effects of organic functionalized nanosilica on the polymer matrix were found at loading of 2.5% nanosilica functionalized with 2.8% of DGEBA and silane coupling agent respectively. Organic functionalization on the nanosilica particle surface led to different microstructures when compared with that of the pure polymer. Organic functionalization on the nanosilica particle surface produced good interfacial adhesion and homogeneous dispersion in the polymer matrix, while the use of nanosilica resulted in aggregated silica particles in the polymer matrix. There was no significant improvement in thermal stability and mechanical properties when only nanosilica was added to the pure polymer. On the contrary, the addition of pretreated nanosilica with organic functional modifiers led to an increase of thermal stability from 313–363°C, elastic modulus and toughness from 0.12–0.18 GPa and 3.23–9.81 MJ/m³ respectively.     

Development of an Exfoliated Nanocomposite Prepared by Vinyl Acetate and Organic Montmorillonite: Structure,Dynamic Mechanical Properties and Thermal Degradation

Using in-situ emulsion polymerization, the exfoliated nanocomposites were prepared from vinyl acetate (VAc) and organic montmorillonite (OMMT) through five different experimental conditions. The different experimental conditions and OMMT had little effect on the structure of PVAc–OMMT, but significant effect on the dynamic mechanical properties. They produced a combined effect on the modulus, loss tangent and glass transition temperature (T _g). OMMT could lower T _g of PVAc, and improved PVAc's low temperature resistance. PVAc and PVAc–OMMT all were homogeneous amorphous linear polymers and they all displayed cold crystallization. The different experimental conditions and OMMT had some effects on the thermal degradation. The thermal degradation process was found to consist of eight phases, and those of PVAc and PVAc–OMMT were similar. OMMT had no obvious effect on the thermal degradation temperature, but mainly delayed the thermal degradation process.     

Novel Jute/Polycardanol Biocomposites: Effect of Fiber Surface Treatment on Their Properties

In the present study, novel biocomposites with chopped jute fibers and thermosetting polycardanol were prepared using compression molding technique for the first time. Prior to biocomposite fabrication, jute fiber bundles were surface-treated at various concentrations using 3-glycidoxypropyltrimethoxy silane (GPS) and 3-aminopropyltriethoxy silane (APS), respectively. The interfacial shear strength, flexural properties and thermal properties of jute/polycardanol biocomposites reinforced with untreated and silane-treated jute fibers were investigated by means of single fiber microbonding test, three-point flexural test, dynamic mechanical analysis, thermogravimetric analysis and thermomechanical analysis. Both GPS and APS treatments played a role in improving the interfacial adhesion, reflecting that the organofunctional groups located at the end of silane coupling agents may contribute to linking between jute fibers and a polycardanol resin. As a result, it gave rise to increased interfacial shear strength of the biocomposites. Such interfacial improvement also led to increasing the flexural strength and modulus, storage modulus, thermal stability and thermomechanical stability.     

Composites from Brazilian natural fibers with polypropylene: mechanical and thermal properties

Brazil has a well established ethanol production program based on sugarcane. Sugarcane bagasse and straw are the main by-products that may be used as reinforcement in natural fiber composites. Current work evaluated the influence of fiber insertion within a polypropylene (PP) matrix by tensile, TGA and DSC measurements. Thus, the mechanical properties, weight loss, degradation, melting and crystallization temperatures, heat of melting and crystallization and percentage of crystallinity were attained. Fiber insertion in the matrix improved the tensile modulus and changed the thermal stability of composites (intermediary between neat fibers and PP). The incorporation of natural fibers in PP promoted also apparent T _c and ΔH _c increases. As a conclusion, the fibers added to polypropylene increased the nucleating ability, accelerating the crystallization process, improving the mechanical properties and consequently the fiber/matrix interaction.     

The Effects of Morphological Properties of Henequen Fiber Irradiated by EB on the Mechanical and Thermal Properties of Henequen Fiber/PP Composites

The aim of this study was to investigate the effects of electron beam (EB) irradiation on the morphological properties, crystallinity and surface area of henequen fiber and on the mechanical and thermal properties of henequen fiber reinforced polypropylene (PP) composites. The structure of henequen fiber was characterized by X-ray diffraction, mercury porosimetry and BET surface area analysis. The EB irradiation of 10 kGy led to the increasing of crystalline and surface pore area of henequen fiber, which contributed to the number of interlocking places with PP. From the results of tensile and impact strength tests, the highest value was observed for the composite reinforced with the henequen fiber treated with EB dose of 10 kGy, decreasing overall as EB dose increased. This tendency was also shown by coefficient of thermal expansion (CTE) measurements, but the value of CTE decreased until 50 kGy, meaning that a large total surface area can provide many interlocking places and so improve adhesion between fiber and matrix. Therefore, it can be concluded that the optimum pore surface area by 10 kGy irradiation contributes to successful mechanical interlocking between fiber and matrix and consequently enhances the mechanical and thermal properties of the composites.     

邻氯苯甲酸稀土配合物的合成、表征及结构

本文合成了邻氯苯甲酸与十五种稀土的配合物REL~3·H~2O(RE=Y,La～Lu,L=Clc~6H~4CO~2H),研究了它们的热分解及红外光谱.测定了钕、铽及镥三种稀土的配合物晶体结构,均属单斜晶系,空间群P2~1/n,稀土离子配位数为9,配合物呈无限链状聚合结构.     

双吡唑啉酮类螯合剂1,6-双[4'-(1'-苯基-3'-甲基-5'-氧代)吡唑啉基]-1.6-已二酮与铀、钍固体配合物合成及表征

本文报道了1,6-双[4'-(1'-苯基-3'-甲基-5'-氧代)吡唑啉基]-1,6-已酮与铀、钍固体配合物的组成。从红外光谱、质子核磁共振谱、差热曲线及微分热重曲线的数据, 得到了其配位状态方面信息。     

二维网状结构双核配合物[Ca_2(C_(10)H_8N_2O_4)_2(DMSO)_2(H_2O)_4]·2DMSO的合成、热分解及晶体结构

以2-羰基丙酸水杨酰腙(C_(10)H_(10)N_2O_4)作为配体与碳酸钙在水中反应， 在DMF(N,N'-二甲基甲酰胺)和DMSO（二甲基亚砚）的混合溶剂中培养了单晶，其组 成为 [Ca_2(C_(10)H_8N_2O_4)_2(DMSO)_2(H_2O)_4]·2DMSO [C_(10)H_8N_2O~2- _4为2-羰基丙酸水杨酰腙负离子]。测字了单晶的结构，该单晶为黄色，属单斜晶 系，空间群为P2(1)/C，晶胞参数a=1.0634(3)nm, b=1.7035(5)nm, c=1.2183(3) nm, β=106.180(5)°, V=2.1192(10)nm!, Dc=1.412Mg·m~(-3), Z=2, F(000) =944, μ=0.534m~(-1)，GOF=0.867。所测单晶是以2-卷曲在丙酸水杨酰腙羧基上 的一个氧原子作为桥联的双核钙（II）配合物，两个Ca~(2+)均处于五角双锥的七 配位环境中，锥底为配体2-羰基丙酸水杨酰腙中的三个配位原子，以及另一2-羰基 丙酸水杨酰腙羧基上的桥联氧原子和一个水分子的配位氧原子，锥顶为一配位水和 一想位的DMSO分子，即溶剂DMSO也参也了配位，从晶胞结构看，晶体中除配位的 DMSO分子外，还有自由的DMSO溶剂分子，它们与配位水以氢键连接存在于晶格之中 ，在空间形成的二维网状结构。通过TG-DTG还测定了配合物的热稳定性。     

P[(NH3)5CoimM(tren)](ClO4)4·2H2O[M=Cu(II), Zn(II)]的合成、表征及咪唑桥的断裂

本文合成了两个新的异双核咪唑桥联配合物[(NH3)5CoimM(tren)](ClO4)4·2H2O[M=Cu(II), Zn(II); im=咪唑基], 用热重差热、反射光谱、ESR等手段进行表征, 证实咪唑桥的存在, 用PH法结合计算机拟合, 定量地模拟了异双核配合物中咪唑桥的断裂过程, 表明在水溶液中, 金属-咪唑键首先从非钴(III)端断裂。