Preparation,morphology and properties of acid and amine modified multiwalled carbon nanotube/polyimide composite

The precursor of polyimide, polyamic acid, was prepared by reacting 4,4′-oxydianiline (ODA) with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA). Unmodified, acid-modified and amine-modified multiwall carbon nanotubes (MWCNT) were separately added to the polyamic acid and heated to 300 °C to produce polyimide/carbon nanotube composite. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) microphotographs reveal that acid-modified MWCNT and amine-modified MWCNT were dispersed uniformly in the polyimide matrix. The effect of the acid and amine-modified MWCNTs on the surface and volume electrical resistivities of MWCNT/polyimide composites were investigated . The surface electrical resistivity of the nanocomposites decreased from 1.28 × 10¹⁵ Ω/cm² (neat polyimide) to 7.59 × 10⁶ Ω/cm² (6.98 wt% unmodified MWCNT content). Adding MWCNTs influenced the glass transition temperatures of the nanocomposites. Modified MWCNTs significance enhanced the mechanical properties of the nanocomposites. The tensile strength of the MWCNT/polyimide composite was increased from 102 MPa (neat polyimide) 134 MPa (6.98 wt% acid modified MWCNT/polyimide composites).     

Dynamic fracture of carbon nanotube/epoxy composites under high strain-rate loading

We investigate dynamic fracture of three types of multiwalled carbon nanotube (MWCNT)/epoxy composites and neat epoxy under high strain-rate loading (${10}^5''–''{10}^6$ s⁻¹). The composites include randomly dispersed, 1 wt%, functionalized and pristine CNT/epoxy composites, as well as laminated, ∼50 wt% CNT buckypaper/epoxy composites. The pristine and functionalized CNT composites demonstrate spall strength and fracture toughness slightly higher and lower than that of neat epoxy, respectively, and the spall strength of laminated CNT buckypaper/epoxy composites is considerably lower; both types of CNTs reduce the extent of damage. Pullout, sliding and immediate fracture modes are observed; the fracture mechanisms depend on the CNT–epoxy interface strength and fiber strength, and other microstructures such as the interface between CNT laminates. Compared to the functionalized CNT composites, weaker CNT–epoxy interface strength and higher fiber strength lead to a higher probability of sliding fracture and higher tensile strength in the pristine CNT composites at high strain rates. On the contrary, sliding fracture is more pronounced in the functionalized CNT composites under quasistatic loading, a manifestation of a loading-rate effect on fracture modes. Despite their helpful sliding fracture mode and large CNT content, the weak laminate–laminate interfaces play a detrimental role in fracture of the laminated CNT buckypaper/epoxy composites. Regardless of materials, increasing strain rates leads to pronounced rise in tensile strength and fracture toughness.     

The mechanical properties of ionoplast interlayer material at high strain rates

Ionoplast material has been recently introduced and extensively used as interlayer material for laminated glass to improve its post-glass breakage behavior. Due to its sound mechanical performance, the applications of laminated glass with ionoplast interlayer have been widely extended to the protection of glass structures against extreme loads such as shock and impact. The properties of this material at high strain rates are therefore needed for properly analysis and design of such structures. In this study, the mechanical properties of ionoplast material are studied experimentally through direct tensile tests over a wide strain rate range. The low-speed tests are performed using a conventional hydraulic machine at strain rates from 0.0056 s⁻¹ to 0.556 s⁻¹. The high strain-rate tests are carried out with a high-speed servo-hydraulic testing machine at strain rates from approximately 10 s⁻¹ to 2000 s⁻¹. It is found that the ionoplast material virtually exhibits elasto-plastic material properties in the strain rate range tested in this study. The testing results show that the material behavior is very strain-rate dependent. The yield strength increases with strain rate, but the material becomes more brittle with the increase in strain rate, with the ultimate strains over 400% under quasi-static loading, and decreasing to less than 200% at strain rate around 2000 s⁻¹. The testing results indicate that simply applying the static material properties in predicting the structure responses of laminated glass with ionoplast interlayer subjected to blast and impact loads will substantially overestimate the ductility of the material and lead to inaccurate predictions of structure response. The testing results obtained in the current study together with available testing data in the literature are summarized and used to formulate the dynamic stress–strain curves of ionoplast material at various strain rates, which can be used in analysis and design of structures with ionoplast material subjected to blast and impact loads.     

Low-temperature superplasticity of Al2O3(p)/Ni–Co nanocomposites

Nanocomposites of Al₂O₃/Ni–Co prepared using Al₂O₃ of various particle sizes were fabricated by pulse current electrodeposition. Their superplastic tensile deformation was investigated at strain rates of 8.33 × 10⁻⁴ s⁻¹ and 1.67 × 10⁻³ s⁻¹ and temperatures of 723–823 K. The Al₂O₃ particle sizes and the deformation temperature had significant influence on the elongation of the deposited materials. The optimal superplastic condition and the maximum elongation were determined. A low temperature superplasticity with elongation of 632% was achieved at a strain rate of 1.67 × 10⁻³ s⁻¹ and 823 K. Scanning electron microscopy and transmission electron microscopy were used to examine the microstructures of the deposited and deformed samples. The grains grew to a micrometer dimensions and were elongated along the tensile direction after superplastic deformation. Superplasticity in electrodeposited nanocomposites is related to the presence of S at grain boundaries and to deformation twinning.     

Temperature effects on the fracture behavior and tensile properties of silane-treated clay/epoxy nanocomposites

We investigated the effects of clay silane treatment on the fracture behaviors of clay/epoxy nanocomposites by comparing the compliance, critical fracture load, and fracture toughness of silane-treated samples with those of untreated samples. The fracture toughnesses of untreated and silane-treated clay/epoxy nanocomposites were 8.52 J/m² and 15.55 J/m², respectively, corresponding to an 82% increase in fracture toughness after clay silane treatment. Tensile tests were performed at ?30 °C, 25 °C, 40 °C, and 70 °C. Tensile strength and elastic modulus were higher at ?30 °C than at 25 °C for both samples. However, the tensile properties decreased as temperature increased for both samples. In particular, at 70 °C, the tensile properties were less than 10% of the original value at room temperature, independent of surface treatment. The fracture and tensile properties of silane-treated clay/epoxy nanocomposites increased due to good dispersion of the clay in epoxy and improvement in interfacial adhesive strength between epoxy and clay layers.     

Microstructural correlations to micromechanical properties of polyamide-6/low density polyethylene-grafted-maleic anhydride/nanoclay ternary nanocomposites

Ternary nanocomposites were fabricated based on an optimized impact modified polyamide-6 (PA-6)/low density polyethylene grafted maleic anhydride (LDPE-g-MA) blend composition with varied concentration (∼0–6 wt.%) of organoclay, Cloisite 30B™. The microstructural attributes such as state of intercalation/exfoliation/crystalline organization and fractured surface topography of the nanocomposites by using electron microscopic and X-ray diffraction techniques. The X-ray diffraction studies have revealed that the crystallinity of the nanocomposites remained inappreciably affected. Dynamic mechanical analysis revealed an increase in T_g of the nanocomposites relative to the neat PA-6 and the optimized PA-6/LDPE-g-MA blend matrix indicating the reinforcement effects/mechanical restrictions imposed by the nanoclay layers to the polymer chain mobility. The quasi-static mechanical response and micromechanics aspects concerning interfacial effects and stress-transfer efficiency of the nanocomposites using Halpin-Tsai, Hui-Shia, Takayanagi and Pukanszky models have been investigated. Micromechanical analysis based on minimalistic assumptions revealed interphase-thickness reduction at higher nanoclay content with a correspondence to the reduction in reinforcement-efficiency. Scanning electron microscopy of the cryo-fractured xylene-etched nanocomposite surfaces have indicated a nanoclay content dependent transition from homogeneous to inhomogeneous deformation assisted by the formation of random microfibril-like interconnected networks.     

Effect of clay and PEO-PPO-PEO block copolymer on the microstructure and properties of cyanate ester/epoxy composite

In this study, processing, morphology and properties of poly (ethylene oxide)-block-poly (propylene oxide)-block-poly (ethylene oxide) (PEO-PPO-PEO) triblock copolymer and clay modified cyanate ester/epoxy hybrid nanocomposites were investigated. The PEO-PPO-PEO triblock copolymer preferentially reaction-induced microphase separate into spherical micelles in the cyanate ester/epoxy matrix. PEO-PPO-PEO was used as both nanostructuring agent for cyanate ester/epoxy blended resin and thus the predominantly intercalated and few exfoliated platelets of were also observed with clay, which successfully reduced the brittleness of the cyanate ester/epoxy blended resin increasing the toughness of designed materials. The stiffness and heat resistance of the neat BCE/EP resin could be retained in the BCE/EP/F68/clay hybrid nanocomposites. The optimum property enhancement was observed in the hybrid nanocomposites containing 5 wt% PEO-PPO-PEO and 3 wt% clay. The thermo/mechanical properties of the hybrid nanocomposites depend on microstructure, dispersion state and the ratio between organic and inorganic modifiers content.     

Thermally reduced graphene oxide acting as a trap for multiwall carbon nanotubes in bi-filler epoxy composites

The effect of thermally reduced graphene oxide (TRGO) on the electrical percolation threshold of multi wall carbon nanotube (MWCNT)/epoxy cured composites is studied along with their combined rheological/electrical behavior in their suspension state. In contrast to MWCNT and carbon black (CB) based epoxy composites, there is no prominent percolation threshold for the bi-filler (TRGO–MWCNT/epoxy) composite. Furthermore, the electrical conductivity of the bi-filler composite is two orders of magnitude lower (∼1 × 10⁻⁵ S/m) than the pristine MWCNT/epoxy composites (∼1 × 10⁻³ S/m). This result is primarily due to the strong interaction between TRGO and MWCNTs. Optical micrographs of the suspension and scanning electron micrographs of the cured composites indicate trapping of MWCNTs onto TRGO sheets. A morphological model describing this interaction is presented.     

Analytical and experimental studies on mechanical behavior of composites under high strain rate compressive loading

An analytical method is presented for the prediction of compressive strength at high strain rate loading for composites. The method is based on variable rate power law. Using this analytical method, high strain rate compressive stress–strain behavior is presented up to strain rate of 5000 s⁻¹ starting with the experimentally determined compressive strength values at relatively lower strain rates. Experimental results were generated in the strain rate range of 472–1957 s⁻¹ for a typical woven fabric E-glass/epoxy laminated composite along all the three principal directions. The laminated composite was made using resin film infusion technique. The experimental studies were carried out using compressive split Hopkinson pressure bar apparatus. It was generally observed that the compressive strength is enhanced at high strain rate loading compared with that at quasi-static loading. Also, compressive strength increased with increasing strain rate in the range of parameters considered. Analytically predicted results are compared with the experimental results up to strain rate of 1957 s⁻¹.     

Effect of short nylon-6 fibres on natural rubber-toughened polystyrene

Composites based on polystyrene and natural rubber at a ratio of 85/15 were prepared by melt mixing with nylon-6 fibres using an internal mixer. The loading of short nylon-6 fibre, untreated and resorcinol formaldehyde latex (RFL)-treated, was varied from 0 to 3 wt.%. Tensile and flexural test samples were punched out from sheets and tested to study the variation of mechanical and dynamic mechanical properties. The tensile behaviour of the composite has been determined at three different strain rates (4.1 × 10⁻⁴ s⁻¹, 2 × 10⁻³ s⁻¹ and 2 × 10⁻² s⁻¹). Both the tensile strength and Young’s modulus of the composite increased with strain rate. The tensile strength, tensile modulus, flexural strength and flexural modulus increased with the increase in fibre content up to 1 wt.%, above which there was a significant deterioration in the properties. The RFL-treated fibre composites showed improved mechanical properties compared to the untreated one. Dynamic mechanical analysis (DMA) showed that the storage modulus of the composite with RFL-treated fibre was better compared to the untreated one. The fibre–matrix morphology of the tensile fractured specimens was studied by scanning electron microscopy (SEM). The results suggested that the RFL treatment of nylon fibre promoted adhesion to the natural rubber phase of the blend, thereby improving the mechanical properties of the composite.     

The dynamic mechanical response of SiC particulate reinforced 2024 aluminum matrix composites

The compression properties of the aluminum alloy 2024 metal matrix composites reinforced with 50 vol.% SiC particles were investigated using Instron testing machine and split Hopkinson pressure bar (SHPB) in this paper. The compression stress–strain curves were obtained at the strain rates ranging from 1 × 10^− 3 to 2.5 × 10³/s. The fracture surfaces were characterized by scanning electron microscopy. The results showed that SiCp/2024 Al composites exhibited high strain-rate sensitivity. The strength of composites tended to increase–decrease with increasing of strain rates. The effect of the strain rate on elongation was also discussed.     

Thermal,mechanical and electrical properties of polyurethane/(3-aminopropyl) triethoxysilane functionalized graphene/epoxy resin interpenetrating shape memory polymer composites

Functionalized graphene (FG) was successfully synthesized by treating graphene oxide with (3-aminopropyl) triethoxysilane (KH-550) and then reduced by hydrazine hydrate. Subsequently, significant reinforcement of polyurethane/epoxy resin (PU/EP) composites in situ synthesized on the FG is prepared. Morphologic study shows that, due to the formation of chemical bonding, the FG was dispersed well in the PU/EP matrix and the mechanical performance is improved. Meanwhile, the thermal degradation temperature was enhanced almost 50 °C higher than that of PU/EP. The conductivity of PU/FG/EP nanocomposites was 82.713 × 10⁻⁶ S/m at 2.0 wt% loadings. The resulting composites exhibited 96% shape fixity, 94% shape recovery, enhanced shape recovery force to realize thermo-electric dual-responsive property. Comparing with the results in literature, the composites used in this study have shown a progress between electrical conductivity and shape memory property.     

Mechanical behavior and deformation micromechanisms of polypropylene nonwoven fabrics as a function of temperature and strain rate

The mechanical behavior and the deformation and failure micromechanisms of a thermally-bonded polypropylene nonwoven fabric were studied as a function of temperature and strain rate. Mechanical tests were carried out from 248 K (below the glass transition temperature) up to 383 K at strain rates in the range ≈10⁻³ s⁻¹ to 10⁻¹ s⁻¹. In addition, individual fibers extracted from the nonwoven fabric were tested under the same conditions. Micromechanisms of deformation and failure at the fiber level were ascertained by means of mechanical tests within the scanning electron microscope while the strain distribution at the macroscopic level upon loading was determined by means of digital image correlation. It was found that the nonwoven behavior was mainly controlled by the properties of the fibers and of the interfiber bonds. Fiber properties determined the nonlinear behavior before the peak load while the interfiber bonds controlled the localization of damage after the peak load. The influence of these properties on the strength, ductility and energy absorbed during deformation is discussed from the experimental observations.     

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.     

Dielectric response and energy storage efficiency of low content TiO2-polymer matrix nanocomposites

TiO₂/epoxy nanocomposites were prepared at different filler concentrations varying from 3 to 12 phr (parts per hundred resin per weight). The dispersion of TiO₂ was examined by Scanning Electron Microscopy and proved to be adequate. Differential Scanning Calorimetry was implemented to determine the glass to rubber transition temperature of the polymer matrix. The dielectric analysis was performed via Broadband Dielectric Spectroscopy in a wide frequency and temperature range. Five different mechanisms were observed in the spectra of the examined composites which are identified, in terms of increasing temperature at constant frequency, as γ, β, Intermediate Dipolar Effect (IDE), α and Interfacial Polarization (IP) relaxation modes. The activation energies of all relaxation modes were calculated. Finally, the dielectric response of the TiO₂ nanocomposites compared to that of the TiO₂ microcomposites reveals that the former exhibit significantly higher energy storage efficiency even at lower TiO₂ concentration than the corresponding of the microcomposites.     

Effects of strain rate on transverse tension properties of a carbon/epoxy composite: studied by moiré photography

The dependence on strain rate of the mechanical properties of a high performance carbon fibre/epoxy composite loaded in transverse tension has been investigated. Dog-bone shaped specimens have been tested in quasi-static and dynamic loading conditions. The dynamic tests were performed in a split Hopkinson bar at strain rates between 100 and 800 s⁻¹. A moiré technique combined with high-speed photography, at framing rates of 0.25–1 MHz, was used for extraction of the local strain fields. The transverse mechanical properties were found to have weak or no dependence on strain rate. The average transverse modulus did not depend on strain rate, whereas the strain to and stress at failure were found to increase slightly with increased strain rate. For these dog-bone shaped specimens the strain evaluated by conventional Hopkinson bar technique was found to underestimate the true strain field measured by moiré technique. Finally, the moiré technique facilitated crack-propagation monitoring in real time. Crack speeds up to 2300 m s⁻¹ were measured at transverse crack propagation.     

Mechanically improved and optically transparent polycarbonate/clay nanocomposites using phosphonium modified organoclay

The present study deals with the properties of polycarbonate (PC)/clay nanocomposites prepared through melt and solution blending at two different clay loadings (0.5 phr and 1 phr) with preserved optical transparency of PC. The organoclay was prepared by exchanging the Na⁺ ions presented in the clay galleries of Na-MMT with butyltriphenylphosphonium (BuTPP⁺) ions, and denoted as BuTPP-MMT. The outstanding thermal stability of the BuTPP-MMT (∼1.44 wt% loss at 280 °C, after 20 min), concomitant with the increase in gallery height from 1.24 nm to 1.83 nm, proved its potentiality as nanofiller for melt-blending with PC. The X-ray diffraction analysis (XRD) revealed the destruction of the ordered geometry of aluminosilicate layers in the nanocomposites. However, from direct visualization through transmission electron microscopy, a discernible amount of clay was found to be localised in PC matrix in the 1 phr clay loaded nanocomposites (TEM). The differential scanning calorimetric (DSC) study revealed a nominal increase in glass transition temperature (T_g) of the PC in the nanocomposites. The thermal stability of the nanocomposites was increased with increase in clay loading. The nanocomposites possessed improved tensile strength and modulus than that of the virgin PC and the properties were related to the amount of clay loading and degree of clay dispersion. The dynamic mechanical analysis (DMA) revealed that the storage modulus increased in both the glassy and rubbery region with increase in clay loadings in the nanocomposites. Moreover, the optical transparency of the PC was retained in the PC/clay nanocomposites without development of any colour in the nanocomposites.     

Parametric study of twin screw extrusion for dispersing MMT in vinylester using orthogonal array technique and grey relational analysis

This paper presents the experimental results of the influence of co-rotating twin screw extrusion, a high shear process for dispersing MMT in vinylester, on the properties of the nanocomposites. Four main factors namely, MMT (3, 4 and 5 wt.%) loading in vinylester, speed (100, 200 and 300 rpm), temperature (5, 15 and 30 °C) and number of passes (5, 10 and 15) were considered for the design of L₂₇ OA lay-out. Four response factors such as glass transition temperature of the MMT/vinylester gelcoat; and UTS, interlaminar shear strength, and flexural strength of the MMT/vinylester/glass nanocomposites were studied. The Tg of MMT/vinylester increased with MMT loading and the maximum increase was 34.8% in 5 wt.% compared to that of vinylester specimens. MMT loading was found highly significant, followed by the number of passes, based on the ANOVA results for Tg. Grey relational grade for the mechanical properties of MMT/vinylester/glass was highest for the factor level combination of 4 wt.% MMT, 5 °C, 100 rpm and 15 passes, which was also evidenced by the X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) results of MMT exfoliation. Scanning Electron Microscopy (SEM) of tensile fractured specimens showed good interfacial bonding for the same combination. The mechanical properties increased up to 4 wt.% MMT loading in MMT/vinylester/glass and decreased for 5 wt.% loading. MMT loading followed by temperature were found significant based on the ANOVA for the mechanical properties.     

Fabrication of microwave exfoliated graphite oxide reinforced thermoplastic polyurethane nanocomposites: Effects of filler on morphology,mechanical, thermal and conductive properties

Different formulations of microwave-exfoliated graphite oxide (MEGO) based thermoplastic polyurethane (TPU) nanocomposites were successfully prepared via melt blending followed by injection molding. The spectroscopic study indicated that a strong interfacial interaction had developed between the MEGO and the TPU matrix. The microscopic observations showed that the MEGO layers were homogeneously dispersed throughout the TPU matrix. Thermal analysis indicated that the glass transition temperatures (T_g) of the nanocomposites increased with increasing MEGO content and their thermal stability improved in comparison with pure TPU matrix. The mechanical properties of nanocomposites improved substantially by the incorporation of MEGO into the TPU matrix. Electrical conductivity test indicated that a conductivity of 10⁻⁴ S cm⁻¹ was achieved in the nanocomposite containing only 4.0 wt.% of MEGO.     

Nylon 610/functionalized multiwalled carbon nanotubes composites by in situ interfacial polymerization

Nylon 610 (poly(hexamethylenesebacamide)) nanocomposites containing well dispersed multiwalled carbon nanotubes (MWCNT) were prepared using an in situ interfacial polymerization. Scanning electron microscopy showed that the MWCNT were well embedded and adhered to the nylon 610 matrix. The interfacial interaction of nylon 610/MWCNT on the grafted nylon 610 chains on the MWCNT was enhanced by improving the compatibility with nylon 610. This allowed a homogeneous dispersion of MWCNT in the nylon 610 matrix. Furthermore, the mechanical properties of nylon 610 were greatly improved by incorporating a small amount of MWCNT (0.1 wt.%). Because MWCNT are electrically conducting, the resulting electrical properties of the composites were approximately 5 orders of magnitude higher than pure nylon 610 matrix (from 10^− 17 S/cm to 10^− 12 S/cm). Overall, the results suggest that in situ polymerization is an ideal technique for producing a perfect dispersion of MWCNT in polymeric matrices.