Effect of coupling agents on thermal and electrical properties of mica/epoxy composites

The influence of 3-aminopropyltriethoxysilane, 3-glycidyloxypropyltrimethoxysilane, and neoalkoxytric(dioctyl pyrophosphato)zirconate on thermal expansion behavior, dielectric strength, and arc resistance of mica/epoxy composites has been investigated. The addition of mica up to 30% resulted in the reduction of thermal expansion with respect to neat resin. However, the coefficient of linear thermal expansion of 30% mica treated with aminosilane was the least among the various coupling agent-coated filler/epoxy composites. Mica (30%)/epoxy composites showed the highest dielectric strength values (26 kV/mm), but the highest arc resistance was obtained in zirconate-treated mica (30%)/epoxy composite. © 1995 John Wiley & Sons, Inc.     

Effect of organosilane coupling agents on microstructure and properties of nanosilica/epoxy composites

Three types of silane coupling agents, γ‐aminopropyltriethoxysilane, γ‐glycidoxypropyltrimethoxysilane, and γ‐methacryloxypropyltrimethoxysilane, were used as modifiers to modify the surface of the nanosilica, respectively, and the nanocomposites of the epoxy resin filled with nano‐sized silica modified by three silane coupling agents were prepared by physical blending. The properties of the modified silica nanoparticles were characterized by Fourier transform infrared spectrum and particle‐size analyzer. The microstructure, mechanical behavior, and heat resistant properties of the nanocomposites were investigated by transmission electron microscopy, scanning electron microscopy, thermo gravimetric analyses, differential thermal gravity, differential scanning calorimetry, and flexural tests. The results showed that these modifiers are combined to the surfaces of nanosilica by the covalent bonds, and they change the surface properties of nanosilica. The different structures of coupling agents have different effects on the dispersibility and stability of modified particles in the epoxy matrix. In comparison, the silica nanoparticles modified by γ‐glycidoxypropyltrimethoxysilane exhibit a good dispersivity. The nanocomposites with 4 wt% weight fraction nanosilica modified by γ‐glycidoxypropyltrimethoxysilane have higher thermal decomposing temperature and glass transition temperature than those of the other two composites with the same nanosilica contents, and they are raised by 43.8 and 8°C relative to the unmodified composites, respectively. The modified silica nanoparticles have good reinforcing and toughening effect on the epoxy matrix. The ultimate flexural strengths of the composites with 4 wt% nanoparticles modified by γ‐aminopropyltriethoxysilane, γ‐glycidoxypropyltrimethoxysilane, and γ‐methacryloxypropyltrimethoxysilane are increased by 10, 30, and 8% relative to the unmodified composites, respectively. The flexural fracture surfaces of modified composites present ductile fracture features. POLYM. COMPOS. 2012. © 2012 Society of Plastics Engineers     

Effects of glass fibers and polypropylene/glass fiber hybrid fibers on the kinetics and mechanical properties of epoxy composites

Curing reactions of diglycidyl ether of bisphenol F (DGEBP‐F) and pre‐catalyzed methyltetrahydrophthalic anhydride (MTHPA) with benzyl triethyl ammonium chloride (BTEAC) were studied and effects of glass fibers evaluated. The influence on the kinetics of glass fibers and a hybrid blend of maleated polypropylene + glass fibers is studied. Isothermal and dynamic kinetic parameters are determined by differential scanning calorimetry (DSC). Applicability of the autocatalytic model is investigated. The model serves well in the range of degrees of conversion between 25 and 80%. At high conversion rates the diffusion control becomes apparent. Glass fibers accelerate the curing, shortening the time needed to reach the maximum reaction rate; this is reflected in lower activation energies for curing in comparison to the neat resin. The effects observed can be explained by a reaction between the amine group present on the fiber surfaces and the epoxy glycidyl groups. The result of both isothermal and non‐isothermal curing of resin + glass fibers commingled with polypropylene are close to those for the neat resin. The reinforcement increases the elastic modulus 12 times, the tensile strength 2 times, and the impact strength 285 times. The glass fibers + commingled polypropylene reinforcement provides comparable mechanical properties as glass fibers alone when normalized with respected to the density fraction of the fibers.     

Effects of organo‐montmorillonite on the mechanical and morphological properties of epoxy/glass fiber composites

Epoxy composites filled with glass fiber and organo‐montmorillonite (OMMT) were prepared by the hand lay‐up method. The flexural properties of the epoxy/glass fiber/OMMT composites were characterized by a three‐point bending test. The flexural modulus and strength of epoxy/glass fiber were increased significantly in the presence of OMMT. The optimum loading of OMMT in the epoxy/glass fiber composites was attained at 3 wt%, where the improvement in flexural modulus and strength was approximately 66 and 95%, respectively. The fractured surface morphology of the epoxy/glass fiber/OMMT composites was investigated using field emission scanning electron microscopy. It was found that OMMT adheres on the epoxy/glass fiber interface, and this is also supported by evidence from energy dispersive X‐ray analysis. Copyright © 2007 Society of Chemical Industry     

Preparation and properties of silicon nitride/glass fiber/epoxy composites

Silicon nitride/glass fiber (Si₃N₄/GF) hybrid fillers are performed to prepare the Si₃N₄/GF/epoxy composites. Results showed the thermal conductivities of the Si₃N₄/GF/epoxy composites that are improved with the addition of Si₃N₄, and the thermal conductive coefficient λ is 1.412 W/mK with 38 vol% modified Si₃N₄/GF hybrid fillers (30 vol% Si₃N₄ + 8 vol% GF), seven times higher than that of pure epoxy resin. The flexural strength and impact strength of the composites are optimal with 13 vol% modified Si₃N₄/GF hybrid fillers (5 vol% Si₃N₄ + 8 vol% GF). The dielectric constant and dielectric loss of the composites are increased with the increasing addition of Si₃N₄. For a given Si₃N₄/GF hybrid fillers loading, the surface modification can further improve the thermal conductivities of the Si₃N₄/GF/epoxy composites. POLYM. COMPOS., 35:1338–1342, 2014. © 2013 Society of Plastics Engineers     

Effect of coupling agents on the mechanical properties of fly ash/polyester particulate composites

Fly ash (FA)/general purpose unsaturated polyester resin (GPR) particulate composites were made. The effect of the surface treatment of FA with two different silane coupling agents (CAs) on the mechanical properties, such as the tensile, flexural, compressive, and impact strengths and hardness, of FA–GPR composites were studied. The properties of FA–CA–GPR were also compared with that of GPR and CaCO₃–GPR. An enhancement in the tensile, flexural, compressive, and impact strengths and a decrease in the tensile and flexural moduli were observed when FA was surface treated with CA. Hardness also increases with CA‐treated FA. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1755–1760, 2001     

Effect of the various coupling agents on the mechanical and physical properties of thermoplastic‐bagasse fiber composites

Various types of bonding agents have been tried with blends of bagasse fibers and some thermoplastics such as low‐density polyethylene (LDPE), high‐density polyethylene (HDPE), polystyrene (PS), polypropylene (PP), and polyvinyl chloride (PVC). These bonding agents are, namely, pentaerythritol tetracrylate (PETA), 1,6 hexandiol diacrylate (HDA), and dicumyl peroxide (DCP). In addition, a traditional coupling agents 3‐aminopropyltrimethoxy silane (AMPS) and di‐aminopropyltrimetoxy silane (DAMPS) were included for comparison. Electron beam (EB) irradiation is applied only for LDPE and HDPE at 40 and 10 kGy, respectively, before mixing with bagasse fibers. The data obtained reveal that incorporation of bonding agents remarkably increases the mechanical properties for all samples under investigation; the maximum improvement is observed in LDPE followed by HDPE, PP, PS, and PVC composites. Also, the physical properties enhanced but not at the same degree as mechanical properties. Among the tested bonding agents, it was found that PETA, DCP followed by DAMPS have highest efficiency in LDPE, whereas in case of HDPE, EB radiation was higher than PETA followed by DCP. PETA was superior in case of PS composites. Furthermore, PETA and HDA experienced higher efficiency than DAMPS and AMPS in case of PP and PVC composites. Comparison between the properties of thermoplastic composites and medium density fiberboard (MDF) reveals that most of the properties of thermoplastics composites are better than MDF. However, modulus of rupture of MDF was found to be slightly higher than thermoplastics except for PVC composite. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Study on the mechanical properties and microstructure of high-performance carbon fiber/epoxy composites

A high-toughness epoxy has been prepared using carboxyl-terminated butadiene acrylonitrile (CTBN) as a toughening agent to modify the AG-80 epoxy resin. High-performance carbon fiber/epoxy (CF/EP) composites are fabricated using the CTBN-toughened epoxy resin as the matrix and two types of CF, namely, T800SC and T800HB, as reinforcement. The mechanical properties of the matrix, surface properties of the CFs, tensile properties, and fracture morphologies of the composites are systematically investigated to elucidate the key factors influencing interfacial bonding in high-performance CF/EP composites. The results reveal that the most significant improvement in toughness is achieved when the CTBN content is 6.90 wt.% in the epoxy resin. Owing to the high content of polar functional groups and excellent surface wettability of T800SC, the T800SC/EP composite exhibits superior mechanical properties compared with the T800HB/EP composite.     

Effects of fiber length on the tensile strength of epoxy/glass fiber and polyester/glass fiber composites

In discontinuous fiber-reinforced composites, the shear strength at the fiber–matrix interface plays an important role in determining the reinforcing effect. In this paper, a method was devised to accurately determine this shear strength, taking the strength distribution of glass fiber into consideration. Calculated strength values based on the shear strenght obtained by the method were in better agreement with the experimental observations than those calculated by employing the shear strength obtained on the assumption that the fiber strength was uniform. The tensile strength of composites increases with increasing aspect ratio of the reinforcing fibers. This trend is almost the same regardless of the kind of matrix, the nature of interfacial treatment, and the environmental temperature. When composites are reinforced with random-planar orientation of short glass fibers of 1.5 times the mean critical fiber length, the tensile strength of composite reaches about 90% of the theoretical strength of composites reinforced with continuous glass fiber. Reinforcing with glass fibers 5 times the critical length, the tensile strength reaches about 97% of theoretical. However, from a practical point of view, it is adequate to reinforce with short fibers of 1.5–2.0 times the mean critical fiber lenght.     

改性空心玻璃微珠/环氧树脂复合材料力学性能研究

采用偶联剂对玻璃微珠表面进行改性处理,借助超声波振动,使改性空心玻璃微珠在环氧树脂中均匀、稳定分散,增强了玻璃微珠与环氧树脂之间的相容并探讨了改性空心玻璃微珠对环氧树脂力学性能的影响。结果表明,复合材料中改性空心玻璃微珠添加质量分数为3%时,其拉伸强度达到最大值68.54 MPa,与空白样相比提高了20.3%;冲击强度达到最大值24.42 kJ/m2,比纯环氧树脂提高了166%;KIC(断裂韧性)达到最大值2.338 MPa/m2,是空白试样的2.27倍,增韧效果较为明显。     

Influence of alkali fiber treatment and fiber processing on the mechanical properties of hemp/epoxy composites

Industrial hemp fibers were treated with a 5 wt % NaOH, 2 wt % Na₂SO₃ solution at 120°C for 60 min to remove noncellulosic fiber components. Analysis of fibers by lignin analysis, scanning electron microscopy (SEM), zeta potential, Fourier transform infrared (FTIR) spectroscopy, wide angle X‐ray diffraction (WAXRD) and differential thermal/thermogravimetric analysis (DTA/TGA), supported that alkali treatment had (i) removed lignin, (ii) separated fibers from their fiber bundles, (iii) exposed cellulose hydroxyl groups, (iv) made the fiber surface cleaner, and (v) enhanced thermal stability of the fibers by increasing cellulose crystallinity through better packing of cellulose chains. Untreated and alkali treated short (random and aligned) and long (aligned) hemp fiber/epoxy composites were produced with fiber contents between 40 and 65 wt %. Although alkali treatment generally improved composite strength, better strength at high fiber contents for long fiber composites was achieved with untreated fiber, which appeared to be due to less fiber/fiber contact between alkali treated fibers. Composites with 65 wt % untreated, long aligned fiber were the strongest with a tensile strength (TS) of 165 MPa, Young's modulus (YM) of 17 GPa, flexural strength of 180 MPa, flexural modulus of 9 GPa, impact energy (IE) of 14.5 kJ/m², and fracture toughness (K_Ic) of 5 MPa m^1/2. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Prefailure damage processes in highly filled glass/mica/epoxy composites

In the present study, the prefailure damage processes of a series of short glass fiber/mica/epoxy composites under three-point bending were elucidated using acoustic emission (AE) coupled with in situ scanning electron microscopy (SEM) observations. This study consisted of a detailed investigation of the damage tolerance of composite systems that had constant inorganic content of 75% by weight with a varying ratio of glass fibers to mica. The flexural strength was found to increase from 11 to 21 ksi as the glass fiber content increased (mica content decreased), while the flexural modulus decreased from 5.0 to 2.5 Msi. By monitoring the AE during flexural deformation of the glass fiber-to-mica ratio composites, it was determined that low amplitude (0–42 db) AE events, which occurred throughout the deformation process, were caused by matrix cracking, whereas the high-amplitude (43–100 db) AE events, which occurred just prior to failure, were caused by a fiber-related mechanism. In situ SEM observations of the composites during flexural deformation allowed a correlation between the AE and the damage mechanisms as a function of strain. In the all-mica composite, microcracking initiated in the linear region at preexisting flaws, on the order of 10 μm, located at the mica interface. These microcracks grew along the mica contours over the majority of the deformation process, emitting low-amplitude events, until final fracture occurred at relatively low strains. In the glass fiber-containing composites, microcracking initiated in the linear region at preexisting flaws and voids, on the order of 10 μm. These microcracks grew slowly, emitting low-amplitude events, as the strain increased, but were prevented from causing failure at low strains because of the toughening effect of the glass fibers. At sufficiently high strains, however, fiber breakage and fiber pull-out occurred that corresponded to the high-amplitude events detected by the AE. At strains just prior to failure, catastrophic crack growth occurred, producing a rapid increase in both low-and high-amplitude events, causing ultimate failure.     

Effect of g-C3N4 nanofiller as filler on mechanical properties of multidirectional glass fiber epoxy hybrid composites

An experimental study was carried out to investigate the flexural strength of glass-fiber-reinforced (multidirectional woven glass fiber) epoxy hybrid composites filled with different proportions (1, 1.5, 2, 2.5, and 3%) of graphitic carbon nitride (g-C₃N₄) filler. g-C₃N₄ powder filled glass epoxy composites were fabricated in conventional hand lay-up method. Results showed an increase in flexural strength of g-C₃N₄ particles content by 2% and beyond which the strength decreased. With the addition of 2 wt % of g-C₃N₄ in glass-fiber-reinforced epoxy composites, the tensile strength increased by 11% and the flexural strength increased by 13%. The eroded surface of the specimen was observed under scanning electron microscope and the results are reported. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48413.     

Influence of silane coupling agents on the surface energetics of glass fibers and mechanical interfacial properties of glass fiber-reinforced composites

The effect of various silane coupling agents on glass fiber surfaces has been studied in terms of the surface energetics of fibers and the mechanical interfacial properties of composites. γ-Methacryloxypropyltrimethoxysilane (MPS), γ-aminopropyltriethoxysilane (APS), and γ-glycidoxypropyltrimethoxysilane (GPS) were used for the surface treatment of glass fibers. From contact angle measurements based on the wicking rate of a test liquid, it was observed that silane treatment of glass fiber led to an increase in the surface free energy, mainly due to the increase of its specific (or polar) component. Also, for the glass fiber-reinforced unsaturated polyester matrix system, a constant linear relationship was observed in both the interlaminar shear strength (ILSS) and the critical stress intensity factor (K_IC) with the specific component, γ_S ^SP, of the surface free energy. This shows that the hydrogen bonding, which is one of the specific components of the surface free energy, between the glass fibers and coupling agents plays an important role in improving the degree of adhesion at the interfaces of composites.     

Influence of different glass fiber sizings on selected mechanical properties of PET/glass composites

The properties of fiber-reinforced plastics are considerably influenced by fiber-matrix interaction. The aim of this study was to investigate the influence of glass fiber surface treatments on the morphology of poly(ethylene terephthalate) (PET) and on selected mechanical properties of unidirectional PET/glass fiber composites. The materials used here were E-glass fibers treated with model sizings including aminosilane as a coupling agent and polyurethane and epoxy resin dispersions as film formers and PET as the matrix. For identification of the degree of crystallinity of the PET matrix, differential scanning calorimetry (DSC) was used. To study the influence of the different sizings on the mechanical properties, the following tests were performed: interlaminar and intralaminar shear tests and a transverse tensile test. Dynamic-mechanical analysis (DMA) was used to characterize the behavior of the composites under dynamical load. The DSC results show that the overall crystallinity and the melting behavior of the PET matrix were hardly influenced by the glass fiber surface treatments used. The various strength properties of the composites are influenced not only by the silane coupling agent, but also by the type of film former. With an epoxy resin dispersion, the mechanical properties were enhanced compared with a polyurethane dispersion. These results were confirmed by characterization of the composites by DMA.     

耐高温高导热环氧树脂／玻纤／BN复合材料的制备

以4,4-二氨基二苯砜（DDS）和内亚甲基四氢邻苯二甲酸酐（NA）为复配固化剂,采用高温模压成型法制备耐高温高导热环氧树脂／玻纤／氮化硼（BN）复合材料。探讨了BN用量和偶联剂处理对复合材料冲击强度、导热性能和电阻率的影响。结果表明：当nDDS：nNA=3：1时,复合材料的耐热性能最佳。当BN质量分数为8％时,复合材料的冲击强度最高;导热性能随BN用量的增加而增加,当BN用量为15％时,热导率为0．7560W／（mk）,此时复合材料仍保持较高的体积、表面电阻率;当BN填充量为一定值时,偶联剂处理使冲击强度和导热性能得到进一步提高。     

Effects of novolac resin modification on mechanical properties of carbon fiber/epoxy composites

The epoxy resin matrix of carbon fiber (CF)‐reinforced epoxy composites was modified with novolac resin (NR) to improve the matrix‐dominated mechanical properties of composites. Flexural strength, interlaminar shear strength (ILSS), and impact strength were measured with unfilled, 7 wt% NR, 13 wt% NR, and 18 wt% NR filled to epoxy to identify the effect of adding NR on the mechanical properties of composites. The results showed that both interfacial and impact properties of composites were improved except for flexural property. The largest improvement in ILSS and impact strength were obtained with 13 wt% loading of NR. ILSS and impact strength were improved by 7.3% and 38.6%, respectively, compared with the composite without NR. The fracture and surface morphologies of the composite specimens were characterized by scanning electron microscopy. Intimate bonding of the fibers and the matrix was evident with the content of 7–13 wt% NR range. Decrease of crosslinking density and formation of NR transition layer were deduced with adding NR. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Multilayered epoxy/glass fiber felt composites with excellently acoustical and thermal insulation properties

In this article, a series of epoxy composites consisting of multilayered ultra-fine glass fiber felts (GFFs) were produced by a hand lay-up process. The incorporation of GFFs greatly enhances the sound-absorption and sound-insulation properties of epoxy composites. It can be mainly attributed to great numbers of voids introduced into the matrix and the increasing interfacial area between glass fiber and epoxy resin, which is confirmed by scanning electron microscopy results. Furthermore, the thermal insulation performance of epoxy/glass fiber felt (EP/GFF) composites is continuously improved with the growing GFF layer, and meanwhile EP/GFF composites exhibit the satisfactory mechanical property. Such novel EP/GFF composites can serve as promising structural, heat-insulated, and soundproof materials in many multifunctional systems including buildings, aircrafts, constructions, vehicles, etc. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46935.     

Preparation and mechanical properties of machinable alumina/mica composites

Using a mica-crystallizing glass powder in which a large amount of mica crystal was precipitated and a larger amount of MgF₂ component was contained as the raw materials of mica, machinable alumina/mica composites were obtained at 1400 °C. In the firing process, magnesia component in the mica crystals reacted with alumina to form spinel at 1150–1200 °C. The reaction made the mica crystals melt. However, the mica crystals were precipitated again during the cooling. Because a larger amount of MgF₂ component was contained in the mica-crystallizing glass powder, the nucleation of the mica crystals was caused during the cooling by the residual magnesium and fluorine in the liquid phase and succeedingly the mica crystals were precipitated. The precipitated mica crystals grew to anisotropicaly larger size than alumina grains, which lowered the bending strength and Vickers hardness and little heightened the fracture toughness.     

Effect of matrix ductility and interface treatment on mechanical properties of glass fiber mat composites

The influence of matrix properties on randomly oriented glass fiber epoxy composites has been studied. It is shown that an increased ductility (flexibility) of the matrix does not result in greater elongation to failure of the composite under tensile and flexural loads. The tensile (and flexural) strength and the modulus of elasticity are decreased as the ductility of the resin is increased. It is concluded that since the matrix material is subjected to a triaxial state of stress when the composite specimen is subjected to uniaxial loads, the effect of matrix modulus, Poisson's ratio, and yield strength are more important than the matrix ductility measured under uniaxial stress. The effect on mechanical properties of various surface treatments applied to the fibers is also investigated. Finally, scanning electron micrographs are presented showing matrix cracks, fiber debonding, and fiber pull-out.