Thermal Stability Behavior Research Articles

Role of Transition Metals in Metal-Organic Frameworks as Nanoporous Ion Emitters for Thermal Ionization Mass Spectrometry.

Thermal ionization mass spectrometry is a powerful analytical technique that allows for precise determination of isotopic ratios. Analysis of low abundance samples, however, can be limited by the ionization efficiency. Following an investigation into a new type of metal-organic hybrid material, nanoporous ion emitters (nano-PIEs), devised to promote the emission of analyte ions and reduce traditional sample loading challenges, this work evaluates the impact that changing the metal in the material has on the ionization of uranium (U). Being derived from metal-organic frameworks (MOFs), nano-PIEs inherit the tunability of their parent MOFs. The MOF-74 series has been well studied for probing the impact various framework metals (i.e., Mg, Mn, Co, Ni, Cu, Zn, and Cd) have on material properties, and thus, a series of nano-PIEs with different metals were derived from this isoreticular MOF series. Trends in ionization efficiency were studied as a function of ionization potential, volatility, and work function of the framework metals to gain a better understanding of the mechanism of analyte ionization. This study finds a correlation between the analyte ionization efficiency and nano-PIE framework metal volatility that is attributed to its tunable thermal stability and degradation behavior.

Synthesis of novel nitrogen‐phosphorus flame retardants and their flameproof to flammable polymers

AbstractTo prepare the efficiently flame retardants (FR) for the highly flammable polymers, the novel nitrogen‐phosphorus based FRs (P‐N FR) (PN‐3, PN‐4, PN‐5, and PN‐6) were prepared via phosphorus halides and amine derivatives with 40‐90 % in yields. The appearances of P‐N FRs are lightly white solid. All P‐N FRs are water‐insoluble and show a melting point above 40 oC. The success of the synthesis was confirmed by NMR analysis. Both 1H and 31P NMR data show clearly the same as the predicted chemical shift signals. The thermal stability behavior of these FRs was studied via TGA analysis. Thermal decomposition occurs in the range of 220‐260oC under N2 gas. The 80% of a mass loss with one step decomposition and 5‐20% of the char residues at 700oC were obtained. The UL‐94 test with self‐extinguishing behavior on ABS and EVA was realized at 20‐25wt% loadings of P‐N FRs. It was observed that the addition of 18‐20 wt% of PN‐5 acquires UL‐94 V‐0 rating for the highly flammable resins (ABS and EVA) whereas to achieve the UL‐94 V‐0 rating, 20‐30 wt% of loadings of PN‐4 and PN‐6 are needed. It was concluded that the structure moieties of P‐N FR affect its FR behaviors.

Large-area deposition of protective (Ti,Al)N coatings onto polycarbonate

Polycarbonate (PC) and protective (Ti,Al)N coatings exhibit extremely different material properties, specifically crystal structure, thermal stability, and elastic and plastic behavior, as well as thermal expansion coefficients. These differences present formidable challenges for the deposition process development as low-temperature synthesis routes have to be explored to avoid a thermal overload of the polymer substrate. Here, a large-area sputtering process is developed to address the challenges by systematically adjusting target peak power density and duty cycle. Adhering (Ti,Al)N coatings with a critical residual tensile stress of 2.2 ± 0.2 GPa are obtained in the pulsed direct current magnetron sputtering range, whereas depositions at higher target peak power densities, realized by high power pulsed magnetron sputtering, lead to stress-induced adhesive and/or cohesive failure. The stress-optimized (Ti,Al)N coatings deposited onto PC with a target peak power density of 0.036 kW cm−2 and a duty cycle of 5.3% were investigated by the cross-cut test, confirming adhesion. By investigating the bond formation at the PC|(Ti,Al)N interface, mostly interfacial CNx bonds and a small fraction of (C−O)−(Ti,Al) bonds are identified by x-ray photoelectron spectroscopy, indicating reactions at the hydrocarbon and the carbonate groups during deposition. Nanoindentation reveals an elastic modulus of 296 ± 18 GPa for the (Ti,Al)N coating, while a Ti–Al–O layer is formed during electrochemical impedance spectroscopy in a borate buffer solution, indicating protective passivation. This work demonstrates that the challenge posed by the extremely different material properties at the interface of soft polymer substrates and hard coatings can be addressed by the systematical variation in the pulsing parameters to reduce the residual film stress.

A versatile, highly effective intumescent flame-retardant synergist for polypropylene and polyamide 6 composites

A novel phosphorus-based macromolecular flame-retardant synergist named DPS was designed and synthesized via three steps from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), dihydroxybenzophenone (DHBP) and pentaerythritol (PER). The prepared synergist was used in combination with a base flame-retardant (melamine-coated ammonium polyphosphate (APP-M), or aluminum diethylphosphinate (ADP)) to create novel binary intumescent flame retardant (IFR) systems for polypropylene (PP) and polyamide 6 (PA6) matrices. The structure of DPS was characterized by fourier transform infrared (FTIR), phosphorus nuclear magnetic resonance spectroscopy (31P NMR) and gel permeation chromatography (GPC) analysis. The thermal stability and combustion behaviors of the flame-retardant polymer composites were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 vertical burning tests. It was found that with a low fraction of DPS (20–25 wt%), the developed binary IFR systems significantly enhanced the flame-retardant performance of both PP and PA6. The results indicate that owing to the rich phosphorus content and abundant aromatic structures, DPS has synergistic actions with the base flame retardants to scavenge free radicals and promote char formation in the gaseous and condensed phases, respectively. Additionally, the mechanical properties of the PP composites were also evaluated, revealing the mechanical reinforcement effect of the binary IFR, i.e., simultaneous improvement of tensile modulus, ultimate tensile strength and impact toughness. This further demonstrates the effectiveness of the developed IFR formulations in terms of well-balanced flame-retardant performance and mechanical properties.

Thermal stability and dynamic mechanical analysis of nano-biofillers blended hybrid composites reinforced by cellulosic Borassus flabellifer L. fiber

The aim of this study is to investigate the dynamic mechanical and thermal stability behavior of rice husk nano-biofillers blend epoxy hybrid composites reinforced by Borassus flabellifer L. leaf fiber. The raw Borassus leaf fibers were treated with 5 wt.% NaOH solution to reduce the disadvantages of hydroxyl bonding. Rice husk nano-fillers (RHNFs) were blended with epoxy resin to modify them with 0.25, 0.45, and 0.65 wt.%, respectively, using sonication and mechanical stirring process. The prepared samples were assessed to evaluate the thermal stability, maximum degradation temperature, storage modulus (E′), loss modulus (E″), damping factor (tan δ) and Cole–Cole plot of the composites. EDX spectroscopy was used to confirm the elemental composition of nano-biofillers. The morphology of RHNFs was analyzed using a scanning electron microscope (SEM). The TG analysis confirmed that the 0.45 wt.% RHNFs blended Borassus leaf fiber (BLF) composites exhibited superior thermal stability (371–384 °C). Derivative thermogravimetry (DTG) analysis exposed that the maximum mass-loss degradation temperature of 0.45 wt.% RHNFs blend composites was 411 °C for the first stage and 678 °C for the second stage, which were more than raw and RHNFs blend (0.25 and 0.65 wt.%) composites. Accordingly, improved E′ (959.16–1637.75 MPa), glass transition temperature (T g) from E″ (90.48–97.69 °C) and, T g from tan δ (103.35–109.67 °C) were derived from the modified composites. Owing to the improved dispersion of the nano-filler, the 0.45 wt.% RHNFs blend composites had a homogeneous polymer system, as verified by the Cole–Cole diagram. The analyzed composites are to be used with versatile functionality for their intended purpose.

Nano-residronate loaded κ-carrageenan-based injectable hydrogels for bone tissue regeneration

Bone tissue possesses intrinsic regenerative capabilities to address deformities; however, its ability to repair defects caused by severe fractures, tumor resections, osteoporosis, joint arthroplasties, and surgical reconsiderations can be hindered. To address this limitation, bone tissue engineering has emerged as a promising approach for bone repair and regeneration, particularly for large-scale bone defects. In this study, an injectable hydrogel based on kappa-carrageenan-co-N-isopropyl acrylamide (κC-co-NIPAAM) was synthesized using free radical polymerization and the antisolvent evaporation technique. The κC-co-NIPAAM hydrogel's cross-linked structure was confirmed using Fourier transform infrared spectra (FTIR) and nuclear magnetic resonance (1H NMR). The hydrogel's thermal stability and morphological behavior were assessed using thermogravimetric analysis (TGA) and scanning electron microscopy (SEM), respectively. Swelling and in vitro drug release studies were conducted at varying pH and temperatures, with minimal swelling and release observed at low pH (1.2) and 25 °C, while maximum swelling and release occurred at pH 7.4 and 37oC. Cytocompatibility analysis revealed that the κC-co-NIPAAM hydrogels were biocompatible, and hematoxylin and eosin (H&E) staining demonstrated their potential for tissue regeneration and enhanced bone repair compared to other experimental groups. Notably, digital x-ray examination using an in vivo bone defect model showed that the κC-co-NIPAAM hydrogel significantly improved bone regeneration, making it a promising candidate for bone defects.

Thermal Behavior of Curaua-Aramid Hybrid Laminated Composites for Ballistic Helmet.

Hybrid composites are expanding applications in cutting-edge technology industries, which need materials capable of meeting combined properties in order to guarantee high performance and cost-effectiveness. This original article aimed for the first time to investigate the hybrid laminated composite thermal behavior, made of two types of fibers: synthetic Twaron® fabric and natural curaua non-woven mat, reinforcing epoxy matrix. The composite processing was based on the ballistic helmets methodology from the North American Personal Armor System for Ground Troops, currently used by the Brazilian Army, aiming at reduced costs, total weight, and environmental impact associated with the material without compromising ballistic performance. Thermal properties of plain epoxy, aramid fabric, and curaua mat were evaluated, as well as the other five configurations of hybrid laminated composites. These properties were compared using thermogravimetric analysis (TGA) with its derivative (DTG), differential thermal analysis (DTA), and thermomechanical analysis (TMA). The results showed that the plain epoxy begins thermal degradation at 208 °C while the curaua mat at 231 °C and the aramid fabric at 477 °C. The hybrid laminated composites curves showed two or three inflections in terms of mass loss. The only sample that underwent thermal expansion was the five-aramid and three-curaua layers composite. In the third analyzed temperature interval, related to the glass transition temperature of the composites, there was, in general, an increasing thermal stability behavior.

Development of Composite Microencapsulated Phase Change Materials for Multi-Temperature Thermal Energy Storage

Phase change energy storage materials have been recognized as potential energy-saving materials for balancing cooling and heating demands in buildings. However, individual phase change materials (PCM) with single phase change temperature cannot be adapted to different temperature requirements. To this end, the concept of fabricating different kinds of microencapsulated PCM (MEPCM) and combing them to form a multiphase change material (MPCM) for multi-seasonal applications in buildings has been proposed. To prove the feasibility of this idea, three kinds of MEPCMs were fabricated and used for the development of three different composite MPCMs, classified as MPCM-1, MPCM-2, and MPCM-3. Analysis of the results shows that each MPCM sample was able to release latent heat at two different temperatures thus making them suitable for multi-temperature thermal energy storage applications. The phase change temperatures of the MPCMs were however found to be slightly reduced by 0.09–0.31 °C as compared with the MEPCMs samples. The measured energy storage capacities for the MPCMs were also reduced in the range of 6.3–11.4% as compared with the theoretical values but they displayed relatively good thermal stability behaviour of up to 197.8–218.8 °C. It was further identified that the phase change temperatures and latent heat of the MPCM was attributed to the weight percentages of individual components, as the theoretical values for the three MPCM samples were all in good accordance with the measured values. Therefore, optimizing the weight ratios of the MEPCM in MPCM samples and their corresponding thermophysical properties based on specific climatic conditions would be a necessary step to take in future investigations. Thermal performance enhancement of the MPCM is also being recommended as an essential part of further research.

Contaminants of emerging concern: Silylation procedures, evaluation of the stability of silyl derivatives and associated measurement uncertainty

Analyte range of gas chromatography–mass spectrometry (GC–MS), widely used in environmental analysis, can be significantly broadened by derivatization. Silyl derivatives have improved volatility and thermal stability, chromatographic and mass spectrometric behaviors, and thus detection, structural elucidation and quantification. However, silylation use is often hindered by the stability of generated derivatives and the need to optimize silylation conditions. In this study, we optimized the derivatization conditions for 70 selected contaminants of emerging concern (CEC) using chemometrics approaches. N-methyl-N-(trimethylsilyl) trifluoroacetamide (MSTFA), N, O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and BSTFA + 1 % trimethylchlorosilane (TMCS) were investigated, among which the latter gave the best yield. CEC were grouped in three derivatization protocols: 60 °C/45 min, 70 °C/90 min, and 70 °C/45 min. The short- and long-term stability of the CEC-trimethylsilyl (TMS) derivatives, i.e. for 28 days and up to 20 weeks were examined in a solvent and artificial wastewater (AWW) extract at 25 °C, 4 °C and − 18 °C, and during repeated five freeze-thaw (F/T) cycles, at two concentration levels: 100 μg/L and 1000 μg/L. Except for TMS derivatives of shikimic acid (SHA), quinic acid (QA) and sulfanilamide (SFA), the remaining derivatized compounds were stable in solvent (EtAc) for 28 days. In AWW extract, TMS derivatives of citric acid (CA), 17β-estradiol (E2), estriol (E3) and 17α-ethinyl estradiol (EE2) were unstable at 25 °C and 4 °C. Within up to 20 weeks, only the TMS derivatives of CA, meso-erythritol (ERY) and bisphenol BP (BPBP) were unstable. The most significant hydrolytic breakdown was observed during repeated F/T cycles. After three cycles, ≤ 20 % of the initial concentration of six and nine CEC-TMS derivatives had degraded in solvent and AWW extracts, respectively. According to the deep statistical comparison (DSC) approach, the most prominent degradation was observed for TMS derivatives of E2, CA, 9-hydroxyfluorene (9-HF), estrone (E1) and trans-3′-hydroxycotinine (T3HC) in solvent; E2, CA, 9-HF, E3 and E1 in AWW extracts and ERY, E2, CA, 9-HF and E1 in both matrices. Finally, the sample concentration of CEC accounted for most of the measurement uncertainty (MU).Based on our findings, we recommend the derivatized samples to be stored at −18 °C for up to 20 weeks to ensure the stability of their TMS derivatives. Sample freezing and thawing of not more than twice is allowed to maintain ≥80 % of the initial CEC-TMS concentration.

Effect of in-situ formed oxide and carbide phases on microstructure and corrosion behavior of Zr/Y doped CoCrFeNi high entropy alloys prepared by mechanical alloying and spark plasma sintering

The present work has examined the microstructural evolution, thermal stability, hardness, and corrosion behavior of Zr/Y doped CoCrFeNi HEAs prepared through high-energy mechanical alloying followed by spark plasma sintering (SPS) at 1100 °C. The achieved microstructures were investigated by XRD and TEM techniques. The results showed that investigated HEAs consist of an fcc solid solution of CoCrFeNi matrix with in-situ formed Cr–C carbides and Cr/Zr/Y based oxide phases. The SPS processing of CoCrFeNi yielded grain growth to 370 ± 60 nm, while 240 ± 160 nm grain size with bimodal grain size distribution and 165 ± 38 nm grain size were achieved with Zr and Y additions, respectively. The effects of microstructural changes on the hardness and corrosion behaviors of HEAs were also investigated. Compared with 372 ± 15 HV hardness of CoCrFeNi HEA, 445 ± 26 HV and 563 ± 58 HV hardness values were determined with Zr and Y doped HEAs, respectively. The increase in hardness is mainly ascribed to the precipitation strengthening of carbide and oxide phases as well as smaller grain sizes. The corrosion analysis showed that, although the achieved smaller grain sizes and the presence of different oxide types when dopped with Y and Zr impaired the corrosion resistance, the investigated HEAs have reasonable resistance to corrosion when compared to SS304 stainless steel.

Co-Influence of Nanofiller Content and 3D Printing Parameters on Mechanical Properties of Thermoplastic Polyurethane (TPU)/Halloysite Nanotube (HNT) Nanocomposites

Thermoplastic polyurethane (TPU) belongs to a polyurethane family that possesses an elongation much higher than 300%, despite having low mechanical strength, which can be overcome by incorporating clay-based halloysite nanotubes (HNTs) as additives to manufacture TPU/HNT nanocomposites. This paper focuses on the co-influence of HNT content and 3D printing parameters on the mechanical properties of 3D printed TPU/HNT nanocomposites in terms of tensile properties, hardness, and abrasion resistance via fused deposition modelling (FDM). The optimum factor-level combination for different responses was determined with the aid of robust statistical Taguchi design of experiments (DoEs). Material characterisation was also carried out to evaluate the surface morphology, nanofiller dispersion, chemical structure, thermal stability, and phase behaviour corresponding to the DoE results obtained. It is evidently shown that HNT level and infill density play a significant role in impacting mechanical properties of 3D-printed TPU/HNT nanocomposites.

Biobased Copolymers via Cationic Ring-Opening Copolymerization of Levoglucosan Derivatives and ε-Caprolactone.

Simultaneous ring-opening copolymerization is a powerful strategy for the synthesis of highly functional copolymers from different types of cyclic monomers. Although copolymers are essential to the plastics industry, environmental concerns associated with current fossil-fuel-based synthetic polymers have led to an increasing interest in the use of renewable feedstock for polymer synthesis. Herein, we report a scalable synthetic platform to afford unique polysaccharides with different pendant functional groups from biomass-derived levoglucosan and ε-caprolactone via cationic ring-opening copolymerization (cROCOP). Biocompatible and recyclable bismuth triflate was identified as the optimal catalyst for cROCOP of levoglucosan. Copolymers from tribenzyl levoglucosan and ε-caprolactone, as well as from tribenzyl and triallyl levoglucosan, were successfully synthesized. The tribenzyl levoglucosan monomer composition ranged from 16% to 64% in the copolymers with ε-caprolactone and 22% to 79% in the copolymers with triallyl levoglucosan. The allylic levoglucosan copolymer can be utilized as a renewably derived scaffold to modify copolymer properties and create other polymer architectures via postpolymerization modification. Monomer reactivity ratios were determined to investigate the copolymer microstructure, indicating that levoglucosan-based copolymers have a gradient architecture. Additionally, we demonstrated that the copolymer glass transition temperature (Tg, ranging from -44.3 to 33.8 °C), thermal stability, and crystallization behavior could be tuned based on the copolymer composition. Overall, this work underscores the utility of levoglucosan as a bioderived feedstock for the development of functional sugar-based copolymers with applications ranging from sustainable materials to biomaterials.

Thermal stability and crystallisation behavior of newly developed Cu–Zr–Ag–Ti–Ni multicomponent bulk metallic glass

A comprehensive understanding of the thermal stability of multicomponent bulk metallic glasses (MBMGs) is imperative for their possible technological applications. In this study, new MBMGs, Cu39Zr42Ag9Ti10 and Cu32Zr39Ag8Ti9Ni12, were developed employing a multilayer perceptron neural network, intelligently expanding the binary Cu50Zr50 BMG. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses were used to confirm the amorphous nature of the as-cast alloys. The crystallisation kinetics of the alloys were investigated using differential scanning calorimetry (DSC) under isochronal conditions at different heating rates coupled with microstructural analyses tools. The thermal attributes suggest that glass transition and crystallisation are more sluggish in the case of Cu32Zr39Ag8Ti9Ni12 compared to Cu39Zr42Ag9Ti10. The local activation energies (Eα) and the Avrami exponent (nα) indicate a diffusion-controlled crystallisation mechanism for both alloys. The nucleation rate of the crystalline phase(s) is relatively lower for Cu32Zr39Ag8Ti9Ni12, indicating sluggish crystallisation. Moreover, the rate of change of nα becomes much slower for Cu32Zr39Ag8Ti9Ni12 MBMG during the later stages of crystallisation owing to higher undercooling and, thus, a higher required driving force for the growth of nucleated phases. The free volume of Cu32Zr39Ag8Ti9Ni12 remains smaller at both room and elevated temperatures, pointing towards its better glass forming ability. XRD and TEM analyses of the crystallised alloys suggested progressively increasing precipitation of the topologically disordered Cu10Zr7 phase from Cu42Zr48Ag10 to Cu32Zr39Ag8Ti9Ni12 MBMG, potentially aiding in its increased thermal stability.

Effect of lignin acetylation on the mechanical properties of lignin-poly-lactic acid biocomposites for advanced applications

Bioplastics that possess characteristics like durability and low cost are desired for versatile applications in industries such as automotive manufacturing, marine transport manufacturing, aerospace applications, and the building industry. The automotive industry is an example of an industry that is now shifting towards a more focused approach addressing the issue concerning sustainability and the development of sustainable material. To achieve a lightweight and sustainable construction, one of the methods used by the automotive original equipment manufacturers is by substituting conventional fossil-based, non-renewable composites, and metallic materials with a bio-based alternative. One of the drawbacks with biobased polymers can be the poor interfacial adhesion, leading to poor mechanical properties when compares to conventional material. The aim of this research is to investigate if a low-cost by-product could be used as a component in a composite matrix material in the automotive industry to reduce the final weight and increase the non-petrochemical material usage of composite material without compromising the thermal and mechanicals properties demanded. In this research, lignin was chemically altered by esterification the functional groups to increase the compatibility with polylactic acid. The esterification was performed with the use of acetic acid anhydride and pyridine. To evaluate and determine the esterification, Fourier transform Infrared Spectroscopy was used. By blending the modified lignin with polylactic acid the intention was to improve the thermomechanical properties and the interfacial linkage between the components. The effects of lignin acetylation on the tensile properties, impact strength, and thermal stability and moisture repellence behaviour were investigated. According to the experimental results the modification of lignin, increased the impact strength for all the blends containing acetylated lignin compares to pristine lignin. The largest increase observed was for blends containing 20 wt% acetylated lignin and polylactic acid, which resulted in a 74% improvement compared with the blend composed of pristine lignin and polylactic acid. Similarly, the thermal stability was improved significantly with acetylation of the lignin. Moreover, the moisture repellence behaviour was also increased. The reason for the improved properties can be explained by the better interfacial compatibility between lignin and polylactic acid matrix. An increased thermal stability and a moisture repellent behaviour of the blends containing chemically modified lignin could be observed when compared with neat polylactic acid which makes the acetylation treatment of lignin a possible approach for the future of biocomposite production.

Fabrication, structural, thermo-mechanical and opto-electrical behavior of anthranilamide compound

Anthranilamide (AAM) compound were fabricated via an alcoholic solvent assisted slow evaporation at room temperature for investigating the multi functional device applications. The solubility test was performed with different concentrations of AAM salt dispersed in 100 mL ethanol solvent to understand the crystallization process of fabricated material. The cell parameters, and diffraction peaks of the title compound were collected through nondestructive tool like single crystal XRD and powder XRD studies, and thus results showed the monoclinic structure. The fabricated material’s functional group, thermal stability, and hardness behavior were tested by various tool viz FT-IR, TG-DTA, and Vickers hardness analysis. With the aid of UV–vis–NIR spectrum, and frequency conversion test technique, optical transmittance and double harmonic generation efficiency values are detected to be 92% and 4.1 mV. Using electrical studies, the dielectric parameters and specific conductance of the title compound values are varied by applying a low frequency to a high frequency region at different temperatures (313, 323, and 333 K).

Effect of stacking sequence and thickness variation on the thermo-mechanical properties of flax-kenaf laminated biocomposites and prediction of the optimal configuration using a decision-making framework

Abstract The use of naturally derived eco-friendly biocomposites became more popular due to growing environmental concerns and hunt for sustainable materials. Biocomposites can reduce the residual waste and carbon emission to the environment during their lifecycle. The present study aims to develop biocomposites by reinforcing flax fiber (F) and kenaf fiber (K) laminates with bio-epoxy matrix at four different arrangements (FFF, FKF, KFK, and KKK). The biocomposite samples were fabricated with three laminated thicknesses (3 mm, 4 mm and 5 mm) and the thermo-mechanical performance was investigated. The results showed that FFF biocomposites recorded higher tensile, flexural, and interfacial properties with lower density and absorption of water compared to KKK biocomposites due to higher cylindrical lumen diameter of flax laminates. The hybridization of flax with kenaf fiber at different stacking sequences provided greater strength, modulus, toughness, stiffness, thermal stability and degradation behaviour due to greater interfacial interaction between laminated fiber and bio-epoxy. The FKF biocomposites showed maximum impact strength (52.96 kJ/m2), tensile strength (110.21 MPa), and compressive strength (139.64 MPa) at 5 mm laminated thickness while, flexural (158.67 MPa) and shear strength (39.45 MPa) were maximum at 4 mm thickness with the highest degradation temperature (336 °C). The optimal biocomposite configuration has been identified through employability of a novel decision-making framework encompassing interval-valued intuitionistic fuzzy sets, TOmada de DecisaoInterativaMulticriterio (TODIM) and Schweizer–Sklar operations. The inclusive evaluation with regard to the applied framework has revealed that FKF and KFK biocomposites with 4 mm thickness (Lam5 and Lam8) configuration to have the optimal configuration. On the other hand, Lam 10, i.e., KKK_3 mm turned out to be inferior to all the considered biocomposite configurations.

Effect of electron beam irradiation on thermal stability and crystallization behavior of flexible copolyester/multiwalled carbon nanotubes nanocomposites

AbstractPoly(butylene adipate‐co‐terephthalate) (PBAT), a biodegradable copolyester, was used as the polymer matrix to prepare nanocomposites with multiwalled carbon nanotubes (MWCNT) by melt‐mixing followed by hot‐pressing. The PBAT/MWCNT nanocomposites were exposed to electron beam (EB) irradiation, and thermal stability, melting and crystallization behavior of irradiated and unirradiated nanocomposites were comparatively investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. TGA results reveal increased thermal stability (up to 17°C) and maximum degradation temperature (Tmax) (up to 15°C) of PBAT/MWCNT nanocomposites, attributed to the high thermal stability of MWCNT and good MWCNT–PBAT interfacial interactions. However, the activation energy for thermal degradation (Ea) decreased with the presence of MWCNT in comparison to neat PBAT regardless of the MWCNT concentration. Both the thermal stability and Tmax of irradiated nanocomposites decreased by 3°C despite the crosslinking which can be attributed to successive minor irradiation‐induced polymer degradation, while Ea remained unchanged. Declined melting temperature (Tm), enthalpy of crystallization, enthalpy of melting and crystallinity of nanocomposites with the presence of MWCNT suggest the formation of less perfect crystals. Meanwhile, their increased glass transition temperature (Tg) and crystallization temperature (Tc) are due to the increased rigidity of PBAT chains and a reduced crystallization process in the presence of MWCNT, respectively. Similarly, reduced crystallinity and values of Tm and Tc of EB‐irradiated nanocomposites by 4.1%, 9.6%, and 7.5%, respectively, signifying the presence of PBAT‐crosslinks resulting in crystal defects.

Influence of shell thickness on the thermal stability and melting-like behavior of Al@Fe core–shell nanoparticles from atomistic simulations: a structural and dynamic description

Core–shell nanoparticles (CSNPs) are a class of functional materials that have received important attention nowadays due to their adjustable properties by a controlled tuning of the core or shell. Understanding the thermal response and structural properties of these CSNPs is relevant to carrying out an analysis regarding their synthesis and application at the nanoscale. The present work is aimed to investigate the shell thickness effect on thermal stability and melting behavior of Al@Fe CSNPs by using molecular dynamics simulations. The results are discussed considering the influence of the Fe shell on the Al nanoparticle and analyzing the effect of different shell thicknesses in Al@Fe CSNPs. In general, calorific curves show a smooth energy decline for temperatures greater than room temperature for different shell thicknesses and sizes, corresponding to the inward and outward atomic movement of Al and Fe atoms, respectively, that produce a mixed Al–Fe nanoalloy. Here, the thermal stability of the Al@Fe nanoparticle is gradually lost passing to a liquid-Al@solid-Fe configuration and reaching a mixed Al–Fe state by an exothermic mechanism. Combining quantities of the atomic diffusion and structural identification, a stepped structural transition of the system is subsequently observed, where the melting-like point was estimated. Furthermore, it is observed that the Al@Fe CSNPs with greater stability are obtained with a thick shell and a large size. The ability to control shell thickness and vary the size opens up attractive opportunities to synthesize a broad range of new materials with tunable catalytic properties.

Physicochemical Properties, Thermal Stability, and Pyrolysis Behavior of Antioxidative Lignin from Water Chestnut Shell Obtained with Ternary Deep Eutectic Solvents.

The molecular weight of lignin extracted from lignocellulosic biomass is an important factor in determining its valorization in industrial processes. Herein, this work aims to explore the extraction of high molecular weight and bioactive lignin from water chestnut shells under mild conditions. Five kinds of deep eutectic solvents were prepared and applied to isolate lignin from water chestnut shells. The extracted lignin was further characterized with element analysis, gel permeation chromatography, and Ultraviolet-visible and Fourier-transform infrared spectroscopy. The distribution of pyrolysis products was identified and quantified with thermogravimetric analysis-Fourier-transform infrared spectroscopy and pyrolysis-gas chromatograph-mass spectrometry. The results showed that choline chloride/ethylene glycol/p-toluenesulfonic acid (1:1.8:0.2 molar ratio) exhibited the highest fractionation efficiency for lignin (84.17% yield) at 100 °C for 2 h. Simultaneously, the lignin showed high purity (90.4%), high relative molecular weight (37,077 g/mol), and excellent uniformity. Furthermore, the aromatic ring structure of lignin remained intact, consisting mainly of p-hydroxyphenyl, syringl, and guaiacyl subunits. The lignin generated a large number of volatile organic compounds during the depolymerization process, mainly composed of ketones, phenols, syringols, guaiacols, esters, and aromatic compounds. Finally, the antioxidant activity of the lignin sample was evaluated with the 1,1-diphenyl-2-picrylhydrazyl radical scavenging assay; the lignin from water chestnut shells showed excellent antioxidant activity. These findings confirm that lignin from water chestnut shells has a broad application prospect in valuable chemicals, biofuels and bio-functional materials.

Effect of multidimensional filler hybridization on the mechanical properties of thermoplastic polyurethane composites prepared by selective laser sintering

AbstractThis paper aims to improve the tensile strength and thermal stability performance of selective laser sintered thermoplastic polyurethane elastomer/spherical alumina/graphene oxide/silicon nitride whisker (TPU/Al2O3/GO/Si3N4ws) composites by investigating the synergistic enhancement of fillers with different dimensions, and solving the problem of excessive porosity, material delamination, and low tensile strength during sintering of semi‐crystalline polymer TPU problems. The results show that the synergistic effect of multidimensional fillers leads to the tensile strength of TPU composites up to 12.1 MPa at 8.9 wt% Al2O3, 0.1 wt% GO and 1.0 wt% Si3N4ws hybrid fillers, which is 38.9% higher than that of pure TPU. In addition, the elongation at break of TPU/Al2O3/GO/Si3N4ws composites was maintained at 254%, which still has good toughness. The effect of fillers on the selective laser sintering (SLS) process, thermal stability, melting, and crystallization behaviors of the composites was also investigated in this work. In general, the multidimensional filler compounding synergistically constructing a three‐dimensional network structure has some improvement on the thermomechanical behavior of TPU composites with a fixed mass component addition.