Peroxy derivatives of epoxy resins based on bisphenol A: Effects of quaternary ammonium salts

Oligomers containing peroxy groups have been synthesized on the basis of epoxides and organic hydroperoxides. Dependence of reaction rates upon the ratio of starting materials, nature, quantity, concentration of ammonium salt catalysts, temperature and also nature of hydroperoxides have been investigated. Activation energies and effective rate constants of reactions between hydroperoxides and epoxy resins were calculated. The reaction proceeds by interfacial catalysis, and therefore with poor yields in solvents which are miscible with water (acetone and 1.4-dioxane) and with good yields in immiscible solvents (chloroform and toluene). Structures of the synthesized peroxy oligomers have been confirmed by IR-spectroscopy. Received: 11 March 1999 / Reviewed and accepted: 12 March 1999     

Synthesis and properties of peroxy derivatives of phenol – formaldehyde resins

Methods of obtaining peroxy derivatives of phenol-formaldehyde resins (PhFRs) have been elaborated. Three different procedures have been pursued: i) chemical modification of PhFRs with hydroperoxides; ii) modification of PhFRs with 1.2-epoxy-3-tert-butylperoxypropane; and iii) polycondensation of peroxy phenols with formaldehyde. Structures of the resins were determined by chemical and spectroscopic methods. The results were also used to create three-dimensional networks involving an unsaturated polyester resin. IR-spectroscopy of the networks shows that, in addition to the peroxy groups and unsaturated bonds, others functional groups participate in the network formation. Received: 21 May 1999 / Reviewed and accepted: 20 July 1999     

Effects of compound curing agent on the thermo-mechanical properties and structure of epoxy asphalt

Epoxy asphalt curing system was prepared by sebacic acid compound with methyl-tetrahydrophthalic anhydride (MeTHPA) or Tung oil anhydride (TOA). Tensile strength, penetration, differential scanning calorimetry, dynamic mechanical thermal analysis, torn section microscopy photographs and scanning electron microscope analysis were utilised to investigate the mechanical properties, thermodynamic behaviour and micro-structure of epoxy asphalt curing systems under different curing agents. The results showed that in the presence of compound curing agent, the tensile strength and surface hardness of the epoxy asphalt curing system effectively improved, the induction period of the curing reaction decreased, the curing reaction mechanism turned to one-step reaction from two-step reaction, the Tg of asphalt phase and epoxy phase could simultaneously increase, and high-temperature damping performance also improved, but the particle size of asphalt dispersed in epoxy resin becomes uneven, while the curing system becomes semi-brittle from toughness. Compared to TOA, the effects of MeTHPA on such performance were more obvious.     

Functional peroxides and peroxy oligoesters on the basis of pyromellitic dianhydride

A series of peroxy oligomers has been synthesized on the basis of pyromellitic dianhydride and tetrachloroanhydride of pyromellitic acid by condensation with polyethylene glycols and tert-butylhydroperoxide. The resulting oligoesters contain two types of functional groups: carboxylic – which can participate in ionic reactions and peroxide – able to initiate certain radical processes. Concentrations of these groups depend on the method of synthesis, the nature of starting monomers, and the molecular mass of polyethylene glycol. Structures of oligoesters have been determined by IR and ¹H-NMR spectroscopy. The oligoesters are able to form three-dimensional networks when heated to 400 K. A mechanism of the network formation is proposed. These materials can be used as curing agents for unsaturated polyesters and also for epoxy + unsaturated polyester resin compositions. Electronic Publication     

硫醇@三聚氰胺甲醛树脂/环氧树脂固化剂的制备及性能表征

采用三聚氰胺-甲醛树脂(PMF)为壁材,三羟甲基丙烷三(3-巯基丙酸酯)(TMPMP)作为芯材,原位乳液聚合法制备了硫醇@三聚氰胺甲醛树脂(TMPMP@PMF)微胶囊固化剂。研究了乳化剂种类及用量,囊壁质量比,反应温度,反应时间,pH值对合成TMPMP@PMF微胶囊粒径及稳定性等影响。结果表明:当反应乳液中芯材的质量分数达到2wt%,同时芯材与壁材的单体质量比达到2∶1时,能制备出粒径在大约100μm,粒径均匀的TMPMP@PMF微胶囊。TMPMP@PMF微胶囊的结构稳定,耐热性好,并且呈闭孔结构。采用TMPMP@PMF微胶囊为固化剂,与环氧树脂(EP)基体混合配制成压敏型TMPMP@PMF/EP固化剂,发现微胶囊结构在受到外力作用时能及时破裂,室温甚至低温下都能短时间使环氧树脂固化,并且能够很好地改善固化剂的抗冲击性能。     

Effects of colloidal nanosilica on the rheological properties of epoxy resins filled with organoclay

The rheological properties of epoxy resins filled with organoclay and colloidal nanosilica were investigated by employing a parallel plate rheometer in flow mode at 25 degrees C. Shear thickening and shear thinning behaviors were observed in the epoxy resins filled with a mixture of organoclay and colloidal nanosilica. Minima were observed in the relaxation time of the systems consisting of epoxy resins filled with organoclay and colloidal silica as the content of colloidal nanosilica was increased. It seems that the colloidal nanosilica increased the mobility of the filled epoxy resins and reduced the interactions between the silicate layers in the systems.     

Relaxation behavior and nonlinear properties of thermally stable polymers based on glycidyl derivatives of quercetin

Cross-linked polymers on the basis of di-, tri and tetraglycidyl ethers of quercetin (3,3′,4′,5,7-pentahydroxyflavone) were synthesized, and then, poled in electrical field of corona discharge. Investigations of structural, thermal and optical parameters of the polymer films were carried out. It was found that the polymers obtained from di- and triglycidyl quercetin ethers had high values of macroscopic quadratic susceptibilities and substantial stability of nonlinear optical (NLO) properties after the poling. Tetraglycidyl ether of quercetin forms the polymer of lower quadratic susceptibility, which demonstrates noticeable relaxation process resulting in decrease of the NLO effect.It is supposed that the difference of the NLO properties is due to peculiarities of physical network of the polymers, namely to the ratio between numbers of hydrogen bonds formed by hydroxyl groups of chromophore fragments and by the ones of interfragmental parts of the polymeric chains.     

Studies on preparation and properties of the multi-walled carbon nanotubes (MWNTs)/epoxy nanocomposites

The MWNTs were coated with polyaniline (PANI) by in situ chemical oxidation polymerization method. FTIR spectroscopy, scanning electron microscope (SEM) and X-ray diffraction (XRD) indicated that the MWNTs were coated with PANI. The MWNTs/epoxy nanocomposites were fabricated by using the solution blending method. Differential scanning calorimetry (DSC), tensile testing, HP 4294A impedance analyzer and SEM were used to investigate the properties of the nanocomposites. The results showed that the modified carbon nanotubes were well dispersed in the polymer matrix. The nanocomposites have enhancements in mechanical, thermal and dielectric properties compare with the neat epoxy resin. The nanocomposites were proven to be a good polymer dielectric material.     

Synergistic effect of organic and inorganic nano fillers on the dielectric and mechanical properties of epoxy composites

Titanium oxide TiO₂/epoxy and TiO₂ with detonation nano-diamond (DND)/epoxy nanocomposites were prepared by using ultrasonication method. TiO₂ and DND particles as reinforcement species and epoxy as matrix were used to produce nanocomposites. The addition of DND particles into TiO₂/epoxy composite improved the dielectric and mechanical properties of nanocomposites in significant amount. The dielectric properties of TiO₂-DND/epoxy nanocomposite demonstrated increase in permittivity and conductivity after addition of the DND particles. The maximum and minimum reflection losses of TiO₂-DND/epoxy nanocomposite for 0.6 and 0.2 wt% DND loading were detected at ?14.5 and ?1.3 dB, respectively. The flexural and tensile strength of TiO₂-DND/epoxy nanocomposites with the addition of 0.4 wt% DNDs were enhanced to 220% and 223%, respectively. Additionally, the energy to break and percent break strain were 3.9 J and 3.86, respectively for 0.4 wt% DND loading in TiO₂-DND/epoxy nanocomposite. Therefore, the present work findings claim that DND particles are well suitable to enrich the dispersion of TiO₂ nanoparticles in epoxy matrix, which develops a strong load transfer interface between the nanoparticles and epoxy matrix and consequently leads to superior properties.     

Effect of DOPO units and of polydimethylsiloxane segments on the properties of epoxy resins

New flame retardant epoxy resins containing phosphorus and/or silicon atoms were prepared by the introduction into the epoxy chemical structure of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and/or of polydimethylsiloxane segments. The structure and morphology of cured epoxy resins were evaluated by Fourier transform infrared spectroscopy and scanning electron microscopy analyses, respectively. The polymers exhibited good thermal stability, having initial decomposition temperature above 310 °C. Thermogravimetric analyses and limiting oxygen index values indicated that the incorporation of DOPO units/polydimethylsiloxane segments in the polymer structure significantly enhanced flame retardancy and thermal stability of char layer at high temperature. Broadband dielectric spectroscopy measurements over a wide range of frequency and temperature revealed two subglass transitions, γ and β. The experimental data were fitted to the Havriliak–Negami and Arrhenius models, and the obtained parameters were analyzed. An α relaxation process attributed to the glass transition was observed in the high temperature and high frequency ranges. The influence of DOPO units and polydimethylsiloxane segments on the properties of the polymers was examined.     

Effects of incorporating chromium acetylacetonate in epoxy matrix on the curing behavior and mechanical properties of Gr/Ep composites

Abstract

The addition of chromium acetylacetonate in N, N, N’, N’, tetraglycidyl diaminodiphenyl methane/diaminodiphenyl sulfone/boron trifluoride‐monoethylene amine epoxy formulations for manufacturing unidirectional Gr/Ep laminates accelerated the curing reaction and increased the viscosity of resin during lamination. Differential scanning calorimetric and infrared spectroscopic results indicated that Cr(acac)₃ acted like a cocatalyst with BF₃MEA during curing. As the laminates were cured, the one incorporating 1 mol% Cr(acac)₃ exhibited the highest G_IC fracture toughness, flexural strength, and transverse tensile strength. The increased mechanical strength of the Gr/Ep laminates was due to the fact that the cohesive strength of the epoxy matrix was increased by the incorporated Cr(acac)₃.     

Effects of plasma-induced epoxy coatings on surface properties of Twaron fibers and improved adhesion with PPESK resins

This work deals with the oxygen and argon plasma-induced coating process on the surface of Twaron fibers to obtain a strong interfacial adhesion between the fibers and PPESK matrices. The epoxy coating resins applied in this study were chemically bonded with the plasma pretreated fibers, which was confirmed by X-ray photoelectron spectroscopy (XPS). The fiber surface morphologies and wettability were analyzed by scanning electron microscope (SEM) and dynamic contact angle analysis, respectively. The interfacial adhesion performance of the Twaron fiber-reinforced PPESK composite was measured by interlaminar shear strength (ILSS) and water absorption tests. The fracture mechanisms of composites were examined by SEM. The results indicated that after coating the surface wettability was improved and the ILSS had an increment of 66.1% for oxygen-plasma-induced coating and 68.9% for argon-plasma-induced coating.     

Effect of boron addition on the microstructure and mechanical properties of K4750 nickel-based superalloy

The effect of boron addition at 0,0.007 wt.% and 0.010 wt.% on the microstructure and mechanical properties of K4750 nickel-based superalloy was studied.The microstructure of the as-cast and heat-treated alloys was analyzed by SEM,EPMA,SIMS and TEM.Lamellar M₅ B₃-type borides were observed in boroncontaining as-cast alloys.After the full heat treatment,boron atoms released from the decomposition of M₅ B₃ borides were segregated at grain boundaries,which inhibited the growth and agglomeration of M₂₃C₆ carbides.Therefore,the M₂₃C₆ carbides along grain boundaries were granular in boron-containing alloys,while those were continuous in boron-free alloys.The mechanical prope rty analysis indicated that the addition of bo ron significantly improved the tensile ductility at room tempe rature and stress rupture properties at 750℃/430 MPa of K4750 alloy.The low tensile ductility at room temperature of 0 B alloy was attributed to continuous M₂₃C₆ carbides leaded to stress concentration,which provided a favorable location for crack nucleation and propagation.The improvement of the stress rupture properties of boron-containing alloys was the result of the combination of boron segregation increased the cohesion of grain boundaries and granular M₂₃C₆ carbides suppressed the link-up and extension of micro-cracks.     

Simultaneous epoxy grafting on SiO2 nanoparticles during bead milling and their effects on the mechanical properties of epoxy-based composites

Epoxy resin-grafted SiO₂ nanoparticles stabilized in toluene were successfully designed by the simultaneous surface modification of SiO₂ nanoparticles during bead milling which involves the adsorption of polyethyleneimine-oleic acid complex (PEI-OA) and epoxy resin grafting to the free amine groups of PEI-OA (PEI-OA-Epoxy). The effectiveness of epoxy grafting on the properties of the SiO₂/epoxy based nanocomposites were investigated using a bead-milled SiO₂/toluene suspension stabilized with PEI-OA, PEI-OA-Epoxy, and a complex of PEI and an anionic surfactant comprising an epoxy-soluble polyethylene glycol-based chain (PEI-AS). While SiO₂ nanoparticles were pulverized with similar sizes (c.a. 126–171 nm) and stabilized in toluene with any of the three surface modifications, PEI-OA-stabilized SiO₂ nanoparticles aggregated during processing epoxy-based composites. PEI-AS- and PEI-OA-Epoxy-stabilized SiO₂ nanoparticles maintained their dispersion stability, however, the epoxy composites with PEI-OA-Epoxy-stabilized SiO₂ nanoparticles exhibited better material properties, such as increase in the strain at fracture and higher T_g.     

Synthesis and electrophosphorescent properties of iridium complexes based on 2-fluorenylquinoline derivatives

A series of cyclometalated iridium complexes with 2-fluorenylquinoline derivative ligands were synthesized and their photophysical and electroluminescent properties examined using multilayered, organic light-emitting diodes fabricated with the complexes as dopant materials. In the device containing the complex 3 dopant, the maximum luminance was 20,200 cd/m² at 14 V, the luminous and power efficiencies were 14.1 cd/A and 11.0 lm/W, respectively, and the CIE coordinates were (0.65, 0.35) which were close to saturated red emission.     

多壁碳纳米管的辐照处理及其对多壁碳纳米管/环氧树脂复合材料热性能的影响

在空气中用高频高压电子加速器辐照多壁碳纳米管(MWCNTs),采用红外光谱、能谱分析、拉曼光谱和透射电镜表征分析辐照处理对碳纳米管结构的影响;通过原位复合法制备MWCNT/环氧树脂(EP)复合材料.采用场发射扫描电镜、热失重分析和动态力学分析研究辐照处理MWCNTs对环氧树脂热稳定性的影响.结果表明:电子束辐照处理使MWCNTs表面接入了少量的含氧基团,同时破坏了MWCNTs的完整结构,当辐照剂量为170 kGy时,接枝含氧基团的量最多(约为4％),且结构破坏程度较小.与原始MWCNT/EP体系相比,经电子束辐照处理后的MWCNTs在EP中分散得更均匀,并能使材料的最大热分解温度和玻璃化转变温度较纯EP有所提高,在EP中加入质量分数0.5％的经170kGy辐照处理后的MWCNTs,能够使材料的最大热分解温度和玻璃化转变温度分别提高约14℃和8℃.     

Effect of boron content and welding current on the mechanical properties of electrical resistance spot welds in complex-phase steels

When complex phase steel where tensile strength is more than 1 GPa grade is joined by resistance spot welding (RSW) optimum boron (B) content should be chosen to satisfy weldability and mechanical properties. Therefore, in this study, the effect of the B content (0–40 ppm) on the tensile-shear strength of the RSW were investigated. As the resistivity of the base metal was independent on the B content it did not affect to nugget diameter. Regardless of the B content the specimens under 5t^1/2 (t = sheet thickness) were fractured at interfacial failure mode. In the low welding current condition (lower than 6.4 kA), measured nugget diameters were smaller than calculated critical nugget diameter regardless of the amount of B addition so that fracture mode was interfacial failure. Pull out failure occurred at the softened zone which was boundary between the base metal and the heat affected zone. Tensile-shear load of the specimen failure at the pull-out mode was increased as the fractured diameter and hardness of the softened zone were increased. Shear load was only dependent on the fractured diameter. The equations to calculate the shear and tensile-shear load were suggested for the specimens fractured at interfacial and pull-out failure modes respectively. Correlation coefficients between measured and calculated values of shear and tensile-shear load were 0.98 and 0.97, respectively. Therefore, shear and tensile-shear load of advanced high strength steel joined by RSW could be predicted successfully using the suggested equation.     

Investigation of the functional network modifier loading on the stoichiometric ratio of epoxy resins and their dielectric properties

Journal of Materials Science - Reactive molecular additives have often been employed to tailor the mechanical properties of epoxy resins. In addition, several studies have reported improved...     

Effect of boron incorporation on the structure and electrical properties of diamond-like carbon films deposited by femtosecond and nanosecond pulsed laser ablation

The influence of the incorporation of boron in diamond-like carbon (DLC) films on the microstructure of the coatings has been investigated. The boron-containing DLC films (a-C:B) have been deposited by pulsed laser deposition (PLD) at room temperature in high vacuum conditions, by ablating graphite and boron targets either with a femtosecond pulsed laser (800 nm, 150 fs, fs-DLC) or with a nanosecond pulsed laser (248 nm, 20 ns, ns-DLC). Alternative ablation of the graphite and boron targets has been carried out to deposit the a-C:B films. The film structure and composition have been highlighted by coupling Field Emission Scanning Electron Microscopy, Electron Energy Loss Spectroscopy and High Resolution Transmission Electron Microscopy. Using the B K-edge, EELS characterization reveals the boron effect on the carbon bonding. Moreover, the plasmon energy reveals a tendency of graphitization associated to the boron doping. Pure boron particles have been characterized by HRTEM and reveal that those particles are amorphous or crystallized. The nanostructures of the boron-doped ns-DLC and the boron-doped fs-DLC are thus compared. In particular, the incorporation of boron in the DLC matrix is highlighted, depending on the laser used for deposition. Electrical measurements show that some of these films have potentialities to be used in low temperature thermometry, considering their conductivity and temperature coefficient of resistance (TCR) estimated within the temperature range 160-300 K.