Influence of carbon fiber surface treatments on the structure and properties of conductive carbon fiber/polyethylene films

Effects of carbon fiber (CF) surface modification on the crystalline structure and both electrical and mechanical properties of conductive CF/high‐density polyethylene (HDPE) films were studied. Three different types of surface‐treated CF, epoxy‐sized, unsized, and sized but thermally treated, were considered. It was found that the uniformity of the transcrystalline zone around CF and the overall crystallinity of the polyethylene matrix decreased when epoxy‐sized CF was used. Epoxy‐sized CF caused a significant reduction not only in electrical resistivity and temperature coefficient of resistivity (TCR) but also tensile strength and coefficient of linear thermal expansion (CLTE) of composite films compared with that of unsized or sized CF that was thermally treated. We observed the systematic changes of TCR and CLTE values in accordance with CF surface modification and CF content in composite films. It was concluded that thermal expansion of the polymer matrix is the main reason for the positive TCR of CF/HDPE films. As the most probable reasons for decreased resistivity and strength of the CF/HDPE films with epoxy‐sized CF, the diffusion of epoxy sizing agent into the polyethylene matrix and the formation of loosened semiconductive interphase structure in the film are considered. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2040–2048, 2002; DOI 10.1002/app.10500     

Temperature effect on graphene‐filled interface between glass–carbon hybrid fibers and epoxy resin characterized by fiber‐bundle pull‐out test

The overall mechanical performance of glass–carbon hybrid fibers reinforced epoxy composites depends heavily upon fiber–matrix interfacial properties and the service temperatures. Fiber‐bundle pull‐out tests of glass (GF) and/or carbon fiber (CF) reinforced epoxy composites were carried out at room and elevated temperatures. Graphene nanoplatelets were added in the interfacial region to investigate their influence on the interfacial shear strength (IFSS). Results show that IFSS of specimens with fiber‐bundle number ratio of GF:CF = 1:2 is the largest among the hybrid composites, and a positive hybridization effect is found at elevated temperatures. IFSS of all the specimens decreases with the increasing of test temperatures, while the toughness shows a contrary tendency. As verified by scanning electron microscopy observations, graphene nanoplatelets on fiber surface could enhance the IFSS of pure glass/carbon and hybrid fibers reinforced epoxy composites at higher temperatures significantly. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46263.     

FTIR and SEM analysis of polyester‐ and epoxy‐based composites manufactured by VARTM process

Polyester‐ and epoxy‐based composites containing glass and carbon fibers were manufactured using a vacuum‐assisted resin transfer molding (VARTM) process. Fourier transform infrared (FTIR) spectroscopy analyses were conducted to determine the interaction between fibers and matrix material. The results indicate that strong interaction was observed between carbon fiber and epoxy resin. However, weak interactions between remaining fiber‐matrix occur. Scanning electron microscopy (SEM) analysis was also performed to take some information about strength of interaction between fibers and matrix material. From SEM micrographs, it is concluded that the findings in SEM analysis support to that obtained in FTIR analysis. Another aim of the present work was to investigate the influence of matrix on composite properties. Hence, the strengths of composites having same reinforcement but different matrix systems in axial tension and transverse tension were compared. Short beam shear test has been conducted to characterize the interfacial strength in the composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Interfacial microstructure and properties of carbon fiber-reinforced unsaturated polyester composites modified with carbon nanotubes

To improve the interfacial properties in carbon fiber (CF)-reinforced unsaturated polyester (UP) composites, we directly introduced functionalized carbon nanotubes dispersed in the fiber sizing onto the fiber surface. For comparing the influence of polymer type on sizing effect, two different polymers (UP MR13006 and water-soluble epoxy (EP)) were used to prepare sizing agent. Morphology and surface energy of CFs were examined by scanning electron microscopy and dynamic contact angle analysis test. Tensile strength was investigated in accordance with ASTM standards. Mechanical properties of the composites were investigated by interlaminar shear strength (ILSS) and impact toughness. Test results indicate that TS, ILSS, and impact toughness were enhanced simultaneously. For UP matrix, the sizing agent containing UP has better reinforcing and toughening effect than the sizing agent containing water-soluble EP.     

Temperature effect on interfacial bonding property of single‐carbon fiber/epoxy resin composite

The changes in interfacial fracture energy of three kinds of commercially sized carbon fiber (CF)/epoxy resin composites in the range from ambient temperature to 130°C were investigated using the single‐fiber fragmentation test to evaluate the heat resistance of the interphase. The effects of CF sizing on the interfacial bonding property were studied using desized CF/epoxy resin composites. Thermogravimetric analysis and differential scanning calorimetry of the combination of sizing and matrix were employed to investigate the role of sizing on the variations in the fiber/matrix interfacial property under elevated temperature. The interfacial fracture energy values of all the studied CF composites were found to decrease quickly during the initial stage of temperature rise and drop gradually at higher temperature. At elevated temperature, the desized CF composites had higher heat resistance than the corresponding sized fiber composites. The differences in the interfacial heat resistance among the three kinds of CF composites and the difference in the interfacial thermal stability between the sized and the desized fiber composites were related to different glass transition temperatures of the interphases. The interaction between sizing and the matrix and the chain motion of the crosslink structure of the interphase has been suggested to determine the interfacial heat resistance. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Effect of adding carbon fiber on conductive stability of acrylonitrile‐butadiene rubber composites

In this work, the conductive composites of acrylonitrile‐butadiene rubber (NBR) and conductive carbon black (CCB) were prepared. The volume resistivity of NBR/CCB composites became stable when the addition content of CCB reached 12 wt %. However, when carbon fiber (CF) was added into the composites, the volume resistivity of NBR/CCB/CF composites continued to decrease with the increase of CF addition, which resulted from the formation of the three‐dimensional conductive network in composite matrix. In addition, the effect of acid oxidation of CF surface on the mechanical proprieties and conductive stability of NBR/CCB/CF composites was studied. The results indicated the acid oxidation of CF surface improved the bond structure between NBR and CF, which further decreased the resistance and significantly improved the mechanical properties of the composites. It was demonstrated that the conductive stability of NBR composites after cyclic mechanical and temperature fatigues was remarkably enhanced with the addition of CF. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46668.     

Three‐dimensionally braided carbon fiber–epoxy composites,a new type of materials for osteosynthesis devices. II. Influence of fiber surface treatment

Interfacial adhesion between carbon fiber and epoxy resin plays an important role in determining performance of carbon–epoxy composites. The objective of this research is to determine the effect of fiber surface treatment (oxidization in air) on the mechanical properties (flexural strength and modulus, shear and impact strengths) of three‐dimensionally (3D) braided carbon‐fiber‐reinforced epoxy (C_3D/EP) composites. Carbon fibers were air‐treated under various conditions to improve fiber–matrix adhesion. It is found that excessive oxidation will cause formation of micropits. These micropits are preferably formed in crevices of fiber surfaces. The micropits formed on fiber surfaces produce strengthened fiber–matrix bond, but cause great loss of fiber strength and is probably harmful to the overall performance of the corresponding composites. A trade‐off between the fiber–matrix bond and fiber strength loss should be considered. The effectiveness of fiber surface treatment on performance improvement of the C_3D/EP composites was compared with that of the unidirectional carbon fiber–epoxy composites. In addition, the effects of fiber volume fraction (V_f) and braiding angle on relative performance improvements were determined. Results reveal obvious effects of V_f and braiding angle. A mechanism was proposed to explain the experimental phenomena. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1040–1046, 2002     

Multi-component nanocomposites of epoxy/silsesquioxane reinforced with carbon fibers and carbon nanotubes processed by resin transfer molding

ABSTRACT

In this work, an epoxy resin modified by silsesquioxane oligomers was used to produce multi-component nanocomposites reinforced with carbon fiber (CF) and multi-walled carbon nanotubes (CNT) by resin transfer molding (RTM). The combination of sonication process with the incorporation of silsesquioxane domains (i.e. increasing the degree of crosslinking of the epoxy matrix), improved the mechanical strength of the hybrid matrix and hybrid/CF/CNT nanocomposites. The multi-component nanocomposites produced by RTM presented Young modulus of 35 ± 8 GPa, tensile strength of 303 ± 41 MPa and impact strength of 1.0 ± 0.3 kJ m^?1. The results showed a significant increase in the tensile strength and impact resistance of the epoxy matrix by the incorporation of silsesquioxanes and sonication before curing of the matrices, showing the promising potential of this multi-component nanocomposite for pipelines and other structural applications.     

Micro‐Driving behavior of carbon‐fiber‐reinforced epoxy resin for standing‐wave ultrasonic motor

The application of the friction drive of carbon‐fiber‐reinforced composites to a standing‐wave ultrasonic motor was investigated. Friction drive tests were conducted on carbon‐fiber‐reinforced epoxy resins (CF/epoxy) by home‐made test rig, which was based on plate‐rod vibrator. The effects of fiber orientation and ply thickness on dynamic drive and dynamic normal forces were investigated. Fiber orientation angle and ply thickness affected friction drive. Different dynamic drive forces, which varied both in amplitude and period, were observed for CF/epoxy composites with different winding angles. A CF/epoxy composite with a winding angle of 30° showed the largest dynamic drive force (∼0.45 N) and the shortest contact period (∼26 μs). The period of dynamic normal force was uniform (∼65 μs) for various CF/epoxy composites. Wear traces of different composites exhibited different wear modes, such as scuffing, peeling, and shearing. The anisotropic property of CF/epoxy material affected the drive process of standing‐wave ultrasonic motor. The current study taking the carbon‐fiber‐reinforced epoxy resin as an example of anisotropic materials arise more enough attention on inexpensive, biodegradable, and renewable alternatives for the efficient and durative drive of a standing‐wave ultrasonic motor. POLYM. COMPOS., 37:2152–2159, 2016. © 2015 Society of Plastics Engineers     

Study on the mechanical properties and microstructure of high-performance carbon fiber/epoxy composites

A high-toughness epoxy has been prepared using carboxyl-terminated butadiene acrylonitrile (CTBN) as a toughening agent to modify the AG-80 epoxy resin. High-performance carbon fiber/epoxy (CF/EP) composites are fabricated using the CTBN-toughened epoxy resin as the matrix and two types of CF, namely, T800SC and T800HB, as reinforcement. The mechanical properties of the matrix, surface properties of the CFs, tensile properties, and fracture morphologies of the composites are systematically investigated to elucidate the key factors influencing interfacial bonding in high-performance CF/EP composites. The results reveal that the most significant improvement in toughness is achieved when the CTBN content is 6.90 wt.% in the epoxy resin. Owing to the high content of polar functional groups and excellent surface wettability of T800SC, the T800SC/EP composite exhibits superior mechanical properties compared with the T800HB/EP composite.     

Mechanical and morphological properties of carbon fiber reinforced–modified epoxy composites

Epoxy, prepared through aminomethyl 3,5,5‐trimethylcyclohexylamine hardening of diglycidylether of bisphenol‐A (DGEBA) prepolymer, toughened with polycarbonate (PC) in different proportions, and reinforced with carbon fiber, was investigated by differential scanning calorimetry, tensile and interlaminar shear strength testing, and scanning electron microscopy (SEM). A single glass transition temperature was found in all compositions of the epoxy/PC blend system. The tensile properties of the blend were found to be better than that of the pure epoxy matrix. They increased with PC content up to 10%, beyond which they decreased. The influence of carbon fiber orientation on the mechanical properties of the composites was studied, where the fiber content was kept constant at 68 wt %. Composites with 45° fiber orientation were found to have very weak mechanical properties, and the mechanical properties of the blend matrix composites were found to be better than those of the pure epoxy matrix composites. The fracture and surface morphologies of the composite samples were characterized by SEM. Good bonding was observed between the fiber and matrix for the blend matrix composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3529–3536, 2006     

Effects of chain lengths,molecular orientation,and functional groups of thiols adsorbed onto CF surface on interfacial properties of CF/epoxy composites

In this article, a new treatment method based on molecular self‐assembly on carbon fiber (CF) surface was proposed for obtaining a controlled interface between CF and epoxy matrix in composite system. To form the controlled interfacial region, the surfaces of CF were first metallized by electroless Ag plating, then were reacted with a series of thiols (alkanethiols, aromatic thiol, and heterocyclic thiol) to form self‐assembly (SA) films, which further reacted with epoxy resin to generate a strong adhesion interface. The structure and composition of untreated and treated CF surface were investigated by surface‐enhanced Raman scattering spectroscopy (SERS) and X‐ray photoelectron spectroscopy (XPS), respectively. SERS study showed that thiols chemisorbed on Ag‐plated CF in the form of thiolate species via the strong S? Ag coordinative bond. Moreover, adsorbate orientation of thiols SA films on Ag‐plated CF surfaces was revealed on the basis of SERS selection rules. The XPS study further confirmed the well organized alignment and the chemisorption of thiols. To understand the interfacial adhesion mechanism, the interfacial shear strength of CF/epoxy microcomposites was evaluated by the microbond technique. The results showed that among the parameters such as chain lengths, molecular orientation, and types of functional groups, the chemical nature of functional groups is most important for the improvement of interfacial properties in CF/epoxy composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and properties of water‐soluble‐type sizing agents for carbon fibers

A water‐soluble epoxy resin was synthesized by the reaction between novolac epoxy resin (F‐51) and diethanolamine. Then, the modified F‐51 was mixed with poly(alkylene glycol allyl glycidyl ether) as a film former of a sizing agent. A series of water‐soluble sizing agents for carbon fiber (CF) were prepared. The modified F‐51 was analyzed by Fourier Transform infrared spectroscopy. The surface morphology of the CF was characterized by scanning electron microscopy. The effects of the sizing agent on the handling characteristics were investigated by abrasion resistance, fluffs, and breakage and stiffness tests. The results show that the abrasion resistance of the sized CF increased by 114.5% and reached 2344 times and the mass of fabric hairiness decreased to 3.2 mg. The interlaminar shear strength (ILSS) test indicated that the interfacial adhesion of the composite could be greatly improved. The ILSS of the sized CF composite could reach a maximum value of 42.40 MPa. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39843.     

Preparation and properties of T300 carbon fiber‐reinforced thermoplastic polyimide composites

In this study, a series of T300 carbon fiber‐reinforced polyimide (CFRPI) composites were prepared by laminating premolding polyimide (PI) films with unidirectional carbon fiber (CF) layers. On the basis of PI systems design, the effect of CF volume fraction, processing conditions, and PI molecular structure on the properties of CFRPI composites was studied in detail. In addition, two kinds of nano‐particles, including carbon nano‐tube (CNT) and SiO₂ were filled into the premolding PI films with different concentrations. And the effect of nano‐particles on the properties of CFRPI composites was also investigated. The surface characteristic of T300 CF was measured by X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The properties of premolding PI film and CFRPI composites were measured by dynamic mechanical analysis (DMTA), SANS testing machine, scanning electron microscopy (SEM), and so forth. These experimental results showed that the properties of CFRPI composites were mainly affected by the premolding PI film and molding condition. The change of CF volume fraction from 55% to 65% took little effect on the mechanical properties of CFRPI composites. In addition, the incorporation of nano‐particle SiO₂ could further improve the properties of CFRPI composites, but CNT hardly improved the properties of CFRPI composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 646–654, 2006     

Influence of out‐of‐plane fiber orientation on reaction‐to‐fire properties of carbon fiber reinforced polymer matrix composites

This work investigates the influence of the out‐of‐plane orientation of carbon fibers on the reaction‐to‐fire characteristics of polymer matrix composites. A deep insight into combustion processes is gained, which is necessary to fully understand and assess advantages of composites with out‐of‐plane fiber angles. Epoxy‐based Hexply 8552/IM7 specimens with primarily low fiber angles between 0° and 15° are characterized by cone calorimetry. Heat release during fire is greatly affected by the out‐of‐plane fiber angle because of the thermal boundaries created by the fibers. The advancement of the pyrolysis front during fire was determined from peak heat release rates and validated by temperature measurements along the back surface of the panels, representing a novel method of determining position‐dependent pyrolysis migration velocity. These measurements show a transverse shift in pyrolysis front velocity for increasing out‐of‐plane fiber angles. Pyrolysis pathways between the fiber boundaries facilitate faster combustion through the composite thickness, especially for increasing angles from 0° to 15°. It was determined that under the chosen conditions, the pyrolysis front advances approximately 4 times faster when propagating parallel to the fibers than perpendicular.     

The role of the terminal functional group of self‐assembled monolayers on fiber matrix adhesion

Adhesion at the fiber‐matrix interface of a composite is often influenced by a combination of factors such as mechanical interlocking, physicochemical interactions, and chemical bonding in the fiber‐matrix interphase region. We demonstrate the use of an approach using self‐assembled monolayers (SAMs) for studying the impact of one of the factors, chemical bonding, on the overall adhesion of the glass‐fiber/matrix interface. Transformation of these monolayer surfaces using conventional chemistry with a focus on the creation of a terminal functional group that interacts with epoxy resin is reported. The modified surfaces were characterized by ellipsometry, X‐ray photoelectron spectroscopy, and contact angle techniques for chlorosilane coverage, and in situ conversion. The adhesion of diglycidyl ether of bisphenol‐A resin to modified SAMs on E‐glass fibers was measured by performing single‐fiber fragmentation test. The extent of adhesion between the fiber and matrix was found to be dependent on the type of functional group at the terminal end of the SAM in contact with the epoxy matrix. Methyl terminal group resulted in the least adhesion, while amine terminal groups resulted in the most adhesion. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Localized thermal analysis of carbon fiber‐reinforced polypropylene composites

The effect of carbon fiber (CF) and annealing temperature on polypropylene (PP) microstructure was studied. The crystalline state of polymer matrix was found to be a strong function of thermal history. The effect of annealing temperature on the microstructure evolution of PP in the presence of CFs was characterized by using X‐ray diffraction, DSC and localized thermal analysis. The melting behavior of CF‐reinforced PP composite was strongly dominated by the thermal history and was weakly influenced by the presence of CFs. The interface between a CF and PP matrix was found to be weak. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Development of multiwalled‐carbon‐nanotube‐welded carbon fibers and evaluation of the interfacial strength in epoxy composites

Multiwalled carbon nanotube (MWCNT)‐welded carbon fibers (CFs) were prepared by a three‐step process, which included polyacrylonitrile (PAN) coating, MWCNT absorption, and heat treatment. The structure of these materials was characterized by scanning electron microscopy, Fourier‐transform infrared spectroscopy, and Raman spectroscopy. The MWCNTs were uniformly assembled on the surface of the PAN‐coated CFs and welded by a PAN‐based carbon layer after heat treatment. The contact angle of the MWCNT‐welded CFs in the epoxy resins was 41.70°; this was 22.35% smaller than that of the unsized CFs. The interfacial shear strength (IFSS) of the MWCNT‐welded CF–epoxy composite was 83.15 MPa; this was 28.89% higher than that of the unsized CF–epoxy composite. The increase in the IFSS was attributed to the enhancement of adhesions between the CFs and polymer matrix through the welding of the MWCNTs on the CFs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45027.     

Effect of hygrothermal conditioning on compressive strength after impact in carbon fiber/epoxy composites

Carbon fiber-reinforced polymers have been widely applied in structural parts and components in several sectors, in addition to being constantly used in environments with the presence of humidity and high temperatures, which can affect their density, hardness, and rigidity. In this work, the influence of hydrothermal conditioning on carbon fiber (CF)/epoxy composites was investigated using three types of epoxy resin and two different CF fabric reinforcements, that is, plain weave and eight harness satin (8HS) arrangements. The CF/epoxy composites were subjected to compression after impact (CAI) test by 28 and 40 J energy and then exposed to hydrothermal conditioning for 8 weeks. After the CAI tests, the visual analysis of all composites presented microbuckling mechanisms. The composites tested with 40 J energy absorbed only 2% more moisture compared with the other composites, nonimpacted, and tested with 28 J, indicating that the impact damage did not cause delamination between the layers of the composites, which could facilitate the absorption of water. All composites analyzed showed resistance to CAI even after exposure to humidity, with decreases ranging from 2.8% to 23.8% about the unconditioned specimens. The decrease in CAI also shows the influence of the type of epoxy matrix and the arrangement of the CF in fabrics.     

Effects of debonding and fiber strength distribution on fatigue‐damage propagation in carbon fiber‐reinforced epoxy

In order to design new fatigue‐resistant composites, the underlying fatigue damage mechanisms must be characterized and the controlling microstructural properties should be identified. The fatigue‐damage mechanisms of a unidirectional carbon fiber–reinforced epoxy has been studied under tension–tension loading. A ubiquitous form of damage was one or a few planar fiber breaks from which debonds or shear yield zones grew in the longitudinal direction during fatigue cycling. This leads to a change in stress profile of the neighboring fibers, and an increase in failure probability of these fibers. The breakage of fibers in the composite is controlled by the fiber strength distribution. The interaction between the fiber strength distribution and debond propagation leading to further fiber breakage was investigated by a numerical simulation. It was found that a wider distribution of fiber strength and a higher debond rate lead to more distributed damage and a higher fracture toughness. Implications to fatigue life behavior are discussed, with reference to constituent microstructure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 457–474, 2000