Properties of ball milled thermally treated hemp fibers in an inert atmosphere for potential composite reinforcement

Hemp (émph{Cannabis Sativ L}.) is an important lignocellulosic raw material for the manufacture of cost-effective environmentally friendly composite materials. From an earlier experiment it was found that when hemp bast fibers were heated between 160^∘C and 260^∘C, there was softening of lignin leading to opening of fibers and the preliminary observations showed that heat treatment at 220^∘C in an inert environment seemed to provide enough fiber without affecting the associated tissues of the fibers. However, these heat treated fibers need to be separated by mechanical action. For this experiment, hemp fibers were given heat treatment in an enclosed vessel in a nitrogen environment at 220^∘C for 30 min and then they were ball milled. It was found that there was further opening of fibers upon ball milling of the heated fibers and the total number of fibers increased for the equal weight of fibers. It was not possible to find strength properties of shorter length fibers; however, the results from shorter clamping length indirectly indicated that these fibers were of higher strength. The ball milled fibers also contained copious amount of fines which must be removed before using the fibers for composite manufacturing.     

Determination of mechanical strength properties of hemp fibers using near-infrared fourier transform Raman microspectroscopy

Fourier transform near-infrared (FT-NIR) Raman microspectroscopy was adopted for analyzing the micro mechanical tensile deformation behavior of cellulosic plant fibers. Mechanical strength parameters such as tensile strength, failure strain, and Young's modulus of diversified hemp fibers were determined within the range of single fiber cells and fiber filaments. The analysis of fiber deformation at the molecular level was followed by the response of a characteristic Raman signal of fiber cellulose that is sensitive to the tensile load applied. The frequency shift of the Raman signal at 1095 cm(-1) to lower wavenumbers was observed when the fibers were subjected to tensile strain. Microstructural investigations using electron microscopy under environmental conditions supported the discussion of mechanical properties of hemp fibers in relation to several fiber variabilities. Generally, mechanical strength properties of diversified hemp fibers were discussed at the molecular, microstructural, and macroscale level. It was observed that mechanical strength properties of the fibers can be controlled in a broad range by appropriate mercerization parameters such as alkali concentration, fiber shrinkage, and tensile stress applied to the fibers during the alkaline treatments.     

天然纤维表面化学处理性能研究

针对天然纤维强化复合材料中纤维与基体相容性差和纤维的高吸湿性导致复合材料吸水率高的问题,以大麻、苎麻和黄麻3种麻为原料,采用苯甲酰氯、亚氯酸钠、氢氧化钠和丙烯酸对麻进行表面处理,来考察不同麻种类和不同化学处理方式对麻纤维拉伸强度和吸湿度的影响。研究表明,处理方式和麻种类均对纤维拉伸强度和吸湿度有显著的影响,其中丙烯酸处理的大麻纤维影响最显著;纤维经处理后表面变粗糙,表面积增大。     

Enhanced mechanical properties of electrospun nano-fibers through NaCl mediation

Electrospun (ES) nano-scale polymer fibers are known to exhibit lower Young's modulus and strength than their bulk counterpart. We have discovered that minute additions of sodium chloride (NaCl) during the preparation stage of ES polymethyl methacrylate (PMMA) fibers raises the fiber mechanical properties in a significant way, nearly up to bulk values, over a range of diameters. NaCl-induced electrical effects leading to enhanced molecular alignment during nano-fiber formation is the most likely explanation for this synergistic effect. Moreover, beyond the now-recognized rise in Young's modulus values, we observed that the strength and tensile toughness of the ES fibers also significantly increase at progressively smaller diameters.     

A comparison of the effect of hot stretching on microstructures and properties of polyacrylonitrile and rayon-based carbon fibers

The effect of a different stretching stress at different heat treatment temperatures (HTT) on the structure and the mechanical properties of polyacrylonitrile (PAN)- and rayon-based carbon fibers was studied. The tensile strength increases first and then decreases with increasing stretching stress, whereas the Young’s modulus of the fibers continuously increases. The behavior of PAN- and rayon-based carbon fibers is similar with increasing stretching stress, but the tensile strength of PAN fiber decreased while that of rayon fiber increased with increasing HTT, what is more, the latter have a considerable lower tensile strength and modulus for equivalent processing conditions. The structure of the fibers was investigated with X-ray diffraction. A continuous change toward a nanostructure with a higher order was observed, which explains the increase in the Young’s modulus. For more complex dependence of the tensile strength on the processing conditions, a quantitative model to describe the effect of stretching stress at different HTT on preferred orientation degree and shear modulus is proposed. From the critical stress fracture of carbon fiber analysis, we can understand the different changes of tensile strength of both type fibers with stretching stress at different HTT.     

Tensile properties of elephant grass fiber reinforced polyester composites

Elephant grass stalk fibers were extracted using retting and chemical (NaOH) extraction processes. These fibers were treated with KMnO₄ solution to improve adhesion with matrix. The resulting fibers were incorporated in a polyester matrix and the tensile properties of fiber and composite were determined. The fibers extracted by retting process have a tensile strength of 185 MPa, modulus of 7.4 GPa and an effective density of 817.53 kg/m³. The tensile strength and modulus of chemically extracted elephant grass fibers have increased by 58 and 41%, respectively. After the treatment the tensile strength and modulus of the fiber extracted by retting have decreased by 19, 12% and those of chemically extracted fiber have decreased by 19 and 16%, respectively. The composites were formulated up to a maximum of 31% volume of fiber resulting in a tensile strength of 80.55 MPa and tensile modulus of 1.52 GPa for elephant grass fibers extracted by retting. The tensile strength and the modulus of chemically extracted elephant grass fiber composites have increased by approximately 1.45 times to those of elephant grass fiber composite extracted by retting. The tensile strength of treated fiber composites has decreased and the tensile modulus has shown a mixed trend for the fibers extracted by both the processes. Quantitative results from this study will be useful for further and more accurate design of elephant grass fiber reinforced composite materials.     

Natural and man-made cellulose fibre-reinforced poly(lactic acid) (PLA) composites: An overview about mechanical characteristics and application areas

The paper describes the production and the mechanical characteristics of composites made completely of renewable raw materials. Composites of different kinds of natural fibres like cotton, hemp, kenaf and man-made cellulose fibres (Lyocell) with various characteristics were processed with a fibre mass proportion of 40% and poly(lactic acid) (PLA) by compression moulding. Additionally, composites were made of fibre mixtures (hemp/kenaf, hemp/Lyocell). The composites were tested for tensile strength, elongation at break, Young’s modulus and Charpy impact strength. Their characteristics varied markedly depending on the characteristics of the raw fibres and fibre bundles and fibre mixtures used. While kenaf and hemp/PLA composites showed very high tensile strength and Young’s modulus values, cotton/PLA showed good impact characteristics. Lyocell/PLA composites combined both, high tensile strength and Young’s modulus with high impact strength. Thus, the composites could be applied in various fields, each meeting different requirements.     

Characterization of blue agave bagasse fibers of Mexico

This paper presents physical, chemical, thermal and tensile properties of Mexican cooked blue agave bagasse fibers extracted from this plant. The fibers are 10–12 cm long and 592.34 μm in diameter. The elliptical cells in the fiber are regularly arranged with varying lumen size. The cellulose and lignin contents of the fiber are 73.60% and 21.10% respectively. Fibers showed decreasing average values of ultimate tensile strength and constant values of Young’s modulus and average % strain values with increasing mean gauge length and decreasing mean diameter. Above results are discussed in the light of various factors that affect the properties. These fibers are found to be thermally stable due to their higher values of crystallinity and lignin. Main aim of this work is to characterize these partially degraded fibers with a view to find possible uses for such fibers such as compostable and biodegradable composites of corn starch/cooked blue agave residues.     

高温处理对几种玄武岩纤维成分和拉伸性能的影响

选取5种国产玄武岩纤维,采用X射线荧光光谱法和纤维单丝拉伸测试等方法,研究200~800℃空气气氛和氮气气氛处理前后纤维的化学成分、物理特性和拉伸性能等变化,以揭示玄武岩纤维的耐高温性能。结果表明:空气气氛下高温处理后由于表面处理剂的去除,玄武岩纤维表面更加光滑,直径略微变小,同时质量减少;SiO_2,Al_2O_3质量分数减小,而FeO+Fe_2O_3,CaO,MgO质量分数都增大,其中FeO+Fe_2O_3的质量分数增加最多,增幅最大达到21%。200℃处理后玄武岩纤维单丝拉伸强度有一定降低,强度保留率最大为98.3%,400℃处理后强度明显下降,强度保留率最高达到64.6%,800℃处理后强度保留率均不足20%。此外,纤维断裂伸长率随温度的升高而减小,弹性模量增大。与空气气氛相比,氮气气氛下纤维强度保留率更高,拉伸性能更稳定。     

An amorphous ceramic Al32.4Er7.6O60 fiber with large viscous flow deformation and a high-strength nanocrystallized ceramic fiber

An amorphous ceramic Al_32.4Er_7.6O₆₀ continuous fiber with a diameter of about 20 m could be made successfully by using the melt extraction method. This fiber shows large viscous flow deformation at the supercooled liquid state (about 1273 K). The fiber's tensile strength is about 900 MPa and this strength is maintained up to around 1100 K. A high-strength continuous ceramic fiber with a uniform Er₃Al₅O₁₂ nanocrystalline phase in an amorphous matrix can also be obtained with suitable crystallization from the amorphous state by heat treatment. The heat resistance, Young's modulus, and other properties are therefore improved. The nanocrystallized fiber which was heat-treated at 1373 K for 2 hours in an air atmosphere has a maximum room temperature tensile strength of 1.9 GPa, around twice that of an as-extracted amorphous fiber. The amorphous continuous ceramic fiber is promising as a ceramic that can be easily shaped at relatively low temperatures (about 1273 K), and as a reinforcing fiber for composites that can undergo secondary processing. Furthermore, this fiber can be considered as more superior to glass fibers because of its greater high-temperature strength and its high Young's modulus.     

Natural and artificial radioactivity measurements in Eastern Black Sea region of Turkey

Sorption potential of waste short hemp fibers for Pb(2+), Cd(2+) and Zn(2+) ions from aqueous media was explored. In order to assess the influence of hemp fiber chemical composition on their heavy metals sorption potential, lignin and hemicelluloses were removed selectively by chemical modification. The degree of fiber swelling and water retention value were determined in order to evaluate the change in accessibility of the cell wall components to aqueous solutions due to the fiber modification. The effects of initial ion concentration, contact time and cosorption were studied in batch sorption experiments. The obtained results show that when the content of either lignin or hemicelluloses is progressively reduced by chemical treatment, the sorption properties of hemp fibers are improved. Short hemp fibers are capable of sorbing metal ions (Pb(2+), Cd(2+) and Zn(2+)) from single as well as from ternary metal ion solutions. The maximum total uptake capacities for Pb(2+), Cd(2+) and Zn(2+) ions from single solutions are the same, i.e. 0.078mmol/g, and from ternary mixture 0.074, 0.035 and 0.035mmol/g, respectively.     

Influence of fiber length on the mechanical properties of wood-fiber/polypropylene prepreg sheets

Natural fiber based composites have the potential to improve the mechanical properties of plastics while reducing the cost and weight. This study shows a practical method of blending natural-fiber with polypropylene to form a mat and then consolidated into a sheet by hot pressing. The natural fibers assessed were Pinus radiata and Eucalyptus regnan high temperature thermomechanical pulps and sisal (Agave sisalana) fibers. The tensile strength was shown to decrease with an increase in fiber content, while the tensile modulus was shown to increase. Tensile and flexural modulus were positively influenced by fiber length. The water performance tests of the sheets generally showed approximately 20% weight gain and approximately 3% thickness swell at 30% fiber content. The natural fiber surface chemical composition was determined by X-ray photoelectron spectroscopy and shown to be primarily covered with hydrophobic material such as lignin and extractives, while polypropylene was shown to be partially oxidized. Received: 18 September 2000 / Reviewed and accepted: 20 September 2000     

Effect of a novel coupling agent,alkyl ketene dimer,on the mechanical properties of wood–plastic composites

The objective of this study was to investigate the incorporation of poplar wood fibers both with and without a novel coupling agent, alkyl ketene dimer (AKD), on the mechanical properties of wood fiber/polypropylene (PP) composites. The resulting properties were compared to those obtained with the most commonly used coupling agent, maleic anhydride grafted PP (MAPP). Tensile and impact strengths of the composites decreased with increasing poplar wood fibers content. Tensile modulus of the composites increased by the incorporation of the wood fibers content up to 70 wt% but further increment in the wood fibers decreased the tensile modulus. At the constant content of poplar wood fibers (70 wt%), the tensile strength determined for the coupled composites with 5% AKD increased by 41% in comparison with the non-coupled composites while the tensile modulus increased by 45%, the impact strength of the coupled composites increased by 38%. The performance of 5% AKD on the mechanical properties of the composites is a little better than 3% MAPP. The good performance of 5% AKD is attributed to the enhanced compatibility between the poplar wood fibers and the polymer matrix. The increase in mechanical properties of the composites demonstrated that AKD is an effective coupling agent for wood fiber/PP composites.     

Investigation of physical,chemical and mechanical properties of raw and alkali treated Borassus fruit fiber

The natural fibers nowadays play a major role as reinforcement in composites due to their important properties like lightweight, biodegradability and non-toxicity. Borassus fruit fiber is one such type possessing high cellulose which is inexpensive and available in plenty. The Borassus fruit fibers were extracted and its physical, chemical and mechanical properties such as density, diameter, cellulose, hemicellulose, lignin, wax, denier, tenacity and tensile force were experimentally determined. In this study, the Borassus fruit fibers were treated with 5%, 10% and 15% NaOH and the effect of alkali treatments on the fiber properties were explored. It is interesting to note that 5% NaOH treatment yielded significant improvement in tensile properties of the fibers than the others. The Fourier Transform Infrared Spectrometry (FT-IR) analysis was made to identify the chemical compounds of the raw and alkali treated fibers. The morphological study on raw and alkali treated fibers by Scanning Electron Microscope (SEM) revealed the existence of the impurities on the raw fiber surface and the removal of the same on the treated fibers.     

Investigation of physical,chemical and mechanical properties of raw and alkali treated Borassus fruit fiber

The natural fibers nowadays play a major role as reinforcement in composites due to their important properties like lightweight, biodegradability and non-toxicity. Borassus fruit fiber is one such type possessing high cellulose which is inexpensive and available in plenty. The Borassus fruit fibers were extracted and its physical, chemical and mechanical properties such as density, diameter, cellulose, hemicellulose, lignin, wax, denier, tenacity and tensile force were experimentally determined. In this study, the Borassus fruit fibers were treated with 5%, 10% and 15% NaOH and the effect of alkali treatments on the fiber properties were explored. It is interesting to note that 5% NaOH treatment yielded significant improvement in tensile properties of the fibers than the others. The Fourier Transform Infrared Spectrometry (FT-IR) analysis was made to identify the chemical compounds of the raw and alkali treated fibers. The morphological study on raw and alkali treated fibers by Scanning Electron Microscope (SEM) revealed the existence of the impurities on the raw fiber surface and the removal of the same on the treated fibers.     

The effect of gauge length on tensile strength and Weibull modulus of polyacrylonitrile (PAN)- and pitch-based carbon fibers

Carbon fibers are widely used as a reinforcement in composite materials because of their high specific strength and modulus. Current trends toward the development of carbon fibers have been driven in two directions; ultrahigh tensile strength fiber with a fairly high strain to failure (~2%), and ultrahigh modulus fiber with high thermal conductivity. Today, a number of ultrahigh strength polyacrylonitrile (PAN)-based (more than 6 GPa), and ultrahigh modulus pitch-based (more than 900 GPa) carbon fibers have been commercially available. In this study, the tensile strengths of PAN- and pitch-based carbon fibers have been investigated using a single filament tensile test at various gauge lengths ranging from 1 to 250 mm. Carbon fibers used in this study were ultrahigh strength PAN-based (T1000GB, IM600), a high strength PAN-based (T300), a high modulus PAN-based (M60JB), an ultrahigh modulus pitch-based (K13D), and a high ductility pitch-based (XN-05) carbon fibers. The statistical distributions of the tensile strength were characterized. It was found that the Weibull modulus and the average tensile strength increased with decreasing gauge length, a linear relation between the Weibull modulus, the average tensile strength and the gauge length was established on log–log scale. The results also clearly show that for PAN- and pitch-based carbon fibers, there is a linear relation between the Weibull modulus and the average tensile strength on log–log scale.     

Manufacture of High Performance Carbon Fibers from Precursors of Various Diameters

The effects of fiber diameter on the mechanical properties of PAN-based carbon fibers have been investigated in a series of processing experiments on fibers with different starting filament diameters. The fiber tows, with similar initial mechanical performance, were stretched at high temperatures to produce a large number of fiber types with a wide range of filament diameters. The three starting carbon fibers tows had nominal filament diameters of 5 μm, 6·5 μm, and 10 μm and contained 12000, 6000, and 3000 filaments respectively. These tows were stretched for 5 minutes at 2600^°C with a series of loads of up to 6 kg. For all fiber types and all stretching conditions, substantial increases in Young's moduli were induced, the increases being closely related to the induced extensions. However, it was found that tensile strengths generally decreased if fibers were subjected to high temperatures without significant stretching. On the other hand, the tensile strengths were restored to their original values when greater strains were induced by using higher stresses. Although fibers with a relatively large diameter of 8·3 μm were produced with a modulus of -470GPa and strength of -3·7 GPa, greater improvements in mechanical properties were achieved with smaller diameter fibers. The loads and temperatures involved in these hot stretching experiments were not excessive, and the investigations showed that serious consideration should be given to the feasibility of commercial production of high performance PAN-based carbon fibers by this processing route.     

Structural features of polyacrylonitrile-based carbon fibers

The structural changes as functions of spinning conditions and heat treatments were investigated with respect to the structural feature of PAN-based carbon fibers by scanning tunneling microscopy (STM). The distinct granule structure on the cross section of both high tensile strength and high modulus carbon fibers was observed by SEM, while slender granule-shape domain on the longitudinal surface was revealed by STM. A structure model was proposed, which depicted that the PAN-based carbon fiber was a heterogeneous structure composed of aggregated mesostructural domains. These domains were closely arranged into spiral form along fiber axis, allowing the fibers have high strength and good elongation. The initial shape and size of domains was determined by the precursor composition and spinning conditions and also strongly depended on the heat-treated temperature and stretching conditions. The smaller or slender domain, the higher tensile strength obtained for fibers. We expect that the PAN-based carbon fiber with better performance should be produced by optimizing the size and shape of these domains.     

The effect of surface modification with carbon nanotubes upon the tensile strength and Weibull modulus of carbon fibers

Carbon fibers are widely used as reinforcements in composite materials because of their high specific strength and modulus. Today, a number of ultrahigh strength polyacrylonitrile (PAN)-based (more than 6?GPa), and ultrahigh modulus pitch-based (more than 900?GPa) carbon fibers have been commercially available. In contrast, carbon nanotube (CNT) with the extremely high tensile strength have attracted attention as reinforcements. An interesting technique to modify the carbon fiber is CNT grafting on the carbon fiber surface. CNT-grafted carbon fibers offer the opportunity to add the potential benefits of nanoscale reinforcement to well-established fibrous composites to create micro-nano multiscale hybrid composites. In the present study, the tensile properties of CNT grown on T1000GB PAN- and K13D pitch-based carbon fibers have been investigated. Single filament tensile test at gauge lengths of 1, 5, and 25?mm were conducted. The effect of gauge length on tensile strength and Weibull modulus of CNT-grafted PAN- and pitch-based carbon fibers were evaluated. It was found that grafting of CNT improves the tensile strength and Weibull modulus of PAN- and pitch-based carbon fibers with longer gauge length (≥5?mm). The results also clearly show that for CNT-grafted and as-received PAN- and pitch-based carbon fibers, there is a linear relation between the Weibull modulus and the average tensile strength on log–log scale.     

The effect of high-temperature vapor deposition polymerization of polyimide coating on tensile properties of polyacrylonitrile- and pitch-based carbon fibers

Carbon fibers are widely used as a reinforcement in composite materials because of their high-specific strength and modulus. Current trends toward the development of carbon fibers have been driven in two directions; ultrahigh tensile strength fiber with a fairly high strain to failure (~2 %), and ultrahigh modulus fiber with high-thermal conductivity. Today, a number of ultrahigh strength polyacrylonitrile (PAN)-based (more than 6 GPa), and ultrahigh modulus pitch-based (more than 900 GPa) carbon fibers have been commercially available. In the present work, the tensile properties of polyimide-coated PAN-based (T1000GB, T300, and M60JB) and pitch-based (K13D and XN-05) carbon fibers have been investigated using a single-filament tensile test. The pyromellitic dianhydride/4-4′-oxydianiline polyimide coating was deposited on the carbon fiber surface using high-temperature vapor deposition polymerization (VDP_H). The Weibull statistical distributions of the tensile strength were characterized. The results clearly show that the VDP_H polyimide coating improves the tensile strength and the Weibull modulus of PAN- and pitch-based carbon fibers.