改性凹凸棒土-氧化石墨烯/环氧树脂复合材料的力学性能和热电性能

分别用硅烷偶联剂KH560改性凹凸棒土(Attapulgite，ATP)和氧化石墨烯(Graphene oxide，GO)，并将其复合制备ATP-GO复合物。以环氧树脂(Epoxy，EP)为基体，采用原位聚合法制备ATP-GO/EP复合材料。采用SEM和FTIR对ATP-GO复合物的形貌和化学结构进行表征。结果表明:ATP与GO成功键合并附着在GO表面；ATP-GO的加入，提高了EP的冲击强度、弯曲强度和热稳定性，降低了其介电常数和介电损耗。3wt%ATP-0.5wt%GO/EP复合材料的弯曲强度和冲击强度分别为138.58 MPa和20.80 kJ/m2，比纯EP分别提高了75.5%和351.6%，而其介电常数和介电损耗分别低至3.36和0.0118，比纯EP降低了7.7%和27.3%。      

Study on thermal and mechanical properties of nano-calcium carbonate/epoxy composites

A study on evaluating the effect of nano-CaCO₃ particles on thermal and mechanical properties of epoxy resin cast was performed by TGA and mechanical tests. A silane coupling agent KH550 as an interfacial modifier was introduced into nanocomposites through preparing KH550/nano-CaCO₃ master batch. It is revealed that epoxy resin cast filled with nano-CaCO₃ particles represents higher thermal stability and mechanical strength. The improvement of thermal and mechanical properties is attributed to the surface modification of nano-particles, which can enhance the interfacial properties between nano-CaCO₃ fillers and epoxy resin. The mechanical properties of nano-CaCO₃/epoxy/carbon fibres composites based on the modified epoxy matrix are also enhanced.     

Tensile and fracture properties of epoxy resin filled with flyash particles

The ultimate tensile strength, modulus of elasticity and fracture properties of epoxy resin filled with flyash particles have been evaluated by the tensile test. The tensile strength of epoxy resin filled with flyash particles decreases the fracture properties and the modulus of elasticity increases with increasing percentage of flyash. It is advisable to use flyash when the void formation cannot be controlled effectively.     

Tensile properties of fumed silica filled polydimethylsiloxane networks

Tensile properties of fumed silica filled hydroxylated polydimethylsiloxane (PDMS) networks were investigated in the current work. Similar to unfilled bimodal networks, unimodal networks filled with concentrated fumed silica exhibit non-Gaussian effect and improved ultimate tensile properties. The concept of “hierarchical network” was proposed to depict the networks exhibiting non-Gaussian effect at sufficiently high strains. It was found that the reinforcing effect originates from both the effective volume effect from filler volume and polymer–filler interaction and the synergistic effect between network chains within the “hierarchical network”. Experimental results showed that filler’s dispersion, concentration, specific surface area and surface chemistry have a great influence on the tensile properties, which could be interpreted by analyzing the variation of both effective volume effect and synergistic effect.     

Mechanical properties of epoxy composites filled with silane-functionalized graphene oxide

In this work, the effects of as-produced GO and silane functionalized GO (silane-f-GO) loading and silane functionalization on the mechanical properties of epoxy composites are investigated and compared. Such silane functionalization containing epoxy ended-groups is found to effectively improve the compatibility between the silane-f-GO and the epoxy matrix. Increased storage modulus, glass transition temperature, thermal stability, tensile and flexural properties and fracture toughness of epoxy composites filled with the silane-f-GO sheets are observed compared with those of the neat epoxy and GO/epoxy composites. These findings confirm the improved dispersion and interfacial interaction in the composites arising from covalent bonds between the silane-f-GO and the epoxy matrix. Moreover, several possible fracture mechanisms, i.e. crack pinning/deflection, crack bridging, and matrix plastic deformation initiated by the debonding/delamination of GO sheets, were identified and evaluated.     

Graphite nanoplatelets filled silicone composites with novel electrical and dielectric properties

In the design of medium and low voltage equipment such as cable accessories, generator, motor end windings or bushings, issues with electrical field enhancement occur at interfaces between insulators and conductors, resulting in accelerated material ageing. The purpose of this paper is to present a novel dielectric composite material which has the properties to mitigate this local amplification. It is a functional dielectric which resistivity decreases by several orders with electric field from 10¹⁴ to 10⁹ Ωm up to 1 kV?mm^?1 while the dielectric constant decreases from 15 to 12 in the 10^–2–10⁶ Hz range. This novel material is made with graphite nanoplatelets. It may be used as a resistive or capacitive field grading material in electrical applications.

     

Tensile properties of real unidirectional Kevlar/epoxy composites

Mechanical behaviour, tensile strength and failure modes in real unidirectional Kevlar/epoxy composites, loaded parallel to the fibres, at volume fraction (V_f) range 0.26–0.73, were investigated. It was found that the measured tensile strengths deviated from the expected values calculated from the Rule of Mixture. The deviation, which was minimal at V_f of about 0.5, was mainly due to geometrical deficiencies typical of real composites. At V_f<0.5 it could be explained by non-homogeneous fibre spread and distribution of fibres. At V_f>0.5 the deviation was explained by the increasing lack of matrix between some adjacent fibres and by squeezing of fibres. The initial part of loading was typified by straightening out of non-axial fibres, accompanied by fibre/matrix debonding. The straightening process was completed at a stress level of about 0.6–0.7 of the composite strength. Matrix damage began at this stress level and continued to develop up to final failure. Failure of Kevlar fibres was noted to occur only at an extremely short loading interval coinciding with the catastrophic final failure. This was due to the small scatter of Kevlar fibre strength.     

纳米碳酸钙的负触变机理探究

以纳米碳酸钙填充邻苯二甲酸二辛酯(DOP)糊为研究对象,通过改变纳米碳酸钙表面处理剂的质量分数,考察DOP糊流变特性,研究糊体系负触变结构的形成机理。结果表明:随表面处理剂质量分数的增加,纳米碳酸钙表面羟基密度降低,活化率增大,颗粒分散性得到改善;当碳酸钙未经表面处理或处理剂质量分数超过4.5%时,糊体系中网络结构更新比破坏快,从而表现出负触变性。     

Effect of uncoated calcium carbonate and stearic acid coated calcium carbonate on mechanical,thermal and structural properties of poly(butylene terephthalate) (PBT)/calcium carbonate composites

PBT/CaCO₃ composites were prepared in a single screw extruder with particle content varying from 0–30% by weight. The influence of surface treatment of the particles, with and without stearic acid (SA), on the mechanical, thermal and structural properties was studied. The experiments included tensile tests, impact tests, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy. The composite systems containing SA coated CaCO₃ were found to exhibit better mechanical properties as compared to composite systems containing uncoated CaCO₃, with the S3 system (20% of SA coated CaCO₃) exhibiting best combination of mechanical properties. Thermal study revealed that particle type and content had no influence on the melting temperature but the crystallization temperature, % crystallinity and thermal stability increased on increasing the CaCO₃ content in PBT matrix. Morphological observation indicated that in PBT composites containing SA coated CaCO₃, the coupling agent favours a better polymer filler interaction rendering inorganic polymer interface compatible, which is also evident from better mechanical and thermal properties.     

The electrical properties of epoxy resin composites filled with Cnts and carbon black

This work introduces an experimental activity related to the realization of an epossidic nanostructured material that develops the function of covering for electronic circuits in aeronautical field. This covering meets the demand of protection of these circuits from possible troubles of electromagnetic nature. In order to realize this covering we used an epoxy resin as matrix (Epon 828) loaded with conductive nanofillers or carbon nanotubes (Cnts). To check the efficiency of the coating we have considered the carbon black, filler widely used as a conductive covering for screenings. We have considered different percentages of the different fillers, precisely 0.1%, 0.25% and 0.5% wt (% valued in comparison to the weight of the resin). From every mixture 12 samples have been obtained (the size of every sample is 10 mm x 10 mm x 10 mm). Every sample has been subjected to electrical measurements, that have concerned the measurement of current intensity and resistance (so as to allow the evaluation of the enhancement of the conductivity), through the application of different values of voltage. The results have demonstrated that the epoxy matrix loaded with Cnts yields higher values of electrical conductivity than the same matrix loaded with carbon black.     

石墨烯纳米片/环氧树脂复合材料的制备与介电性能研究

以天然鳞片石墨为原料,通过Hummers法制备氧化石墨,微波热解剥离制备出少层数的石墨烯纳米片。以硅烷偶联剂KH-560为改性剂,超声共混制备石墨烯纳米片/环氧树脂复合材料。采用FT-IR和SEM分析样品的微观结构和形貌,测试其介电性能。结果表明,随着石墨烯纳米片添加量的增加,复合材料介电常数呈现先增大后减小的趋势,当石墨烯纳米片含量为0.3%(质量分数)时,介电常数达到最大;石墨烯纳米片对复合材料介电损耗的影响与之相反;偶联改性使复合材料的介电常数增大,介电损耗减小。     

The properties of epoxy resin coated silica fillers composites

Epoxy resin coated silica fillers composites with high percentage of filler loading, such as 80 to 95 vol.% are able to be produced by a mechanical mixing technique. The advantages of high filler loading of theses materials are noted from the thermal and flexural modulus. Apparently, the materials exhibit low coefficient of thermal expansion (CTE) at as low as or below 10 ppm/°C and high flexural modulus of above 20 GPa. In general, these promising characteristics fulfill the requirement to be used as substrate materials in electronic packaging applications.     

Electrical,mechanical and thermal properties of polyvinyl chloride composites filled with aluminum powder

In this work, the electrical, mechanical and thermal properties of polyvinyl chloride (PVC) composites filled with different content of aluminum powder varying from 0 to 40 wt.% have been prepared. The dielectric properties of these composites were investigated in the frequency range 100 Hz–100 kHz at temperature range from 30 to 98 °C. The percolation threshold concentration, which is the concentration after which the conductivity increases many orders of magnitude with very little increase in the filler content for PVC/Al composites depends upon the measuring temperature, whether it is below or above the glass transition of the polymer matrix. The highest value of the electrical conductivity, σ, of the composites was found to be in the order of 10⁻⁸ S cm⁻¹, this value recommend such composites to be used in electrostatic dissipation applications as the range of conductivity for such application should be in the range of 10⁻⁵–10⁻⁹ S cm⁻¹.     

Fabrication, thermal, and dielectric properties of self-passivated Al/epoxy nanocomposites

The current paper reports the effects of an epoxide-functionalized, silane surface-treated, self-passivated aluminum (Al) nanoparticles on the glass transition, morphology, thermal conductivity, dielectric properties of an epoxy composite. The surface modification of the Al nanoparticles improved the dispersion of the filler, as well as the glass transition temperature, thermal conductivity, and dielectric properties of the epoxy composites. The epoxy/Al nanocomposites showed a dielectric constant transition concentration. The dielectric constant and dissipation factor increased when the Al particle loading exceeded the critical content but gradually decreased with the frequency. The epoxy nanocomposites containing 15 % by weight Al nanoparticles have a high thermal conductivity and a high dielectric constant but a low dissipation factor. The enhancements in the thermal and dielectric properties of the epoxy nanocomposites show potential for future engineering applications.     

Preparation,damping and thermal properties of potassium titanate whiskers filled castor oil-based polyurethane/epoxy interpenetrating polymer network composites

A series of potassium titanate whiskers (PTW) filled castor oil-based polyurethane (PU)/epoxy resin (EP) interpenetrating polymer network (IPN) composites were prepared. The damping properties, thermal stability as well as tensile strength of the IPN composites were studied systematically in terms of composition. Results revealed that the addition of PTW can significantly improve the damping properties of pure PU/EP IPN and can improve the thermal decomposition temperature. Tensile tests showed that the tensile strength of the IPN composites was improved after the incorporation of PTW. It is expected that the PTW filled IPN composites may be used as structural damping materials.     

Crystallization and thermal properties of polyamide 6 composites filled with different nanofillers

The aim of this research is mainly to study the melting and crystallization behavior of polyamide 6 (PA6) when interacting with different nanofillers. The results show that the addition of nanofillers causes the increase of the peak temperature (T_p) during crystallization, which can be explained by the nucleation effect of the nanofiller. For PA6 and nanocomposites, the α crystal is the dominant crystalline phase. However, the γ form crystal appeared in PA6 containing montmorillonite (MMT) and SiO₂, while the crystallization did not appear in the composites with carbon nanotube (CNTs). For the PA6/CNTs nanocomposites, the length and surface properties of CNTs also had an effect on the crystallization of PA6. Although there are more -COOH groups on the surface of CNTs1^#, the crystallization degree of PA6/CNTs1^# is the lowest. The area of the melting peak of CNTs3^# is relatively large for a shorter size. The crystal-particle distribution is also varied for different dimensions of CNTs treated using three methods and the width of the melting peak of PA6/CNTs3^# is the largest.