On depression of glass transition temperature of epoxy nanocomposites

Epoxy composite materials filled with nano-alumina particles were prepared by mechanical mixing techniques. The glass transition temperatures (T _g) of the nanocomposites were found to decline significantly with the increasing filler content. After the addition of 30-phr nanoparticles, the T _g of the filled sample decreased by as high as 55 °C, as compared with that of the neat epoxy polymer. Based on the selective adsorption hypothesis and the molecular diffusion, it is speculated that the hardener molecules were unevenly distributed in the nanocomposites, which caused imbalanced stoichiometry between the epoxy and the hardener and finally decreased the T _g. Some results that may support the adsorption hypothesis were given and discussed.     

丁苯胶/甲基丙烯酸锌/气相法白炭黑纳米复合材料

制备了三相纳米复合材料SBR／ZDMA／气相法白炭黑。采用了两种气相法白炭黑,U—fumed silica是一种未改性的气相法白炭黑,M—fumed silica是一种采用硅烷偶联剂Si69表面改性的气相法白炭黑。主要研究了气相法白炭黑和ZDMA之间的协同补强效应。研究结果显示,单独添加同样份数的改性气相法白炭黑和未改性气相法白炭黑对硫化胶物理机械性能的影响不同,改性气相法白炭黑的效果明显优于未改性气相法白炭黑。单独添加气相法白炭黑,体系的物理机械性能仍然维持在较低值。当同时添加气相法白炭黑和ZDMA时,会观察到明显的协同补强效应。交联密度和丙酮抽出试验表明对气相法白炭黑进行表面改性和在体系中添加ZDMA均会减弱气相法白炭黑表面羟基的影响。扫描电镜显示改性后气相法白炭黑在SBR中的分散性得到提高。在体系中添加ZDMA会提高气相法白炭黑的分散性。     

Dynamic mechanical analysis of fumed silica/cyanate ester nanocomposites

Fumed silica particles with average primary particle diameters of 12 and 40 nm were combined with a low viscosity bisphenol E cyanate ester resin to form composite materials with enhanced storage modulus and reduced damping behavior, as evidenced by dynamic mechanical analysis (DMA). The storage modulus increased with volume fraction of fumed silica in both the glassy and rubbery regions, but the increase was more pronounced in the rubbery region. The maximum increase in storage modulus in the glassy region was 75% for 20.7 vol% of 40 nm fumed silica, while the same composition showed a 231% increase in the rubbery storage modulus. Furthermore, decreases in damping behavior were used to estimate the effective polymer-particle interphase thickness. The glass transition temperature of the nanocomposites was not changed significantly with increasing volume fraction.     

Preparation and characterization of epoxy nanocomposites by using PEO-grafted silica particles as modifier

EP/SiO₂ nanocomposites, which contained PEO flexible chain, have been prepared via epoxy resin and PEO-grafted silica particles. The PEO-silica particles were obtained by endcapping PEO-1000 with toluene 2,4-diisocyanate (TDI), followed by a reaction with silica sols. The chemical structure of the products was confirmed by IR measurements, and the mechanical properties of composites such as impact strength, flexural strength, dynamic mechanical thermal properties were investigated. The results showed that the addition of the PEO-grafted silica particles to the epoxy/DDS curing system, the impact strength is 2 times higher than that of the neat epoxy. While the storage modulus and the glass transition temperature are a little changed. The morphological structure of impact fracture surface and the surface of the hybrid materials were observed by scanning electron microscope (SEM) and atomic force microscopy (AFM), respectively.     

环氧树脂/二氧化硅杂化材料的制备与性能表征

溶胶-凝胶法制备环氧树脂/SiO2杂化材料,利用FTIR、SEM和综合热分析仪对杂化材料的结构、显微形态及热性能进行了表征.结果表明,杂化材料中SiO2与环氧树脂两相间存在氢键作用;SiO2质量分数＜7%时SiO2与环氧树脂之间无明显相界面,可获得有机聚合物链段与无机网络互穿的有机/无机杂化材料;SiO2质量分数为11%时材料具有最佳耐热性能.     

Self-assembled natural rubber/silica nanocomposites: Its preparation and characterization

A novel natural rubber/silica (NR/SiO₂) nanocomposite is developed by combining self-assembly and latex-compounding techniques. The results show that the SiO₂ nanoparticles are homogenously distributed throughout NR matrix as nano-clusters with an average size ranged from 60 to 150 nm when the SiO₂ loading is less than 6.5 wt%. At low SiO₂ contents (4.0 wt%), the NR latex (NRL) and SiO₂ particles are assembled as a core-shell structure by employing poly (diallyldimethylammonium chloride) (PDDA) as an inter-medium, and only primary aggregations of SiO₂ are observed. When more SiO₂ is loaded, secondary aggregations of SiO₂ nanoparticles are gradually generated, and the size of SiO₂ cluster dramatically increases. The thermal/thermooxidative resistance and mechanical properties of NR/SiO₂ nanocomposites are compared to the NR host. The nanocomposites, particularly when the SiO₂ nanoparticles are uniformly dispersed, possess significantly enhanced thermal resistance and mechanical properties, which are strongly depended on the morphology of nanocomposites. The NR/SiO₂ has great potential to manufacture medical protective products with high performances.     

Organoclay effect on transverse compressive strength of glass/epoxy nanocomposites

This research focuses on the fabrication of glass fiber/epoxy nanocomposites containing organoclay as well as understanding the organoclay effect on the transverse compressive strength of nanocomposites. To demonstrate the organoclay effect, three different loadings of organoclay were dispersed, respectively, in the epoxy resin using a mechanical mixer followed by sonication. The corresponding glass/epoxy nanocomposites were produced by impregnating dry glass fiber with organoclay epoxy compound through a vacuum hand lay-up procedure. Unidirectional block specimens were employed for transverse compression tests on a hydraulic MTS machine. Experimental observations indicate that glass/epoxy nanocomposites containing organoclay exhibit higher transverse compressive strength than conventional composites. Furthermore, the failure mechanisms for all tested specimens were found to be fiber and matrix debonding. Therefore, results indicate that the increasing characteristic in transverse failure stress may be ascribed to the enhanced fiber/matrix adhesion modified by the organoclay.     

Storage modulus and glass transition behaviour of CdS/PMMA nanocomposites

The storage modulus and glass transition temperature (T _g) of CdS/PMMA nanocomposites have been evaluated as a function of concentration of CdS nanoparticles. CdS particles have been synthesised via chemical route using cadmium acetate, thiourea and dimethylformamide. The solution-based processing has been used to prepare PMMA composites with CdS nanoparticles at different filler concentration. Size and shape of CdS nanoparticles in PMMA have been determined with the help of small angle X-ray scattering and transmission electron microscope measurements. Dynamical mechanical analysis was carried out on the CdS/PMMA nanocomposites to study storage modulus and tan?δ. It is observed that CdS nanoparticles enhance the storage modulus and T _g for composites. The storage modulus and T _g show the maximum value of 6?wt.% of CdS nanoparticles embedded PMMA composite. The results indicate that the 6?wt.% of CdS nanoparticles in PMMA matrix provides more stability to the composite over the other composites.     

Microstructure of low temperature processed CNFs/glass nanocomposites

Carbon nanofibers/glass (CNF/G) nanocomposites were obtained from a glass powder of low melting point and pristine CNFs. Green bodies containing from 0 to 22 % (v/v) of CNFs were sintered under nitrogen atmosphere in the 550–700 °C temperature range with different holding times. A fully microstructure characterization, by means of Hg porosimetry and N₂ adsorption, was carried out for understanding the CNFs/G composites behavior during the sintering process. This understanding is required to optimize the microstructural design of CNFs/glass nanocomposite materials. During sintering two different and simultaneous phenomena occur the matrix crystallization and the pore formation. The glass matrix crystallization temperature decreases from 650 to 550 °C, when CNFs concentration increases to 22 % (v/v). The glass matrix produces the CNFs degradation and generates gaseous species which lead to homogeneous or foamy materials. This depends on the CNFs concentration and thermal treatment conditions. Foamy nanocomposites present pore size distributions with pores <0.1 and close to 20 μm. The glass matrix wets the CNFs and produce their degradation been of 1 % of carbon loss in all nanocomposites.     

Strength of unidirectional glass/epoxy composite with silica nanoparticle-enhanced matrix

A technique was developed to improve the strength of unidirectional composites by enhancing the matrix properties through nanoparticles infusion. A commercially available standard DGEBA epoxy with silica nanoparticles (Nanopox F 400) was used as the matrix to make fiber composites. The silica nanoparticles in Nanopox were grown in situ via a sol–gel process resulting in a concentration of 40 wt% which was later diluted to 15 wt% particle loading. TEM images showed very uniform dispersion of silica nanoparticles with a size distribution of about 20 nm. Compression test revealed a substantial improvement (40%) in elastic modulus of the modified epoxy. A modified vacuum assisted resin transfer molding process was used to fabricate unidirectional E-glass fiber reinforced silica/epoxy nanocomposites. Inclusion of silica nanoparticles dramatically increased the longitudinal compressive strength and moderately increased the longitudinal and transverse tensile strengths. A microbuckling model was used to verify the compression testing results.     

Mechanical characterization of graphite/epoxy nanocomposites by multi-scale analysis

Mechanical properties of nanocomposites consisting of epoxy matrix reinforced with randomly oriented graphite platelets were studied by the Mori–Tanaka approach in conjunction with molecular mechanics. Elastic constants of graphite nanoplatelets, which are the inclusion phase in the micromechanical model, were calculated based on their molecular force field. The calculated elastic constants compared well with both experimental data and other published theoretical predictions. The results of the Mori–Tanaka micromechanical analysis, using the graphite platelet moduli calculated by molecular mechanics, were found to be insensitive to the variation of out-of-plane modulus E₃ and Poisson’s ratio ν₁₃. However, the nanocomposite modulus is sensitive to the in-plane modulus E₁ and out-of-plane shear modulus G₁₃ of the graphite platelets and less sensitive to the in-plane Poisson’s ratio ν₁₂ for its small range of variation under consideration. The calculations confirm that the modulus of the nanocomposites studied here is strongly dependent on the aspect ratio of the reinforcing particles, but not on their size. The predicted moduli compare favorably with experimental results of several nanocomposites with graphite particles of various aspect ratios and sizes.     

Semiconductor/porous silica glass nanocomposites via the single-source precursor approach

The utilization of single-source molecular precursor approach to obtain II–VI and IV–VI semiconductors encapsulated in porous Vycor glass (PVG) is described. The procedure is based on the impregnation of cadmium and lead(II) diethyl-dithiocarbamate complexes, Cd(S₂CNEt₂)₂ and Pb(S₂CNEt₂)₂, inside the porous environment of PVG followed by a thermal treatment of the glass. The pyrolysis of the impregnated precursor gives rise to binary semiconductors CdS and PbS, respectively. The impregnation step is driven by interactions between the precursors and active sites located at glass pore surfaces. After completing the impregnation–decomposition cycle, it was found that the active glass sites were regenerated, making new cycles possible. The amount of encapsulated semiconductor increases linearly as a function of the number of cycles. Nanocomposites obtained after 1–10 cycles were prepared and characterized by optical spectroscopy, X-ray diffraction powder and transmission electron microscopy.     

Tensile fracture and thermal conductivity characterization of toughened epoxy/CNT nanocomposites

Rubber toughened epoxy/CNT nanocomposites were manufactured at different weight percents between 0 and 1% of multiwall carbon nanotube (MWNT) using a high intensity ultrasonic liquid processor with a titanium probe. Mechanical properties of manufactured dog bone samples were measured in tension and the results indicated a maximum of 23% increase in the elastic modulus at 0.6% by weight of MWNT. However, the fracture strength showed a maximum decrease of about 11% as a function of increasing MWNT loading. Scanning Electron Microscopy (SEM) images from the neat samples revealed a distinct circular pit at the top left edge of the specimen with an overall tearing deformation causing the fracture paths. Comparatively, all nanocomposite samples on an average seemed to show a prominent brittle fracture with little or no evidence of circular pit formation. The amount of tearing deformation seemed to be enhanced in the nanocomposite specimens as compare to the neat ones. Finally, Transmission Electron Microscopy images indicated that different states of dispersion exist in all of the nanocomposite samples. The data showed that agglomeration of nanotubes increases as a function of weight percent. In addition to mechanical property characterization, thermal conductivity of all the samples was determined as a function of temperature between 30 °C and 100 °C using the 3ω method. The tested samples showed an almost 16% increase in thermal conductivity. The minimal enhancement in thermal conductivity has been analyzed from the standpoint of the Effective Medium Theory. Interfacial thermal resistances exhibit no order of magnitude changes explaining the conductivity results.     

Mechanical and thermal behavior of non-crimp glass fiber reinforced layered clay/epoxy nanocomposites

Mechanical and thermal properties of non-crimp glass fiber reinforced clay/epoxy nanocomposites were investigated. Clay/epoxy nanocomposite systems were prepared to use as the matrix material for composite laminates. X-ray diffraction results obtained from natural and modified clays indicated that intergallery spacing of the layered clay increases with surface treatment. Tensile tests indicated that clay loading has minor effect on the tensile properties. Flexural properties of laminates were improved by clay addition due to the improved interface between glass fibers and epoxy. Differential scanning calorimetry (DSC) results showed that the modified clay particles affected the glass transition temperatures (T_g) of the nanocomposites. Incorporation of surface treated clay particles increased the dynamic mechanical properties of nanocomposite laminates. It was found that the flame resistance of composites was improved significantly by clay addition into the epoxy matrix.     

High thermal and mechanical properties enhancement obtained in highly filled polybenzoxazine nanocomposites with fumed silica

Highly filled polybenzoxazine nanocomposites filled with nano-SiO₂ particles were investigated for their mechanical and thermal properties as a function of filler loading. The nanocomposites were prepared by high shear mixing followed by compression molding. A very low A-stage viscosity of benzoxazine monomer gives it excellent processability having maximum nano-SiO₂ loading as high as 30 wt% (18.8 vol%) with negligible void content. Moreover, thermal analysis of the curing process of the compound of the PBA-a/nano-SiO₂ composites was found to be autocatalytic in nature with average activation energy of 79–92 kJ mol⁻¹. Microscopic analysis (SEM) performed on the PBA-a/nano-SiO₂ composite fracture surface indicated a nearly homogeneous distribution of the nano-scaled silica in the polybenzoxazine matrix. In addition, the enhancement in storage modulus of the nano-SiO₂ filled polybenzoxazine composites was found to be significantly higher than that of the recently reported nano-SiO₂ filled epoxy composites. The dependence of the nanocomposites’ modulus on the nano-SiO₂ particles content is well fitted by the generalized Kerner equation. Furthermore, the relatively high micro-hardness of the PBA-a/nano-SiO₂ composites up to about 600 MPa was achieved. Finally, the substantial enhancement in the glass transition temperature (T_g) of the PBA-a/nano-SiO₂ composites was also observed with the ΔT_g up to 16 °C at the nano-SiO₂ loading of 30 wt%. The resulting PBA-a/nano-SiO₂ composite is a highly attractive candidate as coating material in electronic packaging or other related applications.     

The effect of alternate heating rates during cure on the structure-property relationships of epoxy/MMT clay nanocomposites

This paper investigates the effect of both the mixing technique and heating rate during cure on the dispersion of montmorillonite (MMT) clay in an epoxy resin. The combination of sonication and using a 10 °C/min heating rate during cure was found to facilitate the dispersion of nanoclay in epoxy resin. These processing conditions provided a synergistic effect, making it possible for polymer chains to penetrate in-between clay galleries and detach platelets from their agglomerates. As the degree of dispersion was enhanced, the flexural modulus and strength properties were found to decrease by 15% and 40%, respectively. This is thought to be due to individual platelets fracturing in the nanocomposite. Complementary techniques including X-ray diffraction (XRD), small angle X-ray scattering (SAXS), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM) and optical microscopy were essential to fully characterise localised and spatial regions of the clay morphologies.     

聚吡咯衍生物-过渡金属氧化物纳米复合材料的制备与表征

以水作为溶剂,将水溶性吡咯衍生物单体(碘化N,N,N-三甲基-(2-吡咯-1-乙基))与V2O5溶胶混合,进行原位插层聚合反应,合成PTPAI/V2O5插层纳米复合材料.采用XRD,FT-IR和SEM对其结构和形貌进行了分析.聚(N,N,N-三甲基-(2-吡咯-1-乙基)/V2O5的doo1面间距从10.7739nm增大到13.5436nm,表明聚吡咯衍生物已插入V2O5干凝胶的层间,其FT-IR光谱说明聚吡咯与V2O5层存在着较强的相互关系,SEM图谱揭示了聚(N,N,N-三甲基-(2-吡咯-1-乙基)在V2O5层间附着的形貌特征.