Multi-walled carbon nanotubes functionalized with triethylenetetramine as fillers to enhance epoxy dimensional thermal stability

Multi-walled carbon nanotubes (MWCNT) have been used as fillers to improve thermal properties such as glass transition temperature (T _g) of epoxy materials. In this work, nanocomposites based on diglycidyl ether of bisphenol A resin and triethylenetetramine (TETA) were prepared by a three-roll mill process with TETA-functionalized (MWCNT–COTETA) and neat MWCNT. Thermogravimetric analysis of the nanofillers showed that in the case of MWCNT–COTETA, there is a 15 % mass loss that can be attributed to –COTETA and residual oxygen-containing functional groups. The influence of chemical modification on the behavior of the glass T _g was evaluated by dynamic scanning calorimetry. The MWCNT–COTETA allowed a ~20 °C reproducible increase of T _g in concentrations in the range of 0.5–1.0 mass%. Furthermore, images obtained by scanning electron microscopy were used to investigate the morphology of the polymer matrix and its interfaces. The quality of the dispersion and interaction of the nanotubes in the epoxy matrix was assessed from the images. Both the neat epoxy and the nanocomposite with MWCNT showed low thermal shrinkage upon curing.     

Ball milling: An effective technique for the preparation of exfoliated clay filled unsaturated polyester toughened epoxy nanocomposite

This paper investigates the possibility of improving the mechanical and thermal properties of epoxy and unsaturated polyester toughened epoxy resins through the dispersion of octadecyl ammonium ion-exchanged montmorillonite (organoclay) through exfoliated mechanism. The nanocomposites prepared are characterized for their structural change and studied for their crystallite size, mechanical, thermal and water absorption (hydrophilicity) properties. The mechanical data indicates significant improvement in the flexural and tensile properties over the neat epoxy and UP-epoxy matrix according to the percentage content of organoclay. The thermal behavior too shows noticeable enhancement in glass transition temperature T _g and high thermal stability. Hydrophilicity of all the composites decreases irrespective of the concentration of organoclay on the epoxy and UP-epoxy matrices. The homogeneous morphology of epoxy and UP toughened epoxy nanocomposite hybrid systems is ascertained using scanning electron microscope (SEM). X-ray results point out that the cetyl ammonium modified clay filled composites exhibited the exfoliated structure.     

Viscoelasticity and thermal stability of polylactide composites with various functionalized carbon nanotubes

Polylactide (PLA) nanocomposites containing various functionalized multi-walled carbon nanotubes (MWCNTs) were prepared directly by melt compounding. The linear rheology and thermal stability of the PLA nanocomposites were, respectively, investigated by the parallel plate rheometer and TGA, aiming at examining the effect of surface functionalization on the dispersion of MWCNTs by using viscoelastic and thermal properties. Among three MWCNTs used in this work, the carboxylic MWCNTs present better dispersion in PLA matrix than the hydroxy and purified MWCNTs because the corresponding composite shows the lowest rheological percolation threshold, which is further confirmed by the TEM and solution experiments. The presence of all these three MWCNTs, however, nearly cannot improve the thermal stability effectively at the initial stage of degradation and the temperature corresponding to a weight loss of 5 wt% (T_5 wt%) only shows slight increase in contrast to that of the neat PLA while with increase of decomposition level, the presence of carboxylic and purified MWCNTs retards the depolymerization of PLA evidently, showing remarkable increase in the temperature corresponding to maximum rate of decomposition (T_max). Both the dispersion state and the surface functionalization of MWCNTs are very important to the thermal stability of PLA matrix.     

Thermal and dielectric characterization of multi-walled carbon nanotubes−thermoplastic polyurethanes composites

Multi-walled carbon nanotubes–thermoplastic polyurethanes composites were characterized by means of differential scanning calorimetry and dielectric relaxation spectroscopy. The composite is characterized by two glass transition temperatures T _g . The T _g associated with the soft segment decreases by increasing of carbon nanotubes content, while carbon nanotubes content has practically no effect on the value of the T _g associated with the hard segments. It was observed that rising the temperature and carbon nanotubes content resulted in the increased of both the dielectric permittivity and the loss factor. The presence of carbon nanotubes produces an enhancement of charge carriers trapping, increasing the electrical conductivity. The electrical conductivity of the composite was found to exhibit an insulator to conductor transition at a carbon nanotubes critical content, i.e., the percolation threshold, near 6 wt %.     

Carbon nanotube–polyurethane shape memory nanocomposites with low trigger temperature

Ester-based polyurethane (PU) with low glass transition temperature was used to develop shape memory nanocomposites with low trigger temperature. Pristine carbon nanotubes (CNTs) and oxidized CNTs (ox-CNTs) were introduced by melt mixing to improve the mechanical and shape memory properties of the PU matrix. The dispersion of CNTs on the mechanical properties and shape memory behaviors of the nanocomposites were also investigated. The results show that better dispersion of ox-CNTs contributes to more stiffness effect below glass transition temperature (T_g) while lower storage modulus (E′) above T_g. The nanocomposites exhibit high shape fixity and recovery ratio above 98%. The ox-CNT/PU nanocomposite shows higher shape recovery ratio for the first cycle, faster recovery due to better dispersion of CNTs and have potential applications for controlling tags or proof marks in the area of frozen food. The trigger temperature can be tailored by controlling the T_g of the PU matrix or the content of the nanofillers.     

Thermogravimetric, differential scanning calorimetric and experimental thermal transport study of MWCNT/NBR nanocomposites

Pristine multiwalled carbon nanotubes (MWCNTs) were impregnated in acrylonitrile butadiene rubber (NBR) using internal dispersion kneader and two roller mixing mill to investigate the effects of various nanotubes concentrations on the thermal transport/stability of rubber nanocomposites. Thermal conductivity (λ _N) and thermal impedance (R) measurement experimental setups were established according to ASTM E1225-99 and D5470-03. The 1 mass % addition of MWCNTs in the polymer matrix has enhanced R up to 44 % and reduced λ _N of the rubber nanocomposite up to 40 % compare to the base composite formulation. Thermal decomposition and differential thermal analyses of the fabricated composite specimens simulate that the thermal stability and endothermic capability are augmented with increasing the nanotubes contents in the host matrix. The progressive incorporations of carbon nanotubes into the rubber matrix have efficiently influenced the composite specimens regarding glass transition, crystallization, and melting temperatures including their specific enthalpies. Scanning electron microscopy along with the energy dispersive spectroscopy was used to analyze MWCNTs dispersion in NBR matrix, compositional analysis of the nanocomposite, and impregnated nanotubes.     

Polymerized ionic liquid functionalized multi-walled carbon nanotubes/polyetherimide composites

Thin polyetherimide (PEI) films containing 0.1–3 wt.% multi-walled carbon nanotubes (MWCNTs), have been prepared from three types of MWCNTs, namely pristine, oxidized and polymerized ionic liquid (PIL) functionalized CNTs. Oxidized and PIL functionalized CNTs (CNT–PIL) showed better dispersion in the matrix compared to pristine CNTs. For CNT–PIL, alignment of CNTs has been observed in the matrix. Regardless of the type of CNTs, their incorporation led to an increased thermal stability of the polymer matrix. Dynamic mechanical analysis showed that storage modulus increased by up to 25% (3 wt.% CNT–PIL) and an increase in the height of the damping peaks (tan δ). The addition of CNTs did not have any significant influence on the tensile properties and T_g of the polymer, and the electrical conductivity did not decrease in the case of modified CNTs.     

Effect of AlN content on the performance of brominated epoxy resin for printed circuit board substrate

Polymer matrix composites, based on brominated epoxy, a type of material widely used in printed circuit boards (PCBs), as matrix and AlN particle as filler were prepared. The influences of AlN content on the mechanical, thermal, and electrical properties of the composites were investigated by uniaxial tensile test, TMA, thermal conductivity measurement, DMA, and dielectric properties measurement. It was found that the properties of composites monotonically varied with AlN content except that maximum tensile strength and strain of composites corresponded to a filler content of 10 wt %. The results of DMA also showed the AlN reinforcement was more pronounced above T_g, and the peak area of tan δ versus T curves decreased with AlN content, which implied the damping capacity of the composite gradually decreased. The increase in T_g and decrease in damping were probably due to strong interaction between the AlN and epoxy matrix inhibiting the mobility of the epoxy chain. In addition, different theoretical models reported in the literature were used to predict the E, CTE, k, and D_k, and compared with the experimental data. Finally, suitable models were recommended in the present materials system. For the significant improvement of performance of epoxy, we can conclude that these composite materials may be promising for PCB substrate. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1662–1674, 2007     

Dynamic Mechanical Properties of Activated Carbon–Filled Epoxy Nanocomposites

Nano-activated carbons obtained from oil palm empty fiber bunch (AC-EFB), bamboo stem (AC-BS), and coconut shells (AC-CNS) were reinforced in epoxy matrix to fabricate epoxy nanocomposites. The dynamic mechanical analysis of epoxy nanocomposites was carried out, and 5% AC-CNS treated with KOH-filled epoxy composites displayed the highest storage modulus of all the activated carbon–filled epoxy composites. The incorporation of a small amount of AC-BS, AC-EFB, and AC-CNS to the epoxy matrix enhanced the damping characteristics of the epoxy nanocomposites. The 5% AC-EFB treated with H₃PO₄ filled epoxy composites showed the highest glass transition temperature (T_g) in all temperature ranges.     

The chemical and dielectric properties of epoxy/(Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 composites for embedded capacitor application

The characteristics of epoxy/(Ba_0.8Sr_0.2)(Ti_0.9Zr_0.1)O₃ (BSTZ) composites are investigated for the further application in embedded capacitor device. The effects of BSTZ ceramic powder filler ratio on the chemical, physical and dielectric properties of epoxy/BSTZ composites are studied. Differential scanning calorimeter (DSC) thermal analysis is conducted to determine the optimum values of hardener agent, curing temperature, reaction heat, and glass transition temperature (T_g). The hardener reaction process starts at about 115 °C and completes at about 200 °C, for that it is appropriate to process of epoxy/BSTZ composites in the range of temperature. The highest glass transition temperature (T_g) of 155 °C is obtained at one equivalent weight ratio (hardener/epoxy). Only the BSTZ phase can be detected in the XRD patterns of epoxy/BSTZ composites. The more BSTZ ceramic powder is mixed with epoxy, the higher crystalline intensity of tetragonal BSTZ phase are revealed in the XRD patterns. The dielectric constant measured at 1 MHz increases from 5.8 to 23.6 as the content of BSTZ ceramic powder in the epoxy/BSTZ composites increases from 10 to 70 wt%. The loss tangents of the epoxy/BSTZ composites slightly increase with the increase of measurement frequency.     

高性能环氧树脂/碳纳米管复合物的热分析研究

用差示扫描量热仪(DSC)、热失重分析仪(TGA)和动态力学热分析仪(DMTA)研究了多壁碳纳米管(MWNTs)/高性能4,4′-二氨基二苯甲烷四缩水甘油环氧树脂(TGDDM)/4,4′-二氨基二苯基砜(DDS)复合物的热性能.Kissinger和Flynn-Wall-Ozawa的非等温固化动力学研究发现,随着MWNTs含量的增加,复合物固化反应的活化能先减小后增大.TGA研究表明,MWNTs的添加对环氧树脂热稳定性影响很小.碳纳米管填充到TGDDM/DDS体系后,复合物的储存模量随着MWNTs含量的增加而增大,而玻璃化温度却随之减小.     

Synthesis and properties of Fe0.83V1.17O4

Thermal properties of the organic–inorganic bicontinuous nanocomposites prepared via in situ two-stage polymerization of various silanes, epoxy, and amine monomers are investigated, and the impact of filler content and its organic compatibility on thermal stability of these nanocomposites is studied. Two series of epoxy–silica nanocomposites, namely, EpSi-A and EpSi-B containing 0–20 wt% silica, are synthesized. An epoxy–silane coupling agent is employed to improve the organic compatibility of silica in EpSi–B nanocomposites. The composites synthesized via two-stage polymerization are characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric (TG) analysis. DSC and TG/differential thermogravimetric results reveal substantially high glass transition (T _g) and excellent thermal stability of the bicontinuous nanocomposites as compared with pristine epoxy polymer. Both T _g and thermal properties, however, considerably vary depending on the organic compatibility of the nanocomposites. Significantly higher decomposition temperatures are recorded in case of EpSi-B nanocomposites owing to the chemical links between the epoxy and silica phases. Kinetic studies also show relatively higher activation energies of pyrolysis for EpSi-B nanocomposites.     

Calorimetric measurement of the maximum glass transition temperature in a thermosetting resin

The measurement of the maximum glass transitionT _g∞ of a thermosetting resin is usually performed by differential scanning calorimetry in the second scan (T _g2scan), after a previous scan by heating up the sample to a temperature where the exothermic curing reaction has been completed. However, this method can eventually produce thermal degradation, decreasing the crosslinking density and theT _g of the sample. Values ofT _g2scan between 95? and 102?C were found in an epoxy resin based on DGEBA cured with phthalic anhydride. Thermal degradation effects can be avoided if the measurement is performed by isothermal curing and further determination ofT _g. AT _g∞ value of 109?C is achieved, which is the maximum value ofT _g according to the topological limit of conversion.     

Viscoelastic properties and morphology of dicyanate ester/epoxy co-polymers modified with polysiloxane and butadiene–acrylonitrile rubbers

Dynamic mechanical analysis was conducted on specimens prepared from cyanate ester (CE) and epoxy (EP) resins cured together at various mass compositions. Increase of amount of epoxy resin in composition was shown to have a disadvantageous effect on glass transition temperature (T _g). It was shown that post-curing procedure was needed to produce a polymer matrix with a single glass transition relaxation, but increase in post-cure temperature up to 250 °C resulted in slight reduction in T _g for epoxy/cyanate copolymers. TG results proved that the presence of epoxy resin reduces thermal stability of the cyanate/epoxy materials. The neat CE and EP/CE systems containing 30 wt% of epoxy resin were modified using epoxy-terminated butadiene–acrylonitrile rubber (ETBN) and polysiloxane core–shell elastomer (PS). The scanning electron microscopy (SEM) results showed the existence of second phase of ETBN and PS modifiers. Only in the case of EP/CE composition modified with ETBN, well-dispersed second phase domains were observed. Analysis of SEM images for other CE- and EP/CE-modified systems revealed the formation of spherical aggregates.     

Fabrication of Single Wall Carbon Nanotubes-Based Poly(vinyl butyral) Nanocomposites with Enhanced Mechanical and Thermal Properties

In this research, poly(vinyl butyral) (PVB)/single wall carbon nanotubes (SWCNT) composites were prepared via solution blending method. Dispersion degree of SWCNT in the composites was characterized by Scanning Electron Microscopy (SEM) and mechanical properties were measured with tensile testing. Thermal degradation of composites was investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). SEM analysis confirmed good dispersion of the nanotubes in the PVB. The tensile tests showed significant increases in mechanical properties such as exceptional improvement in tensile strength, Young's modulus and flexibility for the composites compared to PVB at low SWCNT content.The TGA curves indicated that adding SWCNT improved the thermal stability of the PVB significantly and the degradation of the polymer matrix shifted to the higher temperatures. For the sample containing 0.6 wt%, an increase of 171% in modulus and a 258.4% enhancement of tensile strength were achieved. Also, elongation at break increased 28.7% at this loading. In fact, intrinsic properties of nanotubes caused enhancement of strength and flexibility simultaneously. Also, for this composite, T_onset and T_max enhanced remarkably and weight loss reduced greatly and residue at 600°C increased to high values. These results are promising for application of the PVB in industry.     

New strategy to reinforce and toughen composites via introducing thorns-like micro/nanofibers

In this work, we report a new strategy of introducing thorns-like fiber into composites, so that the resultant composites substantially benefit from strong fiber–matrix interface adhesion. Specifically, the “thorns” could increase in interlocking molecules chains and entangle with the surrounding matrix resin, which could impede the mobility of polymer chains, as like the roots with uplift capacity. Strong interfacial adhesion between fibers and matrices is suggested by the SEM images and the DMA studies. After the thorns-like fibers are embedded into epoxy resin, the glass transition temperature (T_g) and the storage modulus (E′) are higher than these of neat epoxy and untreated fibers-reinforced epoxy, respectively, and the flexural properties of the composites reinforced with thorns-like fibers are significantly increased. Therefore these novel three dimensional thorns-like fibers will be applicable for composite materials based upon its unique architecture, making it an attractive alternative to increase the performance of any matrix resin.     

Molding versus dispersion: effect of the preparation procedure on the capacitive and cycle life of carbon nanotubes aerogel composites

Binderless carbon nanotubes aerogel (CNAG) composites represent a new class of high-performing electrodes for energy storage applications such as electrochemical double layer capacitors. The composites developed here differ significantly from these previously prepared with dispersion processes. The CNAG material was prepared by a molding procedure that is the synthesis by a chemical vapor deposition method to grow carbon nanotubes directly onto a microfibrous carbon paper substrate. Then the carbon aerogel is synthesized on the carbon nanotubes. The key feature of the method is eliminating the need of controlling the carbon nanotube concentration, which permits optimized dispersion processes to reinforce the aerogel's networks. The CNAG electrode delivered very high specific capacitances of 524 F g⁻¹ in KOH electrolyte and 280 F g⁻¹ in H₂SO₄ electrolyte. Furthermore, this better integration of carbon nanotubes in the matrix of carbon aerogel improved its resistance to the attack by the electrolyte and conferred an excellent cycle life over 5,000 cycles of charge–discharge in both electrolytes.     

Covalent Functionalization of Single-Walled Carbon Nanotubes Through the Fluorination Stage for Integration into an Epoxy Composite

The upper limit of the elastic modulus has been estimated for a polymer–carbon nanotube–epoxy matrix nanocomposite. This limit can be achieved if the nanotubes are integrated into the matrix, i.e., they form a continuous reinforcing network inside the matrix, and if the nanotubes are single-walled or double-walled carbon nanotubes. A technique for carbon nanotube functionalization via fluorination and fluorine substitution and a technique for calculating the degree of nanotube functionalization based on reaction yield measurements are proposed. For fluorine substitution by epoxy-diane resin and diaminodiphenylmethane, the degree of functionalization is С–(FG)_x, x ~ 0.011–0.013 and the FG-molecular fragment containing the epoxy (amino) group corresponding to functionalization of ~5% of the surface С atoms of nanotubes. The control reaction showed that the epoxy groups preserve the chemical activity, while part of the amino groups are deactivated. The grafted epoxy(amino) groups ensure nanotube surface lyophilicity in epoxy composites and integrate the nanotubes into the epoxy matrix owing to the chemical bonds.     

Performance of high-temperature thermosetting polyimide composites modified with thermoplastic polyimide

The preparation of polyimide (PI) resin with high heat resistance and toughness is a significant challenge. In this study, thermoplastic PI (TPI) was used to toughen thermosetting PIs, and toughened PI (TPI/PI) blends were prepared. The modified PI resin system exhibited good thermal stability, excellent heat resistance, and high toughness. The results indicated that the TPI/PI blends maintained the curing behavior and characteristics of the PI oligomer. The T_g of the cured TPI/PI blend exceeded 395 °C, and the T_5% values were in the range of 533–563 °C, suggesting excellent thermal stability and heat resistance. The maximum impact strength was increased by 46% compared with that of pure PI, indicating the excellent toughening effect of the TPI. Carbon fiber-reinforced PI composites were prepared using the toughening system as a matrix. The compression-after-impact values of the carbon fiber-reinforced PI composites were up to 190 MPa, indicating the excellent toughness of the materials.     

TMDSC phase angle for a better nanocomposite interphase identification

The present study suggests a new approach, based on the utilization of temperature modulated differential scanning calorimetry (TMDSC) technique, for identifying and characterizing the organic?Cinorganic interphase of two materials: an epoxy?Cfumed silica nanocomposite and a thermoplastic polyurethane (TPU)?Cmultiwalled nanotube (MWNT) composite. The approach used here makes use of TMDSC data and basically consists of using the phase angle or the derivative of the reversing heat flow instead of the reversing heat flow curve itself. In the case of epoxy?Cfumed silica composites, two glass transition regions were identified. The glass transition temperature (T _g) of the composite was observed to vary as a consequence of the filler content. This study shows that the T _g variation is due to the formation of an organic?Cinorganic interphase, with its own glass transition temperature, which is different from the epoxy matrix T _g. In the case of TPU?CMWNT composites, two relaxations and an additional first order transition were observed: the first relaxation corresponds to the hard segment, the second is related to an interaction between filler and matrix and the third process may be connected to the partial melting of the hard segment. The addition of 0.5?wt% MWNT causes a small reduction in T _g of the TPU. A major nanotube addition, 10?wt%, induces the appearance of a new relaxation that may be associated with the existence of an interface. In general, a better separation between the matrix and interphase glass transitions was obtained by the TMDSC phase angle signal.