Mechanical,thermal and microstructural characteristics of cellulose fibre reinforced epoxy/organoclay nanocomposites

Epoxy nanocomposites reinforced with recycled cellulose fibres (RCFs) and organoclay platelets (30B) have been fabricated and investigated in terms of WAXS, TEM, mechanical properties and TGA. Results indicated that mechanical properties generally increased as a result of the addition of nanoclay into the epoxy matrix. The presence of RCF significantly enhanced flexural strength, fracture toughness, impact strength and impact toughness of the composites. However, the inclusion of 1 wt.% clay into RCF/epoxy composites considerably increased the impact strength and toughness. The presence of either nanoclay or RCF accelerated the thermal degradation of neat epoxy, but at high temperature, thermal stability was enhanced with increased char residue over neat resin. The failure micromechanisms and energy dissipative processes in these nanocomposites were discussed in terms of microstructural observations.     

Microstructure and mechanical properties of epoxy hybrid nanocomposites modified with acrylic tri-block-copolymer and layered-silicate nanoclay

In this study, processing, morphology and mechanical properties of acrylic tri-block-copolymer and organophilic layered-silicate nanoclay modified epoxy hybrid nanocomposites were investigated. The acrylic tri-block-copolymer preferentially self-assembled into spherical micelles in the epoxy matrix, and predominantly intercalated and few exfoliated platelets were observed with nanoclay. Three-phase ternary nanocomposites showed coexistence of both intercalated nanoclay and nanostructured block-copolymer in epoxy. Experimental results revealed that the block-copolymer significantly enhanced fracture toughness. Increased toughness of epoxy coincided with a reduction of tensile stiffness and strength. The nanoclay filled nanocomposites exhibited superior stiffness and slight improvement in tensile strength while compromising ductility. Optimum property enhancement was observed in the case of epoxy hybrid nanocomposites. Mechanical properties of the hybrid nanocomposites depend on microstructure, dispersion state and the ratio between organic and inorganic nanofiller contents.     

Elastomeric epoxy nanocomposites: Nanostructure and properties

In polymer layered silicate nanocomposites, significant differences have been reported between the effects of the nano-reinforcement on rigid and elastomeric nanocomposites. In this paper, we have studied elastomeric nanocomposites based upon DGEBA epoxy resin filled with montmorillonite (MMT) and cured with a long-chain polyoxypropylene diamine, for comparison with analogous rigid nanocomposites. Ultrasonic mixing was used to disperse the MMT in the matrix to improve homogeneity and decrease the agglomerate size. Two different methods of nanocomposite preparation were used in which the MMT was first swollen with either the curing agent or the epoxy before the addition of, respectively, DGEBA or diamine. A better dispersion of the nanoclay in the matrix and a greater amount of intercalation occurred when the MMT was first swollen with the diamine. The effect of MMT concentrations up to 8 wt.% on the mechanical behaviour of the epoxy/MMT nanocomposites was investigated. It was found that the addition of MMT increased the tensile strength and modulus, although SAXS and TEM indicated that a significant fraction of the clay layers were not exfoliated. Nevertheless, the addition of the clay resulted in changes in the fracture surfaces, as indicated by SEM, consistent with the tensile results and indicative of toughening.     

Strain rate sensitivity of glass/epoxy composites with nanofillers

It is understood that small amount of nanoclay in the neat epoxy and fiber reinforced epoxy composite system improves the mechanical properties. The mechanical properties of most of polymer matrix composites are rate sensitive. Most of the researches have concentrated on the behavior of the polymer composites at high strain rates. The present research work is to study the effect of clay on neat epoxy and glass/epoxy composites, at low strain rates. The clay in terms of 1.5, 3 and 5 wt% are dispersed in the epoxy resin using mechanical stirrer followed by sonication process. The glass/epoxy nanocomposites are prepared by impregnating the glass fiber with epoxy–clay mixture by hand lay-up process followed by compression molding. Characterization of the nanoclay is done by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Tensile stress–strain curves are obtained at strain rates of 10⁻⁴, 10⁻³, 10⁻² and 10⁻¹ s⁻¹ by a servo-hydraulic machine and the variation of modulus, strength and failure strain with strain rate are determined. The results show that, even at low strain rates, the longitudinal strength and stiffness increase as strain rate increases for all clay loadings. It is observed that the tensile modulus increases as the clay loading increases for both epoxy and glass/epoxy nanocomposites. Scanning electron microscopy is used to study the adhesion of composites in fracture surfaces.     

The effects of alumina nanofillers on mechanical properties of high-performance epoxy resin

In the past decade extensive studies have been focused on mechanical properties of inorganic nanofiller/epoxy matrices. In this work we systematically investigated the mechanical properties of nano-alumina-filled E-54/4, 4-diaminodiphenylsulphone (DDS) epoxy resins, which were prepared via combining high-speed mixing with three-roll milling. Homogeneous dispersion of nano-alumina with small agglomerates was obtained in epoxy resin, which was confirmed using transmission electron microscopy (TEM). The static/dynamic modulus, tensile strength and fracture toughness of the nanocomposites were found to be simultaneously enhanced with addition of nano-alumina fillers. About 50% and 80% increases of K(IC) and G(IC) were achieved in nanocomposite filled with 18.4 wt% alumina nanofillers, as compared to that of the unfilled epoxy resin. Furthermore, the corresponding fracture surfaces of tensile and compact tension samples were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques in order to identify the relevant fracture mechanisms involved. Various fracture features including cavities/debonding of nanofiller, local plastic deformation as well as crack pinning/deflection were found to be operative in the presence of nano-alumina fillers.     

Mechanical Behavior of Nanodiamond/Epoxy Nanocomposites

The mechanical properties of epoxy-based nanocomposites reinforced by nanodiamond (ND) particles were investigated. The results showed that while the addition of 0.1 wt% of ND improved the Young’s modulus and tensile strength compared with those of the pure epoxy, the mode I fracture toughness did not show any improvement. Furthermore, in order to study the effect of shear deformation on fracture properties of nanocomposites, mixed mode fracture resistance of nanocomposites was investigated. It was found that as the share of shear deformation in mixed mode loading increases, the positive effect of ND particles enhances.     

Localized elastic modulus distribution of nanoclay/epoxy composites by using nanoindentation

The enhancement of mechanical properties by the use of nanoclay platelets in epoxy resin has been extensively investigated through numerous experimental techniques recently. Elastic modulus was obtained mainly from the tensile test of bone-like nanoclay/epoxy specimens. The results from the tensile test have only showed the globalized mechanical properties of composites and their localized elastic modulus distribution has been neglected. Despite the orientation and the degree of exfoliation of nanoclay platelets inside nanoclay/epoxy composites, the localized elastic modulus is important for the understanding of the distribution of agglomerations of nanoclay platelets. The elastic modulus of nanoclay/epoxy composite samples made under different sonication temperatures would be examined by nanoindentation to compare their localized mechanical behaviors. Scanning electron microscopy (SEM) would also be employed to study the distribution of the nanoclay clusters throughout the composites. The results showed that the elastic modulus varied throughout the composites and the nucleation theory of clusters was modified to explain the behavior of nanoclay agglomerations under different sonication temperatures in which the viscosity of the epoxy resin was varied. The gravitational effect was significant to cause the non-uniform distributions of nanoclay clusters at low sonication temperature.     

Fabrication and mechanical properties of well-dispersed multiwalled carbon nanotubes/epoxy composites

Multiwalled carbon nanotubes (MWCNTs)/epoxy nanocomposites were fabricated by using ultrasonication and the cast molding method. In this process, MWCNTs modified by mixed acids were well dispersed and highly loaded in an epoxy matrix. The effects of MWCNTs addition and surface modification on the mechanical performances and fracture morphologies of composites were investigated. It was found that the tensile strength improved with the increase of MWCNTs addition, and when the content of MWCNTs loading reached 8 wt.%, the tensile strength reached the highest value of 69.7 MPa. In addition, the fracture strain also enhanced distinctly, implying that MWCNTs loading not only elevated the tensile strength of the epoxy matrix, but also increased the fracture toughness. Nevertheless, the elastic modulus reduced with the increase of MWCNTs loading. The reasons for the mechanical property changes are discussed.     

Thermal, mechanical and vibration characteristics of epoxy-clay nanocomposites

Diglycidyl ether of bisphenol-A (DGEBA) epoxy resin system filled individually with organoclay (OC) and unmodified clay (UC) were synthesized by mechanical shear mixing with the addition of diamino-diphenylmethane (DDM) hardener. The unmodified clay used was Na⁺-Montmorillonite (MMT) and the organoclay was alkyl ammonium treated MMT clay. The reinforcement effect of OC and UC in the epoxy polymer on thermal, mechanical and vibration properties were studied. X-ray diffraction (XRD) and Transmission electron microscopy (TEM) were used to study the structure and morphology of nanocomposites. Curing study shows that the addition of OC in epoxy resin aids the polymerization by catalytic effect, and UC addition does not show any effect in the curing behavior of epoxy polymer. Thermogravimetry analysis (TGA) shows enhanced thermal stability for epoxy with OC fillers than that of epoxy with UC fillers. The epoxy with OC fillers shows considerable improvement on tensile and impact properties over pure epoxy polymer and epoxy with UC fillers. The improvement in tensile and impact properties of nanocomposites is supported with the fracture surface studies. Epoxy with OC fillers shows enhanced vibration characteristics than that of the pure epoxy polymer and epoxy with UC fillers.     

Reinforcement and toughening mechanisms in polymer nanocomposites – Carbon nanotubes and aluminum oxide

The addition of nanoparticles has been reported as an option to increase the fracture toughness of thermosetting polymers without compromising the stiffness. In this paper, alumina or carbon nanotubes (CNTs), in three different concentrations, were dispersed in an epoxy resin. Mechanical properties were measured through tensile test and the results indicate increases for all nanocomposites, with a maximum for the addition of 0.5% of CNTs (17% in elastic modulus and 22% in ultimate stress). Using TEM images, it was possible to identify the nanostructures and mechanisms that lead to improved stiffness. Fracture toughness tests and SEM images showed that cavitation – shear yielding (for epoxy/alumina nanocomposites) and crack bridging – pull-out (for epoxy/CNTs nanocomposites) are the predominant mechanisms.     

Torsional,tensile and structural properties of acrylonitrile–butadiene–styrene clay nanocomposites

Torsional and tensile behaviour of acrylonitrile–butadiene–styrene (ABS)-clay nano-composites have been investigated and correlated with morphological and rheological characterisations. Nano-composites of ABS are prepared by melt compounding with different loading levels of nanoclay (Cloisite 30B) in a twin screw extruder and have been characterised in terms of torsional, axial and impact behaviour for their application in external orthotic devices. Tensile stress strain curve of nanocomposites are investigated to quantify resilience, toughness and ductility. Torque values of the nanocomposites are observed under torsion (10°–90°) and compared with that of neat ABS. Performance of ABS under torsional load improved by addition of nanoclay. Both modulus of elasticity and rigidity are found to improve in presence of nanoclay. State of dispersion in nano-composites is investigated using conventional methods such as transmission electron microscopy (TEM), X-ray diffraction (XRD), as well as by parallel plate rheometry. Addition of clay exhibits shear thinning effect and results in increase in storage modulus as well as complex viscosity of the nanocomposites. Zero shear viscosity rises tenfold with 1–2% addition of nanoclay, indicating the formation of structural network. It is found that state of dispersion of nanoclay governs the torsional and mechanical properties in ABS-clay nanocomposites.     

Effect of processing parameters and clay volume fraction on the mechanical properties of epoxy-clay nanocomposites

The influence of processing parameters and particle volume fraction was experimentally studied for epoxy clay nanocomposites. Nanocomposites were prepared using onium ion surface modified montmorillonite (MMT) layered clay and epoxy resin (DEGBF). Two different techniques were used for dispersing the clay particles in the epoxy matrix, viz. high-speed shear dispersion and ultrasonic disruption. The volume fraction of clay particles was systematically varied from 0.5 to 6%, and mechanical properties, viz. flexural modulus and fracture toughness, were studied as a function of clay volume fraction and the processing technique. The flexural modulus was observed to increase monotonously with increase in volume fraction of clay particles, while, the fracture toughness showed an initial increase on addition of clay particles, but a subsequent decrease at higher clay volume fractions. In general, nanocomposites processed by shear mixing exhibited better mechanical properties as compared to those processed by ultrasonication. Investigation by X-ray diffraction (XRD) revealed exfoliated clay structure in most of the nanocomposites that were fabricated. Morphologies of the fracture surfaces of nanocomposites were studied using a scanning electron microscopy (SEM). Presence of river markings at low clay volume fractions provided evidence of extrinsic toughening taking place in an otherwise brittle epoxy.     

Mode I interlaminar fracture behavior and mechanical properties of CFRPs with nanoclay-filled epoxy matrix

The mechanical properties and fracture behavior of nanocomposites and carbon fiber composites (CFRPs) containing organoclay in the epoxy matrix have been investigated. Morphological studies using TEM and XRD revealed that the clay particles within the epoxy resin were intercalated or orderly exfoliated. The organoclay brought about a significant improvement in flexural modulus, especially in the first few wt% of loading, and the improvement of flexural modulus was at the expense of a reduction in flexural strength. The quasi-static fracture toughness increased, whereas the impact fracture toughness dropped sharply with increasing the clay content.Flexural properties of CFRPs containing organoclay modified epoxy matrix generally followed the trend similar to the epoxy nanocomposite although the variation was much smaller for the CFRPs. Both the initiation and propagation values of mode I interlaminar fracture toughness of CFRP composites increased with increasing clay concentration. In particular, the propagation fracture toughness almost doubled with 7 wt% clay loading. A strong correlation was established between the fracture toughness of organoclay-modified epoxy matrix and the CFRP composite interlaminar fracture toughness.     

Physicochemical and mechanical interfacial properties of trifluorometryl groups containing epoxy resin cured with amine

A phenyl-trifluoromethyl (-Ph-CF₃) groups modified epoxy resin, diglycidylether of bisphenol A-fluorine (DGEBA-F), was synthesized and the physical properties, such as curing behaviors, thermal stabilities, and dielectric constant of the DGEBA-F/4,4′-diaminodiphenyl methane (DDM) system were investigated and compared with commercial DGEBA/DDM system. For the mechanical behaviors of the specimens, the fracture toughness and impact tests were performed, and their fractured surfaces were examined by using a scanning electron microscope (SEM). The dielectric constant values of the DGEBA-F/DDM system were lower than those of the DGEBA/DDM system and the mechanical properties of the casting DGEBA-F specimens were higher than those of the DGEBA specimens. This was probably due to the fact that the introduction of the -Ph-CF₃ groups into the side chain of the epoxy resin resulted in improving the electrical properties and toughness of the cured DGEBA-F epoxy resin.     

Mechanical properties and water uptake of epoxy–clay nanocomposites containing different clay loadings

Nanocomposites based on diglycidyl ether of bisphenol A (DGEBA) epoxy reinforced with 1–10 wt% I.30E nanoclay were fabricated using high shear mixing technique and characterized to determine the effects of clay loading on their mechanical, thermal, and water uptake properties. The XRD and TEM analyses revealed that the structures of the resultant nanocomposites were a combination of disordered intercalated and exfoliated morphologies. Tensile strength increased for nanocomposite containing 1 % clay loading and decreased for higher nanoclay loading. Unlike strength, the stiffness increased almost linearly with clay loading, showing 46 % improvement in modulus of elasticity for nanocomposites containing 5 % of nanoclay. Water uptake measurements indicated enhancement in the barrier properties of epoxy matrix as nanoclay loading increased from 1 up to 5 wt%.     

复合材料用环氧树脂的韧化(五)增靱机理的探讨

本文工作研究了复合材料用环氧树脂的韧化。该体系由无规羧基丁腈橡胶,双酚A型环氧树脂,2-乙基-4-甲基咪唑组成。无规羧基丁腈橡胶对环氧树脂的增韧效果以及用增韧环氧树脂作基体材料对复合材料性能的影响已作报导[1,2,3]。本文报导无规羧基丁腈橡胶增韧环氧浇注体在应力下的形变特性及裂缝扩展特征。主要阐述橡胶增韧环氧浇注体受拉应力作用时,产生的两个形变过程——裂纹化与剪切变形,并根据双悬臂梁劈裂试件的断裂面形态,讨论了裂缝亚临界扩展区。     

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.     

Improvement of tensile properties and toughness of an epoxy resin by nanozirconium-dioxide reinforcement

Zirconium dioxide (ZrO₂) nanoparticles were systematically added as reinforcement to a diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin. A series of composites with varying amounts of nanoparticles was prepared and their morphology and mechanical properties were studied. The obtained nanocomposites were characterized by tensile tests, dynamic mechanical thermal analysis, and fracture toughness (K_IC) investigations; by standardized methods, to define the influence of the nanoparticle content on their mechanical and thermal properties. The morphological analysis of the composites shows that nanoparticles form small clusters, which are uniformly distributed into the matrix bulk. The tensile modulus (E) and the K_IC of the epoxy matrix increase at rising zirconia content. Improvements of more than 37% on modulus and 100% on K_IC were reached by the nanocomposite containing 10 vol.-% ZrO₂ with respect to the neat epoxy (E_o = 3.1 GPa, K_ICo = 0.74 MPam^0.5). The presence of nanoparticles produces also an increment on glass transition temperature (T _g). The epoxy resin added with 8 vol.-% ZrO₂ records a T _g approximately 8% higher than the unmodified matrix (T _go = 100.3 °C).     

Fracture toughness and water uptake of high-performance epoxy/nanoclay nanocomposites

Aircraft grade epoxy–clay nanocomposites based on tetraglycidyl-4, 4′-diaminodiphenylmethane (TGDDM) cured with diaminodiphenyl sulphone (DDS) were synthesized. Nanoclay was dispersed in both acetone and an acetone epoxy solution with a high pressure mixing (HPM) method to form pastes. The basal spacing of the nanoclay in these pastes was increased as observed from X-ray diffraction (XRD) data. Transmission electron microscopy (TEM) images show that the agglomerates of nanoclay were broken down to form small particles consisting of several clay platelets. Fracture toughness of this epoxy system has been greatly enhanced with the addition of nanoclay. With the addition of only 4.5 phr of clay, the strain energy release rate of the epoxy is increased 5.8 times from the original value. Scanning electron microscope (SEM) was used to examine the characteristics of the fracture surfaces from the different materials. There is also significant reduction in the diffusivity and the maximum water uptake of the epoxy resin with the addition of the nanoclay.     

Enhanced Mechanical Properties of Epoxy Nanocomposites by Mixing Noncovalently Functionalized Boron Nitride Nanoflakes

The influence of surface modifications on the mechanical properties of epoxy‐hexagonal boron nitride nanoflake (BNNF) nanocomposites is investigated. Homogeneous distributions of boron nitride nanoflakes in a polymer matrix, preserving intrinsic material properties of boron nitride nanoflakes, is the key to successful composite applications. Here, a method is suggested to obtain noncovalently functionalized BNNFs with 1‐pyrenebutyric acid (PBA) molecules and to synthesize epoxy–BNNF nanocomposites with enhanced mechanical properties. The incorporation of noncovalently functionalized BNNFs into epoxy resin yields an elastic modulus of 3.34 GPa, and 71.9 MPa ultimate tensile strength at 0.3 wt%. The toughening enhancement is as high as 107% compared to the value of neat epoxy. The creep strain and the creep compliance of the noncovalently functionalized BNNF nanocomposite is significantly less than the neat epoxy and the nonfunctionalized BNNF nanocomposite. Noncovalent functionalization of BNNFs is effective to increase mechanical properties by strong affinity between the fillers and the matrix.