Effects of amino‐functionalized carbon nanotubes on the properties of amine‐terminated butadiene–acrylonitrile rubber‐toughened epoxy resins

Amino‐functionalized multiwalled carbon nanotubes (MWCNT‐NH₂s) as nanofillers were incorporated into diglycidyl ether of bisphenol A (DGEBA) toughened with amine‐terminated butadiene–acrylonitrile (ATBN). The curing kinetics, glass‐transition temperature (T_g), thermal stability, mechanical properties, and morphology of DGEBA/ATBN/MWCNT‐NH₂ nanocomposites were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis, a universal test machine, and scanning electron microscopy. DSC dynamic kinetic studies showed that the addition of MWCNT‐NH₂s accelerated the curing reaction of the ATBN‐toughened epoxy resin. DSC results revealed that the T_g of the rubber‐toughened epoxy nanocomposites decreased nearly 10°C with 2 wt % MWCNT‐NH₂s. The thermogravimetric results show that the addition of MWCNT‐NH₂s enhanced the thermal stability of the ATBN‐toughened epoxy resin. The tensile strength, flexural strength, and flexural modulus of the DGEBA/ATBN/MWCNT‐NH₂ nanocomposites increased increasing MWCNT‐NH₂ contents, whereas the addition of the MWCNT‐NH₂s slightly decreased the elongation at break of the rubber‐toughened epoxy. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40472.     

Nano‐AlN functionalization by silane modification for the preparation of covalent‐integrated epoxy/poly(ether imide) nanocomposites

Aluminum nitride nanoparticle (nano‐AlN) organically modified with the silane‐containing epoxide groups (3‐glycidoxypropyltrimethoxy silane, GPTMS) was incorporated into a mixture of poly(ether imide) (PEI), and methyl hexahydrophthalic anhydride‐cured bisphenol A diglycidyl ether grafted by GPTMS was prepared for nanocomposite. Scanning electron microscopy, transmission electron microscopy, and atomic force microscopy were used to investigate the microscopic structures of nanocomposites. According to experimental results, it was shown that addition of nano‐AlN and PEI into the modified epoxy could lead to the improvement of the impact and bend strengths. When the concentrations of nano‐AlN and PEI were 20 and 10 pbw, respectively, the toughness/stiffness balance could be achieved. Dynamic mechanical analysis (DMA) results displayed that two glass transition temperatures (T_g) found in the nanocomposites were assigned to the modified epoxy phase and PEI phase, respectively. As nano‐AlN concentration increased, T_g value of epoxy phase had gradually increased, and the storage modulus of the nanocomposite at the ambient temperature displayed an increasing tendency. Additionally, thermal stability of the nanocomposite was apparently improved. The macroscopic properties of nanocomposites were found to be strongly dependent on their components, concentrations, dispersion, and resulted morphological structures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and properties of high performance phthalide‐containing bismaleimide modified epoxy matrices

A series of intercrosslinked networks formed by diglycidyl ether of bisphenol A epoxy resin (DGEBA) and novel bismaleimide containing phthalide cardo structure (BMIPP), with 4,4′‐diamino diphenyl sulfone (DDS) as hardener, have been investigated in detail. The curing behavior, thermal, mechanical and physical properties and compatibility of the blends were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), notched Izod impact test, scanning electron microscopy (SEM) and water absorption test. DSC investigations showed that the exothermic transition temperature (T_p) of the blend systems shifted slightly to the higher temperature with increasing BMIPP content and there appeared a shoulder on the high‐temperature side of the exothermic peak when BMIPP content was above 15 wt %. TGA and DMA results indicated that the introduction of BMIPP into epoxy resin improved the thermal stability and the storage modulus (G′) in the glassy region while glass transition temperature (T_g) decreased. Compared with the unmodified epoxy resin, there was a moderate increase in the fracture toughness for modified resins and the blend containing 5 wt % of BMIPP had the maximum of impact strength. SEM suggested the formation of homogeneous networks and rougher fracture surface with an increase in BMIPP content. In addition, the equilibrium water uptake of the modified resins was reduced as BMIPP content increased. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Montmorillonite nanoclay filler effects on electrical conductivity,thermal and mechanical properties of epoxy‐based nanocomposites

Epoxy‐based nanocomposites with 2, 5, and 7 wt% of montmorillonite (MMT) nanoclay were prepared using high shear melt mixing technique. The microstructural features of the nanocomposites were investigated by transmission electron microscopy (TEM). The thermal and mechanical properties were measured using differential scanning calorimetry (DSC), thermogravimetric analyzer (TGA), and dynamic mechanical analyzer (DMA). Further, the effect of voltage, temperature, seawater aging on the electrical conductivity (σ_DC) of the nanocomposites was also measured. To understand the free volume behavior upon filler loading, and to observe the connectivity between microstructure and other properties, positron annihilation lifetime spectroscopy was used. The TEM results revealed that MMT nanoparticles were uniformly dispersed in the epoxy matrix. Experimental results showed that the inclusion of 2 wt% MMT nanofiller increased the T_g, electrical conductivity, thermal stability, modulus, free volume of the epoxy nanocomposite significantly. This is well explained from the results of T_g (DSC and DMA), thermal stability, TGA residue, free volume analysis, and electrical conductivity. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Effect of cloisite 30B clay and sisal fiber on dynamic mechanical and fracture behavior of unsaturated polyester toughened epoxy network

This study examined the dynamic mechanical properties of sisal fiber reinforced unsaturated polyester (UP) toughened epoxy nanocomposites. The chemical structures changes in Epoxy, UP and UP toughened epoxy (Epoxy/UP) systems were characterized by Proton Nuclear magnetic resonance (¹HNMR) spectroscopy. The morphological alterations of the nanocomposites were analyzed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The untreated, chemically treated fibers, nanoclays, and the fiber reinforced Epoxy/UP nanocomposites were confirmed by FTIR spectrometer. The obtained mechanical results showed that alkali‐silane treated fibers improve the tensile strength (96%) and flexural strength (60%) of the Epoxy/UP nanocomposite than that of Epoxy/UP blend due to the strong interfacial bonding between the sisal fiber and matrix. The fracture toughness (K_IC) and fracture energy (G_IC) of treated sisal fiber reinforced DGEBA/UP/C30B nanocomposites found to be higher than that of untreated sisal fiber nanocomposites. The dynamic mechanical analysis (DMA) reveals that the fiber reinforced Epoxy/UP nanocomposites contains 30 wt% treated fiber and 1 wt% nanoclays, exhibits the highest storage modulus and better glass transition temperature (T_g) among the other kind of systems. The surface morphology of the fibers, fractured surface of the resins and composites were confirmed by scanning electron microscope (SEM). POLYM. COMPOS., 37:2832–2846, 2016. © 2015 Society of Plastics Engineers     

Preparation and properties of TiO2‐filled poly(acrylonitrile‐butadiene‐styrene)/epoxy hybrid composites

Poly (acrylonitrile‐butadiene‐styrene) (ABS) was used to modify diglycidyl ether of bisphenol‐A type of epoxy resin, and the modified epoxy resin was used as the matrix for making TiO₂ reinforced nanocomposites and were cured with diaminodiphenyl sulfone for superior mechanical and thermal properties. The hybrid nanocomposites were characterized by using thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), universal testing machine (UTM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The bulk morphology was carefully analyzed by SEM and TEM and was supported by other techniques. DMA studies revealed that the DDS‐cured epoxy/ABS/TiO₂ hybrid composites systems have two T_gs corresponding to epoxy and ABS rich phases and have better load bearing capacity with the addition of TiO₂ particles. The addition of TiO₂ induces a significant increase in tensile properties, impact strength, and fracture toughness with respect to neat blend matrix. Tensile toughness reveals a twofold increase with the addition of 0.7 wt % TiO₂ filler in the blend matrix with respect to neat blend. SEM micrographs of fractured surfaces establish a synergetic effect of both ABS and TiO₂ components in the epoxy matrix. The phenomenon such us cavitation, crack path deflection, crack pinning, ductile tearing of the thermoplastic, and local plastic deformation of the matrix with some minor agglomerates of TiO₂ are observed. However, between these agglomerates, the particles are separated well and are distributed homogeneously within the polymer matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical and morphological properties of epoxy resins modified by poly(phthalazinone ether sulfone ketone)

A series of blends have been prepared by adding a novel thermoplastic poly(phthalazinone ether sulfone ketone) (PPESK) in varying proportions to diglycidyl ether of bisphenol A epoxy resin (DGEBA) cured with p‐diaminodiphenylsulfone (DDS). All the blends showed two‐phase structures characterized by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Addition of the PPESK resulted in great enhancement of glass transition temperatures (T_g) both in the epoxy‐rich phase and in the PPESK‐rich phase by reason of the special structure of PPESK. There was moderate increase in the fracture toughness as estimated by impact strength. Fracture mechanisms such as crack deflection and branches, ductile microcracks, ductile tearing of the thermoplastic, and local plastic deformation of the matrix were responsible for the increase in the fracture toughness of the blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanical and thermal properties of calcium carbonate‐filled PP/LLDPE composite

Polymer blends typically are the most economical means to develop new resins for specific applications with the best cost/performance balance. In this paper, the mechanical properties, melting, glass transition, and crystallization behavoir of 80 phr polypropylene (PP) with varying weights of linear low density polyethylene (LLDPE) at 10, 20/ 20 wt % CaCO₃, 30, 40, and 50 phr were studied. A variety of physical properties such as tensile strength, impact strength, and flexural strength of these blends were evaluated. The compatibility of these composite was examined by differential scanning calorimetry (DSC) to estimate T_m and T_c, and by dynamic mechanical analysis (DMA) to estimate T_g. The fractographic analysis of these blends was examined by scanning electron microscopy (SEM). It has been confirmed that increasing the LLDPE content trends to decreases the tensile strength and flexural strength. However, increasing the LLDPE content led to increases in the impact strength of PP/LLDPE blends. It was also found that up to 40 phr the corresponding melting point (T_m) was not effected with increasing LLDPE content. Each compound has more than one T_g, which was informed that there is a brittle‐ductile transition in fracture nature of these blends, the amount of material plastically deformed on the failure surface seems to increase with the increasing the LLDPE content. And PP/LLDPE blends at temperature (23°C) showed a ductile fracture mode characterized by the co‐existence of a shear yielding process; whereas at lower temperature (−20°C) the fractured surfaces of specimens appear completely brittle. The specimens broke into two pieces with no evidence of stress whitening, permanent macroscopic deformation or yielding. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Characterization of nanosilica‐filled epoxy composites for electrical and insulation applications

We report in this article the results of nanosilica (SiO₂)‐filled epoxy composites with different loadings and their electrical, thermal, mechanical, and free‐volume properties characterized with different techniques. The morphological features were studied by transmission electron microscopy, and differential scanning calorimetry was used to investigate the glass‐transition temperature (T_g) of the nanocomposites. The properties of the nanocomposites showed that the electrical resistivity (ρ), ultimate tensile strength, and hardness of the composites increased with SiO₂ weight fraction up to 10 wt % and decreased thereafter; this suggested that the beneficial properties occurred up to this weight fraction. The temperature and seawater aging had a negative influence on ρ; that is, ρ decreased with increases in the temperature and aging. The free‐volume changes (microstructural) in the composite systems correlated with seawater aging but did not correlate so well with the mechanical properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Development of high‐performance epoxy/clay nanocomposites by incorporating novel phosphonium modified montmorillonite

Novel organoclays were synthesized by several kinds of phosphonium cations to improve the dispersibility in matrix resin of composites and accelerate the curing of matrix resin. The possibility of the application for epoxy/clay nanocomposites and the thermal, mechanical, and adhesive properties were investigated. Furthermore, the structures and morphologies of the epoxy/clay nanocomposites were evaluated by transmission electron microscopy. Consequently, the corporation of organoclays with different types of phosphonium cations into the epoxy matrix led to different morphologies of the organoclay particles, and then the distribution changes of silicate layers in the epoxy resin influenced the physical properties of the nanocomposites. When high‐reactive phosphonium cations with epoxy groups were adopted, the clay particles were well exfoliated and dispersed. The epoxy/clay nanocomposite realized the high glass‐transition temperature (T_g) and low coefficient of thermal expansion (CTE) in comparison with those of neat epoxy resin. On the other hand, in the case of low‐reactive phoshonium cations, the dispersion states of clay particles were intercalated but not exfoliated. The intercalated clay did not influence the T_g and CTE of the nanocomposite. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure and properties of nylon 1010/ethylene‐vinyl acetate rubber–based dynamically vulcanized thermoplastic elastomers filled with SiO2

Dynamically vulcanized Nylon 1010/ethylene‐vinyl acetate rubber (EVM)/SiO₂ nanocomposites were prepared. Maleic anhydride grafted ethylene‐vinyl acetate copolymer (EVA‐g‐MA) and nano‐silica (SiO₂) was used as a compatibilizer and a filler, and silane coupling agent (KH550, 3‐triethoxysilylpropylamine) was used to improve the dispersion of SiO₂ in the nanocomposites. The nanocomposites were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), dynamic mechanical analysis (DMA), differential scanning calorimeter (DSC), and rheology analysis and mechanical properties test. SEM and AFM images showed that the compatibility between Nylon 1010 and EVM was improved by adding the compatibilizer. An increase in SiO₂ content and the addition of the compatibilizer led to an increase in the tensile strength of the nanocomposite. A nanocomposite based on Nylon 1010/EVM/DCP (30/70/0.8) with tensile strength of 16.3 MPa and elongation at break of 180% was obtained by the addition of 15 phr EVA‐g‐MA and 40 phr SiO₂. The non‐isothermal crystallization processes of Nylon/EVM blend were investigated by DSC. It was observed that EVM rubber could act as heterogeneous nuclei for Nylon which was more effective in Nylon/EVM/DCP blend than in Nylon/EVM blend. POLYM. ENG. SCI., 55:581–588, 2015. © 2014 Society of Plastics Engineers     

Mechanical and thermal properties of SEBS‐g‐MA compatibilized halloysite nanotubes reinforced polyethylene terephthalate/polycarbonate/nanocomposites

In this study, the effect of maleic anhydride grafted styrene‐ethylene‐butylene‐styrene (SEBS‐g‐MA) content on mechanical, thermal, and morphological properties of polyethylene terephthalate/polycarbonate/halloysite nanotubes (PET/PC/HNTs) nanocomposites has been investigated. Nanocomposites of PET/PC (70 : 30) with 2 phr of HNTs were compounded using the counter rotating twin screw extruder. A series of formulations were prepared by adding 5–20 phr SEBS‐g‐MA to the composites. Incorporation of 5 phr SEBS‐g‐MA into the nanocomposites resulted in the highest tensile and flexural strength. Maximum improvement in the impact strength which is 245% was achieved at 10 phr SEBS‐g‐MA content. The elongation at break increased proportionately with the SEBS‐g‐MA content. However, the tensile and flexural moduli decreased with increasing SEBS‐g‐MA content. Scanning electron microscopy revealed a transition from a brittle fracture to ductile fracture morphology with increasing amount of SEBS‐g‐MA. Transmission electron microscopy showed that the addition of SEBS‐g‐MA into the nanocomposites promoted a better dispersion of HNTs in the matrix. A single glass transition temperature was observed from the differential scanning calorimetry test for compatibilized nanocomposites. Thermogravimetric analysis of PET/PC/HNTs nanocomposites showed high thermal stability at 15 phr SEBS‐g‐MA content. However, on further addition of SEBS‐g‐MA up to 20 phr, thermal stability of the nanocomposites decreased due to the excess amount of SEBS‐g‐MA. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42608.     

Toughening mechanism of rubber reinforced epoxy composites by thermal and microwave curing

The carboxyl terminated polybutadiene (CTBN) is utilized to improve the toughness of diglycidylether of bisphenol A epoxy cured by heat and microwave. The change of viscosity, chemical groups, and the glass transition temperature (T_g) of system are analyzed. The impact performance is characterized to evaluate the fracture toughness, and tensile properties also are investigated. The fracture morphologies are observed by the scanning electron microscopy for exploring toughening mechanism. The viscosity results indicate that viscosity of system increases with increasing of CTBN, demonstrating the formation of precrosslinking and interpenetrating network structure of two phases. The Fourier transform infrared spectrometer results show that effective chemical bonds are formed between CTBN and epoxy resins. The T_g decreases with introducing CTBN, indicating the decline of crosslinking density, which further suggests inherent three‐dimensional structure have been changed. The impact strength and energy increase with increasing of CTBN, and reach a maximum value of 5.92 kJ/m² and 0.13 kJ at 15% for thermal curing, respectively, increased by 36.8% and 23.1% relative to microwave curing system, while tensile strength and modulus reach the optimum at 5%. Scanning electron microscopy observation finds that “plastic tensile” and “microvoid” deriving from “sea‐island” structure exist, presenting the ductile fracture features. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45767.     

Mechanical,thermal, and transport properties of nitrile rubber–nanocalcium carbonate composites

The article describes the properties of acrylonitrile butadiene copolymer (NBR)–nanocalcium carbonate (NCC) nanocomposites prepared by a two‐step method. The amount of NCC was varied from 2 phr to 10 phr. Cure characteristics, mechanical properties, dynamic mechanical properties, thermal behavior, and transport properties of NBR–NCC composites were evaluated. For preparing NBR nanocomposites, a master batch of NBR and NCC was initially made using internal mixer. Neat NBR and the NBR–NCC masterbatch was compounded with other compounding ingredients on a two roll mill. NCC activated cure reaction upto 5 phr. The tensile strength increased with the nanofiller content, whereas NBR–NCC containing 7.5 phr exhibited the highest modulus. The storage modulus (E′) increased up to 5 phr NCC loading; the reinforcing effect of NCC was seen in the increase of modulus which was more significant at temperatures above T_g. The effect of nanofiller content and temperature on transport properties was evaluated. The solvent uptake decreased with NCC content. The mechanism of diffusion of solvent through the nanocomposites was found to be Fickian. Transport parameters like diffusion, sorption, and permeation constants were determined and found to decrease with nanofiller content, the minimum value being at 7.5 phr. Thermodynamic constants such as enthalpy and activation energy were also evaluated. The dependence of various properties on NCC was supported by morphological analysis using transmission electron microscopy. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Toughening of epoxy systems by brominated epoxy

Blends of brominated epoxy (BE) and conventional epoxy resins were studied following curing with aliphatic triethylenetetramine (TETA), etheric (polyether diamine‐ PEA4), and aromatic (3,3′‐diamino diphenyl sulfone [DDS]) hardeners. The addition of BE resulted in an increase in T_g in all tested blends. Blends with 50 wt% BE cured with TETA demonstrated an increase in flexural modulus and flexural strength, while preserving the elongation. Blends with 40 wt% BE cured with PEA4 and 50 wt% BE cured with DDS resulted in a significant enhanced tensile elongation. The shear strength of all cured systems decreased moderately with the addition of BE exhibiting a mixed mode failure. Analysis of the fracture morphology using electron microscopy supported the increase of toughness levels as a result of incorporating BE to conventional epoxy. A unique nodular and rough fracture morphology was obtained, which is related to a toughening mechanism caused by the addition of BE. It was concluded that blends of BE and conventional epoxy could be used as structural adhesives having high T_g, enhanced mechanical properties and increased toughness. POLYM. ENG. SCI., 59:206–215, 2019. © 2018 Society of Plastics Engineers     

Thermal Properties,Fracture Toughness and Water Absorption of Epoxy-Palm Oil Blends

Epoxidized palm oil (EPO) was blended with cycloaliphatic epoxide, epoxy novolac and diglycidyl ethers of bisphenol-A. The fracture toughness and thermal properties of epoxy/EPO blends were characterized using single-edge notched bending tests and differential scanning calorimetry. Increased EPO loading improved the fracture toughness (K _IC ) of the epoxy blends. The epoxy blends with higher EPO loading exhibited higher degree of conversion. The glass transition temperature (T _g ) of the epoxy blends shifted to higher temperature as the increasing of DSC heating rate. Water absorption caused T _g reduction of epoxy blends but it was determined that the water molecules absorbed were totally reversible.     

Mode I and Mode II delamination resistance and mechanical properties of woven glass/epoxy–PU IPN composites

The effect of polyurethane on the mechanical properties and Mode I and Mode II interlaminar fracture toughness of glass/epoxy composites were studied. Polyurethanes (PU) synthesized using polyols and toluene diisocyanate were employed as modifier for epoxy resin by forming interpenetrating polymer network. The PU/Epoxy IPN was used as matrix material for GFRP. PU modified epoxy composite laminates having varying PU contents were prepared. The effect of PU content on the mechanical properties like interlaminar fracture toughness (Mode I, G_1c and Mode II, G_IIc), tensile strength, flexural strength, and Izod impact strength were studied. The morphological studies were conducted on the fractured surface of the composite specimen by scanning electron microscopy (SEM). Tensile strength, flexural strength, and impact strength of PU‐modified epoxy composite laminates were found to increase inline with interlaminar fracture toughness (G_1c and G_IIc) with increasing PU content to a certain limit and then it was found to decrease with increase in PU content. It was observed that toughening of epoxy with PU increases the Mode I and Mode II delamination toughness up to 17 and 120% higher than that of untoughened composite specimen, respectively. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

The physical and mechanical properties of beta‐nucleated polypropylene/montmorillonite nanocomposites

Polypropylene (PP) and polypropylene/polypropylene‐g‐maleic anhydride/ organomontmorillonite (PP/PP‐g‐MA/OMMT) nanocomposites were modified with 0.05 to 0.3% (w/w) of the aryl amide β‐nucleator to promote the formation of hexagonal crystal modification (β‐phase) during melt crystallization. The nonisothermal crystallization behavior of PP, PP/PP‐g‐MA/OMMT and β‐nucleated PP/PP‐g‐MA/OMMT nanocomposites were studied by means of differential scanning calorimetry. Structure‐property relationships of the PP nanocomposites prepared by melt compounding were mainly focused on the effect and quantity of the aryl amide nucleator. The morphological observations, obtained from scanning electron microscopy, transmission electron microscopy and X‐ray diffraction analyses are presented in conjunction with the thermal, rheological, and mechanical properties of these nanocomposites. Chemical interactions in the nanocomposites were observed by FT‐IR. It was found that the β‐crystal modification affected the thermal and mechanical properties of PP and PP/PP‐g‐MA/OMMT nanocomposites, while the PP/PP‐g‐MA/OMMT nanocomposites of the study gained both a higher impact strength (50%) and flexural modulus (30%) compared to that of the neat PP. β‐nucleation of the PP/PP‐g‐MA/OMMT nanocomposites provided a slight reduction in density and some 207% improvement in the very low tensile elongation at break at 92% beta nucleation. The crystallization peak temperature (T_cp) of the PP/PP‐g‐MA/OMMT nanocomposite was slightly higher (116°C) than the neat PP (113°C), whereas the β‐nucleation increased the crystallization temperature of the PP/PP‐g‐MA/OMMT/aryl amide to 128°C, which is of great advantage in a commercial‐scale mold processing of the nanocomposites with the resulting lower cycle times. The beta nucleation of PP nanocomposites can thus be optimized to obtain a better balance between thermal and mechanical properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Functionalized graphene sheets‐epoxy based nanocomposite for cryotank composite application

Multifunctional high performance functionalized graphene sheets (FGSs) based epoxy nanocomposites were investigated to understand the feasibility that these FGSs‐epoxy nanocomposites can be applied to cryotank composite applications. The FGSs were successfully synthesized from graphite flakes through preparing graphite oxides by oxidizing graphite flakes first and next, thermally exfoliating the formed graphite oxides. These high performance FGSs were next incorporated into epoxy matrix resin system to generate the uniformly dispersed FGSs reinforced epoxy nanocomposites. The resultant FGSs‐epoxy nanocomposites significantly enhanced resin strength and toughness about 30–80% and 200–700% at room and low temperatures of −130°C, respectively, and reduced the coefficient of thermal expansion (CTE) of polymer resin at both below and above T_g about 25% at loading of 1.6 wt% FGSs, and increased T_g of polymer resin about 8°C at low loading of 0.4 wt% FGSs without deteriorating their good processability. We found that these significantly improved properties of FGSs‐reinforced epoxy nanocomposite were closely associated with high surface area and wrinkled structure of the FGSs. The further optimization will result the high performance FGSs‐epoxy nanocomposite suitable for use in the next generation multifunctional cryotank carbon fiber reinforced polymer (CFRP) composite applications, where better microcrack resistance and mechanical and dimensional stability are needed. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Properties of a reactive‐graphitic‐carbon‐nanofibers‐reinforced epoxy

Our previous studies showed that herringbone graphitic GNFs surface‐derivatized with reactive linker molecules bearing pendant primary amino functional groups capable of binding covalently to epoxy resins. Of special importance, herringbone GNFs derivatized with 3,4′‐oxydianiline (GNF‐ODA) were found to react with neat butyl glycidyl ether to form mono‐, di‐, tri‐, and tetra‐glycidyl oligomers covalently coupled to the ODA pendant amino group. The resulting reactive GNF‐ODA (butyl glycidyl)_n nanofibers, r‐GNF‐ODA, are especially well suited for reactive, covalent incorporation into epoxy resins during thermal curing. Based on these studies, nanocomposites reinforced by the r‐GNF‐ODA nanofibers at nanofiber loadings of 0.15–1.3 wt% were prepared. Flexural property of cured r‐GNF‐ODA/epoxy nanocomposites were measured through three‐point‐bending tests. Thermal properties, including glass transition temperature (T_g) and coefficient of thermal expansion (CTE) for the nanocomposites, were investigated using thermal mechanical analysis. The nanocomposites containing 0.3 wt% of the nanofibers gives the highest mechanical properties. At this 0.3‐wt% fiber loading, the flexural strength, modulus and breaking strain of the particular nanocomposite are increased by about 26, 20, and 30%, respectively, compared to that of pure epoxy matrix. Moreover, the T_g value is the highest for this nanocomposite, 14°C higher than that of pure epoxy. The almost constant change in CTEs before and after T_g, and very close to the change of pure epoxy, is in agreement with our previous study results on a chemical bond existing between the r‐GNF‐ODA nanofibers and epoxy resin in the resulting nanocomposites. POLYM. COMPOS., 28:605–611, 2007. © 2007 Society of Plastics Engineers