Non-isothermal Differential Scanning Calorimetry Research Articles

Preparation and properties of self‐healable solid‐state polymer electrolytes based on covalent adaptive networks enabled by disulfide bond

AbstractCovalent adaptive networks (CANs) have numbers of versatile abilities derived from topological reshuffling with interesting potentials. Here, self‐healable solid‐state polymer electrolytes were developed by integrating epoxy‐resin‐based CANs enabled by disulfide bond with a solid lithium salt (LiTFSI). The disulfide bond was introduced by using a disulfide‐containing aliphatic polyamine as the epoxy‐curing agent. To determine the cure cycle of this epoxy‐resin system, the curing kinetics in the presence of LiTFSI was studied by nonisothermal differential scanning calorimetry. The prepared ion‐conducting (IC) CANs with different LiTFSI content were optically transparent and self‐healable at temperatures above glass transition temperature (Tg). The effect of LiTFSI content on the thermal stability and tensile properties was investigated. The electrical properties of the IC CANs were studied by impedance spectroscopy at various temperatures. Their ionic conductivity was analyzed by the Vogel–Tamman–Fulcher model and equivalent‐circuit fitting. Due to the high mobility of charge carriers, the IC CAN sample (containing15 wt% LiTFSI) exhibited the best ionic conductivity, which reached a value of 3.35 × 10−6 S cm−1 at 80 °C and 8.31 × 10−6 S cm−1 at 100 °C, presenting great attraction for self‐healing iontronics.

Biodegradable epoxy resin from vanillin with excellent flame-retardant and outstanding mechanical properties

In this work, the sustainable and biodegradable flame retardant epoxy resin was designed and prepared to replace resource-limited petrochemicals, especially, bisphenol A type epoxy resin (DGEBA). A renewable chemical, vanillin was condensation to produce Schiff-based compound (MAV) employing the novel epoxy resin (MVE) through the epoxidation reaction. The epoxy equivalent of MVE was approximately 217 g/eq and used non-isothermal differential scanning calorimetry (DSC) to study the curing kinetics of MVE/DDM (4,4′-Diaminodiphenylmethane). After curing by DDM, they exhibit outstanding mechanical property and a residual char rate as high as 41.77%, excellent inherent flame retardancy and limited oxygen index (LOI) value higher than 34%, far superior to DGEBA. The total heat release (THR) and smoke release rate (SPR) of MVE/DDM decreased by 67.44% and 64.69% compared with DGEBA/DDM, respectively. The mechanisms for the enhancement of flame retardancy by intrinsic flame retardant epoxy resin were investigated. Moreover, the sustainable epoxy crosslinking could degrade completely benefited from the structure of the Schiff base in the moderate conditions (THF: H2O = 6: 4, 50 °C) within few hours. Overall, this work contributes a multifunctional vanillin-based epoxy monomer and environmentally friendly thermosets with high mechanical property and enhanced flame retardancy.

Cardanol-Derived Epoxy Resins as Biobased Gel Polymer Electrolytes for Potassium-Ion Conduction.

In this study, biobased gel polymer electrolyte (GPE) membranes were developed via the esterification reaction of a cardanol-based epoxy resin with glutaric anhydride, succinic anhydride, and hexahydro-4-methylphthalic anhydride. Nonisothermal differential scanning calorimetry was used to assess the optimal curing time and temperature of the formulations, evidencing a process activation energy of ∼65–70 kJ mol–1. A rubbery plateau modulus of 0.65–0.78 MPa and a crosslinking density of 2 × 10–4 mol cm–3 were found through dynamic mechanical analysis. Based on these characteristics, such biobased membranes were tested for applicability as GPEs for potassium-ion batteries (KIBs), showing an excellent electrochemical stability toward potassium metal in the −0.2–5 V voltage range and suitable ionic conductivity (10–3 S cm–1) at room temperature. This study demonstrates the practical viability of these biobased materials as efficient GPEs for the fabrication of KIBs, paving the path to increased sustainability in the field of next-generation battery technologies.

Sensibility to chemical preparation method and thermal study of lithium zinc iodate mixture and prediction of structure, linear optical properties of αLiZn(IO3)3 polymorph from DFT

The lithium zinc iodate polymorph α-LiZn(IO3)3 has been prepared by two different chemical routes using precipitation and heat treatment methods. The optical bandgap of αLiZn(IO3)3 was found experimentally to be 4.00 eV confirming the theoretical band gap of 3.93eV as obtained by HSE06-DFT approach. The thermal study of nano mixture lithium zinc iodate has been studied by the non-isothermal simultaneous TG and differential scanning calorimetry. The theoretical and experimental mass loss data are in good agreement for the thermal decomposition. Morphological and compositional analyses were carried out by using scanning electron microscopy and energy-dispersive X-ray measurements. The various phases were studied by powder X-ray diffraction were explored. Density functional theory was used to explore structural and optical properties of two predicted Lithium Zinc iodate polymorphs (LZI-P21), and (LZI-P63). The calculated electronic band structure and density of states show that both polymorphs have an indirect band gap an optical birefringence of 0.29 respectively.

Cure process evaluation of CFRP composites via neural network: From cure kinetics to thermochemical coupling

This work focuses on the comprehensive modeling of the cure kinetics and the thermochemical coupling to investigate the cure process of CFRP composites. Neural network (NN) is instead of the general cure kinetics model to find the relationships between the cure kinetics parameters where the temperature rate is also involved. Large data sets from non-isothermal differential scanning calorimetry (DSC) are used for the network training and validation. For comparison, the NN model and general model are respectively written as user subroutine and combined with the thermochemical coupled model to implement the finite element (FE) cure analysis. Compared with the general model, the NN model significantly improves the prediction accuracy of cure behavior. The reaction rates at various temperature rates from the NN model are also coincide with the corresponding experiments. Furthermore, it is also found that the NN model can capture the local trends of the composites during cure by taking into account the effect of the temperature rate on the cure kinetics. The temperature and degree of cure (DoC) gradients of the composite during cure process are reduced than the general model, which provides a new insight for the cure and cure related characteristics analysis.

Influence of Different Kinds of Plant Fibers on the Curing Kinetics of Epoxy Resin

The curing kinetics of the epoxy resin crosslinked by an anhydride hardener with and without plant fibers was investigated. The epoxy composites containing modified pineapple leaf fiber (EASF), banana fiber (EBSF), and bamboo chopsticks fibers (ECSF) were analyzed by non-isothermal differential scanning calorimetry (DSC) technique. Dynamic methods were used to predict the total heat of reaction of the epoxy resin and its activation energy based on the methods of Kissinger and Ozawa. The results showed that, at a low heating rate (5 °C/min), the ΔH of the pure epoxy, EASF, EBSF, and ECSF were 326.2, 307.6, 295.6, and 366.6 J/g, respectively. The curing rate increased, and the activation energy was decreased due to the catalytic role of hydroxyl groups of plant fibers. Based on Kissinger and Ozawa methods, the calculation of activation energy for pure epoxy was 70.08 kJ/mol and 73.21 kJ/mol, EBSF was 68.07 kJ/mol and 71.41 kJ/mol, ECSF was 60.11 kJ/mol and 63.87 kJ/mol, and EASF was 58.71 kJ/mol and 62.49 kJ/mol. The activation energy for the three kinds of epoxy composite modified fibers was less than pure epoxy resin due to the gel effect resulting from the higher viscosity, faster curing rate, and steric hindrance.

Styrene-free synthesis and curing behavior of vinyl ester resin films for hot-melt prepreg process

Vinyl ester (VE) resin films were developed from epoxy resins via esterification with methacrylic acid without a reactive diluent to fabricate carbon fiber (CF) prepregs via a hot-melt impregnation process. The viscosity of VE resins suitable for the hot-melt prepreg method was optimized by mixing two different bisphenol-A epoxy precursors, with low and high molar masses. Unidirectional CF prepregs were fabricated via the hot-melt impregnation method using as-prepared VE films. Manual layup of as-prepared VE prepregs with subsequent curing in an autoclave led to the successful fabrication of CF-reinforced composites with good tensile and flexural strength. The kinetics and mechanism of the radical crosslinking of VE synthesized using various mixing ratios of two different epoxy precursors were studied using nonisothermal differential scanning calorimetry. Quantitative analyses with the autocatalytic model and model-free methods indicated that the higher viscosity of VE causes a higher energy barrier associated with molecular mobility and diffusion.

The Curing Kinetics of Multiscale [Ni(EDTA)]-2 Intercalated Zn-Al Layered Double Hydroxides: Glass Fiber–Epoxy Composite Prepreg

In the present research, the effect of Zn2Al layered double hydroxides (LDH) and nickel (II)-EDTA complex intercalated LDH (LDH-[Ni(EDTA)]-2) on the cure kinetics of glass fiber/epoxy prepreg (GEP) was explored using nonisothermal differential scanning calorimetry (DSC). The results showed that LDH caused a shift in the cure temperature toward lower temperatures while accelerating the curing of epoxy prepregs. The use of LDH-[Ni(EDTA)]-2 more profoundly influenced the acceleration of the curing process. The curing kinetics of prepregs was assessed through the differential isoconversional Friedman (FR) technique and the integration method of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS). A decrease was detected in the E α value of glass fiber/LDH-[Ni(EDTA)]-2/epoxy (GELP) and glass fiber/LDH-[Ni(EDTA)]-2/epoxy (GELNiP) prepregs at small cure degrees relative to GEP, suggesting the catalytic effect of LDH or LDH-[Ni(EDTA)]-2 on the initial epoxy/amine reaction. Furthermore, LDH-[Ni(EDTA)]-2 performed better due to the catalyst role of nickel (II). Moreover, the activation energy exhibited lower reliance on the degree of conversion in the cases of GELP and GELNiP rather than pure epoxy prepregs. An autocatalytic model was used to evaluate the curing behavior of the system. Based on the results, the curing reaction of the epoxy prepreg can be described by the autocatalytic Šesták-Berggren model even after the incorporation of LDH or LDH-[Ni(EDTA)]-2. The kinetic parameters of the autocatalytic model (such as E α , A , m , n ) and the equations explaining the curing behavior of prepregs were introduced as well whose predictions were in line with the experimental findings.

Lignosulfonate-Based Polyurethane Adhesives.

The feasibility of using lignosulfonate (LS) from acid sulphite pulping of eucalyptus wood as an unmodified polyol in the formulation of polyurethane (PU) adhesives was evaluated. Purified LS was dissolved in water to simulate its concentration in sulphite spent liquor and then reacted with 4,4′-diphenylmethane diisocyanate (pMDI) in the presence or absence of poly(ethylene glycol) with Mw 200 (PEG200) as soft crosslinking segment. The ensuing LS-based PU adhesives were characterized by infrared spectroscopy and thermal analysis techniques. The adhesion strength of new adhesives was assessed using Automated Bonding Evaluation System (ABES) employing wood strips as a testing material. The results showed that the addition of PEG200 contributed positively both to the homogenization of the reaction mixture and better crosslinking of the polymeric network, as well as to the interface interactions and adhesive strength. The latter was comparable to the adhesive strength recorded for a commercial white glue with shear stress values of almost 3 MPa. The optimized LS-based PU adhesive formulation was examined for the curing kinetics following the Kissinger and the Ozawa methods by non-isothermal differential scanning calorimetry, which revealed the curing activation energy of about 70 kJ·mol−1.

In-Out Surface Modification of Halloysite Nanotubes (HNTs) for Excellent Cure of Epoxy: Chemistry and Kinetics Modeling.

In-out surface modification of halloysite nanotubes (HNTs) has been successfully performed by taking advantage of 8-hydroxyquinolines in the lumen of HNTs and precisely synthesized aniline oligomers (AO) of different lengths (tri- and pentamer) anchored on the external surface of the HNTs. Several analyses, including FTIR, H-NMR, TGA, UV-visible spectroscopy, and SEM, were used to establish the nature of the HNTs’ surface engineering. Nanoparticles were incorporated into epoxy resin at 0.1 wt.% loading for investigation of the contribution of surface chemistry to epoxy cure behavior and kinetics. Nonisothermal differential scanning calorimetry (DSC) data were fed into home-written MATLAB codes, and isoconversional approaches were used to determine the apparent activation energy (Eα) as a function of the extent of cure reaction (α). Compared to pristine HNTs, AO-HNTs facilitated the densification of an epoxy network. Pentamer AO-HNTs with longer arms promoted an Excellent cure; with an Eα value that was 14% lower in the presence of this additive than for neat epoxy, demonstrating an enhanced cross-linking. The model also predicted a triplet of cure (m, n, and ln A) for autocatalytic reaction order, non-catalytic reaction order, and pre-exponential factor, respectively, by the Arrhenius equation. The enhanced autocatalytic reaction in AO-HNTs/epoxy was reflected in a significant rise in the value of m, from 0.11 to 0.28. Kinetic models reliably predict the cure footprint suggested by DSC measurements.

Improvement in thermal stability and crystallization mechanism of Sm doped Ge2Sb2Te5 thin films for phase change memory applications

The thin films of (Ge2Sb2Te5)100−xSmx(x = 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2) (Sm-GST) phase change material have been investigated employing X-ray photoelectron spectroscopy (XPS) to examine the nature of chemical bonding in as-deposited thin films of Sm-GST. The composition of as-deposited thin films of Sm-GST has been also analyzed from the peak area ratios of XPS core-level spectra and the morphology of the thin film has been studied using field emission scanning electron microscopy (FESEM). The powder samples obtained from the as-deposited thin films have been utilized for the non-isothermal differential scanning calorimetry (DSC) measurements at the constant heating rate of 10 K/min. The values of glass transition temperature (Tg), onset crystallization (Tc), peak crystallization temperature (Tp) and melting temperature (Tm) obtained from DSC curves of Sm-GST thin films have been used for the evaluation of thermal stability parameters. The activation energy for crystallization (Ec) and avrami exponent (n) for fcc and hexagonal phase of Sm-GST thin films have been evaluated using Henderson’s method and Matusita’s method. The impact of Sm doping on the thermal stability, glass-forming ability and crystallization activation energy of as-deposited thin films have been examined and its possible influence on the memory device performance has been correlated.

Thermal study of APNIMMO/CL-20 based propellants fabricated by 3D printing

Energetic photocurable binder has been developed to improve the energy content of 3D printed propellants. Thermal decomposition study is a significant part for evaluating novel binders and relevant propellants. In this paper, acrylate-terminated poly-3-nitratomethyl-3-methyloxetane (APNIMMO) and a series of formulas containing 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) were prepared by the stereolithography (SLA) printing. The thermal performance and decomposition kinetics were investigated by means of the nonisothermal DSC (differential scanning calorimetry) techniques. Additionally, simultaneous DSC-FTIR were employed to corroborate the thermal analysis results. The compatibility of the various admixtures was confirmed through an additional kinetic study for which the Arrhenius parameters were computed by different isoconversional Kissinger method and modified Kissinger-Akahira-Sunose (KAS) method. The decomposition products were also detected by in-situ DSC-MS-FTIR. The obtained results from the different techniques are presented and discussed.

Combustion Behavior and Kinetics Analysis of Isothermal Oxidized Oils from Fengcheng Extra-Heavy Oil

The low-temperature oxidation (LTO) of heavy oil is of great significance for the combustion front stability, which directly influences the efficiency and safety of in-situ combustion (ISC). To provide feasible heating by artificial ignition before the implementation of ISC in the Xinjiang Fengcheng (FC) oilfields, this paper investigates the oxidation behavior of FC extra-heavy oil and its isothermal oxidized oils. Firstly, FC extra-heavy oil was subjected to isothermal oxidation experiments conducted utilizing an oxidation reactor, and the physical properties of the gaseous products and oxidized oils were analyzed. The combustion behavior of the FC extra-heavy oil and oxidized oils was then studied by non-isothermal thermogravimetry and differential scanning calorimetry. Subsequently, the Friedman and Ozawa–Flynn–Wall methods were adopted to perform kinetic analysis. Oxygen consumption was always greater than the production of CO and CO2, so oxygen addition reactions were the main pathway in heavy oil LTO. H/C decreased to 8.31% from 20.94% when the oxidation temperature rose from 50 °C to 150 °C, which deepened the oxidation degree. The density and viscosity of 200 °C to 350 °C oxidized oils increased at a slower rate, which may be related to the LTO heat effect. The change law of temperature interval, peak temperature, and mass loss of the oxidized oils had a good correlation with the static oxidation temperature. Compared with other oxidized oils, the peak heat flow and enthalpy of 350 °C oxidized oil increased significantly with high-temperature combustion, and were 42.4 mW/mg and 17.77 kJ/mol, respectively. The activation energy of 350 °C oxidized oil began to decrease obviously around a conversion rate of 0.4, which indicates that it was beneficial to coke deposition with stronger activity. Finally, we came up with LTO reaction mechanisms and put forward a reasonable preheating temperature for the application of ISC in FC oilfields.

A Deep Insight in the Antioxidant Property of Carnosic Acid: From Computational Study to Experimental Analysis.

Since the deep cause for the anti-oxidation of carnosic acid (CA) against oleic acid (OA) remains unclear, we focused on exploring the CA inhibition mechanism via a combined experimental and computational study. Atomic charge, total molecular energy, phenolic hydroxyl bond dissociation enthalpy (BDE), the highest occupied molecular orbital (HOMO), and the lowest unoccupied orbital (LUMO) energy were first discussed by the B3LYP/6-31G (d,p) level, a density functional method. A one-step hydrogen atom transfer (HAT) was proposed for the anti-oxidation of CA towards OA, and the Rancimat method was carried out for analyzing the thermal oxidation stability. The results indicate that the two phenolic hydroxyl groups located at C7(O15) and C8(O18) of CA exert the highest activity, and the chemical reaction heat is minimal when HAT occurs. Consequently, the activity of C7(O15) (303.27 kJ/mol) is slightly lower than that of C8(O18) (295.63 kJ/mol), while the dissociation enthalpy of phenol hydroxyl groups is much lower than those of α-CH2 bond of OA (C8, 353.92 kJ/mol; C11, 353.72 kJ/mol). Rancimat method and non-isothermal differential scanning calorimetry (DSC) demonstrate that CA outcompetes tertiary butylhydroquinone (TBHQ), a synthetic food grade antioxidant, both in prolonging the oxidation induction period and reducing the reaction rate of OA. The Ea (apparent activation energies of reaction) of OA, TBHQ + OA, and CA + OA were 50.59, 57.32 and 66.29 kJ/mol, revealing that CA could improve the Ea and thermal oxidation stability of OA.

Non-isothermal cold crystallization, melting, and moisture barrier properties of silver-loaded kaolinite filled poly(lactic acid) films

Silver-loaded kaolinite (AgKaol), an antibacterial agent along with a barrier enhancer, was incorporated into poly(lactic acid) (PLA), poly(butylene adipate-co-terephthalate) (PBAT) and tetrabutyltitanate (TBT) blend resulting in the formation of polymer composite. The introduction of AgKaol could improve the barrier and the crystallization properties of PLA/PBAT/TBT blend. The barrier property of composite polymer was investigated by water vapor permeability (WVP) to study the influence of AgKaol content (0.0, 1.0, 2.0, 3.0 and 4.0 phr) in polymer matrix. The values of WVP decreased with increasing AgKaol content and amount of crystallite in PLA composite. The cold crystallization property of this PLA/PBAT/TBT composited with 0.0, 2.0 and 4.0 phr of AgKaol was completely investigated by the non-isothermal differential scanning calorimetry (DSC) technique. From the non-isothermal DSC analysis, the crystallization rates (dX(T)/dt) of PLA composite increased with increasing of the heating rate and AgKaol content. The Avrami, Ozawa and Liu models were applied to describe the non-isothermal crystallization kinetics and determine crystallization parameters for PLA/PBAT/TBT/AgKaol composite. The crystallization mechanism of PLA/PBAT/TBT/AgKaol composite was proposed thorough the nucleation and three dimension growths. The activation energies of crystallization (Ea) were determined by the Kissinger-Akahira-Sunose (KAS) isoconversional method. The determined Ea for the crystallizations of PLA/PBAT/TBT with 4.0 phr of AgKaol were lower than 2.0 and 0.0 phr, respectively. Polarized optical microscopy (POM) showed more and larger spherulites with a nanocrystal structure of PLA/PBAT/TBT/AgKaol composite than neat PLA. The nucleating effect of AgKaol on PLA/PBAT/TBT blend might be useful for preparation of PLA composite as a gas barrier protection material in the future. Corresponding to the melt flow index (MFI) results, PLA composites could produce as a film with promising antibacterial packaging due to silver nanoparticles in AgKaol.

Online Cure Monitoring and Modelling of Cyanate Ester-Based Composites for High Temperature Applications.

A cure kinetics investigation of a high temperature-resistant phenol novolac cyanate ester toughened with polyether sulfone (CE-PES blend) was undertaken using non-isothermal differential scanning calorimetry. Thin ply carbon fiber prepreg, based on the CE-PES formulation, was fabricated, and plates for further in-situ cure monitoring were manufactured using automated fiber placement. Online monitoring of the curing behavior utilizing Optimold sensors and Online Resin State software from Synthesites was carried out. The estimation of the glass transition temperature and degree of cure allowed us to compare real time data with the calculated parameters of the CE-PES formulation. Alongside a good agreement between the observed online data and predicted model, the excellent performance of the developed sensors at temperatures above 260 °C was also demonstrated.

The Curing Kinetics of E-Glass Fiber/Epoxy Resin Prepreg and the Bending Properties of Its Products.

The curing kinetics can influence the final macroscopic properties, particularly the three-point bending of the fiber-reinforced composite materials. In this research, the curing kinetics of commercially available glass fiber/epoxy resin prepregs were studied by non-isothermal differential scanning calorimetry (DSC). The curing kinetic parameters were obtained by fitting and the apparent activation energy Ea of the prepreg, the pre-exponent factor, and the reaction order value obtained. A phenomenological nth-order curing reaction kinetic model was established according to Kissinger equation and Crane equation. Furthermore, the optimal curing temperature of the prepregs was obtained by the T-β extrapolation method. A vacuum hot pressing technique was applied to prepare composite laminates. The pre-curing, curing, and post-curing temperatures were 116, 130, and 153 °C respectively. In addition, three-point bending was used to test the specimens’ fracture behavior, and the surface morphology was analyzed. The results show that the differences in the mechanical properties of the samples are relatively small, indicating that the process settings are reasonable.

Enhanced formation of stereocomplex crystallites in Poly(l-lactic acid)/Poly(d-lactic acid) blends by silk fibroin nanodisc

Blending of poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) is known to form stereocomplex crystallites (SC). In this research, the impact of a biobased filler, silk fibroin nanodisc (SFN), on the crystallizability of the PLLA/PDLA (50/50) blend was examined by differential scanning calorimetry (DSC), polarizing optical microscope (POM), and time-resolved small- and wide-angle X-ray scattering (SWAXS) measurements. The crystallization temperature (Tc), measured by non-isothermal DSC cooling scan, was increased by the addition of 1% SFN in the PLLA/PDLA (50/50) blend. The inclusion of SFN enhanced the formation of SC, as indicated by increasing the melting enthalpy of SC. Isothermal crystallization study at 110 °C by DSC and WAXS suggested that the SFN enhanced the SC crystallization while it suppressed the homocrystal (HC) crystallization, as indicated by crystallization half-time (t0.5) values. It was found that SFN not only enhances the SC crystallizability but also increases the fraction of SC crystals in the PLLA/PDLA blend. The long period of HC and SC lamellar stack was reduced by the addition of SFN, as indicated by the SAXS results. The POM results suggested that SFN significantly enhanced the number of SC nuclei for the isothermal crystallization at 170 °C from the melt.

Crystal Growth Kinetics in GeS2 Glass and Viscosity of Supercooled Liquid.

The crystal growth kinetics and morphology in germanium disulfide bulk glass and glass surface is described. The structural relaxation taking place below the glass transition is slow and the corresponding volumetric change is negligible. Therefore, it does not affect substantially the crystal growth process. The crystal growth rate of low temperature β-GeS2 and high temperature α-GeS2 polymorphs in the bulk glass is comparable, being slightly decoupled from the shear viscosity below the glass transition. The crystal growth rate of β-GeS2 in an amorphous thin film of the same composition is several orders of magnitude faster than that at the surface of bulk glass. This fast surface crystal growth is strongly decoupled from viscosity. Such behavior resembles the glass-to-crystal fast growth mode observed by several authors in some organic molecular glasses. Taking into account previously reported viscosity and heat capacity data, the crystal growth kinetics of both polymorphs can be quantitatively described by the 2D surface growth model for low and high supercooling. The nonisothermal differential scanning calorimetry experiments are analyzed, providing evidence of a complex nature of the overall crystallization process with apparent activation energy comparable to that obtained from isothermal microscopy measurement of crystal growth in the same temperature range.

The Curing Kinetics Analysis of Four Epoxy Resins Using a Diamine Terminated Polyether as Curing Agent

Diamine terminated polyether (DAPE) is used as a novel curing agent for ductile epoxy resins. To investigate the curing kinetics, non-isothermal differential scanning calorimetry (DSC) tests were conducted to investigate four ductile epoxy/DAPE systems, including tetraglycidyl-4,4′-diaminodiphenyl methane (TGDDM)/DAPE, diglycidyl 4,5-epoxycyclohexane-1,2-dicarboxylate (TDE-85)/DAPE, triglycidyl-p-aminophenol (TGPAP)/DAPE and hydantoin epoxy resin (HER)/DAPE systems. According to the Malek method, the four epoxy systems suit the Sestak-Berggren kinetic model (SB (m,n)). The SB (m,n) model can well fit the curing reaction of all epoxy systems. By applying the Friedman method, the activation energies (Ea) at different conversion (α) were calculated, which provide an insight of curing mechanism of the flexible curing agent for ductile epoxy resins.