The effects of cauliflower-like short carbon fibers on the mechanical properties of rigid polyurethane matrix composites

Stress concentration and weak interfacial strength affect the mechanical properties of short carbon fibers (CFs) reinforced polymer composites. In this work, the cauliflower-like short carbon fibers (CCFs) were prepared and the point was to illuminate the effects of fiber morphology on the mechanical properties of the CCFs/rigid polyurethane (RPU) composites. The results indicated that the surface structure of CCFs could increase the surface roughness of the fibers and the contact area between fibers and matrix, thereby promoting the formation of irregular interface. Compared with pure RPU and initial CFs/RPU composites, the strength and toughness of CCFs/RPU composites were simultaneously improved. The satisfactory performance was attributed to the special fibers structure, which played an anchoring role and consumed more energy during crack propagation.     

Synergistic effects of functionalized graphene and functionalized multi-walled carbon nanotubes on the electrical and mechanical properties of poly(ether sulfone) composites

Mixed fillers composed of functionalized graphene (f-G) and functionalized multi-walled carbon nanotubes (f-CNTs) (f-G-f-CNTs) were prepared and their synergistic effects in terms of enhancing the electrical conductivity and tensile modulus of poly(ether sulfone) (PES) composites were investigated. The results indicate that the electrical conductivity of the 5 wt% f-G-f-CNTs(W_f-G/W_f-CNTs = 1:1)/PES composite was 2.2 times higher than that of the 5 wt% f-G/PES composite and 8.9 times higher than that of the 5 wt% f-CNTs/PES composite. Moreover, the tensile modulus of the 5 wt% f-G-f-CNTs(W_f-G/W_f-CNTs = 1:1)/PES composite relative to that of the 5 wt% f-G/PES composite and 5 wt% f-CNTs/PES composite increased by 16.5% and 50.6%, respectively. Additionally, enhancements in the electrical conductivity and tensile modulus of the PES composite depended on the weight ratio of f-G and f-CNTs in the mixed fillers. The electrical conductivity and tensile modulus exhibited maximum values when the weight ratios of f-G and f-CNTs were 1:3 and 1:1, respectively. When the weight ratio of f-G and f-CNTs was fixed at 1:1, the f-G-f-CNTs(W_f-G/W_f-CNTs = 1:1)/PES composite showed a percolation threshold of 0.22 vol%, much lower than that of the f-G/PES composite.     

Self-reinforced composites obtained by the partial oxypropylation of cellulose fibers. 2. Effect of catalyst on the mechanical and dynamic mechanical properties

This work describes the partial oxypropylation of filter paper cellulose fibers, employing two different basic catalyst, viz., potassium hydroxide and 1,4-diazabicyclo [2.2.2] octane, to activate the hydroxyl groups of the polysaccharide and thus provide the anionic initiation sites for the “grafting-from” polymerization of propylene oxide. The success of this chemical modification was assessed by FTIR spectroscopy, X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis and contact angle measurements. The study of the role of the catalyst employed on the extent of the modification and on the mechanical properties of the ensuing composites, after hot pressing, showed that both the Brønsted and the Lewis base gave satisfactory results, without any marked difference.     

Friction and wear properties of combined surface modified carbon fabric reinforced phenolic composites

Carbon fabric (CF) was surface treated with silane-coupling agent modification, HNO₃ oxidation, combined surface treatment, respectively. The friction and wear properties of the carbon fabric reinforced phenolic composites (CFP), sliding against GCr15 steel rings, were investigated on an M-2000 model ring-on-block test rig. Experimental results revealed that combined surface treatment largely reduced the friction and wear of the CFP composites. Scanning electron microscope (SEM) investigation of the worn surfaces of the CFP composites showed that combined surface modified CFP composite had the strongest interfacial adhesion and the smoothest worn surface under given load and sliding rate. SEM and X-ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that the fiber surface became rougher and the oxygen concentration increased greatly after combined surface treatment, which improved the adhesion between the fiber and the phenolic resin matrix and hence to improve the friction-reduction and anti-wear properties of the CFP composite.     

Enhanced mechanical properties of carbon fiber composites by grafting different structural poly(amido amine) onto fiber surface

The mechanical properties of carbon fiber composites depend on the interfacial strength between fiber and epoxy matrix. Different poly (amido amine) (PAMAM) dendrimers were grafted onto carbon fiber to improve the interfacial strength of the resulting composites. Functional groups on the carbon fiber surface were examined by X-ray photoelectron spectroscopy. The surface morphology of the resulting materials was characterized by scanning electron microscopy and atomic force microscope. The characterization results revealed that PAMAM dendrimers were chemically grafted onto the surface of carbon fiber. More importantly, the mechanical properties of the resulting composites were enhanced owing to the presence of sufficient functional groups on the carbon fiber surface. In addition, after PAMAM containing chair conformations were grafted, the interlaminar shear strength had the highest increase of 53.13%, higher than that of the fiber grafted with PAMAM containing terminated linear amine. This work provides an alternative approach to enhance the mechanical properties of fiber composites by controlling the interface between fiber and epoxy matrix.     

Comparison of four methods for determining fiber content of carbon fiber/epoxy composites

The most fundamental parameter that controls the properties of fiber/epoxy composites is fiber content. Thus, exact calculation of carbon fiber content is important for product quality control and process optimization. In this study, four methods for calculating fiber content of continuous carbon fiber/epoxy composites were investigated. These four methods are processing statistical (PS), optical microscopy (OM), thermogravimetric analysis (TGA), and carbonization-in-nitrogen (CIN). The results show that the CIN and PS methods have high repeatability with no more than 4.7 wt.% deviation, and a relatively exact estimation of fiber content can be obtained by using both of them. A larger difference was generated when the TGA and OM methods were used to determine the fiber content. This is because the small amount of samples required by these methods is not sufficiently representative of the whole carbon fiber composite structure. The PS and CIN methods can be used as approved ways to calculate fiber content of carbon fiber/epoxy composites effectively.     

Study of the thermal properties of polyester composites loaded with oriented carbon nanofibers using the front-face flash method

In this work, we have prepared polyester resin based composites, loaded with carbon nanofibers decorated with magnetite nanoparticles (m-CNF) in several volumetric concentrations covering from 0 to 3.25% and oriented applying a constant magnetic field before polymerization. A study of the heat transfer along the direction of the alignment of the fibers was performed by measuring the in-depth thermal diffusivity and thermal effusivity using the laser flash method in the front-face configuration. For the maximum volumetric concentration of aligned nanofibers along the thickness of the sample, an improvement of 80% of the thermal conductivity above the thermal conductivity of the polyester resin was observed. In contrast, the increment of the thermal conductivity was only of 20% above the value of the matrix for samples with non-oriented carbon nanofibers. The effects of the m-CNF and their orientation on the effective thermal conductivity of the composites were analyzed using a simple theoretical model, which takes into account the thermal mismatch between the matrix and the fillers, as well as the aspect ratio of the embedded fibers.     

Mechanical and thermal properties of Acacia leucophloea fiber/epoxy composites: Influence of fiber loading and alkali treatment

In this work, the influence of fiber content and alkali treatment on the mechanical and thermal properties of Acacia leucophloea fiber-reinforced epoxy composites was studied. Ten composite samples were fabricated by varying fiber content (5, 10, 15, 20, and 25 wt%); both untreated and treated fiber were soaked in a 5% NaOH solution for 45 min by using hand-layup method. The composite reinforced with 20 wt% treated fiber content exhibited better mechanical properties and thermal properties. Fourier transform infrared analysis, morphological analysis by atomic force microscope, and scanning electron microscope of composites were also performed.     

Orientation and mechanical properties of laser‐induced photothermally drawn fibers composed of multiwalled carbon nanotubes and poly(ethylene terephthalate)

This study presents a novel photothermal drawing of poly(ethylene terephthalate) (PET)/multiwalled carbon nanotube (MWCNT) fibers. The photothermal drawing was carried out using the near infrared laser‐induced photothermal properties of MWCNTs. An uniform fiber surface was obtained from a continuous necking deformation of the undrawn fibers, particularly at a draw ratio of 4 and higher. The breaking stress and modulus of the photothermally drawn PET/MWCNT fibers were significantly enhanced, in comparison to those of hot drawn fibers at the same draw ratio. The enhanced mechanical properties were ascribed to the increased orientation of PET chains and MWCNTs as well as PET crystallinity due to photothermal drawing. In particular, a significantly higher degree of orientation of the MWCNTs along the fiber axis was obtained from photothermal drawing, as shown in polarized Raman spectra measurements. The photothermal drawing in this study has the potential to enhance the mechanical properties of fibers containing MWCNTs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 603–609     

Syntheses and properties of fluorinated carbon materials

In this review, the more recent topics in the field of fluorinated carbon materials are given with the emphasis on the research work presented by our group. The direct fluorination and/or oxyfluorination of various carbon materials, especially of new carbon materials, i.e. nanotubes, carbon fibers, and activated carbon fibers have been described. It has been shown that fluorination can be one of the most effective methods to modify and control physico-chemical properties of carbon materials.     

Influence of compatibilizing agent molecular structure on the mechanical properties of phosphate glass fiber‐reinforced PLA composites

Eight compatibilizing agents were studied to investigate their effect on the quality of the interface between a phosphate glass fiber and a poly(lactic acid) (PLA) matrix. After application of the agents via dip‐coating, the fibers were Soxhlet extracted to remove any unreacted compatibilizer. To assess the interface quality, single fiber tensile tests of treated fibers and interfacial shear strengths (IFSS) of single fiber composites (SFC) were assessed. Of the agents tested, Glycerol‐2‐phosphate disodium pentahydrate (GP) and low molecular weight PLA with a sodium salt terminal group (PLA‐Na) showed the highest IFSS values, which were significantly higher than those of the control. Oligomeric PLA with a carboxylic acid end group and alendronate sodium trihydrate also showed an improvement over the control fibers. The hydrolytic degradation of these single fiber composites was studied over 7 days in water at 37 °C and a significant decrease in IFSS was observed in all cases, with the treated samples dropping to the level of the control. TGA and XPS analysis of the sized fibers showed that GP and PLA‐Na had been applied successfully to the fiber surface. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3082–3094, 2010     

Crystallization,mechanical, thermal and rheological properties of polypropylene composites reinforced by magnesium oxysulfate whisker

Polypropylene(PP) composites containing magnesium oxysulfate whisker(MOSw) or lauric acid(LA) modified MOSw(LAMOSw) were prepared via melt mixing in a torque rheometer. The heterogeneous nucleating effect of LAMOSw was clearly observed in polarized light microscopy(PLM) pictures with the presence of an abundance of small spherulites. MOSw exhibited no nucleation effect and formed a few spherulites with large size. Compared with PP/MOSw composites, PP/LAMOSw exhibited better impact strength, tensile strength and nominal strain at break, ascribing to three possible reasons:(i) more β-crystal PP formed,(ii) better dispersity of LAMOSw in PP matrix and(iii) the plasticizing effect of LA. The results of dynamic mechanical thermal analysis(DMTA) indicated that brittleness of the PP matrix at low temperature was improved by the addition of LAMOSw, while the interfacial interactions between MOSw and PP matrix were actually weakened by LA, as evidenced by the higher tanδ values over the entire range of test temperatures. In terms of the rheological properties of the composites, both the η* and G′ at low frequencies increase with the addition of MOSw or LAMOSw, indicating that the PP matrix was transformed from liquid-like to solid-like. However, a network of whiskers did not form because no plateau was found in the G′ at low frequencies. With low filler content, LAMOSw produced a stronger solid-like behavior than MOSw mainly due to the better dispersion of the LAMOSw in PP matrix. However, for highly-filled composites, the η* of PP/LAMOSw at low frequencies was smaller than that of PP/MOSw composite, since the particleparticle contact effect played a major role.     

Effect of thermal cycling and open-hole size on mechanical properties of polymer matrix composites

This paper investigates the effects of thermal cycling on mechanical degradation of polymer matrix composites (PMCs). Un-notched and open-hole specimens are tested using developed thermal cycling apparatus and tensile test machine. In addition, the hole-size effect of open-hole tension glass/epoxy composite laminates is investigated. The tensile strength, mass loss and surface degradation of the specimens were obtained during 250 cycles. Experimental results showed that the holes diameter is the main parameter to control the thermal cycling effects on open hole structure. Also, it is found that laminates with smaller holes have higher tensile strength variation than those with larger holes. The results showed that increment of the hole diameter and number of cycles decreases the tensile strength.     

Wettability of carbon fibers modified by acrylic acid and interface properties of carbon fiber/epoxy

The oxidation-reduction and pre-irradiation induced methods were employed to study the effect of acrylic acid modification on the wetting and adsorption ability of carbon fiber (CF) in epoxy solution and the interfacial properties of CF/epoxy. Systematic experimental work was conducted to determine the surface topography, surface energy, surface chemical composition, absorbability and tensile strength of carbon fibers and interfacial adhesion of CF/epoxy before and after modification. The roughness, surface energy, amount of containing-oxygen functional groups and wetting ability were all found to increase significantly after modifications. The tensile strength of carbon fibers was improved marginally by γ-ray pre-irradiation while was decreased little by oxidation-reduction modification. Consequently, the surface modifications of carbon fibers via both oxidation-reduction and pre-irradiation led to an improvement (more than 15%) of the interlaminar shear strength of CF/epoxy composites. The mechanisms of interfacial improvement of modified CF/epoxy composites are proposed.     

Analysis of degradation processes of C/C composites and coating layers with tracer elements in an air-acetylene flame by two-dimensional atomic absorption spectrometry

This paper describes a novel measurement technique for in-situ monitoring of the degradation processes of coated C/C composites (carbon fiber-reinforced carbon composites) in combusting fields. The samples tested in this experiment were C/C composites with double coating layers of SiC and glass materials doped with Ca and/or Mg as tracer elements. These samples were exposed in an C₂H₂/air flame emitted the diatomic molecules, and the light from the Mg-Ca hollow cathode lamp passed through the flame around the sample. The spectrally and spatially resolved images of emission were observed with a spectro CCD camera developed by our group. In this work, two-dimensional atomic absorption spectrometry by using the spectro CCD camera was applied to in-situ monitor the degradation processes of each coating layer and the substrate. The results indicated that the temporal changes in the spatial distribution of atomic absorption caused by Ca and Mg atoms proved to be a good measure for in-situ monitoring of the degradation processes of coated C/C composites in a high temperature flame.     

Mechanical characterization of polymethyl methacrylate composites reinforced with surface-coated carbon fibers

Using trihydroxy polyether polyol (PPG), diphenylmethane diisocyanate (MDI) as soft segment and hard segment, carbon fiber (CF) as reinforcement, and self-crosslinking CF/polymethyl methacrylate (PMMA) composite was prepared by prepolymer method. In this study, starch and octanoyl chloride were esterified to obtain esterified starch (SE). The fiber is then melt blended with PMMA matrix to prepare PMMA composite. Fourier-transform infrared spectroscopy (FTIR) and SEM were used to analyze and characterize the composites produced. The results show that the composite material was prepared by separately modifying the fiber with NaOH and SE, respectively. The mechanical properties of the composite materials prepared by the modified fiber are improved, and the fiber and the PMMA matrix showed better compatibility. The mechanism of comodified fiber enhanced the mechanical properties of its composites.     

Effect of alkali and ultraviolet aging on physical,thermal, and mechanical properties of fibers for potential use as reinforcing elements in glass/silicate composites

This work reports the effect of an alkaline environment and ultraviolet (UV) radiation on the physical, thermal, and tensile properties of different fibers selected as potential reinforcing elements to enhance the impact properties of brittle glass/silicate composites. The fibers, which included regenerated cellulosic (viscose and rayon), synthetic (ultrahigh molecular weight polyethylene, polypropylene, polyamide, acrylic), glass, ceramic, and steel, were aged in different alkaline solutions with pH ranging from 11.1 to 13.6 at 70°C for different periods of time and exposed to UV radiation for 330 h. The physical and thermal properties of aged fibers were studied using tensile testing, scanning electron microscopy, and simultaneous differential and thermogravimetric analysis. Results showed that the regenerated cellulosic fibers, acrylic, E‐glass, and A‐glass fibers could not withstand the highly alkaline environment. Overall, ultrahigh molecular weight polyethylene, UV‐stable polypropylene, polyamide 6.6, AR‐glass, ceramic (alumino borosilicate), and steel fibers performed very well under all conditions, indicating that they have the potential to be used as reinforcing elements in glass/silicate composites. Copyright © 2011 John Wiley & Sons, Ltd.     

Electrical properties of conductive polymer composites prepared by an innovational method

<正>An innovational method that poly(styrene-co-maleic anhydride)(SMA),a compatibilizer of immiscible nylon6/polystyrene(PA6/PS) blends,was first reacted with carbon black(CB) and then blended with PA6/PS,has been employed to prepare the PA6/PS/(SMA-CB) composites of which CB localized at the interface.In PA6/PS/CB blends,CB was found to preferentially localize in the PA6 phase.However,in the PA6/PS/(SMA-CB) blends,it was found that CB particles can be induced by SMA to localize at the interface.The electrical porperties of PA6/PS/(SMA-CB) composites were investigated.The results showed that the composites exhibited distinct triple percolation behavior,i.e.the percolation is governed by the percolation of CB in SMA phase,the continuity of SMA-CB at the interface and the continuity of PA6/PS interface.The percolation threshold of PA6/PS/(SMA-CB) was only 0.15 wt%,which is much lower than that of PA6/PS/CB.Moreover,the PTC(positive temperature coefficient) intensity of PA6/PS/(SMA-CB) composites was stronger than that of PA6/PS/CB and the negative temperature coefficient(NTC) effect was eliminated.The electrical properties of PA6/PS/(SMA-CB) were explained in terms of its special interface morphology:SMA and CB localize at interphase to form the conductive pathways.     

Synergetic effects of carbon nanotube and graphene addition on thermo-mechanical properties and vibrational behavior of twill carbon fiber reinforced polymer composites

The effect of carbon based nanoparticles addition, such as Multi Wall Carbon Nanotube (MWCNTs) and Graphene Nano Platelets (GNPs), on mechanical and thermal properties of Carbon Fiber Reinforced Polymer Composites (CFRPs) was experimentally investigated. 2/2 twill woven carbon textile was used to fabricate the CFRP samples. The main aim of this study was to improve the weak interface behavior of carbon fibers with polymers by using its own nanoparticles in the structure of CFRPs. The obtained results from thermal tests, such as storage modulus, loss factors, glass transition temperature and loss weight percentage, were compared to reveal the influence of nanoparticles in the structure of CFRPs. The effects of MWCNTs and GNPs addition on natural frequency and damping ratio of multi scale composites were studied by using vibrational tests. The effect of nanoparticles addition on water uptake nature of CFRPs was investigated by hydrophobicity test. The results showed that MWCNT and GNP nanoparticles improved the mechanical and dynamic behavior of CFRP composite materials by improving the modulus of elasticity, tensile strength, flexural modulus, strength, ILSS, critical buckling load, and natural frequency. Furthermore, the thermal characteristics of CFRPs, such as storage modulus, thermal stability and thermal conductivity, were improved by the addition of carbon based nanoparticles. It was observed that the MWCNT multi scale composites had better performance than the GNP. According to the results of hydrophobicity test, the addition of MWCNTs enhanced the hydrophobic nature while the GNPs increased the hydrophilic nature of CFRPs.     

Strength and toughness of carbon fibers reinforced rigid polyurethane composites by adsorbing tannic acid and refining Ni grains on carbon fibers surface

In this article, short carbon fibers (CFs) reinforced rigid polyurethane (RPU) composites were prepared with the aim of improving both strength and toughness. A tannic acid (TA)‐nickel (Ni) composite coating was spontaneously co‐deposited onto CFs surface by a one‐step electrodeposition method to strengthen the interface bonding of the composites. The satisfactory mechanical properties of the composites were mainly attributed to the superior interfacial adhesion. On the one hand, TA could play a role in refining Ni grain during electrodeposition. On the other hand, the hydroxyl groups attached to composite coating, which were introduced by TA, could react with the RPU matrix to form chemical bonds. When the composites were under stress, the chemical bonds could effectively transfer the stress from matrix to the interface, while the refined Ni crystals could greatly increase the stress transfer path, and thus improve the strength and toughness of the material. Compared with pure RPU, the tensile strength, bending strength,interlaminar shear strength, and impact strength of TA‐Ni‐coated CFs/RPU composites were improved by 14.8%, 83.1%, 28.7%, and 121.4%, respectively.