Dynamic Differential Scanning Calorimeter Research Articles

Effects of Curing Defects in Adhesive Layers on Carbon Fiber-Quartz Fiber Bonded Joint Performance.

Due to their mechanical load-bearing and functional wave transmission, adhesively bonded joints of carbon fiber-quartz fiber composites have been widely used in the new generation of stealth aviation equipment. However, the curing defects, caused by deviations between the process environment and the setting parameters, directly affect the service performance of the joint during the curing cycle. Therefore, the thermophysical parameter evolution of adhesive films was analyzed via dynamic DSC (differential scanning calorimeter), isothermal DSC and TGA (thermal gravimetric analyzer) tests. The various prefabricating defects within the adhesive layer were used to systematically simulate the impacts of void defects on the tensile properties, and orthogonal tests were designed to clarify the effects of the curing process parameters on the joints' bonding performance. The results demonstrate that the J-116 B adhesive film starts to cure at a temperature of 160 °C and gradually forms a three-dimensional mesh-bearing structure. Furthermore, a bonding interface between the J-116 B adhesive film and the components to be connected is generated. When the curing temperature exceeds 200 °C, both the adhesive film and the resin matrix thermally degrade the molecular structure. The adhesive strength weakens with an increasing defect area ratio and number, remaining more sensitive to triangle, edge and penetration defects. By affecting the molecular structure of the adhesive film, the curing temperature has a significant impact on the bonding properties; when the curing degree is ensured, the curing pressure directly impacts the adhesive's performance by influencing the morphology, number and distribution of voids. Conversely, the heating rate and heat preservation time have minimal effects on the bonding performance.

Research on the thermal hazard of N-Nitrodihydroxyethyl dinitrate (DINA) under the action of diethanolamine

N-Nitrodihydroxyethyl dinitrate (DINA) is a commonly used energetic material. In this work, the effect of diethanolamine (DEA) on the thermal stability of DINA was studied. Firstly, the decomposition kinetics of DINA under the influence of DEA was analyzed by applying dynamic differential scanning calorimeter (DSC) experiments. Then, isothermal DSC tests with the “Interruption and re-scanning” method determined that the decomposition reactions of DINA containing 29% DEA consists of four continuous steps: the first step is a n-order reaction, and the last three steps are autocatalytic reactions. The kinetic parameters of the four-step reaction model were calculated by model-fitting method. Finally, the thermal risk parameter like TMRad was predicted based on the kinetic parameters, which has certain guiding significance for the process production of DINA.

Investigation of the decomposition kinetics and thermal hazards of 2,4-Dinitrotoluene on simulation approach

As a major intermediate in the synthesis of explosives, the destructive nature and thermal hazards of 2,4-DNT are enormous. To evaluate the potential thermal hazards for its decomposition, the differential scanning calorimeter (DSC) experiments under non-isothermal and isothermal conditions were performed to determine the decomposition kinetic model and parameters. According to the dynamic DSC results, 2,4-DNT underwent a melting process before thermal decomposition, the endothermic peak and exothermic peak are identified at about 67–70 ℃ and 245–272 ℃, respectively. Combined with the results of non-isothermal and isothermal tests, the proper decomposition kinetic model of 2,4-DNT consists of two consecutive reactions has been created and verified. Thermal behaviors under different scenarios and thermal explosion have been simulated separately to predict the thermal hazard parameters. It can also be concluded from the simulation under external fire exposure scenario, with increasing of the filling ratios for sample, the induction period of the exothermic decomposition reaction is also continuously shortened, accompanied by greater danger.

Simulation approach to decomposition kinetics and thermal hazards of hexamethylenetetramine

The thermal stability of HMT under dynamic, isothermal and adiabatic conditions was investigated using differential scanning calorimeter (DSC) and accelerating rate calorimeter (ARC), respectively. It is found from the dynamic DSC results that the exothermic decomposition reaction appears immediately after endothermic peak, a coupling phenomenon of heat absorption and generation, and the endothermic peak and exothermic peak were indentified at about 277–289 and 279–296 °C (Tpeak) with the heating rates 1, 2, 4 and 8 °C min−1. The ARC results reveal that the initial decomposition temperature of HMT is about 236.55 °C, and the total gas production in decomposition process is 6.9 mol kg−1. Based on the isothermal DSC and ARC data, some kinetic parameters have been determined using thermal safety software. The simulation results show that the exothermic decomposition process of HMT can be expressed by an autocatalytic reaction mechanism. There is also a good agreement between the kinetic model and kinetic parameters simulated based on the isothermal DSC and ARC data. Thermal hazards of HMT can be evaluated by carrying out thermal explosion simulations, which were based on kinetic models (Isothermal DSC and ARC) to predict several thermal hazard indicators, such as TD24, TD8, TCL, SADT, ET and CT so that we can optimize the conditions of transportation and storage for chemical, also minimizing industrial disasters.

Thermal stability evaluation of β-artemether by DSC and ARC

The thermal stability of β-artemether under dynamic, isothermal and adiabatic conditions were investigated by differential scanning calorimeter (DSC) and accelerating rate calorimeter (ARC), respectively. The dynamic DSC measurements at various heating rates (1, 2, 4 and 8°Cmin−1) displayed that β-artemether experienced polymorph transformation in the melting process. According to the isothermal DSC results at different temperatures 86, 88, 90 and 92°C, β-artemether decomposed after the completion of the melting and the polymorph transformation, and the thermal decomposition of β-artemether is hazardous for its characteristic of autocatalytic decomposition. The kinetics analysis dynamically and isothermally described by Friedman method indicated the thermal decomposition of β-artemether did not comply with a single mechanism. The ARC results showed that the pressure increased with the increase of temperature, and indicated obvious linear relationship. Based on the ARC data, the value of SADT of β-artemether in 50kg package was obtained.

Blends of cardanol-based epoxidized novolac resin and CTBN for application in surface coating: a study on thermal, mechanical, chemical, and morphological characteristics

Blend samples of cardanol-based epoxidized novolac resin and different weight percentages of carboxyl-terminated butadiene acrylonitrile (CTBN) were developed and cured with stoichiometric amounts of aliphatic amine. The formation of various products during the curing of blend samples has been studied by Fourier-transform infrared spectroscopy. The dynamic differential scanning calorimeter scans showed that the pure epoxies and their blend samples with CTBN cured in the temperature range of 100–150°C. The blend sample containing 15 wt% CTBN showed the least cure time (at 120°C) among all other blend samples. Upon evaluation, it was found that blend samples exhibit better properties compared to pure epoxy resin in terms of increase in impact strength and elongation-at-break of the casting and gloss, scratch hardness, adhesion, and flexibility of the film. The improvement in these properties indicates that the rubber modified resin would be more durable than the epoxy based on cardanol. Chemical and morphological properties of the formulated resins were also determined. The thermal stability of the blend samples containing 15 wt% CTBN in epoxy resin was the highest among all other prepared systems. The blend morphology, studied by scanning electron microscope, showed the presence of precipitated discrete rubber particles, which dispersed throughout the epoxy matrix—i.e., they revealed the presence of two-phase morphological features.

TTT Diagram Used to Control Phase Structure of 2/4 Functional Epoxy Blends for Advanced Composites

This article uses a 2/4 functional epoxy blend system (E-54/AG-80) cured with diaminodiphenyl sulphone(DDS) as a raw material and develops a methodological procedure to establish a cure kinetic model with isothermal and dynamic differential scanning calorimeter(DSC) method and a gelation model with round-disk compression mode dynamic mechanical analyzer(DMA), thus acquiring a series of experimental data. Characteristic temperatures such as initial glass transition temperature Tg0, gelation glass transition temperature gelTg, and infinite glass transition temperature Tg∞ are determined. The cure degree at gelation is turned out to be 0.45, while gelTg is found to be 70.2 °C. The data are then used to form time-temperature-transition(TTT) diagram of the system, which serves to be a tool for process optimization of epoxy-matrix composites. A new cure processing is therefore derived from the TTT diagram. The final phase structure obtained from a controllable method is identified through scanning electron microscope(SEM) photographs to be of ‘ex-situ’ phase morphology.

Reaction kinetics and thermal properties of cyanate ester‐cured epoxy resin with phenolphthalein poly(ether ketone)

AbstractThis article describe the influence of phenolphthalein poly (ether ketone) (PEK‐C) on the cure behaviors and thermal properties of the diglycidyl ether of bisphenol A (DGEBA) epoxy resin with cyanate ester as curing agent. The curing kinetics and reaction pathways were monitored using dynamic differential scanning calorimeter and Fourier transform infrared spectroscopy. The dependence of activation energy on the conversion degree for all the studied systems was calculated in the light of Ozawa‐Flynn‐Wall method. Furthermore, the thermomechanical properties and the thermal stability of the cured resins were also evaluated by dynamic mechanical analysis and thermogravimetric analysis, respectively. Conclusions can be drawn as follows: the main reaction pathways did not vary with the inclusion of PEK‐C, but the reaction rate of the blend was found to be higher than that of the neat epoxy. The glass transition temperature of the blend was not changed by the addition of PEK‐C, while the initial decomposition temperature slightly decreased with increase in PEK‐C content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

An Investigation on Wetting Characteristics of Solder Particle for Solderable Electrically Conductive Adhesives (ECAs)

A novel electrically conductive adhesives (ECAs) with solder particle have been developed. The kinetics of the curing reaction were investigated using isothermal differential scanning calorimeter (DSC). The dynamic DSC scans were also conducted to investigate the temperature dependant curing degree. The temperature dependant viscosity characteristic of polymer was investigated using rheometer. The wetting characteristic of two solders on two kinds of metals were investigated using an optical microscope. It was found that developed resin material showed good fluxing capacity against Sn-Bi solder on Ni/Au and the wetting angles was about 24º.

Curing and Morphology of BPA Epoxy Resin/LC Epoxy Resin PEPEB Composites

Liquid crystalline epoxy resin (LC epoxy resin) – p-phenylene di{4-[2-(2,3-epoxypropyl)ethoxy]benzoate} (PEPEB) was synthesized. The mixture of PEPEB with bisphenol-A epoxy resin (BPAER) was cured with a curing agent 4,4-diamino-diphenylmethane (DDM). The curing process and thermal behavior of this system were investigated by differential scanning calorimeter (DSC) and torsional braid analysis (TBA). The morphological structure was measured by polarizing optical microscope (POM) and scanning electron microscope (SEM). The results show that the initial curing temperature Ticu (gel point) of this system is 68.1°C, curing peak temperature T pcu is 102.5°C, and the disposal temperature T fcu is 177.6°C. LC structure was fixed in the cured epoxy resin system. The curing kinetics was investigated by dynamic DSC. Results showed that the curing reaction activation energy of BEPEB/BPAER/DDM system is 22.413 kJ/mol. The impact strength is increased 2.3 times, and temperature of mechanical loss peak is increased to 23°C than the common bisphenol-A epoxy resin, when the weight ratio of BEPEB with BPAER is 6 100.

Cure Kinetic Behavior of 191<sup>#</sup> Unsaturated Polyester Resin Used in Advanced Composites

The cure kinetic properties of 191# resin was studied by means of the differential scanning calorimeter (DSC) data. Dynamic DSC scanning at four different heating rates (5, 10, 15 and 20/min) are employed to investigate the cure kinetics. DSC curves show that there are two exothermal peaks. Kissinger’s method is applied to processing the data. The activation energy E and pre-exponential factor A were gained by linear regress and the cure kinetics model was developed. Based on T − β method, the temperatures of cure reaction beginning, maximum reaction rate and reaction ending were obtained. These will help to process designing of unsaturated polyester resin used in advanced composite materials.

Morphology and mechanical properties of poly(ether-imide)-modified polycyanurates

A high temperature thermosetting bisphenol A dicyanate (BADCy) was modified with a novel thermoplastic poly(ether-imide) (PEI) at various compositions. Fourier transform infrared spectroscopy was used to measure the conversion of BADCy. Curing kinetics of the BADCy/PEI blend were studied by the dynamic differential scanning calorimeter method. Morphologies of PEI-modified polycyanurates were investigated by scanning electron microscopy (SEM). It was found that the phase structures of the blends changed dramatically with the PEI content and molecular weight. The tensile results showed that the mechanical properties could be correlated with the morphologies. The blend with cocontinuous morphology had the highest tensile strength and elongation at break while the blend with ribbon-like morphology had the lowest one despite PEI molecular weight.

Synthesis of novel bisphenol containing phthalazinone and azomethine moieties and thermal properties of cured diamine/bisphenol/DGEBA polymers

A novel bisphenol(1,2-dihydro-2-(4-((4-hydroxy)phenyliminomethylidene)phenyl)-4-(4-((4-(4-hydroxy)phenyliminomethylidene)phenoxy)phenyl)(2H)phthalazin-1-one, DPP) and a diamine(1,2-dihydro-2-(4-aminophenyl)-4-(4-(4-aminophenoxy)phenyl)(2H)phthalazin-1-one, DAP) were synthesized and characterized. The novel epoxy polymers containing phthalazinone and/or azomethine moieties were prepared by binary polymerization of DAP (or DPP) with diglycidyl ether of biphenyl A (DGEBA) and ternary polymerization of hybrid curing agents, DAP/DPP (DAP and DPP under different molar ratios) with DGEBA. The cure behaviors of these new epoxy systems were studied by dynamic differential scanning calorimeter (DSC) and Infrared (IR) scans. Especially, the activation energy of DAP/DGEBA calculated by Kissinger and Ozawa methods were 73.8 and 77.4 kJ/mol, respectively. For ternary epoxy system, it was found that hybrid curing agents of DAP/DPP exhibited significant associated effect on their reactivity towards the oxirane group. Glass transition temperatures ( T g's) of these new epoxy polymers were all above 150 °C from the results of DSC, and the initial thermal decomposition temperatures ( T d,5%'s) and integral procedure decomposition temperatures (IPDT's) of these new epoxy polymers are above 350 and 850 °C, respectively from results of thermogravimetric analyses (TGA). These results show that new epoxy polymers containing phthalazinone and/or azomethine moieties exhibited excellent thermal properties. Especially, thermal properties of the ternary epoxy polymers could be modified by changing the content of DAP and DPP. The linear relationships between char yield ( Y c,wt%) and the structural compositions of these new polymers (weight percentage of phthalazinone, azomethine and nitrogen, C/H weight ratio) were built.

Cure Kinetic Model, Heat of Reaction, and Glass Transition Temperature of AS4/3501-6 Graphite–Epoxy Prepregs

A new isothermally-based, cure kinetic model for the carbon graphite–epoxy AS4/3501-6 prepreg is presented using an industrially supplied prepreg rather than the neat epoxy resin. A two-stage model is used: first, rate-controlled (autocatalytic); then diffusion-controlled. A Differential Scanning Calorimeter (DSC) is employed to investigate the prepreg’s cure kinetics using both isothermal and dynamic DSC scans, although only isothermal DSC scan data is used to fit the model’s parameters. A Thermogravimetric Analyzer (TGA) is used to determine the mass fraction of the epoxy resin in the prepreg. The coefficients are provided for a prepreg having 37.4% resin mass fraction; they must be re-evaluated for prepregs having significantly different resin mass fractions. The ultimate heat of reaction of the resin incorporated within the prepreg is measured as 433.7 J/g (based upon a linear baseline) or 422.7 J/g (based upon a specific-heat-corrected baseline) using dynamic DSC scans at 20°C/min. This value is 8–17% less than the reported 472–508 J/g for the neat 3501-6 epoxy also measured using dynamic DSC scans at 20°C/min. Important to manufacturing applications, dynamic DSC scans reveal that the prepreg’s ultimate heat of reaction is sensitive to scan rate. Finally, the prepreg’s carbon fiber and/or sizing appears to suppress the curing reaction and decrease the ultimate heat of reaction over that for the neat epoxy resin. The glass transition temperature Tg (°C) of partially-cured AS4/3501-6 prepregs is measured using DSC and is expressed as a function of degree of cure: Tg = 22.9 exp(2.16α) – markedly similar to 3501-6 neat resin Tg data measured earlier using a dynamic mechanical analyzer. The small specimen DSC thermal scans provide an effective means to measure the Tg of completely- or partially-cured prepregs. The Tg of the 100%-cured prepreg was experimentally determined to be 199°C, slightly higher than the 193°C reported for the 100%-cured neat epoxy resin. The AS4 fibers play little or no role in the degree-of-cure dependence of the AS4/3501-6 prepreg’s Tg. Recommended for general purpose structural applications, the AS4/3501-6 prepreg is composed of continuous, PAN-based, AS4C carbon (graphite) fibers and an amine-cured epoxy resin system. The epoxy resin, 3501-6, is a tetraglycidyl diamino diphenyl methane (TGDDM) with diaminodiphenylsulfone (DDS) catalyzed with boron trifluoride monoethylamine. 3501-6 was developed to operate in atemperature environment of up to 350°F (177°C).

Runaway Hazard Assessment of Cumene Hydroperoxide From the Cumene Oxidation Process

Cumene hydroperoxide (CHP) is normally produced by the cumene oxidation process. Severe fire and explosion incidents have occurred in oxidation and concentration processes due to the thermal instability of CHP. In this study, we used DSC and ARC thermal analysis techniques to measure the runaway thermokinetic data. Data such as adiabatic time to maximum rate (TMRad), adiabatic temperature rise (ΔTad), self-heating rate (dT/dt), thermal inertia (φ), etc., are used for runaway hazard evaluation. The thermal decomposition of CHP in cumene was found to be dependent on the CHP concentration which was characterized by the Accelerating Rate Calorimeter (ARC) test, isothermal and dynamic Differential Scanning Calorimeter (DSC) tests. The reaction order of 35 wt% CHP decomposition was determined to be 0.5. The Arrhenius parameters were measured to be Ea (kJ mol-1) = 120.6 ± 3.0 and lnA (min-1M1/2) = 30.2 ± 1.3. By using the thermokinetic data, plant vessel conditions, and the Semenov model, one can evaluate the criteria of critical vessel conditions, such as temperature of no return (TNR) and critical heat transfer parameter, (US/V)cr. Thermal hazards affected by CHP concentration were also discussed.

AC calorimetric aspect of dynamic differential scanning calorimetry

A dynamic differential scanning calorimeter (dynamic DSC) works simultaneously as a differential scanning calorimeter and an AC calorimeter, using the same apparatus with AC temperature modulation superposed on a linear temperature ramp. From the AC calorimetric (ACC) operation, we can determine the absolute value of the heat capacity by making the best of the twin-type apparatus, although the temperature resolution is a little lower than in a high precision AC calorimeter. In addition, it should be pointed out that in the ACC operation, heat capacity can be determined easily in comparison with differential scanning calorimetric (DSC) operation. Therefore, at a second order phase transition, the ACC operation is useful for obtaining linear heat capacity and furthermore, the frequency dispersion of linear heat capacity is obtainable. On the other hand, at a first order phase transition, the situation is complicated. In this case, we have to pay attention to non-linear heat capacity. The analysis of the waveform of AC temperature observed at a steady temperature might be useful to obtain evidence for the kinetic mechanism.

Application of dynamic differential scanning calorimetry to study of phase transitions

A dynamic differential scanning calorimeter (dynamic DSC) works simultaneously as a differential scanning calorimeter and an AC calorimeter, using the same apparatus with AC temperature modulation superposed on a linear temperature ramp. From AC calorimetric (ACC) operation in which the part responding to AC temperature modulation is taken into account, we can determine the absolute value of heat capacity by making the best of the twin-type apparatus, although the temperature resolution is a little lower than in high precision AC calorimetry. Therefore, at a second order phase transition, ACC operation is useful for obtaining temperature dependence of linear heat capacity and furthermore, the frequency dispersion of the linear heat capacity is obtainable. On the other hand, at a first order phase transition, the situation is complicated. Nevertheless, latent heat at a first order phase transition can be estimated precisely from the both results of DSC operation and ACC operation. For further study, we have to pay attention to non-linear heat capacity. When a first order transition takes place over a certain temperature range, the analysis of the waveform of AC temperature observed at a steady temperature in this range gives evidence for a kinetic mechanism. The experimental test is performed for sodium nitrite, which undergoes both first and second order phase transitions.

Cure kinetics of different molar ratios of 4,4′‐bismaleimidodiphenylmethane and bisphenol A dicyanate

AbstractBismaleimide‐triazine (BT) resins are thermosets derived from the addition polymerization of different molar ratios of 4,4′‐bismaleimidodiphenylmethane (BM) and bisphenol A dicyanate (BA). The possible cross‐linking reactions involved in the formation of BT resins are addition polymerization of BM, cyclocrimerization of BA, and heteropolymerization between BM and BA. Fourier‐transform infrared spectroscopy reveals that cyclotrimerization of BA occurs during the cure of a 1 : 2 molar ratio of BM to BA (as 1M2A). No sign of cyclotrimerization is observed for the case of the 1 : 1 molar ratio of BM to BA (as 1M1A). A dynamic differential scanning calorimeter (DSC) is employed to study the cure kinetics. The apparent activation energy evaluated from the Prime method is increased with the content of the BM component in the starting mixture. The different pattern of activation energy with fractional conversion (α) indicates the different chemical nature for the cure reactions of 1M1A and 1M2A. The empirical rate functions thus evaluated are 2.32 × 105 + 5.62 α 105α − 8.61 × 105α2 and 6.07 × 105 + 1.06 × 106α − 1.66 × 106α2s−1 for the cure reactions of 1M1A and 1M2A, respectively. © 1994 John Wiley & Sons, Inc.

Synthesis, characterization, and kinetic study of compatible SIN's based on diallyl phthalate and epoxy resin

AbstractDiallyl phthalate (DAP) was blended with diglycidyl ether of bisphenol A (DGEBA) in various weight ratios: 100/0, 75/25, 50/50, 25/75, and 0/100. These blends were then cured simultaneously with dicumyl peroxide (DCP) and hexahydrophthalic anhydride (HHPA) in conjunction with 2‐cyanoethyl‐4‐methyl immidazole (EMI‐CN, 0.5% as catalyst) to obtain simultaneous interpenetrating polymer networks (SIN's). H‐bonding between DAP and DGEBA was detected with FTIR. The SIN's thus obtained were characterized with rheometric dynamic spectroscopy (RDS) and differential scanning calorimeter (DSC) to check the compatibility of components. Gel fractions were measured with a Soxhlet extractor. Viscosity increases of all SIN's were measured with a Brookfield viscometer at curing temperatures. Conversions of C  C and epoxide versus cure time were monitored with FTIR and kinetic parameters were calculated and discussed. Experimental results revealed that H‐bonding in the DAP/DGEBA blends was evidenced from the shift of the IR band (vc=o) to a lower wave number, as well as the shift of epoxide band (vδ) to a higher wave number. Complete compatibility between DAP and DGEBA was supported from the single damping peak in DRS and single glass transition in DSC for each of SIN's. Cure dynamic DSC showed shifts of exothermic peaks to higher temperatures for all SIN's. During SIN formation, the slower viscosity increases of SIN's were found, compared with pure DAP and pure DGEBA, indicating retarded cure rates for all SIN's. In addition, lower gel fractions of SIN's were observed, indicating incomplete cure of SIN's. The retarded cure rate was further confirmed by kinetic study. Lower rate constants with higher activation energies for all SIN's were found. An effect of network interlock was proposed to account for these findings. © 1993 John Wiley & Sons, Inc.

Static and dynamic calorimetric studies on the three kinds of phase transition in the systems of l- and dl-dipalmitoylphosphatidylcholine/water

Thermodynamic studies on the phase transitions of two systems composed of l- or dl-dipalmitoylphosphatidylcholine (DPPC) and water were performed by using the static adiabatic calorimeter, in addition to the dynamic differential scanning calorimeter (DSC) usually used in previous investigations, focusing our attention in particular on the subtransition phenomenon. The static method revealed that, compared with the l-DPPC system, the dl-DPPC system shows smaller transition entropies ( ΔS) and enthalpies ( ΔH) associated with the sub- and pretransitions, indicative of the heavy dependence on the main transition of the appearance of the liquid crystalline, L α, phase. In particular, for the subtransition of the l-DPPC system, about 15-fold larger thermodynamic values were found as compared to those obtained for the dl-DPPC system, and a total of 145 h was required to complete this transition. This behavior of the l-DPPC system observed by using thermal equilibrium measurements demonstrated that the extremely low rate of the subtransition may be ascribed to the interaction between the l-DPPC and water molecules.