Tropical wood polymer nanocomposite (WPNC): The impact of nanoclay on dynamic mechanical thermal properties

In this study, wood polymer nanocomposites (WPNCS) were manufactured from five Malaysian tropical wood species by vacuum-impregnation attended by in situ polymerization using phenol–formaldehyde resin and montmorillomite nanoclay. Percentage weight gain and density of wood polymer nanocomposites depended on wood species. Thermo-mechanical properties of wood samples were investigated by the dynamic mechanical thermal analysis (DMTA) over the temperature range of −100 °C to 200 °C. The intrinsic properties of the components, morphology of the system and the nature of interface between the phases were also determined through DMTA test. Storage modulus (E′) of WPNC samples exhibited significant improvement over the temperature range, in both glassy region and rubbery plateau in relation to their corresponding raw wood samples and wood polymer composites (WPCs). Furthermore, damping (loss tan δ) peaks of all wood species were lowered by PF-Nanoclay system treatment, an indication of improved surface interphase of wood. Dynamic Young’s modulus (E_d) of wood was also calculated using free–free vibration testing. A significant increment was obtained for the PF-Nanoclay impregnated WPNC samples.     

N2 plasma-assisted grafting of fluorinated chains onto partially cured epoxy resins

Two routes for the grafting of fluorinated molecules to an epoxy resin were studied. The first one deals with the grafting of the liquid-state resin whereas the second one is focused on the grafting onto the solid-state resin. These grafting reactions were shown to be similar as studied through FTIR and XPS spectroscopies. However, it appears that the grafting onto the solid-state resin is limited by the curing advancement. N₂ plasma-activation was used to solve this drawback and enhanced the grafting yield. This grafting improvement was mainly explained in terms of the surface wetting improvement and the attachment of nitrogen containing groups at the surface of the treated resin.     

Effect of surfactant treatment on thermal stability and mechanical properties of CNT/polybenzoxazine nanocomposites

The mechanical and thermo-mechanical properties of polybenzoxazine nanocomposites containing multi-walled carbon nanotubes (MWCNTs) functionalized with surfactant are studied. The results are specifically compared with the corresponding properties of epoxy-based nanocomposites. The CNTs bring about significant improvements in flexural strength, flexural modulus, storage modulus and glass transition temperature, T_g, of CNT/polybenzoxazine nanocomposites at the expense of impact fracture toughness. The surfactant treatment has a beneficial effect on the improvement of these properties, except the impact toughness, through enhanced CNT dispersion and interfacial interaction. The former four properties are in general higher for the CNT/polybenzoxazine nanocomposites than the epoxy counterparts, and vice versa for the impact toughness. The addition of CNTs has an ameliorating effect of lowering the coefficient of thermal expansion (CTE) of polybenzoxazine nanocomposites in both the regions below and above T_g, whereas the reverse is true for the epoxy nanocomposites. This observation has a particular implication of exploiting the CNT/polybenzoxazine nanocomposites in applications requiring low shrinkage and accurate dimensional control.     

Hybridization effect on the mechanical and dynamic mechanical properties of curaua composites

This study aims to evaluate the performance of curaua/glass hybrid composites focusing on mechanical and dynamic mechanical analysis (DMA). Composites with distinct glass/curaua fiber loading ratios were studied. Flexural strength and modulus, impact strength and Barcol hardness increased for higher glass fiber content. The same was found for storage and loss modulus. The activation energy of the relaxation process in the glass transition region showed a maximum for the all-glass composite, corroborating with the results of concentration of elastic chains (υ_e). Cole-Cole plots were obtained and found to follow the same trend regardless of the glass content, whereas peak height and peak width at half-height were maximum for the all-glass composite.     

Surface migration of fluorinated additive during the curing of epoxy resin

Driving forces, responsible for the migration of a fluorinated additive added to a thermoset resin, toward the air/solid interface, were investigated. On this subject, the surface chemistry as characterized by XPS analyses was compared to theoretical models based on the rheological properties of the blend. It appears that the migration of the fluorinated molecules toward the surface cannot be described by a conventional diffusion model. A second model derived from the latter suits better to the experimental data and should be presented as another proof that additional motion forces drive the fluorine molecules migration in curing epoxy resin.     

Electrical and dielectric properties of polypropylene nanocomposites based on carbon nanotubes and barium titanate nanoparticles

Functional polypropylene (PP) nanocomposites were prepared by melt compounding with multiwalled carbon nanotubes (MWNT) as the electrically conductive component and barium titanate (BT) spherical nanoparticles as the ferroelectric component. To make PP electrically conductive, more than 3 wt.% MWNT is required. Surface modification of either MWNT or BT with titanate coupling agent further improves the electrical conductivity of the PP/MWNT/BT ternary nanocomposites. Interestingly, by modifying both MWNT and BT, 2 wt.% MWNT are sufficient to make the ternary nanocomposite electrically conductive. In addition, the incorporation of MWNT greatly increases the dielectric permittivity of PP/BT nanocomposites. However, to retain a low dielectric loss, the MWNT loading should be slightly less than the percolation threshold of the nanocomposites. The improved electrical conductivity and dielectric properties make the ternary nanocomposites attractive in practical applications.     

Effects of functional group of carbon nanotubes on mechanical properties of carbon fibers

The effects of surface functionalization of carbon nanotubes (CNTs) on the mechanical properties of carbon fibers (CFs) have been investigated. The surface functionalization of CNTs was carried out with a diazonium reagent. Compared to pure PAN, only the fluoro phenyl functionalized CNTs (F-Ph-CNT) incorporated PAN composites showed a significant increase up to 22 °C of T_g and displayed the second peak due to the interfacial interaction between F-Ph-CNT and PAN. Among the samples, 0.5wt% of F-Ph-CNT reinforced CFs exhibited a 46% increase in tensile strength (4.1 GPa) and a 37% increase in modulus (302 GPa), respectively compared to that of pure CFs.     

Influence of feeding conditions in twin-screw extrusion of PP/MWCNT composites on electrical and mechanical properties

The influence of feeding conditions of multiwalled carbon nanotube (MWCNT) materials, namely Baytubes® C150P and Nanocyl™ NC7000, into polypropylene (PP) was investigated with respect to achieving suitable nanotube dispersion, high electrical conductivity, and good mechanical properties. Both MWCNT materials were fed at selected concentrations either in the hopper of the twin-screw extruder or using a side feeder under otherwise identical extrusion conditions (rotation speed, throughput, temperature profile) using a Berstorff ZE 25 twin-screw extruder. Afterwards, injection molding was performed under identical conditions. The results indicate that the more compact Baytubes® C150P agglomerates should be added into the hopper, as the dispersion assessed by light microscopy is better, electrical resistivities measured on compression and injection molded samples are lower, and elastic modulus, yield strength and impact strength are higher as compared to side feeding. On the other hand, for the more loosely packed Nanocyl™ NC7000 agglomerates, addition using the side feeder leads to better dispersion, lower electrical resistivity, and higher mechanical properties.     

Compressive behavior of MWCNT/epoxy composite mats

Mats of vertically-aligned multiwall carbon nanotubes were grown in an thermal CVD reactor with simultaneous feed of the catalyst and carbon precursors. Mats were soaked into epoxy resin solutions without any prior chemical modification and then cured to produce composite plates of z-axis nano-reinforcement. Direct observations of the epoxy–CNT interactions at the nanoscale revealed that epoxy interacted naturally with the MWCNTs without affecting their physical characteristics, alignment, or the mat’s morphology. The compressive behavior of the pristine and composite mats was consistent with mechanical predictions accounting for an elastic regime followed by elastic instability and compaction. Strong evidence of reinforcement in the MWCNT/epoxy composites was indicated by increased strength, stiffness and toughness values with respect to the as-grown mats and pure polymer. The elastic instability strain of the composites was of the order of 0.4.     

Improving the mechanical properties of multiwalled carbon nanotube/epoxy nanocomposites using polymerization in a stirring plasma system

Uniform treatment of multiwalled carbon nanotubes by plasma treatment has been investigated using a custom-built stirring plasma system. A thin plasma polymer with high levels of amine groups has been deposited on MWCNTs using a combination of continuous wave and pulsed plasma polymerization of heptylamine in the stirring plasma system. Scanning electron microscopy showed that the plasma polymerization improved the dispersion and interfacial bonding of the MWCNTs with an epoxy resin at loadings of 0.1, 0.3 and 0.5 wt%. The flexural and thermal mechanical properties of plasma polymerized MWCNT/epoxy nanocomposites were also significantly improved while untreated MWCNT/epoxy nanocomposites showed an opposite trend. The epoxy with 0.5 wt% plasma polymerized MWCNTs had the greatest increase in flexural properties, with the flexural modulus, flexural strength and toughness increasing by about 22%, 17% and 70%, respectively.     

Effect of oxygen plasma treatment of PPTA and PBO fibers on the interfacial properties of single fiber/epoxy composites studied by Raman spectroscopy

The interfacial micromechanics of single poly(p-phenylene terephthalamide (PPTA) and poly(p-phenylene benzobisoxazole (PBO) fibers embedded in an epoxy resin has been investigated by determining the interfacial shear stress distributions along the fiber length. The effects of an oxygen plasma treatment on the interfacial shear stress of the fiber-epoxy systems are analyzed. Raman spectroscopy was used to map the stress distributions along the fiber when the composite is subjected to a small axial tensile strain (3.5% for PPTA and 2.5% for PBO). The quality of the interface or adhesion was improved after the surface treatment, supporting the ability of plasma oxidation to enhance the adhesion of high-performance fibers to epoxy resins. The tensile behavior of fiber-reinforced systems was different in each case. PPTA reinforcements underwent fragmentation, likely by fiber microfailure, whereas debonding or bridging is the most probable fragmentation mechanism in the case of PBO.     

Fracture mechanisms of epoxy filled with ozone functionalized multi-wall carbon nanotubes

This work focused on the fracture mechanisms and reinforcing effects of ozone-treated multi-walled carbon nanotubes (MWCNTs) in epoxy matrix. Ozone functionalization of MWCNTs was found to be of help for a better dispersion and stronger interfacial bonding with epoxy matrix, which in turn improve the strength and fracture toughness of the resin. The MWCNT/epoxy composites showed complicated failure modes than the conventional fibrous composites, which have been quantitatively investigated and correlated with the fracture toughness of the nanocomposites studied.     

A strategy for improving mechanical properties of a fiber reinforced epoxy composite using functionalized carbon nanotubes

Carbon fiber reinforced epoxy composite laminates are studied for improvements in quasi static strength and stiffness and tension-tension fatigue cycling at stress-ratio (R-ratio) = +0.1 through strategically incorporating amine functionalized single wall carbon nanotubes (a-SWCNTs) at the fiber/fabric-matrix interfaces over the laminate cross-section. In a comparison to composite laminate material without carbon nanotube reinforcements there are modest improvements in the mechanical properties of strength and stiffness; but, a potentially significant increase is demonstrated for the long-term fatigue life of these functionalized nanotube reinforced composite materials. These results are compared with previous research on the cyclic life of this carbon fiber epoxy composite laminate system reinforced similarly with side wall fluorine functionalized industrial grade carbon nanotubes. Optical and scanning electron microscopy and Raman spectrometry are used to confirm the effectiveness of this strategy for the improvements in strength, stiffness and fatigue life of composite laminate materials using functionalized carbon nanotubes.     

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.     

Rheological properties and electrical conductivity of irradiated MWCNT/PP nanocomposites

Novel rheological features and conductivity results of irradiated PP/MWCNT nanocomposites are presented. Elongational flow measurements reveal a strain hardening behaviour which is compatible with the creation of long chain branched macromolecules provoked by irradiation. However, oscillatory shear flow results suggest that irradiation does not affect interactions of MWCNTs with PP chains. The addition of carbon nanotubes brings about conductivities of the order of 10⁻² S/cm, but its scavenger effect reduces the number of radicals generated by irradiation, lessening the strain hardening effect. The employed mixing method provides a dispersion of MWCNTs in a PP matrix, which followed by an ad hoc irradiation, allows obtaining an electrical conductive polypropylene with a strain hardening behaviour. The obtained results open novel routes to conductive nanocomposites apt to be processed using methods discarded for linear PPs, such extrusion-blowing and others.     

Cryogenic mechanical behaviors of carbon nanotube reinforced composites based on modified epoxy by poly(ethersulfone)

Cryogenic mechanical properties are important parameters for epoxy resins used in cryogenic engineering areas. In this study, multi-walled carbon nanotubes (MWCNTs) were employed to reinforce diglycidyl ether of bisphenol F (DGBEF)/diethyl toluene diamine (DETD) epoxy system modified by poly(ethersulfone) (PES) for enhancing the cryogenic mechanical properties. The epoxy system was properly modified by PES in our previous work and the optimized formulation of the epoxy system was reinforced by MWCNTs in the present work. The results show that the tensile strength and Young’s modulus at 77 K were enhanced by 57.9% and 10.1%, respectively. The reported decrease in the previous work of the Young’s modulus of the modified epoxy system due to the introduction of flexible PES is offset by the increase of the modulus due to the introduction of MWCNTs. Meanwhile, the fracture toughness (K_IC) at 77 K was improved by about 13.5% compared to that of the PES modified epoxy matrix when the 0.5 wt.% MWCNT content was introduced. These interesting results imply that the simultaneous usage of PES and MWCNTs in a brittle epoxy resin is a promising approach for efficiently modifying and reinforcing epoxy resins for cryogenic engineering applications.     

Grafting of nano-TiO2 onto flax fibers and the enhancement of the mechanical properties of the flax fiber and flax fiber/epoxy composite

In this article, a flax fiber yarn was grafted with nanometer sized TiO₂, and the effects on the tensile and bonding properties of the single fibers and unidirectional fiber reinforced epoxy plates were studied. The flax fiber yarn was grafted with nanometer sized TiO₂ through immersion in nano-TiO₂/KH560 suspensions under sonification. The measured grafting content of the nano-TiO₂ ranged from 0.89 wt.% to 7.14 wt.%, dependent on the suspension concentration. With the optimized nano-TiO₂ grafting content (∼2.34 wt.%), the tensile strength of the flax fibers and the interfacial shear strength to an epoxy resin were enhanced by 23.1% and 40.5%, respectively. The formation of Si–O–Ti and C–O–Si bonds and the presence of the nano-TiO₂ particles on the fiber surfaces contributed to the property enhancements. Unidirectional flax fiber reinforced epoxy composite (V_f = 35.4%) plates prepared manually showed significantly enhanced flexural properties with the grafting of nano-TiO₂.     

A comparative study of the electrical and mechanical properties of epoxy nanocomposites reinforced by CVD- and arc-grown multi-wall carbon nanotubes

In this study, three different types of multi-wall carbon nanotubes (MWCNTs) were compared as nanostructured reinforcements in epoxy polymers: commercially available CVD-MWCNTs, synthesised in an industrial process, aligned-CVD-MWCNTs and arc-grown MWCNTs, both obtained from a lab-scale processes. The nanocomposite properties were characterised by means of electron microscopy, rheological, electrical and mechanical methods. Industrial CVD-MWCNTs are favourable for the implication of an electrical conductivity in the epoxy due to their high tendency to form conducting networks. The less entangled structure of aligned-CVD-MWCNTs turns out to be favourable for an easy dispersion and low viscosity in epoxy at similar conductivities compared to the CVD-MWCNTs. Additionally, they provide the highest increase in fracture toughness (∼17%). Arc-grown MWCNTs do not offer any electrical conductivity in epoxy without sufficient purification methods. Their high level of impurities and short length further complicate the transfer of their good electrical and mechanical properties into the nanocomposite.     

Effect of crystal morphology transition of polypropylene on interfacial properties of carbon fiber-reinforced composites through AlOOH surface treatment

Carbon fiber reinforced thermoplastics (CFRTPs) have many advantages, such as short processing cycle times, recyclability and design flexibility. However, CFRTPs have weak interfacial properties due to the non-polarity of carbon fibers. In this study, AlOOH surface treatment was applied on carbon fibers to improve the interfacial properties between the fiber and the matrix. The effect of the surface treatment on the crystal morphology of isotactic polypropylene (i-PP) at the interface was investigated by polarized optical microscopy (POM). The mechanical properties of fabricated CFRTPs were evaluated by measuring the interlaminar shear strength (ILSS). The ILSS of the AlOOH treated specimens after epoxy desizing increased by 106.8% compared with that of the untreated specimens.     

Woven hybrid biocomposites: Dynamic mechanical and thermal properties

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