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Identification of archaeological and historical textile fibres is important because it gives insight into resource management in former times. The arrival of new tools such as table-top scanning electron microscopes, have led to an increased interest in the topic. Unfortunately, there have been cases where a lack of documentation regarding instrument settings and selection criteria has led to questionable conclusions being drawn. Optical and scanning electron microscopy are powerful techniques, but they must be used correctly and with proper knowledge of their limitations. Furthermore, ancient fibre material is often difficult to examine due to issues such as sample degradation, mineralization and the scarcity of material, which means that conclusions based on a statistical analysis of a large number of fibres are essentially not possible. In a cultural heritage context, it is therefore essential to distinguish between characteristic features, by which we mean features that are often, but not always present in a particular species and distinguishing features, which are always present in a particular species and can therefore be used for identification even if only a small amount of sample material can be examined. We argue that the community will have to accept that, quite often, a secure identification is not possible and that absolute statements such as: "This textile is made of flax" will often have to be replaced by relative statements such as "The material is likely to be flax". In this paper, we address these issues as follows: first, we present a fibre identification diagram which can be used, with some limitations, to distinguish between flax, hemp, nettle, jute, hops, and cotton using optical and electron microscopy. We then move on to highlight some of the typical pitfalls of using optical and electron microscopy for fibre identification. Finally, we present measurement documentation tables for optical and electron microscopy images, which we suggest should always be included in publications. Material scarcity means that the amount of material used for investigations should be kept at an absolute minimum. It is thus crucial that results are published with proper documentation so that measurements do not need to be repeated (more material is used) in future studies. It is our hope that the measurement documentation tables will be adapted by the community and used in future publications in the field. The paper finishes with a demonstration example, presenting a fibre analysis of Viking Age textile fragments from the 10th Century with documentation tables. [ABSTRACT FROM AUTHOR]

Global warming has led to a change in climatic conditions. Since 2006, drought has contributed to a reduction of food production and other agriculture-based products in many countries. The accumulation of greenhouse gases in the atmosphere has caused some changes in the composition of fruits and vegetables, making them less nutritious. To analyse this situation, a study was conducted on the effect of drought on the quality of fibres provided by the main fibre crops in Europe, namely flax (Linum usitatissimum). The experiment consisted of growing flax under controlled comparative conditions with designed different irrigation levels, such as 25%, 35% and 45% field soil moisture. Three varieties of flax were grown in 2019, 2020 and 2021 in the greenhouses of the Institute of Natural Fibres and Medicinal Plants in Poland. Fibre parameters, such as linear density, length and strength, were evaluated according to relevant standards. In addition, scanning electron microscope images of the cross-section and longitudinal view of the fibres were analysed. The results of the study indicated that deficiency of water during the flax growing season resulted in lowering of fibre linear density and tenacity. [ABSTRACT FROM AUTHOR]

A persistent rise in the costs of construction materials has led to the need to address this problem in line with the Sustainable Development Goals. This research employed vegetal soft and rigid fibers in a screed mortar to produce a sustainable fabric–cement matrix. Four different vegetal-dried fibers (hemp, flax, miscanthus, and bamboo) with dosages of 0.4, 0.6, 0.8, 1.2, 2, and 4 kg/m3 were used. Laboratory investigations were slump test, bulk density, air occluded, shrinkage, and mechanical strength. Scanning Electron Microscope (SEM) assessments were performed and analyzed on the natural fibers and the screed formulation. The results highlight that fiber dosages significantly influence the above-mentioned properties. [ABSTRACT FROM AUTHOR]

Organic fiber biocomposites have figured prominently in various industries of commerce during the last 3 to 5 years owing to their remarkable physical and mechanical abilities. The main purpose of this experimental research is to evaluate the biomechanical and geomorphologic belongings of nanostructured substance under naturalistic situations. To accomplish such a cognitive approach, flaxseed strands are employed as reinforcing, nano-based graphene as an additive, and epoxy as a matrix phase, with the following restrictions in imagination: (i) fiber lengths, (ii) fiber volume fraction, and (iii) weight proportions of nanoparticles. The nanocomposites are combined by means of the hand lay-up process based on the Taguchi orthogonal specification. The material characteristics of the substance, like bending, tension, and shock characteristics, are assessed in line with the standard specification. The material properties of mixtures' second levels are the highest when compared to all other configurations. The elastic modulus of nanoparticle biocomposites revealed that 2% graphene provides 32.39 percent, 4% graphene provides 36.39 percent, and 6% nanoparticle pertains to 31.23 percent. Fractured images captured using scanning electron microscope of cracked samples have been used to comprehend the overall failure mechanism of a composite in mechanical characterization. [ABSTRACT FROM AUTHOR]

A mixed microbiologically composite made from natural Linum usitatissimum fibers with nano-reinforced organic plastics can improve properties while being environmentally friendly. The inclusion of aluminium tris hydroxide particles into an organic polymer enables it to maintain stiffness without sacrificing durability, even while improving barriers and material characteristics. A study of numerous composite samples verified this complementary effect, with combinations including 10 percent EMS and 2.6 wt.% ATH retaining the resin's stiffness, stress to breakage, and mechanical properties while improving durability. Mechanical tests such as tensile and impact strength were discovered using the conventional ASTM test plan. Best-practice designs which maximize constituent interactions are thus attainable, and the research findings serve as the basis for discovering this balance, thereby broadening the spectrum of microbiologically polymer nanocomposites. The cracked surfaces of the nanomaterials, and the amount of dispersion of an ATH filler, were examined using a scanning electron microscope. [ABSTRACT FROM AUTHOR]

The natural fibre-reinforced polymeric composites attract the manufacturing industries due to their recyclability, cost-effectiveness and eco-friendly nature. The natural hybrid reinforced polymeric (HNRP) composite overcomes the limitations in mechanical properties of the mono-natural fibre-reinforced composites. In this research work, the effect of barium sulphate ( BaSO 4 ) on the mechanical characterization of HNRP (aloevera/flax/barium sulphate) composites was examined as per ASTM standard. BaSO 4 is preferred as a filler based on the absence of self-motion, high density and high melting point (1580 ∘ C). The thermal stability of the HNRP composite was determined by thermogravimetric analysis (Model: TG/DTA 6200). The water absorption and dynamic mechanical properties of the HNRP composites were estimated. The fractography images were analysed to recognize the fractured surface morphology using a scanning electron microscope. The HNRP5 composite has the maximum tensile strength of 34.72 MPa, predominantly based on the interlocking of the flax fibre and plasticity of the composite improved by the influence of BaSO 4 . The impact strength decreased noticeably with the addition of barium sulphate in the composite. The weight reduction of around 7–9% was observed in the temperature range of 100–200 ∘ C. The mono-composites (HNRP1&2) absorbed, respectively, 4.8 and 3.5% of moisture; with the addition of BaSO 4 , the same combination absorbed 4.2 and 3.2% of water content, which was due to the low water absorption capability of BaSO 4 . The storage modulus of the HNRP5 composite has maximum magnitude in the glassy region and minimum in the rubber region. [ABSTRACT FROM AUTHOR]

Geopolymer composites reinforced with flax fabrics (FF) and nanoclay platelets are synthesised and studied in terms of physical and mechanical properties. X-Ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscope (SEM) techniques are used for phase and microstructure characterisation. The nanoclay platelets are added to reinforce the geopolymer matrices at 1.0%, 2.0%, and 3.0% by weight. It is found that 2.0 wt.% nanoclay enhances the density, decreases the porosity and subsequently improves the flexural strength and toughness. The microstructural analysis results indicate that the nanoclay behaves not only as a filler to improve the microstructure of the binder, but also as an activator to support the geopolymeric reaction producing higher content of geopolymer gel. This enhances the adhesion between geopolymer matrix and flax fibres, which improves the mechanical properties of the geopolymer nanocomposites reinforced with flax fabrics. [ABSTRACT FROM AUTHOR]

Despite their scarce resistance to humid or wet conditions, natural fiber reinforced composites (NFRCs) seem to be able to partially recover their performances under discontinuous exposition to marine environment. To investigate this peculiarity, flax fiber reinforced composite was at first subjected to salt-fog spray condition at 35 °C for 15 and 30 days, respectively, and then stored in "dry" condition (i.e., 50% R.H. and 22 °C) between 0 and 21 days. The performances evolution was evaluated through flexural tests, water uptake and contact angle measurements. Moreover, the morphology of fractured mechanical samples was examined by using 3D optical microscope and scanning electron microscope (SEM). Flax fiber reinforced composite experienced phenomena of both reversible and irreversible degradation during the wet phase thus evidencing a relevant mechanical recovery thanks to the drying. Quite interestingly, the laminate showed an almost complete recovery of the flexural strength, meaning that this property is more strictly related to mainly reversible aging phenomena whereas the greater stiffness loss is more probably due to irreversible ones. • Natural Fiber Reinforced Composites were aged under alternated salt-fog and dry steps. • Flexural tests, water uptake and water contact angle measurements were performed. • NFRCs experienced reversible and irreversible degradative phenomena. • Due to the drying, NFRCs showed an almost complete recovery of flexural strength. • A topological map discriminating reversible and irreversible aging zones was created. [ABSTRACT FROM AUTHOR]

Numerous artefacts from the area of textile production as well as finished products, fabrics and netting, dating from the period between 3900 and 800 b.c. have survived in the archaeological layers of late Neolithic and Bronze Age wetland settlements in eastern Switzerland. Archaeological investigations, experiments in textile technology and comparisons with Egyptian wall paintings, as well as analyses under the scanning electron microscope, allow us to almost completely reconstruct Neolithic textile production in prehistoric pile dwellings. [ABSTRACT FROM AUTHOR]

This study optimizes flexural properties of composites made from waste materials, corn stalk, seed flax and Agave americana fibres along with waste linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) matrices. The surface morphology of fibres and composites was characterized with light and scanning electron microscopes. Thermal behaviour of the corn stalk outer rings and pith parenchyma was shown using thermogravimetric analysis. There was no significant difference between the LLDPE composites made with corn stalk outer rings versus whole stalks, possibly due to an insignificant role played by parenchymatous part of the pith. Water retted seed flax fibres in LLDPE matrix optimized the composite flexural strengths at 6–8 days of retting, above which the properties declined. Field retted seed flax varieties in LLDPE matrix showed no significant differences in their flexural strengths. With additional fibre loading, flexural strength of A. americana HDPE composites first dropped before improving after extrusion, and only improved when using the layer method. [ABSTRACT FROM AUTHOR]

The study investigated the effectiveness of the combination of chemical and physical methods of natural fibers' modification. The long flax fibers were subjected to various types of modification. These were silanization, plasma modification and a combination of these methods. For the silanization process, two types of silanes were used: amino- and vinylsilane. The application of structurally different compounds allowed us to acquire knowledge about the effect of the modifier structure on its properties. Various properties of flax fibers were investigated, comparing the results before and after different modification processes. The flammability of prepared samples were tested by pyrolysis combustion flow calorimeter (PCFC). In the effect of the natural fibers' modifications, flammability was reduced even by 30%. The thermal stability of modified fibers increased. The FTIR tests of the gases released during thermal degradation of the tested fibers allowed us to determine the important compounds and prove a lower degree of flax-fiber decomposition after modification. Flax fibers were also tested to evaluate their physical properties (linear mass, average diameter, aspect ratio and hygroscopicity). Changes in surface morphology were observed by scanning electron microscope (SEM). The properties of natural fibers improved significantly, thus contributing to an increase in their suitability for the use in composites. [ABSTRACT FROM AUTHOR]

This study assessed the impact of alkali treatment of hemp and flax fibers on mechanical properties (determined by means of the uniaxial tensile test, impact tensile strength test and hardness test), processing properties (the course of the extrusion and injection process) and usable properties (shrinkage of molded pieces, degree of water absorption) of biocomposites on the base of poly (3-hydroxybutyric-co-3-hydroxyvaleric acid) (PHBV) biopolymer. For this purpose, 1 mm of length flax and hemp fibers was surface-modified by means of aqueous solution of NaOH (sodium hydroxide) with concentrations of 2%, 5% and 10%. The composites were made using the extrusion technology. The test specimens were produced by injection molding technology. In total, eight types of biocomposites with modified and non-modified fibers were produced, and each biocomposite contained the same filler content (15 wt.%). Their properties were compared in some cases with pure PHBV polymer. In the case of biocomposites filled with hemp fibers, it was noted that an increase of the alkalizing solution concentration improved most of the tested properties of the obtained biocomposites. On the other hand, in the case of flax fibers, there was a significant decrease in most of the mechanical properties tested for the composite containing fibers etched by 10% NaOH solution. The obtained results were verified by examining fibers and the destroyed specimens with a scanning electron microscope (SEM) and an optical microscope, which confirmed, especially, the significant geometry changes of the flax fibers etched by 10% NaOH solution. This procedure also resulted in a significant change of processing properties—a composite of this fiber type required about 20 °C lower temperature during the extrusion and injection molding process in order to obtain the right product. These results lead to the important conclusion that for each filler of the plant-origin and polymer matrix, the fiber alkalization method should be selected individually in order to improve the specific properties of biocomposites. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the effect of water absorption on the cutting behavior of biocomposites using flax fiber reinforced polylactic-acid (PLA) and the orthogonal cutting process. Different immersion times have been considered from 1 to 150 days in order to investigate both transient and saturated hygrometric regimes. Machining forces are measured during the cutting process and the machined surfaces are analyzed using a scanning electron microscope and an optical interferometer. The in-situ removed chip morphologies are captured by a high-speed camera. Results show a functional relationship between the multiscale hygro-mechanical properties of flax fiber composites and their shear mechanisms that are controlled by the water content. The water uptake modifies the cellulosic structure of natural flax fibers in the transient regime and damages the fiber/matrix interfaces in the saturated regime, which affects considerably the cutting mechanisms and the machinability of the biocomposite structure at different scale levels. • Flax fibers reinforced biocomposites are machined under different hygrometric conditions. • Chip morphology, cutting forces, and surface analysis are considered to investigate the machinability. • Cutting mechanisms differ when switching from transient to saturated hygrometric regime. • Cutting behavior of biocomposites is related to their multiscale hygro-mechanical properties. [ABSTRACT FROM AUTHOR]

The deformation behaviour of single elementary flax fibres was investigated in an ESEM, using a modified loop test. Plastic deformation starts on the compressive side of the loop, whereas fibre failure occurs on the tensile side of the loop. The primary and the secondary cell wall show a different deformation behaviour. The primary cell wall breaks in a brittle manner, whereas in the secondary cell wall, due to its fibrillar nature, a coarse crack grows, bridged by fibrils. The secondary cell wall was found to split relatively easily along the length direction, indicating that the lateral strength of the fibre is lower than its tensile strength, which also accounts for the lower compressive strength of the fibre compared to its tensile strength. [ABSTRACT FROM AUTHOR]

The goal of this paper is to evaluate the effectiveness of a cost-effective and eco-friendly treatment based on the use of sodium citrate (Na3C6H5O7) on the mechanical properties of flax fiber reinforced composites. To this scope, flax fibers were soaked in mildly alkaline solutions of the sodium salt at different weight concentration (i.e., 5%, 10% and 20%) for 120 h at 25 °C. The modifications on fibers surface induced by the proposed treatment were evaluated through Fourier transform infrared analysis (FTIR), whereas scanning electron microscope (SEM) and helium pycnometer were used to obtain useful information about composites morphology. The effect of the concentration of the treating solution on the mechanical response of composites was determined through quasi-static tensile and flexural tests, Charpy impact tests and dynamical mechanical thermal (DMTA) tests. The results revealed that composites reinforced with flax fibers treated in 10% solution exhibit the best mechanical performances as well as the lowest void contents. SEM analysis supported these findings showing that, by treating fibers in solutions with concentration up to 10%, composites having better morphology can be manufactured, in comparison to untreated ones. Conversely, higher Na3C6H5O7 concentrations negatively affect both the morphology and the mechanical properties of composites. [ABSTRACT FROM AUTHOR]

This work investigates the efficiency of sol–gel treatments to flame retard flax fabric/PA11 composites. Different sol–gel treatments applied to the flax fabrics were prepared using TEOS in combination with phosphorus and/or nitrogen containing co-precursors (DEPTES, APTES) or additives (OP1230, OP1311). When the nitrogen and the phosphorus co-precursors were used, two coating methods were studied: a 'one-pot' route and a successive layer deposition method. For the "one-pot" method, the three precursors (TEOS, DEPTES, and APTES) were mixed together in the same solutions whereas for the different layers deposition method, the three different treatments were deposited on the fibers successively, first the TEOS, then a mix of TEOS/DEPTES, and finally a mix of TEOS/APTES. After deposition, the sol–gel coatings were characterized using scanning electron microscope, electron probe microanalyzer, and 29Si and 31P solid-state NMR. When only TEOS or a mix of TEOS and DEPTES is used, homogeneous coatings are obtained presenting well-condensed Si units (mainly Q units). When APTES is added, the coatings are less homogenous and agglomerates are present. A lower condensation rate of the Si network is also noticed by solid-state NMR. When additives are used in combination with TEOS, the TEOS forms a homogenous and continuous film at the surface of the fibers, but the flame retardants are not well distributed and form aggregates. The flame retardant (FR) efficiency of the different treatments on flax fabrics was evaluated using horizontal flame spread test. The following ranking of the different systems is obtained: TEOS + Additives > TEOS > TEOS + DEPTES ~ TEOS + DEPTES + APTES > multilayers. All the sol–gel coatings improve the flame retardant properties of the flax fabric, except the multilayer treatment. Based on these results, the three most efficient sol–gels were selected to prepare sol–gel-modified flax/PA11 composites. The composite modified with only TEOS showed the best FR properties. Surprisingly, the composite modified with the phosphorus-based flame retardant (AlPi) did not exhibit improved FR properties. This effect was attributed to the fact that the amount of the FR additive deposited on the fabrics was too low. [ABSTRACT FROM AUTHOR]