Thermochimica Acta最新文献

A prototype of an innovative isothermal calorespirometer was developed to measure simultaneously heat production rate (calorimetry) and CO₂ evolution rate (respirometry) in real-time in a static batch vessel system. The relationship between these two variables forms the calorespirometric ratio, which serves as a crucial indicator for metabolic processes and allows for the differentiation of various metabolic pathways in simple (pure culture) and complex (e.g. soil) biological systems. The heat production rate is gauged by a thermoelectric generator situated at the bottom of the measuring channel (calorimetric unit), while the CO₂ evolution rate is monitored through a conductometric cell fixed on the lid of the channel (respirometric unit). The prototype is designed with a twin configuration, featuring both sample and reference channels. The spatial separation of the calorimetric and respirometric measuring units ensures the simultaneous measurement of the two rates from a single sample without the occurrence of crosstalk effects between the signals.

The electrical calibration of the calorimetric unit reveals heat losses (approx. 30 %) and response times (approx. 6 min) that are comparable to those of established isothermal calorimeters. In parallel, growth experiments conducted with baker`s yeast demonstrate the applicability of the calorespirometer prototype to biological systems.

There is a lack of research on the spontaneous combustion phenomenon and its main influencing factors in ultra-deep high-pressure shale oil reservoirs with additional fracturing. In this study, we examine the exothermic characteristics of shale oil oxidation using high-pressure differential scanning calorimetry (HP-DSC) and accelerating rate calorimetry (ARC). Subsequently, a reaction kinetics model is built by integrating the HP-DSC and ARC data. Furthermore, the main factors affecting spontaneous combustion are identified by combining the simulation results with range and variance analyses. The HP-DSC and ARC results indicate a positive potential for achieving spontaneous combustion in shale oil. The developed reaction kinetics model successfully captures the exothermic characteristics of shale oil oxidation. The simulation results demonstrate that spontaneous combustion occurs approximately 5 m away from the injection well, with a delay time of 10.74 days. The critical factors determining the occurrence of spontaneous combustion are O₂ concentration and oil saturation.

The research into using waste plastics as a substitute for coal powder and coke as a reducing agent has garnered significant attention, driven by various factors such as increased environmental concerns and growing interest in sustainable materials. This study investigates the process of carbothermal reduction using a mixture of waste polyvinyl chloride (PVC) and iron concentrate. Thermogravimetric analysis demonstrated that the heat-treated polyvinyl chloride products (PVC370) exhibited superior reaction properties compared to anthracite. Reduction tests indicated that PVC370-bearing pellets were less sensitive to temperature changes than anthracite-bearing pellets, highlighting a potential advantage of PVC370 in industrial applications. Moreover, the metallization ratio of PVC370-bearing pellets exceeded that of anthracite-bearing pellets before reaching 1150 °C. At a temperature of 1100 °C and a C/O of 0.8, the metallization ratio of PVC370-bearing pellets peaked at 83.17 %. During the reduction process of PVC370-bearing pellets, hydrogen (H₂), carbon monoxide (CO), and hydrogen chloride (HCl) were efficiently released at relatively low temperatures. The efficiency of gas release in the reduction process could be attributed to certain factors, such as the composition or structure of the PVC370-bearing pellets. Notably, the quality of gasses generated during the reduction process of PVC370-bearing pellets is superior to that of anthracite-bearing pellets, even when considering chlorine content.

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 (T_d,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 %.

Transition metal nanomaterials are widely applied as flame retardants in materials. Herein, an oxidation-mediated strategy was developed for temporally controlling the in situ growth of Fe(OH)₃ nanoparticles on wool/nylon (W/N) fabrics. The formed particles exhibit homogeneous dispersion on the surface of W/N fabrics, with an average particle diameter of about 60 nm. These Fe(OH)₃ nanoparticles can simultaneously enhance both the flame retardancy (the limiting oxygen index increased by 18.8 % and passed the UL-94 burning test of V-0 rating) and mechanical performance (the tensile strength increased by 9.13 %) of the W/N fabrics. Meanwhile, the obtained W/N fabrics exhibit remarkable smoke-suppressant properties, demonstrating a reduction of 76.4 % and 65.5 % in smoke production rate and total smoke production, respectively, compared to the pure W/N fabrics. Furthermore, the prepared W/N fabrics exhibit good durability. This innovative strategy may be also extended for synthesizing other nanomaterials and pave a new path to develop high-performance flame-retardant materials.

Phase change materials (PCMs) can improve thermal comfort of occupants acting as thermal energy storage systems. During their service life, PCMs undergo many phase change transitions. However, there is a lack of feasible and cost-effective techniques to evaluate the effect of thermal cycling on the long-term stability and performance of PCMs, which can influence their selection and restrict a broader acceptance of these materials by the construction sector. This study developed a novel accelerated thermal cycling multi-technique to assess the stability and reliability of PCMs under dynamic thermal conditions. All investigated PCMs showed remarkable stability in terms of phase change temperature and latent heat energy even after undergoing 10,000 thermal cycles. The Thermogravimetric Analysis (TGA) results underscore the suitability of these PCMs for built environments, with minimal mass loss at lower temperatures (below 150 °C). The Fourier Transform Infrared spectroscopy (FT-IR) and ¹H Nuclear Magnetic Resonance (NMR) results revelled no molecular changes induced by thermal cycling. The novel accelerated thermal cycling technique provides more accurate results than thermal cycling using Differential Scanning Calorimetry (DSC) only, overcoming the issues of contamination and subcooling of smaller samples in DSC measurements.

In this study, high-pressure differential scanning calorimetry (HP-DSC) was used to examine the curing process of a peroxide-cured silicone rubber (SR) system under compressed CO₂ to investigate the influence of pressure and CO₂ on the curing process. We found that the curing reaction occurred in two parts, described as cure separation, because of the dual effect of CO₂ pressure and solvation at 6 MPa CO₂. Consequently, peak fitting was used to calculate the kinetic parameters of the two-part reaction at 6 MPa CO₂. Results indicate that pressure and CO₂ exerted a combined effect on the curing reaction. In particular, pressure and CO₂ solvation effects changed with varying conversion rates and CO₂ pressures. This study provides an effective analysis methodology and an accurate kinetic model for characterizing and predicting high-pressure cure kinetics and unexpected cure separation in a peroxide-cured SR system under compressed CO₂.

Replacing antimony trioxide (ATO) in flame retardant formulations is an urgent task due to its toxicity. There are indications that calcium hypophosphite (CaP) may be a promising replacement. This study investigates the decomposition, fire behavior, and smoke release of brominated flame-retarded acrylonitrile butadiene styrene (ABS) under various fire scenarios like ignition, developing fire and smoldering, while replacing ATO with CaP and CaP/talc. Adding 4 wt.-% of talc to CaP formulations showed beneficial effects on flammability due to changes in the viscosity and barrier properties. Synergism between 8 wt.-% talc and CaP improved the protective layer in the developing fire scenario, resulting in a ∼60 % decrease in the peak of heat release rate and reduction of ∼21 % in total smoke production (ref. ABS+Br+ATO). With a conventional index of toxicity (CIT) of below 0.75, ABS+Br+CaP passes the highest requirements according to EN 45545-2. Overall, the CaP/talc materials improve flame retardancy, show less smoke emission under forced flaming conditions, and prevent chronic intoxication and environmental pollution through smoke particles contaminated with antimony.

The purpose of this study was to determine the quantitative and qualitative effects of the form of natural phenolic compounds (NPCs) on the decomposition of polylactide (PLA) under different measurement conditions. For this purpose, thermogravimetry analysis (TGA), differential scanning calorimetry (DSC), and pyrolysis-combustion flow calorimetry (PCFC) analyses were carried out not only on individual raw materials like calcium lignosulfonate (BX), tannic acid (TA), BX chemically modified with TA (BMT), but also on PLA/BX, PLA/TA, and PLA/BMT composites with 3, 6, and 9 wt.% of filler. Moreover, the work checked whether to obtain satisfactory results it is necessary to carry out chemical modification lasting many hours, or whether simple physical mixing of ingredients (TABX) is enough, e.g. in proportions 1:2, 2:4, 3:6. The results of these analyses showed that TA is neither a good flame retardant nor a highly swelling material, but when combined with BX physically or chemically, it can produce an interesting synergistic effect. This work proves that chemically obtained BMT hybrid material allows to reduce flammability by 30 % compared to PLA which cannot be achieved by physically mixing these components in a polymer melt. On the other hand, the addition of TABX is sufficient to achieve a good thermal stabilization effect under processing conditions.