Isothermal Thermogravimetric Analysis Research Articles

Isothermal co‐pyrolytic kinetics investigation of polystyrene/polymethyl methacrylate blended Bakelite

AbstractThe widespread use of Bakelite, polystyrene (PS), and polymethylmethacralate (PMMA) has caused significant pollution, requiring advanced recycling methods. Pyrolysis, co‐pyrolysis, and catalytic co‐pyrolysis are key for recycling these wastes, necessitating kinetic studies and specific reactor designs of their thermal degradation. Isothermal thermogravimetric analysis at 300, 350, 400, 450, and 500°C was used to study thermal degradation kinetics, based on the non‐isothermal degradation zone of Bakelite. The batch pyrolysis of discarded Bakelite and PS/PMMA–Bakelite blends was conducted at 450°C. The thermal decomposition of Bakelite and its blends increases with higher isothermal pyrolytic temperatures. The addition of PS or PMMA to Bakelite substantially accelerates its thermal decomposition. The maximum weight loss of Bakelite, PS–Bakelite, and PMMA–Bakelite are 55%, 96.75%, and 89.51% at 500°C, respectively. The kinetic analysis is crucial for designing specific reactors, utilizing the D1‐diffusion‐based method for Bakelite, with an activation energy (Ea) of 17.178 kJ/mol and Arrhenius constant (A) of 0.095 min−1. The A2‐ and A3‐Avrami–Erofeyev methods explain the isothermal degradation of PS–Bakelite and PMMA–Bakelite blends, with activation energies of 9.031 and 12.59 kJ/mol, and Arrhenius constants of 0.056 and 0.075 min−1, respectively. The co‐pyrolysis of PS–Bakelite yields the highest condensable products (66.76%) and needs the longest reaction time (320 min). The Fourier transform Infrared (FTIR) and gas chromatography–mass spectrometry (GC–MS) analyses confirm the presence of alkanes, cycloalkanes, alkenes, cycloalkenes, aromatic hydrocarbons, and oxygenated compounds in the pyrolytic oils. This study provides unique kinetic parameters and product analyses, showing effects of blending on the decomposition rates and yields valuable compounds, advancing recycling technologies.

Influence of polypropylene and high-density polyethylene on isothermal pyrolytic degradation of discarded bakelite: Kinetic analysis and batch pyrolysis studies

The recycling of thermosetting plastics such as discarded bakelite poses greater challenges than thermoplastic polymers like polypropylene (PP) and high-density polyethylene (HDPE), particularly through pyrolysis requiring specialized reactors. This study examines the isothermal thermal degradation kinetics and batch pyrolysis behaviors of bakelite, along with its blends with PP and HDPE, emphasizing the characterization of pyrolytic oils for designing optimized reactors. For the study on isothermal thermal degradation kinetics, isothermal thermogravimetric analysis was performed at specified temperatures (300, 350, 400, 450, and 500°C), chosen based on the predominant non-isothermal degradation behavior of bakelite. The batch pyrolysis of discarded bakelite and blended bakelite with PP/HDPE is carried out at 450°C. The chemical composition analysis of pyrolytic oils is performed using Fourier transform infrared (FTIR) spectroscopy, with comprehensive compound analysis conducted using Gas Chromatography-Mass Spectrometry (GCMS). Isothermal thermogravimetry at temperatures ranging from 300°C to 500°C reveals increased thermal degradation with rising pyrolytic temperatures, reaching maximum weight losses of 55 % for bakelite, 82.74 % for PP-bakelite blends, and 90.8 % for HDPE-bakelite blends at 500°C. The isothermal kinetics study reveals that bakelite degrades via D1-diffusion, polypropylene-blended bakelite via A2-Avrami-Erofeyev, and high-density polyethylene-blended bakelite via A3-Avrami-Erofeyev, with activation energies of 17.178, 7.193, and 3.550 kJ/mol, and Arrhenius constants of 0.095, 0.042, and 0.017 min.−1, respectively. The highest condensable yield of 58.76 % during PP-blended bakelite co-pyrolysis underscores its potential for resource recovery. FTIR and GC-MS confirm the presence of alkanes, cycloalkanes, alkenes, cycloalkenes, aromatic hydrocarbons, and oxygenated compounds in the pyrolytic oils, providing detailed insights into their chemical composition. These findings offer critical insights into the thermal degradation behavior and kinetics of bakelite and polypropylene/high-density polyethylene-blended bakelite, highlighting opportunities for efficient waste plastic utilization through pyrolysis for resource recovery and energy generation, and providing essential knowledge for designing isothermal pyrolysis reactors.

Enhancing mechanical properties of cementitious composites by boron nitride nanosheets modified carbon fiber

Carbon fiber (CF) is commonly employed to enhance the mechanical properties, electrical conductivity, and electromagnetic absorption properties of cementitious composites. However, its weak interfacial bonding with the matrix limits its application in such composites. In this study, boron nitride (BN) nanosheets were synthesized via the solid-state reaction and used to modify CF surface. The flexural and compressive strengths of cementitious composites incorporating BN nanosheets coated CF (BN@CF) increased by 18.45 % and 29.38 %, respectively, with CF doping at only 0.2 wt%. Isothermal calorimetry and TGA results revealed that BN nanosheets on CF surface would provide nucleation sites for the formation of C–S–H and CH. The microstructure and bonding properties of BN@CF were characterized using SEM/EDS, FTIR, XPS, finite element analysis, and single fiber pullout test. The results showed that the significant improvement of interfacial properties between the fiber and the matrix contributed to the increase of mechanical properties of cementitious composites. These findings provide an effective strategy for the strength development of CF-reinforced cementitious composites.

Characterization of Carbamide Peroxide: Stability Studies, and Degradation Kinetics under Isothermal Conditions for Industrial Application

Background: Carbamide peroxide (CP) is a hydrogen peroxide derivative bonded with urea. It is a solid substitute for liquid hydrogen peroxide in the chemical, cosmetics, and pharmaceutical industries, mainly as a disinfectant and bleaching application. However, it has an unstable nature, and there are scant studies on CP thermal analysis. Objective: This study focuses on CP thermal analysis and degradation behavior. Methods: CP was characterized by differential scanning calorimetry, thermogravimetric analysis, Fourier-transformed infrared, diffraction by X-ray, as well as, thermal and photodegradation was determined by ultraviolet spectrophotometer. Results: CP was characterized with a sharp endothermic event (88.50 oC; ΔH= -643.20 J.g-1), and a thermal decomposition behavior in a four-steps process. The pattern diffraction presented sharp peaks at 2θ: 15.2, 25.1 and 26.0o. The Arrhenius plot obtained by isothermal thermogravimetric analysis showed a linear relation with temperature in two steps. The first step the activation energy values was Ea = 45.73 J.mol-1.K-1. The thermal degradation recovery was 3.29% after 5 days, and 11.31% against 97.4% under the dark control to photostability. Conclusion: The study contributed to characterizing the CP and the results suggest that degradation depends on the surface transition state and the ternary formed system (CP-urea-water) and that the temperature influenced this system. The data were obtained through quick and easy techniques, which use wispy raw material and presented a significant result that can be used by the entire industry in the development of new formulations.

Antimicrobial Solid Starch-Iodine Complex via Reactive Extrusion and Its Application in PLA-PBAT Blown Films.

In this study, a solid masterbatch of starch-iodine complex with 6.7 wt.% iodine was prepared in pellet form using a ZSK-30 twin-screw extruder. Thermogravimetric (TGA) and isothermal TGA analysis of the pellets revealed that there was no significant loss of iodine due to sublimation during reactive extrusion. These solid pellets demonstrated antifungal properties when applied to strawberries via dip coating in an aqueous solution, extending their shelf life from two days to eight days, thereby reducing fungal growth and visual decay. Furthermore, the solid pellets displayed antibacterial activity against E. coli, as evidenced by the clear zone of inhibition observed in the Kirby-Bauer test. To enhance practical application, these pellets were further blended with PLA-PBAT film formulations at 10 and 18% by wt. to make blown films with effective iodine loadings of 0.7 and 1.3% by wt. These films showed superior antibacterial activity against E. coli compared with PLA control films and the commercial silver antimicrobial-containing films during direct inoculation tests as per ISO 22196. Tensile strength and elongation at break in machine direction (MD) for the starch-iodine-containing blown films were comparable to the control films in MD, but tensile strength was reduced to 37-40% in the transverse direction (TD). This was due to a non-uniform dispersion of the starch-iodine complex in the films, as confirmed by the visual and SEM analyses. Thus, this study illustrates the practical utility of the solid starch-iodine complex as a safe and efficient means of introducing iodine into an environment, mitigating the typical hazards associated with handling solid iodine.

Simulation and Experimental Study of the Isothermal Thermogravimetric Analysis and the Apparent Alterations of the Thermal Stability of Composite Polymers.

Composite polymers are an interesting class of materials with a wide range of applications. Among the properties of polymers which are currently being enhanced via the development of composite materials is their thermal stability, which is typically evaluated via thermogravimetric analysis (TGA). In this work, a paradox is recognized regarding the considered relationship between the polymer-filler interactions leading to a good dispersion of the filler and the improvement of thermal stability. Simulation of the TGA signal during isothermal measurements of composite polymers is performed along with experimental measurements. It is shown that there are at least three factors that can cause apparent alterations of the thermal stability of composite polymers, namely, the different buoyancy due to the different densities of the composites and the neat polymer, the different thermal diffusivity of the composites and the fact that the mass loss (or remaining mass) of the composites, conventionally, is expressed per overall mass of the composite and not per mass of polymer. The relative contributions of these factors are evaluated and it is found that the conventional expression of mass loss has the most profound effect. Furthermore, it is shown that it is proper to express and evaluate the TGA results of composite polymers per degradable (polymer) mass of the composite and not per overall mass of the composite.

Tris(2-hydroxyethyl)ammonium-Based Protic "Ionic Liquids": Synthesis and Characterization.

The proton transfer associated with the synthesis of protic ionic liquids (PILs) is often incomplete, meaning that the parent compounds may coexist with the ionic species. However, PILs are proposed for many applications as pure compounds without analysis of their ionicity. This work focuses on tris(2-hydroxyethyl)ammonium-based PILs with lactate, hydrogen succinate, hydrogen malate, and dihydrogen citrate anions. The interest of these anions lies in their low toxicity and capacity to disrupt the hydrogen-bonding network inherent to biopolymers. To improve current synthesis methods of this kind of PILs, which frequently lead to impurities derived from decomposition of reactants, working in the absence of solvents and at moderate temperatures is proposed. Through NMR studies, the ionicity of these systems was found to be low, from 20% to 86%, so the widely used term "ionic liquid" is not rigorous and must be used with caution. The un-ionized acid and base species coexist with the corresponding ionic forms, and this has to be considered in the studies involving these chemicals. The thermal characterization of the PILs was carried out. The influence of the anion on the thermal stability was found to be low. Isothermal thermogravimetric analysis showed that mass loss of these PILs starts at temperatures close to 350 K.

Early age reaction, rheological properties, and environment impact of NaOH-activated fly ash mixtures at ambient environment

To improve the performance of NaOH alkali-activated fly ash (AAFA) cured at ambient temperature, silica fume (SF) and metakaolin (MK) were utilized as partial replacements for fly ash (FA). Subsequently, the rheology, compressive strength, and environmental impact of these mixtures were examined. Besides, the geopolymerisation mechanisms were studied by Isothermal calorimetry, LF-NMR, XRD, TGA, and FTIR tests. The results show that the rheological properties of all mixtures conform to the Bingham model. Both SF and MK can improve the rheological properties of FA-based geopolymer pastes by increasing exothermic heat and shortening T2 relaxation time. MK could enhance geopolymerisation by decreasing the Si/Al ratio, thus promoting the precipitation of aluminosilicate gel. However, it is difficult for the SiO2 in SF to geopolymerize under ambient temperature. As a result, MK improves the compressive strength of FA-based geopolymer, while SF hinders the development of strength. The environmental impact assessment shows that the carbon emissions of the developed FA/SF/MK geopolymer pastes are much lower than those of OPC. Production of NaOH FA geopolymers at ambient temperature without the addition of high-carbon footprint Na2SiO3 contributes to the industrialization of green low-carbon FA geopolymers.

Study on association and thermal stability of binary imidazolium ionic liquid mixtures

Ionic liquid (IL) mixtures with specific properties can be designed by the combination of different ionic liquids (ILs), but there are few studies on the physicochemical properties of IL mixtures with different ratios. Thus, this work explores the association and thermal stability of binary imidazolium IL mixtures. In particular, the physicochemical properties of binary IL mixtures at different ratios were investigated. Four different ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), 1-butyl-3-methylimidazolium nitrate ([BMIM][NO3]), 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM][TFO]), and 1-butyl-3-methyl-imidazolium trifluoroacetate ([BMIM][CF3COO]), were selected as the parent salts to form the different binary imidazolium IL mixtures. These IL mixtures were tested at different temperatures (25, 30, 35, 40, 45, and 50 °C) and ratios (1:9, 3:7, 5:5, 7:3, and 9:1) by viscometer, conductivity meter, and then by isothermal thermogravimetric analysis in the temperature rise range of 30–500 °C. It was found that the increase in temperature decreased the association of IL mixtures, thus destroying the association behavior between the parent salts. Accordingly, different ratios of the parent salts had no significant effect on the thermal stability of some IL mixtures. Moreover, the results showed that smaller anions were more likely to combine with cations to form ion clusters or ion pairs, enhancing the association of binary IL mixtures. Thus, it increased the thermal stability of IL mixtures.

Design a novel Ca-Mn perovskite oxygen carrier with balanced performance in chemical looping combustion

The cornerstone of chemical looping combustion (CLC) is oxygen carriers (OCs), and most OCs have one or more ever-present problems with performance, cost, stability, and service life. It is vital to develop OCs with balanced performance. A novel CM0.625TF-Mg OC is proposed in this study via B-site elemental substitution of CaMnO3 perovskite. Systematic experiments using a thermogravimetric analyzer (TGA), a batch fluidized bed reactor, a fixed bed reactor, and an air jet attrition apparatus are performed to evaluate various aspects of the performance of the OC manufactured by the hydraulic molding method. First, in isothermal TGA redox cycles, CM0.625TF-Mg OC exhibits a high oxygen donation ratio (∼5.0 wt.%) and excellent cyclic stability. Mg substitution eliminates the activation effect and promotes lattice oxygen release. Then, the CH4-fueled CLC experiments on a batch fluidized bed demonstrate that Mg B-site substitution promotes oxygen uncoupling (0.2 wt.% gaseous oxygen) and significantly improves its reactivity with CH4. Following that, an agglomeration resistance test on a packed bed reveals that CM0.625TF-Mg OC particles expand slightly yet exhibit remarkable agglomeration resistance. Further characterization results from SEM, EDS, and XRD analysis show that the perovskite phase is formed in fresh CM0.625TF-Mg OC via solid-phase synthesis at 1350 °C, and OC has high thermal and chemical stability during the multiple redox cycles. According to the attrition test results, CM0.625TF-Mg OC has an 8333-hour service life. Last, CM0.625TF-Mg OC has a material cost of $0.892/kg and a use cost of 0.00217 ($/kg[O]/h). In summary, this CM0.625TF-Mg OC has excellent and balanced performance in reactivity, stability, agglomeration resistance, attrition resistance, and cost, which is of great value for industrial demonstration of CLC in the later stage.

Hydrogen production from dry reforming of methane, using CO2 previously chemisorbed in the Li6Zn1-xNixO4 solid solution

Li6ZnO4 was chemically modified by nickel addition, in order to develop different compositions of the solid solution Li6Zn1-xNixO4. These materials were evaluated bifunctionally; analyzing their CO2 capture performances, as well as on their catalytic properties for H2 production via dry reforming of methane (DRM). The crystal structures of Li6Zn1-xNixO4 solid solution samples were determined through X-ray diffraction, which confirmed the integration of nickel ions up to a concentration around 20 mol%, meanwhile beyond this value, a secondary phase was detected. These results were supported by XPS and TEM analyses. Then, dynamic and isothermal thermogravimetric analyses of CO2 capture revealed that Li6Zn1-xNixO4 solid solution samples exhibited good CO2 chemisorption efficiencies, similarly to the pristine Li6ZnO4 chemisorption trends observed. Moreover, a kinetic analysis of CO2 isothermal chemisorptions, using the Avrami-Erofeev model, evidenced an increment of the constant rates as a function of the Ni content. Since Ni2+ ions incorporation did not reduce the CO2 capture efficiency and kinetics, the catalytic properties of these materials were evaluated in the DRM process. Results demonstrated that nickel ions favored hydrogen (H2) production over the pristine Li6ZnO4 phase, despite a second H2 production reaction was determined, methane decomposition. Thereby, Li6Zn1-xNixO4 ceramics can be employed as bifunctional materials.

Porous Electrode Optimization for PEMFCs Using 3D Printing Technology

Proton Exchange Membrane Fuel Cells (PEMFCs) represent a class of fuel cells that transform the chemical energy of fuels, ideally hydrogen and oxygen, into electrical power. Utilized in diverse applications, PEMFCs power vehicles and supply backup energy to buildings. The core of a PEMFC is the membrane electrode assembly (MEA), composed of a polymer electrolyte membrane, an anode, and a cathode. Oxygen, protons, and electrons merge at the cathode, forming water. One challenge PEMFCs face is water-induced cathode flooding at low temperatures, a consequence of the electrochemical reaction's water accumulation. This reduces the oxygen supply, potentially leading to decreased cell performance or even failure. This issue can have substantial undesired consequences, as PEMFCs depend on oxygen availability at the cathode to generate electricity.Gas Diffusion Layers (GDLs) serve as critical PEMFC components, providing porous structures that facilitate reactant access to the catalyst layer and enabling electron flow through the external circuit. GDLs also offer structural support and promote reactant distribution across the membrane surface. Water accumulation in the cathode may cause pore clogging within the GDL, restricting reactant flow, and reducing cell performance. Additionally, water build-up increases pressure drop across the GDL, hindering reactant access to the catalyst layer and diminishing fuel cell efficiency.Three-dimensional (3D) printing has emerged as a potential technique for fabricating GDLs in PEMFCs. 3D printing enables the creation of GDLs with ordered pore size structures, offering a more uniform surface than traditional GDLs with randomly oriented fibres. This uniformity enhances reactant distribution across the membrane surface and mitigates water accumulation risks. In addition, to prevent cathode flooding, 3D printed GDLs are immersed in PTFE solution to increase hydrophobicity.This talk delves into the creation and evaluation of 3D printed carbonized GDLs for PEMFC implementation. A desktop 3D printer constructed a polymer framework, which was subsequently carbonized in a high-temperature tube furnace. Isothermal thermogravimetric analysis (TGA) tests were performed to identify weight change across a temperature range of 30-900 °C under an N2 atmosphere, optimizing the carbonization step to reduce structural distortion and increase electrical conductivity.The 3D printed GDLs displayed pore size diameters spanning 80 to 120 μm and fibre radii of 20-30 μm. The 3D printing technique produced GDLs characterized by a consistent, planar structure without blocked pores that are normally caused by excess resin residue. Electrical conductivity assessments were conducted on the carbonized specimens, and tensile and compression tests measured their mechanical properties.GDLs possessing minimal pore sizes and thicknesses were integrated into membrane electrode assemblies (MEAs) and examined in low-temperature PEMFCs. Diverse spraying methodologies were investigated, involving either the catalyst being sprayed onto the 3D printed GDL or the membrane receiving a catalyst coating. Commercial MEAs, comprising Nafion membranes and platinum electrodes, acted as benchmarks for MEAs featuring 3D printed GDLs. Furthermore, the current challenges facing 3D printed GDLs, including material selection, production consistency, compatibility with other PEMFC components, costs, and scaling up are highlighted in the talk.These findings underscore the promise of 3D printed carbonized GDLs in boosting PEMFC performance, showing their potential as a cost-effective and proficient substitute for conventional carbon paper based GDLs. Figure 1

Sulfur- and Nitrogen- Containing Molybdenum Films with a Thermally Stable Precursor

As devices become more and more complex with each generation, process requirements become more stringent and new materials are necessary. This also translates to the need of new precursors, in particular halide free organometallic precursors with high thermal stability. This combination prevents halide contamination/corrosion of the deposited and neighboring films, and expands the ALD window for processes. However, higher thermal stability should not compromise the reactivity of the precursors in the desired processes.We designed and successfully synthesized a new halide-free Mo precursor. It was characterized by 1H-, and 13C- NMR spectroscopy, and its molecular structure have been confirmed by x-ray crystallography. We studied its thermal stability, volatility, and chemical properties. Thermogravimetric analysis shows good volatility, with T½ of 230 oC and residual mass below 1%.Isothermal TGA at 130 °C indicates that the chemical is volatile and deliverable to the reaction chamber. Its thermal stress analysis showed that it is stable at 200 oC for more than 1 day, with ~1% residue mass. Pyrolysis experiments showed little decomposition at 475 °C.We used this precursor to attempt to deposit MoO, MoN and MoS based materials in mild conditions. ALD with NH3 afforded non uniform films with C contamination, and very low gpc. Similar results were obtained with H2O. On the other hand, films deposited with H2S were of uniform thickness with good gpc and selectivity for W over Si. The S content on the Mo-rich films was dependent on the deposition conditions and values as low as 6% could be obtained. Figure 1

Compressive Stress Dewaterability Limit in Fluid Fine Tailings

Reclamation of fluid fine tailing (FFT) storage facilities to their pre-disturbance equivalent landforms is hampered because micrometer size fines, whose surface-area-to-volume ratio is remarkably high, are occupied with siloxane and hydroxy groups, which bind water strongly. The purpose of this study is to differentiate the forms of water physically distributions in FFT and determine their propensities for dewaterability under compressive stresses. Two thermal and two mechanical methods were used to analyze water distributions in FFT. Dynamic and isothermal thermogravimetric analyses of FFT gave a transition from predominately bulk water to coevolution with water of higher enthalpy of vaporization at 81% (w/w) solids. Differential scanning calorimeter studies were used to determine the non-freezable water amount, with the premise that water that does not freeze by −30 °C is also unlikely to be removable by compressive stresses encountered in tailing treatment processes. The solid weight percent of FFTs with the non-freezable water was 79.6%. A 1D finite-strain model simulation using the constitutive relations of void ratio and effective stress, void ratio, and hydraulic conductivity show that deep-pits filled with such clayey-silt FFT will consolidate to a maximum solids content of 74% (w/w). For separation by centrifugation, the solids content plateaued to a mean of 74% (w/w) for total centrifugal force of ≥30 mega Newtons. These solid contents represent upper thresholds and demonstrate dewatering limit property of an FFT under compressive stresses.

Long-Term Insect Repellent Electrospun Microfibers from Recycled Poly(ethylene terephthalate).

In recent years, there has been an increase in the incidence of insect-borne diseases. Topically applied insect repellents are used to prevent these infectious diseases, but concerns of skin permeability and rapid evaporation rates have made way for alternative preventative methods. Encapsulation of insect repellents in polymeric materials allows for nonskin contact methods of repellent delivery with extended-release profiles without the need for reapplication. Poly(ethylene terephthalate) (PET) is widely used in textiles as well as food packaging and other single-use applications. This short product lifespan makes PET a major environmental pollutant; thus, recycling of PET is of great interest and utility. We report on the fabrication and evaluation of recycled PET microfibers containing N,N-diethyl-meta-toluamide (DEET) and picaridin and the first evaluation of dual repellent loading (DEET/picaridin) via electrospinning. The electrospun microfibers displayed a repellent retention up to 97% within the polymer network upon processing. Release profiles were characterized by isothermal thermogravimetric analysis (TGA). Hansen solubility parameters correlated release profiles with the chemical affinity between PET and the repellent substrate. Insect repellency was assessed against live mosquitoes using a novel bioassay method. Repellency was observed to be as high as 100% for over 1 week and 80% for over 3 weeks. Our method allows for long-lasting repellency with the potential for large-scale textile manufacturing.

Insights into the effect of different macromolecular architectures on the charring ability of polyethylene

The induction period preceding the ignition is a fundamental stage in controlling the protection of polymeric materials from fire. In fact, at this stage, the formation of a non-pyrolyzable carbonaceous layer (char) onto the material surface could prevent the development of a sustained flame, hence delaying or preventing polymer burning. In this work, the charring ability of four samples of high- and low-density polyethylene was evaluated in different scenarios, namely isothermal oxidative conditions and cone calorimetry tests at different heat fluxes, aiming at assessing the possible influence of the polymer macromolecular architecture on their charring ability. First, the selected polymers were characterized from a thermal and rheological point of view; the obtained results allowed for disclosing the different microstructure of the materials, in terms of molecular weight and possible presence of short- or long-chain branching. Then, isothermal thermogravimetric analyses and cone calorimetry tests were performed, demonstrating a different charring ability of the investigated polyethylenes. Finally, the observed behaviours were correlated to the different chemical structure and to the specific macromolecular architecture of the polymers, allowing a systematic evaluation of the relationship between the molecular weight or the presence of branched structures and the mechanism and rate of char formation.

Characterization and piezo-resistivity studies on graphite-enabled self-sensing cementitious composites with high stress and strain sensitivity

Carbon-based conductive fillers have recently been incorporated into a cement matrix to develop an intrinsic self-sensing concrete for data monitoring without the need for embedded, attached, or remote sensors while maintaining or improving its mechanical properties and durability. This paper studies cementitious composites filled with graphite as a novel self-sensing construction material. Experiments were systematically conducted to investigate the dispersion, chemical, mechanical, electroconductivity and piezo-resistivity properties of the composites. Experimental results showed an effective mixing with uniform dispersion of the graphite which acted as an inert filler in the mix and did not alter the microstructure of cement hydration products. Isothermal calorimetry, TGA and rheology tests showed good hydration and adequate workability of the composites with low graphite concentration (≤ 10%), while the effect of adding graphite on the compressive strength is insignificant for graphite concentrations of up to 10%. Monotonic and cyclic compressive test results indicated a repeatable piezo-resistivity performance for low graphite concentration cementitious composites whose stress sensitivity values vary from 0.75 to 7.25%/MPa, and strain sensitivity/gauge factor (GF) 150–1250 with some hysteresis. These combinations showed a stable and reliable piezo-resistivity and the ability to detect damage upon failure.

Steam gasification of cellulose pulp char: Insights on experimental and kinetic study with a focus on the role of Silicon

This paper deals with steam gasification kinetics of cellulose pulp extracted from biomass with on the focus silicon effect. Isothermal TGA tests were performed under various operating conditions. The gasification reactivity increased with increasing temperature and steam pressures. The reactivity of cellulose pulp biochar was 3 times lower than that of the biomass char. This is attributed to the difference in the inorganic content, namely AAEM and Si. The gasification of pulp biochar revealed the negative effect of Si, which was the main inorganic element present in the cellulose pulp. Biochar reactivity decreased with increasing Si concentration. The reactivity could be correlated to Si content. The morphological structure had an impact at a low conversion rate, although it was less influential than Si. Thus, a kinetic model for describing the gasification kinetics was developed using %Si as a key-parameter. The comparison to the experimental data showed that the proposed model can reasonably predict the gasification behavior of different biochars with satisfactory accuracy (<10%) as far as industrial processes are concerned. Further analysis of alkaline-washed cellulose confirmed the inhibiting effect of Si on the gasification process. The reaction time was 2.5 times lower after the partial elimination of Si.

Synergistic Effect and Mechanism of Nano-C-S-H Seed and Calcium Sulfoaluminate Cement on the Early Mechanical Properties of Portland Cement.

The combined utilization of mineral accelerators and nano-seeding materials is a novel method to promote the early strength of cement-based materials. In this paper, the effects of nano-C-S-H seed (NCS) on the early compressive strength of the Portland cement (PC)- calcium sulfoaluminate cement (CSA) binder were investigated. The results showed that NCS and CSA synergistically contributed to the early strength of PC. In detail, a 326.3% increase in the 10 h compressive strength of PC paste was obtained through the addition of NCS (2 wt%) and CSA (5%) in common. This was higher than the sum of the increases observed with the single additions of CSA (157.9%) or NCS (87.6%), with the same above dosage, in PC. Meanwhile, the early strength enhancement effects of NCS and CSA, when used together in PC, lasted longer than the effects of either used alone. Moreover, the synergetic effect mechanism was analyzed by isothermal calorimeter, QXRD, TGA, MIP, and SEM techniques. The calorimetry, XRD, and TGA results demonstrated that the synergistic mechanism was associated with the synergistic promotion effects of CSA and NCS on the hydrates. The fast hydration of CSA produced large amounts of ettringite and also consumed partial free water to promote the performance of the seeding effect of NCS which, simultaneously, further accelerated the precipitation of C-S-H gel and CH. The high alkie environment was also beneficial for the continuous generation of ettringite. In addition, the results of MIP and SEM measurements showed that the micro-filling effect of NCS significantly optimized the pore structure of a PC-CSA blend-hardened paste. Thus, the synergistic strength enhancement effects of CSA and NCS on PC were attributed to the matching of the promotion of hydration generation and the optimization of pore structures in hardening cement paste. The results of this article provide a new approach to achieving the rapid development of the early strength of cementitious materials, with potential applications in precast concrete and low-temperature construction.

Multistep kinetic study of Fe2O3 reduction by H2 based on isothermal thermogravimetric analysis data deconvolution

The multistep kinetics of Fe2O3 reduction by H2 is investigated by data deconvolution in this study. The reduction process was conducted in a TGA apparatus isothermally in the temperature range of 750–950 °C. The stepwise reduction of Fe2O3, i.e. Fe2O3–Fe3O4, Fe3O4–FeO, and FeO–Fe, was successfully decoupled from each other without controlling the reduction gas atmosphere. The overlapping, as well as the reaction rate, of each reduction step can be described by the deconvoluted data with R2 > 0.995 for all the tested temperatures. Based on the deconvolution, relatively stable activation energy with increasing the conversion was obtained for each step with the model-free iso-conversion method, indicating the rationality of the decoupled multistep profiles. Master plot was then applied to evaluate the suitability of kinetic models reported in the open literature. The JMA model (Avrami-Erofe'ev equation), corresponding to the nucleation and growth mechanism, was found to be most suitable for describing each reduction step. The activation energies obtained by the JMA model fitting for Fe2O3–Fe3O4, Fe3O4–FeO, and FeO–Fe were 10.3, 26.7, and 24.8 kJ/mol, respectively, which also agree well with the Ea obtained by the model-free method.