Effects of plasma treatment of carbon fibers on interfacial properties of BMI resin composites

High performance continuous fiber surface modification by inductively coupled RF plasma (ICP) and dielectric barrier discharge (DBD) low temperature plasma were conducted. X-ray photoelectron spectroscopy (XPS) and other analytical testing methods systematically studied plasma treatment time, discharge power, discharge pressure, etc, on fiber surface state, surface composition, and surface shape changes in the appearance and wetting properties. The results show that after plasma treatment the surface of the fiber is grafted with a large number of polar functional groups such as carboxyl groups and hydroxyl groups. The surface roughness increases, the surface free energy increases, and the fiber wetting property is significantly improved, resulting in improvement in interlaminar shear strength (ILSS) between the fiber and the resin matrix. Finally, the surfaces of the fibers and its relationship with interfacial properties of fiber reinforced bismaleimide composites are also discussed.     

Influence of an oxidation of the carbon fiber surface by boiling nitric acid on the adhesion strength in carbon fiber‐acrylate composites cured by electron beam

A time‐dependent oxidation of carbon fibers in boiling nitric acid was used to investigate the influence of a modification of the fiber surface properties on the adhesion strength with an acrylate resin cured by electron beam (EB). For each time of treatment, a characterization of the surface topography and the surface chemistry was done (topography at a micrometric and nanometric scale, specific surface area, temperature programmed desorption, X‐ray photoelectron spectroscopy analysis). The oxidation of the fiber surface in boiling nitric acid created a rough surface, which significantly increased the specific surface area, and also generated a high density of hydroxyl groups, carboxylic acids and lactones in comparison to untreated fibers. The adhesion strength with the acrylate resin cured by EB was measured by a pull‐out test. For comparison, an isothermal ultraviolet curing of the matrix was also investigated. The value of the interfacial shear strength, determined by the Greszczuk's model, was increased by the oxidation of the carbon fiber surface for both curing processes, but lower values were systemically obtained with EB curing. Copyright © 2012 John Wiley & Sons, Ltd.     

E‐glass/DGEBA/m‐PDA single fiber composites: New insights into the statistics of fiber fragmentation

The interfacial shear strength is a critical parameter for assessing composite performance and failure behavior. This parameter is usually obtained from a single‐fiber fragmentation test that induces sequential fracture with increasing strain of a single embedded fiber with output being the distribution of fragment lengths. An exact analytical form for the expected fragment length distribution is still not known. Such data are often fit empirically to Weibull, shifted‐exponential, or lognormal distribution functions. In this report, new insights into the sequential fiber fracture process are provided by detailed analyses of the fiber break locations along the length of the embedded fiber. From this approach, the high degree of uniformity of the break coordinate loci strongly suggests that there can be no mechanistic rationale for the use of the Weibull, or lognormal, or exponential functions to fit the fragment lengths. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2301–2312, 2009     

Synthesis of non‐destructive amido group functionalized multi‐walled carbon nanotubes and their application in antistatic and thermal conductive polyetherimide matrix nanocomposites

Thermal conductive and antistatic polyetherimide (PEI) nanocomposites were fabricated by encapsulating non‐destructive amido group functionalized multi‐walled carbon nanotubes (MWCNTs) into the PEI matrix. Briefly, nearly half of acyl chloride groups in poly (acryloyl chloride) reacted with sodium azide and formed acyl azide groups, which could conjunct with MWCNTs via non‐destruction nitrenes addition reaction. The remaining acyl chloride groups in poly (acryloyl chloride) hydrolyzed into carboxyl groups, therefore COOH‐rich MWCNTs (MWCNTs@azide polyacrylic acid) were synthesized without serious damage to the MWCNTs. Then, MWCNTs@azide polyacrylic acid were then reacted with p‐Phenylene diamine (PPD) and transformed to amido group functionalized MWCNTs (MWCNTs@PPD). MWCNTs@PPD could participate into the in situ polymerization of PEI matrix, where the conjunction between bisphenol A dianhydride and amido groups on MWCNTs@PPD guaranteed the strong covalent bonding at the PEI/MWCNTs interface, which directly avoided the aggregation of MWCNTs. Owing to the non‐destructive modification of MWCNTs and tight matrix/filler interface, the volume electric and thermal conductivity of as‐prepared nanocomposites was up to 6.4 × 10^?8 S/cm (1.0 wt%, MWCNTs@PPD) and 0.43 W/(m · K) (4.0 wt%, MWCNTs@PPD), respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of fiber length and composition on mechanical properties of carbon fiber‐reinforced polybenzoxazine

The mechanical strength and modulus of chopped carbon fiber (CF)‐reinforced polybenzoxazine composites were investigated by changing the length of CFs. Tensile, compressive, and flexural properties were investigated. The void content was found to be higher for the short fiber composites. With increase in fiber length, tensile strength increased and optimized at around 17 mm fiber length whereas compressive strength exhibited a continuous diminution. The flexural strength too increased with fiber length and optimized at around 17 mm fiber length. The increase in strength of composites with fiber length is attributed to the enhancement in effective contact area of fibers with the matrix. The experimental results showed that there was about 350% increase in flexural strength and 470% increase in tensile strength of the composites with respect to the neat polybenzoxazine, while, compressive properties were adversely affected. The composites exhibited an optimum increase of about 800% in flexural modulus and 200% in tensile modulus. Enhancing the fiber length, leads to fiber entanglement in the composites, resulted in increased plastic deformation at higher strain. Multiple branch matrix shear, debonded fibers and voids were the failures visualized in the microscopic analyses. Defibrillation has been exhibited by all composites irrespective of fiber length. Fiber debonding and breaking were associated with short fibers whereas clustering and defibrillation were the major failure modes in long fiber composites. Increasing fiber loading improved the tensile and flexural properties until 50–60 wt% of fiber whereas the compressive property consistently decreased on fiber loading. Copyright © 2008 John Wiley & Sons, Ltd.     

Sulfonated carbon nanotubes/sulfonated poly(ether sulfone ether ketone ketone) composites for polymer electrolyte membranes

A series of composite membranes consisting of sulfonated carbon nanotubes (sCNTs) and sulfonated poly(ether sulfone ether ketone ketone) were successfully fabricated via the solution casting method. The chemical structure, as well as the long‐term stability of the sCNTs in different solvents, was investigated by Fourier transform infrared (FTIR) analysis and solubility experiment, respectively. The morphology, tensile strength, proton conductivity, and methanol permeability of the composite membranes were also investigated. The scanning electron microscope (SEM) observation indicated the good dispersion of the carbon nanotubes in polymer matrix as well as the strong interfacial bonding between the sulfonated poly(ether sulfone ether ketone ketone) (SPESEKK) matrix and sCNTs. The addition of either pristine carbon nanotubes or modified carbon nanotubes significantly enhanced the tensile strength of the SPESEKK membrane. The proton conductivity of the SPESEKK membrane increased while the methanol permeability decreased as the sCNTs content increased, showing a strong interaction between the modified nanotubes and SPESEKK. Copyright © 2010 John Wiley & Sons, Ltd.     

Epoxy/amine‐functionalized short‐length vapor‐grown carbon nanofiber composites

Short length vapor‐grown carbon nanofibers (VGCNFs) were functionalized with 4‐aminobenzoic acid in polyphosphoric acid/phosphorous phentoxide medium via “direct” Friedel‐Crafts acylation reaction to afford aminobenzoyl‐functionalized VGCNFs (AF‐VGCNFs). The AF‐VGCNFs as a cocuring agent were mixed with epoxy resin by simple mechanical stirring in methanol which was added to help efficient mixing. After evaporation of methanol, 4,4′‐methylenedianiline as a curing agent was added to the mixture, which was then cured at elevated temperatures. The resultant composites displayed uniform dispersion of AF‐VGCNFs into cured epoxy matrix. During curing process, the amine functionalities on AF‐VGCNF together with 4,4′‐methylenedianiline were expected to be involved in covalent attachment to the epoxy resin. As a result, both tensile modulus and strength of the composites were improved when compared with those of pure epoxy resin. Thus, the AF‐VGCNFs play a role as an outstanding functional additive, which could resolve both dispersion and interfacial adhesion issues at the same time by functionalization of VGCNFs and covalent bonding between the additive and matrix, respectively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7473–7482, 2008     

Polyaniline‐coupled graphene/nickel hydroxide nanohybrids as flame retardant and smoke suppressant for epoxy composites

Graphene‐polyaniline/nickel hydroxide ternary hybrid (RGO‐PANI/Ni(OH)₂) was synthesized and incorporated into epoxy resin (EP) to improve the fire retardant property. Thermogravimetric analysis results showed that the RGO‐PANI/Ni(OH)₂ nanohybrid could catalyze the thermal degradation of epoxy matrix that was essential to trigger the char formation. The char yield of the RGO‐PANI/Ni(OH)₂/EP composite was improved compared with that of the samples with graphene and polyaniline only. With 3.0‐wt% RGO‐PANI/Ni(OH)₂, significant reduction in peak heat release rate (40%) and peak smoke production rate (36%) was observed in the cone calorimeter tests. Thermogravimetric analysis/infrared spectrometry (TG‐IR) results indicated that the flammable volatiles of the RGO‐PANI/Ni(OH)₂/EP composite was reduced compared with those of the EP and RGO‐PANI/EP. The superior flame retardant and smoke suppressant behaviors of the RGO‐PANI/Ni(OH)₂ nanohybrid over RGO‐PANI were attributed to the combination of good barrier effect of graphene with catalytic ability of char formation of PANI and metal hydroxide.     

Mechanical hysteresis,interface and filler–filler structural breakdowns in ethylene vinyl acetate organoclay composites internally lubricated via radiolytically degraded PTFE microparticles

Inclusion of two or more distinct fillers (hybrid fillers) in a matrix is envisaged to entail synergetic advantages. This study reports synthesis and property evaluation of a novel hybrid filler‐based polymer composite containing two types of fillers with distinct attributes namely mechanical reinforcement and internal lubrication. Poly(tetrafluoroethylene) micro‐particles (PTFEMP) were synthesized via radiolytic‐mechanical degradation and used as an internal lubricant for organoclay (OC) reinforced ethylene vinyl acetate (EVA) matrix. Mechanical hysteresis, nonlinear and linear small amplitude oscillatory shear rheology, morphology, small angle X‐ray scattering (SAXS), dynamic coefficient of friction (DCoF), surface wetting and thermoxidative stability of binary and ternary composites were investigated. In EVA/OC composites, PTFEMP acted as an internal lubricant and reduced DCoF in a volume fraction‐dependent fashion. OC and PTFEMP both increased the mechanical hysteresis of EVA; though the magnitude of hysteresis was much less in PTFEMP. Intriguingly, PTFEMP reduced mechanical hysteresis of EVA/OC composites that is work done during loading and unloading stress–strain cycles was considerably reduced with the inclusion of PTFEMP in EVA/OC composites. SAXS results revealed mass fractals and the presence of an interfacial layer in EVA/OC composites but not in EVA/PTFEMP composites. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 509–519     

Mechanical,thermal, and UV‐shielding behavior of silane surface modified ZnO‐reinforced phthalonitrile nanocomposites

In the present work, zinc oxide nanoparticles were treated with aminopropyl trimethoxy silane‐coupling agent and used as a new kind of reinforcement for a typical high performance bisphenol‐A‐based phthalonitrile resin. The resulted nanocomposites were characterized for their mechanical, thermal, and optical properties. Results from the tensile test indicated that the tensile strength and modulus as well as the toughness state of the matrix were all enhanced with the increasing of the nanoparticles amount. Thermogravimetric analysis showed that the starting decomposition temperatures and the residual weight at 800°C were highly improved upon adding the nanofillers. At 6 wt% nanoloading, the glass transition temperature and the storage modulus were considerably enhanced reaching about 359°C and 3.7 GPa, respectively. The optical tests revealed that the neat resin possesses excellent UV‐shielding properties, which were further enhanced by adding the nanofillers. Furthermore, the fractured surfaces of the nanocomposites analyzed by scanning electron microscope exhibited homogeneous and rougher surfaces compared with that of the pristine resin. Finally, the good dispersion of the reinforcing phase into the matrix was confirmed by a high resolution transmission electron microscope. Copyright © 2015 John Wiley & Sons, Ltd.     

The effect of coupling agents on the interfacial properties of wood‐fiber–reinforced polyimide composites

Wood‐fiber–reinforced polyimide (PI) has been widely used in many engineering fields because of its high specific strength and stiffness. However, PI does not adhere well with wood fibers because it has a low free surface energy. In addition, high viscosity in the melted phase causes poor impregnation. In this study, surface treatment methods, ie, coupling agents with plasma treatment on wood fibers, were applied to increase the interfacial strength between the wood fibers and the PI matrix. The modified wood fiber surfaces were analyzed by X‐ray photoelectron spectroscopy and scanning electron microscopy. To analyze the effectiveness of the surface treatment method, the interlaminar shear strength (ILSS) was measured using the 3‐point bending test. From the test results, the ILSS of the specimens treated with the silane coupling agent after the plasma treatment increased by 48.7% compared with those of the untreated specimens.     

Influence of surface properties on the interfacial adhesion in carbon fiber/epoxy composites

A polyacrylonitrile‐based carbon fiber was electrochemically oxidized in an aqueous ammonium bicarbonate solution with current density of up to 2.76 A/m² at room temperature. X‐ray photoelectron spectroscopy revealed that the oxygen content increased with increasing current density before approaching saturation. The increase can be divided into two regions, the rapid increase region (0–1.78 A/m²) and a plateau region (1.78–2.76 A/m²). The surface chemistry analysis showed that the interlaminar shear strength (ILSS) value of the carbon fiber/epoxy composite could be improved by 24.7%. The carbon structure was examined using Raman spectroscopy in terms of order/disorder in the graphite structure and the results indicated that the relative percentage of graphite carbon in the form of sp² hybridization increased above a current density of 1.39 A/m². The increasing non‐polar graphite carbon on the carbon fiber surface decreased the surface energy. As a result, both the surface free energy () and its polar component () decreased when current density increased above 1.78 A/m². The ILSS value had no direct relationship with the nature and surface density of the oxygen‐containing functional groups nor with the carbon structure. It is the surface free energy (), especially the polar component (), which played a critical role in affecting the interfacial adhesion of carbon fiber/epoxy composites. The ILSS value changed with increasing current density and could be divided into three distinct regions, as chemical interaction region (I), anchor force region (II) and matrix damage region (III). Copyright © 2013 John Wiley & Sons, Ltd.     

Self‐reinforced composites based on commercial PP woven fabrics and a random PP copolymer modified with quartz

Self‐reinforced composites based on commercial polypropylene (PP) woven fabrics and a random PP copolymer modified with quartz were obtained by film stacking. The effect of the incorporation of quartz on the materials fracture and failure behavior was studied through uniaxial tensile tests and quasi‐static fracture experiments. Acoustic emission analysis was also performed in situ in the tensile tests. A higher consolidation quality was obtained for the composites containing quartz. In the composite with random PP modified with 5 wt% quartz, the higher consolidation and the better dispersion of quartz particles positively impacted on the materials tensile and fracture behavior. From the results of acoustic emission analysis, fiber fracture appears as the dominant failure mechanism in the investigated composites. Copyright © 2016 John Wiley & Sons, Ltd.     

The tensile properties of HNO3‐treated carbon fiber reinforced ABS/PA6 composites

In this study, acrylonitrile‐butadiene‐styrene (ABS) terpolymer was reinforced with HNO₃‐treated short carbon fibers (SCFs) [(hollow carbon fibers (HCFs)]. The effects of HCF concentration on the tensile properties of the composites were examined. Increasing the HCF concentration in the ABS matrix from 10 to 30 wt% resulted in improved tensile strength and tensile modulus. To obtain a strong interaction at the interface, polyamide 6 (PA6) at varying concentrations was introduced into the ABS/10 wt% SCF composite. The incorporation and increasing amount of PA6 in the composites increased tensile properties of the ABS/PA6/HCF systems due to the improved adhesion at the interface, which was confirmed by the ratio of tensile strength as an adhesion parameter. These results were also supported by scanning electron micrographs of the ABS/PA6/HCF composites, which exhibited an improved adhesion between the SCFs and the ABS/PA6 matrix. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of heat treatment on electromagnetic properties of polyimide/carbon black composites

A kind of absorbing materials was prepared by hot pressing method using polyimide as matrix and carbon black (CB) as filler. The mechanical properties, the electromagnetic properties, and the thermal stability of polyimide/CB composites were studied. The results showed that the complex permittivity increased from 6.82 + 1.38i to 18.69 + 9.47i, whereas the flexural strength decreased from 108 MPa to 77 MPa, respectively, when the CB content increased from 2 wt% to 8 wt%. The reflection loss curves shifted to low frequency with increase of the thickness at the same content. The reflection loss below ?10 dB could be obtained in the X band with 6 wt% CB content and did not display significant difference before and after the heat treatment at 400°C for 5 h. When the content of CB was 8 wt%, the decomposition temperature (at 5% weight loss) increased approximately 42°C compared with pure polyimide matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermoelectrical and optical properties of double wall carbon nanotubes:polyaniline containing boron n‐type organic semiconductors

The electrical conductivity, thermoelectrical, and optical properties of the polyaniline containing boron/double wall carbon nanotubes (CNTs) composites have been investigated. The electrical conductivities of the composites prepared with 1%, 5%, and 8% CNT concentrations at 300 K were found to be 5.31 × 10^?6, 2.72 × 10^?4, and 1.12 × 10^?3 (S/cm), respectively. The thermoelectrical results indicate that all the samples exhibit n‐type electrical conductivity. The optical band gaps of the samples were found to be 3.71 eV for 0% DWNT, 3.32 eV for 1% DWNT, 3.15 eV for 5% DWNT, and 3.12 eV for 8% DWNT. The obtained results suggest that the electrical conductivity of PANI‐B polymer is improved by DWNT doping. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of carbon nanofibers on mechanical and electrical behaviors of acrylonitrile‐butadiene rubber composites

Recently, carbon nanofibers have become an innovative reinforcing filler that has drawn increased attention from researchers. In this work, the reinforcement of acrylonitrile butadiene rubber (NBR) with carbon nanofibers (CNFs) was studied to determine the potential of carbon nanofibers as reinforcing filler in rubber technology. Furthermore, the performance of NBR compounds filled with carbon nanofibers was compared with the composites containing carbon black characterized by spherical particle type. Filler dispersion in elastomer matrix plays an essential role in polymer reinforcement, so we also analyzed the influence of dispersing agents on the performance of NBR composites. We applied several types of dispersing agents: anionic, cationic, nonionic, and ionic liquids. The fillers were characterized by dibutylphtalate absorption analysis, aggregate size, and rheological properties of filler suspensions. The vulcanization kinetics of rubber compounds, crosslink density, mechanical properties, hysteresis, and conductive properties of vulcanizates were also investigated. Moreover, scanning electron microscopy images were used to determine the filler dispersion in the elastomer matrix. The incorporation of the carbon nanofibers has a superior influence on the tensile strength of NBR compared with the samples containing carbon black. It was observed that addition of studied dispersing agents affected the performance of NBR/CNF and NBR/carbon black materials. Especially, the application of nonylphenyl poly(ethylene glycol) ether and 1‐butyl‐3‐methylimidazolium tetrafluoroborate contributed to enhanced mechanical properties and electrical conductivity of NBR/CNF composites.     

Improved mechanical properties of epoxy composites reinforced with surface‐treated UHMWPE fibers

The surface treatment of ultra‐high molecular weight polyethylene fiber using potassium permanganate and the mechanical properties of its epoxy composites were studied. After treatment, many changes were happened in the fiber surface: more O‐containing groups (―OH, ―C═O, and ―C―O groups), drastically decreased contact angles with water and ethylene glycol, slightly increased melting point and crystallinity, and formed cracks. Different contents (0.1–0.5 wt%) ultra‐high molecular weight polyethylene fibers/epoxy composites were prepared. The results indicated that the surface treatment decreased the tensile strength of epoxy composites, but increased the bending strength. When the fiber content was 0.3 wt%, the above properties reached the maximum. At the same fiber content, the interlaminar shear strength of the composites was increased by 26.6% up to the as‐received fiber composites. Dynamic mechanical analysis of the composites suggested the storage modulus and tanδ were decreased due to the surface treatment. Fractured surface analysis confirmed that the potassium permanganate treatment was effective in improving the interface interaction.     

Comparative study of the effects of nano‐sized and micro‐sized CF and PTFE on the thermal and tribological properties of PEEK composites

The tribological characteristics of PEEK composites fretting against GCr 15 steel were investigated by a SRV‐IV oscillating reciprocating ball‐on‐disk tribometer. In order to clarify the effect of type and size of fillers on the properties of PEEK composites, nano‐sized and micro‐sized CF and PTFE fillers were added to the PEEK matrix. The thermal conductivity, hardness, and fretting wear properties of PEEK composites reinforced by CF or PTFE were comparatively studied. The results showed that the type and size of the fillers have an important effect on both the friction coefficient and wear rate, by affecting their thermal conductivity, hardness, as well as the surface areas of their transfer films. In comparison, the effect on improving the tribological properties of micro‐sized CF was superior to that of nano‐sized CF, while the effect of nano‐sized PTFE was superior to that of micro‐sized PTFE. Considering the acceptable friction coefficient and wear rate of the composite under the fretting wear test, it seemed that 4% nCF, 20% mCF, 2% nPTFE and 10% mPTFE were desired additive proportions. And it also can be found that during the fretting wear test, the abrasive and adhesive wear resulted in accumulative debris at the contacting surface. The transfer films made of debris were formed on the counterfaces.     

Mechanical properties of plasma‐treated carbon fiber reinforced PTFE composites with CNT

This paper is concerned with the effects of the plasma surface treatment and the addition of CNT on the mechanical properties of carbon fiber/polytetrafluoroethylene (PTFE) composite. The tensile and flexural strength of composites containing CNT and plasma‐treated carbon fibers improved. The flexural strength first decreases with respect to the CF content. The flexural strength increases to 179 MPa for the plasma‐treated composite as compared with 167 MPa for the neat carbon fiber composites. The overall improvement is thus nearly 8%.