Processing and characterization of epoxy nanocomposites reinforced by cup-stacked carbon nanotubes

The effect of the dispersion, ozone treatment and concentration of cup-stacked carbon nanotubes on mechanical, electrical and thermal properties of the epoxy/CSCNT nanocomposites were investigated. Ozone treatment of carbon fibers was found to increase the surface oxygen concentration, thereby causing the contact angle between water, epoxy resin and carbon fiber to be decreased. Thus, the tensile strength, modulus and the coefficient friction of carbon fiber reinforced epoxy resin were improved. Moreover, the dispersion of fibers in polymer was increased and the electrical resistivity was decreased with the addition of filler content. The dynamic mechanical behavior of the nanocomposite sheets was studied. The storage modulus of the polymer was increased by the incorporation of CSCNTs. But the glass transition temperature decreased with increasing fiber loading for the ozone treated fiber composites. The ozone treatment did affect the morphology, mechanical and physical properties of the CSCNT.     

T700碳纤维复合材料耐湿热老化研究

选用TDE-85和E-51作为主体树脂,制备了一种T700碳纤维复合材料,并对这种复合材料进行耐湿热老化研究,分别测定其抗剪切强度、抗拉伸强度及模量和玻璃化转变温度随老化时间的变化值。结果表明,该T700碳纤维复合材料耐湿热老化性能较好,其力学性能在2 000 h的老化过程中变化不太大,但是其玻璃化转变温度值降低很多。     

The effect of kevlar fiber reinforcement on the curing,thermal, and dynamic‐mechanical properties of an epoxy/anhydride system

Curing, thermal, and dynamic‐mechanical relaxational behavior of an epoxy/‐anhydride resin and a Kevlar‐fiber/epoxy composite were compared. Reinforcement by Kevlar fibers had a catalytic effect on the curing reaction. Reinforced formulations produced higher extents of reaction than neat formulations at the same curing time. Curing kinetics was also studied by means of DSC heating scans. When the Kevlar content increased, the heat flow curves and the exothermic peak temperature shifted significantly to lower temperatures. The glass transition temperature of the matrix also decreased as the Kevlar content increased. Postcuring reduced the differences between the neat and reinforced formulations. Loss tangent and storage modulus versus frequency master curves were obtained from isothermal dynamic‐mechanical measurements. The effect of fiber addition on the main dynamic‐mechanical relaxation was analyzed with a simple mechanical model.     

Dynamic mechanical properties of oil palm fiber/phenol formaldehyde and oil palm fiber/glass hybrid phenol formaldehyde composites

The dynamic mechanical properties of oil palm fiber reinforced phenol formaldehyde (PF) composites and oil palm/glass hybrid fiber reinforced PF composites were investigated as a function of fiber content and hybrid fiber ratio. The dynamic modulus of the neat PF sample decreases with decrease in frequency. Glass transition attributed with the α relaxation of the neat PF sample was observed around 140°C. Tanδ values and storage modulus show great enhancement upon fiber addition. The value increases with increase in fiber content. The loss modulus shows a reverse trend with increase in fiber loading. Incorporation of oil palm fiber shifts the glass transition towards lower temperature value. The glass transition temperature of the hybrid composites is lower than that of the unhybridized composites. The highest value of mechanical damping is observed in hybrid composites. Storage modulus of the hybrid composites is lower than unhybridized oil palm fiber/PF composite. A similar trend is observed for loss modulus. Activation energies for the relaxation processes in different composites were calculated. Activation energy is increased upon fibrous reinforcement. Complex modulus variations and phase behavior of the composites were studied from Cole‐Cole plots. Finally, master curves for the viscoelastic properties of the composites were constructed on the basis of time‐temperature superposition principle. POLYM. COMPOS., 26:388–400, 2005. © 2005 Society of Plastics Engineers     

Dynamic mechanical properties of sisal fiber reinforced polyester composites fabricated by resin transfer molding

The dynamic mechanical properties of sisal fiber reinforced polyester composites fabricated by resin transfer molding (RTM) were investigated as a function of fiber content, frequency, and temperature. Investigation proved that at all temperature range the storage modulus (E′) value is maximum for the composites having fiber loading of 40 vol%. The loss modulus (E″) and damping peaks (tan δ) were lowered with increasing fiber content. The height of the damping peaks depends upon the fiber content and the fiber/matrix adhesion. The extent of the reinforcement was estimated from the experimental storage modulus, and it has been found that the effect of reinforcement is maximum at 40 vol% fiber content. As the fiber content increases the T_g from tan δ curve showed a positive shift. The loss modulus, storage modulus, and damping peaks were evaluated as a function of frequency. The activation energy for the glass transition increases upon the fiber content. Cole–Cole analysis was made to understand the phase behavior of the fiber reinforced composites. Finally, attempts were made to correlate the experimental dynamic properties with theoretical predictions. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

The effect of time and temperature on the mechanical behavior of epoxy composites

A crosslinked epoxy resin consisting of a 60/40 weight ratio of Epon 815 and Versamid 140 and composites of this material with glass beads, unidirectional glass fibers and air (foams) were tested in tension, compression and flexure to determine the effect of time and temperature on the elastic properties, yield properties and modes of failure. Unidirectional continuous fiber-filled samples were tested at different fiber orientation angles with respect to the stress axis. Strain rates ranged from 10^?4 to 10 in./in.-min and the temperature from ?1 to 107°C. Isotherms of tangent modulus versus strain rate were shifted to form master modulus curves. The moduli of the filled composites and the foams were predictable over the entire strain rate range. It was concluded that the time-temperature shift factors for tangent moduli and the time-temperature shift factors for stress relaxation were identical and were independent of the type and concentration of filler as well as the mode of loading. The material was found to change from a brittle-to-ductile-to-rubbery failure mode with the transition temperatures being a function of strain rate, filler content, filler type and fiber orientation angle, indicating that the transition is perhaps dependent on the state of stress. In the ductile region, an approximately linear relationship between yield stress and log strain is evident in all cases. The isotherms of yield stress versus log strain rate were shifted to form a practically linear master plot that can be used to predict the yield stress of the composites at any temperature and strain rate in the ductile region. The time-temperature shift factors for yielding were found to be independent of the type, concentration and orientation of filler and the mode of loading. Thus, the composite shift factors seem to be a property of the matrix and not dependent on the state of stress. The compressive-to-tensile yield stress ratio was practically invariant with strain rate for the unfilled matrix, while fillers and voids raised this ratio and caused it to increase with a decrease in strain rate. The yield strain of the composites is less than the unfilled matrix and is a function of fiber orientation and strain rate.     

Thermal conductivity of ramie fiber drawn in water in low temperature

To understand the effect of extension of molecular chain in amorphous region in polymer fibers to thermal conductivity, the thermal conductivity, tensile modulus and crystal orientation angle of ramie fibers and those drawn by the stress of 17.4 kg/mm² (water treatment) in the water were investigated. The tensile modulus of ramie fiber in fiber direction increased from 61 to 130 GPa by drawing in the water. The crystal orientation angles of ramie fiber with and without water treatment were measured by X‐ray diffraction. The orientation degrees of ramie fibers without and with water treatment were estimated as 92.9 and 93.6%, respectively. Therefore, the tensile modulus increases two times as that of blank ramie by water treatment although crystal orientation angle does not change distinctly. The increasing of tensile modulus of ramie fiber by water treatment was explained by extension of the molecular chains in the amorphous region. Thermal conductivities of ramie fibers with and without water treatment were measured in the fiber direction in the temperature range from 10 to 150 K. Thermal conductivity of ramie fiber in the fiber direction increased by water treatment. The increasing ratio of thermal conductivity by water treatment agreed to that of sound velocity induced by increasing tensile modulus. Those results suggest that thermal conductivity of polymer fiber increase by the extension of molecular chains in the amorphous region. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2196–2202, 2006     

Experimental study on dielectric relaxation in alfa fiber reinforced epoxy composites

Investigation on dielectric properties and behavior of thermoset epoxy composite based on cellulosic fibers has been carried on. Dielectric spectra were measured in the frequency range 0.1 Hz–100 kHz and at temperature intervals from ambient to 200°C. For the composite, four relaxations processes were identified, namely the orientation polarization imputed to the presence of polar water molecules in Alfa fiber, the α mode relaxation associated with the glass transition of the epoxy resin matrix, the relaxation process associated with conductivity occurring as a result the carriers charges diffusion noted for high temperature above glass transition and low frequencies, and interfacial or Maxwell‐Wagner‐Sillars relaxation that is attributable to the accumulation of charges at the Alfa fibers/epoxy resin interfaces. Dielectric relaxation analysis revealed evolution in water relaxation and it is thus concluded that the chemical treatment of the fiber can strongly influence the dielectrical properties and interfacial polarization processes in composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Influence of carbon nanotubes on the thermal, electrical and mechanical properties of poly(ether ether ketone)/glass fiber laminates

Novel poly(ether ether ketone) (PEEK)/single-walled carbon nanotube (SWCNT)/glass fiber laminates incorporating polysulfone as a compatibilizing agent were fabricated by melt-blending and hot-press processing. Their morphology, mechanical, thermal and electrical properties were investigated and compared with the behavior of similar non-compatibilized composites. Scanning electron micrographs demonstrated better SWCNT dispersion for samples with polysulfone. Thermogravimetric analysis indicated a remarkable improvement in the thermal stability of PEEK/glass fiber by the incorporation of SWCNTs wrapped in the compatibilizer, ascribed to a significant thermal conductivity enhancement. Differential scanning calorimetry showed a decrease in the crystallization temperature and crystallinity of the polymer with the addition of both wrapped and non-wrapped SWCNTs. The laminates exhibit anisotropic electrical behavior; their conductivity out-of-plane is lower than that in-plane. Dynamic mechanical studies revealed an increase in the storage modulus and glass transition temperature in the presence of polysulfone. Mechanical tests demonstrated significant enhancements in stiffness, strength and toughness by the incorporation of wrapped nanofillers, whilst the mechanical properties of non-compatibilized composites only improved marginally. Samples with laser-grown SWCNTs exhibit enhanced overall performance. This investigation confirms that SWCNT-reinforced PEEK/glass fiber compatibilized composites possess excellent potential to be used as multifunctional engineering materials in industrial applications.     

玻璃纤维／环氧树脂复合材料的热性能

本文采用E-玻璃纤维作为增强材料、双酚A环氧树脂和芳胺类固化剂作为基体制成复合材料试样,利用动态与静态热分析方法测定玻璃纤维／环氧树脂基复合材料的热性能,研究了玻璃纤维含量对复合材料动态热机械性能、玻璃化温度等热性能的影响。     

紫外老化对芳纶／环氧复合材料性能和结构的影响

通过紫外老化试验（温度（40±5）℃,湿度40％）,研究了芳纶、环氧及其复合材料的力学性能、玻璃化转变温度、失重随老化时间的变化,并用红外光谱分析了芳纶的结构变化。结果表明：经紫外老化后,芳纶／环氧的拉伸强度、失重率有明显的变化,芳纶结构和复合材料的玻璃化转变温度无明显的变化。     

Neutron scattering, electron microscopy and dynamic mechanical studies of carbon nanofiber/phenolic resin composites

Carbon nanofiber (CNF)/resole phenolic resin (Hitco 134A) composites exhibited very large increases of bending storage modulus above the glass transition temperature and had higher glass transition temperatures with increasing CNF weight percentage. Small angle neutron scattering (SANS) from dilute suspensions of surface-oxidized CNF in D₂O exhibited a Guinier plateau in the q range examined, indicating that isolated scatterers exist. The CNF dispersion, average fiber diameter, average core diameter and polydispersity within the composites and in D₂O were quantified by approximating the small angle neutron scattering data with a hollow tube model. The scattering from CNF/phenolic resin composites exhibited a q⁻⁴ power law behavior, indicating the presence of sharp interfaces between fibers and phenolic resin. Surface-oxidized (PR-19-PS) CNF nanocomposites exhibited lower surface to volume ratio values and larger shell thickness compared with heat-treated (PR-19-HT) CNF composites. However, carbon nanofibers, with and without oxygenated surface groups, exhibited some agglomerates with fractal dimensions within the phenolic resin composites. Fiber surface treatment with nitric acid appears to promote dispersion and results in looser bundles of nested fiber networks.     

深潜壳体用高模量树脂基体的研究——基体模量对复合材料抗压抗剪性能的影响

制备了高模量树脂基单向复合材料，测试了单向复合材料的纵向压缩性能和平面剪切性能。研究了基体模量对单向复合材料抗压强度及复合材料平面剪切性能的影响，结果表明：单向复合材料的抗压强度与基体模量成线性比例关系，随基体模量的提高而提高，复合材料的平面剪切性能与基体模量基本上呈线性关系，平面剪切强度亦随基体模量的提高而提高。以模量达５．３６ＧＰａ的环氧树脂作为复合材料的树脂基体制备的，单向玻璃纤维增强复合材料其抗压强度高达１．２９５ＧＰａ，碳纤维增强的复合材料抗压强度高达１．３７２ＧＰａ，与普通环氧树脂的单向复合材料相比，分别提高了５５％和４５．８％；复合材料的平面剪切强度达６４．５ＭＰａ，比普通环氧树脂复合材料的平面剪切强度提高了４４．３％，满足了深潜壳体对复合材料抗压强度的要求。     

Preparation and properties of nanoparticle and long-fiber-reinforced unsaturated polyester composites

In this study, a new approach was used to prepare polymer composites reinforced by both nanoparticles and continuous fibers. Carbon nanofibers were prebound onto glass fiber mats, and then unsaturated polyester composites were prepared by vacuum-assisted resin transfer molding. Mechanical and thermal properties of these composites were measured and compared with those of the composites synthesized by premixing carbon nanofibers with the polymer resin. Flexural strength and modulus of composites improved with the incorporation of nanoparticles. Specifically, the property improvement was higher in the case of the composites prepared by the new prebound method. It was also found that carbon nanofibers increased the glass transition temperature and reduced the thermal expansion coefficient of unsaturated polyester composites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

涤纶工业丝动态粘弹性的研究

采用动态热机械分析仪分析纺丝温度对涤纶工业丝动态粘弹性的影响,研究了纤维储能模量(E')、损耗模量(E″)及损耗因子(Tanδ)的温度依赖性。结果表明:纺丝温度300℃,涤纶工业丝初生纤维取向及结晶几率低,链段运动能力强,经后拉伸可有效提高纤维强度;在玻璃化转变温度范围内,E',E″及Tanδ均出现极大值,随温度升高,E'及E″下降,在120℃左右E'和E″再次升高,140℃左右则趋于平衡。     

Hybrid fiber fabric composites from poly ether ether ketone and glass fiber

Poly ether ether ketone (PEEK) polymer was extruded into filaments and cowoven into unidirectional hybrid fabric with glass as reinforcement fiber. The hybrid fabrics were then converted into laminates and their properties with special reference to crystallization behavior has been studied. The composite laminates have been evaluated for mechanical properties, such as tensile strength, interlaminar shear strength (ILSS), and flexural strength. The thermal behavior of the composite laminates were analyzed using differential scanning calorimeter, thermogravimetric analyzer, dynamic mechanical analyzer (DMA), and thermomechanical analyzer (TMA). The exposure of the fabricated composite laminates to high temperature (400 and 500°C) using radiant heat source resulted in an improvement in the crystallanity. The morphological behavior and PEEK resin distribution in the composite laminates were confirmed using scanning electron microscope (SEM) and nondestructive testing (NDT). Although DMA results showed a loss in modulus above glass transition temperature (T_g), a fair retention in properties was noticed up to 300°C. The ability of the composite laminates to undergo positive thermal expansion as confirmed through TMA suggests the potential application of glass–PEEK composites in aerospace sector. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117:1446–1459, 2010     

Change of orientation by thermal contraction of polyacrylonitrile fiber

Polyacrylonitrile polymer powder was dissolved in 70% nitric acid and spun into isotropic filament through a glass nozzle of 0.5 mm. diameter in a coagulating bath of 30% nitric acid. Stretching was carried out in two stages: the first stretching was done in water at 20°C. followed by drying, and the second stretching was done in a boiling saturated solution of ammonium sulfate. The total stretching ratio was 23. These filaments were shrunk freely in water at 70–180°C. The change in orientation factors was traced by x-ray, infrared dichroism, visible dichroism, and sonic modulus methods. The relation between the reciprocal absolute temperature of thermal contraction and the logarithm of fiber length is a straight line which has two inflection points at 93 and 175°C. The orientation factors by x-ray and infrared dichroism remain unchanged up to 175°C. On the contrary, the orientation factors by visible dichroism and sonic modulus drop suddenly at about 90°C. This indicates the occurrence of relaxation of the amorphous chain at the glass transition temperature and shows the polymer is not perfect single-phase material. Orientation of crystalline and amorphous phases is stable from 100 to 170°C. in spite of considerable thermal contraction. The stability of orientation can be explained by the growth of a folded structure in the polymer.     

Application of dynamic mechanical analysis for the study of the interfacial region in carbon fiber/epoxy composite materials

The application of dynamic mechanical analysis (DMA) for quantifying interfacial interactions in composites is briefly reviewed. Carbon fiber/epoxy composites with fiber volume fractions of 12, 17, 38 and 61 vol% were subjected to flexural deformation on a Dupont DMA 983 instrument. The dependencies of dynamic mechanical properties of the composites on experimental parameters such as oscillation mode, amplitude, frequency, and temperature were investigate. As opposed to the storage modulus, the loss modulus is found to be sensitive to all parameters. In a fixed multiple frequency mode, the loss modulus of the composites increases with oscillation amplitude and decreases with frequency and the number of tests. The information produced in the resonant mode is more reproducible. An additional damping at the interfaces, apart from those of the constituents, suggests a poor interface adhesion in these composites. A linear relationship between the excess damping at the interfaces and the fiber volume fraction shows a similar interface quality for these composites having different fiber volume fractions. The detection of interfacial properities was found to be more sensitive in the flexural deformation mode than in the torsional mode. At temperatures higher than the glass transition temperature of the matrix, the effective volume fraction of the matrix is reduced. Such a reduction can be interpreted from the mismatch of thermal expansion of the matrix and the fibers.     

Use of an epoxidized oil‐based resin as matrix in vegetable fibers‐reinforced composites

Hemp fibers were used as natural reinforcement in composites of thermosetting vegetal oil based resin. Boards with fibers content from 0 to 65 vol % were produced by hot pressing. The mechanical properties were investigated with flexural testing. The effect of effect has been observed on both modulus and strength, indicating a good fiber–matrix interfacial adhesion, which was confirmed by means of scanning electron microscopy observations. Dynamic mechanical analysis also showed an important reinforcement effect in the polymer rubbery region, where at 180°C the storage modulus increased from 17 MPa for the neat resin to 850 MPa for 65 vol % fiber content composites. It also revealed an glass transition temperature decrease when fiber amount in the composite increased. Additional experiments based on differential scanning calorimetry show a weakly accelerated cure when fibers content increases, which usually lead to a lower T_g. But, this phenomenon alone cannot explain the observed T_g change. Contact angle on hemp evolution with time for the resin components show that anhydride is totally absorbed after a few seconds, whereas contact angle of epoxydized oil decreases slowly. This indicates probably a preferential anhydride absorption that leads to a lower amount of anhydride in the matrix and as a consequence to a reduced T_g. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4037–4043, 2006     

Mechanical and thermal properties of hierarchical composites enhanced by pristine graphene and graphene oxide nanoinclusions

Epoxy resin nanocomposites incorporated with 0.5, 1, 2, and 4 wt % pristine graphene and modified graphene oxide (GO) nanoflakes were produced and used to fabricate carbon fiber‐reinforced and glass fiber‐reinforced composite panels via vacuum‐assisted resin transfer molding process. Mechanical and thermal properties of the composite panels—called hierarchical graphene composites—were determined according to ASTM standards. It was observed that the studied properties were improved consistently by increasing the amount of nanoinclusions. Particularly, in the presence of 4 wt % GO in the resin, tensile modulus, compressive strength, and flexural modulus of carbon fiber (glass fiber) composites were improved 15% (21%), 34% (84%), and 40% (68%), respectively. Likewise, with inclusion of 4 wt % pristine graphene in the resin, tensile modulus, compressive strength, and flexural modulus of carbon fiber (glass fiber) composites were improved 11% (7%), 30% (77%), and 34% (58%), respectively. Also, thermal conductivity of the carbon fiber (glass fiber) composites with 4% GO inclusion was improved 52% (89%). Similarly, thermal conductivity of the carbon fiber (glass fiber) composites with 4% pristine graphene inclusion was improved 45% (80%). The reported results indicate that both pristine graphene and modified GO nanoflakes are excellent options to enhance the mechanical and thermal properties of fiber‐reinforced polymeric composites and to make them viable replacement materials for metallic parts in different industries, such as wind energy, aerospace, marine, and automotive. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40826.