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Hemp fibers derived from Cannabis sativa L. have experienced a resurgence in popularity over the past few decades, establishing themselves as one of the most sought-after fibers. This article delves into the intricacies of the hemp production chain, offering a comprehensive understanding from field to fiber. Key aspects covered include the botany of hemp, cultivation requirements, the impact of various factors on plant growth, the harvesting process, different methods of fiber extraction, fibers properties, and suitable spinning processes. Recent studies of hemp's Life Cycle Assessment are explored, shedding light on how it compares to other sustainable crops and providing insights into the true sustainability of hemp, substantiated by numerical data. The article also addresses challenges encountered throughout the hemp production chain and speculates on future directions that may unfold in the coming years. The overall goal of this study is to provide a knowledge base encompassing every facet of hemp fiber production. It elucidates how different technological approaches and the technical properties of fibers play pivotal roles in determining their ultimate applications. By offering a comprehensive overview, this article contributes to the broader understanding of hemp as a valuable and sustainable resource in the textile industry. [ABSTRACT FROM AUTHOR]

Sticky rice–lime mortar, a representative ancient binding material widely employed in construction applications across Asian countries, has been a subject of substantial academic research and development efforts for its restoration. However, conventional sticky rice–lime mortar is characterized by suboptimal strength and limited toughness, necessitating further enhancements to expand its practical utility. This study presents the formulation of a high-performance sticky rice–lime mortar by incorporating metakaolin and hemp fibers. A comprehensive investigation of various parameters influencing the compressive and flexural properties of the resulting composite was undertaken, encompassing the volume content of hemp fibers, the mass content of sticky rice paste, and the mass content of metakaolin. The experimental outcomes demonstrate the efficacy of metakaolin and sticky rice paste in significantly elevating the compressive strength of the sticky rice–lime composite. Notably, the presented sticky rice–lime mortar attains a remarkable compressive strength of up to 3.5 MPa, exceeding that of conventional sticky rice–lime mortar by more than threefold. Moreover, the introduction of hemp fibers effectively enhances the flexural strength of the sticky rice–lime composite through fiber bridging mechanisms. The research culminates by proposing a relationship equation, derived from the empirical data, to characterize the compressive and flexural strength of the high-performance sticky rice–lime composite. Overall, these findings emphasize the importance of optimizing sticky rice–lime mortar through the integration of advanced constituents, thus highlighting its potential as a durable and versatile binding material for historical preservation and sustainable construction practices within Asian contexts and beyond. [ABSTRACT FROM AUTHOR]

NAO brake friction materials with 4%, 5%, and 6% (w/v) sodium hydroxide treated hemp fiber reinforcement having 25% wt. fiber loading and fixed percentage of phenol formaldehyde resin content (20% wt.) along with other fillers have been studied and reported by the authors earlier. However, the effect of variations in the resin content on the tribological performance has been studied and reported in the present paper. Five variants were prepared with varying percentages of phenol formaldehyde resin from 12% wt. to 22% wt. with incremental steps of 2% wt, along with the optimum of 6% (w/v) sodium hydroxide treated hemp fibers and other fillers. The prepared test variants' tribological characterization was done using Taguchi's L25 orthogonal array on a pin-on-disc experimental setup, as per ASTM G99, at room temperature and compared with the best of the earlier studied friction composite. Fade and recovery tests of the best of the earlier studied and present ones were performed on a chase tribology tester per SAE J661 standards. The results revealed moderate coefficient of friction of 0.4496, lower wear rate of 0.57 gm, and better fade recovery for the HF25P20 variant compared to its counterparts studied here. [ABSTRACT FROM AUTHOR]

As a sustainable concrete material, hemp and recycled aggregate concrete (HRAC) is produced by partial replacement of natural coarse aggregates (NCA) with recycled concrete coarse aggregates (RCA) and industrial hemp fibers. The objective of the reported research was to investigate the structural performance of reinforced concrete beams prepared with HRAC and designed to fail in flexure, shear, or bond splitting modes of failure, and to compare that performance with companion control beams cast with conventional concrete. The significance stems for the fact that no previous research is reported on mixtures using such a combination of hemp fibers and RCA. Test results indicated that HRAC beams with 0.75% volumetric percentage hemp fibers and 50% RCA replacement had comparable peak load capacities to the control beams with no RCA and no fibers, with ±4% difference for all tested modes of failure. Additionally, the fracture energy of the HRAC beam was higher than the control beam by 3.6%, 17.9%, and 14.4% for the flexure, shear, and bond modes of failure, respectively. Moreover, a life cycle analysis (LCA) was considered to compare HRAC mix with conventional concrete mix in terms of the environmental aspects. LCA results indicated that HRAC is a sustainable concrete, specifically with respect to structural performance and lower environmental impact. [ABSTRACT FROM AUTHOR]

A significant increase in the consumption of recycled fiber products has been observed worldwide, and the industry is forced to solve the challenges of recycled fiber quality and add strength agents and/or virgin fibers to reach sufficient properties. In order to investigate whether the mechanical and air permeability properties of waste fiber (WF) material can be significantly improved by adding wood kraft fibers (KF), hemp soda fibers (HF), and ammonium persulfate oxidated cellulose nanofibrils (CNF), different fiber blends were prepared and tested. Results revealed the excellence of hemp fibers over wood fibers regarding the improvement of WF products. The results of WF after the addition of 10% mixed fibers (KF + HF) were higher than the results of a 50% KF addition. The impact of CNF depended on fiber composition and properties. A formula for modeling the CNF impact on different fiber compositions was proposed. Obtained fiber material samples showed suitability for home composting, thus contributing to the goals of the European Green Deal regarding reducing landfill waste and the development of cleaner products. [ABSTRACT FROM AUTHOR]

This article investigates the effects of combining a novel protic ionic liquid-based fire retardant (FR) with alkalized hemp fiber. A pivotal importance of this study refers to the hydrophilic properties and limits regarding poor thermal resistance of green composites where standard guidelines for fire risks are crucial. Although it is well-studied that alkalization is essential for green composite's moisture and mechanical durability, research on the flammability of such a combined treatment for natural fiber-reinforced biopolymer composites is lacking. The alkaline treatment used in the current study follows a process already studied as optimal, particularly for the selected hemp fiber. The fire performance was examined using a bench scale approach based on self and piloted ignition from cone calorimeter tests. The result from the Fourier-transform infrared analysis of the hemp fiber confirms phosphorylation following the fire-retardant treatment, which was visible from the morphological examination with scanning electron microscope. The presence of FR in the composites led to impactful moisture sorption. However, the FR composites demonstrated an enhanced response to fire, indicating potential use as a Class B standard for building construction, and hazard level 3 (HL3) classification as an interior material in vehicles, provided the problem of high emission of smoke is mitigated. [ABSTRACT FROM AUTHOR]

Hemp is finding a strong renewal of interest in the production of fine fibers for garment textiles. This resource of long-line fibers would come as a complement to the highly demanded flax fibers, whose large production in the north-west of Europe cannot be extended. In Normandy, where a complete industrial value chain exists for flax, it is intended to adapt it to hemp, and this was demonstrated from the field to the scutched fibers with a complete value chain. In this region, early harvesting is necessary to leave enough time for dew-retting and permit dry storage of stems before mid-September. An early-flowering variety (USO-31) was harvested using dedicated hemp equipment to obtain a 1 m parallel and aligned windrow that can be further processed by flax equipment. The scutching process as well as the fiber's morphological and mechanical properties were particularly studied. Adapted scutching process parameters with reduced advancing speed and beating turbine velocity led to long fiber yields of about 18% of the stem mass. Stem yields were reaching about 6 tons/ha leading to a production of 1.1 tons/ha of long fibers. The tensile properties of the long fibers were highly sufficient for textile applications, and their thickness after hackling was in the range suitable for the production of fine yarns. Compared to other crops grown in Normandy, the hemp as produced in this 2020 case study provides good incomes to the farmer, higher than traditional crops such as wheat or barley, and the results of this study should encourage farmers to grow hemp for textile purposes. [ABSTRACT FROM AUTHOR]

Integrating bio‐resources in materials allows to reduce the environmental impact of the building industry. This study deals with fire‐retardant treatments, alternative to boric acid and ammonium salts solutions, applied to hemp fibers for thermal insulation application. The aim is to limit the energy, sanitary and environmental impacts of the treatment, while optimizing the technical performances. A laboratory protocol evaluates the flame‐retardant effect of the developed treatments. Treated fibers, including commercial treatments, are subjected to characterization tests: direct ignition small flame, thermal analysis (thermogravimetric analysis [TGA], differential thermal analysis [DTA]), pyrolysis‐combustion flow calorimeter and cone calorimeter. Some of the methods have been adapted to be applied to fibrous materials. The obtained results orientate the formulation of a treatment and highlight the complementarity of the analysis methods. Coupling the results, the ConeTools's predictive model leads to the estimation of the reaction to fire class according to the Euroclass. Euroclass C appears accessible with a tailored treatment. [ABSTRACT FROM AUTHOR]

Natural fibers-reinforced polymer composites have progressed rapidly due to their undeniable advantages. Most of the commercial polypropylene (PP)-based materials are characterized by either high impact toughness or high stiffness, while the manufacture of PP composites with both good toughness and stiffness is challenging at present. In this work, poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) and poly(styrene-b-butadiene-b-styrene) (SBS) copolymers were used in different amounts as modifiers in PP/hemp fibers (HF) composites, with the aim to use them for electrical vehicle parts. The interface in these multiphase systems was controlled by the addition of maleated polypropylene (MAPP). SEBS and SBS showed different effects on the elongation at break of the blends and the corresponding composites due to the HF that stiffened the multiphase systems. Similarly, a different action of MAPP was observed in the composites containing SEBS or SBS: higher Young's and storage moduli were obtained for the composite containing SBS, while greater elongation at break and impact strength values were recorded for the SEBS-containing system. In addition, a remarkable dispersion in the MAPP-containing composite and two times smaller average particle size were revealed by the SEM analysis for the SEBS particles compared to the SBS ones. The higher affinity of SEBS for PP compared to that for SBS and the different morphological characteristics of the systems containing SEBS and SBS may explain the different effects of these impact modifiers on the mechanical properties of the composites. The composites developed in this work were designed as substitutes for the fully synthetic polymeric materials or metal components used in the manufacturing of automotive parts. [ABSTRACT FROM AUTHOR]

Hemicellulose and lignin were progressively removed from hemp fiber by hydrolysis. SEM, FTIR, XRD analysis and tensile properties evaluation on technical fibers were carried out to understand the structural and mechanical properties of hemp fibers. Significant influence of hemicellulose and lignin content on tensile properties was verified by ANOVA. The fiber tensile strength and initial modulus were decreased with the extensive removal of hemicellulose, along with a constant increasing of elongation at rupture. Torsion and expansion were observed in hemp fibers. It was suggested that the internal structure destruction and reorganization in the ultimate fiber cells was the main reason for the variation of mechanical properties when hemicellulose was gradually dissolved. On the other hand, fiber individualization was achieved by lignin removal and contributed to the elevation of fiber tensile properties. The elongation at break of the hemp fibers decreased slightly with the removal of lignin. NaClO2 solution treatment affected the fiber cells slightly, but effectively changed the properties of the middle lamella jointing between the ultimate fiber cells. The mechanical properties of the hemp fiber were mainly decided by the shearing between single fibers caused by the plastic-like deformation of the middle lamella. [ABSTRACT FROM AUTHOR]

Motivated by green building applications (bio-composite and insulation materials), thermogravimetric and kinetic analysis is applied to investigate the thermal degradation of cleaned hemp fibers (F), obtained after water retting and mechanical decortication of dioecious plant stalks, and technical fiber (TF), obtained after field retting of monoecious plant stalks. Celluloses (microcrystalline PH105 cellulose and cotton linter cellulose) are used for comparison. F and TF dynamic curves are well described by a four-step scheme. The dominant one concerns pseudo-cellulose decomposition with the release of 70 and 54 mass% volatile matter, respectively. The corresponding activation energies are in the range of typical cellulose values (223 and 211 KJ mol−1). Fiber pretreatments (water washing, mild torrefaction, mercerization) modify the pseudo-cellulose content (release of 73–80 mass% volatile matter) and properties, as testified by the higher activation energies (229–248 kJ mol−1) of the decomposition process. The decortication method also contributes remarkably to the characteristics of the fiber cellulose. [ABSTRACT FROM AUTHOR]

The current development of " Cannabis sativa L." hemp fibers for technical textiles and biocomposites demands through consideration of the retting process's effect on fiber quality. Field retting, though crucial, remains insufficiently managed due to its reliance on empirical methods and dependence to weather conditions. This study aims to improve the understanding of the retting process in the case of the "Futura 75" hemp stems harvested at the end of the flowering period and retted in southern France, which is characterized by a dry Mediterranean climate. Various analyses were performed, including color evolution, morphological (optical microscopy), surface (SEM), biological (density of bacterial and fungal community using qPCR approach), and biochemical (solvent extraction and spectro-colorimetry) analyses. The results showed that retting had a major impact on the chemical composition of the fibers, resulting in a significant loss of pectic substances. This result correlated with microscopic observations, which showed the decohesion of fiber bundles during retting. Since an increase in cellulose proportion was observed, this was associated with both the degradation of the non-cellulosic components and an increase in cellulose crystallinity. A color change from green to black during retting, mainly due to microbial colonization was also observed. This result was further supported by the qPCR results, which indicated an increasing presence of bacterial and fungal populations on the hemp stems during the retting process. All the obtained results are statistically analyzed to identify correlations that, in the long term, could eventually lead to the identification of simple indicators to better control the field retting of hemp and obtain stable fiber properties. The statistical findings suggest correlations between variables related to microbial community, pectin degradation, and climatic data throughout the retting process. • Hemp field retting successfully achieved in a Mediterranean climate. • Retting significantly impacts the physico- and bio-chemical hemp fibres properties. • Microbial colonization promotes fibre bundle decohesion during retting. • Statistical analysis reveals links among microbial, chemical, and climatic factors. [ABSTRACT FROM AUTHOR]

The process of obtaining of microcrystalline cellulose from hemp fibers using alkali extraction, peracetic cooking, chelation and hydrolysis was studied. It was determined that the application of the proposed technology allowed to obtain microcrystalline cellulose from hemp fibers, that meets the requirements of the European Pharmacopoeia. The resulting product is recommended as a filler in the manufacturing of solid dosage forms, or as a stabilizer and an emulsifier in cosmetics industry. [ABSTRACT FROM AUTHOR]

In this research work, the effects of sodium carbonate and hydrogen peroxide treatment of hemp fiber on the water absorption, mechanical, and tribological properties of hemp fiber reinforced epoxy composites (HFREC) were investigated. The change in surface roughness and fiber size after chemical treatment was confirmed by the scanning electron microscopy (SEM) images. Fourier transform infrared analysis confirmed the removal of hemicellulose and lignin content of the fiber after both the chemical treatment. X‐ray diffraction analysis showed an increase in the crystallinity index of the chemically treated fiber. The experimental results also revealed that both sodium carbonate and peroxide modification have resulted in enhancement of water resistance and mechanical properties such as tensile strength and tensile modulus and reduction in impact properties of treated HFREC. Tribological test results revealed that the treated HFREC have improved wear and frictional properties in comparison with untreated HFREC. The best tribological and mechanical properties were exhibited by peroxide treated HFREC, which was also confirmed through the SEM images of worn and fractured surfaces of the composites. [ABSTRACT FROM AUTHOR]

Hemp fiber has excellent performance as a renewable fiber material. It is of great significance to study more efficient, energy-saving and environmentally friendly pre-treatment methods of hemp textiles. A novel hemp fiber scouring method based on electrochemical techniques was presented in the research. A type of water solution with high and stable oxidative potential due to in-situ- generated oxidative components was produced by the proposed electrical method, and was applied to scouring treatment of raw hemp fibers by just soaking the fibers in it. Hemp fibers with different treatments were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction, and residual gum rate, lignin content and whiteness of the samples were tested. Experiment results show that electrochemical scouring has a similar degumming effect of hemp fibers compared with traditional chemical scouring, with a better lignin removal and whiteness, implying an effective and short process method of hemp textiles pre-treatment with low impact on the environment. [ABSTRACT FROM AUTHOR]

The need for the development of new biodegradable materials and modification of the properties the current ones possess has essentially increased in recent years. The aim of this study was the comparison of changes occurring in poly(ε-caprolactone) (PCL) due to its modification by high-energy electron beam derived from a linear electron accelerator, as well as the addition of natural fibers in the form of cut hemp fibers. Changes to the fibers structure in the obtained composites and the geometrical surface structure of sample fractures with the use of scanning electron microscopy were investigated. Moreover, the mechanical properties were examined, including tensile strength, elongation at break, flexural modulus and impact strength of the modified PCL. It was found that PCL, modified with hemp fibers and/or electron radiation, exhibited enhanced flexural modulus but the elongation at break and impact strength decreased. Depending on the electron radiation dose and the hemp fibers content, tensile strength decreased or increased. It was also found that hemp fibers caused greater changes to the mechanical properties of PCL than electron radiation. The prepared composites exhibited uniform distribution of the dispersed phase in the polymer matrix and adequate adhesion at the interface between the two components. [ABSTRACT FROM AUTHOR]

The raw materials features, product development ideas and spinning technology of Australian wool/hemp/cashmere 60/30/10 knitted yarns (19.2 texx2) were characterized in this paper. The fabric blended with hemp fiber, Australian wool and cashmere blended woven fabric have natural antibacterial function. In order to meet consumers' requirements on antibacterial fabrics, it is necessary to improve the antibacterial ability of yarns. Antibacterial finishing of Australian wool and cashmere fibers with green antibacterial agent can improve the antibacterial ability of Australian wool / hemp / cashmere blended fabric against candida albicans from 93% to 98%. The semi-worsted process was used to optimize each process, which solved the issue of the difference between the suitable spinning process of hemp fiber and Australian wool and cashmere fiber. The product is bright in color, with comfortable and warmth of wool, fresh and breathable of hemp, smooth of cashmere. [ABSTRACT FROM AUTHOR]

In the paper are analysed the results of experimental test effectuated on concrete prepared with fly ash and hemp fibers as disperse reinforcement. The density and compressive strength of fly ash concrete were determined and analysed. As practical application the fly ash concrete was used to manufacture hollow concrete blocks which were tested in compression. The compressive strength and type of failure of blocks under compression were presented. [ABSTRACT FROM AUTHOR]

This study investigated the use of hemp fibers for improving the fire resistance of concrete. The characterization of the fibers was carried out through SEM, TGA/DSC, FTIR and crystallinity index. A reference concrete mixture, polypropylene fibers mixture, and four mixtures with different chemically treated hemp fibers were prepared. The concrete specimens were heated to 400 °C and cooled. Their compressive strength, static modulus of elasticity, residual weight, and residual ultrasonic pulse velocity were then determined and compared. The addition of fibers did not significantly influence the fire resistance of the concrete in terms of the residual properties. Visual observations from scanning electron microscope and microimages of the concrete mixtures showed that the hemp fibers were partially disintegrated within the concrete after being heated; thus, the incompletely disintegrated hemp fibers could reduce crack propagation at high temperatures thus improving the fire resistance of concrete. [ABSTRACT FROM AUTHOR]

Fine hemp fibers (cottonized hemp) were processed using steam explosion. The quantification of the defibration rate was performed by image processing. Based on this method, the hemp defibration was optimized using a response surface methodology based on three-variable central composite design for the production of elementary fibers with low variability. Optimal parameters for the steam processes were as follows: time = 4.1 min; temperature = 191℃. Biomass was impregnated with a solution of NaOH (8%) before treatment, leading to a defibration rate of 91.2%, which is producing ≈50% fibers with length <3 mm, in good agreement with the experimental data. Damaged fibers originating from the conjugated effect of steam explosion and alkali hydrolysis were also observed. [ABSTRACT FROM AUTHOR]

Natural Fibers Reinforced Composites (NFRC) are finding much interest as a substitute for glass or carbon reinforced polymer composites, like for instance automobile interior linings (roof, rear wall, side panel lining), shipping pallets, construction products (i.e. composite roof tiles), furniture and household products (i.e. storage containers, window and picture frames as well as food service trays, toys and flower pots) as well as fan houses and blades. However, a notable disadvantage of lignocellulosic fibers as reinforcements is their polarity which makes it incompatible with hydrophobic thermoplastic matrix. This incompatibility results in poor interfacial bonding between the fibers and the matrix. This in turn leads to impaired mechanical properties of the composites. This defect can be remedied by chemical modification of fibers so as to make it less hydrophilic. In this paper experiments have been performed to further the development of natural fiber reinforced composites. Untreated and treated surfaces of hemp fibers were characterized using Fourier Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM). Fiber-matrix adhesion was promoted by fiber surface modifications using an alkaline treatment and (3-Glycidyloxypropyl) trimethoxysilane coupling agent. The mechanical behaviour of epoxy matrix composite reinforced with woven hemp was studied and mechanical test results show that silane treatment of hemp fibers improves, both tensile and flexural properties of the composites, although no high values are obtained. [ABSTRACT FROM AUTHOR]

In this study, the effect of fiber content, fiber length and alkali treatment on mechanical properties of hemp fiber and thermoplastic polyurethane (TPU) composite were investigated. It focused on the correlative effect of rigid hemp fiber and elastomeric polyurethane on tensile and flexural properties. Furthermore, the stress-strain behavior and the fracture analysis of the composite were discussed. To evaluate the influence of fiber length, three different lengths according to critical fiber length were chosen and examined. Interlaminar shear strength (ILSS) test, Fourier transfer infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were conducted to understand the effect of fiber treatment on fiber-matrix interactions and fiber contents. Results presented that by increasing fiber volume content to 40%, flexural strength enhanced 193.24%. Additionally, 15 mm hemp fiber was found to be the optimum fiber length, where flexural strength at 40% fiber volume was further increased to 274.3%. ILSS tests of treated and untreated hemp fibers showed slight difference. However, FTIR spectra, XRD analysis and Scanning Electron Microscopy micrographs indicated the extraction of non-cellulosic materials from the surface in treated fibers, without altering the cellulose structure. It was found that, there are possibilities to balance the flexural properties and tensile properties by hemp fiber and TPU which is not achievable by glass fibers. [ABSTRACT FROM AUTHOR]

Waste hemp (Cannabis sativa) fibers were used as sustainable and renewable raw materials for production of low-cost biocarbon sorbent for heavy metals removal. Carbon precursors of different chemical composition were obtained by oxidative and alkaline treatments of hemp fibers. Influence of lignocellulosic precursor chemical composition on hemp fibers-based biocarbon (HFB) characteristics was examined by BET surface area measurement, scanning electron microscopy and mass titration. It was found that lignin content and polymorphic transformation of cellulose increase the SBET of microporous HFBs, while hemicelluloses induce more homogeneous distribution of adsorption active sites. Heavy metal ions adsorption onto HFBs is primarily influenced by the amount of surface oxygen groups, while specific surface area plays a secondary role. Equilibrium data obtained for lead ions adsorption were analyzed by different nonlinear adsorption isotherms, and the best fitting model was chosen using standard deviation and Akaike information criterion (AICC). The maximum adsorption capacities of HFBs ranged from 103.1 to 116.3 mg Pb/g. Thermodynamic parameters showed that Pb2+ adsorption onto HFBs is a spontaneous and complex endothermic process, suggesting the coexistence of physisorption and chemisorption mechanisms.Waste hemp (Cannabis sativa) fibers were used as sustainable and renewable raw materials for production of low-cost biocarbon sorbent for heavy metals removal. Carbon precursors of different chemical composition were obtained by oxidative and alkaline treatments of hemp fibers. Influence of lignocellulosic precursor chemical composition on hemp fibers-based biocarbon (HFB) characteristics was examined by BET surface area measurement, scanning electron microscopy and mass titration. It was found that lignin content and polymorphic transformation of cellulose increase the SBET of microporous HFBs, while hemicelluloses induce more homogeneous distribution of adsorption active sites. Heavy metal ions adsorption onto HFBs is primarily influenced by the amount of surface oxygen groups, while specific surface area plays a secondary role. Equilibrium data obtained for lead ions adsorption were analyzed by different nonlinear adsorption isotherms, and the best fitting model was chosen using standard deviation and Akaike information criterion (AICC). The maximum adsorption capacities of HFBs ranged from 103.1 to 116.3 mg Pb/g. Thermodynamic parameters showed that Pb2+ adsorption onto HFBs is a spontaneous and complex endothermic process, suggesting the coexistence of physisorption and chemisorption mechanisms. [ABSTRACT FROM AUTHOR]

In this research hemp fibres have been modified by the sol-gel method in different combinations to implement silica nanolevel coating on fibres surface without compromising the mechanical properties of the fibres and ensure sustainable coverage to achieve matrix-filler compatibility in composite as filler. The coatings of samples prepared using different proportions of nano-sols. The fibres were immersed in the prepared sols made of ethanol, tetraethyl orthosilicate (TEOS), distilled water and hydrofluoric acid. Scanning electron microscopy (SEM) has been used to examine the nature of the surface modification. Energy dispersive X-ray (EDX) analysis was used for chemical composition analysis on coated fibres surface. Analyses based on the SEM show that small sol components proportion differences significantly affect coating adhesion. [ABSTRACT FROM AUTHOR]

Experimental and numerical studies of sustainable sandwich bio-composites were presented. The bio-composites were developed using plant-based materials. The laminated face sheets comprised woven hemp fabric and a tree sap–based epoxy, while the core comprised castor oil-based polyurethane foam reinforced with waste rice hulls ashes. Uniaxial compression, tension, and three-point flexural bending tests were performed. Finite element models were developed. Good agreements between experimental and numerically simulated flexural responses were found. From numerical simulation results, the sandwich bio-composites were found to be a structurally acceptable replacement for standard gypsum drywall. Further experimental works are needed to validate the applications. [ABSTRACT FROM AUTHOR]

To discuss the influence of different activation and microdissolve methods for the tensile properties of hemp/cotton blended yarns. The steps are as follows, treated fabrics and hemp fibers with pretreatment and LiCl/DMAc microdissolution, fibers were analyzed by FT-IR and XRD methods, tensile properties of yarns were tested by Instron. The result shows that the main groups have no obvious changes in fibers, cellulose derivative reaction has not been found during microdissolution. The yarns’ breaking force increases and elongation decreases in different degrees except craft one, the greatest increase of the breaking force of treated yarns reached 46.4%. [ABSTRACT FROM AUTHOR]

Hemp fiber-reinforced unsaturated polyester (UPE) composites were prepared by hand lay-up compression molding. The UPE resins were modified with butyl methacrylate (BMA) to improve the flexibility and toughness of the hemp-UPE composites. The results indicate that the toughness of the composites significantly increased as BMA usage increased. Compared to the unmodified UPE composites, the composites obtained from BMA-modified UPE resins had 27.4, 63.0, and 36.6% greater elongation at break, flexural strain, and impact strength, respectively. The optimum BMA usage to achieve an adequate balance of stiffness and toughness is 20 to 30%. Dynamic mechanical analysis (DMA) indicated that incorporation of BMA significantly decreased the storage modulus and glass transition temperature of the composites and increased its damping parameter due to the introduction of flexible segments into the UPE resins. Thermogravimetric analysis showed that the thermal stability of the composites decreased slightly following the incorporation of BMA. Scanning electron microscopy images of the impact-fractured surfaces of the composites revealed that BMA incorporation improved interfacial adhesion between hemp fibers and UPE matrices and that the main mechanism for the increase in the toughness of the composites was the added ductility of the matrices. [ABSTRACT FROM AUTHOR]

Simultaneous influence of polypropylene-graft-maleic anhydride (MAPP) and silane-treated hemp fibers (HF) on morphology, thermal and mechanical properties of high-flow polypropylene (PP) modified with poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) was studied in this paper. The addition of SEBS reduced the efficiency of MAPP in PP composites with HF, thus silane-treated fibers (HFs) were used to improve polymer–fiber interface. Thermal stability of HF was improved after silane treatment and less than 2% weight loss was observed at 240 °C in composites with 30 wt% HF. Better dispersion of fibers and better efficiency in enhancing static and dynamic mechanical properties of PP, doubling its strength and stiffness were observed in composites with treated fibers compared to untreated ones. High ability to absorb and dissipate energy and well-balanced strength and stiffness were showed by PP modified with SEBS and MAPP containing 30 wt% HFs. These composites were studied as an alternative to conventional PP/glass fibers composites for injection molding of small to medium auto parts. [ABSTRACT FROM AUTHOR]

Hemp cultivation is one of the possibilities to use agricultural land of Latvia. Mechanical and physical properties of hemp fiber and its chemical structure is suitable for using as a reinforcement, but polypropilene (PP) fibers and PolyLactic Acid (PLA) fibers as a matrix for bio-composites. Compression molding is the most common composite processing technology. Composites with the content of 20 % - 40% of natural fiber could provide optimal mechanical properties. The demand for bio-composites with improved properties will be increasing in the future. Sandwich structure of bio-composite is one of the ways to protect natural fiber from heating degradation. [ABSTRACT FROM AUTHOR]

Hemp fibers were modified with 3-isopropenyl-dimethylbenzyl isocyanate (TMI), in presence of dibutyltin dilaurate (DBT) as a catalyst. Then reinforced hemp-unsaturated polyester (UPE) composites were prepared with modified fibers by means of hand lay-up compression molding. The fiber treatments significantly increased the tensile strength (TS), flexural strength (FS), and water resistance of the resulting composites, while their flexural modulus (FM) was not influenced. The tensile-fractured surfaces of the composites were observed by SEM and the images revealed that fiber treatments significantly improved the interfacial adhesion between hemp fibers and UPE resins. FT-IR spectra and X-ray photoelectron spectroscopy (XPS) analysis indicated that the treated-fibers were partly covalently bound to TMI. [ABSTRACT FROM AUTHOR]

• A layer by layer approach was used to produce composites based on hemp fiberboards. • The influence of the number of layers on physical properties was investigated. • A decrease in burning rate were observed in samples treated with cloisite. • A mechanism concerning the flame retardancy was proposed. The paper presents a hybrid and smart methodology, using the layer-by-layer approach, to produce high performant multi-layered composites based on hemp fiberboards with improved physical properties. The effect of an inorganic component, such as a natural clay, and the surface covering with an organic compound, such as stearic acid, was investigated through the analysis of morphological, spectroscopic, thermal, mechanical and barrier properties of the composites. Vertical burning test confirmed the improvement in flame retardancy of layered composites since the presence of clay. The oil adsorption capacity was evaluated and correlated to the number of clay layers. Finally, a possible mechanism of combustion was proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

In past studies, industrial hemp (Cannabis sativa L.) has been shown to tolerate stress from heavy metals and to accumulate the metals in its tissues. Nonetheless, up to now, it remained unclear whether hemp grown on contaminated soil could be safely used in the textile industry and integrate a phytoattenuation strategy. A growth experiment was set up to screen 6 hemp cultivars for their ability to take up heavy metals in the different plant parts when grown on soil contaminated with Cd, Pb, and Zn. The potential safe use of the produced biomass in comparison to industrial quality guidelines, especially the fibers, was analyzed. Plant tissues show different patterns of Cd, Pb, and Zn uptake and it could not be stated that one plant part accumulates a higher amount of all elements compared to the others. While Pb and Zn concentrations followed the trend leaves>shives>fibers, Cd was mostly concentrated in the fibers. The lowest concentrations in fibers were found in the early cultivars USO 31 and Bialobrezskie respectively for Cd (0.59 ± 0.15 mg/kg) and Pb (1.6 ± 0.7 mg/kg), and in the semi-late cultivar Dacia Secuieni for Zn (7.2 ± 1.4 mg/kg). The late cultivar Carmagnola Selected displayed the highest concentrations for Cd (1.7 ± 0.5 mg/kg) and Zn (13 ± 2 mg/kg), as the early cultivar USO 31 did for Pb (11 ± 1 mg/kg). Nevertheless, both Cd and Pb concentrations in the fibers were far below the heavy metal thresholds for textile product safety in all cultivars, while Zn is not considered toxic in textile production. In addition, low Pb, Cd, and Zn concentrations in the shives suggest the potential safe use of this residual fraction of hemp fiber production as well. These results are promising in terms of safe use of the produced hemp fibers in the textile industry and thus of the potential valorization of contaminated land through hemp cultivation and the development of non-food value chains within a phytoattenuation strategy. [Display omitted] • Bioconcentration factor below 1 shows that industrial hemp is no hyperaccumulator. • Metal uptake in the fibers differs depending on the heavy metal and hemp variety. • Zn concentrations in contaminated and control fibers are similar. • Cd and Pb concentrations are significantly higher in contaminated fibers. • Cd and Pb concentrations in the fibers are far below toxicity limits for textiles. [ABSTRACT FROM AUTHOR]

Highlights: [•] We investigate the mechanical properties of hemp fibers (Fedora 17 variety). [•] Significant differences of morphology were highlighted. [•] Biochemical analysis evidences, comparing with flax fiber, important differences for the nonstructural and matrix pectins distribution and quantity. [•] Nanoindentation investigations show that, no matter the location in the stem, the mechanical properties of the S2 layer were similar. [•] X-ray diffraction analysis highlights the presence of a significant amorphous matrix polymer rate. [Copyright &y& Elsevier]

Hemp fibers--reinforced unsaturated polyester (UP) composites were prepared by hand lay-out compression molding. Hemp fibers were treated with isocyanatoethyl methacrylate (IEM), using dibutyltin dilaurate as a catalyst. The results indicated that fiber treatment significantly increased tensile strength, flexural strength, flexural modulus, and water resistance of the resulting composites, and yet decreased the impact strength of the composites. The water absorption characteristics for composite samples immersed in water at room temperature followed Fickian behaviour, but for those evaluated at temperature 100 °C, there was a deviation from Fickian behaviour. Scanning electron microscope graphs of the tensile-fractured surface of hemp-UP composites revealed that fiber treatment with IEM greatly improved the interfacial adhesion between hemp fibers and UP resins. Fourier transform infrared analysis of the treated fibers showed that some IEM was covalently bonded onto hemp fibers. [ABSTRACT FROM AUTHOR]

The application of hemp fibers as a reinforcement of composite materials necessitates the characterization of fiber strength scatter and the effect of fiber length on its strength. With this aim, elementary hemp fibers were tested in tension at two different gage lengths. Due to the similar morphology of hemp and flax fibers, the probabilistic strength models derived and verified for the latter were applied to the former. The fiber strength was found to agree with the modified Weibull distribution. The modeling approaches developed for describing the variability of the strength and failure strain of elementary flax fibers are shown to be also applicable to hemp fibers. [ABSTRACT FROM AUTHOR]

In this study, antimicrobial silver-loaded hemp fibers were prepared by selective TEMPO-mediated oxidation, i.e., oxidation with sodium hypochlorite, catalytic amount of sodium bromide and the 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO), followed by silver sorption from aqueous silver nitrate solution. The most suitable experimental conditions for the selective TEMPO-mediated oxidation were determined by changing the oxidation conditions, i.e., the concentration of sodium hypochlorite and the duration of oxidation. The obtained results showed that the maximum sorption capacity of 0.703 mmol of silver per gram of modified hemp fibers was obtained for the sample oxidized with 9.67 mmol NaClO per gram of fibers for 4 h. SEM Microphotographs of the modified hemp fibers with incorporated silver showed uniformly distributed silver particles on the surface of fibers, with isometric shapes and sizes from 10 to 100 nm, despite the fact that silver was sorbed from an ionic solution. The antibacterial activity of the TEMPO-oxidized hemp fibers with silver particles was confirmed in vitro against two strains: Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922), and the antifungal activity against Candida albicans (ATCC 24433). The best antimicrobial activity of silver-loaded TEMPO-oxidized hemp fibers was showed against strain S. aureus. [ABSTRACT FROM AUTHOR]

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Abstract: The elaboration of composites with natural fibers and polymeric matrices has to face two major difficulties: natural fibers present a hydrophilic character (absorption of water and possible deterioration of the properties) and thermal sensitivity (the fibers can be degraded during composite elaboration and/or in certain applications). In addition, common polymers are generally hydrophobic, which induces poor compatibility at the polymer/fiber interface. It has been demonstrated that the quality of the interface between the natural fibers and the polymeric matrix is a key issue which should be controlled in order to improve the mechanical properties, the durability and the recyclability of such composites. In this purpose, our approach is to develop a new method of fibers/polymer coupling consisting in a unique operation of reactive compounding, based on an original chemistry of organosilanes in the polymer melt. Our objective is to enhance the fibers/polymer interface by using two functionalized organosilanes simultaneously. The method is then to graft covalently one of these functions on the polymer chains and the other one onto hemp surface. In parallel, formation of Si–O–Si network between the two grafted organosilanes occurs during reactive extrusion. The achievement of this grafting of hemp fibers and thermoplastic matrix during a single compounding operation constitutes a new route for the elaboration of bio-based composites. Mechanical properties (tensile and impact) and thermal behavior of these new composites were compared to those of fibers/polymer composites without coupling agent or with a single classical one (Vinyltrimethoxysilane). Results showed that the presence of two organosilane coupling agents enhances considerably the tensile strength (+40%) of the newly developed composite. Their thermal decomposition, as shown by TGA, was shifted to higher temperatures and their water uptake at room temperature was decreased. Morphological characterizations by SEM suggest better adhesion at the interface, which can explain the properties enhancement. [Copyright &y& Elsevier]

Chemical modifications of hemp fibers were performed with acetic anhydride (AA) and vinyl acetate (VA) in the presence of pyridine or potassium carbonate as catalysts. Hemp fibers (Cannabis sativa) were successfully acetylated by VA in the presence of potassium carbonate (15% WPG), but no weight gain was obtained when pyridine was used as catalyst. Hemp fibers were also modified with acetic anhydride (AA) in the presence of potassium carbonate and pyridine as catalyst (14% and 16% WPG, respectively) under identical conditions, and the results were compared with those obtained using the VA technique. AA-modified, VA-modified, and control hemp fibers were characterized by Infrared (FTIR), 13C CP MAS NMR and thermo gravimetric analysis (TGA). [ABSTRACT FROM AUTHOR]

This article reports on the effect of skin thickness, core density, and skin composition on the mechanical properties of sandwich structural foams. In this study, the skin layers are polypropylene reinforced by different amounts of hemp fibers while the core is the same polypropylene foamed using different amounts of chemical blowing agent. The sandwich structures are characterized mechanically in terms of tensile and flexural properties. The results show that fiber introduction in the skins not only improved the mechanical properties, but also produced finer cell structures in the core. Finally, a mechanical model including fiber concentration, skin thickness, and density profile in the core is proposed to predict with high accuracy the elastic modulus of the sandwich foams. [ABSTRACT FROM PUBLISHER]

Abstract: This study investigated the influence of hemicelluloses and lignin removal on the sorption and electric properties, as well as fineness of hemp fibers. Hemp fibers with different content of either hemicelluloses or lignin were obtained by chemical treatment with 17.5% sodium hydroxide or 0.7% sodium chlorite. The sorption properties of hemp fibers were evaluated as moisture and iodine sorption, while electric properties were evaluated as volume electric resistance. Hemicelluloses removal increases in higher extent fiber liberation than lignin removal; the modified hemp fibers were finer up to 12 times in relation to unmodified fibers. Furthermore, hemicelluloses removal increased the moisture and iodine sorption, as well as electric resistance of hemp fibers compared to unmodified fibers, while lignin removal decreased both moisture and iodine sorption, and only slightly increased the electric resistance of modified hemp fibers. [Copyright &y& Elsevier]

In this study we focus on some key problems encountered in the processing of bast fibers from hemp for the production of textiles. These problems include the high content of pectin, the excessive rigidity and the poor "spinnability" of hemp fibers. The results of a thorough analysis of the physical and chemical properties of the fibers at each step of the process are presented. The parameters measured include the length, fineness, surface appearance, tensile properties, moisture absorption, flexibility and crystallinity of the fibers. The refinement of the processing described here results in fibers that are thinner, cleaner, more flexible and more uniform in length, all of which contributed to an improved spinning performance of the hemp fibers. [ABSTRACT FROM AUTHOR]

• With increasing Foam content, the mixtures revealed higher slump values due to decreasing solid content. • Porosity and water absorption of 28 aged-foam concretes increased with increasing foam content. • As the foam content increases, the compressive strength of the mixtures decreases. • Hemp fiber reduced drying shrinkage of foam concretes. • It has been observed that glass fiber improves the durability properties of foam concretes. This study presents investigation on microstructural, mechanical, durability and thermal characteristics of hemp fibers (HFs) reinforced foam concrete with fly ash (FA) and Taguchi optimization approach. Three series of foam concretes mixtures were produced with foam contents of 50, 75 and 100 kg/m3. There is a reference mixture without HFs and FA. Thus, mixtures contain FA as cement replacement at the concentrations of 0%, 10%, 20%, 30%, 40% and 50%. HFs with varying fiber length were introduced into mixes at concentrations of 0.75%, 1.5% and 3% by weight of cement. Slump test was done to see workability. Compression and flexural properties were determined at 7, 28 and 91 days. Durability was investigated by high temperature, freeze–thaw and sulphate exposures. Thermal conductivity, drying shrinkage, porosity, water absorption and dry unit weight properties of foam concretes were also investigated. Experimental results were analyzed using Taguchi optimization approach. Addition of HFs provides very large compressive and flexural strength enhancements. FA addition reduces the drying shrinkage and thermal conductivity while it increases the high temperature resistance of foam concretes. [ABSTRACT FROM AUTHOR]

This study investigated the effect of hemp fiber pretreatments (water and sodium hydroxide) combined with silane treatment, first on the fiber properties (microscale) and then on polylactide (PLA) composite properties (macroscale). At the microscale, Fourier transform infrared, thermogravimetric analysis, and scanning electron microscopy investigations highlighted structural alterations in the fibers, with the removal of targeted components and rearrangement in the cell wall. These structural changes influenced unitary fiber properties. At the macroscale, both pretreatments increased the composites' tensile properties, despite their negative impact on fiber performance. Additionally, silane treatment improved composite performance thanks to higher performance of the fibers themselves and improved fiber compatibility with the PLA matrix brought on by the silane couplings. PLA composites reinforced by 30 wt.% alkali and silane treated hemp fibers exhibited the highest tensile strength (62 MPa), flexural strength (113 MPa), and Young's modulus (7.6 GPa). Overall, the paper demonstrates the applicability of locally grown, frost-retted hemp fibers for the development of bio-based composites with low density (1.13 to 1.23 g cm−3). [ABSTRACT FROM AUTHOR]

• The Ca(OH) 2 pre-treatment improves thermal stability of hemp fibers. • Hemp fiber-reinforced mortars show higher pre-cracking flexural stiffness values. • Treated hemp fiber-reinforced mortars show higher load-carrying capacity. • Treated hemp fiber-reinforced mortars show higher energy absorption capacity. • Latex and defoamer increase resistance to penetration of fibers-reinforced mortars. In this study, authors propose and investigate a strategy aimed to improve the interaction at the fiber–matrix interface, while tailoring matrix resistance to penetration, in hemp fiber-reinforced cement based mortars. It consists of a chemical modification of the hemp fibers carried out through a Ca(OH) 2 pre-treatment and of a matrix modification using an acrylic elastomeric polymer dispersion as additive. The effect of the pre-treatment, on the thermal and chemical properties of the hemp fibers, has been investigated using X-ray diffractometry, Fourier-transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. Results showed that chemical pre-treatment is effective in removing hemicelluloses, lignin and waxes thus providing a clean fibers' surface and a higher thermal stability. Fiber-reinforced cement based mortars have been manufactured using pristine and treated 12 mm long hemp fibers at 0.5 wt%, 1 wt% and 1.5 wt% on cement. Their mechanical performance, capillary water absorption and drying shrinkage behavior have been investigated. Hemp fiber-reinforced mortars show a post peak response in flexural tests, being their energy absorption capacity and load-carrying capacity after crack onset positively affected by hemp fibers content and remarkably improved by chemical pre-treatment. Shrinkage behavior of fiber reinforced mortars is characterized by an initial limited expansion that can be associated to fibers swelling due to water absorption. The acrylic latex fills the matrix pores and reduces by 50% the sorpitivity of the composites. [ABSTRACT FROM AUTHOR]

This paper reports on the first phase of a multi-phase research program conducted at the American University of Beirut (AUB) on "Hemp and Recycled Aggregates Concrete" (HRAC). HRAC is a new sustainable concrete material where hemp fibers are incorporated in the mix, the coarse aggregate content is reduced by 20% of the concrete volume, and 50% of the natural coarse aggregates (NCA) are replaced by recycled concrete aggregates (RCA), thus saving on natural resources and addressing the problem of waste material disposal. The effect of the new material on concrete consistency and hardened mechanical properties was studied. Also, few durability tests were conducted. Variables included percentage replacement of NCA by RCA (0 or 50%), maximum size aggregate (10 or 20 mm), hemp fiber length (20 or 30 mm), and hemp fiber treatment (alkali or silane or acetyl). Fiber characterization tests were conducted including morphology, crystallinity, and thermal analysis. The tests indicated that alkali and acetyl fiber treatments were better than the silane treatment in removing impurities on the fiber surface. Also, alkali and acetyl treatments have increased the crystallinity of the fibers while silane treatment decreased it. Results of mechanical properties tests showed that while HRAC has considerable lower compressive strength and modulus of elasticity than plain concrete, the flexural strength and splitting tensile strength are not significantly affected. The flexural stress–strain behavior of HRAC is ductile as compared to the brittle behavior of the plain concrete beams indicating positive impact on toughness and energy dissipation. The durability tests indicated that whereas HRAC mixes have higher absorption than plain concrete, they have better thermal properties and their resistance to freeze–thaw cycles is comparable to plain concrete. All test results were not significantly affected by fiber length or fiber treatment. [ABSTRACT FROM AUTHOR]

• Steam explosion cottonization of hemp fibers enhanced thermal stability. • Flame retardant hemp fibers were produced. • Fine fibers modified with high P and N contents have been produced. • A synergistic effect between N and P induced a stable char. The goal is to produce cottonized hemp fibers with improved thermal stability. It was first found that the fine hemp fibers produced from technical non-retted hemp fibers by steam explosion exhibited an enhanced thermal stability. An efficient and low-cost process was developed using a mixture of urea/etidronic acid in aqueous solution in order to achieve a high phosphorus content and produce flame retardant fibers by chemical grafting. ICP, 31P and 13C NMR, SEM, thermogravimetric, Pyrolysis-Combustion Flow Calorimetry analyses and a flame test were used to characterize the grafted fibers. Fibers modified with relatively high P and N contents have been produced (≈ 6 wt % and ≈ 4 wt % respectively) but lower grafting rates (P ≈ 0.5 % and N ≈ 0.35 %) are sufficient to produce non-flammable fibers. A synergistic effect between N and P has been proposed to induce the formation of a stable char. [ABSTRACT FROM AUTHOR]