Use of Sucrose‐based Epoxy ­Formulations and Cellulosic Fibers in ­the Design,Preparation, and Screening ­of New Composite Insulation Materials

Non‐woven composite insulation materials were generated from cotton, kenaf, jute, polyester, polypropylene, sucrose‐based epoxy formulations, and aluminum foil. The needlepunched fiber batts were rendered flame resistant by use of inorganic reagents and urea. To discover suitable epoxy formulations to bind the cellulose fibers to themselves or to dissimilar surfaces and to make flexible composites, a comparison of the performance of the known epoxy allyl sucroses (EAS), epoxy crotyl sucroses (ECS), and diglycidyl ether of bisphenol‐A (DGEBA) was made. The epoxies were cured with commercial diethylenetriamine (DETA), and UNIREZs‐2142 and 2355®, to discover a formulation with the following characteristics: (a) low cure temperature; (b) low Young's moduli and glass transition temperatures of cured thermosets for flexible composites; (c) ample bond strength between the fabric and the bonded surfaces; and (d) non‐cytotoxicity and non‐mutagenicity of the epoxies. Based on results following these criteria, EAS was selected, and the formulation comprising EAS and UNIREZ‐2355® was deemed suitable to bind fiber batts to surfaces of any type and geometry. ASTM guidelines were used to construct a wooden frame cube (heat box) for the simultaneous rapid screening of cellulosic fiber batts and composites. The new materials were compared against R‐19 fiberglass insulation for their ability to resist heat flow (denoted by relative R‐values) and time taken to approach thermal equilibrium. Plain non‐woven cellulosic fiber batts showed relative R‐values of 4.0 °F ft² hr/Btu per inch thickness (0.27 K m²/W per cm), and took about 2 hr to establish equilibrium heat flow. Commercial fiberglass batts showed relative R‐values­of 2.2 per in (0.15 per cm) and took 1 hr to attain equilibrium heat flow. When 6.25 in (15.9 cm) thick batts of fiberglass were needle punched to a thickness of 1 in (2.54 cm), relative R‐values and equilibrium heat flow times were 4.0 per in (0.27 per cm) and 2 hr, respectively. This denoted that the densities and thermal resistances of non‐conducting materials are raised concurrently. Anisotropic heat flow behavior was observed in cellulosic fiber composites with aluminum foil (shiny side out) bonded on one side. It depended upon whether the aluminum foil side or the fibers side faced the heat source. In the latter orientation the aluminum acted as a heat sink, and in the former orientation the foil acted as a poor heat reflector. The poor performance of these insulation composites was related to the fact that aluminum was directly bonded to the fiber batts and was acting as a heat conductor. When cellulose fiber shims (spacers) were placed between the fiber batts and the aluminum foil, the R‐values of the composites were comparable to those of plain batts but the times taken to approach thermal equilibrium increased to >3 hr, denoting that the foil was acting more as a reflector and less as a conductor. Copyright © 2001 John Wiley & Sons, Ltd.     

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     

Synthesis and characterization of an adipic acid–derived epoxy resin

Adipic acid, a highly abundant chemical that can be produced from biomass, was used to prepare an aromatic‐free epoxy resin. Synthesis of the diglycidyl adipate was performed by a one‐step process using epichlorohydrin and by a two‐step process comprising allylation and epoxidation. The viscosity of diglycidyl adipate is 25 mPa·s, which is 99% lower than the diglycidyl ether of bisphenol A (DGEBA). The storage modulus at 25 °C for cured diglycidyl adipate and DGEBA is 2000 and 3200 MPa, respectively. The alpha transition temperature through peak of the loss modulus and the peak of tan(δ), are 77 °C and 90 °C, respectively. Low‐viscosity epoxy applications are discussed herein. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2625–2631     

High resolution solid‐state 13C‐NMR study of as‐cured and irradiated epoxy resins

This article presents the effects of strong ionizing radiations on the physico‐chemical modifications of aliphatic or aromatic amine‐cured epoxy resins based on diglycidyl ether of bisphenol A (DGEBA). Such epoxy resins have a considerable number of applications in the nuclear industrial field and are known to be very stable under moderate irradiation conditions. Using extensively high resolution solid‐state ¹³C‐NMR spectroscopy we show that the aliphatic amine‐cured resin (DGEBA‐TETA) appears much more sensitive to gamma rays than the aromatic amine‐cured one (DGEBA‐DDM). On the one hand, qualitative analyses of the high resolution solid‐state ¹³C‐NMR spectra of both epoxy resins, irradiated under similar conditions (8.5 MGy), reveal almost no change in the aromatic amine‐cured resin whereas new resonances are observed for the aliphatic amine‐cured resin. These new peaks were interpreted as the formation of new functional groups such as amides, acids and/or esters and to alkene groups probably formed in the aliphatic amine skeleton. On the other hand, molecular dynamics of these polymers are investigated by measuring the relaxation times, T_CH, T_1ρH and T_1C , before and after irradiation. The study of relaxation data shows the formation, under irradiation, of a more rigid network, especially for the aliphatic amine‐cured system and confirms that aromatic amine‐cured resin [DGEBA‐4,4′‐diaminodiphenylmethane(DDM)] is much less affected by ionizing radiations than the aliphatic amine‐cured resin [DGEBA‐triethylenetetramine(TETA)]. Moreover, it has been shown that the molecular modifications generated by irradiation on the powder of the aliphatic‐amine‐cured resin appear to be homogeneously distributed inside the polymers as no phase separations can be deduced from the above analyses. Copyright © 2001 John Wiley & Sons, Ltd.     

Influence of the Curing Temperature in the Mechanical and Thermal Properties of Nanosilica Filled Epoxy Resin Coating

0.5–3 wt% nanosilica was added to an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) and cured at 25, 40 or 60 °C using isophoronediamine (IPDA) as hardener. Aggregates of nanosilica were properly dispersed into the DGEBA-IPDA resin and agglomerates formation was avoided. Addition of nanosilica increased the storage modulus E′ and the area and height of the tan δ curve of DGEBA-IPDA resin cured at 25 °C, but no significant differences were found by curing at higher temperature. Gel time measurements and the results obtained by applying the Kamal model to isotherm DSC curing of DGEBA-IPDA-nanosilica revealed that nanosilica catalysed the curing reaction between DGEBA and IPDA, in less extent by increasing the curing temperature.     

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     

Molecular motion,morphology, and thermal properties of multiwall carbon nanotube/polysilsesquioxane composite

Diglycidyl ether of bisphenol A (DGEBA)‐bridged polyorganosiloxane precursors have been prepared successfully by reacting diglycidyl ether of bisphenol A epoxy resin with 3‐aminopropyltriethoxysilane. Acid‐modified and unmodified multiwalled carbon nanotube (MWCNT) were dispersed in the diglycidyl ether of bisphenol A‐bridged polyorganosiloxane precursors and cured to prepare the carbon nanotube/diglycidyl ether of bisphenol A‐bridged polysilsesquioxane (MWCNT/DGEBA‐PSSQ) composites. The molecular motion of MWCNT/DGEBA‐PSSQ nanocomposites was studied by high‐resolution solid‐state ¹³C NMR. Acid‐modification can improve the affinity between MWCNT and the polymer matrix. The molecular motion of the DGEBA‐PSSQ decreased with acid‐modified MWCNT content. However, when unmodified MWCNT was used, the molecular motion of the DGEBA‐PSSQ was increased. SEM and TEM microphotographs confirm that acid‐modified MWCNT exhibits better dispersion than unmodified MWCNT in DGBEA‐PSSQ. The dynamic mechanical properties of acid‐modified MWCNT/DGBEA‐PSSQ composites are more favorable than those of unmodified MWCNT. T_g of the DGEBA‐PSSQ decreased from 174.0 °C (neat DGEBA‐PSSQ) to 159.0 °C (1 wt % unmodified MWCNT) and 156.0 °C (1 wt % acid‐modified MWCNT). The storage modulus (at 30 °C) of the DGEBA‐PSSQ increased from 1.23 × 10⁹ Pa (neat DGEBA‐PSSQ) to 1.65 × 10⁹ Pa (1 wt % acid‐modified MWCNT). However, when unmodified MWCNT was used, the storage modulus of the DGEBA‐PSSQ decreased to 6.88 × 10⁸ Pa (1 wt % unmodified MWCNT). At high temperature, above 150 °C, storage modulus of nanocomposites was higher than that of neat polymer system. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 472–482, 2008     

Tannic acid: A sustainable crosslinking agent for high glass transition epoxy materials

Epoxy thermosets have revolutionized the coating, adhesive, and composite industries but the chemicals from which they are synthesized have significant effects on the environment and human health not only precure but also after crosslinking has occurred. In this study, we propose tannic acid (TA) as an alternative epoxy hardening agent for commercially available epoxy resin, the diglycidyl ether of bisphenol A (DGEBA). The resulting thermosets were characterized by Fourier transform infrared spectroscopy, optical microscopy, dynamic mechanical analysis, differential scanning calorimetry, compression testing, and thermogravimetric analysis. The results from this study showed that at temperatures above 100 °C, the compatibility of TA in DGEBA was significantly increased for loading levels up to 37% weight of TA in DGEBA, something that has not been seen before in literature. It was also discovered that at high loading levels, the resulting materials had glass transition temperatures at and above 200 °C. The resulting material was proposed as a more sustainable alternative to amine or acid hardened epoxy thermosets and was particularly useful in high‐temperature applications. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1468–1480     

Synthesis of a novel DPPA‐containing benzoxazine to flame‐retard epoxy resin with maintained thermal properties

The flame‐retarded epoxy resin with improved thermal properties based on environmentally friendly flame retardants is vital for industrial application. Hereby, a novel reactive‐type halogen‐free flame retardant, 10‐(3‐(4‐hydroxy phenyl)‐3,4‐dihydro‐2H‐benzo[e] [1,3] oxazin‐4‐yl)‐5H‐phenophosphazinine 10‐oxide (DHA‐B) was synthesized via a two‐step reaction route. Its structure was characterized using ¹H, ¹³C, and ³¹P NMR and HRMS spectra. For 4,4′‐diaminodipheny ethane (DDM) and diglycidyl ether of bisphenol A (DGEBA)‐cured systems, the epoxy resin with only 2 wt% loading of DHA‐B passed V‐0 rating of UL‐94 test. Significantly, its glass transition temperature (T_g) and initial decomposition temperature (T_5%) were as high as 169.6°C and 359.6°C, respectively, which were even higher than those of the corresponding original epoxy resin. Besides, DHA‐B decreased the combustion intensity during combustion. The analysis of residues after combustion suggested that DHA‐B played an important role in the condensed phase.     

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 P/Si flame retardant and its application in epoxy systems

In this report, a novel phosphorus/silicon‐containing reactive flame retardant, hexa(3‐triglycidyloxysilylpropyl)triphosphazene (HGPP), was synthesized and characterized by Fourier transform infrared spectrometry and nuclear magnetic resonance spectra (¹H, ³¹P, and ²⁹Si), respectively. To prepare cured epoxy, HGPP had been co‐cured with diglycidyl ether of bisphenol‐A (DGEBA) via 4,4‐diaminodiphenylsulfone as a curing agent. The mechanical, thermal, and flame retardant properties of the cured epoxy were evaluated by dynamic mechanical analysis, thermogravimetric analysis, and limiting oxygen index (LOI). According to these results, it could be found that incorporation of HGPP in the cured epoxy system showed good thermal stability, high LOI values, and high char yield at high temperature. As moderate loading of HGPP in the epoxy system, its storage modulus and glass transition temperature were higher than those of neat DGEBA. Copyright © 2011 John Wiley & Sons, Ltd.     

Studies on epoxy resins cured by cationic latent thermal catalysts: The effect of the catalysts on the thermal,rheological, and mechanical properties

To investigate the effect of catalysts on the thermal, rheological, and mechanical properties of an epoxy system, a resin based on diglycidyl ether of bisphenol‐A (DGEBA) was cured by two cationic latent thermal catalysts, N‐benzylpyrazinium hexafluoroantimonate (BPH) and N‐benzylquinoxalinium hexafluoroantimonate (BQH). Differential scanning calorimetry was used for the thermal characterization of the epoxy systems. Near‐infrared spectroscopy was employed to examine the cure reaction between the DGEBA and the latent thermal catalysts used. The rheological properties of the blend systems were investigated under an isothermal condition with a rheometer. To characterize the mechanical properties of the systems, flexure, fracture toughness (K_IC), and impact tests were performed. The phase morphology was studied with scanning electron microscopy of the fractured surfaces of mechanical test samples. The conversion and cure activation energy of the DGEBA/BQH system were higher than those of the DGEBA/BPH system. The crosslinking activation energy showed a result similar to that obtained from the cure kinetics of the blend systems. The flexure strength, K_IC, and impact properties of the DGEBA/BQH system were also superior to those of the DGEBA/BPH system. This was a result of the substituted benzene group of the BQH catalyst, which increased the crosslink density and structural stability of the epoxy system studied. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 187–195, 2001     

Study of the physical aging of an epoxy/cycloaliphatic amine resin modified with abs

Using differential scanning calorimetry (DSC) we have studied the physical aging of an epoxy resin based on the diglycidyl ether of bisphenol A (DGEBA) modified by two different contents of an acrylonitrile-butadiene-styrene (ABS) and cured with 1,3-bisaminomethylcyclohexane (1,3-BAC). Samples fully cured were annealed at temperature of 125°C for periods of time of 72 and 120 h, to determine the process of physical aging. The apparent activation energy for the enthalpy relaxation, Dh*, is determined as the sample is heated at 10°C min^-1 following cooling at various rates through the glass transition region. DSC studies suggested that the presence of thermoplastic inhibits the process of relaxation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Flame‐retardant epoxy resins with high glass‐transition temperatures. II. Using a novel hexafunctional curing agent: 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐yl‐tris(4‐aminophenyl) methane

We synthesized a novel phosphorus‐containing triamine [9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐yl‐tris(4‐aminophenyl) methane (dopo‐ta)] from the nucleophilic addition of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide and pararosaniline chloride, using triethylamine as an acid receiver. We confirmed the structure of dopo‐ta by IR, mass, and NMR spectra and elemental analysis. dopo‐ta served as a curing agent for diglycidyl ether of bisphenol A (DGEBA) and dicyclopentadiene epoxy (hp7200). Properties such as the glass‐transition temperature (T_g), thermal decomposition temperature, flame retardancy, moisture absorption, and dielectric properties of the cured epoxy resins were evaluated. The T_g's of cured DGEBA/dopo‐ta and hp7200/dopo‐ta were 171 and 190 °C, respectively. This high T_g phenomenon is rarely seen in the literature after the introduction of a flame‐retardant element. The flame retardancy increased with the phosphorus content, and a UL‐94 V‐0 grade was achieved with a phosphorus content of 1.80 wt % for DGEBA/dopo‐ta/diamino diphenylmethane (DDM) systems and 1.46 wt % for hp7200/dopo‐ta/DDM systems. The dielectric constants for DGEBA/dopo‐ta and hp7200/dopo‐ta were 2.91 and 2.82, respectively, implying that the dopo‐ta curing systems exhibited low dielectric properties. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5971–5986, 2005     

Novel quaternary ammonium borates as latent catalysts for epoxy–phenolic resins

Novel tetrabutylammonium tetrakis(substituted benzoyloxy)borate salts ( 1a – 1d ) were synthesized by the reaction of tetrabutylammonium tetraphenylborate and corresponding substituted benzoic acids. Polyaddition reactions of diglycidyl ether of bisphenol A (DGEBA) and 4,4′‐bisphenol F (44BPF) or bisphenol F (BPF‐D) with the ammonium borates were investigated as model reactions of epoxy/phenol–novolac resin systems with respect to the thermal latency and storage stability of the catalyst. The polyaddition of DGEBA/44BPF with the ammonium borates in diglyme at 150 °C for 6 h proceeded up to 84–94% conversions and gave polymers with number‐average molecular weights of 3750–5750, whereas the polyaddition at 80 °C for 6 h gave less than 9% conversions. The catalytic activity of ammonium borates 1a – 1d depended on the substituent of the phenyl group of the borates, and the order of activity was 1b (p‐OMe) > 1a (? H) > 1c (p‐NO₂) > 1d [3,5‐(NO₂)₂]. The ammonium borate catalyst with the substituent that yielded lower acidity of the corresponding substituted benzoic acid tended to reveal higher activity. In comparison with tetrabutylammonium bromide (TBAB) as a conventional ammonium salt, 1a – 1d revealed better thermal latency. The storage stability of DGEBA/BPF‐D with the ammonium borate catalysts in bulk at 40 °C was better than that with TBAB. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2689–2701, 2002     

Hydrogen bonding interactions,crystallization, and surface hydrophobicity in nanostructured epoxy/block copolymer blends

Hydrogen bonding interactions, phase behavior, crystallization, and surface hydrophobicity in nanostructured blend of bisphenol A‐type epoxy resin (ER), for example, diglycidyl ether of bisphenol A (DGEBA) and poly(ε‐caprolactone)‐block‐poly(dimethyl siloxane)‐block‐poly(ε‐caprolactone) (PCL–PDMS–PCL) triblock copolymer were investigated by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, transmission electron microscopy, small‐angle X‐ray scattering, and contact angle measurements. The PCL–PDMS–PCL triblock copolymer consisted of two epoxy‐miscible PCL blocks and an epoxy‐immiscible PDMS block. The cured ER/PCL–PDMS–PCL blends showed composition‐dependent nanostructures from spherical and worm‐like microdomains to lamellar morphology. FTIR study revealed the existence of hydrogen bonding interactions between the PCL blocks and the cured epoxy, which was responsible for their miscibility. The overall crystallization rate of the PCL blocks in the blend decreased remarkably with increasing ER content, whereas the melting point was slightly depressed in the blends. The surface hydrophobicity of the cured ER increased upon addition of the block copolymer, whereas the surface free energy (γ_s) values decreased with increasing block copolymer concentration. The hydrophilicity of the epoxy could be reduced through blending with the PCL–PDMS–PCL block copolymer that contained a hydrophobic PDMS block. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 790–800, 2010     

A Well-Defined Cyclotriphosphazene-Based Epoxy Monomer and Its Application as A Novel Epoxy Resin: Synthesis,Curing Behaviors,and Flame Retardancy

Abstract

A novel cyclotriphosphazene-based epoxy monomer, hexa-[4-(glycidyloxycarbonyl) phenoxy]cyclotriphosphazene (HGCP), was synthesized via a four-step synthetic route, and fully characterized by ¹H, ¹³C, and ³¹P NMR spectroscopy, high-resolution mass spectrometry, and elemental analysis. Thermosetting systems based on HGCP with three curing agents, for example, 4,4′-diaminodiphenylsulfone (DDS), 4,4′-diaminodiphenylmethane (DDM), and dicyandiamide (DICY), were used for making a comparison of their thermal curing behaviors. The curing behaviors were measured by differential scanning calorimetry. Moreover, flame retardancy of HGCP thermosetting systems was estimated by Limiting Oxygen Index (LOI) and Vertical Burning Test (UL-94). The resulting HGCP thermosetting systems exhibited better flame retardancy than the common epoxy resins diglycidyl ether of bisphenol A (DGEBA) and the regular brominated bisphenol A epoxy resin (TBBA) cured by DDS, respectively. When HGCP was cured by DDS, its thermosetting system gave the most char residues, met the UL-94 V-0 classification, and had a limiting oxygen index value greater than 35.     

Cure kinetics of epoxy resin and thermoplastic polymer

The cure kinetics and morphology of diglycidyl ether of bisphenol A (DGEBA) modified with polyvinyl acetate (PVAc) using diaminodiphenylmethane (DDM) as hardener were investigated through differential scanning calorimetry (DSC) and environmental scanning electron microscopy (ESEM). Isothermal curing measurements were carried out at 150, 120 and 80°C. The kinetic parameters were obtained using the general autocatalytic chemically controlled model. The comparison of the kinetic data indicates that the presence of PVAc does not change the autocatalytic nature of the cure reaction. Two T _g’s were observed in the fully cured samples of the modified systems. ESEM micrographies confirm the biphasic morphology.     

Synthesis and thermal characterization of phosphorus containing siliconized epoxy resins

Siliconized epoxy matrix resin was developed by reacting diglycidyl ethers of bisphenol A (DGEBA) type epoxy resin with hydroxyl terminated polydimethylsiloxane (silicone) modifier, using γ-aminopropyltriethoxysilane crosslinker and dibutyltindilaurate catalyst. The siliconized epoxy resin was cured with 4, 4-diaminodiphenylmethane (DDM), 1,6-hexanediamine (HDA), and bis (4-aminophenyl) phenylphosphate (BAPP). The BAPP cured epoxy and siliconized epoxy resins exhibit better flame-retardant behaviour than DDM and HDA cured resins. The thermal stability and flame-retardant property of the cured epoxy resins were studied by thermal gravimetric analysis (TGA) and limiting oxygen index (LOI). The glass transition temperatures (T_g) were measured by differential scanning calorimetry (DSC) and the surface morphology was studied by scanning electron microscopy (SEM). The heat deflection temperature (HDT) and moisture absorption studies were carried out as per standard testing procedure. The thermal stability and flame-retardant properties of the cured epoxy resins were improved by the incorporation of both silicone and phosphorus moieties. The synergistic effect of silicone and phosphorus enhanced the limiting oxygen index values, which was observed for siliconized epoxy resins cured with phosphorus containing diamine compound.     

Physical aging of poly(ether sulfone)-modified epoxy resin

The physical aging process of 4,4′-diaminodiphenylsulfone (DDS) cured diglycidyl ether bisphenol-A (DGEBA) blended with poly(ether sulfone) (PES) was studied by differential scanning calorimetry (DSC) at four aging temperatures between T_g-50°C and T_g-10°C. At aging temperatures between T_g-50 and T_g-30°C, the experimental results of epoxy resin blended with 20 wt% of PES showed two enthalpy relaxation processes. One relaxation process was due to the physical aging of PES, the other relaxation process was due to the physical aging of epoxy resin. The distribution of enthalpy relaxation process due to physical aging of epoxy resin in the blend was broader and the characteristic relaxation time shorter than those of pure epoxy resin at the above aging temperatures (between T_g-50 and T_g-30°C). At an aging temperature between T_g-30 and T_g-10°C, only one enthalpy relaxation process was found for the epoxy resin blended with PES, the relaxation process was similar to that of pure epoxy resin. The enthalpy relaxation process due to the physical aging of PES in the epoxy matrix was similar to that of pure PES at aging temperatures between T_g-50 and T_g-10°C. © 1997 John Wiley & Sons, Inc.