Single Fiber Tensile Test Research Articles

Biofiber from Musa paradisiaca L., Peduncle Biomass Waste: Extraction and Characterization for Polymer Composites Suitability Study

ABSTRACT The Musa paradisiaca L. peduncle natural fiber (MPPNF) was characterized by atomic force microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR), chemical analysis (CA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), single fiber tensile test (SF-TS), X-Ray diffraction (XRD), and thermogravimetric analysis (TGA). AFM result suggests that this fiber has less impurity and a spiky topology. The FTIR graph confirms the presence of cellulose (CE) as there is a disappearance of C-O stretch at 1305 cm−1 peak. Chemical analysis shows a CE content of 67.9%. The SF-TS has shown that the TS of the fiber is 172 MPa. The modulus and elongation % were evidenced as 4.81 GPa and 4.8%, respectively. The results obtained suggest that it has a crystallinity index (CI) of 48%. The density of this fiber was found to be 1040 kg/m3. The thermal stability of the fiber remains intact until the degradation occurs at 339°C. All the above results convincingly prove that this MPPNF can be used as reinforcement for composites.

Effect of hybrid sizings on the surface morphology, mechanical behavior of basalt fibers, and fiber/epoxy composite properties

AbstractIn the present study, the basalt fibers (BFs) were treated with hybrid sizings consisting silane coupling agent (3‐Glycidoxypropyl)trimethoxysilane, and silicon dioxide nanoparticles (SNPs). Using acetone washing and heat treatment, the commercial sizing previously on the BFs was removed. Next, the fibers were dip‐coated, and silanes condensed on the surface of the fibers. Fiber samples were characterized using thermogravimetric analysis (TGA), atomic force microscopy (AFM), X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The test findings demonstrate that acetone extraction was an effective way to remove sizings. The AFM analysis and SEM micrographs demonstrate that SNP and silane particles were dispersed uniformly across the fiber surface. The single fiber tensile testing results indicated that the deposition of hybrid sizings enhanced the fibers strength. Because of the better adhesion between the fiber and epoxy, the hybrid sizings also improved the flexural strength by 22.28% and the interlaminar shear strength by 20.75%.Highlights Hybrid sizings (silanes and nano‐particles) on the basalt fiber surface. Characterization of the sizings and understanding of surface morphology. Hybrid sizings resulted in better tensile strength. Failure mechanisms of the fibers were observed using fractography. The effect of hybrid sizing on ILSS and flexural properties was observed.

Single-fibre tensile testing of plant fibres: Set-up compliance as a key parameter for reliable assessment of their mechanical behaviour

The use of plant fibres as reinforcements in engineering applications requires reliable determination of their mechanical properties. This work focuses on single-fibre longitudinal tensile testing and the significance of the tensile system compliance for obtaining reliable results. Four types of fibre are tested, namely basalt, aramid, elementary flax fibres and flax fibre bundles. An automated laser scanning method is used to determine their cross-sectional area (CSA) based on circular and elliptical morphological models. The compliance of the tensile system is evaluated by standard and photomechanical analyses, and its influence on the assessment of mechanical properties of the fibres is discussed. Our results show that the evaluation of the compliance is highly dependent on fibre type, but also on the choice of CSA morphological model. The resulting correction on maximum tensile moduli ranges from 6.5 % to 37.6 % for small-diameter fibres, and can reach 55.1 % for large-diameter fibres as flax fibre bundles. Moreover, we evidence that the tensile system compliance is not necessarily constant and evolves with the force range covered during the tensile test. This can have a significant impact on the shape of the stress-strain curves, and hence on the analysis of the overall mechanical behaviour of the fibres.

Micromechanical modeling of longitudinal tensile behavior and failure mechanism of unidirectional carbon fiber/aluminum composites involving fiber strength dispersion

This paper examines the longitudinal tensile behavior and failure mechanism of a new unidirectional carbon fiber reinforced aluminum composite through experiments and simulations. A Weibull distribution model was established to describe the fiber strength dispersion based on single-fiber tensile tests for carbon fibers extracted from the composite. The constitutive models for the matrix and interface were established based on the uniaxial tensile and single-fiber push-out tests, respectively. Then, a 3D micromechanical numerical model, innovatively considering the fiber strength dispersion by use of the weakest link and Weibull distribution theories, was established to simulate the progressive failure behavior of the composite under longitudinal tension. Due to the dispersion of fiber strength, the weakest link of the fiber first fractures, and stress concentration occurs in the surrounding fibers, interfaces, and matrix. The maximum stress concentration factor for neighboring fibers varies nonlinearly with the distance from the fractured fiber. Both isolated and clustered fractured fibers are present during the progressive failure process of the composite. The expansion of fractured fiber clusters intensifies stress concentration and material degradation which in turn enlarges the fractured fiber clusters, and their mutual action leads to the final collapse of the composite.

A round-robin study on the tensile characterization of single fibres: A multifactorial analysis and recommendations for more reliable results

In this benchmark, the tensile properties of three types of organic fibres – flax, hemp and aramid − were determined using single-fibre tensile tests performed by nine research groups. Flax and hemp were chosen due to their prevalence among European fibre plants. Aramid was selected for its synthetic nature and comparable dimensional properties. Due to the morphological complexity and variability of plant fibres, the scatter in the apparent tangent modulus and strength is more pronounced for flax and hemp compared to aramid. The primary source of scatter in the tensile properties results from human factors and experimental procedures, particularly regarding the fibre selection, the measurement of the fibre cross-sectional area and of the tensile strain. The post-processing procedure also turns out to be a key factor. Finally, recommendations and guidelines for best practices are proposed to reduce the main sources of dispersion associated with the reproducibility of single fibre tensile tests.

Porous Melt Blown Poly(butylene terephthalate) Fibers with High Ductility and High-Temperature Structural Stability.

In this study, porous poly(butylene terephthalate) (PBT) fibers were produced by melt blowing cocontinuous blends of PBT and polystyrene (PS) and selectively extracting the interconnected PS domains. Small amounts of hydroxyl terminated PS additives that can undergo transesterification with the ester units in PBT were added to stabilize the cocontinuous structure during melt processing. The resulting fibers are highly ductile and display fine porous structural features, which persist at temperatures over 150 °C. Single fiber tensile testing and electron microscopy are presented to demonstrate the role of rapid quenching and drawing of the melt blowing process in defining the fiber properties. The templated highly aligned pore structure, which is not easily produced in solvent-based fiber spinning methods, leads to remarkable mechanical properties of the porous fibers and overcomes the notoriously poor tensile properties common to other cellular materials like foams.

Study on the interfacial bonding properties between alkali-treated bamboo fibers and high-performance seawater sea-sand concrete

In this paper, the interfacial bonding properties between alkali-treated bamboo fibers and the matrix in fiber-reinforced high-performance seawater sea-sand concrete (HPSSC) materials were investigated. The natural bamboo fibers were modified with NaOH solution, and the cellulose crystallinity, chemical composition, and microstructure of the bamboo fibers before and after modification were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The impact of alkali treatment on the water absorption and mechanical properties of bamboo fibers were evaluated by water absorption test and single fiber tensile test. In addition, the influences of NaOH concentration, treatment time, and embedded length on the interfacial bonding properties were analyzed by pull-out test. Subsequently, the bonding mechanism between the fibers and the matrix was revealed based on the SEM scans of the extracted fiber surfaces. The experimental results indicate that appropriate alkali treatment could significantly eliminate the non-structural substances on the surface of bamboo fibers, reduce the water absorption, and increase the cellulose crystallinity. This process made the bamboo fibers exhibit better stability and bonding performance while ensuring the initial mechanical properties. Moreover, various fiber embedded lengths have a significant impact on the pull-out behavior of bamboo fibers. The maximum pull-out force of bamboo fibers increased with the increase of embedded length, while the fiber-matrix interfacial shear strength decreased. Based on the experimental results, a theoretical model for the pull-out behavior of bamboo fibers was proposed, and the predicted results showed a strong correlation with the experimental results.

Experimental Study on Single Fiber Tensile Properties of Sisal Fibers Using a Digital Image Correlation Method as a Strain Measurement

ABSTRACT The development of natural fibers in engineering applications requires an accurate measurement of their dimensional characteristics and mechanical properties. Fiber cross-sectional area (CSA) obtained from lateral dimensional measurements should consider the specific cross-sectional shape (CSS) of the fibers and their wide lengthwise variations. In this study, the dimensional measurements of water-retted and unretted sisal fibers were conducted by laser scanning microscopy (LSM) and calculation-based methods. Single fiber tensile tests were performed using the digital image correlation (DIC) method. Results show that the diameters of water-retted and unretted fibers measured by LSM were 233 ± 45 µm and 236 ± 42 µm, respectively. The diameters of water-retted and unretted fibers obtained by calculation were 192 ± 17 µm and 178 ± 20 µm, respectively. The tensile strengths of water-retted and unretted fibers were 679 ± 118 MPa and 718 ± 106 MPa, respectively. The strain at failure and elastic modulus of water-retted and unretted fibers were 2.0 ± 0.6% and 34 ± 8 GPa, as well as 1.5 ± 0.2% and 48 ± 6 GPa, respectively. Water retting seems to predominantly influence the strain at failure and elastic modulus of sisal fibers, as confirmed by the ANOVA analysis.

Improvement of tensile strength and toughness in aramid/epoxy composites by sequential air plasma and (3-glycidyloxypropyl) trimethoxysilane treatments

This work explores sequential surface treatments involving atmospheric-air plasma and (3-glycidyloxypropyl) trimethoxysilane (GLYMO) to enhance the tensile properties of aramid/epoxy composites. To prove the technical advantages of this approach, aramid fibers received individual (atmospheric-air plasma or GLYMO) or sequential (plasma followed by GLYMO, and vice versa) surface treatments. Single fiber tensile tests (SFT) and X-ray photoelectron spectroscopy (XPS) were employed to characterize changes in aramid fibers upon the surface modifications. SFT revealed that none of the surface treatments compromised their tensile strength (σ max ). Applying GLYMO, whether individually or in sequence (GLYMO followed by plasma and plasma followed by GLYMO), led to a significant enhancement in the fibers’ elastic modulus (E). Composites with plasma-treated fibers displayed a 5% increase in E and an 8.5% increase in σ max , with no changes in toughness. However, the most notable improvements were achieved through sequential plasma followed by GLYMO treatments, resulting in a ~ 10% increase in σ max and a remarkable ~ 40% improvement in toughness. Plasma introduces oxygen-containing groups to the fiber surface, facilitating GLYMO grafting. Subsequent crosslinking of GLYMO with the epoxy resin strengthens the fiber-matrix interface. This sequential surface modification offers an alternative pathway for fabricating composites with superior toughness and σ max .

Exploring the potential of sustainable natural cellulosic fiber from Sorghum bicolor (Sorghum vulgare var. technicus) stem for textile and composite applications

AbstractIn the present research, the usability of cellulosic-based fibers obtained from the Sorghum bicolor plant stem as reinforcing fibers in composites and textiles was investigated. The fibers were obtained from a Sorghum bicolor plant growing wild in the Adana region in the South of Turkey. Density, chemical structure analysis, FTIR, XRD, TGA, XPS SEM, and single fiber tensile tests characterized Sorghum bicolor fiber (SBF). SBF contains cellulose (73.6%), hemicellulose (13.3%), and lignin (12.1%). The oxygen/carbon ratio of 0.43 found as a result of XPS analysis indicates that fibers have a hydrophilic character. SBF has a 59.34% crystallinity index, 284.6 MPa tensile strength, 4.71% GPa tensile modulus, and 21.44% elongation at break. The maximum degradation temperature of the fibers was determined as 364.22 °C. Sorghum bicolor fiber, through detailed characterization, emerges as potential promising reinforcement for the composite industry with relatively good strength and high cellulose content for the textile industry.

Extrusion and characterization of eggshell-based composite filaments for sustainable development in additive manufacturing

Additive manufacturing (AM) is an extending manufacturing method which has many advantages such as minimalistic material wastage, less fabrication time and so on, over other manufacturing technologies such as subtractive, moulding, casting, etc. Strength enhancement of additively fabricated structures is an active area of study and much research was evolved in terms of developing innovative feedstock for AM. Polymers and their composites gain great attention in the research community. Even though many composites available commercially were observed with enhanced properties, most of them are not sustainable and recyclable in nature. Eggshell is a naturally available calcium carbonate, which gets wasted in a huge amount. Such eggshells were synthesized and transformed into nanosized for inclusion of filler in polylactic acid (PLA) matrix. PLA is a bio-degradable polymer with numerous applications and is one of the popular feedstocks for fused deposition modelling. This study explains the proper procedure to extrude commercial-grade eggshell-based composite filaments and qualities of such composites would be elaborately discussed with the help of single fibre tensile test, scanning electron microscopy and X-ray diffraction. Totally five filaments such as PLA, 5, 10, 15 and 20 wt % of eggshell in composites were extruded by following proper sonication and suitable filament extrusion process. 15 wt % composite seems to be the best among all filaments and possesses better characteristics than all other filaments.

Influence of optimal alkali treated Areca catechu L. peduncle fiber for light weight polymer composites applications

AbstractThe chemical, physico‐mechanical, morphological, and thermal characteristics of alkali treated natural cellulosic sustainable eco‐friendly fiber from peduncle of Areca Catechu tree were investigated. Areca Catechu fruit peduncle fiber (ACFPF) treated with 5% (w/v) NaOH solution for 60 min is found as optimally alkali treated ACFPF (OAACFPF) witnessed an increase in cellulose content by 17%. Single fiber tensile test perceived that OAACFPF enhanced tensile strength by 12.9% and x‐ray diffraction analysis depicts crystallinity index of OAACFPF improved by 14.2% compared with ACFPF. Also, Fourier transform infrared spectroscopy analysis endorsed partial removal of amorphous contents from fibers due to alkali treatment. In addition, alkali treatment has enhanced thermal stability of OAACFPF from 226°C to 235°C verified through Thermogravimetric analysis. Likewise, Differential scanning calorimetry analysis confirmed improvement in thermal degradation temperature of OAACFPF after alkali treatment. Moreover, the rougher surface of OAACFPF confirmed through scanning electron microscope and atomic force microscopy is due to partial removal of amorphous contents thus ensuing in good interfacial bonding characteristics with the matrix during reinforcement for bio‐composite fabrication. The above findings validated OAACFPF as a worthy substitute to harmful synthetic fibers for development of eco‐friendly and sustainable bio‐composites.

The impact of thermal treatment parameters on the preservation of carbon fiber mechanical properties after reclamation

Carbon fiber, despite its exceptional properties, remains underutilized due to monetary and environmental concerns. Concurrently, the imminent challenge associated with rising quantities of End-of-Life CFRP (carbon fiber reinforced polymer) demands the further development of recycling strategies. This study focuses on optimizing the recycling process parameters of pyrolysis and oxidation thermal treatment to maximize the retention of mechanical properties in the recycled fibers in the shortest process time. To assess the result of the pyrolysis, single fiber tensile tests were executed to measure strength and stiffness. Additionally, microscopy and spectroscopy studies were carried out to evaluate fiber geometry as well as surface quality. At the laboratory scale, experiments demonstrated that the combination of pyrolysis and oxidation yields clean, reusable fibers with mechanical properties suitable for secondary applications. The influence of various treatment parameters on the strength and stiffness of the recycled fibers was explored, establishing a clear correlation. The outcome is a set of optimized parameters that contribute to mechanical property retention, including a novel recycling method that allows for reduced processing times, as short as 10 min. This work paves the way for a more eco-friendly and cost-effective approach to harnessing the potential of carbon fiber in a wide range of applications while mitigating environmental concerns associated with landfill disposal.

Recycling of wet carbon fiber-reinforced plastic laminates by thermal decomposition coupled with electrical treatment

The use of carbon fiber-reinforced plastics (CFRPs) produces moisture-absorbing CFRP waste, which is usually recycled via thermal decomposition treatment (TDT). However, the oxygen gas generated during heating can hardly penetrate dense CFRPs, resulting in nonuniform damage to the recovered carbon fibers (rCFs) collected from the outer (oCFs) and inner (iCFs) parts of CFRP waste. Herein, TDT was coupled with electrical treatment (ET) to improve the recycling performance of CFRP laminates waste. The tensile strength of the rCFs measured via the single-fiber tensile tests was analyzed using a two-parameter Weibull distribution. Absorbed water was preferentially evaporated from the laminates by Joule heating during ET, resulting in extensive pore formation. Following TDT, the oCFs and iCFs showed nearly identical average tensile strengths because the pores formed by ET served as efficient diffusion pathways for oxygen gas. The proposed recycling technology may potentially be applied to other types of moisture-absorption waste.

Effect of Fiber Sizing Levels on the Mechanical Properties of Carbon Fiber-Reinforced Thermoset Composites.

Fiber sizing is one of the most important components in manufacturing composites by affecting mechanical properties, including strength and stiffness. The sizing of manmade fibers offers many advantages, such as improving fiber/matrix adhesion and bonding properties, protecting fiber surfaces from damage during the processing and weaving stages, and enhancing the surface wettability of polymer matrices. In this work, the influence of fiber sizing levels on carbon fibers' (CFs) mechanical properties is reported at room temperature using single fiber tensile testing (Favimat+), single fiber pullout testing (SFPO), and interfacial elemental analysis by X-ray photoelectron spectroscopy (XPS). Standard modulus CFs (7 ± 0.2 μm in diameter) were sized using two commercially available Michelman sizing formulations. The average solid content for each sizing formulation was 26.3 ± 0.2% and 34.1 ± 0.2%, respectively. HEXION RIMR 135 with curing agent RIMH 137 was used as a model thermoset epoxy matrix during SFPO measurements. A predictive engineering fiber sizing methodology was also developed. Sizing amounts of 0.5, 1, and 2 wt.% on the fiber surface were achieved for both sizing formulations. For each fiber size level, 50 single-fiber tensile testing experiments and 20 single-fiber pull-out tests were conducted. The ultimate tensile strength (σult) of the carbon fibers and the interfacial shear strength (τapp) of the single fiber composite were analyzed. The sizing levels' effect on interfacial shear stress and the O/C (Oxygen/Carbon) surface composition ratio was investigated. Based on our experimental findings, an increase of 6% in fiber performance was recorded for ultimate tensile and interfacial shear strengths. As a result, generalized fiber sizing and characterization methods were established. These developed methods can be used to characterize the strength and interfacial shear strength of manmade fibers with different sizing formulations and solid contents irrespective of the matrix, i.e., thermoset or thermoplastic.

Enhancing properties and sustainability: Surface modified Cymbopogon flexuosus stem fiber for green composite materials

AbstractThe lignocellulosic fiber has distinct capacities and properties from diverse perspectives. As there is a crucial need for the development of green products, many industries are racing to identify potential fibers for their products. This work focuses first on the property enhancement using chemical modification techniques for Cymbopogon flexuosus stem fiber (CFS), which is extracted from the waste residue of an oil industry. The chemically treated fibers resulted in higher cellulose (77.35%) and lower hemicellulose‐lignin contents (8.36% and 14.5%), which favors composite manufacturing. Morphological analysis on the fiber surface through scanning electron microscope (SEM) and atomic force microscope (AFM) evidenced the surface was rough, and a single fiber tensile test reveals an average tensile strength of 635 ± 4.5 MPa. Further x‐ray diffraction examination verified the existence of semi‐crystalline cellulose with a size of 14.32 nm and a higher crystallinity index of 55.17%. Secondly, to explore fiber prospective qualities against the commercially available bio‐composite, epoxy resin‐based composites were prepared by varying the weight and length of fiber reinforced. The surface‐modified CFS epoxy composite has the highest tensile strength (77.71 MPa), tensile modulus (5.26 Gpa), flexural strength (87.4 MPa), flexural modulus (1.85 GPa), hardness (64 HRRW), and impact strength (9.31 J/cm2). The thermogravimetric analyses were evaluated to assess their weight loss under heat influence. Tensile fractography was also investigated to establish the structure–property relationship between the composite and fiber. Thus, unique fiber was identified as an ecologically benign and economically viable raw material to build lightweight green materials for industrial applications.Highlights Studies explores the potential of CFSF, which is typically an industrial waste. Chemical modification reveals the enhancement of properties. Identifies optimum parameters that enhance composite properties. This aligns with the broader trend of sustainable and green manufacturing.

Extraction and characterization of a novel cellulosic fiber derived from the bark of Rosa hybrida plant

The current investigation aims to choose an alternate potential replacement for the nonbiodegradable synthetic fibers used in polymer composites. This goal motivated the thorough characterization of Rosa hybrida bark (RHB) fibers. The research explored fiber characterization such as morphological, mechanical, thermal, and physical properties. The suggested fiber features a percentage of cellulose, hemicellulose molecules, and lignin of 52.99 wt%, 18.49 wt%, and 17.34 wt%, respectively according to chemical composition studies, which improves its mechanical properties. It is suitable for lightweight applications due to its decreased density (1.194 gcm−3). The purpose of the Fourier transform infrared spectroscope was to observe and record how various chemical groups were distributed throughout the surface of the fiber. The presence of 1.41 nm-sized crystalline cellulose and further XRD analysis showed a crystallinity index of 75.48 %. Scanning electron microscope studies revealed that RHB fibers have a rough surface. According to a single fiber tensile test, for gauge length (GL) 40 mm, Young's modulus and tensile strength of RHB fibers were 6.57 GPa and 352.01 MPa, respectively, and for GL 50 mm, 9.02 GPa and 311 MPa, respectively. Furthermore, thermo-gravimetric examination revealed that the isolated fibers were thermally stable up to 290 °C and the kinetic activation energy was found to be 75.32 kJ/mol. The fibers taken from the Rosa hybrida flower plants' bark exhibit qualities similar to those of currently used natural fibers, making them a highly promising replacement for synthetic fibers in polymer matrix composites.

Effect of Multi-Walled Carbon Nanotubes on the Mechanical and Thermal Properties of Curauá Natural-Fiber-Reinforced Composites

The main objective of this research centered on investigating the effect of the addition of multi-walled carbon nanotubes (MWCNTs) on the mechanical and thermal properties of curauá-fiber-reinforced composites. The MWCNTs were added either to the fiber surface or into the resin matrix as the second reinforcing phase. The MWCNT-modified curauá fibers as well as raw fibers were characterized using a single-fiber tensile test, TGA, and FTIR analysis. Further, different composite samples, namely, pure curauá, (curauá + MWCNTs) + resin and curauá+ (resin + MWCNTs), were manufactured via compression molding and tested to determine their mechanical and thermal properties. Scanning electron microscopy (SEM) analysis was used to examine the surfaces of the tested fibers. It was found that the addition of MWCNTs to the curauá fibers resulted in positive effects (an enhancement in properties was found for the MWCNT-modified fibers and their composites). The addition of MWCNTs also increased the thermal stability of the natural fibers and composites.

Study on Properties of New Biodegradable Plant Fiber (Agave Decipiens) for Polymer Reinforcement

<p>The article involves in the process of study on novel plant fiber from agave plant species known as agave decipiens. The fiber was mechanically extracted from their leaves and fiber was chemically treated using sodium hydroxide by 5% (w/v). Using various analyses, the fiber was characterized and its properties were obtained. From chemical constituent analysis it was confirmed that hemicellulose, amorphous lignin, and other impurities were removed to some extent, and using x-ray diffraction (XRD), an improvement in crystallinity index was observed (i.e. from 47.99% to 52.29%). Increased crystallinity provides better tensile stress from 479.302 MPa to 494.172 MPa, which was confirmed by single fiber tensile test. A change in physical diameter was observed using a digital microscope, the outer diameter was reduced to 117.66µm from 121.84µm. Change in chemical components was identified by Fourier Transform Infrared Spectroscopy (FTIR). Alkaline-treated (AT) fiber sustains a temperature of about 240oC during thermogravimetric analysis (TGA). Study on surface morphology was conducted with help of scanning electron microscope (SEM). Concluding that alkaline treatment made some impact on fiber characteristics and made it suitable for reinforcement.</p>

Effect of enzyme retting conditions on bast bundle differentiation and mechanical properties of flax technical fibers

Compared to conventional dew retting, enzymatic retting has the potential to control fiber extraction process and produce high quality plant fibers for industrial scale composite applications where low Family videovariation in properties are desired. While most studies depend upon retting duration and fiber fineness as measures for effective retting degree, in this study we report the effect of enzyme concentration and enzyme retting duration on the flax bast-woody core bond strength and resulting technical fiber fineness. Fiber peel tests and microscopy coupled with statistical analysis showed that while only retting duration has significantly effect on fiber fineness, the bond strength between the bast-woody core interphase is significantly affected by both enzyme concentration and time. Single fiber tensile tests were conducted on flax fibers from different retting conditions at 10 mm and 30 mm gauge lengths. Fibers extracted from a high degree of enzymatic retting performed well at 10 mm gauge length but showed lower tensile strength at 30 mm gauge length, indicating over-retting. These findings can guide optimizing the enzyme retting process conditions at industrial scale for improved fiber properties with reduced variability.