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.     

Interfacial shear strength in carbon fiber‐reinforced poly(phthalazinone ether ketone) composites

We studied interfacial shear strength (IFSS) in carbon fiber (CF)‐reinforced poly (phthalazinone ether ketone) (PPEK) composites system, with emphasis on the influence of forming temperature of composite and sizing agent on CFs. To obtain apparent IFSS of CF‐reinforced PPEK composites shaped at various forming temperatures ranged from 20 up to 370°C, microbond test was carried out at single‐fiber composites. Results of microbond test showed that apparent IFSS was directly proportional to the difference between the matrix solidification temperature (forming temperature) and the test temperature and approximately 80% of the apparent IFSS in CF/PPEK composite system was attributed to residual radial compressive stress at the fiber/matrix interface. By sizing CF with sizing agent, the wettability of the fiber by the matrix was improved and the final apparent IFSS was also improved. POLYM. COMPOS., 34:1921–1926, 2013. © 2013 Society of Plastics Engineers     

Improvement of Interfacial Adhesion of Glass Fiber/Epoxy Composite by Using Plasma Polymerized Glass Fibers

This study intends to produce plasma polymer thin films of γ-glycidoxypropyltrimethoxysilane (γ-GPS) on glass fibers in order to improve interfacial adhesion of glass fiber-reinforced epoxy composites. A low frequency (LF) plasma generator was used for the plasma polymerization of γ-GPS on the surface of glass fibers at different plasma powers and exposure times. X-ray photoelectron spectroscopy (XPS) and SEM analyses of plasma polymerized glass fibers were conducted to obtain some information about surface properties of glass fibers. Interlaminar shear strength (ILSS) values and interfacial shear strength (IFSS) of composites reinforced with plasma polymerized glass fiber were evaluated. The ILSS and IFSS values of non-plasma polymerized glass fiber-reinforced epoxy composite were increased 110 and 53%, respectively, after plasma polymerization of γ-GPS at a plasma power of 60 W for 30 min. The improvement of interfacial adhesion was also confirmed by SEM observations of fractured surface of the composites.     

High residual mechanical properties at elevated temperatures of bamboo/glass reinforced‐polybenzoxazine hybrid composite

We successfully added bamboo and glass fibers into bisphenol A‐aniline based benzoxazine (BA‐a) resin by hot‐pressing method. In order to improve the interfacial adhesion between bamboo fibers and the matrix, bamboo fibers were pretreated in 6 wt% NaOH solutions for 12 h. The results showed alkali‐treatment had a positive effect on mechanical properties of the composites at both room and elevated temperatures (60°C, 110°C, 160°C, and 210°C). Due to the incorporation of glass fibers, the bamboo/glass reinforced‐polybenzoxazine hybrid composites exhibited highest strength and modulus among all samples and had high residual mechanical properties at elevated temperatures (residual mechanical properties refers to the ratio of strength and modulus of the composites at elevated temperatures to that measured at room temperature). The fractured surface morphologies of the composites were observed by scanning electron microscope. The results showed with the increase of temperature, the debonding and fiber pull‐out became apparent, and the matrix softening could be clearly observed at 210°C. In addition, thermal and thermomechanical properties of neat benzoxazine and the composites were also investigated through thermogravimetric analysis and dynamic mechanical analyzer, respectively. POLYM. ENG. SCI., 59:1818–1829, 2019. © 2019 Society of Plastics Engineers     

Experimental study on dielectric relaxation in alfa fiber reinforced epoxy composites

Investigation on dielectric properties and behavior of thermoset epoxy composite based on cellulosic fibers has been carried on. Dielectric spectra were measured in the frequency range 0.1 Hz–100 kHz and at temperature intervals from ambient to 200°C. For the composite, four relaxations processes were identified, namely the orientation polarization imputed to the presence of polar water molecules in Alfa fiber, the α mode relaxation associated with the glass transition of the epoxy resin matrix, the relaxation process associated with conductivity occurring as a result the carriers charges diffusion noted for high temperature above glass transition and low frequencies, and interfacial or Maxwell‐Wagner‐Sillars relaxation that is attributable to the accumulation of charges at the Alfa fibers/epoxy resin interfaces. Dielectric relaxation analysis revealed evolution in water relaxation and it is thus concluded that the chemical treatment of the fiber can strongly influence the dielectrical properties and interfacial polarization processes in composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Surface ammonification of the mutual‐irradiated aramid fibers in 1,4‐dichlorobutane for improving interfacial properties with epoxy resin

The mutual irradiated aramid fibers in 1,4‐dichlorobutane was ammoniated by ammonia/alcohol solution, in an attempt to improve the interfacial properties between aramid fibers and epoxy matrix. Scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), dynamic contact angle analysis (DCA), interfacial shear strength (IFSS), and single fiber tensile testing were carried out to investigate the functionalization process of aramid fibers and the interfacial properties of the composites. Experimental results showed that the fiber surface elements content changed obviously as well as the roughness through the radiation and chemical reaction. The surface energy and IFSS of aramid fibers increased distinctly after the ammonification, respectively. The amino groups generated by ammonification enhanced the interfacial adhesion of composites effectively by participating in the epoxy resin curing. Moreover, benefited by the appropriate radiation, the tensile strength of aramid fibers was not affected at all. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44924.     

Loading rate effects on mechanical properties of polymer composites at ultralow temperatures

E‐glass fibers of 55, 60, and 65 weight percentages were reinforced with epoxy matrix to prepare the laminated composites. They were exposed to ?40, ?60, and ?80°C temperatures for different times. The 3‐piont bend test was conducted on the conditioned samples at those temperatures. Mechanical test was carried out at 2 mm/min and 500 mm/min crosshead speeds. The main emphasis of the investigation was to evaluate the roles of percentage matrix phase and interfacial areas on the interlaminar shear failure mechanism of glass/epoxy composites at ultralow temperatures for different loading speeds. The mechanical performances of the laminated specimens at low temperatures were compared with room temperature property. The loading rate sensitivity of the polymer composites appeared to be inconsistent and contradictory at some points of conditioning time and as well as at a temperature of conditioning. This Phenomenon may be attributed to low‐temperature hardening, matrix cracking, misfit strain due to differential thermal coefficient of the constituent phases, and also to enhanced mechanical keying factor by compressive residual stresses at low temperatures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2289–2292, 2006     

Interfacial stress transfer in nylon‐6/E‐Glass microcomposites: Effect of temperature and strain rate

In this study, the interfacial properties between E‐glass fibers with different commercial sizings have been investigated on model composites with a nylon‐6 matrix. In particular, the fiber critical length was measured by means of the single‐fiber fragmentation test over a wide range of temperatures (from 25 to 175°C) and strain rates (from 0.0008 to 4 min⁻¹). The general trend observed is that the fiber critical aspect ratio increases as the temperature increases and it decreases as strain rate is increased. The fiber critical aspect ratio for unsized fibers resulted to be reasonably well linearly related to the square root of the fiber to matrix modulus ratio. This results is in accordance with the Cox's shear‐lag theoretical model and the Termonia's numerical simulations. Sized fibers display an higher deviation from the theoretical prevision probably because of the presence of interphases whose properties are different from the bulk matrix. As a consequence, the interfacial shear strength values resulted to be dependent on the fiber sizing. In particular, the fibers coated with an epoxy sizing showed a superior thermal stability of the fiber matrix‐interface with respect to the unsized or nylon compatible sized fibers.     

Unsaturated polyester‐toughened epoxy composites: Effect of sisal fiber on thermal and dynamic mechanical properties

In the present study, the mechanical and thermal properties of sisal fiber‐reinforced unsaturated polyester (UP)‐toughened epoxy composites were investigated. The sisal fibers were chemically treated with alkali (NaOH) and silane solutions in order to improve the interfacial interaction between fibers and matrix. The chemical composition of resins and fibers was identified by using Fourier‐transform infrared spectroscopy. The UP‐toughened epoxy blends were obtained by mixing UP (5, 10, and 15 wt%) into the epoxy resin. The fiber‐reinforced composites were prepared by incorporating sisal fibers (10, 20, and 30 wt%) within the optimized UP‐toughened epoxy blend. Scanning electron microscopy was used to analyze the morphological changes of the fibers and the adhesion between the fibers and the UP‐toughened epoxy system. The results showed that the tensile and flexural strength of (alkali‐silane)‐treated fiber (30 wt%) ‐reinforced composites increased by 83% and 55%, respectively, as compared with that of UP‐toughened epoxy blend. Moreover, thermogravimetric analysis revealed that the (alkali‐silane)‐treated fiber and its composite exhibited higher thermal stability than the untreated and alkali‐treated fiber systems. An increase in storage modulus and glass transition temperature was observed for the UP‐toughened epoxy matrix on reinforcement with treated fibers. The water uptake behavior of both alkali and alkali‐silane‐treated fiber‐reinforced composites is found to be less as compared with the untreated fiber‐reinforced composite. J. VINYL ADDIT. TECHNOL., 23:188–199, 2017. © 2015 Society of Plastics Engineers     

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     

A Novel Route to Modify the Interface of Glass Fiber-Reinforced Epoxy Resin Composite via Bacterial Cellulose

A simple and novel method to modify the surface of glass material with Acetobacter xylinum bacteria to deposit bacterial cellulose (BC) around glass material during the process of fermentation was described. The modified glass material with more hydrophobic and rougher surface was characterized by FTIR, SEM, XPS, peeling experiments, and water/air contact angle. It was found that heat treatment at 140 ～ 150°C was able to improve the interaction between BC and glass material owing to the increase in chemical bonds between them. The biological modified glass fibers were compounded with epoxy resin. The influence of incubation time and high temperature on the interfacial shear strength (IFSS) between glass fibers and epoxy resin was identified by Microbond Test. The strongest IFSS could be obtained with incubation time of 1 hour and temperature of 140°C, which then offers a biological approach to improve the interface of silicates materials and resin matrix.     

Experimental evaluation of the interfacial properties of carbon nanotube coated carbon fiber reinforced hybrid composites

A floating catalyst chemical vapor deposition (CVD) unit was utilized to grow CNT onto the surface of carbon fiber (CF). The surface morphology of the resultant fibers, CNT population density and alignment pattern were found to be depended on the CNT growth temperature, growth time, and atmospheric conditions within the CVD chamber. In contrast to the neat‐CF reinforced composites, improved interfacial shear strength (IFSS) between CF and matrix were obtained when the surface of CF was coated by CNT. Particularly, CF treatment condition for CNT‐coating with 700°C reaction temperature and 30 min reaction time has shown a considerable increase in IFSS approximately of 45% over that of the untreated fiber from which it was processed. The proper justification of fiber–matrix adhesion featured by composite interfacial properties was explained through IFSS. POLYM. COMPOS., 36:1941–1950, 2015. © 2014 Society of Plastics Engineers     

Improvement of the interfacial shear strength of poly(p‐phenylene benzobisoxazole) fiber/epoxy resin composite via a novel surface coating agent

Poly(p‐phenylene benzobisoxazole) (PBO) fiber with a smooth surface exhibits limited interfacial interaction with resin matrix. One of the effective strategies to improve the adhesion between the fiber and resin matrix is through surface modification of the fiber. In this study, we have proposed a novel surface treatment agent based on phosphoester cross‐linked castor oil (PCCO) for effective surface treatment of PBO fibers. The surface treatment agent was prepared by a simple cross‐linking reaction between hydroxy phosphorylated castor oil (PCO) and epoxy resin, with alcohol as the solvent at 65°C. Once the PBO fiber was treated with this agent, the interfacial adhesion between the PBO fiber and the epoxy resin could then be improved. Systematic analyses suggest that the surface treatment with (PCO + epoxy)/alcohol solution improves the interaction of the PBO fiber with the epoxy resin matrix. The PCCO coated onto the surface of PBO fiber acts as a coupling agent, improving the interfacial shear strength (IFSS) of the PBO fiber/epoxy resin composite. Results indicate a 156% increase in IFSS without compromising the mechanical properties of the fiber. POLYM. COMPOS., 37:1198–1205, 2016. © 2014 Society of Plastics Engineers     

Improving delamination resistance of carbon fiber reinforced polymeric composite by interface engineering using carbonaceous nanofillers through electrophoretic deposition: An assessment at different in-service temperatures

In this article, modification of carbon fiber surface by carbon based nanofillers (multi-walled carbon nanotubes [CNT], carbon nanofibers, and multi-layered graphene) has been achieved by electrophoretic deposition technique to improve its interfacial bonding with epoxy matrix, with a target to improve the mechanical performance of carbon fiber reinforced polymer composites. Flexural and short beam shear properties of the composites were studied at extreme temperature conditions; in-situ cryo, room and elevated temperature (−196, 30, and 120°C respectively). Laminate reinforced with CNT grafted carbon fibers exhibited highest delamination resistance with maximum improvement in flexural strength as well as in inter-laminar shear strength (ILSS) among all the carbon fiber reinforced epoxy (CE) composites at all in-situ temperatures. CNT modified CE composite showed increment of 9% in flexural strength and 17.43% in ILSS when compared to that of unmodified CE composite at room temperature (30°C). Thermomechanical properties were investigated using dynamic mechanical analysis. Fractography was also carried out to study different modes of failure of the composites.     

The effect of silica (SiO2) nanoparticles and ammonia/ethylene plasma treatment on the interfacial and mechanical properties of carbon-fiber-reinforced epoxy composites

A nanoparticle dispersion is known to enhance the mechanical properties of a variety of polymers and resins. In this work, the effects of silica (SiO₂) nanoparticle loading (0–2 wt%) and ammonia/ethylene plasma-treated fibers on the interfacial and mechanical properties of carbon fiber–epoxy composites were characterized. Single fiber composite (SFC) tests were performed to determine the fiber/resin interfacial shear strength (IFSS). Tensile tests on pure epoxy resin specimens were also performed to quantify mechanical property changes with silica content. The results indicated that up to 2% SiO₂ nanoparticle loading had only a little effect on the mechanical properties. For untreated fibers, the IFSS was comparable for all epoxy resins. With ethylene/ammonia plasma treated fibers, specimens exhibited a substantial increase in IFSS by 2 to 3 times, independent of SiO₂ loading. The highest IFSS value obtained was 146 MPa for plasma-treated fibers. Interaction between the fiber sizing and plasma treatment may be a critical factor in this IFSS increase. The results suggest that the fiber/epoxy interface is not affected by the incorporation of up to 2% SiO₂ nanoparticles. Furthermore, the fiber surface modification through plasma treatment is an effective method to improve and control adhesion between fiber and resin.     

Surface‐modified sisal fiber‐reinforced eco‐friendly composites: Mechanical,thermal, and diffusion studies

To improve the fiber/matrix interaction, sisal fibers were subjected to various chemical and physical modifications such as mercerization, heating at 100°C, permanganate treatment, benzoylation, and silanization. Polyester composites were fabricated using compression molding. Tensile and flexural properties increased for every treated fiber‐reinforced composites with a reduction in the impact strength. This is attributed to the improved interfacial adhesion between fiber and polyester matrix. An increase in thermal stability was observed for the treated fiber‐reinforced composites especially at lower temperature. Significant reduction in water uptake occurred for the treated fiber‐reinforced composites at 30°C and 90°C. Scanning electron micrograph studies have been used to substantiate the above observations. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Effect of silane coupling agents on basalt fiber–epoxidized vegetable oil matrix composite materials analyzed by the single fiber fragmentation technique

The fiber–matrix interfacial shear strength (IFSS) of biobased epoxy composites reinforced with basalt fiber was investigated by the fragmentation method. Basalt fibers were modified with four different silanes, (3‐aminopropyl)trimethoxysilane, [3‐(2‐aminoethylamino)propyl]‐trimethoxysilane, trimethoxy[2‐(7‐oxabicyclo[4.1.0]hept‐3‐yl)ethyl]silane and (3‐glycidyloxypropyl)trimethoxysilane to improve the adhesion between the basalt fiber and the resin. The analysis of the fiber tensile strength results was performed in terms of statistical parameters. The tensile strength of silane‐treated basalt fiber is higher than the tensile strength of the untreated basalt fiber; this behavior may be due to flaw healing effect on the defected fiber surfaces. The IFSS results on the composites confirm that the interaction between the fiber modified with coupling agents and the bio‐based epoxy resin was much stronger than that with the untreated basalt fiber. POLYM. COMPOS., 36:1205–1212, 2015. © 2014 Society of Plastics Engineers     

Chemical interaction between carbon fibers and surface sizing

Functional groups on the surface of Polyacrylonitrile (PAN)‐based carbon fibers and in fiber surface sizing are likely to react during the curing process of composites, and these reactions could affect the infiltration and adhesion between the carbon fibers and resin. T300B‐3000‐40B fibers and fiber surface sizing were heat‐treated at different temperatures, and the structural changes of both the fiber surface sizing and extracted sizing after heat treatment were investigated by Fourier transform infrared spectroscopy. The results show that the concentration of epoxy groups in both the fiber surface sizing and extracted sizing decreased with increasing heat‐treatment temperature and decreased to zero after treatment at 200°C. The concentration of epoxy groups in the extracted sizing was lower than that of the fiber surface sizing after treatment under the same conditions; this indicated that the rate of reaction between the carbon fibers and fiber surface sizing was higher than the reaction rate of the fiber surface sizing system. X‐ray photoelectron spectroscopy analysis reveals that the content of C? O bonds and activated carbon atoms on the surface of the desized treated carbon fibers was the highest when the heat‐treatment temperature was 150°C; this proved the reaction between the carbon fibers and the fiber surface sizing. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of a new class of thermosetting resins: Allyl and propargyl substituted cyclopentadiene derivatives

A series of all-hydrocarbon resins were synthesized by reacting cyclopentadiene allyl chloride, propargyl chloride, or a mixture of allyl chloride and propargyl ide, under phase transfer conditions. Phase transfer reactions with and without added solvents, and with either quaternary ammonium or crown ether catalysts, yielded similar products consisting of a mixture of 1,1-disubstituted cyclopentadiene (minor amount) and 2-3 isomers each of tri-, tetra-, penta-, and hexa-substituted derivatives. No further reaction of each these components possible. The overall substitution pattern varied little with changes in reaction conditions although limiting the allyl chloride content led to still reactive, partially substituted products. Incorporation of all-propargyl and high propargyl-to-allyl mixed functionalities on cyclopentadiene yielded products whose stability was very hindering their thorough characterization. Preliminary evaluation was there-carried out for mixed resins with lower propargyl functionality. The allyl substituted resin (allylated cyclopentadiene, ACP) underwent thermal cure lout initiator at around 200°C while allyl/propargyl substituted resin (7:1 ratio, APCP) showed a faster, lower temperature cure at around 120°C. Cationic cure of ACP was also initiated by a novel sulfonium salt at around 100°C. Neat resin when cured at 200°C gave material with a flexural storage modulus 2 of about 300 MPa. Further cure at 250°C raised the modulus to 1.2 GPa. resin gave composites with excellent properties when used with glass and on fibers. Flexural modulus values (by DMA) of ∼ 66 GPa were obtained for ACP/carbon fiber composites compared with 42 GPa for epoxy/carbon composites made in our laboratories using commercially available materials. The modulus values at 300°C dropped to 10% of the room temperature value for the epoxy composites, while the ACP/carbon composite maintained 60% of its room temperature value at 300°C. When brought back to ambient temperature, the modulus of latter sample had increased to 80 GPa and that of the epoxy composite dropped to 23 GPa. Glass fiber ACP composites performed similar to an epoxy composite up to 200°C but maintained properties up to 300°C while those of the epoxy were drastically reduced. TGA analysis of both cured ACP resin and its composites showed decomposition beginning at 375°C. Three-point-bending tests indicated very high modulus with brittle failure for ACP composites. Scanning electron micrographs showed moderate bonding of the new resin to both carbon glass fiber surfaces. This new class of thermosetting resins offers excellent potential for application in low-cost glass and carbon composites with good thermal and physical properties.     

淀粉纳米晶对玻璃纤维的表面改性研究

采用自制的淀粉纳米晶(SNC)对玻璃纤维进行表面处理,增加其与环氧树脂基体的界面剪切强度(IFSS)。研究了处理方式、处理时间、SNC乙醇分散液浓度、热处理温度等工艺参数对SNC在玻璃纤维表面沉积情况的影响,以及对改性玻璃纤维与环氧树脂的界面性能的影响规律。采用扫描电子显微镜、单纤维强力仪对处理前后玻璃纤维进行表征,并采用微脱粘法测试玻璃纤维与环氧树脂的界面粘结情况。结果表明,当重力静置处理时间24 h,SNC乙醇分散液浓度为1 g/100 m L时,SNC在玻璃纤维表面均匀沉积,且能显著提高玻璃纤维与环氧树脂的IFSS,为27.29 MPa,较未处理的纤维增加29.3%。150℃热处理4 h后,X射线光电子能谱结果显示SNC与玻璃纤维形成化学键合,进一步增加纤维与环氧树脂的界面粘结,IFSS值达到32.30 MPa,较未处理的纤维增加53%,且纤维的拉伸强度得到较好的维持。