Flax fibres are renewable alternatives to synthetics, backed by well-established supply chains. However, they are vulnerable to prolonged droughts, which threaten their yield, quality and use under future climate scenarios. While drought effects on yields are documented, impacts on technical fibres remain underexplored. Our work provides an illustrative case study of how drought affects the composition and structure of bast fibre elements and impacts fibre extractability at pilot scale. Using a broad set of complementary techniques, we investigated two batches of flax (Damara variety), grown under contrasting water conditions and industrially processed. Our results revealed no major disruption in fibre composition or cell-wall organization under drought, but subtle biochemical and microstructural adjustments. These included enhanced mannans’ acetylation and enrichment in hydrophobic n-alkanes, consistent with lower but more tightly bound water evidenced by hygroscopic measurements. Protein biosynthesis also increased, with specific upregulation of proteins involved in cell wall remodelling, defense and stress response. At a macromolecular level, drought-stressed fibres displayed polymers modified compared to control ones,and exhibited more pronounced kink-bands consistent with increased extraction difficulty and reduced yields. Overall, flax largely preserved its structural integrity under drought conditions; however, the minor alterations observed impaired its processability, potentially compromising its sustainable use under future climate scenarios.

This research delves into the impact of varying printing angles in the range (0°, 15°, 30°, 45°) on the thermal and mechanical characteristics of carbon fibre-PLA/PHA composites fabricated via fused filament fabrication (FFF). The microstructural arrangement within the 3D-printed PLA/PHA is unveiled through the application of SEM, X-ray microtomography and optical imaging. Tensile loading conditions are employed to extract meaningful mechanical parameters such as Young's modulus, tensile strength, elongation at break, and mechanical energy, all of which are associated with the printing angle settings. The results indicate that the filaments exhibit a porosity of approximately 3%, while the porosity of the printed structure ranges from 27% to 38%, depending on the printing angle. Tensile modulus in the range 840 to 890 MPa is found not to be highly sensitive to the printing angle. However, tensile strength reaches 37 MPa for a printing angle of 30°. The variations across conditions are limited to approximately 6% in tensile stiffness and 16% in tensile strength. Finite element simulations based on 3D imaging indicate that an effective modulus of the solid phase between 1.6 and 1.8 GPa provides the closest agreement between experimental measurements and numerical predictions. This study presents novel findings concerning the deformation mechanisms associated with different length scales, from filament composite to filament arrangement, in the carbon fibre-PLA/PHA composite. This study highlights that while printing angle has a moderate influence on mechanical response, the overall structural integrity and interlayer cohesion of carbon fibre-PLA/PHA composites remain robust across a wide range of processing parameters, demonstrating their potential for reliable structural applications in additive manufacturing.

This study investigates the microstructure–property relationships of additively manufactured PLA composites reinforced predominantly with calcium carbonate (CaCO3) mineral fillers. A combined experimental and numerical approach is employed, integrating tensile testing, X-ray micro-tomography, and finite element computation based on reconstructed microstructures. The results show that printing angle strongly affects mechanical performance through its influence on porosity, filament architecture, and interfacial bonding. Mechanical performance improves from 0° to 30°, reaching maximum values of 755 MPa in Young's modulus and 44 MPa in tensile strength. A slight reduction in both stiffness and tensile strength is observed at 45°, indicating that mechanical performance does not increase monotonically with printing angle and that an intermediate angle (30°) provides the most favourable balance between filament architecture and defect distribution. Finite element simulations reveal pronounced stress heterogeneity and confirm the dominant role of microstructural defects in load transfer.The effective mechanical properties are significantly lower than predictions based on the rule of mixtures, indicating inefficient reinforcement and a response approaching the Reuss bound. This behaviour is attributed to limited interfacial load transfer and microstructural defects, demonstrating that interface quality and architecture govern the mechanical response of ceramic-filled PLA systems.

We investigate 3D-printed composite materials composed of a photosensitive polylactic acid (PLA) resin blended with 10% starch and fabricated by Digital Light Processing. We synthesize the 3D-printed composites by incorporating a post-processing stage involving thermomoulding at various temperatures ranging from 50 °C to 150 °C. The composition, structure, and thermal and mechanical performance of the 3D-printed composites are evaluated using infrared spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), synchrotron X-ray microtomography and tensile testing assisted with digital image correlation. Our results indicate that post-treatment influences the mechanical behaviour of the composites, leading to a moderate increase in stiffness while the tensile strength remains slightly reduced compared with the reference condition, particularly when moulding temperatures reach 100 °C. Our 3D printing approach combined with the photosensitive/starch blend provides a cost-effective alternative for obtaining 3D-printed biosourced components, maintaining technical performance at a reasonable cost.

This study investigates the interrelation between thermal cycling, microstructural evolution, thermal and mechanical performance in 3D-printed PLA/PHA-wood composites produced via fused filament fabrication (FFF). Despite the growing interest in bio-based materials for FFF, the coupled effects of thermal processing, micro-structural evolution, and resulting functional properties remain insufficiently understood. Understanding these relationships is essential for optimizing printing parameters and enabling the design of sustainable multifunctional components with tailored mechanical and thermal performance. Using high-resolution infrared imaging, synchrotron X-ray micro-tomography, and the transient plane source (TPS) method, we assess the effects of printing parameters such as temperature, base temperature, and layer height on thermal gradients, heat distribution during deposition, effective thermal transport, as well as thermal properties of 3D-printed parts. Results indicate that deposition conditions significantly influence microstructural features, with porosity levels ranging from 22 % to 33 %, and pore alignment predominantly following the extrusion direction. Tensile testing reveals that mechanical performance is highly dependent on printing angle and infill rate, with peak results (Young's modulus of 484 MPa and tensile strength of 19.7 MPa) achieved at a 0 degrees angle and 100 % infill, where filament alignment maximizes structural integrity. Thermal characterization shows that conductivity (2) scales with infill density (0.06-0.13 W/m center dot K), with 20 % infill structures meeting high-performance insulation criteria (2 = 0.06 W/m center dot K). These findings demonstrate that, by strategically modulating printing architecture, these sustainable composites can be multifunctionalized, serving as either lightweight thermal barriers or high-strength structural components in advanced engineering applications.

Projected impacts of global warming on hemp and flax crops are examined based on potential changes in production volumes, yields, and geographic distribution, as well as the multifaceted qualities of bast fibres. More specifically, this work analyses current knowledge regarding the adaptation of hemp and flax to abiotic and subsequent biotic stresses, economic data, and strategies employed by farmers and stakeholders in the value chain. The analysis also emphasises on the perspective of end-users, particularly in relation to bio-based composites, and will outline our questions and perspectives for the future. The COP26, under the UN Framework Convention on Climate Change (UNFCCC), and its renewal at COP28, aims to limit temperature increases, with the goal of achieving net-zero GHG emissions by 2050. To meet this critical target, it is essential to adopt more sustainable materials and reduce reliance on petroleum-based products. Hemp and flax bio-based composites have received significant attention in recent decades due to their attractive attributes, including carbon sequestration, renewable carbon content, acceptable mechanical properties from an industrial perspective, superior end-of-life scenarios like biodegradability or recyclability, and abundance. Those current opinions are discussed, while also critically examining the potential of Artificial Intelligence as a tool for managing heterogeneous data to predict and mitigate future challenges on these industrial fibre crops.

In this study, we explore how the addition of flax fibre residues affects the microstructure and mechanical properties of modified mortars. Flax fibre residues from the individualization process are considered as fillers. Various formulations of mortar are adjusted by incorporating different proportions and sizes of flax fibre residues. The workability of fresh modified mortars is assessed through flow table experiments. X-ray mu -tomography is employed to investigate microstructural changes, focusing on pore content and the 3D spatial arrangement and content of natural residues. Mechanical performance is evaluated through compression tests conducted at different curing times. The findings indicate that flax residues can serve as effective substitutes, resulting in moderate loss in mechanical strength if the particle size is kept below 3 mm. Optimal formulations are found to require sieving of residues particle sizes resulting in small particles of 1 mm for an overall weight content of 5 % in the total weight of the cement used in the mix. These results demonstrate superior mechanical performance compared to all other tested conditions within only 7 curing days.

This study investigated the functionalization of flax yarn via in situ chemical polymerization of conductive polypyrrole (FY-PPy) and polypyrrole-silver (FY-PPy-Ag). Voltage-controlled experiments were conducted to assess the electrothermal properties of the modified yarns, with a focus on the Joule effect. FY-PPy exhibited significantly higher electrical conductivity (826 S.m- 1) and thermal conductivity (8583 J.S- 1 m- 1.degrees C- 1) than FYPPy-Ag did, which had values of 505 S.m- 1 and 5616 J.S- 1 m- 1.degrees C- 1, respectively. This enhanced conductivity resulted in a greater temperature increase during Joule heating, with the superior electrothermal performance of FY-PPy linked to the coated material formed during polymerization. Quantitative assessments of the coated conductive material were performed, revealing 25.5 wt% of PPy in the FY-PPy sample and 16.5 wt% of PPy and 26.1 wt% of silver in the FY-PPy-Ag sample. Gas chromatography tests revealed that the cellulosic content of the initial yarn remained unchanged after both functionalization methods were applied; however, the non-cellulosic polysaccharide content decreased significantly due to acidic treatment. Longitudinal tensile tests and sorption-desorption characterizations indicated that FY-PPy retained properties closer to those of the unfunctionalized yarn, whereas FY-PPy-Ag exhibited greater property loss. Our findings provide essential insights into the enhanced characteristics of functionalized flax yarns, highlighting their potential applications in the advanced electronics and composite industries.

The concept of fiber reinforced concrete (FRC) was invented to reinforce concrete with a wide range of fibers such as steel fibers, glass fibers, synthetic fibers, polyethylene fibers or carbon fibers. The addition of superplasticizers (SP) has enabled to gradually reduce W/B ratio and improves binder dispersion, which in turn improves mechanical properties of the cementitious matrix. In this study, two different types of fibers were mixed. It was studied the workability of cementitious mortars and the impact of fiber length and dosage. Natural fibers such as hemp, miscanthus and flax fibers were mixed with FIBRAFLEX fibers. FIBRAFLEX fibers are amorphous metallic fibers resistant to corrosion and chemical attacks. Two different sizes of fibers (FF13E7, FF15E0) were mixed with natural fibers in six different formulations. The composition of the granular skeleton and fibers have an impact on the workability of different formulations, and this aspect was studied using the slump cone. For the analysis of the cementitious matrix and the fiber/matrix interface, tomography was used to analyze the microstructure, observe the natural fiber/FIBRAFLEX fibers/cementitious matrix interaction and analyze material heterogeneity and fiber tortuosity within the cementitious matrix. Mechanical strength tests at 1, 7 and 28 days using 3-point bending and compressive strength tests were carried out, enabling us to gain a better understanding of the material characteristics obtained via tomography tests. This study investigates how fiber affects mechanical properties.

This study investigates the 3D printing of carbon fibre-reinforced copolyester (COP-CF) composites using fused filament fabrication (FFF) technology, with a focus on the influence of printing parameters on mechanical performance and microstructure. We explore the effects of different printing angles (0 degrees to 90 degrees) on the tensile behaviour, pore connectivity, and microstructural characteristics of 3D-printed COP-CF specimens. Synchrotron X-ray microtomography is employed to analyse the internal structure of printed parts, revealing insights into porosity distribution and fibre alignment. Our results indicate that a 45 degrees printing angle yields the highest mechanical performance, with a tensile strength improvement approaching 70 MPa and a Young's modulus nearing 1 GPa, attributed to filament alignment in the loading direction and optimal load transfer. Additionally, the elongation at break reaches approximately 10 %, indicating a balance between strength and ductility. The study also highlights the role of process-induced porosity and its impact on mechanical properties. Additionally, the design and testing of a 3D-printed curved hook demonstrate the material's potential for functional applications under mixed-mode loading conditions effectively at a 45 degrees printing angle-outperforming other angles by a factor of 1.71. The findings underscore the importance of printing angle and microstructure control in optimizing the mechanical performance of 3D-printed COP-CF composites for technical applications.

This study investigates the development of biodegradable, scented bio-composite filaments incorporating industrial residues, specifically spent coffee grounds (SCG) and lignin (LI), into a PLA matrix for FDM 3D printing. Two fragrance additives, essential oil (EO) and microencapsulated fragrance powder (FP), were introduced (3%) to enhance sensory properties. The research investigates the effects of filler content (5%, 10%, and 15%) and fragrance additives on the surface chemistry (FTIR), thermal stability (TGA and DSC), mechanical properties (Tensile, flexural and impact), microstructure, and dimensional stability (Water absorption test and thickness swelling). Incorporating industrial residues and additives into PLA reduced the thermal stability, the degradation temperature and the glass transition temperature but increased the residual mass and the crystallinity. The effect of lignin was more pronounced than that of SCG, significantly influencing these thermal properties. Increasing the filler content of spent coffee grounds and lignin also led to a progressive decrease in tensile, flexural, and impact strength due to poor interfacial adhesion and increased void formation. However, lignin-based biocomposites exhibited enhanced stiffness at lower concentrations (≤10%), while biocomposites containing 15% SCG doubled their elongation at break compared to pure PLA. Adding fragrance reduced the mechanical strength but improved ductility due to plasticizer-like interactions. Microstructural analysis revealed heterogeneity in the biocomposites’ fracture surface characterized by the presence of pores, filler agglomeration, and delamination, indicating uneven filler dispersion and limited interfacial adhesion, particularly at high filler concentrations. The water absorption and dimensional stability of 3D-printed biocomposites increased progressively with the addition of residues. The presence of essential oil slightly improved water resistance by forming hydrogen bonds that limited moisture absorption. This article adds significant value by extending the potential applications of biocomposites beyond conventional engineering uses, making them particularly suitable for the fashion and design sectors, where multi-sensory and sustainable materials are increasingly sought after.

Flax fiber reinforcements weaken with aging and microstructural changes, limiting their applications. Here, we examine the effects of microstructure and aging on flax fiber elements’ performance by using 4000-year-old and modern Egyptian flax as references through multi-scale numerical modeling. This study introduces a novel investigation into the tensile stress distribution behavior of archaeological and modern flax yarns. The finite element (FE) model is derived from 3D volumes obtained via X-ray microtomography and tensile testing in the elastic domain. At the microscale, fibers exhibit higher axial stress concentrations around surface defects and pores, particularly in regions with kink bands and lumens. At the mesoscale, fiber bundles show increased stress concentrations at inter-fiber voids and lumen, with larger bundles exhibiting greater stress heterogeneity, especially around pores and surface roughness. At the macroscale, yarns display significant stress heterogeneity, especially around microstructural defects like pores and fiber–fiber cohesion points. Aged fibers from ancient Egyptian cultural heritage in particular demonstrate large fiber discontinuities due to long-term degradation or aging. These numerical observations highlight how porosity, surface imperfections, and structural degradation increase stress concentration, leading to fiber rupture and mechanical failure. This insight reveals how aging and defects impact flax fiber performance and durability.

ABSTRACT Residual stress and internal strain in 3D printing can result in cracking and delamination. Here, we investigate the strain incurred during the deposition process in fused filament fabrication with a focus on polylactic acid (PLA) polymer. Specific geometries are employed to analyse thermal cycling and strain development, utilizing high‐resolution infrared camera and strain gauges. We investigate various printing parameters such as printing temperature, base temperature, and printing speed. Both thermal cycling and strain development were characterized throughout the printing procedure. Our results show that strain arises from both mechanical pressure exerted by the nozzle and thermal transfer between layers. During heating, strain reached up to 0.25 µε (microstrain), while cooling induced compressive behavior. The real strain, independent of thermal effects, peaked at 0.07 µε, with the first five layers showing the largest variations. Increasing base temperature to 80°C reduced strain fluctuations (0.009–0.010 µε). X‐ray microtomography revealed 0.22% porosity, and thermal imaging measured heat penetration up to 4 mm, with cooling rates of −130°C/s slowing to −75°C/s. These findings highlight the critical role of printing parameters on residual stresses and structural integrity in 3D printed PLA.

Residual stresses and internal strains in 3D printing can lead to issues such as cracking, warping, and delamination—challenges that are amplified when using functional composite materials like magnetic PLA filaments. This study investigates the thermo-mechanical strain evolution during fused filament fabrication (FFF) of magnetite-filled PLA using an integrated methodology combining strain gauge sensors, high-resolution infrared thermal imaging, and synchrotron X-ray microtomography. Printing parameters, including nozzle temperature (190–220 °C), build platform temperature (30–100 °C), printing speed (30–60 mm/s), and cooling strategy (fan on/off) were systematically varied to evaluate their influence. Results reveal steep thermal gradients along the build direction (up to −1 °C/µm), residual strain magnitudes reaching 0.1 µε, and enhanced viscoelastic creep at elevated platform temperatures. The addition of magnetic particles modifies heat distribution and strain evolution, leading to strong sensitivity to process conditions. These findings provide valuable insight into the complex thermo-mechanical interactions governing the structural integrity of magnetically functionalized PLA composites in additive manufacturing.

This study investigates the mechanical performance, microstructural characteristics, and optimisation strategies for 3D-printed PET, focusing on the effects of printing temperature and angle. Tensile behaviour analysis reveals that while temperature variations (200-230 degrees C) have a minor effect, the printing angle plays a pivotal role in determining mechanical properties. Lower angles (<= 15 degrees) enhance stiffness, tensile strength, and elongation at break by minimizing porosity and improving interfilament bonding. Conversely, higher angles (theta = 30 degrees) result in increased porosity (up to 2.1 %), leading to reduced mechanical performance. Microstructural analysis highlights the influence of filament arrangement and cohesive layering on stress distribution and mechanical integrity. Finite element simulations predict stress heterogeneity and align qualitatively with experimental results, demonstrating the significant impact of porosity and filament orientation on mechanical properties. To validate practical applicability, a bike bottle holder was successfully 3D-printed using PET. The design, occupying only 4.52 % of the design domain volume, achieved a balance between material efficiency, mechanical performance, and energy consumption, with optimal settings of a 0 degrees printing angle and an intermediate temperature of 210 degrees C. These findings underscore the importance of optimizing printing parameters to enhance the structural performance and energy efficiency of 3D-printed PET components, providing valuable insights for future applications in additive manufacturing.

In this study, we examined how printing temperature affects the microstructure and mechanical properties of polylactic acid (PLA) composite reinforced with iron oxide i.e., magnetite manufactured using a material extrusion technique. The composite was printed at temperatures from 185 °C to 215 °C. Microstructure analysis via synchrotron radiation X-ray microtomography revealed changes in both iron oxide and porosity contents within the printed structures. Mechanical testing results demonstrated a limited effect of the printing temperature on tensile performance. Finite element computation is considered to predict the elasticity behavior of the printed composite by converting 3D images into 3D structural meshes. When implementing a two-phase model, the predictions show a leading role of the iron oxide content, and an overestimation of the stiffness of the composite. A three-phase model demonstrates a better matching of the experimental results suggesting a limited load transfer across the PLA-iron oxide interface with Young’s moduli in the interphase zone as small as 10% of PLA Young’s modulus. Magnetic actuation demonstrates that experiments on PLA-iron oxide plates reveal a pronounced thickness-dependent limitation, with the maximum deflection observed in thin strips of 0.4 mm.

This paper presents a study case on the structural topology optimization of biomedical wrist orthosis. The manufacturing process integrates photosensitive resign that enables production of geometries that are both impact-resistant and exhibit a smooth, refined surface finishing which is essential for biomedical applications. The 3D printing is based on Digital Light Processing (DLP). Based on extensive biomechanical studies for accurate simulation parameters, four loading cases were defined for topology optimization. Maximam stresses and displacements were considered at upper limits for the optimization problem with weigh reduction.

This study investigates the biodegradation of 3D printed biocomposites under aerobic composting conditions. Biodegradable containers were prepared using forest biomass, wood ash (WA), wood sawdust (WS), and cellulose fiber (CF), as fillers and polylactic acid (PLA) as matrix and were processed via fused filament fabrication (FFF). Biodegradability tests were conducted in a laboratory-scale installation using the compost burial method for three months. Weight loss measurements were measured every 7 days throughout testing. The physicochemical and morphological properties of the samples were characterized. Of the biocomposites, PLA with 20 wt% wood sawdust showed the highest water absorption. The kinetic mechanisms followed typical Fickian diffusion behavior. The crystallinity improved with the addition of 20 wt% cellulose fibers. PLA degrades in a two-step process. Initially, temperature and moisture break down the PLA chains into lactic acid monomers. Subsequently, microorganisms in the compost convert these compounds into carbon dioxide, water, and biomass. A 97 % PLA weight loss was achieved after 3 months, with added fillers decreasing the biodegradability rate. Cracks on the surface and color changes were noted. Microorganisms were observed to settle in the spaces between the layers created by 3D printing. Fourier transform infrared spectra, scanning electron microscope micrographs, and synchrotron X-ray microtomographs revealed a microbial biofilm layer on the sample surfaces. After biodegradation, biocomposites can serve as soil fertilizer. Therefore, 3D printed biodegradable containers offer eco-friendly solutions that help minimize agricultural plastic waste accumulation and lower greenhouse gas emissions.

Flax yarns are widely used in composites and textiles, yet their mechanical performance is limited by factors like microstructure and durability, necessitating in-depth investigation of their tensile behavior. This study aimed to evaluate the dynamic response of flax yarns under tensile loading, using in situ SEM tensile testing to reveal realtime failure mechanisms and microstructural behavior. Novelty lies in the unprecedented examination of 4,000-year-old Egyptian yarns, offering unique insights into the effects of aging on fiber morphology and strength. This research included single and ply yarns from modern Egypt, France, and ancient Egypt. Findings indicate significant strength differences due to strong morphological variations. Morphological analysis demonstrates that, with aging, ancient yarns exhibit greater number of kink bands and fiber separation, indicating structural weakening and compound middle lamella (CML) degradation. Failure analysis revealed fiber breakage is the primary failure mode in modern yarns, contrasting with combined breakage and slippage in ancient yarns, indicating distinct degradation mechanisms. Kink-bands were identified as critical to tensile behavior, initiating cracks that propagate, causing fiber rupture and subsequent breakage in bundles within yarns. These results highlight the evolution in yarn production and durability, emphasizing the impact of fiber microstructure and aging on performance, contributing essential insights for advancing the mechanical performance of flax-based materials.

Defects in flax fibres limit the use of more sustainable load bearing composites in industry, which highlights the need for a thorough understanding of their nature. In this work, X-ray micro-tomography of flax revealed pores in the cell wall of elementary fibres: kink-bands pores and longitudinal pores, a previously unseen defect. Their morphology and organisation are examined, highlighting fibre deterioration and locally increased porosity up to 14.86 %. Finite element modelling under a 1.5 % tensile strain reveals that kink-band pores concentrate stress up to 7.15 times, while longitudinal pores reach 2.35 times compared to defect-free areas. Under tension, cracks are thus likely to initiate at kink-band defects, may propagate through longitudinal pores to other kink-bands, and lead to fibre and composite failure as these defects are favoured zones for crack initiation and propagation. In situ peeling of fibres due to knot tightening under scanning electron microscopy suggests interlaminar decohesion between cellulose macrofibrils as the origin of the longitudinal pores. The study explores hypotheses on the origin of these weak interfaces related to fibre growth and extraction processes. It provides insights for improving flax fibre properties and widening the use of more sustainable composites.