Thermal Degradation Behavior Research Articles

Influence of char‐forming lignin in combination with aluminium phosphinate on thermal stability and combustion properties of polyamide 11 blends

AbstractPolyamide 11 (PA) blends based on char‐forming industrial lignin and aluminum phosphinate (AlP) were prepared to improve flame retardant (FR) properties using a green and eco‐friendly approach. This study investigates the thermal degradation and combustion behavior of PA blends prepared by using AlP in combination with two different types of industrial lignins (i.e., kraft lignin (DL) and lignosulphonate lignin (LL). Thermogravimetric (TG) analysis showed that ternary blends containing LL and AlP developed higher char residue up to 10.7 wt% upon decomposition in inert atmospheres. The combination of lignin and AlP increases the thermal stability by shifting the initial decomposition temperature (T5%) and temperature at maximum decomposition (Tmax) to a higher temperature range, attributed to the stabilization of decomposition products. Furthermore, combustion behavior studied by cone calorimeter (forced combustion) and pyrolysis combustion flow calorimeter (PCFC) tests presented a significant reduction in the peak of heat release rate (PHRR) and total heat release (THR). It was found that LL and AlP‐containing blends more effectively decreased fire parameters like PHRR and THR than that of DL and AlP‐containing blends. The best interaction with reduced fire‐retardant properties was obtained when 10 wt% loading of lignin (DL/LL) and AlP was used. The reduction in heat release parameters was mainly ascribed to the condensed phase mechanism by forming an efficient protective char layer, which acts as a barrier against heat and mass transfer between the condensed and the gas phases. Raman spectroscopy analysis also confirmed the formation of the protective graphitic layer in the condensed phase.

Co-gasification of waste shiitake substrate and waste polyethylene in a fluidized bed reactor under CO2/steam atmospheres

This study investigated the co-gasification of agricultural and plastic wastes, which is a potential method for waste disposal. Waste shiitake substrate (WSS) and polyethylene (PE) were selected and their properties were investigated. The thermal degradation behavior and gases produced were explored using thermogravimetric analysis coupled with Fourier-transform infrared spectrometry (TG-FTIR). In addition, the activation energy was determined by the FWO method, and the synergistic effect and gas yield were estimated. The co-gasification of WSS and PE assisted by CO2 and steam was conducted using a bubbling fluidized bed gasifier. Results indicate that BR60 % had the maximum C–O band, C–C bond, C–H band, and CO yields. Blending WSS and PE resulted in an evident synergistic effect. The activation energies of BR20 % had the lowest value. The Taguchi method was used to determine the optimal parameters, maximum normalized H2 concentration, H2/CO ratio, CGE, and exergy efficiency. The H2 yield and H2/CO ratio were predominantly affected by the CO2/(CO2+H2O) ratio, and the best concentration and ratio were 28.6 % and 1.34. The CGE and exergy efficiencies were predominantly affected by gasification temperature, and the best results were 71.6 % and 72.4 %, respectively. Finally, the collected tars were analyzed using gas chromatography-mass spectrometry (GC/MS).

Chemical kinetics of SARA fractions pyrolysis: Resins

This work presents a predictive and generally applicable approach to resin pyrolysis modeling. Resins extracted from heavy fuel oil 380 (HFO) and vacuum residue oil (VRO) were tested for elemental composition, chemical structure, thermal degradation behavior, and distribution of pyrolysis products using different state-of-the-art experimental techniques. The in-house experiments, together with extensive literature research, guided the formulation of five pseudo-components for the definition of a fuel surrogate. The atomic ratios of the surrogate molecules were defined to be able to replicate the elemental composition of all the data with their linear combination. This approach makes the model flexible and readily applicable to any resin sample just by knowing its elemental composition. The kinetics mechanism was developed by coupling each pseudo-component with a decomposition reaction pathway. The choice of the kinetics parameters was driven by the experimental information available. The model presented a satisfactory agreement with experimental data used for the validation. The kinetic model represents a step of a more comprehensive project aimed at reconstructing the chemical kinetics of heavy and residual oils as a combination of their saturate, aromatic, resin, and asphaltene (SARA) fractions.

Waste-to-energy: Co-pyrolysis of potato peel and macroalgae for biofuels and biochemicals

Waste-to-energy conversion presents a pivotal strategy for mitigating the energy crisis and curbing environmental pollution. Pyrolysis is a widely embraced thermochemical approach for transforming waste into valuable energy resources. This study delves into the co-pyrolysis of terrestrial biomass (potato peel) and marine biomass (Sargassum angastifolium) to optimize the quantity and quality of the resultant bio-oil and biochar. Initially, thermogravimetric analysis was conducted at varying heating rates (5, 20, and 50 °C/min) to elucidate the thermal degradation behavior of individual samples. Subsequently, comprehensive analyses employing FTIR, XRD, XRF, BET, FE-SEM, and GC-MS were employed to assess the composition and morphology of pyrolysis products. Results demonstrated an augmented bio-oil yield in mixed samples, with the highest yield of 27.1 wt% attained in a composition comprising 75% potato peel and 25% Sargassum angastifolium. As confirmed by GC-MS analysis, mixed samples exhibited reduced acidity, particularly evident in the bio-oil produced from a 75% Sargassum angastifolium blend, which exhibited approximately half the original acidity. FTIR analysis revealed key functional groups on the biochar surface, including O–H, CO, and C–O moieties. XRD and XRF analyses indicated the presence of alkali and alkaline earth metals in the biochar, while BET analysis showed a surface area ranging from 0.64 to 1.60 m2/g. The favorable characteristics of the products highlight the efficacy and cost-effectiveness of co-pyrolyzing terrestrial and marine biomass for the generation of biofuels and value-added commodities.

Reutilization of Reclaimed Asphalt Binder via Co-Pyrolysis with Rice Husk: Thermal Degradation Behaviors and Kinetic Analysis.

Realizing the utilization of reclaimed asphalt binder (RAB) and rice husk (RH) to reduce environmental pollution and expand the reutilization technique of reclaimed asphalt pavement (RAP), co-pyrolysis of RAB with RH has great potential. In this study, the co-pyrolysis behaviors, gaseous products, and kinetics were evaluated using thermogravimetric analysis and Fourier transform infrared spectroscopy (TG-FTIR). The results showed that incorporating RH into RAB improved its pyrolysis characteristics. The interactions between RAB and RH showed initial inhibition followed by subsequent promotion. The primary gaseous products formed during co-pyrolysis were aliphatic hydrocarbons, water, and carbon dioxide, along with smaller amounts of aldehydes and alcohols originating from RH pyrolysis. All average activation energy values for the blends, determined through iso-conversional methods, decreased with RH addition. The combined kinetic analysis revealed two distinct mechanisms: (1) at the lower conversion range, the pyrolysis of the blend followed a random nucleation and three-dimensional growth mechanism, while (2) at the higher conversion range, the control mechanism transitioned into three-dimensional diffusion.

Synthesis and DFT calculations of metal(II) oxime complexes bearing cysteine as coligand and investigation of their biological evolutions in vitro and in silico

New complexes with the formula of [ML(Cys)(H2O)2] were obtained as a result of the reaction between the oxime ligand [HL: 4-(4-bromophenylaminoisonitrosoacetyl)biphenyl], cysteine (Cys), and the metal(II) salts (Mn, Ni, Co, Zn, Cu). The newly synthesized compounds were characterized using conventional techniques such as molar conductance, magnetic measurements, elemental analysis, infrared spectroscopy, and thermal analysis (TGA/DTA). Based on the conductivity measurements in DMF, it was determined that the complexes were non-electrolytes. The TGA/DTA analysis was performed to examine the thermal stability and degradation behavior of all samples, and results demonstrated that metal oxides or sulfides formed as a result of the decompositions. In conjunction with other data obtained, the elemental analysis confirmed the octahedral coordination of the complexes with deprotonated oxime (O, O-donor) and amino acid (N, S-donor) ligands and two coordinated waters. The compounds’ optimized geometries, molecular electrostatic potential diagrams, and frontier molecular orbitals were computed at the DFT/B3LYP level using the 6-311 G(d,p) and LANL2DZ basis sets. The antibacterial and DNA cleavage activities of all synthesized compounds were also screened, and molecular docking simulations were performed. According to the results of molecular docking studies conducted with three different proteins, the best interaction was found to be between HL-1HNJ with a binding energy of −9.5 kcal/mol. The stability of the HL-1HNJ complex was also verified by a molecular dynamics simulation performed for 50 ns. Communicated by Ramaswamy H. Sarma

Growth, structural, thermal, and optical characteristics of L-asparagine monohydrate doped magnesium sulphate heptahydrate semiorganic crystals

A novel semi-organic crystal has been grown using slow evaporation technique by doping organic compound L-asparagine monohydrate (C4H8N2O3·H2O) with inorganic material Magnesium sulphate heptahydrate (MgSO4·7H2O). The crystallographic parameters like strain, dislocation density and crystallite size were calculated by powder X-ray diffraction method. Functional groups were identified and bond length, force constants were calculated from FT-IR spectroscopy. Energy dispersive X-ray (EDX) analysis was used to identify the constituent elements of the crystal. Kinetic and thermodynamic parameters, such as, activation energy Ea, change in Gibb's free energy (ΔG) and change in enthalpy (ΔH) have been determined by thermogravimetric analysis (TGA) analysis. Ea, ΔH and ΔG show positive values and change in entropy (ΔS) shows negative ones. The thermal degradation behavior of the crystals has been analyzed by differential scanning calorimetry (DSC) analysis. Various optical constants such as optical band gap, lattice dielectric constant, absorbance, extinction coefficient, the ratio of free charge carrier concentration to the effective mass, Urbach energy, optical and electrical conductivities were estimated from UV–vis transmittance data. High optical conductivity (1010 s−1) justifies the good photo response nature of the semi-organic crystal.

Antibacterial durability of L-methionine modified cotton fabrics functionalized with ZnO nanoparticles

Cotton fabric based textiles utilizing metal oxide nanoparticles (NPs), offer potential options for reducing spreading of infection by bacteria due to their excellent antimicrobial properties, which depend on the nanoparticle's structure and morphology, as well as the fiber functionalization process. In this work, a simple padding and rolling technique for preparing antibacterial cotton fabrics by functionalizing their surface with nanostructured ZnO is demonstrated. L-methionine amino acid is utilized as a binding reagent due to its low toxicity to mammalian cells, biocompatibility with living tissues, and the presence of amine and carboxylic groups, which enhance its coordination capacity to improve ZnO adhesion. Zn(NO3)2·3H2O was precipitated as Zn(OH)2(s) using an alkali mixture of (NaOH+NaBH4), which was then converted into ZnO NPs up on heat treatment on the surface of modified cotton (LCt). Fourier transform infrared spectroscopy (ATR-FTIR) was utilized to confirm the chemical alteration of the fabrics by L-methionine. X-ray diffraction (XRD) investigations confirmed the crystalline structure, purity, and average crystallite size of the ZnO NPs (15.72 nm). X-ray photoelectron spectroscopy (XPS) tests revealed that the NPs were successfully coordinately bonded to the textiles. HR-SEM and energy-dispersive X-ray (EDS) mapping demonstrated that NPs were well-covered on the fabric fibers. The thermal degradation behavior of the modified and functionalized cotton was examined by thermal gravimetric analysis (TGA). The functionalized fabric shown outstanding antibacterial activity against gram-negative bacteria, E. coli and P. aeruginosa, as well as gram-positive bacteria S. aurous and S. pyogenes, with washing durability of up 50 wash cycles. After 50 wash cycles, approximately 88 % of the Zn was retained. This indicated a strong bond between the fabrics. Furthermore, the change has little effect on cotton qualities such as vapor permeability, water absorption, and water transport.

Ablation behavior, microstructure, phase evolution and in situ ceramization mechanism of ZrC-LaB6 modified carbon fiber/phenolic resin ceramizable composite

Carbon fiber/phenolic resin composite (CF/Ph) has drawn great interest in thermal protection for its characteristics of high specific strength and easy fabrication. However, oxidation failure limits further application of CF/Ph in hostile environments. Herein, a novel carbon fiber/phenolic resin ceramizable composite modified with ZrC and LaB6 was reported. The synergistic effects between ZrC and LaB6 on high-temperature thermal degradation behavior, oxidative corrosion and ablation resistance were systematically studied based on thermal analysis and oxyacetylene ablation experiment of the resulting ceramizable composite as well as microstructure evolution, phase evolution, and thermodynamic calculation analysis of the ablated surface. The resulting ceramizable composite exhibited excellent oxidative corrosion and ablation resistance, with the residue yield at 1500 °C as high as 32.8 % and the linear ablation rate at 4.3 MW/m2 for 30 s as low as -0.00231 mm/s, respectively. Further, the ablation mechanisms were revealed. Dense B-C-O-Zr-La ceramic layers with a mosaic structure, which acted as efficient thermal protection barriers, were constructed in situ, and significantly reduced corrosion to carbon. Moreover, an intense endothermic effect during the carbothermal reaction between ZrO2, B2O3 and PyC led to an abnormally better insulation capacity.

Sulfite incorporated thermoplastic cassava starch blended PBAT blown films as antimicrobial and antibrowning packaging

Microbial growth and browning cause quality loss in intermediate moisture foods. This research developed and characterized novel active films to prevent microbial growth and brown discoloration in dried meat and fruits. Biodegradable films based on thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate) (PBAT) blends incorporating sodium metabisulfite (SM) (up to 7% w/w) were developed using blown film extrusion. SM interacted with the TPS phase, involving O-H stretching vibration and hydrogen bonding which modified the thermal degradation behavior of the TPS phase and improved the smoothness of the film microstructures. Excessive SM formed crystal particles at ≥ 3% that were detected by X-ray diffraction. Addition of SM decreased the mechanical properties but film clarity and hydrophobicity improved, with enhanced water vapor barrier properties. The SM blend film showed significant antibacterial activity against E. coli, B. cereus, and S. aureus. TPS/PBAT/SM active films effectively prevented mold growth and darkening in packaged salami for at least 16 days, while the non-SM blend film was only effective for 6 days at room conditions. Active films with SM loading, particularly at > 3% prevented browning reaction and darkening in dried bananas and longans at both ambient (60% RH) and 85% RH stored at room temperature. SM addition improved packaging characteristics and functional efficiency, resulting in higher dried fruit and meat product quality. TPS/PBAT/SM composite films showed promise as sustainable active packaging and an alternative technique to sulfite treatment for dried fruit and meat.

Polyethylene Composite Particles as Novel Water Plugging Agent for High-Temperature and High-Salinity Reservoirs

Water channeling has always been one of the urgent problems during oilfield development. Especially for fractured reservoirs with high temperature, high salinity, and severe heterogeneity (e.g., deep carbonate reservoirs), it is difficult for the existing plugging agents to realize effective water plugging. In this paper, chemically stable polyethylene (PE) was selected as the main component to prepare multiscale PE composite particles that can be easily dispersed in water as a novel water plugging agent for fractured reservoir with high temperature and high salinity. The characteristics of the prepared PE composite particles, including thermal stability, salinity resistance, dispersibility, coalescence properties, and microscopic morphology, were systematically studied. Finally, the plugging performance of the particles was evaluated through visual physical simulation experiments. The prepared PE composite particles can be pulverized to a minimum of 6 μm, and the particle size is controllable within 6 μm to 3 mm by adjusting the pulverization parameters. The PE composite particles are easily dispersed in water by adding the dispersant, which is conducive to injectivity during the field application process. The particle size remains unchanged under the condition of salinity of 0–3.0 × 105 mg/L, which indicates that the prepared particles have good salt-resistant stability. After high-temperature aging, the particles adhere to each other, and the size of the agglomerations reach a size dozens of times larger than the initial size of the particle, which is conducive to effective plugging in fractures. Thermal degradation behavior analysis shows that the PE composite particles could theoretically withstand a temperature of 434.4 °C. It can be seen from the SEM images that after high-temperature melting and kneading with other components, the microstructure changes from a fibrous structure to a dense flake structure. Physical simulation experiments show that the PE composite particles accumulate in fracture after injection and form effective plugging through coalescence and adhesion of the particles, thereby realizing water flow diversion.

Thermal degradation and upcycling of stereoregular polyesters

In this study, the thermal degradation behavior and the decomposition products obtained during the pyrolysis of a new polyester, poly(HASA/CHO) (PHC), were investigated. Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses indicated that the pyrolysis of PHC could be divided into three stages. The average activation energies for stages I and III were estimated using the Kissinger method. The pyrolytic processes were monitored using gel permeation chromatography (GPC), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and ultraviolet-visible UV–vis spectroscopy. The effects of the PHC configuration on the thermal stability and evolution of the thermal process were explored. The results demonstrated that, compared to the cis-PHC, the trans-PHC is more likely to release anthracene via a retro-Diels-Alder reaction, and exhibits higher main chain stability. Interestingly, PHC could be reversibly recycled via the Diels-Alder reaction, leading to potential upcycling of the copolymer.

Kinetic Analysis of Thermal Decomposition of Polyvinyl Chloride at Various Oxygen Concentrations

PVC plastic products are common combustible substances seen in fires, but their thermal degradation behavior under different oxygen concentrations has not been adequately studied. The thermal degradation behavior of PVC materials in atmospheres with different oxygen concentrations was analyzed via thermogravimetric–Fourier transform infrared spectroscopy (TG-FTIR). The TG results show that the thermal degradation process of PVC under a non-oxygenated atmosphere occurred in two stages, and the activation energies of the two stages were 130–175 KJ mol−1 and 230–320 KJ mol−1, respectively; under the oxygenated atmosphere, the thermal degradation process occurred in three stages. The activation energies of the three stages were 130–175 KJ mol−1, 145–510 KJ mol−1 and 75–190 KJ mol−1, respectively. And the reaction mechanism of the second stage of thermal degradation was changed from D-ZLT3 to En by the higher oxygen concentration. Infrared spectroscopy (FTIR) was used to analyze the pyrolysis process of PVC in the non-oxygenated atmosphere, and the eight major components were as follows, in descending order according to amount released: C-H stretching > HCl > C-Cl stretching > H2O > CO2 > C-H bending > C-H aliphatic bending > CH2. For the reaction of PVC at an oxygen concentration of 7%, the nine major components, in descending order according to amount released, were as follows: CO2 > HCl > H2O > CO > C-H stretching > C-Cl stretching > C-H aliphatic bending > C-H bending > CH2. For PVC reactions at oxygen concentrations of 14% and 21%, the five major components, in descending order according to amount released, were CO2 > HCl > CO > C-Cl stretching > H2O.

Mg-Doped PLA Composite as a Potential Material for Tissue Engineering-Synthesis, Characterization, and Additive Manufacturing.

Magnesium (Mg)/Polylactic acid (PLA) composites are promising materials for bone regeneration and tissue engineering applications. PLA is a biodegradable and biocompatible polymer that can be easily processed into various shapes and structures, such as scaffolds, films, and fibers, but has low biodegradability. Mg is a biocompatible metal that has been proven to have good biodegradability and osteoconductivity, which makes it suitable for bone tissue engineering. In this study, we prepared and characterized a Mg/PLA composite as a potential material for direct ink writing (DIW) in 3D printing. The results showed that the addition of Mg has a significant impact on PLA's thermal and structural properties and has also significantly increased the degradation of PLA. XRD was used to determine the degree of crystallinity in the PLA/Mg composite, which provides insight into its thermal stability and degradation behavior. The crystallization temperature of PLA increased from 168 to 172 °C for a 15 wt% Mg incorporation, and the melting temperature reduced from 333 °C to 285 °C. The surface morphology and composition of these films were analyzed with SEM. The films with 5 wt% of Mg particles displayed the best-ordered honeycomb structure in their film form. Such structures are considered to affect the mechanical, biological and heat/mass transfer properties of the Mg/PLA composites and products. Finally, the composite ink was used as a feed for direct ink writing in 3D printing, and the preliminary 3D printing experiments were successful in resulting in dimensionally and structurally integral scaffold samples. The shape fidelity was not very good, and some research is needed to improve the rheological properties of the ink for DIW 3D printing.

PROCESSING AND CHARACTERIZATION OF MICRO AND NANOCELLULOSE FIBRES PRODUCED BY A LAB VALLEY BEATER (LVB) AND A SUPER MASSCOLLOIDER (SMC)

Cellulose nanofibers, known for their high aspect ratio (>150), are difficult to process and characterize due to a variety of reasons, including lower diameters. In this work, cellulose micro and nanofibers produced by a Lab Valley Beater (LVB) and a Super Masscolloider (SMC) were characterized using optical microscopy and SEM. The thermal degradation behavior was analyzed using thermogravimetric analysis and solar radiation tests. With decreasing clearance between two grinders, SMC refining resulted in fibres with smaller diameter (400 nm to 8 μm) and a marginal increase in the number of fines was noted. LVB refining resulted in fibres with shorter length (500 μm), but a significant increase in the number of fines, contributing to higher tensile strength. The tensile strength of SMC sheets was 10-fold lower and severe ductile fracture was observed when compared to LVB refining. However, a 30 °C increase in thermal stability was found for fibres produced by SMC compared to LVB refining. This could be due to lesser heterogeneity in fibre morphology (reduced packing density), lack of surface fibrillation (reduced mechanical interlocking) and altered cellulose-lignin interaction for SMC refined fibres. Hence, it can be recommended to use blends of LVB and SMC refined fibres to make sheets for applications involving higher temperatures (250 °C) and higher tensile strengths (25 MPa), but the sheets need to be fabricated using the cast evaporation technique by maintaining the water bath temperature at 95-98 °C. The dust capturing ability of SMC sheets was tested using a dust sampler and it was found that sheet SMC_0.01 can capture PM2.5 dust particles, i.e. a weight increase of 7% was noticed in 6 h.

Thermal Degradation Studies of Poly(2-ethyl hexyl acrylate) in the Presence of Nematic Liquid Crystals.

The thermal degradation behavior of Poly(2-ethyl hexyl hcrylate) (Poly(2-EHA)), blended with a commercially available nematic liquid crystal (LC) mixture, was investigated by thermal gravimetric analysis (TGA). Different heating rates, ranging from 5 to 200 °C/min, were applied under an inert atmosphere. Based on the TGA results, activation energies (Eα) at different conversion rates (α) were determined using three integral isoconversion methods: Flynn-Wall-Ozawa (FWO), Tang, and Kissinger-Akahira-Sunose (KAS). It can be noticed that the global evolution of these activation energies was the same for the three models. The coefficient of determination R2 presented values generally higher than 0.97. Using these models, the Eα value for the LC remains constant at 64 kJ/mol for all conversions rates. For the polymer Poly(2-EHA), applying the Tang and FWO models, the activation energy presents a variation ranging from 80 kJ/mol, for conversion α = 0.1, to 170 kJ/mol, for α = 0.9. For the third model (KAS), this energy varies between 80 and 220 kJ/mol in the same range of α.

Understanding the Thermal Degradation Mechanism of High-Temperature-Resistant Phthalonitrile Foam at Macroscopic and Molecular Levels.

Polymer foam, a special form of polymer, usually demonstrates some unexpected properties that rarely prevail in the bulky polymer. Studying the thermal degradation behavior of a specific polymer foam is important for its rational design, quick identification, objective evaluation, and industrial application. The present study aimed to discover the thermal degradation mechanism of high-temperature-resistant phthalonitrile (PN) foam under an inert gas atmosphere. The macroscopic thermal decomposition of PN foam was carried out at the cost of size/weight loss, resulting in an increasing number of open cells with pyrolyzation debris. Using the TGA/DTG/FTIR/MS technique, it was found that PN foam involves a three-stage thermal degradation mechanism: (I) releasing gases such as H2O, CO2, and NH3 generated from azo-containing intermediate decomposition and these trapped in the closed cells during the foaming process; (II) backbone decomposition from C-N, C-O, and C-C cleavage in the PN aliphatic chain with the generation of H2O, CO2, NH3, CO, CH4, RNH2, HCN, and aromatic gases; and (III) carbonization into a final N-hybrid graphite. The thermal degradation of PN foam was different from that of bulky PN resin. During the entire pyrolysis of PN foam, there was a gas superposition phenomenon since the release of the decomposition volatile was retarded by the closed cells in the PN foam. This research will contribute to the general understanding of the thermal degradation behavior of PN foam at the macroscopic and molecular levels and provide a reference for the identification, determination, and design of PN material.

Effect of high-temperature thermo-oxidation on the mechanical and electrical properties of phenylethynyl-terminated polyimide/carbon fiber composite

The thermal degradation behaviors of phenylethynyl-terminated polyimide and their carbon fiber reinforced composites (CFRC) are significant to be evaluated comprehensively as their high-temperature applications are gradually expanded. It is found that ether-containing thermoset polyimide (PI) film shows unique degradation behaviors near glass transition temperature (Tg). Though the triethylamine (Et3N) chemical imidization method is applied, the PI backbone shows thermal stability at 371℃ thermo-oxidation condition and the main degradation parts site at the curing structure. More aliphatic (CC) linkages will be formed in the thermo-oxidation process and they are ascribed to the further crosslinking behaviors of polyene structure. However, the PI film shows stable mechanical properties after thermo-oxidation. Meanwhile, the formation of an amorphous carbon structure is found after thermo-oxidation treatment, which endows the composite with enhanced electrical properties. Though the micro-cracking phenomenon happens at the matrix/CF interface of composite surface and thus degrades its mechanical properties, the in-plane longitudinal and transverse conductivity of the composite perform an increase, factors of 1.13 to 2.56×104 S/m and 2.28 to 454.8 S/m, respectively. Mechanism study indicates that the formation of amorphous carbon components is caused by the structural rearrangement of the degrading polyene curing structure and becomes more in the thermo-oxidation process, not affecting the backbone integrity and mechanical stability of the PI matrix. As a result, thermo-oxidation treatment degrades the mechanical properties of the composite, whereas the formed amorphous carbon component acts as a self-growing carbon-based nano-filling structure at the PI/CF interface and enhances the electrical contact of the carbon fibers.

Effect of different pre-treatment techniques on thermogravimetric characteristics and kinetics of lignocellulosic biomass pyrolysis

In this study, effect of pre-treatments on biomass pyrolysis kinetics was evaluated. Fir wood sawdust (F), pine wood sawdust (P) and hazelnut shell (H) were selected as raw biomass sample. Acidic pre-treatment was applied by using 1M-H2SO4 at room conditions and hydrothermal pre-treatment applied by using high pressure and temperature reactor. Thermogravimetric analysis was executed to specify thermal degradation behavior of the samples. Thermogravimetric analysis was also used to determine kinetic parameters of thermal degradation for biomass and pre-treated biomass samples. Having knowledge thermal degradation behavior and kinetic parameters of pyrolysis process such as activation energy and reaction rate are very important for reactor design. Kissinger-Akahira-Sunose (KAS), Ozawa-Flynn-Wall (OFW) and Coats-Redfern (CR) methods were used to investigate the effect of different pre-treatment techniques on the kinetic parameters. Activation energies of pyrolysis reactions for F, P and H were found as 158.47 ± 1.08 kJ/mol, 126.0 ± 1.78 kJ/mol and 158.66 ± 1.24 kJ/mol, respectively. The calculated activation energy values increased while acidic and hydrothermal pre-treatment were applied to each biomass samples. In conclusion, acidic and hydrothermal pre-treatments influenced the serial and parallel reaction rates during the thermal degradation process and the calculated activation energy values changed accordingly. Inorganics that catalyzed the pyrolysis reactions were removed by acid pre-treatment. The condensed species during hydrothermal pre-treatment prevented the easy volatilization. As a result of experimental studies and kinetic calculations, it has been determined that pre-treatments applied to biomass increased the activation energy value in thermal degradation reactions.

Thermal and chemical durability of metal halide perovskite CsPbBr3 single crystals

Halide perovskite CsPbBr3 single crystals have shown promising applications in high-energy radiation detection because of their high gamma-ray blocking capability, strong hole carrier transport capability, and manufacturing feasibility. However, the soft ionic properties of perovskite octahedral lattice facilitate the phase transformation of CsPbBr3 under a hydrothermal environment, which significantly limits their application. The current work systematically studied the phase stability of the CsPbBr3 single crystals under high temperatures and high humidity to accelerate their potential application in high-energy radiation detection. Thermal and water degradation behaviors of the CsPbBr3 single crystals under elevated temperature were investigated for the first time via in situ Raman spectroscopy and semi-dynamic leaching testing methods. Results indicated that the CsPbBr3 single crystals exhibited good thermal stability below 460 °C without obvious phase degradation and rapidly transformed to CsPb2Br5, followed by PbBr(OH) with the continuous water interaction. The water interaction and phase degradation mechanism of single crystals with the preferential release of Cs, surface reorganization, and formation of PbBr(OH) alteration layer with rod-like structure was revealed. The phase degradation of CsPbBr3 single crystals along surface defects from the growth process was further confirmed, which can be used to guide subsequent work on single-crystal stability regulation.