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Natural fibers such as kenaf, hemp, flax, jute, and sisal have become the subject of much research as potential green or eco-friendly reinforcement composites, since they assure the reduction of weight, cost, and CO2 release with less reliance on oil sources. Herein, an inexpensive and eco-friendly waterglass treatment is proposed, allowing the production of silica-coated fibers that can be easily obtained in micro/nano fibrils through a low power mixer. The silica coating has been exploited to improve the chemical compatibility between fibers and the polymer matrix through the reaction of silanol groups with suitable coupling agents. In particular, silica-coated fibers easily functionalized with (3-Aminopropyl) triethoxysilane (APTS) were used as a filler in the manufacturing of epoxy-based composites. Morphological investigation of the composites through Scanning Electron Microscopy (SEM) demonstrated that the filler has a tendency to produce a web-like structure, formed by continuously interconnected fibrils and microfibrils, from which particularly effective mechanical properties may be obtained. Dynamic Mechanical Analysis (DMA) shows that the functionalized fibers, in a concentration of 5 wt%, strongly affect the glass transformation temperature (10 °C increase) and the storage modulus of the pristine resin. Taking into account the large number of organosilicon compounds (in particular the alkoxide ones) available on the market, the new process appears to pave the way for the cleaner and cheaper production of biocomposites with different polymeric matrices and well-tailored interfaces.

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.

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]

In this current study, alkali treated eco-friendly hemp fibers were chosen to reinforce thermosetting resin blend composed of cyanate ester and benzoxazine resin. For various volume fractions ranging from 5 to 20 vol % with a regular increment of 5 vol%, their effects on the morphological, mechanical behaviour and water uptake properties were experimentally evaluated using the scanning electron microscopy, flexural, tensile and water uptake tests. The produced composites possessed much ameliorated flexural properties as compared to those of the unfilled resin. Data from the tensile test revealed a continuous increase in the composites' tensile strength and modulus as the proportion of the treated fibers augmented. Furthermore, the tensile experimental results were compared to the most commonly used empirical models like the rule of mixture (ROM), revised rule of mixture (RROM), inverse rule of mixture (IROM), Halpin Tsai (HT), Lewis and Nielson (LN), and Halpin Kardos (HK) models. It was found that the alkali treated fibers were arranged in a 3D random fiber arrangement according to the RROM model and the HK model was identified to fit well the tensile experimental results. The experimental results and theoretical modeling confirmed that the water absorption in the produced composites was increased and governed by the Fickian diffusion. These effects took place due to the chemical and morphological changes in the treated fiber external surfaces, which promoted better interfacial adhesion between the plant fibers and the polymer blend matrix. [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]

The degradation behaviors of hemp fibers reinforced PP biocomposites under outdoor and artificial weathering were compared to establish a correlation. For this purpose, several measurements were performed throughout the expositions. Mechanical performance was tested by three-point bending test. Microstructure and chemical composition changes were also assessed. Otherwise, visual aspect and topography were determined. The artificial weathering effectively accelerated the degradation mechanisms. Oxidation pathways and surface aspect alteration of both polymer and biocomposites occurred faster. However, whereas biocomposites were mainly subjected to outdoor conditions due to high sensitivity of hemp fibers, neat PP was globally mostly affected by laboratory chamber conditions. Its oxidation rate largely outstripped reinforced materials ones. Principal Component Analysis was used for verifying the differences of variables correlations profiles between artificial and exterior ageing dataset in order to compare the degradation mechanisms. Through the statistical analysis, some attempts were made to find equivalence between artificial and outdoor weathering times thanks to properties degradation rate similarities. [ABSTRACT FROM AUTHOR]

This work aims to investigate exterior and under glass weathering representing decking and car interior end uses of hemp fibers reinforced polypropylene (PP) biocomposites. For this reason, mechanical flexural tests were firstly performed. Then, the evolution of the PP matrix microstructure was determined through Differential Scanning Calorimetry (DSC). The chemical composition was studied by infrared spectroscopy to understand the photo- and thermo-chemical mechanisms. CIELab system-based colorimetric measurements were carried out to determine the evolution of the chromaticity and lightness. Through a new approach, gloss was obtained by determining the type of reflection of materials as either specular or diffuse, and the surface aspect was characterized by rugosimetry. The influence of the rate of hemp fibers (from 0 to 30 wt%) was studied. Results showed that biocomposites were generally more sensitive than neat PP whatever the weathering conditions. However, each type of weathering assessment allowed understanding the contribution of each degradation factor. Indeed, rainfall or UV-A rays induced an increase in the vinyl concentration and the formation of cracks on the surface whereas the carbonyl functional groups rate was not influenced by the type of weathering. The high temperatures under windshield glass favored a chemicrystallization and biocomposites yellowing at the first period of exposition whereas outdoor exposure induced red color loss. [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]

A novel self-exothermic curing agent, effectively able to cure the diglycidyl ether of bisphenol-A (E51 epoxy resin) at room temperature, has been synthesized by blending 4, 4’-diaminodiphenylmethane (DDM) and acrylic acid (AA). The chemical structure of prepared curing agent was characterized by 1 H nuclear magnetic resonance ( 1 H NMR) and Fourier transform infrared (FTIR). The curing behavior of epoxy with synthesized room temperature hardener was studied by differential scanning calorimetry (DSC) and FTIR. Results confirmed that the curing reaction was completed in only 3 h, which can be attributed to the high reactivity of the acryl amide groups with epoxy and high heat release from DDM and AA reaction. The 5 wt% NaOH treated short hemp fibers (TF) were sandwiched in room temperature curing epoxy resin to obtain rapid prototyping high performance composites. The effects of fiber content on the mechanical properties of composites were studied in terms of tensile, flexural, and impact load. The tensile strength of the composites was increased with the increase of the TF content, and the elongation at break was decreased. Compared with the cured neat epoxy resin, an increase of about 233% in impact strength, 52% in flexural modulus, and 213% in Young's modulus were recorded for the cured composite having 7.5 wt% TF content. We used dynamic mechanical analyzer (DMA) and thermogravimetric analysis (TGA) to study the effect of fiber content on the thermal properties of composites. The scanning electron microscope (SEM) revealed excellent adhesion between TF and epoxy resin cured at room temperature. [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]

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]

Most materials used in daily life are polymeric materials based on petrochemistry. The used polymeric materials can cause land pollution and air pollution after landfill or incineration. In contrast, natural fiber reinforced (NFR) composites are more suitable for the environment, however the reliability in terms of the durability and weatherability of NFR composites is still lacking. Thus, NFR composites require the reliability involved with durability and weatherability. In this work, poly(butylene terephthalate-co-glutarate) (PBTG), with a chemical structure similar to biodegradable PBAT, was used as the matrix in the composites, and hemp fibers were used as the reinforcement. Hemp/PBTG composites were fabricated by stacking hemp-fiberwebs and PBTG films with various fiber contents and thermal exposure times. Characteristics of the composites, such as the morphological structure, chemical structure, tensile properties, compressive properties, flexural properties, and impact strength, were analyzed to obtain the effects of fiber volume fraction and thermal exposure. As a result, hemp/PBTG composites were hardened in proportion to fiber volume fractions, and the hardening behavior of the composites increased tensile strength and flexural strength. However, the hardened structure of the composites decreased the impact strength and compressive strength of the composites. On the other hand, the mechanical properties of hemp/PBTG composites with thermal exposure times, were governed significantly by the brittleness behavior of the resin and the increased crystallinity of hemp fibers. Thus, the hemp fibers contributed to the improvements on structural stability, tensile strength and flexural strength of the hemp/PBTG composites, and increased the thermal durability of the composites with various thermal exposures. [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]

In the sustainable development context, the possibility of recycling, reuse and reintegration in nature, environmental protection and efficient management of natural resources are significant indicators. Adobe bricks type masonry units meet successfully these requirements. This paper presents a series of experimental research conducted to explore the clay material recycling possibility of the adobe bricks type masonry units, previously used for various purposes. The used testing methods were chosen so as to pursue the preservation or not of some essential physical and mechanical characteristics (mechanical strength, density, axial shrinkage, thermal conductivity). The results indicated the followed parameters preservation for the specimens performed from recycled clay, compared to similar specimens, in whose composition has not been introduced recycled material. Also, the experimental results have indicated the reinforcing possibility with vegetable fiber (straw or hemp fibers), even if the binder was made using the recycled clay. [ABSTRACT FROM AUTHOR]

The postcracking behavior of fiber-reinforced concrete (FRC) is mostly influenced by the type of fiber, the amount of fibers, fiber orientation, and the concrete strength. Manufacturers of fibers propose a minimum mixing duration after fibers are added to concrete to obtain an acceptable dispersion of fibers. What about the maximum mixing time? Fiber properties (tensile strength, length, surface characteristics, shape, and density) are normally specified by the fiber producer. However, the properties of hardened FRC are influenced by the properties of fibers after mixing. An important question is whether the properties of fibers change due to an occasionally long mixing time. Can surface characteristics, length, or tensile strength of fibers change during mixing and can this affect the properties of FRC? In an extensive experimental study, two types of macro polymer fibers, two types of steel fibers (without coating or with brass coating), two basalt fibers (with different lengths), and two braids of hemp fibers (without protection and with linseed oil protection) were tested. The test results indicate possible deterioration for some of the fibers in concrete for too long mixing times. Possible modes of deterioration are shown. [ABSTRACT FROM AUTHOR]

This work reports the thermal degradation kinetics of five formulations of polyethylene terephthalate (PET) reinforced with 1, 5, 10, 15, and 20 % hemp fibers based on thermogravimetric investigations. Two consecutive degradation steps were observed between 573 and 773 K. Moreover, their kinetic triplets were determined by nonlinear curve fitting methods, with the Sestak-Berggren and the truncated Sestak-Berggren models, respectively. The resulting kinetic parameters varied with the fiber's concentration in the following ranges: 1.8 ≤ A ≤ 5, 2.25 ≤ n ≤ 3.17, 7.05 ≤ m ≤ 12.74, and −2.21 ≤ p ≤ −1 for the first step; and 1.76 ≤ A ≤ 10, 1.37 ≤ n ≤ 2.49, and 0.77 ≤ m ≤ 2.35 for the second. This work further confirms the thermal stability of PET-hemp fiber composites and provides key information for the reaction mechanism, a crucial developmental step for bio-composite materials with high-melting thermoplastic matrices. [ABSTRACT FROM AUTHOR]

In the last two decades intensive grow of industry of building materials from renewable resources is observed. Such situation is related to some aspects: global warming, environmental pollution, impact on human health, environmental impact of materials at their end-of-life. In current study development of thermal insulation materials from hemp and polylactide fibres are analysed. While main parameter for thermal insulation materials is thermal conductivity, rational density of composite 40 kg/m3 was chosen. For experiments 11 compositions were prepared. One composition was prepared just with hemp and polylactide fibres, five compositions with different amount of hydrophobic agent and 5 compositions with different amount of fire retardant. Experimentally thermal conductivity, sound absorption coefficient, short-term water absorption, fire resistance, water vapour transfer properties and compressive strength were determined. Rational amount of hydrophobic agent and fire retardants was chosen.

In this paper, the preparation of the antimicrobial silver loaded hemp fibers were carried out by selective TEMPO-mediated oxidation, i.e. oxidation with sodium hypochlorite and catalytic amount of sodium bromide and 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 oxidation conditions: concentration of sodium hypochlorite and duration of sorption. The obtained results showed that the maximum sorption capacity (0.703 mmol of silver per gram of fibers) of modified hemp fibers was obtained for the sample modified with 9.67 mmol NaClO per gram of fibers, during 4 hours. 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 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 fungi Candida albicans (ATCC 24433). The best antimicrobial activity of silver-loaded TEMPO-oxidized hemp fibers was showed against strain Staphylococcus aureus. [Projekat Ministarstva nauke Republike Srbije, br. Acknowledgments. This study has been supported by Ministry of Education, Science and Technological Development of the Republic of Serbia, br. OI 172029]

The research was focused on the separation of single hemp (Cannabis sativa L.) fibre cells with low fineness from mechanically extracted fibre bundles of high fineness. The fiber bundles were treated with enzymes, namely panzym, pectinase, hemicellulase, and cellulase, along with a combination of panzym and ultrasonic treatments. Changes in the fiber structure were followed at molecular and microscopic levels by means of NIR FT Raman spectroscopy and Environmental Scanning Electron Microscopy (ESEM). Buffer-panzym treatments of hemp fibers had a prominent effect in loosening of the fiber cells. The best of refining was achieved when the fiber bundles were treated with buffer-panzym solution in combination with ultrasonic treatment.

Natural fiber-reinforced composites with thermoplastic matrices are gaining prominence in society as their applications are found in varied industries, e.g., automotive and aerospace. A recent trend shows the use of hemp fibers as reinforcements for the manufacture of bio-based composites, which are thermally and dimensionally stable, and durable. In this work, polypropylene (PP) was reinforced with 5, 10, 20, 30, and 40 wt% hemp fibers, having undergone an alkaline treatment, were processed, and investigated. Results showed that the composites made of hemp fibers with PP have exhibited good mechanical properties. A value of 2.12 GPa for young's modulus is achieved from a biocomposites containing 30 wt% of hemp fibers which is significantly higher than the 0.85 GPa of PP matrix. The full potential of hemp fibers as reinforcement for the PP matrix is demonstrated by this maximum, which represents a rise of 149% for the young's modulus and 40% for the tensile strength. Flexural modulus increased of 46%, 165%, and 232% compared to virgin PP at 10, 30, and 40 wt% fiber content. Such stiffness increases were followed by flexural strength increases of 52%, 78%, and 92% relative to virgin PP in the presence of 20, 30, and 40 wt% hemp fibers, respectively. A study was also conducted to evaluate the effects of various parameters on the thermo-mechanical properties of the final composites, which were hybrids made of PP reinforced with both hemp fibers and wood flour. These hybrid bio-composites prepared with 20 and 40 wt% hemp fibers and wood flour and variable ratios of the two reinforcements showed a positive hybridization effect. Nevertheless, the modulus of the hybrid biocomposites reinforced by both fibers, hemp/Wood floor (20/20), is 166% greater than the modulus of unreinforced PP and 34% greater than the Hemp/PP composite with 40% fiber content. Finally, a comparative study shows that the newly formulated hybrid composite has the potential to replace various existing natural fiber-reinforced composites. This study's approach is, although we know, unique. • Hemp fiber/wood floor/PP composites were produced by extrusion/injection processes. • The thermo-mechanical properties of the hybridized composites were evaluated. • Good properties and synergistic effects between hemp fibers and wood floor were obtained. [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]

The aim of this work is the study of the thermal flux through a multilayer insulation specimen, whose final panels could be designed for the green building field. The specimen was fabricated using an expanded styrofoam base, the mortar and milk cements, a fiberglass, and hemp fibers chopped and scattered into a surface smoothing. The dimensions of the specimen are 230 x 75 x 30.2 [mm]. The need to analyze a reduced surface in the development of a 3D visualization follows a computational aspect, i.e., to limit the number of degrees of freedom to be solved. Specifically, the research is focused on a comparative analysis among numerical simulations through the data processing by means of Matlab® - using the finite difference method (FDM) in the 1D domain -, and Comsol Multiphysics® - using the finite element method (FEM), both in 2D and 3D domains -. In addition, an experimental analysis centred on the detecting of the sub-superficial fiberglass by means of infrared thermography (IRT) technique is carried out. A specific Matlab® script was also implemented. Finally, can be observed that Comsol Multiphysics® not only allows a visualization of the flow, as it is done in Matlab®, but also of the entire specimen geometry with the possibility of realizing a video of the thermal transient during the heating and cooling phases. [ABSTRACT FROM AUTHOR]

In the last two decades intensive grow of industry of building materials from renewable resources is observed. Such situation is related to some aspects: global warming, environmental pollution, impact on human health, environmental impact of materials at their end-of-life. In current study development of thermal insulation materials from hemp and polylactide fibres are analysed. While main parameter for thermal insulation materials is thermal conductivity, rational density of composite 40 kg/m3was chosen. For experiments 11 compositions were prepared. One composition was prepared just with hemp and polylactide fibres, five compositions with different amount of hydrophobic agent and 5 compositions with different amount of fire retardant. Experimentally thermal conductivity, sound absorption coefficient, short-term water absorption, fire resistance, water vapour transfer properties and compressive strength were determined. Rational amount of hydrophobic agent and fire retardants was chosen. [ABSTRACT FROM AUTHOR]

Housing construction technology using clay soil in various forms - paved, adobe bricks form or other - is already known and used since ancient times. Over the years, there have been numerous studies and research to improve this technology and to obtain more resistant, comfortable and durable structures. This paper presents an experimental study regarding the effectiveness of natural fiber disperse reinforcement in the adobe bricks. The results indicate an improved mechanical strength and a better thermal conductivity of the clay composite material. The variation of watched physical-mechanical parameters was influenced by the type of the used organic material, hemp fiber or straw, and of the amount entered in the mixture. By analyzing simultaneously all watched physical-mechanica parameters, for the used clay mixture, it was set an optimum addition of hemp fibers, as 9-10% percent by volume, respectively an optimal straw addition, 30-40% percent by volume. [ABSTRACT FROM AUTHOR]

This work investigates the rupture of bast fiber type from hemp, to attain better control over the ultimate tensile and fracture strength properties of hemp composites. Crack propagation in both individualized and bundles of hemp fibers is studied. Crack initiation is controlled using generated defects within fibers. A non-contact-ablation apparatus creates these defects using a laser beam directed by high-precision optics. V- and U-type notches are processed, with sizes ranging from 2 to 30 μm in depth. The micromechanical testing of damaged fibers is coupled to a high-speed camera, allowing for the measurement of ultimate properties as well as monitoring of the crack propagation. Finite element simulation is developed to identify possible damage scenarios for bundles and elementary fibers. Microcracks are allowed to initiate, grow and coalesce based on non-prescribed crack propagation (i.e., not imposed or with direction update) and stress criteria. High speed camera recording indicate a wide variability in crack propagation speed in the range 2–149 m/s. Both longitudinal and transverse cracking are observed depending on the notch geometry. Our results demonstrate that the damage kinetics is a combination of growth and coalescence of microcracks. These damage mechanisms compete depending on the notch geometry and fiber element dimensions. [ABSTRACT FROM AUTHOR]

In the present work, the effective use of polyethylene-grafted maleic anhydride (PE-g-MA) copolymer as a compatibilizer in high-density polyethylene composites containing 10-50 mass% hemp fibers was evaluated through mechanical and thermal properties measurements. The results revealed a significant reinforcement on the tensile strength of the composites as a consequence of the incorporation of the compatibilizer. Less pronounced effects were found on the elongation at break and impact strength of the composites. The notable enhancement of tensile strength on the compatibilized composites was related to the improved adhesion of hemp with the matrix in the presence of PE-g-MA, which was revealed through scanning electron microscopy observations. Furthermore, Fourier transform infrared spectroscopy analyses suggested that covalent bonding occurs between the fibers and the matrix in the highest PE-g-MA concentrations. Differential scanning calorimetry experiments revealed that the presence of compatibilizer increases the crystallinity of the composites. Thermogravimetry studies revealed that for low compatibilizer concentrations the thermal stability of the composites is further reduced, while for the highest concentration, when bonding occurs, it is enhanced. The biodegradation studies of all the composites revealed that the incorporation of compatibilizer enhances the stability of the composites, especially in the higher concentrations, and reduces their final residue. [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]

Non-exhaust brake dust and pollution arising from metal, semi-metal, and ceramic brake pads have made recent research consider their replacement by potential natural fibers such as hemp, flax, sisal, etc. These natural fibers are lightweight, biodegradable, and cheap. This paper discusses the wear and friction analysis of hemp fiber reinforced polymer brake pad material. Three test specimens viz. HF4P20, HF5P20, and HF6P20 were prepared per ASTM G99 standards for the pin-on disc tribo-test. The test trials and validation were done using the Taguchi design of experiments and ANOVA. The optimum result showed a consistent coefficient of friction and lowered specific wear rate for HF6P20 brake pad material. Worn surface morphology was done using scanning electron microscopy.

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]