Improved shape memory effects in multiwalled‐carbon‐nano‐tube reinforced thermosetting polyurethane composites

Shape memory thermosetting polyurethane (SMPU) composites containing different amount of multiwalled carbon nanotube (MWCNT) ranging from 0 to 0.250 phr were prepared. The shape memory behavior, tensile stress, and recovery stress were determined by using conventional thermomechanical cycle; however, the modified thermomechanical cycle designated as progressive stretch–relax–stretch (PSRS) cycle was also employed to create shape memory effects in studied composites. The test was carried out in water bath which was equipped with an electric heater, temperature controller, and tensile stress and strain measuring setup. The recovery and tensile stresses both were showing higher values for PSRS samples as compared with conventional samples. Loading of MWCNT improved the recovery stress of SMPU, thereby confirming reinforcing effect. The maximum recovery stress of 2.17 MPa for 0.188 phr MWCNT loading was observed as compared with 1.09 MPa of unreinforced SMPU specimen. The recovery time was also improved on reinforcement as demonstrated in this article. The morphology of fractured surface and degree of dispersion of MWCNT was studied using Field Emission Scanning Electron Microscope. The impact on glass transition temperature was also observed for MWCNT reinforcement on SMPU, which depends on the degree of dispersion and loading of MWCNT in the specimen. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44389.     

Effects of zinc oxide on pretreated multiwalled‐carbon‐nanotube‐reinforced biobased polyesters

In this study, the effects of the incorporation of microsized zinc oxide (ZnO) on multiwalled carbon nanotube (MWCNT)‐reinforced palm‐oil‐based polyester (POPE) were investigated in terms of the UV absorbability, mechanical strength, thermal stability, surface resistivity, and morphology. POPE was prepared by alcoholysis and an esterification process with glycerol, palm oil, and phthalic anhydride. The MWCNTs were dispersed into POPE under in situ conditions during the esterification reaction, whereas ZnO was distributed into the MWCNT‐filled POPE resin with an ultrasound technique. The surface morphology was examined to understand the dispersion of the fillers inside the polymer matrix with field emission scanning electron microscopy. In addition, UV absorbability was observed with a UV–visible spectrophotometer. From the results analysis, the surface resistivity was found to be unchanged by the presence of the ZnO particles. In addition, incorporation of ZnO improved the UV absorbability. Moreover, the tensile strength of the ZnO‐based POPE was found to be slightly lower compared with that of the MWCNT‐filled POPE. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44627.     

Influences of different gravity environments on the curing process and cured products of carbon‐nanotube‐reinforced epoxy composites

The influences of different gravity environments on the curing process and the cured products of carbon‐nanotube‐reinforced epoxy composites were investigated in this study. Different gravity environments were simulated with a superconducting magnet on the basis of which resin matrix composites with different amino‐functionalized multiwalled carbon nanotube (NH₂‐MWCNT) concentrations of 0.1, 0.3, 0.5, and 1 wt % were tested. Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, thermomechanical analysis (TMA), thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, and three‐point bending tests were used to analyze the characteristics of different curing processes and cured products. From the results, we observed that the curing rate of the epoxy composites was influenced by different gravity values, and there was anisotropy in the NH₂‐MWCNT‐reinforced epoxy composites cured in the simulated microgravity environment. More effects of gravity on the curing process and cured products could be obtained through detailed experiments and discussion; this is important and fundamental for improving and enhancing the properties of composite materials used in different gravity environments. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41413.     

Simultaneous improvement in strength,toughness, and thermal stability of epoxy/halloysite nanotubes composites by interfacial modification

This work investigated the effect of silane modification of halloysite nanotubes (HNTs) on the mechanical properties of epoxy/HNTs nanocomposites. Three kinds of silane coupling agents, including 3‐(2‐aminoethyl)‐aminopropyltrimethoxysilane (AEAPS), (3‐glycidyloxypropyl)‐trimethoxysilane (GPTMS), and octyltriethoxysilane (OTES), were employed. It was shown that the modified HNTs exhibited a better dispersion in the epoxy matrix compared with pristine one. Because of strong interfacial interaction between AEAPS modified HNTs and the epoxy matrix, the nanocomposites exhibited the highest glass transition temperature and modulus among all the samples. On the other hand, AEAPS and GPTMS modified HNTs/epoxy nanocomposites showed enhanced tensile strength and toughness. The toughing mechanisms were identified by the SEM micrographs of the fracture surfaces of the different kinds of samples. In this study, simultaneous enhancement of strength, toughness, and thermal stability of epoxy by the modified HNTs provides a novel approach to produce high‐performance thermosets. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43249.     

Stress relaxation behavior of starch powder‐epoxy resin composites

The purpose of the present study is to investigate the quasi‐static and the viscoelastic behavior of epoxy resin reinforced with starch powder. An increase in the elastic modulus on the order of 42% was achieved; a behavior that was predicted by the modulus prediction model (MPM). Next, the composite was subjected to flexural relaxation experiments, in order to determine the relaxation modulus, at different filler‐weight fractions and flexural deflections imposed. The viscoelastic models of the standard linear solid, the power law model and the residual property model (RPM) were applied in order to simulate/predict the stress relaxation curves. Predicted values derived from the application of the above models were compared to each‐other as well as to respective experimental findings. From the above comparison it was proved the superiority of the RPM model in predicting both the linear and the nonlinear viscoelastic response of the materials investigated. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41697.     

Layer‐by‐layer fabrication of nacre inspired epoxy/MMT multilayered composites

The organic–inorganic hybrid multilayered composites are prepared using a unique combination of poly[(o‐cresyl glycidyl ether)‐co‐formaldehyde] (CNER), amino modified montmorillonite (NH₂‐MMT), and polyethyleneimine (PEI). This tricomponent composite multilayer PEI(CNER/NH₂‐MMT/PEI)_n deposited via layer ‐ by ‐ layer technique is based upon synergistic combination of covalent and hydrogen bonding. The growth of multilayer was monitored using UV–vis spectroscopy and ellipsometry. When subjected to optical analyses, the prepared multilayered composite films revealed profound optical transmittance ～83%–87%. The surface morphological analysis by atomic force microscopy and scanning electron microscopy revealed uniform arrangement of organic–inorganic components with relative increase in intensity of elements (C, N, O, Si) as confirmed by X‐ray photoelectron spectroscopy studies. The multilayered composites possess 1.99 GPa hardness making them potential candidate for a number of applications where mechanical strength is desired. Moreover, significant resistance against alkaline and organic solvents at minimal deterioration of circa 0.12% has also been observed for the prepared films. The epoxy clay based thin films being robust, scratch resistant, hydrophilic, chemically inert, and mechanically strong are potential candidates for advanced environmental applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46079.     

Preparation of a branched amine and physical and thermal studies of epoxy compositions including the amine compound

A branched amine, abbreviated as EATP, was synthesized by reacting ethylene diamine with methyl acrylate, followed by reaction with xylylene diamine via a two‐step process. The prepared EATP (in the range of 5–30 parts per resin) was added to epoxy compositions with bisphenol A epoxy resin and a curing agent, xylylene diamine. The epoxy compositions were cured at high temperatures and processed for flexural strength testing and dynamic mechanical analysis. The results showed that the flexural strength was improved by 13% when 10% EATP was present in the epoxy matrix, but there was a decrease in tan δ and storage modulus values. Moreover, the degree of fire hazard of the epoxy compositions and EATP was studied by measuring the heat release rate (HRR). The reduction in the HRR with higher amounts of EATP in the epoxy indicated that the xylylene groups of EATP enhance the thermal stability of the resin. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46233.     

Investigation of mechanical properties of alumina nanoparticle‐loaded hybrid glass/carbon‐fiber‐reinforced epoxy composites

This research work investigates the tensile strength and elastic modulus of the alumina nanoparticles, glass fiber, and carbon fiber reinforced epoxy composites. The first type composites were made by adding 1–5 wt % (in the interval of 1%) of alumina to the epoxy matrix, whereas the second and third categories of composites were made by adding 1–5 wt % short glass, carbon fibers to the matrix. A fourth type of composite has also been synthesized by incorporating both alumina particles (2 wt %) and fibers to the epoxy. Results showed that the longitudinal modulus has significantly improved because of the filler additions. Both tensile strength and modulus are further better for hybrid composites consisting both alumina particles and glass fibers or carbon fibers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39749.     

High-thermal conductivities of epoxy composites via p-phenylenediamine interfacial modification and process intensification

High loadings of fillers are usually needed to achieve high-thermal conductivity (TC) of polymer-based composites, which inevitably sacrifices processability and meanwhile causes high-cost. Therefore, it is of great significance to achieve high-TC composites under low-filler loading. Here, a novel p-phenylenediamine (PPD) modified expanded graphite (EG-PPD)/epoxy (EP) composite with high TC and low-filler content was successfully prepared via pre-dispersion and vacuum assisted mixing strategy. With the improved interfacial compatibility between EG and EP by PPD, the prepared EG-PPD/EP composite exhibited excellent thermal management performance, resulting in the TC of which reached 4.00 W·m⁻¹·K⁻¹ with only 10 wt% (5.59 vol%) of EG-PPD, which is approximately 19 times higher than that of pure EP. Meantime, the interface thermal resistance of EG-PPD/EP composite between EG-PPD and EP is reduced by 33% compared with EG/EP composite. This composite with excellent TC property is expected to be used in thermal management field.     

Multifunctional epoxy resin/polyacrylonitrile‐lithium trifluoromethanesulfonate composites films with very high transparency,high dielectric permittivity,breakdown strength and mechanical properties

Multifunctional transparent composite films with high dielectric permittivity (high‐k), breakdown strength, and mechanical properties are urgently required by cutting‐edge fields. Herein, novel multifunctional films were facilely prepared through building unique cross‐linked structure based on epoxy resin (EP) and polyacrylonitrile (PAN)‐lithium trifluoromethane sulfonate (LiTf) complex. Compared with high‐k materials reported previously, EP/(PAN‐LiTf) films simultaneously show very high transparency, good flexibility, high tensile, and breakdown strengths. For 0.22EP/(PAN‐LiTf) film with 22 wt % EP, its average transmittance and elongation at break are as high as 91% (600–800 nm) and 12.7%, respectively; moreover, its dielectric permittivity, AC breakdown strength and the maximum energy density are severally about 4.9, 1.8, and 15.2 times of those of EP resin, completely overcoming the sticky problems in conductor/polymer composites. The origin behind these attractive properties is intensively discussed, and believed to be attributed to the unique structure of EP/(PAN‐LiTf) films. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45218.     

The ultrasound‐based interfacial treatment of aramid fiber/epoxy composites

The quality of interfacial adhesion of aramid/epoxy composites affects the mechanical performance of the material, and thus there is a need to improve the condition by using the ultrasound‐based interfacial treatment. To do so, an ultrasonic transducer has been developed and evaluated under various operational conditions when it is installed in the winding system. It has demonstrated several key characteristics such as low power, high amplitude (more than 80 μm), and continuous working (more than 8 h) without water‐cooling. Subsequently, experiments were carried out to determine the mechanical performance of the polymer material with and without ultrasound treatment, showing that the ultrasonic treatment has improved the interfacial performance up to 10%, compared with those without any ultrasound‐treatment. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Improving thermal conductivity and shear strength of carbon nanotubes/epoxy composites via thiol‐ene click reaction

This study investigates the effect of the thiol‐ene click reaction on thermal conductivity and shear strength of the epoxy composites reinforced by various silane‐functionalized hybrids of sulfhydryl‐grafted multi‐walled carbon nanotubes (SH‐MWCNTs) and vinyl‐grafted MWCNTs (CC‐MWCNTs). The results of Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermal gravimetric analysis (TGA), and transmission electron microscopy (TEM) show that the sulfhydryl groups and vinyl groups are successfully grafted onto the surface of MWCNTs, after treatment of MWCNT with triethoxyvinylsilane and 3‐mercaptopropyltrimethoxysilane, respectively. Scanning electron microscopy (SEM), HotDisk thermal constant analyzer (HotDisk), optical microscope, and differential scanning calorimetry (DSC) are used to characterize the resultant composites. It is demonstrated that the hybrid of 75 wt % SH‐MWCNTs and 25 wt % CC‐MWCNTs has better dispersion and stability in epoxy matrix, and shows a stronger synergistic effect in improving the thermal conductivity of epoxy composite via the thiol‐ene click reaction with 2,2′‐azobis(2‐methylpropionitrile) as thermal initiator. Furthermore, the tensile shear strength results of MWCNT/epoxy composites and the optical microscopy photographs of shear failure section indicate that the composite with the hybrid MWCNTs has higher shear strength than that with raw MWCNTs. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44579.     

Wedge test of carbon‐nanotube‐reinforced epoxy adhesive joints

Epoxy adhesives reinforced with carbon nanotubes (CNTs) were developed. The distribution of the CNTs in the epoxy matrix was observed with transmission electron microscopy. Joints were formed by unclad 2024‐T3 aluminum adherents bonded with the CNT‐filled epoxy adhesives. The durability of the joints was studied with a wedge test under water at 60°C. The addition of CNTs to the epoxy greatly improved the adhesive joint durability. The initial crack length of the joint with 1 wt % CNTs, which was obtained before the wedge specimen was put into water, was only about 7% of that with neat epoxy. After immersion of the specimens in 60°C water, the joint with neat epoxy failed after 3 h, but all of the joints adhered with different fractions of CNTs were still bound together after the experimental time of 90 h. The significant enhancement by CNTs of the adhesive joint durability was mainly attributed to the high mechanical properties of the CNTs and their ability to resist water. Nevertheless, the experimental results also reveal that the durability of the joints showed an optimum value at approximately 1 wt % CNTs, beyond which a decrease in the property was observed. In addition, the failure mechanism of the joints was also investigated in terms of interfacial failure and cohesive failure. Cohesive dominated failure was found for the joint bonded with 1 wt % CNT‐filled epoxy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal,mechanical properties,and low‐temperature performance of fibrous nanoclay‐reinforced epoxy asphalt composites and their concretes

Epoxy asphalt (EA) concretes have been widely used in the pavement of orthotropic steel bridge decks. The objective of this study was to figure out the enhanced effects of natural fibrous attapulgite (ATT) as a reinforced nanofiller in ATT/EA nanocomposites through a comparison of the properties of the composites with a series of various nanoclay loadings. The rheological properties, glass transition, thermal stability, mechanical properties, and morphology of the ATT/EA composites were characterized. Furthermore, the low‐temperature flexibility of the ATT/EA concretes was investigated. The test results show that the addition of ATT had no significant effect on the rotational viscosity of EA in the initial stage of the curing reaction. In addition, the ATT/EA composites showed better performance than the neat one in thermal stability with a higher glass‐transformation temperature. The tensile strength and elongation at break of the ATT/EA composites at a loading of 0.5 wt % ATT were 21 and 22% higher than those of the neat EA. The addition of ATTs also enhanced the low‐temperature flexibility of the EA concretes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41694.     

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     

Synthesis and properties of novel trifunctional epoxy triglycidyl of 4‐(4‐aminophenoxy)phenol with high toughness

A trifunctional epoxy containing oxyphenylene unit, triglycidyl of 4‐(4‐aminophenoxy)phenol (TGAPP) was synthesized and characterized. The chemical structure of TGAPP was confirmed with FTIR and ¹H‐NMR. DSC analysis revealed that the reactivity of TGAPP with curing agent 4, 4′‐diaminodiphenylsulfone (DDS) was significantly lower than that of triglycidyl para‐aminophenol (TGPAP). Rheological analysis showed that the processing window of TGAPP/DDS was 20°C wider compared with that of TGPAP/DDS. The thermal and mechanical properties of cured TGAPP/DDS were investigated and compared with those of the cured TGPAP/DDS. Experimental results showed that, due to the introduction of oxyphenylene unit, the heat resistance and flexural strength were slightly reduced, while the tensile strength and impact strength were enhanced. SEM also confirmed that the introduction of oxyphenylene unit could enhance the toughness of the TGAPP/DDS as evident from ridge formation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41878.     

Producing high‐quality precursor polymer and fibers to achieve theoretical strength in carbon fibers: A review

The precursor fiber quality has a large impact on carbon fiber processing in terms of its performance, production yield, and cost. Polyacrylonitrile precursor fibers have been used commercially to produce strong carbon fibers with average tensile strength of 6.6 GPa. There is a scope to improve the average tensile strength of carbon fibers, since only 10% of their theoretical strength has been achieved thus far. Most attempts to increase the tensile strength of carbon fibers have been made during the conversion of precursor fiber to carbon fiber. This review highlights the potential opportunities to enhance the quality of the polyacrylonitrile‐based precursor fiber during polymer synthesis, spinning, and postspinning. These high‐quality precursor fibers can lead to new generation carbon fibers with improved tensile strength for high‐performance applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43963.     

Mechanical properties of graphene nanoplatelet/epoxy composites

Because of their high‐specific stiffness, carbon‐filled epoxy composites can be used in structural components in fixed‐wing aircraft. Graphene nanoplatelets (GNPs) are short stacks of individual layers of graphite that are a newly developed, lower cost material that often increases the composite tensile modulus. In this work, researchers fabricated neat epoxy (EPON 862 with Curing Agent W) and 1–6 wt % GNP in epoxy composites. The cure cycle used for this aerospace epoxy resin was 2 h at 121°C followed by 2 h at 177°C. These materials were tested for tensile properties using typical macroscopic measurements. Nanoindentation was also used to determine modulus and creep compliance. These macroscopic results showed that the tensile modulus increased from 2.72 GPa for the neat epoxy to 3.36 GPa for 6 wt % (3.7 vol %) GNP in epoxy composite. The modulus results from nanoindentation followed this same trend. For loadings from 10 to 45 mN, the creep compliance for the neat epoxy and GNP/epoxy composites was similar. The GNP aspect ratio in the composite samples was confirmed to be similar to that of the as‐received material by using the percolation threshold measured from electrical resistivity measurements. Using this GNP aspect ratio, the two‐dimensional randomly oriented filler Halpin–Tsai model adjusted for platelet filler shape predicts the tensile modulus well for the GNP/epoxy composites. Per the authors' knowledge, mechanical properties and modeling for this GNP/epoxy system have never been reported in the open literature. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Interfacial evaluation of epoxy/carbon nanofiber nanocomposite reinforced with glycidyl methacrylate treated UHMWPE fiber

Interface interactions of fiber–matrix play a crucial role in final performance of polymer composites. Herein, in situ polymerization of glycidyl methacrylate (GMA) on the ultrahigh molecular weight polyethylene (UHMWPE) fibers surface was proposed for improving the surface activity and adhesion property of UHMWPE fibers towards carbon nanofibers (CNF)‐epoxy nanocomposites. Chemical treatment of UHMWPE fibers was characterized by FTIR, XPS analysis, SEM, and microdroplet tests, confirming that the grafting of poly (GMA) chains on the surface alongside a significant synergy in the interfacial properties. SEM evaluations also exhibited cohesive type of failure for the samples when both GMA‐treated UHMWPE fiber and CNF were used to reinforce epoxy matrix. Compared with unmodified composite, a ～319% increase in interfacial shear strength was observed for the samples reinforced with both 5 wt % GMA‐grafted UHMWPE and 0.5 wt % of CNF. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43751.     

Development of high Tg epoxy resin and mechanical properties of its fiber‐reinforced composites

A new epoxy resin with high glass transition temperature (T_g) (～ 180°C) and a viscosity low enough for infiltration into dry reinforcements at 40°C was developed for the vacuum‐assisted resin transfer molding process. To study the curing behavior and viscosity, several blends were formulated using multifunctional resin, aromatic hardener, and reactive diluents. Effects of these components on the viscosity and T_g were investigated by thermomechanical analysis, dynamic scanning calorimetry, and rheometer. Experimental results showed that a liquid aromatic hardener and multifunctional epoxy resin should be used to decrease the viscosity to <1 Pa·s at 40°C. Moreover, the addition of a proper reactive diluent decreased the viscosity and simultaneously minimized the deterioration of T_g. Mechanical properties of the composite produced with the optimized blend were evaluated at both room‐temperature and high‐temperature conditions. According to the results, the composite showed comparable mechanical properties with that of the current commercial resin. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013