Processing and properties of poly(methyl methacrylate)/carbon nanofiber composites

Single wall carbon nanotubes, multiwall carbon nanotubes, as well as carbon nanofibers (CNF) are being used for reinforcing polymer matrices. In this study, poly(methyl methacrylate) (PMMA) nanocomposites have been processed by melt blending, containing two different grades (PR-21-PS and PR-24-PS) of CNF manufactured by Applied Sciences Inc. The amount of nanofibers used was 5 and 10% by weight, respectively. The PMMA/CNF composites were processed into 4 mm diameter rods and 60 μm diameter fibers using the small-scale melt processing fiber spinning equipment. At 5 wt% CNF, composite rods as well as fibers show over 50% improvement in axial tensile modulus as compared to the control PMMA rod and fibers, respectively. The reinforcement efficiency decreased at 10 wt% CNFs. The PMMA/CNF nanocomposite fibers also show enhanced thermal stability, significantly reduced shrinkage and enhanced modulus retention with temperature, as well as improved compressive strength. CNF reinforcement efficiency has been analyzed using the modified Cox model.     

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.     

Effect of exfoliated graphite nanoplatelets on the mechanical and viscoelastic properties of poly(lactic acid) biocomposites reinforced with kenaf fibers

The focus of this study is to explore synergy between nanomaterials such as exfoliated graphite nanoplatelets (xGnP) and micro-size reinforcements such as kenaf natural fibers, in poly(lactic acid) based composites. The nano-biocomposites are made by melt-mixing followed by injection molding. Prior to melt-mixing the kenaf fibers were coated with the xGnP using sonication. The reinforcement content used in the study was up to 5 wt% and up to 40 wt% for xGnP and kenaf fibers, respectively. The flexural strength and modulus and the viscoelastic properties such as storage modulus were determined. It was found that addition of 5 wt% xGnP did not increase the viscosity of the polymer melt, enhanced the flexural modulus by 25–30% at any fiber loading used but did not increase the strength, indicating insufficient load transfer at the polymer-xGnP or xGnP-kenaf interface. Finally, addition of xGnP had a positive effect on the heat distortion temperature but only at higher fiber loadings.     

Morphology and modulus of vapor grown carbon nano fibers

Two types of morphologies have been observed in vapor grown carbon nano fibers (CNFs) using transmission electron microscopy (TEM). In one case, a truncated cone microstructure was observed, with outer and inner diameters of 60 and 25 nm, respectively. In this type of CNF, graphite sheets were oriented at about 15° to the fiber axis. The second type of fiber was a double-layer CNF with outer and inner diameters of 83 and 20 nm, respectively. A truncated cone structure was also observed in the double-layer CNF. Graphite sheets in the outer layer of the double-layer fibers were oriented along the nano fiber axis. Tensile modulus for the first type of nano fiber along its axis was calculated to be 50 GPa, and for the second type of fiber the calculated modulus value was in the 100–775 GPa range, depending on the outer layer orientation. Modulus calculations based on these two morphologies explain the wide ranging experimental CNF modulus values reported in the literature.     

Processing and properties of poly(ε-caprolactone)/carbon nanofibre composite mats and films obtained by electrospinning and solvent casting

Composite materials based on poly(ε-caprolactone) (PCL) and carbon nanofibres (CNFs) were processed by solvent casting and electrospinning. The main objective was to investigate the effects of the CNFs on the microstructural, thermal and mechanical properties of the PCL matrix composites processed by two different routes. The hybrid materials obtained with different CNF content (1, 3 and 7 wt%) were analysed by electron microscopy (FESEM), differential scanning calorimeter (DSC), thermogravimetry (TGA) and mechanical testing. The composite films showed a good dispersion in the PCL matrix while electrospun samples were consisted of homogeneous and uniform fibres up to 3 wt% CNFs with average fibre diameter ranged between 0.5 and 1 μm. Composite films and mats revealed an increased crystallization temperature with respect to the neat PCL matrix. Mechanical properties of solvent cast films and electrospun mats were assessed by uniaxial tensile tests. A stiffness increase was achieved in PCL films depending on the CNF content, while mechanical properties of mats were only slightly affected by CNF introduction.     

Effect of maleic anhydride modified MWCNTs on the morphology and dynamic mechanical properties of its PMMA composites

This study successfully grafted multiwalled carbon nanotubes (MWCNTs) with maleic anhydride (Mah-g-MWCNTs) via Friedel–Crafts acylation with the aluminum chloride catalyst (AlCl₃), investigated by Raman and TGA analysis. The covalent bonds and carboxylic groups of maleic anhydride provided additional active species, improving adhesion between the MWCNTs and poly(methyl methacrylate) (PMMA). This investigation also studied the morphology and dynamic mechanical properties of pristine MWCNTs (P-MWCNTs) and modified MWCNTs (Mah-g-MWCNTs) reinforced with PMMA. Findings show a homogeneous distribution of MWCNTs throughout the matrix for Mah-g-MWCNTs/PMMA composites, as revealed by transmission electron microscope (TEM). The addition of both MWCNTs influenced the molecular arrangement of the PMMA matrix and also increased the dynamic mechanical properties of MWCNTs/PMMA composites. Glass transition temperature (Tg) and storage moduli (E′) of the Mah-g-MWCNTs/PMMA composites increased significantly comparing with P-MWCNTs/PMMA composites, attributed to improved interfacial adhesion between the reinforcement and the matrix. DMA studies revealed that adding 4.76 wt% Mah-g-MWCNTs into PMMA generates a 184% enhancement in the storage modulus and a 19 °C increase in Tg. However, adding 4.76 wt% P-MWCNTs into PMMA only generates 108% enhancement in the storage modulus and a 14 °C increase in Tg.     

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.     

Preparation,processing and analysis of physical properties of calcium ferrite-CNTs/PET nano-composite

The present work is focused on the preparation of composites based on Poly(ethylene terephthalate) (PET) and novel nano-hybrid filler composed of Calcium Ferrite (CF)-Carbon Nanotubes (CNTs), obtained by direct growth of CNTs on CF based iron catalysts. The carbon content in the hybrid filler was 76 wt%. Composites loaded with 1.0, 1.5, 2.0, 3.0 wt% of filler were obtained by melt compounding and processed by thin-wall injection molding. Unfilled Poly(ethylene terephthalate) was processed using the same techniques. Structural characterization and physical properties (thermal, mechanical and electrical) were analyzed and correlated to the hybrid filler loading, and to the percentage of carbon nanotubes.     

Improving the mechanical properties of epoxy using multiwalled carbon nanotubes functionalized by a novel plasma treatment

Achieving both uniform dispersion and good interfacial adhesion have been long-term challenges in optimizing the properties of carbon nanotube reinforced polymer nanocomposites. A novel and effective plasma method, which combines continuous and pulsed plasma modes in a nitrogen and hydrogen gas mixture (15% H₂), has been developed to better meet this need. It has yielded high levels of primary amines on the surface of multiwalled carbon nanotubes which improved their dispersion and interfacial bonding with an epoxy resin. By adding just 0.1 wt% of these nanotubes to Bisphenol F epoxy resin, the mechanical properties of the nanocomposites, from nano to macro, were significantly improved. Nanoindentation tests showed that the hardness and elastic modulus increased by 40% and 19%, respectively, using the functionalized nanotubes. Macro-mechanical properties from thermo-mechanical and flexural analysis were also enhanced, with a nearly 40% improvement in toughness.     

Production and characterization of polymer nanocomposites with highly aligned single-walled carbon nanotubes

We report the production and characterization of polymer nanocomposites with single-walled carbon nanotubes having improved mechanical properties and exceptional nanotube alignment. High-pressure carbon monoxide nanotubes (HiPco) were efficiently distributed in polystyrene (PS) and polyethylene (PE) with a twin-screw compounder. Nanotube concentrations were 1, 5, 10, and 20 wt% in PE composites and 0.7 wt% in PS composites. PE composites were melt-spun into fibers to achieve highly aligned nanotubes. Polarized Raman spectroscopy shows that the degree of alignment increases with decreasing fiber diameter and decreases with increasing nanotube loading. The orientation distribution function of a 1 wt% HiPco/PE composite had a full width at half-maximum of approximately 5 degrees. The elastic modulus increases up to 450% relative to PE fibers for 20 wt% nanotube loading at an intermediate fiber diameter of 100 microns.     

The relationship of crystallization behavior,mechanical properties,and morphology of polypropylene nanocomposite fibers

This study aimed at the fabrication of lightweight and high performance nanocomposite fibers. Polypropylene/multiwalled carbon nanotubes (PP/MWCNTs) nanocomposite fibers (0–5 wt% of MWCNTs) were prepared via melt spinning process. The MWCNTs were dispersed in the dispersing agent before mixing with PP powder. After mixing, the dispersing agent was removed. Then the nanocomposites were spun into fibers. The fibers were spun and stretched with 7.5 draw ratios. Crystallization behavior and thermal properties of PP/MWCNTs nanocomposite fibers were studied using the differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA). The DSC curves of PP/MWCNTs nanocomposite fibers showed the crystallization peak at a temperature higher than that of neat PP fibers. These results revealed that the MWCNTs acted as nucleating sites for PP crystallization. The additions of MWCNTs into PP leaded to an increase in both crystallization temperature and crystallization enthalpy. However, no significant changes in the melting temperatures of the PP nanocomposites were detected. Degradation temperature of samples obtained from the TGA curves showed increase thermal degradation behavior for the PP/MWCNTs with the content of MWCNTs. It was found that the increase of tensile strength and modulus corresponded well with the increase of crystallinity of the composite fibers.     

Effect of fiber diameter on the deformation behavior of self-assembled carbon nanotube reinforced electrospun Polyamide 6,6 fibers

High precision electrospinning technique was used to obtain self-assembled carbon nano-tube (CNT) reinforced polyamide (PA) 6,6 fibers. The reinforcement factors were critically evaluated with respect to the effects of fiber diameter and inclusion of CNTs. The average fiber diameter ranged from 240 to 1400 nm and the CNT contents were 0, 1 and 2.5 wt%. A sharp increase in modulus and strength of the fibers was demonstrated when the size of the fiber was decreased below ∼500 nm, which could be attributed to ordered arrangement of crystals and the spatial confinement effect of the fibers. Also, investigation of the deformation behavior of fibers as a function of CNT content revealed that tensile fiber modulus and strength improved significantly with increase of CNTs. Addition of CNTs restricted the segmental motion of polymer chains and provided the confinement effect to the neighboring molecules.     

The effect of carbon nanotubes on the fracture toughness and fatigue performance of a thermosetting epoxy polymer

Multi-walled carbon nanotubes, with a typical length of 140 μm and a diameter of 120 nm, have been used to modify an anhydride-cured epoxy polymer. The modulus, fracture energy and the fatigue performance of the modified polymers have been investigated. Microscopy showed that these long nanotubes were agglomerated, and that increasing the nanotube content increased the severity of the agglomeration. The addition of nanotubes increased the modulus of the epoxy, but the glass transition temperature was unaffected. The measured fracture energy was also increased, from 133 to 223 J/m² with the addition of 0.5 wt% of nanotubes. The addition of the carbon nanotubes also resulted in an increase in the fatigue performance. The threshold strain-energy release-rate, G _th, increased from 24 J/m² for the unmodified material to 73 J/m² for the epoxy with 0.5 wt% of nanotubes. Electron microscopy of the fracture surfaces showed clear evidence of nanotube debonding and pull-out, plus void growth around the nanotubes, in both the fracture and fatigue tests. The modelling study showed that the modified Halpin–Tsai equation can fit very well with the measured values of the Young’s modulus, when the orientation and agglomeration of the nanotubes are considered. The fracture energy of the nanotube-modified epoxies was predicted, by considering the contributions of the toughening mechanisms of nanotube debonding, nanotube pull-out and plastic void growth of the epoxy. This indicated that debonding and pull-out contribute to the toughening effect, but the contribution of void growth is not significant. There was excellent agreement between the predictions and the experimental results.     

Carbon nanotube reinforced small diameter polyacrylonitrile based carbon fiber

Polyacrylonitrile (PAN) and PAN/carbon nanotube (CNT) composite (99/1) based carbon fibers with an effective diameter of about 1 μm have been processed using island-in-a-sea bi-component cross-sectional geometry and gel spinning. PAN/CNT (99/1) based carbon fibers processed using this approach exhibited a tensile strength of 4.5 GPa (2.5 N/tex) and tensile modulus of 463 GPa (257 N/tex), while these values for the control PAN-based carbon fiber processed under the similar conditions were 3.2 GPa (1.8 N/tex) and 337 GPa (187 N/tex), respectively. Properties of these 1 μm diameter carbon fibers have been compared to the properties of the larger diameter (>6 μm) PAN and PAN/CNT based carbon fibers.     

碳纳米管增强PA6纤维的性能

将碳纳米管(CNT)在分散剂或分散剂和聚合物(PA6)载体中处理后制备出两种母粒,将其作为增强材料分别和PA6切片熔融共混纺丝,制备出碳纳米管的增强PA6纤维,研究其结构和力学性能.CNT含量低于0.5%(质量分数)时,使用两种母粒制备出的纤维强度和模量都提高,NT含量为0.03%时增强的效果最好.由碳纳米管和分散剂组成的母粒增强效果更好,NT的含量为0.03%时就能使PA6纤维的强度和模量分别提高23%和76%.这种增强纤维是一种微纤增强纤维,纳米CNT在纤维中均匀分散且沿着纤维轴的方向取向.这种结构能有效地转移载荷,具有增强作用,且取向性越好,增强效果越好.     

Fabrication and characterization of carbon nanotube reinforced poly(methyl methacrylate) nanocomposites

Multiwall carbon nanotube (CNT) reinforced poly(methyl methacrylate) (PMMA) nanocomposites have been successfully fabricated with melt blending. Two melt blending approaches of batch mixing and continuous extrusion have been used and the properties of the derived nanocomposites have been compared. The interaction of PMMA and CNTs, which is crucial to greatly improve the polymer properties, has been physically enhanced by adding a third party of poly(vinylidene fluoride) (PVDF) compatibilizer. It is found that the electrical threshold for both PMMA/CNT and PMMA/PVDF/CNT nanocomposites lies between 0.5 to 1 wt% of CNTs. The thermal and mechanical properties of the nanocomposites increase with CNTs and they are further increased by the addition of PVDF For 5 wt% CNT reinforced PMMA/PVDF/CNT nanocomposite, the onset of decomposition temperature is about 17 degrees C higher and elastic modulus is about 19.5% higher than those of neat PMMA. Rheological study also shows that the CNTs incorporated in the PMMA/PVDF/CNT nanocomposites act as physical cross-linkers.     

Processing and characterization of TLCP fibers reinforced by 1?wt% MWCNT

A thermotropic liquid crystalline polymer (TLCP) blend with 1?wt% multiwall carbon nanotubes (MWCNTs) was prepared by melt compounding. Morphological observations of the blend show that the chemical-treated MWCNTs were well dispersed in the TLCP matrix with a good interface. MWCNTs have little effects on the thermal and rheological properties of pure TLCP. TLCP fibers with and without MWCNTs were prepared at certain drawing ratios by a melt spinning method. The degree of orientation of TLCP chains is enhanced by MWCNT micro-clusters during the fiber formation. The mechanical properties of TLCP/MWCNT fibers are significantly increased by 34.5?% for tensile strength and 38.0?% for tensile modulus in comparison with those of pristine TLCP fibers, due to the synergistic effects of MWCNT and TLCP.     

Fracture toughness and creep performance of PMMA composites containing micro and nanosized carbon filaments

Chopped carbon fiber (CCF), multiwall carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs) were introduced to polymethylmethacrylate (PMMA) via melt compounding. Fracture toughness and creep performance of these composites are presented. A constant volume concentration of 1 vol.% was used. Dispersion was evaluated on both micro- and nano-scales. Flexural modulus was also measured.     

Development of ductile composite reinforcement bars for concrete structures

In order to overcome the deficiencies of current composite reinforcement bars such as low elastic moduli, low pre-rupture elongation, brittle fracture as well as high cost, a new core-shell model of hybrid composite reinforcement bar has been developed in this study. In this model, steel and glass fibers are randomly dispersed across the cross section of the core while Twaron and carbon fibers are placed within the shell to improve the elastic modulus as well as to serve as a shield for protecting the glass fibers from alkaline attack; and the steel fibers from moisture and chloride induced corrosion. Glass composite reinforcement bars and hybrid composite reinforcement bars were fabricated by hand winding method. The tensile modulus and strength of the new hybrid reinforcement bars were determined to be 142 GPa and 628 MPa, respectively. New hybrid reinforcement bars were also conditioned in different alkaline environments and were evaluated for their alkaline resistance properties. Compared with glass composite reinforcement bars, the new hybrid composite reinforcement bars possess characteristics of alkaline resistance, good ductility and increased modulus of elasticity, while the material costs of such hybrid composite reinforcement bars are slightly higher than the glass composite reinforcement bars.     

Multi-scale reinforcement of CFRPs using carbon nanofibers

In this paper, stacked-cup carbon nanofibers (CNF) were dispersed in the matrix phase of carbon-fiber-reinforced composites based on a high-performance epoxy system with and without modification by an elastomeric triblock copolymer (TCP) for increased toughness. The addition of the TCP provided an enhancement in toughness at the cost of a slight degradation in modulus and strength. The CNFs, on the other hand, provided significantly enhanced strength and stiffness in matrix-dominated configurations, including tension of quasi-isotropic composites and short beam shear strength of both quasi-isotropic and unidirectional composites. Scanning electron microscopy revealed enhanced adhesion between the matrix and carbon fibers with the addition of either TCP or CNFs. However, CNF agglomeration in the studied systems partially offset the energy dissipation processes brought about by the nanofibers, thereby limiting interlaminar fracture toughness enhancements by CNF addition. These results show good promise for CNFs as low-cost reinforcement for composites while offering insight into the codependent morphologies of multi-scale phases and their influence over bulk properties.