Reinforcing polyamide 1212 nanocomposites with aligned carbon nanofibers

In this study, the mechanical properties and structure orientation of pure polyamide 1212 (PA1212) were compared with those of PA1212–carbon nanofibers (CNFs) nanocomposites. The tensile strength of the composite containing 0.3 wt.% modified CNFs was improved from 328 MPa (pure PA1212) to 373 MPa after drawing. The reinforcing effect was investigated in terms of crystallization behavior, crystal morphology, alignment of CNFs, and crystal orientation degree. Spherulites developed into oriented crystals after drawing, and the CNFs aligned along the drawing direction. The heterogeneous nucleation effect of the aligned CNFs improved the crystal orientation degree, which produced the reinforcing effect. The oriented fibril structures with rigid nanofibers acting as nuclei reinforced the entire oriented crystals in the composites.     

Flexural fatigue behavior of synthesized graphene/carbon-nanofiber/epoxy hybrid nanocomposites

In the present research, effects of adding a combination of synthesized graphene nanosheets and carbon nanofibers (CNFs) on the flexural fatigue behavior of epoxy polymer have been investigated. Graphene nanosheets are synthesized based on a changing magnetic field. The flexural bending fatigue life of 0.5 wt.% of graphene/CNF/epoxy hybrid nanocomposites has been considered at room temperature. The samples were subjected to different displacement amplitudes fatigue loadings. Due to the addition of hybrid nanoparticles, a remarkable improvement in fatigue life of epoxy resin was observed in comparison with results obtained by adding 0.25 wt.% graphene or 0.25 wt.% CNF into the resin. Experimental observations show that at a strength ratio equal to 43% by using 0.5 wt.% of hybrid nanoparticles; 37.3-fold improvement in flexural bending fatigue life of the neat epoxy was observed. While, enhancement of adding only graphene or CNF was 27.4 and 24-fold, respectively.     

Microstructure and macroscopic properties of hybrid carbon nanofiber/silica fume cement composites

The effect of up to 2 wt% of “as received” carbon nanofiber (CNF) loading on the microstructural, physical, and mechanical (compressive and splitting tensile strengths) properties of hybrid CNF/silica fume cement composites has been studied. Silica fume (SF) facilitated CNF dispersion due to its small particle size and improved the interfacial interaction between the CNFs and the cement phases. The CNFs were found embedded as individual fibers throughout the paste and self-aggregated as clumps in pockets. Mechanically, the CNFs embedded in the paste and at the pocket edges acted to offset the effect of defects created by the pockets. The addition of CNFs promoted pore refinement of the composites and increased the pore volume in the 6–200 nm pore diameter range, ascribed in part to interstitial pores between the entangled CNFs.     

Development of carbon nanofiber reinforced hydroxyapatite with enhanced mechanical properties

In order to improve fracture toughness, carbon nanofibers (CNF) were used as reinforcement for hydroxyapatite (HA) composites. The powder mixture of CNF/HA were obtained with ball-milling technique. CNF/HA composites were sintered by hot-pressing with 7.81 and 15.6 MPa sintering pressure. Maximum sintering pressure was 1200 °C. Mechanical and physiological bio-compatibility were evaluated by four-point bending tests, indentation tests and immersion tests in simulated body fluid (SBF). The strength values of 10 vol.% CNF/HA composites sintered at 15.6 MPa is 90 MPa, which is within those of cortical bone. The fracture toughness values for CNF/HA composites are around 1.6 times higher than those obtained for HA. Equal bioactivity are obtained for CNF/HA composites.     

Effects of extrusion temperature on the rheological,dynamic mechanical and tensile properties of kenaf fiber/HDPE composites

The effects of extrusion processing temperature on the rheological, dynamic mechanical analysis and tensile properties of kenaf fiber/high-density polyethylene (HDPE) composites were investigated for low and high processing temperatures. The rheological data showed that the complex viscosity, storage and loss modulus were higher with high processing temperature. Complex viscosities of pure HDPE and 3.4 wt% composite with zero shear viscosity of ⩽2340 Pa s were shown to exhibit Newtonian behavior while composites of 8.5 and 17.5 wt% with zero shear viscosity ⩾30,970 Pa s displayed non-Newtonian behavior. The Han plots revealed the sensitivity of rheological properties with changes in processing temperature. An increase in storage and loss modulus and a decrease in mechanical loss factor were observed for 17.5 wt% composites at high processing temperature and not observed at low processing temperature. Processing at high temperature was found to improve the tensile modulus of composites but displayed diminished properties when processed at low processing temperature especially at high fiber content. At both low and high processing temperatures, the tensile strength and strain of the composite decreased with increased content of the fiber.     

Size-scale effects of silica on bis-GMA/TEGDMA based nanohybrid dental restorative composites

The present study focuses on the effect of size-scale combination of silica on the mechanical and dynamic mechanical properties of acrylate based (50% Bis-GMA and 50% TEGDMA by weight) composites with an aim to overcome the conventional problem of high-volume fraction filling of acrylate based composites, typically used in restorative dentistry. Two classes of light-cured composites based on the size-scale combination of silica (7 nm + 2 μm; 14 nm + 2 μm) as the filler were prepared. FTIR spectroscopy revealed functionality and interactions whereas morphological investigations concerning the state of distribution and dispersion of nano- and micro-silica has been carried out by SEM–EDX Si-dot mapping. The dynamic mechanical properties, compressive, flexural and diametral tensile strengths were characterized. Micromechanical analysis of viscoelastic storage moduli following Kerner composite model has revealed an enhancement in the reinforcement efficiency of the nanohybrid composites based on the filler size-scale combination of 14 nm + 2 μm with 10 wt.% nanofiller loading. The compressive strength of the micro-filled composite (with 2 μm silica only) was found to remain comparable to that of the nanohybrid with 5 wt.% of 7 nm silica and 10 wt.% of 14 nm silica filled composites. Diametral tensile strength has been observed to be influenced by the size-scale combination and extent of nanofiller loading. The effective volume fractions in the composites validating the experimentally determined DTS were calculated following Nicolais–Narkis model. Our study demonstrates the conceptual feasibility of exploring the optimization of size-scale combinations of filler for enhancement in reinforcement efficiency by manipulating the volume fraction of filler induced immobilized polymer chains by resorting to the principle of micromechanics.     

Transparent and flexible cellulose nanofibers/silver nanowires/acrylic resin composite electrode

In this study, we report a novel, eco-friendly and simple method to fabricate cellulose nanofibers (CNFs)/silver nanowires (AgNWs)/acrylic resin (AR) composite electrode. CNFs with average diameter of 15 nm were disintegrated only by one time-pass grinding. Aqueous dispersion of AgNWs was embedded onto the surface of CNFs film by simple vacuum filtration. The final composite electrode was obtained by impregnating CNFs/AgNWs film to AR with the assist of adhesive tape. This electrode with AgNWs density of 134 mg/m² showed low sheet resistance (4 Ω/sq), and high light transmittance (85%) which was 6% lower than that of neat AR. The coefficient of thermal expansion of the composite electrode was as low as 25.32 ppm K⁻¹. The tensile strength and Young’s modulus of CNFs/AgNWs/AR composite film were 35.71 MPa and 1.63 GPa, which were about 8 and 5.8 times larger than neat AR film, respectively.     

Effect of matrix glass transition on reinforcement efficiency of epoxy-matrix composites with single walled carbon nanotubes,multi-walled carbon nanotubes,carbon nanofibers and graphite

This study compares the mechanical and thermal properties of glassy and rubbery epoxy–matrix composites reinforced with 1 and 4 wt.% single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), graphite, and carbon nanofibers (CNFs). The tensile modulus of most glassy composites was higher than that of the epoxy and increased with higher filler concentration and 4% graphite/epoxy and 4% SWCNT/epoxy exhibited approximately the same highest tensile modulus. The elongation of glassy composites was significantly lower than that of the epoxy and decreased with increasing filler loading. Most rubbery composites showed a higher tensile modulus and elongation than the epoxy and the modulus increased with rising filler content and 4% SWCNT/epoxy showed the highest tensile modulus and tensile strength. In the rubbery regime, glassy and rubbery composites displayed a higher storage modulus than the corresponding epoxy and 4 wt.% SWCNT/epoxy composites showed a 300% improvement in storage modulus compared to the epoxy.     

Thermally mendable epoxy resin strengthened with carbon nanofibres

This paper investigates the strengthening and toughening effects of carbon nanofibres (CNFs) on a self-healing thermoset/thermoplastic blend, i.e. an epoxy/poly (ε-caprolactone) (PCL) blend. The self-healing material system was prepared by polymer blending that produced a co-continuous phase-separated structure. The addition of CNFs altered the phase structures, leading to smaller domain sizes or even completely altering the phase separation mechanism, e.g. conversion from a co-continuous phase-separated structure to a particulate phase structure when the CNF content reached a certain level (0.3 wt% in this work). As the content of CNFs increased, the resulting nanocomposite became stronger and tougher, but the self-healing efficiency diminished; the optimal CNF content was found to be 0.2 wt%, which produced the highest strength, toughness and hardness, while achieving around 70% of healing efficiency.     

Heat treated wood–nylon 6 composites

Heat treatment is a relatively benign modification method that is growing as an industrial process to improve hygroscopicity, dimensional stability and biological resistance of lignocellulosic fillers. There also has been increased interest in the use of lignocellulosic fillers in numerous automotive applications. This study investigated the influence of untreated and heat treated wood fillers on the mechanical and rheological properties of wood filled nylon 6 composites for possible under-the-hood applications in the automobile industry where conditions are too severe for commodity plastics to withstand. In this study, exposure of wood to high temperatures (212 °C for 8 h) improved the thermal stability and crystallinity of wood. Heat treated pine and maple filled nylon 6 composites (at 20 wt.% loading) had higher tensile strengths among all formulations and increased tensile strength by 109% and 106% compared to neat nylon 6, respectively. Flexural modulus of elasticity (FMOE) of the neat nylon 6 was 2.34 GPa. The FMOE increased by 101% and 82% with the addition of 30 wt.% heat treated pine and 20 wt.% heat treated maple, where it reached maximum values of 4.71 GPa and 4.27 GPa, respectively. The rheological properties of the composites correlated with the crystallinity of wood fillers after the heat treatment. Wood fillers with high crystallinity after heat treatment contributed to a higher storage modulus, complex viscosity and steady shear viscosity and low loss factor in the composites. This result suggests that heat treatment substantially affects the mechanical and rheological properties of wood filled nylon 6 composites. The mechanical properties and thermogravimetric analysis indicated that the heat treated wood did not show significant thermal degradation under 250 °C, suggesting that the wood-filled nylon composites could be especially relevant in thermally challenging areas such as the manufacture of under-the-hood automobile components.     

Effect of cellulose nano fiber (CNF) on fatigue performance of carbon fiber fabric composites

The effect of cellulose nano fibers (CNF): micro-fibrillated cellulose and bacteria cellulose fibers were investigated on the fatigue life of carbon fiber (CF) fabric/epoxy (EP) composites. Epoxy used as the matrix was physically modified with CNF in advance before fabricating the laminates. The high cycle fatigue strength was significantly improved at 0.3 wt% CNF. There exists an appropriate CNF content which makes the fatigue life longest. An increase of adhesive strength between CF and matrix results due to physical modification with CNF. The adhesive strength much increases with increasing the CNF content. Almost no interfacial debonding occurs at 0.8 wt% CNF content when CF breakage takes place. On the other hand, some debonding occurs along CFs from the breaking point at 0.3 wt% CNF. Debonding is more significant in the case of no CNF addition to the matrix. An appropriate interfacial strength brought at 0.3 wt% CNF is the key of fatigue life extension.     

Sol–gel derived nanoscale bioactive glass (NBG) particles reinforced poly(ε-caprolactone) composites for bone tissue engineering

This study investigated the effect of the addition of sol–gel derived nanoscale bioactive glass (NBG) particles on the mechanical properties and biological performances of PCL polymer, in order to evaluate the potential applications of PCL/NBG composites for bone tissue regeneration. Regardless of the NBG contents (10, 20, and 30 wt.%), the NBG particles, which were synthesized through the sol–gel process using polyethylene glycol (PEG) polymer as a template, could be uniformly dispersed in the PCL matrix, while generating pores in the PCL/NBG composites. The elastic modulus of the PCL/NBG composites increased remarkably from 89 ± 11 MPa to 383 ± 50 MPa with increasing NBG content from 0 to 30 wt.%, while still showing good ultimate tensile strength in the range of 15–19 MPa. The hydrophilicity, water absorption and degradation behavior of the PCL/NBG composites were also enhanced by the addition of the NBG particles. Furthermore, the PCL/NBG composite with a NBG content of 30 wt.% showed significantly enhanced in vitro bioactivity and cellular response compared to those of the pure PCL.     

Solvent infusion processing of all-cellulose composite laminates using an aqueous NaOH/urea solvent system

All-cellulose composites are high performing green materials and solvent infusion processing makes their upscaled manufacturing possible. This study explored the use of aqueous 7 wt.% NaOH/12 wt.% urea solution as cost effective and environmentally friendly cellulose solvent for solvent infusion processing. A short dissolution time of 5 min led to all-cellulose composite laminates with a tensile strength of 114 ± 1.9 MPa and a Young’s modulus of 7.8 ± 0.5 GPa. A decrease of tensile strength and Young’s modulus with increasing dissolution time from 5 to 60 min was linked to changes in composite microstructure and fine structure of the reinforcing rayon fibres. It was shown that aqueous NaOH/urea solution is a promising alternative solvent, as it offers the advantages of shorter processing times and reduced solvent costs by 97%, while resulting in 25% stronger laminates, when compared to using ionic liquids.     

Effect of alkali treatment on interfacial bonding in abaca fiber-reinforced composites

Abaca fibers demonstrate enormous potential as reinforcing agents in composite materials. In this study, abaca fibers were immersed in 5, 10 or 15 wt.% NaOH solutions for 2 h, and the effects of the alkali treatments on the mechanical characteristics and interfacial adhesion of the fibers in a model abaca fiber/epoxy composite system systematically evaluated. After 5 wt.% NaOH treatment, abaca fibers showed increased crystallinity, tensile strength and Young’s modulus compared to untreated fibers, and also improved interfacial shear strength with an epoxy. Stronger alkali treatments negatively impacted fiber stiffness and suitability for composite applications. Results suggest that mild alkali treatments (e.g. 5 wt.% NaOH for 2 h) are highly beneficial for the manufacture of abaca fiber-reinforced polymer composites.     

Electrically conductive polymer nanocomposites of polymethylmethacrylate and carbon nanofibers prepared by chaotic mixing

Electrically conductive composites of poly(methyl methacrylate) and carbon nanofibers (CNF) were prepared in a low-shear chaotic mixer. These materials showed a percolation threshold of approximately 2 wt.% CNF compared to 6 wt.% for materials prepared in an internal mixer under comparable conditions of mean shear rate. It was found in materials prepared by chaotic mixing that nanofibers were pulled out of the bundles and oriented along the flow directions to produce electrically conductive networks. Electrical conductivity showed great sensitivity to mixing time around percolation threshold and remained almost unchanged with prolonged chaotic mixing above the percolation threshold. Thermal, thermo-mechanical and mechanical properties of the composites were investigated.     

Enhancement on physical properties of flame retarded ethylene-vinyl acetate copolymer/ferric pyrophosphate composites through electron beam irradiation

Ferric pyrophosphate (FePP) with silica-gel microencapsulated ammonium polyphosphate (MCAPP) and char forming agent (CFA) in the flame retardation of ethylene-vinyl acetate copolymer has been studied through LOI and UL-94 test. The UL-94 data show that EVA with 20 wt.% IFR only has V-2 rating. However, with the addition of 1 wt.% FePP and 19 wt.% IFR, it can reach V-0 rating. The properties of the composites before and after the electron beam irradiation are compared. The volume resistivity, mechanical and thermal properties of the irradiated EVA composites are also evidently improved at appropriate irradiation dose as compared with those of un-irradiated ones. The tensile strength of EVA/IFR/FePP composites with 160 kGy irradiation is 21.8 Mpa, which is much higher than that of un-irradiated one (12.7 MPa). Furthermore, the thermal aged test and water resistance test results demonstrate that EVA/IFR/FePP composites have good thermal aging property and water durability.     

Mechanical properties improvements in two-phase and three-phase composites using carbon nano-fiber dispersed resin

Static strength tests were carried out for cured carbon nano-fiber (CNF) dispersed resin as tow-phase composites and for CFRP laminates using CNF dispersed resin as three-phase composites. To obtain these CFRP laminates, the CNF dispersed resin was impregnated to CF reinforcement and cured by hot press. The CNF used was a cup-stacked type of nano-fiber, CARBERE^®, made by GSI CREOS Corporation, Japan. Two CNF aspect ratios of 10 and 50 were employed. These fiber lengths of the CNF were controlled about 1000 nm (AR10) and 5000 nm (AR50), respectively. The CNF was dispersed to EPIKOTE 827^® epoxy resin in two values of CNF weight ratios, 5 and 10% to the resin. TORAYCA^® C6343 plain woven fabric was used for reinforcement of the CFRP laminates. The cure condition with the agent of aromatic amine EPIKURE W^® was 100 °C for two hours followed by a post cure of 175 °C for 4 h. The static strength tests led to the conclusion that the dispersion of CNF into epoxy improves mechanical properties of the tow-phase composites, and that CFRP laminates with CNF dispersed resin also exhibit higher compressive strength than CFRP laminates without CNF as control. Possibilities of improvement in mechanical properties were confirmed in the two and three-phase composites. Moreover, a proportional tendency in strength improvements to CNF weight content was found in the two present composites so far in the present test results.     

Mechanical performance of epoxy matrix hybrid nanocomposites containing carbon nanotubes and nanodiamonds

A novel class of epoxy matrix hybrid nanocomposites has been developed containing multiwalled carbon nanotubes (MWCNTs) and nanodiamonds (NDs) to explore the combined effect of nanoreinforcements on the mechanical performance of nanocomposites. Both the nanofillers were functionalized before incorporating into epoxy matrix to promote interfacial interactions. The concentrations of both MWCNTs and NDs in the nanocomposites were increased systematically, i.e. 0.05 wt.%, 0.1 wt.% and 0.2 wt.% while composites containing individual nanoreinforcements were also manufactured for comparison. The developed nanocomposites were characterized microstructurally by scanning electron microscopy (SEM) and mechanically by tensile, flexural, impact and hardness tests. Homogeneous dispersion of MWCNTs and NDs was observed under SEM, which resulted in the enhancement of mechanical properties of nanocomposites. The composites containing 0.2 wt.% MWCNTs and 0.2 wt.% NDs showed 50% increase in hardness while tensile strength and modulus enhanced to 70% and 84%, respectively. Flexural strength and modulus also showed a rise of 104% and 56%, respectively. Interestingly, fracture strain also increased in both the tensile and flexural testing. The impact resistance increased to 161% showing a significant improvement in the toughness of hybrid nanocomposites.     

The bimodal effect of La on the microstructures and mechanical properties of in-situ A356–TiB2 composites

In this work, in-situ A356–2.5 wt.% TiB₂ composites were fabricated via a re-melting and diluting (RD) approach. The effects of lanthanum (La) on the microstructures and mechanical properties of the composites were investigated. The results demonstrated that the addition of La can, simultaneously, refine the second dendrite arm spacing (SDAS) of the α-Al grains and modify the coarse lamellar eutectic Si into fine fibrous particles. The optimum addition levels for refinement and modification lay at 0.1 wt.% and 0.8 wt.%, respectively, due to the distinct mechanisms between the two. Since the resultant mechanical properties are a combined function of refinement and modification, the tensile properties of the composites show a bimodal distribution with the first peak value at 0.1 wt.% and the latter one at 0.8 wt.% La, in accordance with the optimum refinement and modification, respectively.     

Mechanical,thermal expansion,and flammability properties of co-extruded wood polymer composites with basalt fiber reinforced shells

Basalt fiber (BF) filled high density polyethylene (HDPE) and co-extruded wood plastic composites (WPCs) with BF/HDPE composite shell were successfully prepared and their mechanical, morphological and thermal properties characterized. The BFs had an average diameter of 7 μm with an organic surfactant surface coating, which was thermally decomposed at about 210 °C. Incorporating BFs into HDPE matrix substantially enhanced flexural, tensile and dynamic modulus without causing a noticeable decrease in the tensile and impact strength of the composites. Micromechanical modeling of tensile properties for the BF/HDPE composites showed a good fit of the selected models to the experimental data. Compared to neat HDPE, BF/HDPE composites had reduced linear coefficient of thermal expansion (LCTE) values. The use of the pure HDPE and BF/HDPE layers over a WPC core greatly improved impact strength of core–shell structured composites. However, the relatively less-stiff HDPE shell with large LCTE values decreased the overall composite modulus and thermal stability. Both flexural and thermal expansion properties were enhanced with BF reinforced HDPE shells, leading to well-balanced properties of core–shell structured material. Cone calorimetry analysis indicated that flammability performance of core–shell structured composites was improved as the BF content increased in the shell layer.