Electrospinning core‐shell nanofibers for interfacial toughening and self‐healing of carbon‐fiber/epoxy composites

This article reports a novel hybrid multiscale carbon‐fiber/epoxy composite reinforced with self‐healing core‐shell nanofibers at interfaces. The ultrathin self‐healing fibers were fabricated by means of coelectrospinning, in which liquid dicyclopentadiene (DCPD) as the healing agent was enwrapped into polyacrylonitrile (PAN) to form core‐shell DCPD/PAN nanofibers. These core‐shell nanofibers were incorporated at interfaces of neighboring carbon‐fiber fabrics prior to resin infusion and formed into ultrathin self‐healing interlayers after resin infusion and curing. The core‐shell DCPD/PAN fibers are expected to function to self‐repair the interfacial damages in composite laminates, e.g., delamination. Wet layup, followed by vacuum‐assisted resin transfer molding (VARTM) technique, was used to process the proof‐of‐concept hybrid multiscale self‐healing composite. Three‐point bending test was utilized to evaluate the self‐healing effect of the core‐shell nanofibers on the flexural stiffness of the composite laminate after predamage failure. Experimental results indicate that the flexural stiffness of such novel self‐healing composite after predamage failure can be completely recovered by the self‐healing nanofiber interlayers. Scanning electron microscope (SEM) was utilized for fractographical analysis of the failed samples. SEM micrographs clearly evidenced the release of healing agent at laminate interfaces and the toughening and self‐healing mechanisms of the core‐shell nanofibers. This study expects a family of novel high‐strength, lightweight structural polymer composites with self‐healing function for potential use in aerospace and aeronautical structures, sports utilities, etc. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Enhancement of interlaminar fracture toughness of carbon fiber–epoxy composites using polyamide‐6,6 electrospun nanofibers

In this study, carbon fiber–epoxy composites are interleaved with electrospun polyamide‐6,6 (PA 66) nanofibers to improve their Mode‐I fracture toughness. These nanofibers are directly deposited onto carbon fabrics before composite manufacturing via vacuum infusion. Three‐point bending, tensile, compression, interlaminar shear strength, Charpy impact, and double cantilever beam tests are performed on the reference and PA 66 interleaved specimens to evaluate the effects of PA 66 nanofibers on the mechanical properties of composites. To investigate the effect of nanofiber areal weight density (AWD), nanointerlayers with various AWD are prepared by changing the electrospinning duration. It is found that the electrospun PA 66 nanofibers are very effective in improving Mode‐I toughness and impact resistance, compressive strength, flexural modulus, and strength of the composites. However, these nanofibers cause a decrease in the tensile strength of the composites. The glass‐transition temperature of the composites is not affected by the addition of PA 66 nanofibers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45244.     

Mechanical and anticorrosion properties of furan/epoxy‐based basalt fiber‐reinforced composites

A furan/epoxy blend applicable to composite manufacture was studied and corresponding basalt fiber‐reinforced composites were prepared. The processability, mechanical properties, and reasons for the improved mechanical properties of this blend were investigated by rheology machine, mechanical testing machine, and scanning electron microscopy. With excellent processability, furan/epoxy was suitable for manufacturing composites. Furan/epoxy with the ratio of 5/5 showed the best properties, and the impact strength, flexural strength and flexural modulus were 15.43 kJ/m², 102.81 MPa, and 3209.40 MPa, respectively. The river‐like fracture surface of the furan/epoxy system was well consistent with the mechanical properties. The mechanical and anti‐corrosive properties of basalt fiber‐reinforced furan/epoxy composites were also studied. The mechanical properties of composites changed the same as those of furan/epoxy matrix did. Furan resin effectively improved the anti‐acid but not anti‐alkali property of composites, probably because furan could be cured in acidic condition and basalt fiber was resistant to acid and alkali. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44799.     

High thermal conductive m‐xylylenediamine functionalized multiwall carbon nanotubes/epoxy resin composites

In this study, multiwall carbon nanotubes (MWNTs) functionalized by m‐xylylenediamine is used as thermal conductive fillers to improve their dispersibility in epoxy resin and the thermal conductivity of the MWNTs/bisphenol‐A glycidol ether epoxy resin composites. Functionalization with amine groups of MWNTs is achieved after such steps as carboxylation, acylation and amidation. The thermal conductivity, impact strength, flexural strength, and fracture surfaces of MWNTs/epoxy composites are investigated with different MWNTs. The results show that m‐xylylenediamine is successfully grafted onto the surface of the MWNTs and the mass fraction of the organic molecules grafted onto MWNTs is about 20 wt %. The thermal conductivity of MWNTs/epoxy composites is further enhanced to 1.236 W/mK with 2 wt % m‐MWNTs. When the content of m‐MWNTs is 1.5 wt %, the impact strength and flexural strength of the composites are 25.85 KJ/m², 128.1 MPa, respectively. Scanning electron microscope (SEM) results show that the fracture pattern of composites is changed from brittle fracture to ductile fracture. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41255.     

Preparation of multiscale graphene oxide‐carbon fabric and its effect on mechanical properties of hierarchical epoxy resin composite

Graphene oxide (GO) was used to modify the surface of carbon fiber layers through electrophoretic deposition, forming a multiscale reinforcement fabric. By adjusting the experimental parameters, the resulting GO‐carbon fabric showed productive and homogenous distribution of thin and less‐agglomerate GO platelets on carbon fiber surface, remarkably enlarging the surface area and roughness of carbon fabric. To investigate the effect of GO sheets on composites, GO‐carbon fabric and carbon fabric‐reinforced hierarchical epoxy resin composites were respectively manufactured. Mechanical tests demonstrated that after introducing GO flakes on carbon fabric, both the flexural strength and interlaminar shear strength of composite had achieved an increase, especially the interlaminar shear strength rising by 34%. Through fractography analysis, it was found that in pure carbon fabric‐reinforced epoxy composite, the fiber/matrix debonding fracture mechanism predominated, while after the GO decoration on carbon fiber surface, the composite featured a stronger interfacial bonding, leading to the enhancement in mechanical properties of hierarchical epoxy resin composite. POLYM. COMPOS., 37:1515–1522, 2016. © 2014 Society of Plastics Engineers     

环氧树脂/短切碳纤维复合材料性能研究

制备出了短切碳纤维增强TDE-85环氧树脂复合材料,研究了碳纤维的含量对复合材料力学性能和耐热性能的影响。结果表明,碳纤维的加入有利于复合材料力学性能和耐热性能的提高,并在碳纤维含量为0.25%时,复合材料的拉伸强度、冲击韧性、弯曲强度和弯曲模量达到最大,分别提高了29.33%、25.31%、30.28%和68.93%。此外,对复合材料的弯曲断裂面进行了微观形貌分析,结果表明一定量的碳纤维可以较好地分散在树脂基体中,同时,碳纤维原丝和树脂基体的界面结合比较弱,主要依赖于两相之间的物理嵌合。     

Incorporation of silicon dioxide nanoparticles at the carbon fiber‐epoxy matrix interphase and its effect on composite mechanical properties

Functionalized silicon dioxide nanoparticles (nano‐fSiO₂) were uniformly deposited on the surface of carbon fibers (CFs) using a coating process which consisted of immersing the fibers directly in a suspension of nano‐fSiO₂ particles and epoxy monomers in 1‐methyl‐2‐pyrrolidinone (NMP). The 0° flexural properties, 90° flexural properties, and Interlaminar shear strength (ILSS) mechanical properties of unidirectional epoxy composites made with nano‐fSiO₂+epoxy sized carbon fibers, with control fibers, and with epoxy‐only sized fibers were measured and compared. An obvious increase of the fiber/matrix adherence strength was obtained with the nano‐fSiO₂+epoxy coating. The nano‐fSiO₂+epoxy sized CF/epoxy composites showed a relative increase of 15%, 50%, and 22% in comparison to control fibers, for the Interlaminar shear strength, the 90^° flexural strength and the 90° flexural modulus, respectively, but little e difference was measured between the different systems for the 0° flexural properties. The observation of the fracture surfaces by scanning electron microscopy of composite fracture confirmed the improvement of the interfacially dependent mechanical properties. POLYM. COMPOS., 38:1474–1482, 2017. © 2015 Society of Plastics Engineers     

Regeneration efficiency of composites containing two‐sized capillaries

The aim of this work is to develop a composite material containing a regeneration system and to demonstrate its self‐healing properties. For this purpose, we will study the self‐healing behavior of composites that are fabricated with a regeneration system consisting of two‐sized capillaries filled with epoxy resin and hardener. Composites with restorative systems containing identical microtube diameters can be found in the literature, but until now no comparative studies with multiple diameter structures have been published. We will prove that a regeneration system containing two types of capillaries with diameters of 100 and 50 μm is more efficient (68% recovery of bending strength and Young's modulus after third regeneration) than a regeneration system containing capillaries with the same diameter (44% recovery of bending strength and 44% recovery of Young's modulus after third regeneration). POLYM. COMPOS. 37:1223–1230, 2016. © 2014 Society of Plastics Engineers     

Resin modification on interlaminar shear property of carbon fiber/epoxy/nano‐CaCO3 hybrid composites

Epoxy resin was modified by adding a silane coupling agent/nano‐calcium carbonate master batch. Then, samples of binary carbon fiber/epoxy composites and ternary fiber/nano‐CaCO₃/epoxy were prepared by hot press process. The interlaminar shear strength (ILSS) of the carbon fiber/epoxy composites was investigated and the results indicate that introduction of the treated nano‐CaCO₃ enhances ILSS obviously. In particular, the addition of 4 wt% nano‐CaCO₃ leads to 36.6% increase in the ILSS for the composite. The fracture surfaces of the carbon fiber/epoxy composites and the mechanical properties of epoxy resin cast are examined and both of them are employed to explain the change of ILSS. The results show that the change of ILSS is primarily due to an increase of the epoxy matrix strength and an increase of the fiber/epoxy interface. The bifurcation of propagating cracks, stress transfer, and cavitation are deduced for the reasons of strengthening and toughening effect of nano‐CaCO₃ particles. POLYM. COMPOS., 38:2035–2042, 2017. © 2015 Society of Plastics Engineers     

Effect of deposited carbon nanotubes on interlaminar properties of carbon fiber‐reinforced epoxy composites using a developed spraying processing

Carbon fiber‐reinforced epoxy composites, with incorporated carboxylic multiwall carbon nanotubes (CNTs), were prepared using vacuum‐assisted resin infusion (VARI) molding, and the in‐plane and out‐of‐plane properties, including mode‐I (G_Ic) and mode‐II (G_IIc) interlaminar fracture toughness, interlaminar shear strength (ILSS), tensile, and flexural properties were measured. A novel spraying technique, which sprays a kind of epoxy resin E20 with high viscosity after spraying the CNTs, was adopted to deposit the CNTs on the surface of carbon fiber fabric. The E20 was used to anchor CNTs on the fabric surface, avoiding that the deposited CNTs were removed by the infusing resin during VARI process. The spraying processing, including spraying amount and spraying sequence, was optimized based on the distribution of CNTs on the fibers. After that, three composite specimen groups were fabricated using different carbon fiber fabrics, including as‐received, CNT‐deposited with E20, and CNT‐deposited without E20. The effects of CNTs on the processing quality and mechanical properties of carbon fiber‐reinforced polymer composites were studied. The experimental results show that all studied laminates have uniform thickness with designed values and no obvious defects form inside the laminates. Compared with the composite without CNTs, depositing CNTs with E20 increases by 24% in the average propagation G_Ic, by 11% in the propagation G_IIc and by 12% in the ILSS, while it preserves the in‐plane mechanical properties, However, depositing CNTs without E20 reduces interlaminar fracture toughness. These phenomena are attributed to the differences in the distribution of CNTs and the fiber/matrix interfacial bonding for different spraying processing. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers     

Hybrid multi‐scale epoxy composites containing conventional glass microfibers and electrospun glass nanofibers with improved mechanical properties

A mechanically flexible mat consisting of structurally amorphous SiO₂ (glass) nanofibers was first prepared by electrospinning followed by pyrolysis under optimized conditions and procedures. Thereafter, two types of hybrid multi‐scale epoxy composites were fabricated via the technique of vacuum assisted resin transfer molding. For the first type of composites, six layers of conventional glass microfiber (GF) fabrics were infused with the epoxy resin containing shortened electrospun glass nanofibers (S‐EGNFs). For the second type of composites, five layers of electrospun glass nanofiber mats (EGNF‐mats) were sandwiched between six layers of conventional GF fabrics followed by the infusion of neat epoxy resin. For comparison, the (conventional) epoxy composites with six layers of GF fabrics alone were also fabricated as the control sample. Incorporation of EGNFs (i.e., S‐EGNFs and EGNF‐mats) into GF/epoxy composites led to significant improvements in mechanical properties, while the EGNF‐mats outperformed S‐EGNFs in the reinforcement of resin‐rich interlaminar regions. The composites reinforced with EGNF‐mats exhibited the highest mechanical properties overall; specifically, the impact absorption energy, interlaminar shear strength, flexural strength, flexural modulus, and work of fracture were (1097.3 ± 48.5) J/m, (42.2 ± 1.4) MPa, (387.1 ± 9.9) MPa, (12.9 ± 1.3) GPa, and (30.6 ± 1.8) kJ/m², corresponding to increases of 34.6%, 104.8%, 65.4%, 33.0%, and 56.1% compared to the control sample. This study suggests that EGNFs (particularly flexible EGNF‐mats) would be an innovative type of nanoscale reinforcement for the development of high‐performance structural composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42731.     

Effects of organo‐montmorillonite on the mechanical and morphological properties of epoxy/glass fiber composites

Epoxy composites filled with glass fiber and organo‐montmorillonite (OMMT) were prepared by the hand lay‐up method. The flexural properties of the epoxy/glass fiber/OMMT composites were characterized by a three‐point bending test. The flexural modulus and strength of epoxy/glass fiber were increased significantly in the presence of OMMT. The optimum loading of OMMT in the epoxy/glass fiber composites was attained at 3 wt%, where the improvement in flexural modulus and strength was approximately 66 and 95%, respectively. The fractured surface morphology of the epoxy/glass fiber/OMMT composites was investigated using field emission scanning electron microscopy. It was found that OMMT adheres on the epoxy/glass fiber interface, and this is also supported by evidence from energy dispersive X‐ray analysis. Copyright © 2007 Society of Chemical Industry     

Mechanical behavior of hybrid fiber‐reinforced composites manufactured by pulse infusion

Epoxy/carbon fiber composites have been manufactured by Pulse Infusion. Pulse Infusion allows to control the pressure of the vacuum bag on the dry fiber reinforcement by using a proper designed pressure distributor that induces a pulsed transverse action and promotes the through thickness resin flow. The adopted one‐component commercial epoxy resin has been preliminary modified by adding 0.05% (w/w) of multiwalled carbon nanotubes, in order to take advantage of carbon nanotubes at low concentration. Both neat and hybrid realized composite panels have been mechanically characterized by performing experimental tests to evaluate tensile, interlaminar, and fracture properties in order to investigate the effect of Pulse Infusion and carbon nanotubes on the mechanical and fracture behavior of composites. Results demonstrated an improvement of 36.2% for the interlaminar shear strength, of 35% for the fracture energy at the crack initiation and of 14% for the fracture toughness in mode II. POLYM. COMPOS., 38:2254–2260, 2017. © 2015 Society of Plastics Engineers     

Recent progress in interfacial toughening and damage self‐healing of polymer composites based on electrospun and solution‐blown nanofibers: An overview

In this article, we provide an overview of recent progress in toughening and damage self‐healing of polymer–matrix composites (PMCs) reinforced with electrospun or solution‐blown nanofibers at interfaces with an emphasis on the innovative processing techniques and toughening and damage self‐healing characterization. Because of their in‐plane fiber architecture and layered structure, high‐performance laminated PMCs typically carry low interfacial strengths and interlaminar fracture toughnesses in contrast to their very high in‐plane mechanical properties. Delamination is commonly observed in these composite structures. Continuous polymer and polymer‐derived carbon nanofibers produced by electrospinning, solution blowing, and other recently developed techniques can be incorporated into the ultrathin resin‐rich interlayers (with thicknesses of a few to dozens of micrometers) of these high‐performance PMCs to form nanofiber‐reinforced interlayers with enhanced interlaminar fracture toughnesses. When incorporated with core–shell healing‐agent‐loaded nanofibers, these nanofiber‐richened interlayers can yield unique interfacial damage self‐healing. Recent experimental investigations in these topics are reviewed and compared, and recently developed techniques for the scalable, continuous fabrication of advanced nanofibers for interfacial toughening and damage self‐healing of PMCs are discussed. Developments in the near future in this field are foreseen. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2225–2237, 2013     

Concentration effect of γ‐glycidoxypropyltrimethoxysilane on the mechanical properties of glass fiber–epoxy composites

In this study, glass fibers were modified using γ‐glycidoxypropyltrimethoxysilane of different concentrations to improve the interfacial adhesion at interfaces between fibers and matrix. Effects of γ‐glycidoxypropyltrimethoxysilane on mechanical properties and fracture behavior of glass fiber/epoxy composites were investigated experimentally. Mechanical properties of the composites have been investigated by tensile tests, short beam tests, and flexural tests. The short‐beam method was used to measure the interlaminar shear strength (ILSS) of laminates. The tensile and flexural properties of composites were characterized by tensile and three‐point bending tests, respectively. The fracture surfaces of the composites were observed with a scanning electron microscope. On comparing the results obtained for the different concentrations of silane solution, it was found that the 0.5% GPS silane treatment provided the best mechanical properties. The ILSS value of heat‐cleaned glass fiber reinforced composite is enhanced by ∼59% as a result of the glass fiber treatment with 0.5% γ‐GPS. Also, an improvement of about 37% in tensile strength, about 78% in flexural strength of the composite with the 0.5% γ‐GPS treatment of glass fibers was observed. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Short‐beam and three‐point‐bending tests for the study of shear and flexural properties in unidirectional‐fiber‐reinforced epoxy composites

The bending properties of composite materials are often characterized with simply supported beams under concentrated loads. The results from such tests are commonly based on homogeneous beam equations. For laminated materials, however, these formulas must be modified to account for the stacking sequence of the individual plies. The horizontal shear test with a short‐beam specimen in three‐point bending appears suitable as a general method of evaluation for the shear properties in fiber‐reinforced composites because of its simplicity. In the experimental part of this work, the shear strength of unidirectional‐glass‐fiber‐reinforced epoxy resin composites was determined in different fiber directions with the short‐beam three‐point‐bending test. Also, the elastic constants and flexural properties of the same materials were determined from bending experiments carried out on specimens in the 0, 15, 30, 45, 60, 75, and 90° fiber directions with high span–thickness ratios. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 63–74, 2004     

Effect of compaction treatment on laminated CFRP composites fabricated by vacuum‐assisted resin‐transfer molding

Carbon fiber‐reinforced polymer (CFRP) composites were fabricated using ordinary and compaction setups (OS and CS, respectively) in the vacuum‐assisted resin‐transfer molding (VARTM) process. The mechanical properties and acoustic emission (AE) spectra of the CFRP composites were compared among fabricated samples. The CFRP plates with sequences of [+30/−30]₆ were sectioned to make specimens for Mode I interlaminar fracture tests and three‐point bending tests. The difference between the material properties and AE characteristics of the OS and CS specimens were statistically compared using one‐way analysis of variance. The OS specimens had a thicker resin layer, a higher resin fraction, larger average fracture toughness, and AE energy corresponding to the Mode I fracture, whereas the CS specimens had more macro‐scale voids and higher bending strength. AE analysis showed that frequency bands in the interlaminar fracture tests corresponding to matrix‐related fracture were dominant for the OS specimens, whereas those corresponding to the mixed fracture mode of the fiber and matrix fracture were dominant for the CS specimens. In the bending tests, mixed fiber‐matrix fractures were dominant for the OS specimens, and fiber‐related fractures were dominant for the CS specimens. In conclusion, the compaction treatment diminished interlaminar fracture toughness, due to the enhanced formation of macro‐scale voids around the fiber bundles during the resin impregnation stage. However, the bending strength improved with an increased fiber volume fraction. POLYM. COMPOS., 38:217–226, 2017. © 2015 Society of Plastics Engineers     

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     

Toughened carbon fiber fabric‐reinforced pCBT composites

Toughened carbon fiber‐fabric reinforced polymerized cyclic butylene terephthalate (pCBT) composites were obtained by chemical modification of cyclic butylene terephthalate (CBT) with small amounts of epoxy resin and isocyanates as chain extenders. Homogeneous CBT/epoxy and CBT/isocyanate blends were prepared by melt blending the components in a lab‐scale batch mixer at low temperatures and high shear rate. Melt blending was stopped before the ring‐opening polymerization of CBT could start. The modified CBT was the starting material for carbon fiber fabric‐reinforced pCBT composites (fiber content at about 65 wt%) which were prepared by ring‐opening polymerization during compression molding using a simple powder prepreg method. Interlaminar shear strength, flexural strength, and failure strain of the chemically modified composites increased up to 60% with respect to unmodified pCBT composites. Nevertheless, the flexural moduli slightly decreased due to the toughening effect of the chain extender on the pCBT matrix. Drop weight impact tests revealed that the energy absorption of the modified composites was relatively higher as compared to unmodified pCBT composites. POLYM. COMPOS., 37:1453–1460, 2016. © 2014 Society of Plastics Engineers     

Influence of epoxy sizing of carbon‐fiber on the properties of carbon fiber/cyanate ester composites

The high modulus carbon fiber (M40J) sized by epoxy resin E51 and E20 reinforced bisphenol A dicyanate (2,2′‐bis(4‐cyanatophenyl) isopropylidene resin composite was prepared in order to investigate the influence of epoxy sizing of the fiber on the properties of the composite. Differential scanning calorimetry (DSC) and fourier transforms infrared (FTIR) analysis showed that epoxy resin have catalytic effect on cure reaction of cyanate ester. Mechanical properties of the composite revealed that M40J fiber sized by epoxy resin could improve the flexural strength and interlaminar shear strength of M40J/bisphenol A dicyanate composites. The micro‐morphology of the composite fractures was studied by means of scanning electron microscopy (SEM). Reduced flaws were observed in the M40J‐bisphenol A dicyanate interface when the sized fiber was used. Water absorption of the composites was also investigated. It was found that the water absorption descended at the initial boiling stage (12 h). POLYM. COMPOS, 27: 591–598, 2006. © 2006 Society of Plastics Engineers