Non-isothermal Differential Scanning Calorimetry Research Articles

Comparative study of the kinetic behaviors and properties of aromatic and aliphatic bismaleimides

In this paper, three aromatic bismaleimides (BMI-70, BMI-DE and BMI-80) and two aliphatic bismaleimides (BMI-DDA and BMI-C36) were synthesized. The structures were characterized using nuclear magnetic resonance (NMR) spectra and Fourier transform infrared (FT-IR) spectra. Their polymerization behaviors were discussed by non-isothermal differential scanning calorimetry (DSC). The thermal and dielectric properties of the poly(bismaleimide) were investigated using thermogravimetric analysis (TGA), dynamic thermo-mechanical analysis (DMA), and an impedance analyzer. The results indicate that the aliphatic bismaleimides exhibit lower apparent activation energies and dielectric properties, with BMI-DDA displaying an average activation energy of 105.5 kJ mol−1 and the dielectric constant of P(BMI-C36) is 2.558 @ 10 MHz. The aromatic polybismaleimides possessed better thermal stability, among which, the 5 % thermal decomposition temperature (Td,5) of P(BMI-70) was 513.5 °C, and the residual carbon rate at 800 °C was 44.6 %. In additional, water absorption was studied and their saturated water absorption was less than 4 %.

Effect of high copper content in Cux(As2Se3)100-x glass on properties relevant for engineering of thermally induced processes

ABSTRACT Kinetic analysis of thermally induced processes was carried out in Cux(As2Se3)100-x glass with high copper content, x = 20 and 25 at.%. Non-isothermal differential scanning calorimetry at different heating rates was used to analyze the glass-transition and crystallization processes. It was shown that the glass-transition temperature increases with the increase in the copper content and that the examined glasses during the glass transition process do not show large configurational changes in the structure. Apparent activation energy of crystallization was determined using Kissinger method. In the composition with 25 at.% of copper the crystallization of three structural units was detected: CuAsSe2, Cu3AsSe4 and Cu2Se. Analysis of the crystallization mechanism and determination of parameters that depend on the morphology of nucleation and growth showed that volume nucleation and three-dimensional growth occur with a constant number of nucleation centers. Isoconversional analysis showed that the activation energy does not change significantly during the crystallization process.

Polymerization behaviors and properties of benzoxazine resins based-on meta-substituted anilines

The molecular structure of benzoxazine is closely related to its polymerization activity and the properties of its polymer. In this work, benzoxazines were successfully synthesized from phenol, paraformaldehyde and meta-substituted anilines. Their polymerization behaviors were discussed by non-isothermal differential scanning calorimetry (DSC). Moreover, the thermal properties of corresponding polybenzoxazines were evaluated using DSC and thermogravimetric analysis. The results showed that the electron-withdrawing substituent increased the polymerization temperature while the electron-donating substituent lowered the polymerization temperature. The glass transition temperature decreased for polybenzoxazine with electron-donating substituent but elevated for polybenzoxazine with electron-withdrawing substituent. Besides, the thermal stability and thermal degradation mechanism of polybenzoxazine were significantly affected by the substituent. This work supplied further insight in the structure-property relationship of benzoxazine resin.

Non-isothermal kinetics of the organocatalytic ring-opening polymerization of ε-caprolactone with metal-free α‑hydroxy acids: Eco-friendly and facile synthesis process

Metal-free and green α‑hydroxy acids (AHA) such as l-malic (MA), DL-mandelic acid (MDL), and citric acid (CA) were successfully and effectively utilized as an effective initiator for the solvent-free ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). The performance of AHAs in the polymerization of ε-CL was completely and powerfully investigated via the non-isothermal differential scanning calorimetry (DSC). The proceed of ROP of ε-CL with AHAs could be real-time monitored by the obtained polymerization exotherms at different heating rates. The polymerization exotherms obtained from the ROP of ε-CL with CA occurred at a lower temperature range than MA, and MDA, respectively. From the kinetics study, the average activation energy (Ea) values for the ROP of ε-CL with CA (38.0 ± 1.8 kJ mol−1) were lower than MA (45.2 ± 3.6 kJ mol−1) and MDA (48.8 ± 6.2 kJ mol−1). Using the first-order model fitting, the values of pre-exponential factor (lnA0) for the ROP of ε-CL with CA, MA, and MDA were 7.0 ± 0.3, 8.5 ± 0.2, and 8.9 ± 0.3, respectively. The effectiveness of AHAs in the synthesis of PCL was clarified by conducting a larger-scale (4.0000 g) polymerization using conventional heating and microwave (MW) irradiation methods. From conventional heating, the green AHAs produced PCL with the number average molecular weight (Mn) and dispersity (Đ) values in the range of 5.18 × 103 - 1.43 × 104 g mol−1 and 1.14–2.02, respectively. The irradiation by MW could enhance the synthesis of PCL by reducing the synthesis time. By using the MW power of 450 W and irradiation time of 30 min, the PLC was obtained from the ROP of ε-CL with MA and MDA initiators, and the Mn of the obtained PCL from MW heating was 4.28 × 103 - 8.45 × 103 g mol−1. The mechanism for the ROP of ε-CL with all AHAs was proposed through the activated monomer mechanism.

Simulation of thermal hazards risk in octogen based on non-isothermal DSC data

To evaluate the possible thermal risks associated with the storage of octogen (HMX), non-isothermal differential scanning calorimetry (DSC) experiments were conducted in order to ascertain the kinetic model and parameters governing its thermal decomposition. DSC measurements indicate that HMX underwent a crystal transformation prior to thermal decomposition. A kinetic model for the autocatalytic thermal decomposition process was developed through the analysis of its primary exothermic peaks. Subsequently, numerical simulations were performed using the aforementioned kinetic model to assess the potential thermal explosion hazard of HMX under two distinct storage conditions. The comparison was made between the models of HMX autocatalytic decomposition temperature and thermal explosion critical temperature under two distinct storage conditions. The prediction of the influence of ambient temperature on the critical temperature of thermal explosion is conducted simultaneously. Finally, the thermal hazard parameters of HMX under different package quality are given.

Carbohydrate Core-Shell Electrosprayed Microcapsules for Enhanced Oxidative Stability of Vitamin A Palmitate.

Vitamin A is an essential micronutrient that is readily oxidized. In this study, the encapsulation of vitamin A palmitate (AP) within a core-shell carbohydrate matrix by co-axial electrospray and its oxidative stability was evaluated. The electrosprayed core-shell microcapsules consisted of a shell of octenyl succinic anhydride (OSA) modified corn starch, maltose (Hi-Cap), and a core of ethyl cellulose-AP (average diameter of about 3.7 µm). The effect of different compounds (digestion-resistant maltodextrin, soy protein hydrolysate, casein protein hydrolysate, and lecithin) added to the base core-shell matrix formulation on the oxidative stability of AP was investigated. The oxidative stability of AP was evaluated using isothermal and non-isothermal differential scanning calorimetry (DSC), and Raman and Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy methods. The core-shell carbohydrate matrix minimizes the amount of AP present at the microparticle surface, thus protecting AP from oxidation. Furthermore, the most effective oxidation protection was achieved when casein protein hydrolysate was added to the core of the microcapsule due to hydrophobic and hydrogen bond interactions with AP and by the resistant maltodextrin in the shell, which acted as a filler. The utilization of ethanol as a solvent for the dispersion of the core compounds increased the hydrophobicity of the hydrolyzed proteins and contributed to the enhancement of their antioxidant ability. Both the carbohydrate core-shell microcapsule prepared by co-axial electrospray and the addition of oxidation protection compounds enhance the oxidative stability of the encapsulated AP.

The effect of cross-linking system and reinforcement on the cross-linking reaction of peroxide vulcanized ethylene-propylene-diene terpolymer (EPDM) matrix

In this work, the effect of using of dicumyl-peroxide (DCP) (2, 5 & 8 phr) and co-agent triallyl-cyanurate (TAC) (2, 4 & 6 phr) as cross-linking system as well as multi-walled carbon nanotubes (MWCNTs) (5, 8 και 10 phr) as a filler, for ethylene-propylene-diene terpolymer (EPDM) was investigated. Differential scanning calorimetry (DSC) was employed in order to study the progress of the cross-linking reaction, based on the exothermic vulcanization peaks of isothermal (at 160, 170, 180, 190 °C) and non-isothermal experiments (with heating rates 5, 10, 25, 50 °C min−1). The autocatalytic model was successfully applied to the results of isothermal experiments and the activation energy (Ea) of the reaction was calculated, based on the Arrhenius equation. The Ozawa-Kissinger equations were also applied to the data obtained from the non-isothermal study. From the results obtained from isothermal DSC experiments, an increase was observed in the reaction rates accompanied with a decrease in Ea with the increase of DCP content, whereas a proportional relationship between TAC content and the enthalpy and Ea of the reaction was recorded. The incorporation of MWCNT’s in EPDM increased its Ea. From the non-isothermal DSC experiments, a significant increase in the enthalpy and Ea of the cross-linking reaction was observed at higher DCP content, whereas TAC content did not show any notable effect on the reaction. Based on the results of this research, it is concluded that the increase of peroxide content facilitates the vulcanization of EPDM, whereas inhibition was observed by the incorporation of MWCNT’s.

Activities of cellulose acetate and microcrystalline cellulose on the thermal and morphomechanical performances of a biobased hybrid composite made polybutylene succinate

Microcrystalline cellulose (MCC–30 wt%) was extruded with a blend of polybutylene succinate (PBS) and cellulose acetate (CADS=2.5–20 wt%) to produce two grades of binary (PBS/CA, PBS/MCC) and ternary (PBS/CA/MCC) specimens by injection into a mold previously thermostated at 22 °C and 78 °C. The structure-property relationships of neat PBS (n-PBS) and PBS-based blends were investigated by Fourier transform infrared (FTIR) spectroscopy, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, scanning electron microscopy (SEM), rheology, differential scanning calorimetry (DSC), thermogravimetry, and mechanical (tensile, bending) tests. FTIR/DRIFT outcomes revealed physical interactions between the ingredients through hydrogen bonds. Rheology and SEM evidenced the presence of entanglements and micro-voids absent in n-PBS. Non-isothermal DSC showed that 22 °C-molded formulations displayed crystalline degrees higher than 78 °C-specimens, except for PBS/MCC. DSC-isothermal analysis showed a hindrance effect of CA on PBS/CA crystallinity and a nucleating impact of MCC on PBS/MCC. Tensile and bending moduli increased for both material grades while the elongation at break decreased. Entanglements and micro-voids had detrimental effects on stress levels because the maximum tensile strength decreased when each or both biofillers were added to PBS. These structural configurations were beneficial for bending strengths since all blends' stiffness relatively increased regardless of material grade.

Cure behavior and mechanism of cyanate ester with aromatic amines at room temperature

Herein, the catalytic effects of aromatic amines with different structures on the room temperature curing of bisphenol E cyanate (BECy) have been studied using differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectroscopy. Our results revealed that the mixed amine comprised of aniline and N,N-dimethyl-p-phenylenediamine (AN/NNDPA) bearing primary amino groups in its structure was a highly effective catalyst for the room temperature curing of cyanate esters. When the cyanate ester and mixed amine were combined at a molar ratio of 100:5 and cured at room temperature for 5 days, the curing degree of BECy resin reached 79.7%. The room temperature curing mechanism of the BECy-AN/NNDPA system was investigated using pyrolysis gas chromatography-mass spectrometry (PY GC-MS). Our results showed that the formation reactions of the intermediate structure and cyclotrimerization reactions occurred during the room-temperature curing process. The activation energies of BECy and different aromatic amine systems at different heating rates were determined using non-isothermal DSC. The results further demonstrated the catalytic effect of AN/NNDPA on the cyanate ester curing reaction. BECy-AN/NNDPA cured at room temperature has suitable heat resistance and a 5% weight loss temperature (Td5) of 361°C.

Catalytic effect of high thermal conductive SiC on the kinetics and thermodynamics of vulcanization reaction of SBR/BR-filled nano-SiC

Nano-silicon carbide (SiC) as a high thermal conductive material with an intrinsic thermal conductivity of ~ 490 W/m K was used to improve the cure characteristics, kinetics, and thermodynamics of curing reaction of styrene-butadiene rubber/butadiene rubber (SBR/BR) compounds. The considerations were carried out by non-isothermal differential scanning calorimetry (DSC). Results revealed that the presence of SiC shifted the peak and end temperatures of the curing peak to lower temperatures. The calculated activation energy of the curing reaction based on the Kissinger approach showed a descent from 409.8 to 93.8 kJ/mol by adding SiC from 0 to 7.5 phr (part per hundred rubber). Moreover, the obtained Gibbs free energy variation and equilibrium constant of the curing reaction proved that the reaction was absolutely forced and irreversible, which can be increasingly characterized as a one-way process. According to the results, SiC accelerated the curing reaction because of the increment of heat transfer into the compound. This phenomenon caused the increment of enthalpy variation of the vulcanization reaction, particularly at the SiC content of 5 phr. The achieved kinetic parameters via fitting an autocatalytic model based on the Sestàk–Berggren model by the Màlek method to describe the kinetics of the curing reaction indicated that the SiC filler had a catalytic effect on the curing reaction of SBR/BR-SiC, particularly after 2.5 phr of the filler.

Curing Kinetics and Mechanical Properties of Epoxy-Cyanate Ester Composite Films for Microelectronic Applications.

In general, although abundant literature studies are available on epoxy resin systems, a complete description of the curing kinetics in epoxy-cyanate ester composites relevant to the microelectronics industry is still lacking. Herein, curing behaviors of Ajinomoto build-up films, which are epoxy/silica composites, were studied by the non-isothermal differential scanning calorimetry method, and then, three non-isothermal curing kinetics models and model-free curing methods were used to analyze curing behaviors. In addition, a copper layer was also deposited onto the surface of the build-up film, and its interfacial adhesion property was also analyzed at different pre-curing conditions. The results showed that the curing reaction of the build-up film contains two curing reaction processes, and the first curing process is suited for the autocatalytic curing model, while the other curing process is suited for the Kamal curing kinetics model. Three model-free curing methods were used to calculate the activating energy at different degrees of curing, which indicated that the activating energy is variable during the whole curing process. The interfacial adhesion strength between the build-up film and copper layer decreased with the increase in the degree of curing, which is attributed to the contribution of mechanical anchoring. This work will offer guidance in curing behaviors for improving interfacial bonding force and controlling warpage behavior for chip substrates in the future.

Towards Improved Cold-Start Capability of PEFCs: Patterned Gas Diffusion Layers

Polymer electrolyte fuel cells (PEFCs) are electrochemical energy converters with high efficiency and zero pollutant emissions. The unassisted cold-start of PEFCs at -30 °C is one of the major challenges for automotive applications due to the freezing of supercooled water generated by the cathodic oxygen reduction reaction (ORR). Once triggered by the nucleus in cathode gas diffusion layers (GDLs), ice propagates through the active area, leading to oxidant gas blockage and cold-start failure1.The cold-start capability of PEFCs can be improved by preventing ice propagation, especially in GDLs. In our previous work2,3, after the GDLs were segmented by polytetrafluoroethylene (PTFE) into two regions, the PEFC kept operating for another 30 minutes after the first freezing event in one region. Nevertheless, the PTFE barrier limited the active area as well as the heat and electric conductivity of PEFCs. In contrast, patterned GDLs allow water cluster separation without the abovementioned limitations. The improvement of water management and cell performance under technical operating conditions was demonstrated4. Yet, the cold-start capability with patterned GDL needs to be further investigated.This work studies the effect of patterned GDLs on the water-ice phase transition and cold-start capability of PEFCs. First, non-isothermal differential scanning calorimetry (DSC) measurements were conducted to determine the onset freezing temperature distribution of supercooled water in patterned GDLs, taking into account various properties such as coating load and pattern size. It was observed that independent freezing events occurred in patterned GDLs in all cycles, as several freezing/exothermic peaks can be seen in Figure 1b. In contrast, ice propagated immediately in untreated GDL, as only one freezing peak was observed in all cycles (Figure 1d). By computing the integral of the heat flux curve, we obtained the corresponding cumulative icing ratio over 60 cycles, as presented in Figures 1a and 1c. The effective prevention of ice propagation is only observed in patterned GDLs. Second, to assess the cold-start capability, statistical isothermal cold-start measurements were conducted using a 4.4 cm2 differential cell, with the cell temperature held at -7.5 °C, -10 °C, -15 °C, and 20 °C. In summary, nonconcurrent freezing events in patterned GDLs indicate that the use of patterned GDLs significantly improved the cold-start capability of PEFCs under isothermal subfreezing conditions.The findings of this work enhance the understanding of the cold-start dependence on the GDL and contribute to the development of unassisted freeze-start technology for PEFCs and the expansion of PEFCs applications. Figure 1

Thermal properties investigation of paraffin wax/titania nanocomposites as phase change materials

The use of phase change materials (PCMs) for thermal storage, thermal management, and thermal insulation has been widespread for many years. Thermal storage systems (TES) based on PCMs can be improved and optimized by adding nanoparticles (NPs) to them. Throughout this study, PCM nanocomposites (NCs) based on paraffin wax (PW) loaded by anatase titania (TiO2) NPs were fabricated and characterized to examine their thermal performance as phase change materials. The as-synthesized TiO2 NPs were obtained by hydrolysis technique and showed a well-defined spherical shape with a diameter in the nanoscale range and a crystallite size ~ 22.75 nm. Throughout the used concentrations of TiO2 NPs, 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, and 0.5%, the morphological feature for the PW/TiO2 NCs revealed a good dispersion of NPs in PW. The non-isothermal differential scanning calorimetry (DSC) measurements at a constant heating rate of 10 °C min−1 were used in order to get the melting point (Tm), latent heat of fusion (LH), and latent heat rate (LHR) as a function of TiO2 NP concentrations for the investigated PW/TiO2 NCs. Both LH and LHR values for PW/TiO2 NCs are higher than those obtained for a pure PW sample. The significant enhancement in LH and LHR values for PW/TiO2 NCs was found to be 21.2% and 134.3% in comparison with the pure PW sample, respectively. The thermal stability of the investigated PW/TiO2 NCs was examined using thermal gravimetric (TG) scans. It is found that the thermal stability varies with TiO2 NP concentrations with a non-monotonic trend. At concentrations up to 0.25 mass%, the thermal stability improved. For concentrations over 0.25 mass%, the degradation process became rapid.

How 4-(7-Octen-1-yl)-N,N-diphenylaniline co-units induce strong melt memory effects in isotactic polypropylene random copolymers

The random incorporation of comonomer units in isotactic polypropylene usually disrupts the chemical regularity of the macromolecular chain, thereby remarkably affecting the crystallization and melting processes. We study the influence of a novel comonomer 4-(7-Octen-1-yl)-N,N-diphenylaniline (ODPA), in the concentration range of 1.1–6.8 mol%, on the crystallization and self-nucleation behavior of isotactic polypropylene copolymers. Non-isothermal and isothermal differential scanning calorimetry experiments demonstrated that crystallization kinetics are significantly retarded upon comonomer incorporation as the ODPA co-units are excluded to the amorphous regions. Furthermore, ODPA comonomer incorporation leads to a sharp increase in nucleation density; thus, spherulitic superstructures become significantly smaller. Remarkably, the ODPA co-units induce a strong melt memory effect that can persist even above the equilibrium melting temperature for copolymers with 4.4–6.8 mol% ODPA. The width of Domain IIa (exclusive melt-memory domain), an indicator of the self-nucleation strength, starts to increase sharply once the content of ODPA exceeds 1.8 mol%. In contrast, the width of Domain IIb (self-seeding domain) remains constant. We attribute the self-nucleation effect in these ODPA copolymers to the aggregation of co-units in the interlamellar amorphous regions that hinder, upon melting, the motion of the chain sequences that were initially packed within the crystal lattice. In this way, to reach the isotropic melt state, the sample must be heated to much higher temperatures than its apparent or even equilibrium melting point, depending on the comonomer content. Consequently, nucleation upon cooling from the self-nucleated melt becomes easier and faster.

Cure Kinetics of a Carbon Fiber/Epoxy Prepreg by Dynamic Differential Scanning Calorimetry

Investigating the curing kinetics of a fiber prepreg system is beneficial to the controlling of prepreg laminate curing process. In the present work, a dicyandiamide (DICY)-cured carbon fiber/epoxy prepreg system was investigated by non-isothermal differential scanning calorimetry (DSC) at 2, 5, 10, and 20°C/min to attain the glass transition temperature for uncured prepreg and fully cured sample, which were estimated to be 7.6°C and 106.2°C, respectively. The activation energy (Ea) of the prepreg system was evaluated by Kissinger and Ozawa methods, and Friedman method was also employed to reveal the evolution of Ea as a function of curing degree. The kinetic parameters were determined by fitting the average Ea value obtained by Friedman method into Málek methodology, and the two parameters Šesták–Berggren model was found to best describe the curing kinetic of the prepreg system. The preexponential factor was calculated to be 6.0 × 10 8 min−1, with the overall reaction order at nearly 2.5. The prediction curves, based on Friedman method and autocatalytic model, were in good agreement with the experimental data.

Phenolic resin/coal char composites: Curing kinetics and thermal/mechanical performance

Curing behavior plays a key role in determining the ultimate properties of thermosetting polymers. With the use of fillers, curing behavior and reaction kinetics are affected. Here, we report the study of the curing process and thermal and mechanical behaviors of phenolic composites reinforced with 50 wt% of an economic filler, coal char. Curing kinetics were investigated using non-isothermal differential scanning calorimetry (DSC) measurements and analyzed by model-free isoconversional methods for determining kinetic parameters. The study revealed that the coal char had a retarding effect on the curing of the phenolic resin. The curing reaction was also influenced by the processing method of the composite. Mixing of the char in tetrahydrofuran (THF) led to higher activation energies than via dry mixing. The mechanical properties and thermal stability of the phenolic resin were significantly improved in the presence of the filler. The information reported in this work can be used for optimal curing of phenolic resin/coal char composites as well as tuning performance by choosing an appropriate processing technique.

Direct comparison of surface crystal growth kinetics in chalcogenide glass measured by microscopy and DSC

AbstractSurface crystallization in fine powder Se70Te30 chalcogenide glass was studied by differential scanning calorimetry (DSC) and optical microscopy. A complex kinetic analysis of these experimental data reveals that the contracting sphere mechanism (R3 model) is the rate determining step of crystal growth, and the conventional Johnson–Mehl–Avrami–Kolmogorov model cannot be used in this case. Moreover, it is clearly shown that the particle size distribution should be considered in crystallization studies. Actually, when the particle size effect is taken into account, the simulated DSC curves for the R3 model agree very well with the experimental data over the entire temperature range. The crystallization kinetics determined from the nonisothermal DSC data are consistent with previously reported isothermal crystallization data for the same powder fraction. The crystal growth rate calculated from isothermal and nonisothermal DSC data agrees very well with the microscopically measured surface and bulk crystal growth rate.

Preparation of biphenyl-containing polybenzoxazines with low dielectric constants and high thermal stability

In this work, two biphenyl-containing benzoxazine monomers (C-tfmb and C-dmb) have been synthesized using 2,2′-bis(trifluoromethyl)benzidine/2,2′-dimethylbenzidine, 4-cyclohexylphenol and paraformaldehyde as raw materials. The thermal curing behaviors of the benzoxazine monomers were investigated by Fourier transform infrared spectroscopy and non-isothermal differential scanning calorimetry. After curing, the biphenyl-containing polybenzoxazines (PC-tfmb and PC-dmb) exhibited high thermal stability with the 5% weight loss temperatures at 335 °C and 367 °C, respectively. Moreover, both polybenzoxazine films showed high hydrophobicity and low dielectric properties. Due to the presence of low-polarity and bulky cyclohexyl and trifluoromethyl groups, PC-tfmb had a dielectric constant of 2.78 and a dielectric loss of 0.0035 at 1 MHz.

DSC Analysis of the Effect of Cold Deformation on the Precipitation Kinetics of a Binary Cu-Sc Alloy.

The present study aimed to investigate the effect of cold deformation on the precipitation kinetics of a binary CuSc alloy containing 0.4 wt.% scandium using the experimental analysis method of differential scanning calorimetry (DSC). Non-deformed and 75% cross-section-reduced cold-rolled supersaturated specimens were tested in non-isothermal DSC runs at up to five different heating rates. The DSC results showed that cold rolling significantly accelerated the precipitation process in the binary alloy, leading to a decrease in the initial and peak temperatures of the exothermic reactions. The activation energies calculated with the Kissinger method indicated that the precipitation activation energy decreased with increasing cold deformation. The findings of this study provide worthy implications to further optimize the processing of Cu-Sc alloys with improved mechanical properties.

Synthesis of a vanillin-derived bisDOPO co-curing agent rendering epoxy thermosets simultaneously improved flame retardancy, mechanical strength and transparency

To prepare transparent and flame-retardant epoxy thermosets, a vanillin-derived bisDOPO co-curing agent (DVD) was synthesized from vanillin and DOPO. The influence of DVD on the curing kinetics of the epoxy systems was investigated by non-isothermal differential scanning calorimetry (DSC). The introduction of DVD increased the activation energy of the curing process. Compared with pure epoxy, the storage modulus at 30 °C and tensile strength of EP/DVD-5% increased by 35.7% and 145%, respectively. Additionally, the epoxy thermosets still maintained excellent transparency. The addition of DVD improved the flame-retardant performance of epoxy thermosets by promoting the formation of char and reducing the thermal decomposition rate. Most importantly, DVD showed high flame retardant efficiency for the resulting epoxy thermosets. Specifically, with the incorporation of 5 wt% DVD (only 0.42 wt% phosphorus loading), the resulting epoxy thermoset exhibited a limiting oxygen index (LOI) value of 30.5% and reached a UL-94 V-0 rating. The cone calorimetry results showed that the total heat release (THR), peak value of heat release rate (PHRR), and total smoke production (TSP) of EP/DVD-5% decreased by 32%, 42%, and 21%, respectively, compared with the unmodified EP. The modes of action of flame retardant analysis indicated that DVD exhibited high flame retardant efficiency by serving as a charring promotor in the condensed phase and acting as a radical scavenger in the gaseous phase. The above results demonstrate that DVD is a promising flame retardant agent to render epoxy thermosets simultaneously improved flame retardancy, mechanical strength and transparency.