Simulation of compositional profile in functionally graded materials

The development of a polymer based functionally graded material (FGM) of desired composition profile by the centrifugation technique requires control on centrifugation, size, shape, and concentration of suspended particles, time, viscosity variation of polymerizing fluid, etc. A simulation was conducted to observe the compositional variations with time at different places of FGM, using a modified terminal velocity equation for particle movement in polymerizing fluid. It was further modified for the particles having different sizes. The simulation demonstrated two graded‐composition profiles each one in low concentration region from where particles were moved to the other part of sample and second high concentration profile in which particles entered to increase the concentration. The third region situated between the two composition profiles was observed as that of uniform distribution of particles and the length of this region can be controlled by adjusting the size of the centrifuged sample. The simulation was compared with the experimental results of FGM having SiC particles in polysulphide epoxy resin. POLYM. ENG. SCI. 46:1660–1666, 2006. © 2006 Society of Plastics Engineers     

Concentration profile of glass fiber bundles in epoxy‐based gradient composites during centrifugation

The short fiber bundles separated from the machining waste of a printed circuit board (PCB) manufacturing plant were used in preparing functionally graded composites using polysulfide‐modified epoxy resin. The graded material was developed using centrifugation technique. The centrifugation time was varied to obtain different gradient profiles. The concentration profile was then compared with the theoretical HD model (Hashmi‐Dwivedi model), which was modified to accommodate the changes in the shape of suspending particles. A shape factor was introduced in terminal velocity estimation. The simulated results are in agreement with the experimental trends. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The effect of long-term ultraviolet light irradiation on polymer matrix composites

This study reports the individual and combined effects of ultraviolet light and thermal shock on the physical properties of polymer matrix composites in air and in a “near-vacuum system.” The longest exposure time was 180 days. It was found that the weight loss of composites increased with irradiation time. In the graphite/epoxy system, the weight loss in air was 2–3 times that in a “near-vacuum system.” Similarly, the weight loss of the glass/epoxy system in air was 3–6 times that in a “near-vacuum system.” The weight loss of the glass/epoxy system was always larger than that of the graphite/epoxy system. In all cases, the UV irradiation and 1000 times thermal shock did not change the fracture mechanism—it was always brittle fracture in addition to fiber pullout. Surface erosion was observed in the irradiated surfaces by scanning electron microscopy. For both graphite/epoxy and glass/epoxy composites, the tensile strength decreased with increasing irradiation time irrespective of the irradiation environment. However, the decrease was not significant. By SEM, cracks could be observed in the up-surface and side-surface of the glass/epoxy system that was irradiated more than 1 month in air and through 1000 times thermal shock. Obviously, UV light cannot deeply penetrate the sample, and only the surface of the sample will be influenced. The UV radiation initiated microcracks, which propagated through the thermal shock.     

Three‐body abrasive wear behavior of E‐glass fabric reinforced/graphite‐filled epoxy composites

The present article summarizes an experimental study on three‐body abrasive wear behavior of glass fabric reinforced/graphite particulate‐filled epoxy composites. The wear behavior was assessed by rubber wheel abrasion tests (RWAT). The angular silica sand particle sizes in the range 200–250 μm were used as dry and loose abrasives. The tests were carried out for 270, 540, 810, and 1,080 m abrading distances at 22 and 32 N loads. The worn surfaces were examined using scanning electron microscopy (SEM). The results showed varied responses under different abrading distance due to the addition of glass fabric/graphite filler into neat epoxy. It was observed that the glass fabric reinforcement to epoxy matrix (G‐E) is not beneficial to abrasive wear resistance. Further, inclusion of graphite filler to glass fabric reinforced epoxy composite performed poorly resulting in significant deterioration in wear performance while the neat epoxy showed better wear performance. Selected mechanical properties such as hardness, ultimate tensile strength, and elongation at fracture were analyzed for investigating wear property correlations. The worn surface features were studied using SEM to give insight into the wear mechanisms. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Performance of expanded graphite and expanded milled‐graphite fillers in thermosetting resins

Epoxy/expanded graphite (EG) and polyester/EG composites were prepared with the aid of sonication, while epoxy/expanded‐milled graphite (epoxy/milled‐EG) and polyester/expanded‐milled graphite (polyester/milled‐EG) composites were prepared on a three‐roll paint mill. The epoxy/EG and polyester/EG composites exhibit a sharp insulator/semiconductor transition at markedly low percolation thresholds, due to the vermicular shape of EG having high aspect ratio and surface area. The morphologies of epoxy and polyester resins incorporated with EG and milled‐EG fillers were observed by scanning electron microscopy (SEM). The results of dynamic mechanical analysis of the composites reveal that both EG and milled‐EG fillers increase the T_g of the epoxy matrix. Milled‐EG increases the G′ of the epoxy matrix, while EG decreases the G′ of the epoxy matrix, due to the existence of abundant pores in EG. The milled‐EG filler has the same effect on the polyester matrix as on the epoxy matrix, but the EG filler has no significant effect on the mechanical properties of polyester matrix. POLYM. COMPOS., 26:526–533, 2005. © 2005 Society of Plastics Engineers     

离心法制备环氧树脂／碳纤维梯度功能材料——结构与耐磨性

梯度功能材料（functionally gradient materials,简称FGM）,又常称倾斜功能材料,严格地说应称为”梯度功能复合材料”,本文扼要介绍了用离心法制得的环氧树脂／短碳纤维梯度功能材料的结构及耐磨性能。     

抗静电耐磨涂层的制备及性能研究

采用低黏度环氧树脂为胶粘剂,以石墨、硫酸钡、炭黑为填料,制备了抗静电耐磨涂层,考查了填料的含量及种类对涂层的磨耗性能、导电性能的影响。结果表明,石墨和硫酸钡具有良好的协同减磨作用,配合使用可以有效地减少磨损量,改善耐磨性;复合涂层的导电性能受到填料种类的影响,采用石墨-硫酸钡-炭黑填料的复合涂层具有更优的导电性能,该涂层可用于复合材料托辊的制造.     

Thermal conductive composites based on silver‐plating graphite nanosheet and epoxy polymer

Silver plating graphite nanosheet (Ag‐NanoG) prepared by electroless plating method with expanded graphite as starting material is an effective approach to increase thermal conductivity of the filler. Herein, a novel thermal conductive composite was prepared by using Ag‐NanoG as thermal conductive filler and epoxy resin as the polymer matrix. The microstructures of NanoG and Ag‐NanoG were characterized by means of scanning electron microscopy, X‐ray powder diffraction and then the thermal conductivity, impact strength, and thermal stability of the composite were investigated. The results showed that the Ag‐NanoG was successfully obtained and it can be homogeneously dispersed in the epoxy resin. The thermal conductivity of composite increased from 0.328 to 1.847 W/m K with 4 wt% Ag‐NanoG filler content. Moreover, the composite exhibited excellent thermal stability and mechanical property. POLYM. COMPOS., 38:2822–2828, 2017. © 2015 Society of Plastics Engineers     

Tribological and electrical properties of silica‐filled epoxy nanocomposites

The tribological and electrical properties of epoxy composites filled with nano‐sized silica particles are studied and discussed in this article. To enhance the interfacial interaction between the fillers and the matrix, nanoparticles were pretreated with silane coupling agent. Dry sliding wear tests were carried out with configuration of composite sample on a rotating steel disc. Electrical measurements such as AC breakdown voltage, at 50 Hz, high voltage‐low current arc resistance and wet tracking resistance were carried out. The results reveal the influence of nanosized silica loading on wear resistance of the epoxy. It is observed that 10 wt% loading of silica is very effective in reducing the wear loss. With further increase of silica filler loading, the nanoparticles agglomerated and resulted in increase of the specific wear rate. The influence of silica particles on the specific wear rate is more pronounced under sliding wear situation. The influence of silica particle loading on epoxy is evident in the results of electrical parameters like dielectric strength, arc resistance and tracking resistance. These parameters showed improvement with filler loading up to 15 wt% and beyond this value of filler loading noticeable deterioration was observed. The effects of electrical stresses in the morphologies of the surfaces of epoxy nanocomposites are discussed. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Electromagnetic wave shielding and microwave absorbing properties of hybrid epoxy resin/foliated graphite nanocomposites

The aim of this study is to prepare and characterize foliated graphite nanosheets (FGNs) reinforced composites based on epoxy resin for the electromagnetic wave shielding and microwave absorbing applications. The microstructure of as prepared FGNs and epoxy reinforced with different content of foliated graphite was examined by means of scanning electron microscopy and transmission electron microscopy. The effect of FGNs on thermal stability of composites was examined by thermal gravimetric. It is found that the inclusion of FGNs into the epoxy resin matrix enhances the microstructure core of epoxy resin composites. Static electric properties such as electrical conductivity, carrier mobility, number of charge carriers, and thermoelectric power of composites were studied in details. Dielectric properties of epoxy/FGN composites were characterized as a function of composition and frequency in the range of 1–18 GHz. The electromagnetic wave shielding as a function of frequency of composites was examined and compared with theoretical values. The highest shielding effectiveness was obtained for high foliated graphite loading sample FG40 at frequency of 18 GHz it equals to 62 dB. Finally, the electromagnetic wave properties such as absorption loss and reflection loss as a function of frequency were investigated. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Development of functionally graded vapor‐grown carbon‐fiber/polymer materials

We successfully produced vapor‐grown carbon‐fiber (VGCF)‐incorporated polymer‐based functionally graded materials (FGMs) using a centrifugal method. Gradual VGCF incorporation within an epoxy resin effectively produced depth gradients in the fiber distribution, microstructure, mechanical, and electrical conductivities and microwave absorbing properties. This VGCF‐grading capability indicated that it is possible to tailor desired gradient filler content distributions by careful selection of the processing parameters to control variations in the property and microstructure precisely. The results confirmed that the volume content of VGCF in the epoxy substrate increased as a function of the normalized thickness along the centrifugal force direction, which caused a gradient. A uniform VGCF gradient in the composite can also be observed using field‐emission scanning electron microscopy. In the case of the electrical properties, for example, the volume resistance exhibited a depth‐graded distribution in the matrix as the electrical conductivity of the FGM nicely followed the grading direction; this is considered to be ideal for applications demanding an electrically conductive surface and an insulating core for FGMs. The results of microwave absorption behavior of FGMs indicate that the grading structure can lead to a graded absorption ability, which could be a better design for microwave absorption materials. The concept of FGMs bridges conventional materials and nanocomposites and will be effective for wider material applications. POLYM. COMPOS., 34:1774–1781, 2013. © 2013 Society of Plastics Engineers     

环氧树脂基复合涂层摩擦磨损性能研究

研究了不同质量分数石墨、碳纤维、纳米ZrO2对环氧树脂(EP)涂层摩擦磨损性能的影响,并用扫描电子显微镜观察了涂层磨损表面形貌并探讨了磨损机理。结果表明:石墨质量分数为20%时复合涂层的磨损率仅为纯EP的7.75%;纳米ZrO2质量分数为4%时复合涂层的磨损率为纯EP的30%;纳米ZrO2与碳纤维以及石墨的协同作用提高了EP的摩擦磨损性能。EP复合涂层的磨损机理以粘着磨损、磨粒磨损以及疲劳磨损为主。     

Structure and mechanical properties of composites with diamond particles dispersed into modified epoxy matrix

The structure and properties of epoxy matrix composites embedded with up to 30 wt.% of diamond particles were investigated by means of thermal analysis, mechanical testing and scanning electron microscopy, SEM. In particular, the effect of matrix deformability on the composite performance was evaluated by changing the epoxy monomer to hardener ratio. The results showed that the dynamic mechanical parameters improved with the amount of diamond particles and are markedly affected by modifications in the epoxy matrix. By contrast, the quasi-static mechanical properties decrease with the amount of diamond, which could be explained by SEM analysis. This behavior was attributed to the development of a weak diamond/epoxy interface and corroborated by the analysis of the fracture surfaces as well as the variation of the dynamic mechanical parameters for the investigated conditions.     

凹凸棒土/石墨复合材料电极的制备及性质

以酸化处理的凹凸棒土粉和膨胀处理的石墨粉为原料、环氧树脂为粘合剂,制得凹凸棒土/石墨复合材料电极。采用扫描电镜、红外光谱等对其形貌和结构进行表征。探讨了电极材料类型、富集时间、平行测定次数对模拟苯酚废水峰电流的影响。研究结果表明,凹凸棒土/石墨复合材料电极比普通石墨电极对峰电流的响应更明显,且稳定性好,无二次污染。     

Influence of Submicron TiO2 Particles on the Mechanical Properties and Fracture Characteristics of Cured Epoxy Resin

Submicron titanium dioxide (TiO₂) was used in different weight fractions as a toughening agent for amine-cured epoxy resin. After the use of X-ray photoelectron spectroscopy (XPS), which confirmed that the TiO₂ particles were evenly distributed in the cross-linked epoxy resin matrix, the composites were characterized by tensile and impact testing, followed by scanning electron microscopy of the fracture surfaces. The results indicated that the submicron TiO₂ toughening particles markedly improved the mechanical properties of the cured epoxy resin compared to the untoughened epoxy resin. The optimal properties were achieved at a TiO₂ concentration of 4 wt. %, at which point the toughness and the impact resistance values increased by 65% and 60%, respectively. The results also indicated that an increase in the amount of TiO₂ causes a decrease in toughness. Stress whitening, out-of-plane flaking, and thumbnail markings were the major visible features of the toughening mechanisms.

It is suggested that, at 4 wt. % of the submicron TiO₂ particles, microvoids are developed in the epoxy matrix. These microvoids are able to absorb some of the deformation work applied to the material, and thus enhance the toughness of the material. On increasing the TiO₂ content in the matrix (> 4 wt. %), the submicron particles got closer to each other and the microvoids were converted to macrovoids, which may act as stress concentrating flaws, leading to the deterioration of the mechanical properties of the epoxy resin.     

玻璃纤维及石墨增强聚四氟乙烯复合材料摩擦磨损性能的研究

用机械混合、冷压成型和烧结的方法制备了不同质量分数(5%~30%)的玻纤和石墨填充聚四氟乙烯(PTFE)复合材料制品。用M-2000型磨损试验机评价了不同样品在干摩擦下的磨损性能,揭示了填料玻纤和石墨对PTFE复合材料磨损性能的影响,并对磨损机理进行了探讨。用扫描电镜(SEM)对试样磨损形貌进行观察。结果表明:对玻纤进行改性能极大地提高PTFE复合材料的耐磨性能,同时可提高复合材料硬度;玻纤和石墨协同作用,对改善PTFE摩擦磨损性能有比较显著的效果;20%玻纤 10%石墨填充PTFE复合材料有着较好的摩擦磨损性能。     

环氧树脂/镀银纳米石墨微片导热复合材料的制备与性能

以膨胀石墨为原料,采用超声分散法和化学镀法制得镀银纳米石墨微片,然后将其填充在环氧树脂基体中制备环氧树脂/镀银纳米石墨微片复合材料。结果表明,银粒子均匀镀覆在纳米石墨微片上,银层厚度为100 nm,有利于在环氧树脂基体中形成导热通路;与环氧树脂相比,环氧树脂/镀银纳米石墨微片复合材料的力学性能和热导率能都得到提高;当镀银纳米石墨微片含量为3 %时,复合材料的热导率为1.827 W/(m·K),比纯环氧树脂热导率提高了近5倍。     

Attaining a controlled graded distribution of particles in polymerizing fluid for functionally graded materials

The precise control on concentration profile of dispersion in functionally graded material (FGM) is essential for obtaining a desired material. A suitable simulation of parameters and an appropriate model that describes the motion of particles in the fluid can predict various aspects those are needed to produce FGM, by gravity sedimentation or centrifugation technique. Simulation was conducted to observe the changes in concentration profile, while using the following equations applicable to polymerizing fluid, and to determine the terminal velocities (V_m) of particles; V_m = {D²(ρ_s ? ρ_l)g*(1 ? ?_s)^4.65}/(18μ₀e) for gravity sedimentation and V_m = {D²(ρ_s ? ρ_l)rω²(1 ? ?_s)^4.65}/(18μ₀ e) for centrifugation, where D is the diameter of the spherical particle, ρ_s the density of solid particles, ρ_l the density of fluid, μ the viscosity of fluid, g* the acceleration due to gravity, ?_s is the volume fraction of particles, and t_c is the elapsed time of curing of thermosetting resin. b is a constant, r is the radius, and ω is the angular velocity. This simulation demonstrates that the time of centrifugation/sedimentation, particle size, distribution of particle size, and centrifugal/gravitational forces can be effectively utilized to attain a desired concentration profile in graded materials. Simulation also revealed that there exist the possibility of two graded profiles, namely low concentration profile and high concentration profile, in one sample of graded material, made either by centrifugation or sedimentation. Low concentration profile is more sensitive to particle size distribution as compared to high concentration profile. The present simulation method is also sensitive to concentration‐measuring methods. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Self-sacrificial templating synthesis of flower-like nickel phyllosilicates and its application as high-performance reinforcements in epoxy nanocomposites

The nanocomposites of flower-like nickel phyllosilicate particles incorporated into epoxy resin were fabricated via an in-situ mixing process. The flower-like nickel phyllosilicate particles were firstly synthesized using a mild self-sacrificial templating method, and the morphology and lamellar structure were examined carefully. Several properties of mechanical, thermal and tribological responses of epoxy nanocomposites were performed. It was demonstrated that adequate flower-like nickel phyllosilicate particles dispersed well in the matrix, and the nanocomposites displayed enhanced tensile strength and elastic modulus but decreased elongation at break as expected. In addition, friction coefficient and wear rate were increased first and then decreased along with the particle content, and showed the lowest values at a mass fraction of 5%. Nevertheless, the incorporated flower-like nickel phyllosilicate particles resulted in the continuously increasing thermal stability of epoxy resin (EP) nanocomposites. This study revealed the giant potential of flower-like particles in preparing high-quality EP nanocomposites.     

SiAlON–epoxy nanocomposite coatings: Corrosion and wear behavior

In this study, epoxy powder as a matrix was combined with different contents of silicon–aluminum–oxygen–nitrogen (SiAlON) nanoparticles using a planetary ball mill. Pure epoxy and nanocomposite powders were applied on the surface of plain carbon steel components by the electrostatic spraying method. Curing of the coatings was done in an oven or microwave for the appropriate time. The coating structure and morphology of the SiAlON nanoparticles were studied by scanning electron microscopy and transmission electron microscopy, respectively. The corrosion properties of the coatings were assessed by immersion, Tafel polarization, and electrochemical impedance spectroscopy tests in 3.5% NaCl solution. The results show that addition of 10 wt % SiAlON nanoparticles markedly increases the corrosion resistance of epoxy coatings. Thus, it can be inferred that the corrosion rate of these coatings is 15 to 18 times lower than that of pure epoxy samples and 8 to 11 times lower than coatings with 20 wt % SiAlON. The higher corrosion resistance of nanocomposite coatings can be attributed to the barrier properties of SiAlON nanoparticles. The tribological performance of the coatings was studied with the pin‐on‐disk test. The results of wear testing show that the samples containing 10 wt % SiAlON provide about five times more wear resistance than pure ones and about two times more than coatings with 20 wt % SiAlON. However, the coefficient of friction for nanocomposite coatings is reduced about 50% compared to the pure sample. Also, the curing process in either regime (oven or microwave) has the same effect on the corrosion and wear properties, and the coatings are completely crosslinked. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43855.