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     

Fibers and fiber cocktails to improve fire resistance of concrete

Hybrid organic–inorganic resin matrix, i.e., hexa[3,4-dicyano]-phenyl phosphonitrile trimer (HPPT) has been prepared by the reaction of hexachlorophosphonitrile and 4-hydroxyphthalonitrile in the presence of sodium hydride which on heating at 300 °C yielded a high-temperature-stable highly crosslinked hybrid resin (C-HPPT). The elemental analysis (C, H, and N), FTIR, and ¹H and ¹³C-NMR studies were used to characterize the synthesized hybrid resin. The thermal analysis studies viz. TG and DSC were also carried out to determine the thermal stability and glass transition temperature of the cured resin. The isothermal study of the cured resin after 300 h at 300 °C showed only a mass loss of 4.36%.     

Synthesis and properties of two novel silicon‐containing cycloaliphatic epoxy resins for electronic packaging application

In this paper, two silicon‐containing cycloaliphatic olefins were synthesized through the nucleophilic substitution reactions of cyclohex‐3‐enyl‐1‐methanol with di‐ or tri‐chlorosilane compounds. Then, after epoxidation, two new cycloaliphatic epoxy resins with different epoxy groups were successfully prepared. Their chemical structures were confirmed by ²⁹Si NMR, ¹H NMR, and Fourier‐transform infrared spectra (FTIR). The properties of cured products, including viscoelasticity, glass transition temperature (T_g), coefficient of thermal expansion, thermal stability and water absorption, were investigated. Compared to the difunctional epoxy resin, the trifunctional one exhibited a remarkably increased cross‐linking density from 0.82 to 4.08 × 10^?3 mol/cm³ and T_g from 157 to 228°C. More importantly, prior to curing, they had viscosities of only 240–290 mPa sec at 25°C, which were much lower than that of ERL‐4221 (409 mPa sec), providing the possibility of easy processing. The high glass transition temperatures, good thermal stabilities, and mechanical properties as well as excellent flowability endow the silicon‐containing epoxy resins with promising potential in microelectronic packaging application. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis and characterization of thiocarbonohydrazone-based epoxy resins

Novel epoxy resins of various thiocarbonohydrazones have been synthesized by reacting the aldehyde or ketone derivatives of thiocarbohydrazide with excess of epichlorohydrin. The resins have been characterized by elemental analyses, epoxy equivalents, ¹H-NMR and IR spectra, thermal analyses, and viscosity measurements. Curing of the resins has been carried out by mixing with thiocarbohydrazide or ethylenediamine and heating at 80°C for 48 h. A comparison of the thermal stability of the cured resin samples has been made.     

Curing and thermal behaviour of a flame retardant cycloaliphatic epoxy resin based on phosphorus containing poly(amide–imide)s

The curing behaviour of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate was investigated by the dynamic differential scanning calorimetry (DSC) using phosphorus-containing poly(amide–imide)s (PAIs) having free amine groups, 4,4′-diaminodiphenylmethane (PM) and p-phenylenediamine (PA), in the ratio of 1:1. The PAIs were prepared by co-polymerization of diimide–diacid (DIDA) and phosphorus-containing triamines having phenylene moiety. l-Tryptophan and pyromellitic anhydride were used to synthesize DIDA. Triamines used in the synthesis PAIs were tris(3-aminophenyl) phosphine (TAP), tris(3-aminophenyl) phosphine oxide (TAPO) and bis(3-aminophenyl) aminotolyl phosphine (BAP). TAP-, TAPO- and BAP-containing PAIs were designated as PTAP, PTAPO and PBAP, respectively. These PAIs with free amine groups were characterized by FTIR, ¹H NMR, ¹³C NMR spectroscopic techniques and elemental analysis. The mixture of PAIs and PM or/and PA in the ratios of 0:1, 1:0 and 0.5:0.5 was used for investigation. DSC was used to study the curing of epoxy by recording the DSC scans at heating rates of 10 °C min^?1. Thermal stability of epoxy resin cured isothermally was evaluated by recording thermo gravimetric traces in nitrogen atmosphere at the heating rate of 20 °C min^?1. All samples are highly stable, and the 10 % mass loss found was in the range of 335–520 °C. The percent char yield was highest in case of resin sample E/PM/PTAPO. The flame-retardant properties of cured epoxy resins were investigated by the limiting oxygen index test (LOI) and UL94 test. When phosphorus was incorporated in epoxy resin, the epoxy resin system met the UL94 V-0 classification and the LOI reached at 37.8, because of nitrogen–phosphorus synergistic effect.     

The curing of epoxy resins with aminophenoxycyclotriphosphazenes

Aminophenoxycyclotriphosphazenes have been used as curing agents for epoxy resins. The thermal curing was performed in stages at 120–125 and 175–180°C followed by postcuring at 225°C to give tough brown polymers. The thermal curing reaction was monitored using FTIR and differential scanning calorimetry. Thermogravimetric analysis of the cured resins has shown thermal stability up to 350–340°C. The char yield obtained in nitrogen at 800°C was about 55–42% and in air at 700°C was about 40–32%. Graphite cloth laminates were prepared. The mechanical properties evaluated were found superior to those of commonly used epoxy resin systems. These resins are useful for making fire- and heat-resistant composites, laminates, molded parts, and adhesives.     

Synthesis of a novel epoxy resin containing diphenylether moiety and thermal properties of its cured polymer with phenol novolac

A new type of epoxy resin containing 4,4′-diphenylether moiety in the backbone (2) was synthesized, and was confirmed by gel permeation chromatography, infrared spectroscopy, and ¹H nuclear magnetic resonance spectroscopy. In addition, in order to evaluate the influence of 4,4′-diphenylether moiety in the structure, epoxy resins having 4,4′-biphenylene moiety (4) and having 1,4-phenylene moiety (6) in place of 4,4′-diphenylether moiety were synthesized. The cured polymer obtained through the curing reaction between the new diphenylether-containing epoxy resin and phenol novolac was used for making a comparison of its thermal and physical properties with those obtained from 4, 6, and bisphenol-A (4,4′-isopropylidenediphenol) type epoxy resin. The cured polymer obtained from 2 showed markedly higher anaerobic char yield at 700°C of 44.0 wt %, higher fracture toughness, and higher mechanical strength and modulus. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3687–3693, 1999     

Dynamic mechanical properties of epoxy‐phenolic mixtures

The dynamic‐mechanical properties of different mixtures formed by an epoxy resin (DGEBA type) and a phenolic resin (resole type) cured by trietylenetetramine and/or p‐toluensulphonic acid at different concentrations have been studied by means of dynamic mechanical thermal analysis (DMTA). All samples were cured by pressing at 90 °C during 6 h. The mechanical studies were performed between ?100 to 300 °C at a heating rate of 2 °C/min. This study was also carried out for the epoxy‐TETA and phenolic‐p‐toluensulphonic acid systems. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1548–1555, 2005     

Thermal and mechanical properties of epoxy resin toughened with epoxidized soybean oil

A series of new modified epoxy resin (EP) cured products were prepared from epoxidized soybean oil and commercial epoxy resin, with methyl nadic anhydride as curing agent and 1-methylimidazole as promoting agent. The thermal properties of the resins were characterized by DMA and TG; DSC was used to determine the curing process. Fourier transform infrared spectroscopy was utilized to investigate their molecular structures and scanning electron microscopy was used to observe the micro morphology of their impact fracture surfaces. Tensile and impact testing was employed to characterize the mechanical properties of the cured products. The combination of commercial EP with 20 wt% ESO resulted in a bioresin with the optimum set of properties: 130.5 °C T _g, 396.9 °C T _50 %, 74.89 MPa tensile strength, and 48.86 kJ m^?2 impact resistance.     

Preparation and properties of biocomposites composed of bio‐based epoxy resin,tannic acid,and microfibrillated cellulose

As new bio‐based epoxy resin systems, glycerol polyglycidyl ether (GPE) and sorbitol polyglycidyl ether (SPE) were cured with tannic acid (TA) at various conditions. When the curing conditions were optimized for the improvement of thermal and mechanical properties, the most balanced properties were obtained for the GPE/TA and SPE/TA cured at 160 °C for 2–3 h at the epoxy/hydroxyl ratio of 1/1. The cured SPE/TA had a higher glass transition temperature (T_g) and tensile strength than the cured GPE/TA. Next, biocomposites of GPE/TA and SPE/TA with microfibrillated cellulose (MFC) were prepared by mixing aqueous solution of the epoxy/curing reagent with MFC, and subsequent drying and curing at the optimized condition. For both the GPE/TA/MFC and SPE/TA/MFC biocomposites, T_g and the storage modulus at rubbery plateau region increased with increasing MFC content over the studied range of 3–15 wt %. The tensile strength at 25 °C for GPE/TA/MFC biocomposite with MFC content 10 wt % was 76% higher than that of control GPE/TA, while the tensile modulus was little improved. On the other hand, the tensile strength and modulus of SPE/TA/MFC biocomposite with MFC content 10 wt % were 30 and 55% higher than those of control SPE/TA, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 425–433, 2010     

Thermal and flame retardant properties of epoxy resin cured by a novel phosphorus-containing 4,4′-bisphenol novolac curing agent

A novel flame retardant curing agent for epoxy resin (EP), i.e., a DOPO (9,10-dihydro-9-oxa-10-phosphaphenan-threne-10-oxide)-containing 4,4'-bisphenol novolac (BIP-DOPO) was synthesized and characterized by Fourier transform infrared (FTIR), ¹H NMR, ³¹P NMR spectroscopy, and gel permeation chromatography. The epoxy resin cured by BIP-DOPO itself or its mixture with a commonly used bisphenol A-formaldehyde novolac resin (NPEH720) was prepared. The flame retardancy of the cured EP thermosets were studied by limiting oxygen index (LOI), UL 94 and cone calorimeter test (CCT), and the thermal properties by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results show that the cured epoxy resin EPNP/BI/3/1, which contains 2.2% phosphorus, possesses a value of 26.2% and achieves the UL 94 V-0 rating. The data from cone calorimeter test demonstrated that the peak release rate, average heat release rate, total heat release decline sharply for the flame retarded epoxy resins, compared with those of pure ones. DSC results show that the glass-transition temperatures of cured epoxy resins decrease with increasing phosphorus content. TGA indicates that the incorporation of BIP-DOPO promotes the decomposition of epoxy resin matrix ahead of time and leads to higher char yield. The surface morphological structures of the char residues reveal that the introduction of BIP-DOPO benefits to the formation of a continuous and solid char layer on the epoxy resin material surface during combustion.     

Enhanced fracture toughness and mechanical properties of epoxy resin with rice husk-based nano-silica

This paper reports a novel approach to toughen epoxy resin with nano-silica fabricated from rice husk using a thermal treatment method with a particle size distribution in range of 40–80 nm. The nano-silica content was in the range, 0.03–0.10 phr, with respect to epoxy. The mechanical test showed that with the addition of 0.07 phr of rice husk based nano-silica, the fracture toughness of the neat epoxy resin increased 16.3% from 0.61 to 0.71 MPa m^1/2. The dynamic mechanical analysis test results showed that the glass transition temperature (T _g) of a 0.07 phr nano-silica dispersion in epoxy resin shifted to a higher temperature from 140 to 147°C compared to neat epoxy resin. SEM further showed that the nano-silica particles dispersed throughout the epoxy resin prevented and altered the path of crack growth along with a change in the fracture surface morphology of cured epoxy resin.     

Preparation and properties of epoxy resins cured with silyl esters of phenol novolak and cresol novolak

The curing agents of epoxy resin, trimethylsilyl ethers of phenol novolak (TMSPN) and cresol novolak (TMSCN) were prepared by refluxing phenol novolak and cresol novolak respectively, with the mixture of hexamethyldisilazane and chlorotrimethylsilane in THF. The curing reaction of epoxy resin with these curing agents and the thermal properties of cured resins were examined. The Tg values of epoxy resins cured with TMSPN were a little higher than those cured with TMSCN. The maximum of Tg is 118°C for TMSPN-cured epoxy resin against 112°C for TMSPN-cured epoxy resin. The water absorption of hydrophobic epoxy resins cured with TMSPN was a little lower than those cured with TMSCN. The clear decrease of water absorption is attributed to the difficulty of the micro-void formation caused by the more tight primary structures of TMSPN. The water absorption at 25°C containing trimethylsilyl groups is about one-tenth of that of epoxy resins cured with conventional curing agents and even one-half of that of the epoxy resins cured with active esters. The low water absorption is attributed to the presence of trimethylsilyl groups, which are more hydrophobic than ester groups, and to the absence of hydroxyl groups of the cured resins. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and characterization of itaconic‐based epoxy resins

A trifunctional epoxy resin from itaconic acid (TEIA) was synthesized from a renewable resource‐based itaconic acid by allylation of itaconic acid to form diallyl itaconate by using m‐chloroperoxybenzoic acid as oxidizing agents followed by epoxidation of allylic C═C bond of diallyl itaconate methylhexahydropthalic anhydride as curing agent in the presence of 2‐methyl imidazole as a catalyst. The chemical structure of the synthesized resins was confirmed by Fourier transform infrared and nuclear magnetic resonance (¹H‐NMR and ¹³C‐NMR) spectroscopy analysis. The mechanical, thermal, and rheological performances of the TEIA were also investigated and compared with diglycidyl ether of bisphenol A and a plant‐based epoxidized soybean oil bioresin cured with the same curing agent. The higher epoxy value of 1.02, lower viscosity (0.96 Pa s at 25°C), higher mechanical, and higher curing reactivity toward methylhexahydropthalic anhydride of TEIA as compared with epoxidized soybean oil and comparable with diglycidyl ether of bisphenol A demonstrated significant evidence to design and develop a novel bio‐based epoxy resin with high performance to substitute the petroleum‐based epoxy resin.     

Hyperbranched epoxy resins prepared by proton transfer polymerization from an A<Subscript>2</Subscript> + B<Subscript>3</Subscript> system

Epoxy-terminated hyperbranched polymers(EHBPs)were prepared by proton transfer polymerization and characterized by FT-IR,~1H-NMR and GPC.The solution and thermal properties of the uncured samples and mechanical properties of cured samples were examined.The thermo-stable products had good solubility in polar solvents,low solution viscosity and T_gs ranging from 15℃to 33℃depending on their molecular weights.The mechanical properties of cured films were studied and compared with those of a bisphenol-A type epoxy resin.The films of EHBPs had good impact resistance and high gloss values without sacrificing hardness and adhesion.     

Liquid crystalline epoxies bearing biphenyl ether and aromatic ester mesogenic units: Synthesis and thermal properties

Two liquid crystalline epoxies containing biphenyl ether and aromatic ester mesogenic units, oxybis(4,1-phenylene)bis(4-(oxiran-2-ylmethoxy)benzoate)(LCE1) and oxybis(4,1-phenylene) bis(4-(4-(oxiran-2-yl)butoxy)benzoate)(LCE2), were synthesized and characterized. Subsequently, the epoxy monomers were cured with diaminodiphenylsulfone (DDS). From DSC, XRD and POM results, monomers did not show liquid crystalline phase while the cured samples exhibited nematic phase. The cured samples showed good mechanical properties with strength of 99.1MPa and excellent thermal stabilities with high glass transition temperature up to 168.0?°C, 5% weight loss temperature at 343?°C and high char yield of 24.5% at 800?°C. The relationship between thermal conductivity and network structure was discussed in this work. Due to the introduction of mesogenic units into epoxy networks, the cured resins showed high thermal conductivity as high as 0.292?W/(m*K), more than 1.5times higher than conventional epoxy resins. By introducing alumina (Al₂O₃) into LCE1/DDS cured system, composites of LCE1/DDS/Al₂O₃ with the highest thermal conductivity of 1.61?W/(m*K) was obtained with the content of 80?wt% while that of diglycidyl ether of bisphenol A (DGEBA, E51) epoxy resin/DDS/Al₂O₃ was 1.10?W/(m*K). The as-prepared epoxy resins showed high glass transition temperature and excellent thermal stabilities, indicating the potential of application in microelectronics.     

Synthesis and characterization of a novel cycloaliphatic epoxy resin starting from dicyclopentadiene

A novel tri-functional cycloaliphatic epoxy resin was synthesized starting from dicyclopentadiene. The chemical structures of the resultant epoxy resin and its precursor were characterized with FTIR spectroscopy, EEW, ¹H NMR and Mass spectrographic analyses. The thermal and mechanical properties of the resulting polymer were evaluated with differential scanning calorimeter (DSC), thermo-gravimetric and thermal mechanical analysis. Compared to that of the common cycloaliphatic epoxy resin ERL-4221, the cured polymer of the novel epoxy resin exhibited lower thermal degradation temperature with much higher char yield and similar thermal expansion coefficient. These excellent overall performances make it a promising packaging material.     

Synthesis and characterization of a novel polytriazole resin with low‐temperature curing character

A novel low‐temperature curing polytriazole resin was prepared from a triazide and a tetraalkyne and characterized. The resin can be cured at 70°C. The glass transition temperature T_g and thermal decomposition temperature T_d5 of the cured resin with the molar ratio of azide to alkyne group [A]/[B] = 1.0:1.0 reached 324 and 355°C, respectively. The study on the curing kinetics of the resin shows that the apparent activation energy of the curing reaction is 93 kJ mol^?1. The flexural strength of the cured resin reached 137.6 MPa at room temperature and 102.6 MPa at 185°C. Copyright © 2007 John Wiley & Sons, Ltd.     

Thermal degradation and evolved gas analysis: A polymeric blend of urea formaldehyde (UF) and epoxy (DGEBA) resin

A polymeric blend has been prepared using urea formaldehyde (UF) and epoxy (DGEBA) resin in 1:1 mass ratio. The thermal degradation of UF/epoxy resin blend (UFE) was investigated by using thermogravimetric analyses (TGA), coupled with FTIR and MS. The results of TGA revealed that the pyrolysis process can be divided into three stages: drying process, fast thermal decomposition and cracking of the sample. There were no solid products except ash content for UFE during combustion at high temperature. The total mass loss during pyrolysis at 775 °C is found to be 97.32%, while 54.14% of the original mass was lost in the second stage between 225 °C and 400 °C. It is observed that the activation energy of the second stage degradation during combustion (6.23 × 10⁻⁴ J mol⁻¹) is more than that of pyrolysis (5.89 × 10⁻⁴ J mol⁻¹). The emissions of CO₂, CO, H₂O, HCN, HNCO, and NH₃ are identified during thermal degradation of UFE.     

Syntheses of conductive adhesives based on epoxy resin and polyanilines by using N‐tert‐butyl‐5‐methylisoxazolium perchlorate as a thermally latent curing reagent

Conductive composites consisted of epoxy resin and polyanilines (PANIs) doped with dodecylbenzenesulfonic acid ( 1 ), dodecylsulfonic acid (2), di(2‐ethylhexyl)sulfosuccinic acid (3), and HCl were synthesized by use of N‐tert‐butyl‐5‐methylisoxazolium perchlorate (5) under various reaction conditions. It was found that the composites with PANI doped with acid 2 (PANI‐2) prepared by curing with 10 mol % of reagent 5 at 80 °C for 12 h showed high electroconductivity along with the low conducting percolation threshold (3 wt % of PANI‐2). Furthermore, the composite with even ?10 wt % of PANI‐2 exhibited ?10^?1 S/cm of electroconductivity. The UV–vis and IR measurements indicated that the conductive emeraldine salt form of PANI‐2 in the composite was maintained after the curing reaction. The thermal stability was studied by TGA and DSC measurements, and then, the T_d10 and T_g of the composite with 5 and 10 wt % of PANI‐2 were found to be similar to those with the cured epoxy resin itself. In addition, the similar investigation with an oxetane resin instead of the epoxy resin was also carried out. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 718–726, 2006