Preparation of epoxy resin/silica hybrid composites for epoxy molding compounds

Phenolic novolac/silica and cresol novolac epoxy/silica hybrids were prepared through in situ sol‐gel reaction of tetraethoxysilane (TEOS). The formed hybrids were utilized as a curing agent and an epoxy resin in epoxy curing compositions, respectively. Via the two‐step preparation route, the resulting epoxy resin/silica hybrid nanocomposites exhibited good thermal stability, high glass transition temperatures, and low coefficients of thermal expansion. High condensation degree of the condensed silica was observed with a high content of siloxane bridges, p > 85%, measured by ²⁹Si NMR. The two‐step route also provides feasibility of preparation of epoxy resin/silica hybrid nanocomposites compatible with the current processes of manufacturing of epoxy molding compounds. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 4047–4053, 2003     

Ternary nanocomposites based on epoxy,modified silica,and tetrabutyl titanate: Morphology,characteristics, and kinetics of the curing process

In this study, the effects of unmodified nanosilica and nanosilica modified by an isopropyl tri[di(octyl) phosphate] titanate coupling agent (KR-12; m-nanosilica) on the structure, morphology, thermomechanical properties, and kinetics of the curing process of epoxy–tetrabutyl titanate (TBuT) nanocomposites were investigated. The viscosity, tensile strength, and flexural strength of the cured epoxy and cured epoxy–m-silica–TBuT nanocomposites were determined with a Brookfield viscometer and an Instron 5582-100KN universal machine. The morphology and gel fraction content of the nanocomposites were analyzed with transmission electron microscopy and scanning electron microscopy methods and Soxhlet extraction. The viscosity, mechanical properties, gel fraction content, and morphology results of the cured epoxy–m-silica–TBuT nanocomposites confirm that 5 wt % m-nanosilica was the most suitable for improving the dispersion of m-nanosilica in the epoxy matrix and the properties of these materials. The thermal behavior of the nanocomposites was determined by thermogravimetric analysis and differential scanning calorimetry (DSC) methods. On the basis of DSC data, the average value of the activation energy of the cured epoxy–TBuT system, calculated according to Flynn–Wall–Ozawa and Kissinger equations, was 67.893 kJ/mol. The calculation according to the Crane equation showed that the first-order kinetics complied with the curing reaction for the neat epoxy. When we introduced the unmodified nanosilica and modified nanosilica into the epoxy matrix, the order kinetics of the curing reaction for the nanocomposites also followed first-order kinetics, but the activation energy of their curing reaction decreased significantly. Some other properties were also investigated with dynamic mechanical analysis and Fourier transform infrared analysis and are discussed. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47412.     

Synthesis of epoxy resin–silica nanocomposites provided from perhydropolysilazane as a curing reagent and the precursor of silica domain

Epoxy resin–silica nanocomposites with spherical silica domains with 29.0 nm in diameter in an epoxy resin matrix were synthesized from Bisphenol‐A type epoxide monomer, 2,2‐bis(4‐glycidyloxyphenyl)propane (DGEBA), and perhydropolysilazane (PHPS, ? [Si₂? NH]_n? ). The volume fraction of silica domain in the composite varied from 5.4 to 37.8 vol % by varying the feed ratio of PHPS to the epoxide monomer. The reaction mechanism of epoxy group and PHPS was investigated by using glycidyl methacrylate as a model compound of the epoxy monomer by ¹H‐nucular magnetic resonance and Fourier transform infrared spectrometry. Ammonia gas provided by the decomposition of PHPS with moisture converted PHPS to silica and cured the epoxy monomer. The curing of epoxy monomer preferably proceeded than the conversion of silica. The addition of 1,4‐diaminobutane drastically accelerated the rate of curing; white and hard epoxy resin–silica nanocomposites were obtained. The good thermal stability of the composite prepared with DGEBA/PHPS/1,4‐diaminobutane was observed by thermogravimetric analysis. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Viscoelasticity of epoxy resin/silica hybrid materials with an acid anhydride curing agent

The viscoelasticity of epoxy resin/silica hybrid materials manufactured by the sol–gel process with an acid anhydride curing agent was investigated in terms of morphology. Transmission microscopy observations demonstrated that all the prepared hybrid samples had a two‐phased structure consisting of an epoxy phase and a silica phase. The formed silica had either nanosized particles or coarse domains, depending on the catalyst for the sol–gel process. Raman spectroscopy analysis showed that the formed silica had features typical of sol–gel derived silica glass and that the ring‐opening reactions of the epoxy groups developed in the hybrid samples and in the neat epoxy samples. In dynamic mechanical thermal analysis, there were two transition temperatures due to epoxy chain mobility and epoxy network relaxation, through which the moduli changed by nearly 3 orders of magnitude. The hybridization disturbed epoxy network formation but also reinforced the epoxy network with the formed silica, which was characterized by the activation energy of the network relaxation; therefore, the modulus of the rubbery state was correlated to the activation energy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Solvent-Free One-Pot Synthesis of high performance silica/epoxy nanocomposites

High performance silanized silica/epoxy nanocomposites were prepared through mixing epoxy, tetraethyl orthosilicate (TEOS), (3-aminopropyl)trimethoxysilane (APTMS) and ammonia solution at 50 °C. This all-in-one “Solvent-Free One-Pot Synthesis” results in nanocomposites with uniform dispersion of oval shaped silica nanoparticles and strong adhesion between silica and epoxy matrix. The influence of the synthesis conditions, such as molar ratio of NH₃:TEOS, aging time, curing process and silica content on the thermal mechanical properties of nanocomposites were studied. The silanized silica/epoxy nanocomposite prepared in this study exhibits better thermal mechanical property in comparison with neat epoxy, non-functionalized silica/epoxy and commercialized silica/epoxy systems. The prepared nanocomposite with 3 wt% silanized silica exhibits 20%, 17% and 6% improvements on flexural, tensile and storage modulus over those of neat epoxy, respectively.     

Effects of modifiers in organoclays on the curing reaction of liquid‐crystalline epoxy resin

The effects of three organoclays (Cloisite 10A, 93A, and 30B) with different modifiers on the curing reaction of a liquid‐crystalline epoxy (LCE) resin based on 4,4′‐diglycidyloxybiphenyl and the curing agent sulfanilamide were studied. The curing kinetics of the LCE and clay composites were analyzed with differential scanning calorimetry. The Flyann–Wall–Ozawa and Kissinger–Akahira–Sunose methods were used to calculate the activation energies at different conversions. All three alkylammonium ions lowered the reaction activation energy and catalyzed the epoxy ring‐opening reaction with the diamine curing agent. 30B, with two hydroxy groups of quaternary ammonium, showed the highest catalysis because the hydroxy groups facilitated the curing process. 10A and 93A had similar catalytic abilities. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1329–1334, 2005     

E‐beam‐cured layered‐silicate and spherical silica epoxy nanocomposites

This research demonstrates that an epoxy nanocomposite can be made through electron beam (e‐beam) curing. The nanofillers can be two‐dimensional (layered‐silicate) and zero‐dimensional (spherical silica). Both the spherical silica epoxy nanocomposite and the layered‐silicate epoxy nanocomposite can be cured to a high degree of curing. The transmission electron microscopy (TEM) and small‐angle X‐ray scattering of the e‐beam‐cured layered‐silicate epoxy nanocomposites demonstrate the intercalated nanostructure or combination of exfoliated and intercalated nanostructure. The TEM images show that the spherical silica epoxy nanocomposite has the morphology of homogeneous dispersion of aggregates of silica nanoparticles. The aggregate size is ～ 100 nm. The dynamic mechanical analysis shows that the storage modulus of the spherical silica nanocomposite has been improved, and the glass transition temperature can be very high (～ 175°C). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

环氧树脂插层纳米复合材料固化动力学研究

运用自制的有机蒙脱土，采用浇模固化成型法制备环氧树脂／二乙烯三胺／有机蒙脱土纳米复合材料，对固化产物利用XRD（X射线衍射）分析有机蒙脱土的层间距变化，确定产物为插层型的纳米复合材料，并用DSC（差示扫描量热法）跟踪环氧树脂固化行为。运用Kissinger,Flynn-Wall-Ozawa,Crane方法对环氧树脂的固化反应过程进行分析，求出活化能和反应级数等动力学以在数。结果发现，加入有机化蒙脱土后使固化反应活化能和频率下降，从而有利于固化工艺的实现，便于纳米复合材料实际应用。     

Epoxy/nano‐silica composites: Curing kinetics,glass transition temperatures,dielectric, and thermal–mechanical performances

Nano‐silica particles were employed for enhancement of epoxy vacuum pressure impregnating (V.P.I.) resin. The influences of nano‐silica particles on the curing reaction, glass transition temperatures, dielectric behavior, and thermomechanical performances were investigated. The activation energy (E) for the epoxy curing reaction was calculated according to Kissinger, Ozawa, and Friedman‐Reich‐Lev methods. The glass transition temperatures were determined by means of differential scanning calorimetry, dynamic mechanical analysis, dc conduction, and ac dielectric loss analysis. Relationships between the glass transformation behaviors, the thermomechanical performances, and the dielectric behaviors were discussed. The influences of nano‐silica particles on the mechanical properties were also discussed in terms of non‐notched charpy impact strength and flexural strength. The morphologies were studied by means of SEM and TEM. The results indicated that nano‐silica particles could effectively increase both the toughness and strength of epoxy resin at low loadings (no more than 3 wt %) when nano‐silica particles could be well dispersed in epoxy matrix without any great aggregations. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Interactions between silica nanoparticles and an epoxy resin before and during network formation

In polymer nanocomposites, interactions between filler particles and matrix material play a crucial role for their macroscopic properties. Nanocomposites consisting of varying amounts of silica nanoparticles and an epoxy resin based on diglycidyl ether of bisphenol-A (DGEBA) have been studied before and during network formation (curing). Rheology and mainly temperature modulated differential scanning calorimetry (TMDSC) have been used to investigate interactions between the silica nanoparticles and molecules of the epoxy oligomer or molecules of the growing epoxy network. Measurements of the complex specific heat capacity before curing showed that interactions between the nanoparticles and DGEBA molecules are very weak. An expression for an effective specific heat capacity of the silica nanoparticles could be deduced. Examination of the isothermal curing process after addition of an amine hardener yielded evidences for a restricted molecular mobility of the reactants in the cause of network formation. These restrictions could be overcome by increasing the curing temperature. No evidences for an incorporation of the silica nanoparticles into the epoxy network, i.e. for a strong chemical bonding to the network, were found. Interactions between the silica nanoparticles and the epoxy resins under study are assumed to be of a physical nature at all stages of network formation.     

Biobased cyanate ester composites with epoxidized soybean oil and in situ generated nano‐silica

Biobased cyanate ester (CE) nanocomposites have been prepared from renewable resource, epoxidized soybean oil (ESO) and in situ generated nano‐silica via sol–gel process. The isothermal curing process was investigated by differential scanning calorimetry (DSC) and rheometry. The results indicate that the incorporation of silica accelerates the reaction at the beginning stage of curing process but descends the final isothermal curing conversion. The morphological study of nanocomposites by scanning electron microscope and transmission electron microscope suggests that the silica exists in the forms of both nanoparticles and silica networks, while the diameter of ESO‐rich phase diminished with the increase of silica loading. In addition, the thermal–physical and mechanical properties were evaluated by dynamic mechanical analysis, thermogravimetric analysis, and tensile mechanical test. The biobased CE nanocomposites show effectively improved properties compared to the systems without nano‐silica. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.     

二氧化硅粉体改性E—Si／CE固化动力学的研究

采用非等温差示扫描量热法（DSC）研究了纳米二氧化硅（SiO2）和微米SiO2的混合粉体改性环氧基硅烷（E—Si）／氰酸酯（CE）树脂体系固化动力学;用Kissinger、Crane和Ozawa法确定固化动力学参数。结果表明,Kissinger式求得的表观活化能为66．09kJ／mol;Ozawa法求得的表观活化能为7001kJ／mol;根据Crane理论计算该体系的固化反应级数为0.89。计算了不同升温速率所对应的不同温度的频率因子和反应速率常数;求得了改性体系的固化工艺参数：凝胶温度130．74℃、固化温度160．96℃和后处理温度199.16℃,确定了体系的最佳固化工艺。与E—Si／CE体系对比表明,SiO2的加入可以降低E—Si／CE体系的活化能,使其固化能在较低温度下进行。     

Epoxy‐silica nanocomposites: Preparation,experimental characterization,and modeling

Silica nanoparticles having different sizes were obtained by the sol‐gel process and characterized. The prepared nanoparticles were subsequently used as reinforcing fillers to prepare epoxy‐based composites with a silica content ranging from 1 to 5 wt %. SEM analysis and tensile tests carried out on the silica‐epoxy nanocomposites indicated the absence of particle aggregation and a reinforcing effect in terms of increased elastic modulus. Mechanical properties were also modeled by using a finite element code able to construct a numerical model from a microstructural image of the material. A more reliable model was prepared by considering the presence of an interphase layer surrounding the particles with intermediate elastic properties between the epoxy and the inclusions and a characteristic size proportional to the particle radius. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2382–2386, 2005     

Immobilization of flame-retardant onto silica nanoparticle surface and properties of epoxy resin filled with the flame-retardant-immobilized silica (2)

To prepare silica nanoparticle having flame-retardant activity, immobilization of flame-retardant onto the surface was investigated. The immobilization of phosphorous flame-retardant was achieved by two-step reactions: (1) introduction of cyclotriphosphazene (PH) groups onto silica nanoparticle by the reaction of terminal amino groups of the surface with hexachlorocyclotriphosphazene and (2) immobilization of bis(4-aminophenoxy)phenyl phosphine oxide (BAPPO) onto silica having PH groups by the reaction of PH groups on the surface with BAPPO. The immobilization of BAPPO was confirmed by FT-IR and thermal decomposition GC–MS. The composite of epoxy resin filled with BAPPO-immobilized silica (Silica–PH–BAPPO) was successfully prepared by heating in the presence of curing agents. Thermal decomposition temperature and glass transition temperature of the epoxy resin filled with Silica–PH–BAPPO was higher than that of epoxy resin filled with untreated silica, free HCTP and BAPPO. Moreover, flame-retardant property of epoxy resin filled with Silica–PH–BAPPO was estimated by limiting oxygen index (LOI). The LOI value of epoxy resin filled with Silica–PH–BAPPO was higher than that of epoxy resin filled with untreated silica, free HCTP and BAPPO. This may be due the fact that char yield of the epoxy resin filled with Silica–PH–BAPPO was higher than that filled with free flame-retardant.     

Physical properties of a bisphenol-F epoxy containing a silica filler treated with silane coupling agents

A model epoxy system consisting of a diglycidyl ether of bisphenol-F epoxy resin, 1,4-butanediol, and cured with 4-methyl-2-phenylimidazole has been investigated. Thermal analysis indicated that 3 parts per hundred resin (phr) is the optimum amount of curing agent for this system. The influence of silane-treated amorphous fumed silica fillers on properties of the cured epoxy was also examined. Silica particles were treated with 3-aminopropyldiethoxymethylsilane (APDS) and3-aminopropyltriethoxysilane (APTS) coupling agents. No change in glass transition temperatures was observed with the addition of the filler (with or without coupling agents) to the epoxy. Addition of the filler led to a slight increase in the activation energy for the glass transition; however, no change in activation energy was observed when using the coupling agent. Addition of either coupling agent to the filler surface led to an increase in cooperativity. Fumed silica also did not significantly affect moisture diffusion properties, but a small decrease was observed in the moisture saturation mass with the addition of silica particles treated with APDS.     

Amine-functionalized metal–organic frameworks/epoxy nanocomposites: Structure-properties relationships

Amine-functionalized MIL-101(Cr)-NH₂ metal–organic frameworks (MOF-N)/epoxy nanocomposites with Excellent cure label and high thermal stability were developed. Structure–property relationship was discussed by comparison of the cure state, thermal and viscoelastic behavior of epoxy nanocomposites containing pristine MOF or MOF-N applying differential scanning calorimetry (DSC), thermogravimetric analysis, and dynamic mechanical analysis. Epoxy containing 0.3 wt% MOF-N exhibited high glass transition temperature (T_g) of 96°C compared with 85°C observed for epoxy/MOF system. Thus, MOF-N played the role of catalyst in epoxy/amine curing reaction. Correspondingly, a lower activation energy was obtained based on cure kinetics modeling based on DSC measurements. Besides, incorporation of low amount (0.5 wt%) MOF-N induced an early-state resistance against decomposition, featured by 11°C rise in decomposition temperature at 5% weight loss. This was ascribed to the formation of porous metallic oxides during thermal decomposition of MOF-N in the epoxy system acting as a heat barrier, which increased the activation energy of decomposition. Amine-functionalization considerably prevented from further oxidation of the inner part of the matrix.     

Preparation and thermal properties of epoxy-silica nanocomposites from nanoscale colloidal silica

Epoxy-silica nanocomposites were obtained from directly blending diglycidylether of bisphenol-A and nanoscale colloidal silica and then curing with 4,4-diaminodiphenylmethane. The epoxy-silica nanocompoites showed good transparency and miscibility observed with AFM, SEM, and TEM. The thermal stability of the epoxy resins was improved with the incorporation of the colloidal silica. However, a depression on the glass transition temperature of the resins was observed, owing to the plasticizing effect of the colloidal silica. Moreover, the nanoscale colloidal silica did not show effectively synergistic effect on char formation and flame retardance with phosphorus.     

基于变活化能模型的T800/环氧树脂预浸料固化反应动力学研究

为了深入了解某新型高温固化T800/环氧树脂预浸料的固化行为,借助差示扫描量热仪(DSC),采用非等温DSC法研究了T800/环氧树脂预浸料的固化反应过程。基于唯象模型,系统研究了该预浸料的固化反应特征温度及固化动力学参数,确定该预浸料中环氧树脂的固化反应动力学模型为自催化模型。采用等转化率法,分析了预浸料中环氧树脂的反应活化能随固化度的变化情况,结果表明在整个固化反应过程中,树脂固化反应活化能变化较大,传统模型法基于全固化过程活化能不变的假设无法准确描述该固化反应。采用变活化能自催化模型,利用粒子群全局优化算法,得到了T800/环氧树脂预浸料的固化动力学方程,结果表明该模型能较好地描述实验现象,可为进一步研究该预浸料的热力学性能及其成型过程中的质量控制提供理论基础。     

DSC analysis of epoxy molding compound with plasma polymer–coated silica fillers

Silica fillers were modified by plasma‐polymerization coating of 1,3‐diaminopropane, allylamine, pyrrole, 1,2‐epoxy‐5‐hexene, allylmercaptan, and allylalcohol using RF plasma (13.56 MHz). Modified fillers were then mixed with biphenyl epoxy resin, phenol novolac (curing agent), and optionally triphenylphosphine (catalyst) to prepare samples for DSC analyses. Some samples were also prepared from uncoated silica fillers and monomers used in plasma polymerization coating, instead of plasma polymer–coated silica fillers. Plasma polymer–coated silica fillers were characterized by FTIR, XPS, and water contact angle measurements. In DSC analyses, all samples with plasma polymer–coated silica fillers showed a large peak and an additional one or two small exothermic peaks when catalyst was added, compared to only one large peak with as‐received silica fillers. The large peak could be from epoxy–phenol novolac reaction in the presence of catalyst, whereas small reaction peaks were attributed to the chemical reaction between epoxy resin and functional moieties in the plasma polymer coating, such as amine, OH, and/or SH groups, as evidenced by FTIR and XPS analysis and contact angle measurements. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2508–2516, 2003     

Curing of epoxy resin by ultrafine silica modified by grafting of hyperbranched polyamidoamine using dendrimer synthesis methodology

Hyperbranched polyamidoamine–grafted silica was prepared according to dendrimer synthesis methodology. The modified silica was dispersed uniformly in epoxy resin, and the curing of epoxy resin proceeded successfully by heating in the presence of the modified silica; the gel fraction of the epoxy resin cured by the hyperbranched polyamidoamine–grafted silica (grafting = 80.2%) reached 77% at 170°C after 48 h. The gel fraction increased with increasing terminal amino group content of the hyperbranched polyamidoamine–grafted silica. In addition, the curing ability of the silica increased by complexation of the terminal amino groups of the grafted polyamidoamine with boron trifluoride. The modulus of elasticity of the curing materials obtained using the modified silica as a curing agent was lower than that using conventional a curing agent such as ethylenediamine in the presence of untreated silica. On the other hand, the heat resistance of the curing product using the modified silica was superior to that using ethylenediamine, but no difference in glass‐transition temperature was observed. It is expected that hyperbranched polyamidoamine grafted‐silica is incorporated uniformly with chemical bonds in the matrix of the epoxy resin. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 573–579, 2001