Banana fiber strands–reinforced polymer matrix composites

Banana fiber (BF)-reinforced low-density polyethylene (LDPE) unidirectional composites were fabricated by the compression molding process with 40 wt% fiber loading. The fibers were modified with methylacrylate (MA) mixed with methanol (MeOH) along with 2% benzyl peroxide under thermal curing method at different temperatures (50–90 °C) for different curing times (10–50 min) in order to have better compatibility with the matrix. The effect of fiber surface modification on the mechanical properties (tensile and impact properties) of the composites were evaluated. Monomer concentration, curing temperature, and curing time were optimized in terms of polymer loading and mechanical properties. The mechanical properties were found to be improved based on the improved interaction between the reinforcement and the matrix. Optimized BFs were again treated with 2–5 wt% starch solutions and composites made of 4% starch treated BF showed the highest mechanical properties than that of MA treated composites. Scanning electron microscopy (SEM) was performed to get an insight into the morphology of the composites. Water uptake and soil degradation test of the composites were also investigated.     

Effect of moisture on the interlaminar interface of a carbon fiber polymer–matrix composite,studied by contact electrical resistivity measurement

Moisture was found to have a reversible effect on the interlaminar interface of a continuous carbon fiber epoxy–matrix composite. An increase in humidity increased the resistivity. The reversibility was essentially complete after the first cycle of humidity variation. The effect is attributed to expansion of the matrix at the interlaminar interface due to moisture uptake. It allows use of the composite for humidity sensing.     

Effect of fiber surface treatments on the fiber–matrix interaction in banana fiber reinforced polyester composites

Cellulosic fibers have been used as cost-cutting fillers in plastic industry. Among the various factors, the final performance of the composite materials depends to a large extent on the adhesion between the polymer matrix and the reinforcement and therefore on the quality of the interface. To achieve optimum performance of the end product, sufficient interaction between the matrix resin and the cellulosic material is desired. This is often achieved by surface modification of the resin or the filler. Banana fiber, the cellulosic fibers obtained from the pseudo-stem of banana plant (Musa sepientum) is a bast fiber with relatively good mechanical properties. The fiber surface was modified chemically to bring about improved interfacial interaction between the fiber and the polyester matrix. Various silanes and alkali were used to modify the fiber surface. Modified surfaces were characterized by SEM and FTIR. The polarity parameters of the chemically modified fibers were investigated using the solvatochromic technique. The results were further confirmed by electrokinetic measurements. Chemical modification was found to have a profound effect on the fiber–matrix interactions. The improved fiber–matrix interaction is evident from the enhanced tensile and flexural properties. The lower impact properties of the treated composites compared to the untreated composites further point to the improved fiber–matrix adhesion. In order to know more about the fiber–matrix adhesion, fractured surfaces of the failed composites where further investigated by SEM. Of the various chemical treatments, simple alkali treatment with NaOH of 1% concentration was found to be the most effective. The fiber–matrix interactions were found to be dependent on the polarity of the modified fiber surface.     

Studies of dielectric relaxation in natural fiber–polymer composites

Polymer composites of a polyester resin matrix filled with short palm tree lignocellulosic fibers were studies by means of dielectric spectroscopy in the frequency range 0, 1–100 kHz and temperature interval from 40 °C to 200 °C. Three relaxations processes were identified, namely the orientation polarization imputed to the presence of polar water molecules in Palm fiber, the relaxation process associated with conductivity occurring as a result of the carriers charges diffusion noted for high temperature above glass transition and low frequencies, and the interfacial relaxation that is attributable to the accumulation of charges at the Palm fibers/polyester interfaces.     

Correlation of the mechanical properties to the fiber–matrix adhesion of Nextel 312™ fiber/BN/Blackglas™ composites

Boron nitride (BN)-coated aluminoborosilicate (Nextel? 312) fibers, produced via ammonia nitridation, along with 'as-received' and 'desized' fibers, were composited in a silicon oxycarbide (Blackglas?) matrix. The mechanical properties, failure properties, and fiber–matrix interfacial chemistry of the composite were investigated. BN treated fiber composites show a 90% improvement in flexural strength and substantial increases in shear strength (short beam shear and Iosipescu) over the 'as-received' fiber composite. The composite fabricated with 'desized' fibers underwent spontaneous delamination during pyrolization, precluding mechanical testing. X-ray photoelectron spectroscopy of the starting materials and of composite fracture surfaces combined with scanning electron microscopy and energy dispersive X-ray spectroscopy indicate that the locus of failure of the BN-coated fiber composite occurs at the matrix/BN coating interface.     

Mode-locked L-band bismuth–erbium fiber laser using carbon nanotubes

A passively mode-locked, bismuth–erbium-co-doped fiber (Bi-EDF) with a pulse width of 460 fs is proposed and demonstrated. A highly doped, 180-cm Bi-EDF with an erbium concentration of 3,250 ppm/wt and an absorption rate of 133 dB/m at 1,530 nm serves as the gain medium. The cavity is 11.6 m long with an overall group velocity dispersion of +0.063 ps². The output pulses have a repetition rate, average output power, pulse energy and peak power of 11.18 MHz, 5 mW, 448 pJ and 1 kW, respectively. The system has a high beam quality and a narrow pulse width output in the L-band region.     

On the mechanical behaviours of a craze in particulate–polymer composites

In polymeric composites, well-defined inclusions are incorporated into the polymer matrix to alleviate the brittleness of polymers. When a craze is initiated in such a composite, the interaction between the craze and the surrounding inclusions will greatly affect the composite’s mechanical behaviours and toughness. To the best knowledge of the authors, only little research work has been found so far on the interaction between a craze and the near-by inclusions in particulate–polymer composites. In the current study, the first time, the influences of the surrounding inclusions on the craze are investigated in particulate–polymer composites. The three-phase model is adopted to study the fracture behaviours of the craze affected by multiple inclusions. An iterative procedure is proposed to solve the stress intensity factors. Parametric studies are performed to investigate the influences of the reinforcing particle volume fraction and the shear modulus ratio on fracture behaviours of particulate–polymer composites.     

Phase separation at the fiber–matrix interface in composites based on a thermoplastic/polyester blend

A study of the microstructure developing at the surface of glass fibers in a poly(vinyl acetate) (PVAc)/polyester blend is presented. Three different experimental methods are used: a technique based on the Wilhelmy method to measure the wettability of the fibers before curing, and both optical microscopy and atomic force microscopy in the pulsed-force mode to characterize potential phases splitting at the fiber–matrix interface after curing. It was found that, depending on the curing conditions and the concentration in PVAc, the surface treatment of the fiber could have a significant influence on the microstructure. For a concentration in PVAc lower than 5 wt% and a curing temperature of 80°C, extreme cases, such as the development of layers of one of the phases at the surface or the formation of lenses of one phase, were observed. In other cases, in particular for elevated temperatures and higher concentrations in PVAc, the fibers did not exert a significant influence on the morphology. It was also found that in such a reactive system, surface tension considerations alone are insufficient to explain the configuration of the phases at the surface of the fibers.     

Microdeformation behaviour of Al–SiC metal matrix composites

The satisfactory performance of metal matrix composites depends critically on their integrity, the heart of which is the quality of the matrix-reinforcement interface. The nature of the interface depends in turn on the processing of the MMC component. At the micro-level, the development of local concentration gradients around the reinforcement can be very different according to the nominal conditions. These concentration gradients are due to the metal matrix attempting to deform during processing. This plays a crucial role in the micro-structural events of segregation and precipitation at the matrix-reinforcement interface. Equilibrium segregation occurs as a result of impurity atoms relaxing in disordered sites found at interfaces, such as grain boundaries, whereas non-equilibrium segregation arises because of imbalances in point defect concentrations set up around interfaces during non-equilibrium heat treatment processing. The amount and width of segregation depend very much on (a) the heat treatment temperature and the cooling rate, (b) the concentration of solute atoms and (c) the binding energy between solute atoms and vacancies. An aluminium–silicon–magnesium alloy matrix reinforced with varying amounts of silicon carbide particles was used in this study. A method of calculation has been applied to predict the interfacial fracture strength of aluminium, in the presence of magnesium segregation at metal matrix interface. Preliminary results show that the model succeeds in predicting the trends in relation to segregation and intergranular fracture strength behaviour in these materials. Microhardness profiles of reinforced and un-reinforced aluminium alloys are reported. The presence of precipitates at alloy-reinforcement interface identified by Nano-SEM.     

A numerical-analytical model for the characterization of composites reinforced by carbon nanotubes

A mixed model, numerical-analytical, is presented that allows one to predict the elastic properties of carbon nanotube (CNT)/polymer composites containing a random distribution of CNTs, while taking account of the curvature that they show when immersed in the polymer. This hybrid approach is a significant advance over micromechanical modeling and can be applied to all nanostructured composites.     

Influence of the annealing atmosphere on the properties of LiCoPO4–graphitic carbon foams composites

The investigation on the properties of LiCoPO₄–graphitic carbon foams (LCP-GCF) composites is reported in this work. The diffraction analysis (XRD) on powders confirmed the presence of LiCoPO₄ as major crystalline phase and Li₄P₂O₇ and Co₂P as secondary phases. The morphological investigation of the composites shows a layer of crystalline spongy-like material on the surface of the GCF for t?=?0 h and of acicular crystallites with different dimensions (5–50 μm) for t?≥?0.1 h. The voltammetric curves (cyclic voltammogramms) show mean values of reduction potential above 5.0 V independently of the annealing time. The LCP-GCF composites deliver a discharge-specific capacity of 76mAh g^?1 (t?=?0 h) and of 102mAh g^?1 (t?=?0.1 h) at a discharge rate of C/10 and room temperature. The electrochemical impedance spectroscopy data reveal a decrease of the electrical resistance and the improvement of the Li-ion conductivity as a function of the annealing time.     

Technical study of visible light wavelength division multiplexing using polymer optical fiber

Recently there has been considerable interest in the de-velopment of polymer optical fibers (POF). The ductil-ity of polymers is an important advantage and confers onPOF easy processing, easy handling, low costs, and largecore diameter[1]. POF has an extended applicability, suchas in computer networks, local area networks, data links,automobile, optical sensors, lighting, etc.. The large corediameter, up to 1 mm or more, enables high efficienciesof fiber coupling.We have demonstrated 100-M…     

Fabrication of ceramic oxide-coated SWNT composites by sol–gel process with a polymer glue

The functional copolymer bearing alkoxysilyl and pyrene groups, poly[3-(triethoxysilyl)propyl methacrylate]-co-[(1-pyrene-methyl) methacrylate] (TEPM₁₃-co-PyMMA₃), was synthesized via atom transfer radical polymerization. Attributing the π–π interaction of pyrene units with the walls of single-walled carbon nanotubes (SWNTs), this polymer could disperse and exfoliate SWNTs in different solvents through physical interaction as demonstrated by TEM, UV/Vis absorption, and FT-IR analysis. The alkoxysilyl groups functionalized SWNTs were reacted with different inorganic precursors via sol–gel reaction, and, as a results, silica, titania, and alumina were coated onto the surface of SWNTs, respectively via copolymers as a molecular glue. The nanocomposites of ceramic oxides/SWNTs were characterized by SEM analysis. Dependent upon the feed, the thickness of inorganic coating can be tuned easily. This study supplies a facile and general way to coat SWNTs with ceramic oxides without deteriorating the properties of pristine SWNTs.     

Degradation of methylparaben by sonocatalysis using a Co–Fe magnetic carbon xerogel

The degradation of methylparaben (MP) through 20 kHz ultrasound coupled with a bimetallic Co-Fe carbon xerogel (CX/CoFe) was investigated in this work. Experiments were performed at actual power densities of 25 and 52 W/L, catalyst loadings of 12.5 and 25 mg/L, MP concentrations between 1 and 4.2 mg/L and initial pH values between 3 and 10 in ultrapure water (UPW). Matrix effects were studied in bottled water (BW) and secondary treated wastewater (WW), as well as in UPW spiked with bicarbonate, chloride or humic acid. The pseudo–first order kinetics of MP degradation increase with power and catalyst loading and decrease with MP concentration and matrix complexity; moreover, the reaction is also favored at near–neutral conditions and in the presence of dissolved oxygen. The contribution of the catalyst is synergistic to the sonochemical degradation of MP and the extent of synergy is quantified to be >45%. This effect was ascribed to the ability of CX/CoFe to catalyze the dissociation of hydrogen peroxide, formed through water sonolysis, to hydroxyl radicals. Experiments in UPW spiked with an excess of tert-butanol (radical scavenger), sodium dodecyl sulfate or sodium acetate (surfactants) led to substantially decreased rates (i.e. by about 8 times), thus implying that the liquid bulk and the gas-liquid interface are major reaction sites. The stability of CX/CoFe was shown by performing reusability cycles employing magnetic separation of the catalyst after the treatment stage. It was found that the CX/CoFe catalyst can be reused in up to four successive cycles without noteworthy variation of the overall performance of the sonocatalytic process.     

Preparation of multi-walled carbon nanotube–Fe composites and their application as light weight and broadband electromagnetic wave absorbers

Multi-walled carbon nanotube （MWCNT）-Fe composites were prepared via the metal organic chemical vapor deposi- tion by depositing iron pentacarbonyl on the surface of MWCNTs. The structural and morphological analyses demonstrated that Fe nanoparticles were deposited on the surface of the MWCNTs. The electromagnetic properties of the MWCNTs were significantly changed, and the absorbing capacity evidently improved after the Fe deposition on the MWCNT surface. A minimum reflection loss of -29.4 dB was observed at 8.39 GHz, and the less than -10 dB bandwidth was about 10.6 GHz, which covered the whole X band （8.2-12.4 GHz） and the whole Ku band （12.4-18 GHz）, indicating that the MWCNT-Fe composites could be used as an effective microwave absorption material.     

Tunable mechanical properties of MWCNT–glass fiber fabric reinforced epoxy composites by controlling MWCNTs dispersing conditions

A novel, simple and cost-effective method, which is capable of easily tailoring the dispersion of multi-walled carbon nanotubes (MWCNTs), was developed here to fabricate the MWCNT–glass fiber fabric (MWCNT–GFf) multiscale composites with tunable mechanical properties. MWCNTs were dispersed into the commercial GFfs through the combined effect of the ultrasound and amino silane (AS) firstly, followed by a resin infusion process. By tuning the ultrasonic power and AS concentration, it is possible to control the MWCNTs dispersion level and subsequently mechanical properties of resultant composite. Making use of optimal dispersion conditions, which involves the optimal combination of ultrasonic power and AS concentration, the interlaminar shear strength of MWCNT–GFf reinforced composites was dramatically increased by 40.5%, and the storage modulus in the glassy region and rubbery region was improved by 27.7% and 125.0%, respectively. The work demonstrates the great promise of this novel method toward practical, industrial application in manufacturing fiber-reinforced composites with superior mechanical properties.