X-ray Computed Tomography Analysis Research Articles

Evolution of Soil Pore Structure and Shear Strength Deterioration of Compacted Soil under Controlled Wetting and Drying Cycles

This study investigates the evolution of soil pore structure and shear strength deterioration in compacted clayey soil under controlled wetting and drying (wd) cycles, which are expected to become more frequent due to climate change. Thirty soil samples were compacted at optimal moisture content and 90% maximum dry density. These samples were then subjected to 0, 1, 5, 10, and 15 controlled wd cycles from saturation to the wilting point, and volumetric changes were recorded during each cycle. After the wd treatment, the soil samples were scanned using X-ray computed tomography (CT) at 50 μm resolution and then sheared under unconsolidated–undrained and consolidated–undrained conditions in a triaxial test. Significant shrinkage and swelling of soil samples were observed during wd cycles, with average volumetric strain fluctuating between +12% at saturation and −5% at the wilting point. X-ray CT visualisation and analysis revealed higher porosity, more prominent pores, and increased pore length in soil samples with increasing wd cycles. Both undrained and effective soil shear strength markedly decreased with increasing wd cycles. CT-derived macroporosity and pore length were significant predictors of the soil’s undrained and effective shear strength when exposed to wd cycles. The findings emphasise the considerable impact of climate change, specifically wd cycles, on clayey soil, highlighting the need for consideration in the design of earth-based infrastructure.

Similarities and differences between internal short-circuit current and hydrogen crossover current in a proton exchange membrane fuel cell

The proton exchange membrane (PEM) is the core component of PEM fuel cells and plays an important role in isolating gases and electrons during operation; however, PEMs inevitably encounter degradation problems during operation, resulting in weakening or failure of their core functions, thus leading to safety and service life issues. The PEM degradation produces hydrogen crossover and internal short circuit (ISC) currents, which have similar characteristics. Consequently, it is challenging to estimate these two currents and establish a connection between ex situ parameters and actual operation. The safe use of PEM fuel cells requires a distinction between the characteristics of both current types and their generation mechanisms. Our experimental results show that the hydrogen crossover current caused by pinholes during fuel cell operation is influenced by anode overpressure and hydrogen diffuses upon reaching the cathode side of the fuel cell. Meanwhile, the ISC current is influenced by the electrode potential during ex situ testing and fuel cell operation. Compared with the hydrogen crossover current, the efficiency loss due to the ISC current is the “fastest path” because of both currents have different reaction paths. X-ray computed tomography analyses are consistent with the results of the electrochemical tests.

In-situ X-ray computed tomography of high-temperature tensile behavior for laser powder bed fused Invar 36 alloy

The laser powder bed fusion (PBF-LB) process provides great potential for additive manufacturing of Invar 36 alloy, which possesses a unique low coefficient of thermal expansion. However, the high-temperature tensile behavior of PBF-LB processed Invar 36 alloy has not been explored, severely restricting its applications. Hence, herein, in-situ X-ray computed tomography (XCT) tensile tests were conducted at 200 °C and 600 °C for PBF-LB processed Invar 36 alloy, and the microstructure after heat treatment, fracture morphology, post-mortem microstructure, and nano-precipitates were observed. The in-situ XCT analysis of damage evolution reveals that the tensile behavior at elevated temperatures is sensitive to numerous closely spaced lack-of-fusion (LOF) pores with relatively large equivalent diameters, distributed in the adjacent melt pools or deposited layers. These LOF pores promote the stress concentration and facilitate rapid crack propagation, resulting in a significantly diminished strength and ductility. In contrast, the small number of metallurgical and keyhole pores, possessing large spacing and relatively high sphericity, have negligible influence on the tensile behavior. Therefore, Invar 36 alloy with only metallurgical and keyhole pores can be considered defect-free, displaying an excellent yield strength of 360.0 MPa and a considerable elongation of 65.0% at 200 °C. However, as the temperature increases to 600 °C, both the yield strength and elongation show a marked decrease to 150.0 MPa and 5.4%, respectively. This weakening is accompanied by the observation of a brittle fracture and the formation of secondary cracks. The degradation in mechanical properties can be attributed to the decomposition of Cr-containing SiP2O7, which leads to the formation of numerous small-sized SiO2 and P2O5 precipitates at 600 °C. These precipitates induce embrittlement of the grain boundaries and contribute to the formation of secondary cracks. The anomalous brittle fracture observed is attributed to the intergranular fracture mode, which results from the low grain boundary energy as well as the decomposition of nanoprecipitates. Additionally, the perpendicular orientation of flatter columnar grain boundaries to the loading direction plays a role in the formation of secondary cracks. This high-temperature mechanical performance of strength, elongation, failure mode, and corresponding microcosmic mechanism advances the understanding and widespread application of PBF-LB processed Invar 36 alloy.

Particle size analysis: A comparison of laboratory-based techniques and their application to geoscience

In sedimentary geoscience, the particle size distribution (PSD) of a sediment has a fundamental effect on a sediment's ability to be entrained, eroded, and deposited. Therefore, it is crucial to accurately measure the PSD of sediments. Several laboratory-based methods of particle size analysis are commonly employed in geoscience; however, each method is based on different principles and the comparison of data from one technique to another is challenging. In this study, we have compared the output of four commonly-used laboratory-based techniques: Laser Particle Size Analysis (LPSA), optical point counting, 2D automated image analysis, and X-ray Computed Tomography (XCT). Each technique has been used to measure eight samples of spherical silica particles, all prepared with known particle size ranges. Spherical particles have been used to minimise the effects of variable sorting and particle shape on data output. Here we have compared the differences between the measured PSD and descriptors of each PSD, showing that, at small particle diameters (<150 μm), all techniques agree. However, at particle diameters >150 μm, LPSA overestimates the size of particles, due to limitations in the way that particle diameter is calculated by this technique. In contrast, 2D automated image analysis and optical point counting underestimate the diameters of particles, due to stereology (e.g., the effect of slicing particles during thin section preparation). Results from XCT analyses have the lowest values of sorting (range of measured particle diameters) and are therefore the most tightly constrained. In addition, XCT is the only 3D analysis method, allowing particle shape, orientation, and intraparticle porosity to be measured for a volume of material. We therefore conclude that XCT is the most accurate way to determine a grain size distribution in sediments.

Preservation of strawberries using chitosan incorporated with lemongrass essential oil: An X-ray computed tomography analysis of the internal structure and quality parameters

Preservation of strawberries using chitosan incorporated with lemongrass essential oil: An X-ray computed tomography analysis of the internal structure and quality parameters

Printed layers height calibration curve and porosity in laser melting deposition of Ti6Al4V combining experiments, mathematical modelling and deep neural network

PurposePorosity is a commonly analyzed defect in the laser-based additive manufacturing processes owing to the enormous thermal gradient caused by repeated melting and solidification. Currently, the porosity estimation is limited to powder bed fusion. The porosity estimation needs to be explored in the laser melting deposition (LMD) process, particularly analytical models that provide cost- and time-effective solutions compared to finite element analysis. For this purpose, this study aims to formulate two mathematical models for deposited layer dimensions and corresponding porosity in the LMD process.Design/methodology/approachIn this study, analytical models have been proposed. Initially, deposited layer dimensions, including layer height, width and depth, were calculated based on the operating parameters. These outputs were introduced in the second model to estimate the part porosity. The models were validated with experimental data for Ti6Al4V depositions on Ti6Al4V substrate. A calibration curve (CC) was also developed for Ti6Al4V material and characterized using X-ray computed tomography. The models were also validated with the experimental results adopted from literature. The validated models were linked with the deep neural network (DNN) for its training and testing using a total of 6,703 computations with 1,500 iterations. Here, laser power, laser scanning speed and powder feeding rate were selected inputs, whereas porosity was set as an output.FindingsThe computations indicate that owing to the simultaneous inclusion of powder particulates, the powder elements use a substantial percentage of the laser beam energy for their melting, resulting in laser beam energy attenuation and reducing thermal value at the substrate. The primary operating parameters are directly correlated with the number of layers and total height in CC. Through X-ray computed tomography analyses, the number of layers showed a straightforward correlation with mean sphericity, while a converse relation was identified with the number, mean volume and mean diameter of pores. DNN and analytical models showed 2%–3% and 7%–9% mean absolute deviations, respectively, compared to the experimental results.Originality/valueThis research provides a unique solution for LMD porosity estimation by linking the developed analytical computational models with artificial neural networking. The presented framework predicts the porosity in the LMD-ed parts efficiently.

In situ crystallization of Fe-Ti oxides in the Panzhihua layered intrusion, SW China: Constraints from crystal size distribution and high-resolution X-ray computed tomography analyses

In situ crystallization of Fe-Ti oxides in the Panzhihua layered intrusion, SW China: Constraints from crystal size distribution and high-resolution X-ray computed tomography analyses

In-situ measurement of dynamic micro X-ray CT and dynamic mechanical analysis for rubber materials

Observing the internal state that takes place during deformation is essential for comprehending the mechanical properties of polymeric materials like rubber. For the effective utilization of rubber in damping applications, it is imperative to comprehend the relationship between the loss factor and microstructure. In an earlier study, we developed a dynamic X-ray CT technique tailored for damping materials subjected to tensile amplitude and proposed a method to directly evaluate the internal deformation behavior under dynamic conditions. However, owing to the technical constraints of the shaker employed for dynamic X-ray computed tomography, key variables such as vibration frequency and amplitude could not be incorporated into the analysis. Additionally, it has not been possible to simultaneously measure dynamic viscoelasticity and dynamic micro X-ray CT in situ.In this study, we developed an experimental system that enables simultaneous measurement of dynamic mechanical properties and dynamic X-ray computed tomography (CT). This system facilitates in-situ investigation of internal deformation behavior and the loss factor in rubber materials, allowing for the assessment of variations in loss factors at the micro-scale. We examined the differences between styrene butadiene rubber (SBR) and natural rubber (NR) as base materials and investigated the influence of shape, and particle size of ZnO on the dynamic behavior of SBR composites. Dynamic X-ray computed tomography (CT) was conducted at excitation frequencies of 1 and 2 Hz, excitation amplitudes corresponding to 1% and 1.25% of the inter-chuck distance of the specimens, and a spatial resolution of 0.5 µm. Local strains were extracted from the 3D reconstructed images, and both the local strain amplitudes and their histograms were assessed as characteristics of dynamic behavior. The results indicated that the effect of varying the excitation frequency between 1 and 2 Hz was minimal for the SBR. Additionally, the median value of local strain amplitudes shifted in relation to the magnitude of the excitation amplitude. When comparing base materials (SBR and NR) with significantly different loss factors, no discernible differences were observed in the histograms of local strain amplitudes. The histograms did vary based on the formulation conditions of the SBR microparticle composite, although the loss factor remained unchanged. This lack of change in the loss factor can be attributed to the minimal impact of the particulate composites on the inherent loss factor of pure SBR. Importantly, the study successfully achieved multimodal and simultaneous measurements using dynamic mechanical analysis and dynamic micro X-ray CT.

High‐Rate Discharge Minimizes Volume Expansion of Lithium Metal Electrodes under Lean Electrolyte and High Areal Capacity Conditions

AbstractThe demand for practical implementation of lithium metal batteries (LMBs) is increasing due to their superior energy density. However, poor cycle life and safety concerns regarding dendrite formation remain significant challenges. Recent studies have shown empirical improvements in cycle life through the use of high‐rate discharge protocols, but the precise mechanism behind this enhancement is still unclear due to difficulties in analyzing the lithium electrode, especially in LMB cells with high energy density designs. In this study, X‐ray computed tomography (XCT) analysis, a non‐destructive technique, was employed to investigate the lithium metal electrode in pouch‐type cells with a cell‐level energy density exceeding 350 Wh kg−1. XCT analysis revealed significant volume expansion of the lithium electrode during charge/discharge cycles, particularly under high‐rate charging conditions, which promoted dendritic growth due to inhomogeneous current distribution. However, such undesired volume expansion was largely suppressed during high‐rate discharge, leading to improved cycle life. This study underscores the importance of non‐destructive techniques in comprehending the degradation mechanisms of high‐energy‐density LMBs.

Synchrotron X-ray computed tomography analysis of the morphological characterization of aluminum alloy powders produced by gas atomization

Gas atomization (GA) is a highly efficient and cost-effective method of producing metal powder for additive manufacturing. However, powders with defects can significantly reduce the performance of manufactured components. Therefore, accurately characterizing powder morphology is crucial to evaluating powder quality. This study uses synchrotron X-ray computed tomography (SXCT) to measure the characteristics of aluminum alloy powders. Morphological parameters such as mean Feret diameter, aspect ratio, sphericity, etc., are obtained from reconstructed 3D images. Statistical analysis shows that as particle size increases from <38.5 μm to >100 μm, the proportion of satellite and hollow powders increases from 25.97% to 59.29% and from 3.60% to 13.60%, respectively, while the proportion of irregular powder only slightly decreases about 3%. Additionally, the irregularity of the powder increases with increasing diameter. Overall, this study highlights the importance of characterizing powder morphology and demonstrates the potential of SXCT for such analysis.

Different post-processing methods to improve fatigue properties of additively built Ti-6Al-4V alloy

The fatigue performance of the Ti-6Al-4V alloy built using the laser-powder bed fusion additive method was investigated in this study. Post-process methods such as heat-treatment (HT), machining (M), hot isostatic pressing (HIP), and different combinations thereof were explored to enhance the mechanical as well as the fatigue properties. Load-controlled uniaxial high-cycle fatigue tests were performed using a servo-hydraulic fatigue testing machine at room temperature. The machining (M) of the as-built samples increased its fatigue properties, irrespective of the HT and HIP conditions. The tensile strength decreased considerably after the HT, HIP, and HT + HIP treatment but with increasing ductility. On the other hand, the fatigue strength improved with the HT condition and was further enhanced by five times after the HT + HIP + M condition, in comparison to that of the as-built alloy. The X-ray computed tomography analysis revealed a drastic reduction in the percentage of internal defects after the HIP treatment, from 0.31% to 0.01%. The fractographic analysis revealed that the cracks were mostly initiated from the defects in the as-built and HT conditions while in the HIP condition, it was from the facets in the α-phase. The reasons for the improvement in fatigue properties after the different post-process treatments were attributed to the induced-microstructural changes, surface finish quality, relaxed or compressive residual stresses, and most importantly, the reduced fraction of the crack-initiating process-inherent defects, which are explained and argued in this article.

Mechanical Characterisation and Simulation of the Tensile Behaviour of Polymeric Additively Manufactured Lattice Structures

BackgroundThe mechanical properties of lattice structures have been primarily investigated using uniaxial compression loads. Particularly for polymers, tensile properties are rarely considered because of the difficulties of defining a suitable specimen design in which the fracture occurs within the gauge length.ObjectiveThis work proposes a novel formulation to obtain a specimen for the tensile test with a gradation of the lattice density at the interface with the bulk portion, which realises a uniform stress distribution. The aim is to combine a localisation of the fracture in the gauge length with a specimen geometry accomplishing the EN ISO 527 standard and analyse the correlation between the mechanical performance and the defects induced by the process on such thin structures.MethodsThe formulation is experimentally and numerically (FEM) tested by designed specimens with different cell topology, cell size, strut diameter, and number of cells in the sample thickness. Also, results from uniaxial compression tests are used to validate the tensile properties. The specimens are manufactured in different orientations in the building volume by laser powder bed fusion with Polyamide 12. The effects of the pores morphology, distribution, and inherent anisotropy are investigated using X-ray computed tomography analysis. This data is also used to tune a numerical model.ResultsThe numerical analysis showed a uniform stress distribution; experimentally, the fracture is localised inside the gauge length in respect of the ISO standard. Remarkably, among the different strut-based architectures, the elongation at break is, in the best case, 50% of the corresponding bulk material, while the tensile strengths are comparable. Vertical printed specimens exhibited a slight decrease in tensile strength, and the elongation at break was lower than 50% compared to the counterparts built along the horizontal orientation. Modifying the numerical model according to process-related dimensional deviations between the actual and the nominal structures significantly improved the numerical results. The remaining deviation highlighted the incorrectness of modelling the lattice material from the bulk properties.ConclusionDensity gradation is a reliable approach for describing the tensile behaviour of polymeric lattice structures. However, the lower amount of porosity and the different shape in the lattice led to a different material mechanical performance with respect to the corresponding bulk counterpart. Therefore, for polymeric lattice structures, the relationship between process-design-material appears crucial for correctly representing the structure behaviour.

Application of X-ray computed tomography scanning in describing partition curves of dense medium cyclones

The partition curve is an important tool to evaluate the separation performance of mineral separators like dense medium cyclones (DMCs). This curve is constructed by float-and-sink (FaS) analysis which involves the use of heavy liquids and suspensions. This traditional technique is hazardous to the environment, laborious, and time-consuming. Here, a new technique using X-ray computed tomography (XCT) scanning was successfully developed and applied for describing the partition curve of a DMC at an Australia-based lead–zinc mineral processing plant. The DMC feed, concentrate and reject streams were sampled and sieved into several size classes. The chemical assays and averaged densities according to each class were analysed by X-ray fluorescence spectrometry and gas pycnometry, respectively. The partition behaviour was investigated by XCT analysis. A model was proposed to determine the mass yield value – an important parameter to define partition curves – by mass balance and reconciliation, which is generally unknown during the sampling of continuous separation processes. From the reconstructed XCT images, we obtained detailed information on individual particles such as volume, surface area, mass, and density. Cumulative mass distribution curves and partition curves of the DMC for different size classes were then constructed and agreed with the FaS analysis. Using the XCT technology can help overcome the issues of the traditional FaS analysis. Moreover, this technology would allow for evaluating DMC separation efficiency with continuous, online, and real-time monitoring and control.

Lithium Metal Battery Quality Control via Transformer-CNN Segmentation.

Lithium metal battery (LMB) has the potential to be the next-generation battery system because of its high theoretical energy density. However, defects known as dendrites are formed by heterogeneous lithium (Li) plating, which hinders the development and utilization of LMBs. Non-destructive techniques to observe the dendrite morphology often use X-ray computed tomography (XCT) to provide cross-sectional views. To retrieve three-dimensional structures inside a battery, image segmentation becomes essential to quantitatively analyze XCT images. This work proposes a new semantic segmentation approach using a transformer-based neural network called TransforCNN that is capable of segmenting out dendrites from XCT data. In addition, we compare the performance of the proposed TransforCNN with three other algorithms, U-Net, Y-Net, and E-Net, consisting of an ensemble network model for XCT analysis. Our results show the advantages of using TransforCNN when evaluating over-segmentation metrics, such as mean intersection over union (mIoU) and mean Dice similarity coefficient (mDSC), as well as through several qualitatively comparative visualizations.

X-ray Computed Tomography Analysis of Ferromanganese Nodule Nuclei from the Western North Pacific Ocean: Insights into Their Origins

Ferromanganese nodule nuclei are considered crucial to the formation and distribution of nodules. However, because it is difficult and time-consuming to study ferromanganese nodule nuclei, few studies have been performed, despite the large number of samples. Here, we analyzed the nuclei of 934 ferromanganese nodules from the abyssal seafloor around Minamitorishima Island (western North Pacific Ocean) using X-ray computed tomography (CT). Based on the CT number distribution (describing X-ray absorption in Hounsfield units, HU), we classified the nuclei as Type I (&gt;1800 HU) or Type II (&lt;1800 HU). Additionally, some Type I nuclei had characteristic conical shapes (Type I-C) distinct from the shapes of other nuclei (Type I-O). Based on the chemical compositions determined by microfocus X-ray fluorescence analyses of selected samples, we identified Type I-C, I-O, and II nuclei as fish teeth, hard rocks (volcanic rock, ironstone, or phosphorite), and sediments, respectively. These nucleus types were observed in sufficient quantities at all dive sites that we conclude them to be typical of nodule nuclei in the study area. Fish-tooth nuclei were the rarest at all sites, whereas sediment nuclei dominated at most sites, suggesting their significance for understanding the origin of ferromanganese nodules. Hard-rock nuclei dominated at only three sites and probably originated from seamounts.

Slow release fertilizers based on polyphosphate/montmorillonite nanocomposites for improving crop yield

Nanocomposites are promising materials for the development of novel and environmentally friendly fertilizers that can delay the release of nutrients. In this study, a novel high-strength spherical nanocomposite fertilizer was prepared via agglomeration and granulation using montmorillonite, urea phosphate, urea, and potassium chloride as raw materials. The properties and morphology of the prepared fertilizer were characterized by Fourier Transform Tnfrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Thermogravimetric Analysis (TGA) and X-ray Computed Tomography (XCT) techniques. FT-IR analysis identified the formation of polyphosphate in fertilizer and hydrogen bonds between polyphosphate and montmorillonite. XRD analysis showed increased montmorillonite interlayer spacing and confirmed the formation of polyphosphate-montmorillonite nanocomposites. The effects of raw material mass ratio, reaction time, and reaction temperature on the strength and fluidity of nanocomposite fertilizer granules and the optimum preparation process was obtained by the response surface method (RSM-CCD). The optimum preparation process was obtained as follows: reaction temperature, 103 °C; reaction time, 237 min; and mass ratio, 1:1:0.93:1 (urea phosphate: urea: potassium chloride: montmorillonite). Under these optimum conditions, the particle hardness and angle of repose of the prepared fertilizer were 64.75 ± 0.48 N and 30.84 ± 0.95°. Nutrient release and agronomic effectiveness of the fertilizer was evaluated using column leaching and pot experiments, respectively. The column leaching experiment and XCT analysis demonstrated that the nanocomposite structure was responsible for the slow nutrient release. The pot experiment showed that compared with the traditional fertilizer, the soil nitrate and available phosphorus was increased by 28.02% and 43.45%, respectively, and the maize yield was increased by 24.27% with the application of prepared fertilizer. This work provides support for the preparation of high-strength spherical nanocomposite fertilizers and their large-scale applications in modern mechanical agriculture.

X-ray computed tomography analysis of internal voids in steel slag asphalt mixture under freeze–thaw damage and microwave healing process

In this work, the variation characteristics of different scale voids under freeze–thaw damage and microwave healing were studied by X-ray computed tomography (CT). Firstly, the scale classification of voids was carried out to analyze the initial distribution state of voids. Then the distribution of the horizontal plane and vertical direction was quantitatively characterized, and the source of the damage-healing effect was analyzed by using iterative variation indexes. Finally, the critical void was judged by combining the total and relative iterative variation rates. The results show that the area of small voids (0.15 ∼ 2.0 mm2) accounts for 55.7 %, and the number accounts for 90.17 % of the whole, serious interference with overall development when voids are not classified. The initial distribution of voids at different scales is quite different. The void growth is relatively uniform in the horizontal plane. From the distribution of the number of voids, the inner region is more prone to coherent vertical cracks, and the outer region is more prone to discrete micro-cracks. The role of voids at different scales in the damage-healing process is different. Small voids are the critical voids in the freeze–thaw damage stage. Both small and big voids are critical voids in the healing stage. This work is helpful to better understand the damage-healing process of steel slag asphalt mixture at mesoscale and contribute to the sustainability of asphalt pavement.

X-ray computed tomography for macropore analysis of cured and formed plates in lead acid batteries

When it comes to the properties of lead-acid batteries, macro porosity is seldom considered, even though it influences the active material loading, accessibility of acid into the active bulk material and the structural integrity of the plate. The porosity characteristics of positive and negative cured and formed plates were comprehensively analysed on the micro, meso and macro scale using a combination of BET N2 adsorption, mercury porosimetry and X-ray computed tomography (CT) respectively. Total porosity, pore size distribution, surface area, open and closed pores and surface-area-to-volume were included, where possible, with a plethora of additional data being obtained from X-ray CT analysis. Analysis from a single plate used in Starting, Lighting and Ignition (SLI) type batteries, which included three isolated samples per plate, revealed heterogeneity in macro-porosity across all regions analysed in the negative and positive cured and formed plates respectively. X-ray CT was further applied to thicker plates and a plate from an AGM type battery with a glass mat separator. The use of X-ray CT to study the changes in porosity characteristics can yield valuable insight into the properties of the active material since it remains intact within the grid support of a lead acid battery plate.

Visualizing pseudo‐ductility in carbon/glass fiber hybrid composites manufactured using infusible thermoplastic Elium® resin

AbstractIn this study, two different type of glass and carbon fiber hybrid laminates were manufactured using a low‐viscosity thermoplastic resin that is, Elium®. A detailed microstructure visualization study was conducted using X‐ray computed tomography (XCT) analysis. The viscoelastic properties were examined through dynamic mechanical analysis. The mechanical performance was investigated through flexural and tensile tests along with a fractographic study using optical and scanning electron microscopy. The XCT analysis revealed a weak interface between the Elium® resin and the glass fabric, with glass fiber specimens exhibiting a void content of 1.24%, in contrast to the carbon fiber specimens which showed void content of only 0.28%. Therefore, adding glass fabric layers in the hybrid laminates increased the void content, which had a negative impact on the overall mechanical performance. The average flexural strength of the hybrid specimen having G2C4G2 stacking sequence was observed to be 254% higher than pure GFRPC specimens. Similarly, the tensile strength and Young's modulus of the same hybrid specimen showed 155% and 380% increases, respectively, compared to the GFRPC specimens. This increase was primarily due to higher stiffness of the carbon fibers and their better fiber – matrix interface. Whereas the tensile strain of the hybrid specimen having G3C2G3 stacking sequence was 37% higher than that of the CFRPC specimens. The SEM images highlighted fiber fracture and brittle failure modes in the carbon fiber specimens, in contrast to fiber pullout, interfacial failure, poor fiber‐matrix bonding and ductile failure modes in the glass fiber specimens.

Lignin-based benzoxazines: A tunable key-precursor for the design of hydrophobic coatings, fire resistant materials and catalyst-free vitrimers

The meaningful concept of circular economy has prompted the scientific community to re-think the design of materials. In this work, lignin-based benzoxazines (LBZs) thermosets with tuneable properties were synthesized in agreement with the principles of Green Chemistry, following a straightforward two-step synthetic route. The reactivity of a soda lignin was enhanced by its esterification with phloretic acid, a naturally occurring phenolic acid. Thereafter, the resulting structure enriched in phenolic rings with no ortho substituents, was used to prepare LBZs precursors with a bio-based primary amine via a Mannich-like ring-closure reaction. The structure and properties of each LBZ precursor were confirmed by multiple NMR techniques, Fourier transform infrared spectroscopy, elemental analysis, gel permeation chromatography, differential scanning calorimetry, rheology, and solubility assays. Lignin-based polybenzoxazine with high lignin mass fraction (between 46 and 66 wt.%) were obtained following curing via a vacuum compression molding manufacture process. Lignin-based thermosets exhibit a single-phase confirmed by X-ray computed tomography analysis, a Tg ranging from 136 to 197 °C, and storage moduli from 0.5 to 3.1 GPa. The features of each lignin-based precursor were tuned depending on the structure of the bio-based primary amine used to close the oxazine ring. Stearylamine confers good processability and yields hydrophobic coatings with a water contact angle reaching 91°. Furfurylamine-based LBZs generate high-Tg (197 °C) and fire-resistant materials with a peak of heat release rate of no>47 W.g−1. Finally, ethanolamine produces lignin-based thermosets capable of internally catalysed bond exchange via transesterification, providing vitrimeric properties such as fast stress relaxation (τ*200 °C = 233 s) and a complete circularity.