Alkoxysilane functionalized polycaprolactone/polysiloxane modified epoxy resin through sol-gel process

Incorporating elastic polysiloxane and/or an inorganic silica network in epoxy resin could result in the enhancement of physico-chemical properties due to the existence of Si-O bonds. To improve the compatibility between polysiloxane and epoxy matrices and intensively strengthen the properties of the modified system, here polysiloxane was introduced into epoxy resin through compatibilizing epoxy-immiscible polysiloxane with epoxy-miscible polycaprolactone segments via a sol-gel process. To fulfill the process, a blend containing alkoxysilane-functionalized polycaprolactone/polydimethylsiloxane (PCS-2Si) was firstly synthesized using direct nucleophilic addition between -OH groups of polydiol and -NCO of a silane. And then a series of modified epoxy resins were prepared in different epoxy/PCS-2Si weight ratios. All the modified composites were characterized by conventional methods, and their morphological, thermal degradation and surface properties were studied. The results showed that increasing the PCS-2Si content caused the changes of miscibility between epoxy and polysiloxane. Also, the thermal stability of the modified composites was greatly improved. As for the temperature value at 5% weight loss, it reached to 308.5 °C for the composite containing 50-60% (wt%) PCS-2Si, over 150 °C higher than that for neat amine-cured epoxy resin. Similarly, the modified composites showed good hydrophobicity. The improvement of these properties came from the improved interaction between PCS-2Si and epoxy, the forming of Si-O-Si network and the enrichment of siloxane chains on the surface of films. Therefore, it is believed that this modified epoxy appears promising as new high performance and highly functional materials.     

The absence of size-dependency in flame retarded composites containing low-melting organic-inorganic glass and clay: Comparison between micro- and nanocomposites

Due to optimised processing of epoxy based composite materials containing a low-melting organic-inorganic glass together with an organo clay, the size of the glass particles could be successfully reduced. Thus truly nano-dispersed composites were obtained, with glass particles in the range of 10 nm to 200 nm. The small particle size allowed efficient interaction of glass particles and organo clay layers. The flame retardancy as well as the thermo-mechanical properties were tested, and the results showed that the low-melting glass led to a remarkable reduction of peak heat release rate by forming an enhanced barrier layer. Nevertheless no further improvement could be achieved by lowering the particle size to the nanometre region. For good flame retardancy a microdispersion of the low-melting glass was already sufficient.     

Studies on the synthesis and curing of epoxidized novolac vinyl ester resin from renewable resource material

Cardanol-based epoxidized novolac vinyl ester resin (CNEVER) was synthesized by reacting cardanol-based epoxidized novolac (CNE) resin and methacrylic acid (MA) (CNE:MA molar ratio 1:0.9) in presence of triphenylphosphine as catalyst at 90 °C. The CNE resin was prepared by the reaction of cardanol-based novolac-type phenolic (CFN) resin and epichlorohydrin, in basic medium, at 120 °C. The CFN resin was synthesized by reacting cardanol (C) and formaldehyde (F) (C/F ratio = 1:0.7) with p-toluene sulphonic acid (PTSA) as catalyst (0.5 wt.%) at 120 °C for 7 h. The resin products were analyzed by Fourier-transform infra-red (FTIR) and nuclear magnetic resonance (NMR) spectroscopic analysis. The number-average molecular weight of the prepared CNEVER was found to be 859 gmol⁻¹ as determined by gel permeation chromatographic (GPC) analysis. The resin was cured by using the mixture of resin, benzoyl peroxide, and styrene at 120 °C. The CNEVER resin was found to be cured in 60 min at 120 °C. Differential scanning calorimetric (DSC) technique was used to investigate the curing behaviour. Single step mass loss in dynamic thermogravimetric (TG) trace of CNEVER was observed. Thermal stability of the vinyl ester sample containing 40 wt.% styrene was the highest amongst all other prepared systems.     

Friction and wear behavior of PI and PTFE composites for ultrasonic motors

High‐performance polymer‐based frictional materials have become increasingly important to improve the mechanical output properties of ultrasonic motors. This study discussed the friction and wear behavior of 2 dominating frictional materials of polymer composites for ultrasonic motors, polyimide (PI), and polytetrafluoroethylene (PTFE) filled by aramid fibers (AF) and molybdenum disulfide (MoS₂). To explore the wear mechanisms, the tribo‐pair contact stress was theoretically characterized, and the interface temperature rise was numerically predicted. The predictions showed that the flash temperature on asperity tips could reach the glass transition temperature of the polymer materials. The experimental results indicated that the contact stress and sliding speed have a small effect on the friction of the PI composite but influence considerably the friction of the PTFE composite. A higher contact stress brings about a higher specific wear rate, but a higher sliding speed reduces the wear rate. Compared with AF/MoS₂/PTFE, the AF/MoS₂/PI has much better tribological performance under high loads and speeds.     

Low velocity impact and pseudo-ductile behaviour of carbon/glass/epoxy and carbon/glass/PMMA hybrid composite laminates for aircraft application at service temperature

Carbon/glass hybrid composite (CGHC) laminates are some of the most promising composites for lightweight applications. Sometimes these laminates are used in warm environment, such as aircraft frame structures, and this may affect their performance. In order to investigate this issue, the present research aims to study the effect of temperatures on the impact behavior and pseudo-ductile behaviour of CGHC in presence of different types of thermosets “epoxy” and thermoplastic “acrylic poly-methyl methacrylate-PMMA”. The experiments were started with making of CGHC laminates from different stacking sequences of unidirectional carbon and woven glass fibre layers, using a vacuum-assisted resin transfer method followed by curing treatment. In addition to CGHC laminates, four other neat batches (Carbon/epoxy, Carbon/PMMA, Glass/epoxy, Glass/PMMA) were prepared for comparison. The low velocity impact behaviour of the fabricated panels was evaluated at high temperatures (60 °C and 80 °C) according to ISO 6603-2 standard, using drop tower, while pseudo-ductile behaviour and ductility index (DI) of the specimens were estimated based on the measured total energy and elastic energy. Also, the low-velocity impact response was modeled mathematically based on a modified energy-balance model to predict the absorbed energies. Finally, the failure mechanisms were examined using optical microscope to determine the influence of these damage growth on DI of the composites under different temperatures. The results showed that the impact energy response of both hybrid composites i.e. epoxy and PMMA was stable even as the temperature rose, however, carbon/glass/PMMA exhibited better performance compared with carbon/glass/epoxy with an increase in impact energy response estimated at 50% (25 °C) and 53% (80 °C). Also, the pseudo-ductile phenomenon was strongly evident, which facilitates the predictablility of failure.     

Nonaqueous synthesis of nanosilica in epoxy resin matrix and thermal properties of their cured nanocomposites

Nonaqueous synthesis of nanosilica in diglycidyl ether of bisphenol‐A epoxy (DGEBA) resin has been successfully achieved in this study by reacting tetraethoxysilane (TEOS) directly with DGEBA epoxy matrix, at 80 °C for 4 h under the catalysis of boron trifluoride monoethylamine (BF₃MEA). BF₃MEA was proved to be an effective catalyst for the formation of nanosilica in DGEBA epoxy under thermal heating process. FTIR and ²⁹Si NMR spectra have been used to characterize the structures of nanosilica obtained from this direct thermal synthetic process. The morphology of the nanosilica synthesized in epoxy matrix has also been analyzed by TEM and SEM studies. The effects of both the concentration of BF₃MEA catalyst and amount of TEOS on the diameters of nanosilica in the DGEBA epoxy resin have been discussed in this study. From the DSC analysis, it was found that the nanosilica containing epoxy exhibited the same curing profile as pure epoxy resin, during the curing reaction with 4,4′‐diaminodiphenysulfone (DDS). The thermal‐cured epoxy–nanosilica composites from 40% of TEOS exhibited high glass transition temperature of 221 °C, which was almost 50 °C higher than that of pure DGEBA–DDS–BF₃MEA‐cured resin network. Almost 60 °C increase in thermal degradation temperature has been observed during the TGA of the DDS‐cured epoxy–nanosilica composites containing 40% of TEOS. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 757–768, 2006     

Carbon nanotube—chalcogenide glass composite

This article describes the preparation of multi-walled carbon nanotube—chalcogenide glass composite by direct synthesis and the melt-quenching method. The carbon nanotubes—chalcogenide glass composite was characterized by high-resolution transmission electron microscopy (HRTEM), TEM/energy-dispersive X-ray spectroscopy, low energy electron excited X-ray spectroscopy, Raman spectroscopy, spectroscopic ellipsometry, microhardness, and impedance spectroscopy. CNTs-AgAsS₂ glass composite possess highly increased ionic conductivity, from σ_25 °C=4.38±0.0438×10⁻⁶ to σ_25 °C=6.57±0.0657×10⁻⁶ S cm⁻¹ and decreased refractive index from n=2.652 to 2.631 at the wavelength λ=1.55 μm.     

Surface molecular characterisation of different epoxy resin composites subjected to UV accelerated degradation using XPS and ToF-SIMS

Epoxy resin composites reinforced with E-glass (E), 3D glass (3D) and carbon fibre (CF) were subjected to an intense UV and high temperature accelerated degradation environment. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to provide a molecular characterisation of the surface of the degraded composites. The response at the surface of the epoxy resin composites to oxidative degradation is influenced by the composite reinforcement type and characteristics. XPS results indicate that 3D resin composites exhibit more surface oxidation as a result of the accelerated degradation in comparison with E and CF composites. Principal components analysis (PCA) of the ToF-SIMS positive ion spectra showed that E and 3D resin composites suffered chain scission while CF composites suffered chain scission and cross-linking reactions as a result of the intense UV exposure. The extent of the surface oxidation, cross-linking/condensation reaction and loss of low molecular weight (lower than C₄H_x) aliphatic hydrocarbons may be indicated using PCA of both the ToF-SIMS positive and negative ion spectra. PCA also provides insight for proposing epoxy resin chain scission and oxidation reaction mechanisms.     

Determination of 232Th in seawater by ICP-MS after preconcentration and separation using a chelating resin

This article describes an analytical method for the separation, preconcentration and determination of ²³²Th in seawater samples at sub-ng/L levels using a NOBIAS CHELATE PA1 resin and a sector field (SF) inductively coupled plasma mass spectrometer (ICP-MS). The resin showed excellent adsorption of ²³²Th at a low pH of 2.4 ± 0.4 in a relatively small volume (200 mL) of seawater. ²³²Th adsorbed on the resin was easily eluted using 5 mL of 0.8 M HNO₃. An enrichment factor of 40 was achieved for ²³²Th analysis. Ethylenediamine-tetraacetic acid disodium salt dehydrate (EDTA) was used to investigate the effect of ²³²Th-binding organic ligand on the retention of ²³²Th on the chelating resin. Results obtained using acidified samples (pH of 2.4 ± 0.4) showed EDTA had no significant effect on ²³²Th recovery, indicating that at this low pH, ²³²Th was dissociated from the ²³²Th-binding organic ligand and quantitatively retained on the NOBIAS CHELATE PA1 resin. The developed analytical method was characterized by a separation and preconcentration taking approximately 4 h and a low detection limit of 0.0038 ng/L for ²³²Th, and was successfully applied to the determination of ²³²Th in seawater samples collected from coastal areas, Japan.     

Chemorheological analysis of a gelled resol resin curing under non-isothermal conditions by shear strain

The chemorheological behavior of curing of a resol resin was analyzed under non-isothermal conditions beyond the gelation point. Two heating ramps (0.5 and 1 °C/min) from 0 to 100 °C were performed. The rheological measurements of the resin were performed using oscillatory shear strain. The obtained profiles for the resin’s complex viscosity were applied, after treatment by two calculation methods, to the four- and six-parameter Arrhenius models. These models allow one to establish the viscous flow region of the resin and the kinetic parameters of the material’s curing process. The six-parameter Arrhenius model was selected as the best method for modeling of the resin’s rheological behavior during its curing process. The viscous-flow activation energies determined for the gelled resol resin curing were 67.1 and 58.3 kJ/mol for the 0.5 and 1 °C/min heating rates, respectively. The activation energies of the resin curing process were 41.7 and 67.0 kJ/mol for each temperature ramp.     

石墨烯改性树脂基复合材料力学性能研究进展

树脂基复合材料具有比强度高、比模量大、耐高温、耐腐蚀、质轻等诸多优点,在航天军工、生物医疗、电子封装、体育器材等众多领域得到广泛应用。石墨烯作为一种典型的二维纳米材料,凭借其独特结构以及优异的物理化学性能而备受关注。近年来的研究表明石墨烯可以通过对增强纤维改性和对基体树脂改性的方法来提高树脂基复合材料的力学性能。本文介绍了石墨烯改性树脂基复合材料的增强增韧机理,对石墨烯改性纤维(碳纤维、玻璃纤维、芳纶纤维)增强复合材料以及树脂的改性方法进行了综述;着重阐述了石墨烯改性树脂基复合材料力学性能的研究进展,分析了石墨烯改性树脂基复合材料研究中依旧存在的两大问题,即石墨烯的分散性和界面结合问题,并对石墨烯改性树脂基复合材料的未来发展前景进行了展望。     

Structural and morphological properties of silver nanoparticles–phosphate glass composites

New types of composite materials belonging to the (100 − x) [50P₂O₅ · 30CaO · 20Na₂O]xAg₂O glasses system with 0 ? x ? 0.25 are obtained. Their local structure is analyzed with the help of Raman and infrared spectroscopy and it was found that the glasses structure is built up from predominantly ionic phosphate units. UV–VIS absorption measurements performed on the samples reveal the existence of silver nanoparticles within the soda–calcium-phosphate glass matrix. The electronic absorption spectra and TEM pictures analyses indicate the presence of silver nanoparticles of almost spherical shapes and various sizes inside the glass matrix, depending on the Ag₂O content. By using the experimental UV–VIS data and a theoretical approach important structural and morphological parameters, such as the radius of the silver nanospheres and the volume fraction of the spheres are determined for one of the investigated composites (x = 0.05 mol%).     

Microscopic morphology of blends between a new “all-acrylate” radial block copolymer and a rosin ester resin for pressure sensitive adhesives

With the goal of developing new pressure sensitive adhesive systems, the miscibility and the phase morphology of blends between novel symmetric four-arm star “all-acrylate” block copolymers synthesized by atom transfer radical polymerization (ATRP) and a rosin ester resin tackifier was studied with a combined differential scanning calorimetry (DSC) and atomic force microscopy (AFM) approach. Copolymer-resin compositions with increasing resin content in the blend were studied. The DSC results show good miscibility for compositions lower than 60 wt%, with a single glass transition at a temperature between those of the two pure compounds. The AFM results indicate that the initial two-phase morphology typical of the block copolymer matrix is preserved up to 60 wt% of resin. Above that value, a third phase, attributed to aggregates of the pure resin, is observed. Upon ageing, the homogeneous systems (e.g., blends with 40 wt% of resin) undergo a slow migration of the tackifying resin towards the surface of the sample, which can be understood in terms of surface free energy considerations. This eventually leads to the formation of a layer of pure resin at the surface.     

Enhancement of water barrier properties and tribological performance of hybrid glass fiber/epoxy composites with inclusions of carbon and silica nanoparticles

Water barrier properties and tribological performance (hardness and wear behavior) of new hybrid nanocomposites under dry and wet conditions were investigated. The new fabricated hybrid nanocomposite laminates consist of epoxy reinforced with woven and nonwoven tissue glass fibers and two different types of nanoparticles, silica (SiO₂) and carbon black nanoparticles (C). These nanoparticles were incorporated into epoxy resin as a single nanoparticle (either SiO₂ or C) or combining SiO₂ and C nanoparticles simultaneously with different weight fractions. The results showed that addition of carbon nanoparticles with 0.5 and 1 wt% resulted in maximum reduction in water uptake by 28.55% and 21.66%, respectively, as compared with neat glass fiber reinforced epoxy composites. Addition of all studied types and contents of nanoparticles improves hardness in dry and wet conditions over unfilled fiber composites. Under dry conditions, maximum reduction of 47.26% in weight loss was obtained with specimens containing 1 wt% carbon nanoparticles; however, in wet conditions, weight loss was reduced by 17.525% for specimens containing 0.5 wt% carbon nanoparticles as compared with unfilled fiber composites. Diffusion coefficients for different types of the hybrid nanocomposites were computed using Fickian and Langmuir models of diffusion. Copyright © 2017 John Wiley & Sons, Ltd.     

Mechanical properties of polymer composites based on commercial epoxy vinyl ester resin and glass fiber

The effect of the addition of methyl ethyl ketone peroxide (MEKP) and cobalt naphthenate (CoNaph) on the mechanical behavior of epoxy vinyl ester resin (EVER) laminates has been investigated by using a factorial experimental design, in which the MEKP and NaphCo contents were varied. Previous results showed that there is an interaction effect between the process variables analysed on the mechanical properties evaluated. It was also observed that the MEKP/CoNaph ratio affected the tensile behavior of the EVER/glass fiber composites.     

Preparation and thermal stability of boron-containing phenolic resin/clay nanocomposites

In order to further improve thermal stability of the phenolic resins, we combined boron and clay with phenolic resins to prepare nanocomposites (BH-B, BP-B, and BE-B series). Boron-containing phenolic resin/clay (montmorillonite) nanocomposites were prepared using in situ polymerization of resol-type phenolic resins. Montmorillonite (MMT) was modified by benzyldimethylhexadecylammonium chloride (BH), benzyldimethyphenylammonium chloride (BP), and benzyltriethylammonium chloride (BE). X-ray diffraction measurements and transmission electron microscope (TEM) observations showed that clay platelets were partially exfoliated after complete curing of the phenolic resins. Thermogravimetric analysis showed that thermal decomposition temperatures (T_d) and residual weight at 790 °C of cured boron-containing nanocomposites were much higher than the corresponding nanocomposites without boron. For example, the rise in decomposition temperature of BE-B10% is about 42 °C (from 520 to 566 °C), whereas the increase in char yields is 6.4% (from 66.2% to 72.6%). However, the boron-containing composites were more prone to absorb moisture (ca. 9-14%) than boron-free ones (ca. 3-4%), which was attributed to unreacted or partially reacted boric acid during preparation process.     

A solid phase extraction using a chelate resin immobilizing carboxymethylated pentaethylenehexamine for separation and preconcentration of trace elements in water samples

A chelate resin immobilizing carboxymethylated pentaethylenehexamine (CM-PEHA resin) was prepared, and the potential for the separation and preconcentration of trace elements in water samples was evaluated through the adsorption/elution test for 62 elements. The CM-PEHA resin could quantitatively recover various elements, including Ag, Cd, Co, Cu, Fe, Ni, Pb, Ti, U, and Zn, and rare earth elements over a wide pH range, and also Mn at pH above 5 and V and Mo at pH below 7. This resin could also effectively remove major elements, such as alkali and alkaline earth elements, under acidic and neutral conditions. Solid phase extraction using the CM-PEHA resin was applicable to the determination of 10 trace elements, Cd, Co, Cu, Fe, Mn, Mo, Ni, Pb, V, and Zn, in certified reference materials (EnviroMAT EU-L-1 wastewater and ES-L-1 ground water) and treated wastewater and all elements except for Mn in surface seawater using inductively coupled plasma atomic emission spectrometry. The detection limits, defined as 3 times the standard deviation for the procedural blank using 500 mL of purified water (50-fold preconcentration, n = 8), ranged from 0.003 μg L⁻¹ (Mn) to 0.28 μg L⁻¹ (Zn) as the concentration in 500 mL of solution.     

Chemorheological study of the curing kinetics of a phenolic resol resin gelled

The changes in the resin viscosity, conductivity, mass, and enthalpy during curing reactions have been studied to obtain kinetic parameters that allow modeling of the resin behavior throughout its industrial application. In this work, isothermal rheological tests of a phenolic resol resin were performed in order to study its complex viscosity during crosslinking reactions. Samples were prepared by a precuring treatment in a heated plate press to reach gel point of the resin. Rheological analyses of resol resin curing were carried out at five different temperatures (80-100 °C), and the kinetic models of Arrhenius and Kiuna were applied. The resol resin curing presented an activation energy of 72.1 kJ/mol according to the Arrhenius model. The Kiuna model was proposed to fit the non-linear evolution of the resin’s complex viscosity at the highest temperatures. This kinetic model was suitable for predicting the changes in the complex viscosity of the resol resin after its gelation, and the process activation energy obtained for the second order polynomial applied in this model was 88.1 kJ/mol. In addition, the profile for the degree of curing of resol resin was determined from measurements of the material’s elastic modulus.     

An investigation of the accelerated thermal degradation of different epoxy resin composites using X-ray microcomputed tomography and optical coherence tomography

Epoxy resin composites reinforced with hollow glass microspheres, microlight microspheres, 3D parabeam glass, and E-Glass individually were subjected to accelerated thermal degradation conditions. X-ray microcomputed tomography (XμCT) was used to evaluate density changes, reinforcement filler damage, homogeneity, cracks and microcracks in the bulk of the different epoxy resin composites. XμCT 3D images, 2D reconstructed images and voids calculations revealed microspheres damage, filler distributions and showed cracks in all composites with different shapes and volume in response to the thermal degradation conditions. In addition, expansion of air bubbles/voids was observed and recorded in the microsphere and microlight epoxy composite samples. In a complementary way, optical coherence tomography (OCT) was used as a novel optical characterisation technique to study structural changes of the surface and near-surface regions of the composites, uncovering signs of surface shrinkage caused by the thermal treatment. Thus, combining XμCT and OCT proved useful in examining epoxy resin composites' structure, filler-resin interface and surface characteristics.     

Synthesis and processing of model compound of PMR-15 resin

Aerospace industries have been concerned since long by composite materials using high-performance resins. The PMR-15 resin is now the most commonly used resin for industrial applications at high temperature, i.e., 300°C. Despite its comparative commercial success, the PMR-15 resin and its composites show several disadvantages [toxicity of the aromatic diamine (MDA), poor conservation of monomers solution, laminate microcracking]. The purpose of this work concerns the synthesis, the physico-chemical characterization, and the processing of pure bisnadimide model compound to study the endo/exo isomerization of the endcaps and thermomechanical properties. We show that the isomerization mechanism proceeds by retro Diels-Alder reaction followed by recombination in exo isomer and glass temperature transition is upper than 350°C (380°C). © 1997 John Wiley & Sons, Inc.