Dynamic Differential Scanning Calorimetry Scans Research Articles

Effect of Additives on Mineral Trioxide Aggregate Setting Reaction Product Formation

IntroductionMineral trioxide aggregate (MTA) sets via hydration of calcium silicates to yield calcium silicate hydrates and calcium hydroxide (Ca[OH]2). However, a drawback of MTA is its long setting time. Therefore, many additives have been suggested to reduce the setting time. The effect those additives have on setting reaction product formation has been ignored. The objective was to examine the effect additives have on MTA's setting time and setting reaction using differential scanning calorimetry (DSC). MethodsMTA powder was prepared with distilled water (control), phosphate buffered saline, 5% calcium chloride (CaCl2), 3% sodium hypochlorite (NaOCl), or lidocaine in a 3:1 mixture and placed in crucibles for DSC evaluation. The setting exothermic reactions were evaluated at 37°C for 8 hours to determine the setting time. Separate samples were stored and evaluated using dynamic DSC scans (37°C→640°C at10°C/min) at 1 day, 1 week, 1 month, and 3 months (n = 9/group/time). Dynamic DSC quantifies the reaction product formed from the amount of heat required to decompose it. Thermographic peaks were integrated to determine enthalpy, which was analyzed with analysis of variance/Tukey test (α = 0.05). ResultsIsothermal DSC identified 2 main exothermal peaks occurring at 44 ± 12 and 343 ± 57 minutes for the control. Only the CaCl2 additive was an accelerant, which was observed by a greater exothermic peak at 101 ± 11 minutes, indicating a decreased setting time. The dynamic DSC scans produced an endothermic peak around 450°C–550°C attributed to Ca(OH)2 decomposition. The use of a few additives (NaOCl and lidocaine) resulted in significantly less Ca(OH)2 product formation. ConclusionsDSC was used to discriminate calcium hydroxide formation in MTA mixed with various additives and showed NaOCl and lidocaine are detrimental to MTA reaction product formation, whereas CaCl2 accelerated the reaction.

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.

Study on curing kinetics of a diglycidyl ether of bisphenol A epoxy resin/microencapsulated curing agent system

A modified imidazole curing agent, EMI-g-BGE, was encapsulated for one-package of diglycidyl ether of bisphenol A (DGEBA) epoxy resin system. Polyetherimide (PEI) was used as the wall material, and the emulsion solvent evaporation method was used to form the microcapsules. The morphology and particle size distribution of microcapsules were evaluated by scanning electron microscopy (SEM), mastersizer analyzer. Microcapsules exhibited spherical shapes and the mean particle size was about 745 nm. The curing kinetic of DGEBA/microcapsules curing agent was studied by nonisothermal differential scanning calorimetry (DSC) technique at different heating rates. Dynamic DSC scans indicated the microcapsule was an effective curing agent of epoxy resin. The apparent activation energy Ea was 88.03 kJ/mol calculated through Kissinger method, more than DGEBA/EMI-g-BGE system. This microcapsule of EMI-g-BGE exhibited a long shelf life, and the curing did not occur in this epoxy-microcapsule resin system for more than 3months at room temperature. The kinetic parameters were determined by Málek method and a two-parameter ( m, n) autocatalytic model (Šesták–Berggren equation) was found to be the most adequate selected kinetic model, which showed the encapsulation of the curing agent EMI-g-BGE did not change the cure reaction mechanism of the epoxy resin system. From the experimental data, the nonisothermal DSC curves show the results being in accordant with those theoretically calculated.

Gelling and curing behaviors of benzoxazine/epoxy formulations containing 4,4′-thiodiphenol accelerator

Benzoxazine (BOX)/diglycidyl ether of bisphenol A (DGEBA) based epoxy resins (BOX/DGEBA = 100/0, 75/25 and 50/50 wt.%) with and without 4,4′-thiodiphenol accelerator (DT300) were prepared. The gelling and curing behaviors of the BOX and BOX/DGEBA mixtures in presence and absence of DT300 (10 parts per hundred resin, phr) were investigated using plate–plate rheometry and differential scanning calorimetry (DSC). The gel time was determined in isothermal scans at three different temperatures (T = 180, 200, and 220 °C). Dynamic DSC scans were registered at four heating rates (β = 5, 10, 15, and 20 °C min−1, respectively). The activation energy of gelling was assessed by an Arrhenius, whereas that of the curing by the Kissinger and Ozawa methods. Combination of BOX with DGEBA delayed the gel formation and increased the activation energy of both gelling and curing processes compared to neat BOX resin. By contrast, addition of 4,4′-thiodiphenol as co-reactive accelerator markedly reduced the gel time and the activation energy of both gelling and curing of BOX and BOX/DGEBA formulations.

Studies on Cure Kinetics of a Novel Imidazole Derivative Curing Agent for Epoxy Resin

We used phenyl glycidyl ether (PGE) to modify 2-methylimidazole (2MI) and obtained a novel imidazole derivative named as 2MI-g-PGE. FTIR spectroscopy and 1H NMR spectroscopy have been used to characterize the chemical structure of 2MI-g-PGE. The curing kinetic of diglycidyl ether of bisphenol A (DGEBA) with 2MI-g-PGE as curing agent was studied by dynamic differential scanning calorimetry (DSC) technique. Dynamic DSC scans indicated that 2MI-g-PGE was an effective curing agent of epoxy resin. Both Kissinger method and Ozawa method were adopted to calculate the activation energy (Ea) of DGEBA/2MI-g-PGE system and the values were 74.23kJ/mol and 76.58kJ/mol respectively. By using Crane and Kissinger equations, the characteristic parameters of the curing kinetics including the order of reaction (n) and the pre-exponential factor (A) of DGEBA/2MI-g-PGE system were calculated to be 0.92 and 2.38×1012s-1 respectively.

ANALYSIS OF CURE REACTION KINETICS OF ARAMID/TOUGHENED-EPOXY PREPREG SYSTEM AIMING AT PROCESSING OF COMPOSITE MATERIAL FOR STRUCTURAL APPLICATIONS

This work is aimed at investigating the cure, kinetics and rheological parameters of aramid/toughened epoxy prepreg. The cure reaction evolves simultaneously with changes in rheology, which is normally referred to as rheo-kinetic behavior. Understanding the cure behavior of a resin system is essential in the development and optimization of composite fabrication processes. The cure kinetics and rheological behavior were evaluated using a differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and a rheometer. Values of the kinetic parameters were obtained from dynamic DSC scans using an nth order reaction model. Rheological measurements as a function of temperature and time were made for the prepreg system. With the determination of the kinetics for the cure and of the rheological parameters of the prepreg systems, cure could be established that lead to manufacturing high-performance composite. The intention is to present a simple methodology to devise cure cycles for the automotive structural parts, therefore a simple model was selected which worked adequately for the desired accuracy. The effect of toughener was not taken into consideration as the scope was to aid the decision about the curing process.

Synthesis, characterization, and curing of {2,6–bis‐[2‐(bis‐oxiranylmethyl‐amino)‐methylbenzyl]‐phenyl}‐bis‐oxiranylmethylamine (BPBOMA)

AbstractThe curing behavior of epoxy resin prepared by reacting epichlorohydrin with amine functional aniline acetaldehyde condensate (AFAAC) was investigated using AFAAC as a curing agent. The epoxy resin, {2,6‐bis‐[2‐(bis‐oxiranylmethyl‐amino)‐methylbenzyl]‐phenyl}‐bis‐oxiranylmethylamine (BPBOMA), was characterized by FTIR and 1H‐NMR spectroscopy, viscosity measurement, and determination of epoxy content. Analysis of the curing reaction was followed by differential scanning calorimetry (DSC) analysis. To investigate the curing kinetic with AFAAC, dynamic DSC scans were made at heating rates of 5, 10, 15, and 20°C/min. The activation energy and frequency factor of the AFAAC formulation were evaluated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3168–3174, 2006

Characterization of cure of carbon/epoxy prepreg used in aerospace field

Carbon/epoxy 8552 prepreg is a thermoplastic toughened high-performance epoxy being used in the manufacture of advanced army material. Understanding the cure behavior of a thermosetting system is essential in the development and optimization of composite fabrication processes. The cure kinetics and rheological behavior were evaluated using a differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and a rheometer. Values of the kinetic parameters were obtained from dynamic DSC scans using an nth order reaction model. Rheological measurements as a function of temperature and time were made for the prepreg system. The manufacturer's recommended cure cycle was evaluated and considered adequate to consolidated the studied system.

Cure kinetics of a cobalt catalysed dicyanate ester monomer in air and argon atmospheres from DSC data

A kinetic analysis of the cyclotrimerisation reaction of a dicyanate ester monomer catalysed by cobalt(II) acetylacetonate and nonylphenol in air and argon atmospheres has been carried out by differential scanning calorimetry (DSC). Dynamic and isothermal DSC scans as well as the glass transition temperature are the experimental data obtained. From isothermal scans a higher cyanate conversion in air than in argon was obtained. The cyanate conversions are satisfactorily described with a second-order kinetic equation in the kinetically controlled region, and by m-order ( m<1) equation after vitrification is reached. Activation energies determined by different procedures agree among them, showing slightly higher values in argon than in air.

Study of cure kinetics of epoxy-silica organic–inorganic hybrid materials

Cure kinetics of organic–inorganic hybrids based on epoxy resin was investigated, using differential scanning calorimetry (DSC). Thermoset hybrid materials were prepared from diglycidyl ether of bisphenol A (DGEBA) as organic precursor, and 3-glycidyloxypropyltrimethoxysilane (GLYMO) as inorganic precursor. Precursors were polymerised simultaneously using poly(oxypropylene)diamine (Jeffamine D230) as a curing agent. Isothermal DSC characterisation of DGEBA/Jeffamine system and two hybrid DGEBA/GLYMO/Jeffamine systems, with DGEBA and GLYMO mixed in mass ratios of 2:1 and 1:1, respectively, was performed at different temperatures. Applicability of empirical models, commonly used to describe the curing kinetics of thermosets, to hybrid systems was investigated, and the resulting parameters were tested on dynamic DSC scans. Additionally, prepared materials were studied by FTIR and the extraction in tetrahydrofuran. The presence of inorganic phase was found to hinder complete cross-linking of organic phase and influence the kinetics of cure.

Differential scanning calorimetry study of linseed oil cured with metal catalysts

Differential scanning calorimetry (DSC) has been used to study the autoxidative curing process of linseed oil catalyzed by conventional metal driers and two metal sol-gel precursors, Ti(Oi-Pr) 2(acac) 2 and Ti(Oi-Pr) 4, at elevated temperatures. Linseed oil resins with a range of 0–5.0 wt.% metal sol-gel precursor and 0–9.0 wt.% zirconium dric have been investigated by both dynamic and isothermal methods. The onset, peak and end temperatures of the reaction exotherms were observed as a function of metal catalyst type and content. The Borchardt and Daniels kinetics method was used to quantify the heat of reaction of the dynamic DSC scans. The indention hardness of the resultant coatings in the DSC sample pans was measured as an indication of crosslink density. The inclusion of small quantities of metal catalyst (0–5.0 wt.% titanium alkoxide, 0–2.0 wt.% zirconium drier) caused the reaction exotherm to broaden and shift to lower temperatures. At higher metal catalyst content (>5.0 wt.% Ti(Oi-Pr) 2(acac) 2 or 5.0 wt.% Ti(Oi-Pr) 4) the reaction exotherms became imperceptible. Overall, as the metal catalyst content was increased, the heat of reaction decreased while indention hardness increased. The effects of the two sol-gel precursors on the reaction exotherms were similar to the effects of conventional driers. Combinations of conventional driers were also studied.

Curing of carbon fibre reinforced epoxy matrix composites

The curing kinetics and viscosity of two carbon fibre reinforced epoxy systems, Fibredux 914C and Fiberite HYE 1248M2F, were measured using differential scanning calorimetry (DSC) and torsion rheometry. Fibredux 914C is a high temperature (175°C) cure system and Fiberite is a low temperature (120°C) cure system. Values of kinetic parameters were obtained from dynamic and isothermal DSC scans using an nth order reaction model. Viscosity measurements as a function of time were made for both systems and fitted to an expression relating viscosity to degree of cure.

Vitrification and further structural relaxation in the isothermal curing of an epoxy resin

AbstractIsothermal curing of an epoxy resin based on diglycidyl ether of bisphenol A, using a hardener derived from phthalic anhydride, has been performed at curing temperatures between 30 and 130°C. Samples were cured isothermally at various intervals of time and analyzed by differential scanning calorimetry (DSC), the glass transition temperature Tg, and the conversion degree being determined by the residual enthalpy technique. The vitrification phenomenon and a further structural relaxation process, occurring at curing temperatures (Tc) lower than the maximum Tg (109°C), at which Tg equalizes Tc, have been studied at curing temperatures between 30 and 100°C. The structural relaxation process is analyzed by the endothermic peak that appears superposed on Tg in dynamic DSC scans. The area of this peak (Q) is a measure of the recovery enthalpy, and thus of the extent of the relaxation process. This process begins at higher curing times (tc) when Tc decreases because the vitrification of the system starts later. Both the enthalpy recovery (Q) and the temperature of the endothermic peak (Tm) increase with the annealing time (ta), calculated as the difference between tc and the time in which vitrification occurs, and tend to have a limiting value due to the fact that the system loses mobility when the free volume decreases during its asymptotic approach toward the metastable equilibrium state. Furthermore, the dependence of Q and Tm on ta at different Tc shows that the relaxation process in partially cured resins depends on the conversion degree of the system and consequently on the crosslinking density of the network.

Monitoring the Cross-Linking of Epoxide Resins by Thermoanalytical Techniques

Abstract The curing reaction of bisphenol A diglycidylether with 4,4′-diaminodiphenylmethane (DDM) was studied by thermoanalytical methods. The overall reaction was monitored through the exothermic heat of reaction by differential scanning calorimetry (DSC), and a method is developed for predicting isothermal conversion-time curves over a wide temperature range from the results of two dynamic DSC scans. The reaction mechanism is not specified but it is assumed not to change with conversion, and the rate is assumed to be controlled by a single rate constant of the Arrhenius form. A series of fully cured resins prepared with varying DDM concentration is characterized by penetrometer, thermal expansion, and DSC methods. The Tg's of these resins are compared with those obtained using the stoichiometric quantity of DDM and reacted to different calorimetric degrees of cure. The Tg of the resin increases by about 70[ddot];C in the final 10% of the curing reaction where ΔH measurements are least sensitive, so tha...

Recommended specification for linseed oil, raw, refined and boiled

Differential scanning calorimetry (DSC) has been used to study the autoxidative curing process of linseed oil catalyzed by conventional metal driers and two metal sol-gel precursors, Ti(Oi-Pr)2(acac)2 and Ti(Oi-Pr)4, at elevated temperatures. Linseed oil resins with a range of 0–5.0 wt.% metal sol-gel precursor and 0–9.0 wt.% zirconium dric have been investigated by both dynamic and isothermal methods. The onset, peak and end temperatures of the reaction exotherms were observed as a function of metal catalyst type and content. The Borchardt and Daniels kinetics method was used to quantify the heat of reaction of the dynamic DSC scans. The indention hardness of the resultant coatings in the DSC sample pans was measured as an indication of crosslink density. The inclusion of small quantities of metal catalyst (0–5.0 wt.% titanium alkoxide, 0–2.0 wt.% zirconium drier) caused the reaction exotherm to broaden and shift to lower temperatures. At higher metal catalyst content (>5.0 wt.% Ti(Oi-Pr)2(acac)2 or 5.0 wt.% Ti(Oi-Pr)4) the reaction exotherms became imperceptible. Overall, as the metal catalyst content was increased, the heat of reaction decreased while indention hardness increased. The effects of the two sol-gel precursors on the reaction exotherms were similar to the effects of conventional driers. Combinations of conventional driers were also studied.