CF/EP composite laminates with carbon black and copper chloride for improved electrical conductivity and interlaminar fracture toughness

An experimental study was conducted to improve the electrical conductivity of continuous carbon fibre/epoxy (CF/EP) composite laminate, with simultaneous improvement in mechanical performance, by incorporating nano-scale carbon black (CB) particles and copper chloride (CC) electrolyte into the epoxy matrix. CF/EP laminates of 65 vol.% of carbon fibres were manufactured using a vacuum-assisted resin infusion (VARI) technique. The effects of CB and the synergy of CB/CC on electrical resistivity, tensile strength and elastic modulus and fracture toughness (K_IC) of the epoxy matrix were experimentally characterised, as well as the transverse tensile modulus and strength, Mode I and Mode II interlaminar fracture toughness of the CF/EP laminates. The results showed that the addition of up to 3.0 wt.% CB in the epoxy matrix, with the assistance of CC, noticeably improved the electrical conductivity of the epoxy and the CF/EP laminates, with mechanical performance also enhanced to a certain extent.     

Evaluation on the thermal and mechanical properties of HNT-toughened epoxy/carbon fibre composites

Halloysite nanotubes (HNT) were effectively incorporated into epoxy resin and used for infusion of carbon fibre textiles, resulting in epoxy/halloysite nanotube/carbon fibre (EP/HNT/CF) multi-scale composites. The distribution of nanotubes in the composites was examined by SEM. The thermomechanical properties of the composites were characterized by dynamic mechanical analyser (DMA). A 25% enhancement was recorded for the storage modulus of EP/HNT/CF composite in the glassy state. Moreover, the T_g of the laminates increased with the addition of HNT, and the values were even higher than the T_g of their matrix. Additionally, the Izod impact strength of the composites has been improved. These results indicate a synergistic effect between HNT and carbon fibres.     

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.     

Multiscale molecular modeling of SWCNTs/epoxy resin composites mechanical behaviour

Atomistic and mesoscale simulations were conducted to estimate the effect of the diameter and weight fraction of single walled carbon nanotubes (SWCNTs) on mechanical behaviour and glass transition temperature (T_g) of SWCNTs reinforced epoxy resin composites. Atomistic periodic systems of epoxy resin and epoxy resin/SWCNTs were built with different weight ratios and were subject of an extensive multistage equilibration procedure. Molecular dynamics simulations were used to estimate glass transition temperature, Young modulus and solubility parameter of epoxy resin and epoxy resin/SWCNTs composites. Dissipative particle dynamics method and Flory–Huggins theory was employed to predict epoxy resin/SWCNTs morphologies. The results show that incorporation of SWCNTs with diameters ranging from 10 to 14 Ǻ has beneficial effect on mechanical integrity and T_g. Overall, the agreement between predicted material properties and experimental data in the literature is very satisfactory.     

Multiscale molecular modeling of SWCNTs/epoxy resin composites mechanical behaviour

Atomistic and mesoscale simulations were conducted to estimate the effect of the diameter and weight fraction of single walled carbon nanotubes (SWCNTs) on mechanical behaviour and glass transition temperature (T_g) of SWCNTs reinforced epoxy resin composites. Atomistic periodic systems of epoxy resin and epoxy resin/SWCNTs were built with different weight ratios and were subject of an extensive multistage equilibration procedure. Molecular dynamics simulations were used to estimate glass transition temperature, Young modulus and solubility parameter of epoxy resin and epoxy resin/SWCNTs composites. Dissipative particle dynamics method and Flory–Huggins theory was employed to predict epoxy resin/SWCNTs morphologies. The results show that incorporation of SWCNTs with diameters ranging from 10 to 14 ? has beneficial effect on mechanical integrity and T_g. Overall, the agreement between predicted material properties and experimental data in the literature is very satisfactory.     

Optimum mixing ratio of epoxy for glass fiber reinforced composites with high thermal stability

The optimum condition of glass fiber/epoxy composites was investigated according to mixing ratio of two epoxy matrices. Novolac type epoxy and isocyanate modified epoxy were used as composites matrix. Based on chemical composition of mixing matrix, optimum mixing ratio of epoxy resins was obtained through FT-IR instrument. In order to investigate thermal stability and interface of epoxy resin, glass transition temperature was observed by DSC instrument, and static contact angle was measured by reflecting microscope. Change of IR peak and T_g was conformed according to different epoxy mixing ratios. After fabrication of glass fiber/epoxy composites, tensile, compression, and flexural properties were tested by UTM by room and high temperature. The composites exhibited best mechanical properties when epoxy mixing ratio was 1:1.     

Woven hybrid biocomposites: Dynamic mechanical and thermal properties

The dynamic mechanical and thermal analysis of oil palm empty fruit bunch (EFB)/woven jute fibre (J_w) reinforced epoxy hybrid composites were carried out. The storage modulus (E′) was found to decrease with temperature in all cases, and hybrid composites had showed better values of E′ at glass transition temperature (T_g) compared to EFB and epoxy. Loss modulus showed shifts in the T_g of the polymer matrix with the addition of fibre as reinforcing phase, which indicate that fibre plays an important role in case of T_g. The Tan δ peak height was minimum for jute composites and maximum for epoxy matrix. Complex modulus variations and phase behaviour of the hybrid composites was studied by Cole-Cole analysis. Thermal analysis result indicates an increase in thermal stability of EFB composite with the incorporation of woven jute fibres. Hybridization of EFB composite with J_w fibres enhanced the dynamic mechanical and thermal properties.     

Poly(ether ether ketone) with pendent methyl groups as a toughening agent for amine cured DGEBA epoxy resin

A diglycidyl ether of bisphenol-A (DGEBA) epoxy resin was modified with poly(ether ether ketone) with pendent methyl groups (PEEKM). PEEKM was synthesised from methyl hydroquinone and 4,4′-difluorobenzophenone and characterised. Blends of epoxy resin and PEEKM were prepared by melt blending. The blends were transparent in the uncured state and gave single composition dependent T _g. The T _g-composition behaviour of the uncured blends has been studied using Gordon–Taylor, Kelley–Bueche and Fox equations. The scanning electron micrographs of extracted fracture surfaces revealed that reaction induced phase separation occurred in the blends. Cocontinuous morphology was obtained in blends containing 15 phr PEEKM. Two glass transition peaks corresponding to epoxy rich and thermoplastic rich phases were observed in the dynamic mechanical spectrum of the blends. The crosslink density of the blends calculated from dynamic mechanical analysis was less than that of unmodified epoxy resin. The tensile strength, flexural strength and modulus were comparable to that of the unmodified epoxy resin. It was found from fracture toughness measurements that PEEKM is an effective toughener for DDS cured epoxy resin. Fifteen phr PEEKM having cocontinuous morphology exhibited maximum increase in fracture toughness. The increase in fracture toughness was due to crack path deflection, crack pinning, crack bridging by dispersed PEEKM and local plastic deformation of the matrix. The exceptional increase in fracture toughness of 15 phr blend was attributed to the cocontinuous morphology of the blend. Finally it was observed that the thermal stability of epoxy resin was not affected by the addition of PEEKM.     

Fabrication of transparent polymer-matrix nanocomposites with enhanced mechanical properties from chemically modified ZrO<Subscript>2</Subscript> nanoparticles

Optically transparent nanocomposites with enhanced mechanical properties were fabricated using stable dispersions of sub 10 nm ZrO₂ nanoparticles. The ZrO₂ dispersions were mixed with a commercially available bisphenol-A-based epoxy resin (RIMR 135i) and cured with a mixture of two amine-based curing agents (RIMH 134 and RIMH 137) after complete solvent removal. The colloidal dispersions of ZrO₂ nanoparticles, synthesized through a non-aqueous approach, were obtained through a chemical modification of the ZrO₂ nanoparticle surface, employing different organic ligands through simple mixing at room temperature. Successful binding of the ligands to the surface was studied utilizing ATR–FT-IR and thermogravimetric analysis. The homogeneous distribution of the nanoparticles within the matrix was proven by SAXS and the observed high optical transmittance for ZrO₂ contents of up to 8 wt%. Nanocomposites with a ZrO₂ content of only 2 wt% showed a significant enhancement of the mechanical properties, e.g., an increase of the tensile strength and Young’s modulus by up to 11.9 and 12.5%, respectively. Also the effect of different surface bound ligands on the mechanical properties is discussed.     

Preparation and characterization of epoxy/γ-aluminum oxide nanocomposites

Epoxy/γ-Al₂O₃ nanocomposites were prepared with a homogenizer and followed by a stepwise thermal curing process in this study. The dispersion of γ-Al₂O₃ nanoparticles was examined with a transmission electron microscopy (TEM). Meanwhile, the effects of γ-Al₂O₃ nanoparticles on thermal, dynamic mechanical and tensile properties of epoxy/γ-Al₂O₃ nanocomposites were also investigated and discussed. When the γ-Al₂O₃ content was increased from 1phr to 5phr, results revealed that γ-Al₂O₃ nanoparticles were effective to enhance both the stiffness and toughness of epoxy resin. Meanwhile, the maximum properties of glass transition temperature (T_g), T_d5%, storage modulus, tensile modulus, and elongation at break were observed in the epoxy/5phr γ-Al₂O₃ nanocomposite.     

Effect vapor grown carbon nanofiber on thermal and mechanical properties of epoxy

In the present investigation, dynamic mechanical analysis (DMA), thermo gravimetric analysis (TGA), tensile tests, fatigue tests and the single edge notch tensile (SENT) tests were performed on unfilled, 1, 2 and 3 wt.% vapor grown carbon nanofiber (CNF) filled SC-15 epoxy to identify the loading effect on thermal and mechanical properties of the composites. DMA studies revealed that filling the 3% carbon nanofiber into epoxy can produce 65% enhancement in storage modulus at room temperature and 6 °C increase in T _g. However, TGA results show that thermal stability of composite is insensitive to the CNF content. Tensile tests were carried out at the strain rate range from 0.02 min⁻¹ to 2 min⁻¹. Results show that CNF/epoxy are strain rate sensitive materials, the modulus and tensile strength increased with increasing of strain rate. Experimental results also indicate that modulus of the nanophased epoxy increases continuously with increasing CNF content. But the 2% CNF infusion system exhibit maximum enhancement in tensile strength, fatigue performance and fracture toughness as compared with other system.     

Miscibility, morphology and fracture toughness of tetrafunctional epoxy resin/poly (styrene-co-acrylonitrile) blends

Poly(styrene-co-acrylonitrile) (SAN) was found to be miscible with the tetraglycidylether of 4,4'-diaminodiphenylmethane (TGDDM), as shown by the existence of a single glass transition temperature (T _g) over the whole composition range. However, SAN was found to be immiscible with the 4,4-diaminodiphenylmethane (DDM)-cured TGDDM. Dynamic mechanical analysis (DMA) shows that the DDM-cured TGDDM/SAN blends have two T _gs. A scanning electron microscopy (SEM) study revealed that all the DDM-cured TGDDM/SAN blends have a two-phase structure. The fracture toughness K _IC of the blends increased with SAN content and showed a maximum at 10 wt% SAN content, followed by a dramatic decrease for the cured blends containing 15 wt% SAN or more. The SEM investigation of the K _IC fracture surfaces indicated that the toughening effect of the SAN-modified epoxy resin was greatly dependent on the morphological structures.     

High temperature mechanical properties of high toughness metallic filament composites with polyimide and epoxy matrices

High toughness metallic filament was produced by glass-coated melt spinning. The high temperature mechanical properties of the composite consisting of the filaments uniaxially aligned in polyimide and epoxy matrices were investigated at the temperature range from 423 K to 573 K.The Young's modulus of the composite (E _c) of the polyimide composite at temperatures up to 573 K was higher than that predicted by the linear function of the filament content (V _f) and the filaments fractured tightly in contact with the matrix. The epoxy resin composite had a excellent high temperature mechanical properties in spite of the low T _g of the resin and large thermal expansion mismatch between the filaments and the resin. The value of E _c at 573 K was higher than that of a linear function of the V _f and tensile strength of the composite ( _cu) at 573 K agreed with the simple law of mixture. It is considered that some heat reaction of the resin occurred by incorporating the metallic filaments.     

Fabrication and characterization of carbon fiber reinforced clay/epoxy composite

In this study, dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and flexural tests were performed on unfilled, 1, 2, 3, and 4 wt% clay filled SC-15 epoxy to identify the effect of clay weight fraction on thermal and mechanical properties of the epoxy matrix. The flexural results indicate that 2.0 wt% clay filled epoxy showed the highest improvement in flexural strength. DMA studies also revealed that 2.0 wt% system exhibit the highest storage modulus and T _g as compared to neat and other weight fraction. However, TGA results show that thermal stability of composite is insensitive to the clay content. Based on these results, the nanophased epoxy with 2 wt% clay was then utilized in a vacuum assisted resin transfer molding set up with carbon fabric to fabricate laminated composites. The effectiveness of clay addition on thermal and mechanical properties of composites has been evaluated by TGA, DMA, tensile, flexural, and fatigue test. 5 °C increase in glass transition temperature was found in nanocomposite, and the tensile and flexural strengths improved by 5.7 and 13.5 %, respectively as compared to the neat composite. The fatigue strength was also improved significantly. Based on the experimental result, a linear damage model combined with the Weibull distribution function has been established to describe static failure processing of neat and nanophased carbon/epoxy. The simulated stress–strain curves from the model are in good agreement with the test data. Simulated results show that damage processing of neat and nanophased carbon/epoxy described by bimodal Weibull distribution function.     

Characterization of transverse tensile, interlaminar shear and interlaminate fracture in CF/EP laminates with 10 wt% and 20 wt% silica nanoparticles in matrix resins

The transverse tensile properties, interlaminar shear strength (ILSS) and mode I and mode II interlaminar fracture toughness of carbon fibre/epoxy (CF/EP) laminates with 10 wt% and 20 wt% silica nanoparticles in matrix were investigated, and the influences of silica nanoparticle on those properties of CF/EP laminates were characterized. The transverse tensile properties and mode I interlaminar fracture toughness (G_IC) increased with an increase in nanosilica concentration in the matrix resins. However, ILSS and the mode II interlaminar fracture toughness (G_IIC) decreased with increasing nanosilica concentration, especially for the higher nanosilica concentration (20 wt%). The reduced G_IIC value is attributed to two main competing mechanisms; one is the formation of zipper-like pattern associated with matrix microcracks aligned 45° ahead of the crack tip, while the other is the shear failure of matrix. The ratio of G_IIC/G_IC decreased with the concentration of silica nanoparticles, comparable with similar CF/EP laminates with dispersed CNTs in matrix. Fractographic studies showed that interfacial failure between carbon fibre and epoxy resin occurred in the neat epoxy laminate, whereas a combination of interfacial failure and matrix failure occurred in the nanosilica-modified epoxy laminates, especially those with a higher nanosilica concentration (20 wt%).     

Microstructure and mechanical properties of SiC Whisker reinforced ZrO2–Y2O3 composites

Abstract

The mechanical properties of 20 vol.-%SiC whisker reinforced ZrO₂?V₂O₃ composites containing 2 and 6 mol.-% Y₂O₃ were measured at room temperature and the fracture surface was examined. The results indicate that the mechanical behaviour of the composites is strongly influenced by the Y₂O₃ content. The magnitude of the enhancement of the toughness in composites containing 2 mol.-% Y₂O₃ compared with unreinforced ZrO₂?Y₂O₃ matrix is larger than that for the composites containing 6 mol.-% Y₂O₃. Crack propagation modes were characterised by crack deflection, whisker bridging, and whisker pullout. High resolution electron microscopic observations show that in composites containing 2 mol.-% Y₂O₃ the whiskers are directly bonded to the matrix. However, in composites containing 6 mol.-% Y₂O₃ there is always a thick amorphous layer at the interface, indicating that the high Y₂O₃ content has promoted the formation of interfacial amorphous layers. These interfacial amorphous layers strengthen the interfacial bonding, resulting in a composite with a low fracture toughness.

MST/2043     

Tuning the mechanical properties of glass fiber-reinforced bismaleimide–triazine resin composites by constructing a flexible bridge at the interface

Abstract

We demonstrate a new method that can simultaneously improve the strength and toughness of the glass fiber-reinforced bismaleimide–triazine (BT) resin composites by using polyethylene glycol (PEG) to construct a flexible bridge at the interface. The mechanical properties, including the elongation, ultimate tensile stress, Young’s modulus, toughness and dynamical mechanical properties were studied as a function of the length of PEG molecular chain. It was found that the PEG molecule acts as a bridge to link BT resin and glass fiber through covalent and non-covalent bondings, respectively, resulting in improved interfacial bonding. The incorporation of PEG produces an increase in elongation, ultimate tensile stress and toughness. The Young’s modulus and T_g were slightly reduced when the length of the PEG molecular chain was high. The elongation of the PEG-modified glass fiber-reinforced composites containing 5 wt% PEG-8000 increased by 67.1%, the ultimate tensile stress by 17.9% and the toughness by 78.2% compared to the unmodified one. This approach provides an efficient way to develop substrate material with improved strength and toughness for integrated circuit packaging applications.     

Characterization of mechanical properties of epoxy resin reinforced with submicron-sized ZnO prepared via in situ synthesis method

In this paper, ZnO/epoxy composites with homogeneous dispersion were prepared via two simple steps: firstly, in situ preparation of zinc hydroxide (Zn(OH)₂)/epoxy from the reaction of aqueous zinc acetate (Zn(Ac)₂·2H₂O) and sodium hydroxide (NaOH) at 30 °C in the presence of high viscosity epoxy resin; secondly, thermal treatment of the as-prepared Zn(OH)₂/epoxy hybrid into ZnO/epoxy composites. Meanwhile, the structure, composition and mechanical properties of the resultant products were successfully investigated. From the result of characterization we found that the composite had the optimal mechanical property at ZnO fraction of 5 wt.%. Compared to pure epoxy resin, the improvement of ultimate tensile stress, elongation at break, tensile modulus and flexural strength achieved about 40.84%, 24.35%, 27.27% and 51.43%, respectively. The crack arresting mechanisms included particle matrix debonding, plastic void growth, in the composites with a stronger interface, significant plastic deformation of the matrix around the well bonded particles. At the same time, the possible reactive mechanism of the preparation of ZnO/epoxy composite was discussed in this paper.     

Influences of cellulose nanofiber on the epoxy network formation

The effects of cellulose nanofiber on the curing behavior, dynamic mechanical, and morphology properties of epoxy/diamine systems were investigated. The studies were conducted using an aliphatic triamine, diethylentriamine (Dien), and an aromatic diamine, diaminodiphenylmethan (DDM), as the curing agents in the presence of three different levels of 0.5, 2, and 5 phr of cellulose nanofiber. Calorimetry experiments were used to probe the changes in the reaction enthalpy and in the glass transition temperature (T_g) as a function of the fiber concentration. The results showed that both the T_g and the heat of reaction were increased with increasing the fiber concentration up to 2 phr. The experimental cure data obtained from in situ FT-IR measurements were used to evaluate the kinetic parameters using the modified Avrami theory of phase change. The results showed that the kinetic parameters were less sensitive to the epoxy composition. DMTA measurements showed that the storage modulus and the T_g of the composites were dependant on the level of fiber loading. SEM studies revealed that a reasonable dispersion and adhesion have been achieved between the fiber and the epoxy matrix at low concentration of fiber. It is concluded that the fiber agglomerated at high concentration of cellulose fiber prevented the formation of a homogeneous mixture, thus resulting in weak thermal and mechanical properties.     

Investigation of the long term effects of moisture on carbon fibre and epoxy matrix composites

The aim of this work is to investigate the long term effects of moisture on the interface between a carbon fibre and an epoxy matrix. High modulus carbon fibres were used to prepare single fibre model composites based on an epoxy resin. The samples were immersed in the seawater and demineralised water and their moisture uptake behaviour was monitored. The equilibrium moisture content and diffusion coefficients for the samples were determined. DSC has been used to analyse the moisture effects on glass transition temperature and thermal stability of the pure epoxy specimens. These results showed a reduction in the glass transition temperature (T_g) after moisture absorption. Tensile tests were also carried out for the epoxy specimens and a general decrease in the mechanical properties of the epoxy matrix was observed. Raman spectroscopy was used to observe the effects of moisture on the axial strain of the carbon fibre within the composite and stress transfer at the interface as a function of exposure time. The results show that the decrease in the mechanical and interfacial properties of the model composites under the seawater immersion is more significant than under demineralised water immersion.