Batch foaming of short carbon fiber reinforced polypropylene composites

In this paper, the short carbon fiber (SCF)/PP composite foams with fine open cell were prepared with batch foaming technique using supercritical CO₂. The effects of SCF contents, saturation pressure and depressurization rate on the cell morphology were studied. The experimental results indicate that the cell morphology of foamed composites was significantly influenced by the SCF contents and saturation pressure. It is found that the cell size increased and cell density decreased with the increment of SCF contents while the saturation pressure had the opposite effect. However, depressurization rate showed little impacts on the cell morphology due to the presence of SCF.     

Confocal microscopy measurement of the fiber orientation in short fiber reinforced plastics

To determine three-dimensional fiber orientation states in injection-molded short fiber composites a CLSM (Confocal Laser Scanning Microscope) is used. Since the CLSM optically sections the composites, more than two cross-sections either on or below the surface of the composite can be obtained. Three dimensional fiber orientation states can be determined with geometric parameters of fibers on two parallel cross-sections. For experiment, carbon fiber reinforced polystyrene is examined by the CLSM. Geometric parameters of fibers are measured by image analysis. In order to compactly describe fiber orientation states, orientation tensors are used. Orientation tensors are determined at different positions of the prepared specimen. Three dimensional orientation states are obtained without the difficulty in determining the out-of-plane angles by utilizing images on two parallel planes acquired by the CLSM. Orientation states are different at different positions and show the shell-core structure along the thickness of the specimen.     

Electrical properties of novel polyolefin based thermoplastic elastomer and graphene nanocomposites

Numerous efforts to prepare useful graphene-based nanocomposites have been made and important improvements achieved. In our studies, novel structured polyolefin-based thermoplastic elastomer, poly(ethylene-ter-1-hexene-ter-divinylbenzene) (PEHV) was designed and synthesized. And high quality graphene was manufactured via the exfoliation of graphite. PEHV/graphene nanocomposites were fabricated using solution casting method as the amount of graphene added. The morphologies of nanocomposites were observed using scanning electron microscopy. And density, mechanical properties and electrical properties were also measured. Electrical properties and mechanical properties were improved with the increase of graphene added in nanocomposites. It is expected that PEHV/graphene nanocomposites could be applied to lightweight EMI shielding materials.     

Matrix modification with silane coupling agent for carbon fiber reinforced epoxy composites

To improve interfacial adhesion between carbon fiber and epoxy resin, the epoxy matrix is modified with N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane (YDH602) and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (YDH792), respectively. And the effect of matrix modification on the mechanical performance of carbon/epoxy composites is investigated in terms of tensile, flexural and interlaminar properties. The flexural properties indicate that the optimum concentration of silane coupling agents YDH602 and YDH792 for the matrix modification is approximately 0.5 wt% of the epoxy resin system, and the mechanical properties of the YDH792-modified epoxy composites is better than that of the YDH602-modified epoxy composites at the same concentration. Compared to unmodified epoxy composite, the incorporation of 0.5 wt% YDH792 results in an increase of 4, 44 and 42 % in tensile, flexural and interlaminar shear strength (ILSS) values of the carbon/epoxy composite, respectively, while the corresponding enhancement of tensile and flexural modulus is 3 and 15 %. These improvements in mechanical properties can be considered to be an indication of better fiber/matrix interfacial adhesion as confirmed by SEM micrographs of the fracture surface after interlaminar shear testing. The viscosity of the modified epoxy resin system can be reduced by incorporation of silane coupling agent YDH792, which is beneficial for fiber impregnation or wetting during liquid composite molding process.     

The reinforcement effect of carbon fiber on the friction and wear properties of carbon fiber reinforced PA6 composites

The tribological performance of PA6 and carbon fiber reinforced polyamide 6 (CF/PA6) under dry sliding condition was examined. Different contents of carbon fibers were employed as reinforcement. All filled and unfilled polyamide 6 composites were tested against CGr15 ball and representative testing was performed. The effects of carbon fiber content on tribological properties of the composites were investigated. The worn surface morphologies of neat PA6 and its composites were examined by scanning electron microscopy (SEM) and the wear mechanisms were discussed. Moreover, all filled polyamide 6 have superior tribological characteristics to unfilled polyamides 6. The optimum wear reduction was obtained when the content of carbon fiber is 20 vol%.     

Mechanical properties and water absorption of short snake grass fiber reinforced isophthallic polyester composites

Natural fiber composite replaces the conventional and synthetic materials in many fields especially in light weight applications. The randomly oriented short snake grass fiber reinforced isophthallic polyester composites are prepared by hand lay-up technique and finally compression molded. The various length and weight fraction of fiber are used in composite fabrication. The mechanical properties and water absorption under various climatic conditions are examined according to the prescribed standard. SEM image revealing the fiber pullout and breakage of the tensile and impact fractured composite specimens has been analysed and compared with control through scanning electron microscope. The result shows that the mechanical properties increase with increase in fiber length and weight fraction of the composites. The rate of water absorption increases with increase in temperature and time. Obtained experimental tensile strength of the composite is compared with various theoretical models such as Series, Hirsch’s, Halpin-Tsai, Modified Halpin-Tsai and Modified Bowyer & Brader’s and the obtained inferences are discussed.     

Elastic property of polyolefin elastomer film cross linked by electron beam irradiation

Polyolefin elastomers were extruded to form films and subjected to electron beam (EB) irradiation at various energy levels. The film samples were characterized to illuminate the effects of EB-induced cross-linking through measurements of gel contents, Fourier transform infra-red (FT-IR) spectroscopy, and variations of tensile properties of the films after the EB irradiations. The EB irradiations introduced crosslinking among the molecular chains resulting increases in initial modulus. The elastic recovery was 83 % at 30 % stain, which is increased by 10 % at 150 kGy compared with pristine. The maximum stain was 1,400 % at 150 kGy which is comparable with commercial polyurethane elastomer.     

Thermo-mechanical and morphological properties of short natural fiber reinforced poly (lactic acid) biocomposite: Effect of fiber treatment

Untreated oil palm empty fruit bunch (REFB), alkali treated EFB (AEFB), ultrasound treated EFB (UEFB) and simultaneous ultrasound-alkali treated EFB (UAEFB) short fibers were incorporated in poly(lactic acid) (PLA) for fabricating bio-composites. The REFB fiber-PLA (REPC) and treated EFB (TEFB) fiber-PLA (TEPC) composites were prepared and characterized. Glass transition temperature, crystal melting temperature, decomposition temperature, melt flow index, density and mechanical properties (tensile strength, tensile modulus and impact strength) of TEPC are found to be higher than those of REPC. The observed crystallization temperature of TEPC is lower than that of REPC. Among all samples, TEPC prepared from UAEFB fiber shows better performances than other samples fabricated by REFB and AEFB fibers. Scanning electron microscopy, Fourier transform infrared spectroscopy and XRD analyses well support all the observed results.     

Effects of thermal treatment on durability of short bamboo-fibers and its reinforced composites

This study was performed to investigate the influence of heat treatment on the chemical transformation and associated improved durability of short bamboo-fibers (BF) and its reinforced composites. Results showed that cleavage of acetyl groups of the hemicelluloses developed with increasing temperature and holding time, and completed beyond 190 °C for more than 3 h, resulting in a noticeable increase of cellulose content and a substantial reduction of concentration of accessible hydroxyl groups. Heat treatment improved thermal stability and anti-UV aging properties of treated BF, and also contributed to a decrease of equilibrium moisture content (EMC) of treated BF and consequent improvements of hygroscopicity and the dimensional stability of its reinforced composite. However, immoderate heat treatment for BF wasn’t in favor of improvements of hygroscopicity and the dimensional stability of BF based composites.     

Effect of soaking corrosion on flexural properties of carbon fiber reinforced epoxy syntactic foams

The fiber-reinforced syntactic foam is a type of lightweight materials. In this paper, hollow glass microspheres/epoxy syntactic foams reinforced by carbon fibers are prepared. Carbon fibers of five mass fractions are used to obtain five types of reinforced syntactic foams. The effect of the fiber content and soaking corrosion on the flexural properties of syntactic foams are investigated. The results of soaking test show that the moisture rate in distilled water is greater than that in seawater. The flexural test results show that the flexural strength of syntactic foams increases obviously by adding fibers. The maximum value increases 25.5 % than that of composites without adding fibers when fiber-mass fraction is 5 %. Soaking corrosion reduces the flexural properties of the syntactic foams. The flexural strengths of syntactic foams immersed in water and seawater with 5 % fiber-mass fraction decrease 34.4 % and 37.5 % respectively. The main reasons of the flexural strength reduction of syntactic foams with soaking corrosion are discussed.     

Optimum manufacturing conditions of activated carbon fiber absorbents. II. Effect of carbonization and activation conditions

In this paper, viscose rayon-based knitted fabrics were utilized as the precursor to produce activated carbon fiber absorbents (ACFA). The effects of carbonization and activation conditions on characteristics (ACFA) were examined. Experimental results revealed that increasing the flow rate of environmental gas N₂ and steam activator used in conjunction and decreasing the production rate of ACFA can obtain better pore properties. However, higher flow rate of steam activator and lower production rate of ACFA reduced the weight yield. According to our findings, to maintain good absorption property of ACFA, the optimum manufacturing conditions are flow rate of gas N₂ at 80 cc/min, flow rate of steam activator at 60 ml/min, and production rate of ACFA at 30 cm/min, with flame retardant reagent concentration maintained at 30%. Under these conditions, the weight yield can be up to 40.85% and the BET surface area can exceed 1500 g/m².     

Composites of polyvinyl alcohol and carbon nanotubes decorated with silver nanoparticles

A simple method to decorate carbon nanotubes (CNTs) with silver nanoparticles was developed to enhance the electrical conductivity of CNTs. The acid-treated CNTs were suspended in the silver acetate solution, ammonia solution was then added, and the CNTs decorated with silver nanoparticles (Ag@CNTs) were produced. The Ag@CNTs were dispersed in polyvinyl alcohol (PVA) to fabricate electrically conducting polymer composites. The electrical, thermal and mechanical properties of the composites were measured. The electrical conductivity of the composites containing 0.8 % (o.w.f.) Ag@CNTs was more than four orders of magnitude higher than those of pristine and functionalized CNTs respectively, which confirmed the effectiveness of the Ag@CNTs as conducting filler. However, the improved electrical conductivity led to somewhat decrease of mechanical properties of PVA/Ag@CNTs composites.     

Enhancement of thermal and physical properties of epoxy composite reinforced with basalt fiber

The basalt chopped fiber reinforced epoxy composites using different curing systems were prepared in order to investigate the thermal characteristics of the composites. 2 different curing systems for bisphenol F type epoxy resin — an epoxy-amine curing system and an epoxy-anhydride curing system — were selected and used to investigate the interaction between matrix resin and basalt fiber in the means of thermal properties and physical properties. Through the evaluation of T _g and thermal degradation behavior of both systems, it was deduced that the type of curing system as well as basalt fiber reinforcement have a great role in determining thermal properties of the composites. Also, the tensile and flexural properties of the composites were systematically evaluated in order to further understand the effect of curing agents on the interaction with basalt fiber.     

A study of mechanical behavior and morphology of carbon nanotube reinforced UHMWPE/Nylon 6 hybrid polymer nanocomposite fiber

We report a phenomenal increase in strength, modulus, and fracture strain of ultra high molecular weight polyethylene (UHMWPE) fiber by 103 %, 219 %, and 108 %, respectively through hybridizing this fiber with Nylon 6 as a minor phase and simultaneously reinforcing it with single-walled carbon nanotubes (SWCNTs). Loading of Nylon 6 and SWCNTs into UHMWPE was 20.0 wt% and 2.0 wt%, respectively. Hybridized fibers were processed using a solution spinning method coupled with melt mixing and extrusion. We claim that the enhancement in strain-to-failure of the nanocomposites is due to induced plasticity in the hybridized Nylon 6-UHMWPE polymers. The enhancement in strength and stiffness in the nanocomposites is attributed to the load sharing of the SWCNTs during deformation. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) studies showed that changes in percent crystallinity, rate of crystallization, crystallite size, alignment of nanotubes, sliding of polymer interfaces and strong adhesion of CNT/polymer blends were responsible for such enhancements.     

Compressive and flexural properties of hemp fiber reinforced concrete

The compressive and flexural properties of hemp fiber reinforced concretes (FRC) were examined in this paper. Natural hemp fiber was mixed using dry and wet mixing methods to fabricate the FRC. Mechanical properties of the FRC were investigated. The main factors affecting compressive and flexural properties of the FRC materials were evaluated with an orthogonal test design. Fiber content by weight has the largest effect. The method for casting hemp FRC has been optimised. Under the optimum conditions, compressive strength increased by 4 %, flexural strength increased by 9 %, flexural toughness increased by 144 %, and flexural toughness index increased by 214 %.     

Flexural characteristics of coir fiber reinforced cementitious composites

This study has examined the flexural properties of natural and chemically modified coir fiber reinforced cementitious composites (CFRCC). Coir fibers of two different average lengths were used, and the longer coir fibers were also treated with a 1 % NaOH solution for comparison. The fibers were combined with cementitious materials and chemical agents (dispersant, defoamer or wetting agent) to form CFRCC. The flexural properties of the composites, including elastic stress, flexural strength, toughness and toughness index, were measured. The effects of fiber treatments, addition of chemical agents and accelerated ageing of composites on the composites’ flexural properties were examined. The results showed that the CFRCC samples were 5–12 % lighter than the conventional mortar, and that the addition of coir fibers improved the flexural strength of the CFRCC materials. Toughness and toughness index, which were associated with the work of fracture, were increased more than ten times. For the alkalized long coir fiber composites, a higher immediate and long-term toughness index was achieved. SEM microstructure images revealed improved physicochemical bonding in the treated CFRCC.     

Thermal stability and physical properties of epoxy composite reinforced with silane treated basalt fiber

This study evaluates the influence of different silane coupling agents on the thermal and physical properties of epoxy-anhydride composite reinforced with basalt fiber. The silane coupling agents were selected by their functional groups so that they could have different chemical interactions with the epoxy and anhydride curing agents. The thermal and degradation behavior of the composites with different fiber contents were evaluated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Through the evaluation of T _g and thermal degradation behavior of both systems, it was deduced that the silane coupling agents have a great influence on the thermal properties of the composites as well as interfacial improvement. Also, the tensile properties of the composites were systematically evaluated in order to further understand the effect of silane coupling agents on the interaction with basalt fiber and epoxy matrix.     

Thermal characteristics of basalt fiber reinforced epoxy-benzoxazine composites

This study investigates the possibility of utilizing basalt chopped fiber in order to prepare a thermally stable fiber reinforced composite. Bi-component resin system using epoxy and benzoxazine monomer is proposed and its cure characteristic is evaluated by FT-IR and DSC. Copolymerization of epoxy resin upon curing with benzoxazine is carried out in the absence of a strong catalyst. Through the evaluation of T _g of the epoxy-benzoxazine copolymer resin and its composite, it is clear that the incorporation of basalt fiber in composite has a great role and advantage. Also, this study systematically evaluates the apparent char yield and net char yield gain of the composites using TGA thermograms. Based on the results of DSC and TGA, it is advised that the favorable composite composition can be prepared from the range of 20 % to 50 % of epoxy content with 10 % of basalt fiber.     

Compressional behavior of carbon nanotube reinforced mesophase pitch-based carbon fibers

The tensile-recoil compressional behavior of the carbon nanotube reinforced mesophase pitch (MP)-based composite carbon fibers (CNT-re-MP CFs) was investigated by using Instron and SEM. The CNT-re-MP CFs exhibited improved, or at least equivalent, compressive strength as compared with commercial MP-based carbon fibers. Particularly, when CNT of 0.1 wt% was reinforced, the ratios of recoil compressive strengths to tensile strength of CNT-re-MPCFs were much higher (the difference is at least 10% or higher) than those for the commercial counterparts and even than those for PAN-based commercial carbon fibers. FESEM micrographs showed somewhat different fractography from that of a typical shear failure as the CNT content increased.     

Synthesis of N-4-vinylbenzyl-monoaza-m-phenylene-34-crown-11 and its copolymerization with styrene

A functional monomer, containing a 34-membered monoazacrown ether unit (VACE) as a pendant group has been synthesized by using resorcinol, tetraethylene glycol, p-tolenesulfonyl chloride and 4-vinylbenzyl chloride as starting materials. The product structure was characterized by means of FT-IR,¹H-NMR, EA and MS. Free radical homopolymerized VACE or copolymerized VACE with styrene (ST) by the conventional radical initiator 2,2′-azobis (isobutyronitrile) (AIBN) in toluene solution to afford corresponding polymers. The reactivity ratio of VACE and ST, determined by Fineman-Ross method, gave values 0.6 for VACE, and 1.4 for ST, respectively.