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Morphological characterization of steam-exploded hemp fibers and their utilization in polypropylene-based composites
Abstract
An investigation is described in which the morphology of hemp stem was examined by optical and scanning electron microscopy. We reported the results concerning steam-explosion treatment either on bast fibers impregnated with alkaline liquor or on woody hemp chènevotte samples impregnated under neutral, acidic and alkaline conditions. The influence of steam-explosion treatment parameters were followed by optic and scanning electron microscopy, chemical composition and evolution of the average (DPv) values of the purified samples. Hemp bast fibers purified by steam treatment were compounded with polypropylene (PP), either directly or after surface treatment with polypropylene-maleic anhydride co-polymer (PPMA). Polypropylene/hemp fibers composite films with various amount of fibers were prepared and their mechanical properties were improved, in particular when fibers treated with PPMA were used.
... 22,26 The impacts of introducing individual fibers within polymer composite formulations as well as the relevant influence on mechanical performance have been investigated through experimental studies. [27][28][29][30] The steam explosion process (STEX) was carried out by Vignon et al. 31 with the aim of degrading the pectins from the middle lamella and producing individual fibers for fabrication of hemp fiber polyethylene (PE) composites. Similarly, the thermomechanical milling process was performed by Brendan et al. 32 to yield individual fibers with increased compatibility with polypropylene matrix. ...
... Several researchers have mentioned the positive effect of surface area on the mechanical properties of the composite. 31,65,66 Mohammad et al. 59 studied the effect of surface nanoengineering treatment on the mechanical properties of glass fiber reinforced composites. It was found that the silica-based nanostructured coatings significantly improved the fiber surface area and provided higher tensile and flexural properties (up to 31 %). ...
Natural fiber reinforced composites have garnered significant interests as potential substitutes for conventional materials because of their eco-friendly attribute and favorable physical and mechanical properties. Typically the natural fiber undergoes chemical treatment before processing with the matrix to produce composites, however, the chemical treatment can have a negative impact on the environment. This research work presents an environmentally friendly treatment method for hemp fibers by using boiling water and shear force for specific time periods. The purpose of the treatment is to break down the technical fiber bundles into elementary fibers, which creates a fourfold increase in bonding surface area between the fibers and matrix. The change in fiber length and size before and after the debundling treatment were analyzed using optical microscope, confocal microscope, and scanning electron microscopy. The treated fibers were then made into mats through a wet-laid process and compression molded with low density polyethylene via film stacking. The effects of different fiber treatment variables, including debundling time, on mechanical properties were compared with composites reinforced with conventional alkali treated fibers. The results presented show that the composites reinforced by hemp fiber using the new treatment method have equivalent or improved tensile, flexural and impact properties than the composite reinforced with alkali treated fibers.
... Steam explosion is an efficient and low-energy method of fiber separation as an alternative to environmentally harmful fiber separation methods like water retting. Compared to conventional retting techniques, steam explosion takes less time and is easier to control [29]. Semi-retted bast fiber is separated from the woody core and impregnated with a weak solution of sodium hydroxide under vacuum. ...
... Semi-retted bast fiber is separated from the woody core and impregnated with a weak solution of sodium hydroxide under vacuum. The fibers are drained before loading into a steam reactor and steamed for 90 s at 2000 • C (1.5 MPa) [29]. The quick release of pressure from the steam reactor causes explosive decompression. ...
Hemp (Cannabis sativa Linn) is a high-yielding annual crop farmed for its stalk fiber and oil-producing seeds. This specialized crop is currently experiencing a revival in production. Hemp fiber contains pectin, hemicellulose and lignin with superior strength, while hemp seed oil contains unsaturated triglycerides with well-established nutritional and physiological properties. Therefore, focus on the utilization of hemp in various industries is increasing globally. This study reviewed recent applications of hemp components, including fiber and extract, in food, textile and packaging applications. Hemp fibers mainly consisting of cellulose derivatives have superior strength to be used as reinforcements in thermoplastic packaging and paper. Combined physical and chemical modifications of hemp fibers improved mechanical and barrier properties of composite materials. Physically and chemically processed hemp extracts have been used in food and non-food applications. Functional foods containing hemp oils deliver nutrients by their unsaturated lipids. High-quality hemp fiber with several fiber modifications has been applied in garments. Innovative applications of hemp components and by-products are increasing, thereby facilitating utilization of green sustainable biomaterials.
... Le diamètre moyen mesuré pour les fibres non traitées (41,1 µm) correspond bien aux valeurs trouvées dans la littérature (entre 10 et 50 µm (Lewin, 2007;Masset, 2008;Rodriguez Garcia, 2006;Vignon et al., 1996…)). ...
... Représentation schématique de l'effet de l'explosion à la vapeur sur la morphologie et le degré de polymérisation de la cellulose(Yamashiki et al., 1990)Vignon et al. (1996) ont effectué une explosion (200°C, 90 secondes) de chènevotte après une imprégnation par une solution de soude concentrée à 2 % massique. Selon leurs résultats, le degré de polymérisation de la cellulose chute de 1400-1500 à 900. ...
Depuis des millénaires, le chanvre est cultivé pour ses fibres. Longues et résistantes, elles peuvent notamment entrer dans la composition de matériaux textiles et composites, secteurs industriels en plein essor. Cependant, leur manque d’homogénéité et la complexité de leur affinage ne leur permettent pas encore d’être compétitives face aux fibres synthétiques ou de coton. Mais des fibres de chanvre fines pourraient être produites à partir de fibres brutes en utilisant un traitement par explosion à la vapeur à bas coût, faible consommation d’énergie et avec un faible impact environnemental. Une caractérisation morphologique, chimique et mécanique des fibres a été réalisée avant et après traitement dans le but d’optimiser les paramètres de ce procédé, selon une méthodologie de plan d’expériences. Ces essais ont montré que l’explosion à la vapeur pouvait être utilisée pour produire des fibres correspondant aux critères imposés par l’industrie textile et des matériaux composites. Des éléments ont aussi été apportés sur une éventuelle industrialisation de l’explosion à la vapeur. Là encore, les résultats montrent que ce procédé pourrait être industriellement compétitif en termes de coûts, de consommation en eau et en énergie, et de rendements. Enfin, des fibres ont été produites à partir de sols pollués contenant des métaux lourds. Les teneurs en métaux dans les différentes parties de la plante et dans les fibres ont été mesurées avant et après explosion à la vapeur. Les résultats obtenus ouvrent de nouvelles perspectives quant à un usage durable de Technosols (notamment des friches industrielles) pour la production de fibres de chanvre à usage industriel
... Steam explosion has been widely used as a pre-treatment technology for lignocellulosic materials to improve enzyme catalyzed cellulose degradation (Jacquet et al., 2015). It has also been used for pre-treatment of natural fibres intended for use in composites in order to defibrate fibre bundles into single fibres and small fibre bundles by degrading or disrupting the middle lamella (ML) between the individual fibres (Vignon et al., 1996;Keller, 2003;Thomsen et al., 2006;Kukle et al., 2011). ...
... Composites with a fibre volume fraction of up to 42% of steam exploded hemp fibres having a tensile strength of up to 30 MPa and stiffness of up to 4 GPa could be achieved. Steam explosion was also shown to be more effective in degrading pectin from the middle lamella regions, allowing production of small fibre bundles and elementary bast fibres, when steam explosion treatment was combined with biological retting pre-treatment (Vignon et al., 1996). A similar conclusion was drawn from results showing that steam explosion of retted hemp fibres increased the cellulose content from 73 to 85-90 wt%, while that of raw hemp fibres was increased from 60-64 wt% to 73-75 wt% (Thygesen, 2006). ...
Global interest in the use of plant fibres in natural fibre reinforced composites (NFCs) is growing rapidly. The increased interest is primarily due to the advantageous properties of natural fibres including biodegradability, low cost, low density and high stiffness and strength to weight ratio. In order to achieve strong NFCs, well separated and cellulose-rich fibres are required. Hemp is taking a center stage in this regard as a source of suitable natural plant cellulose fibres because natural hemp bast fibres are long and inherently possess high strength. Classical field and water retting methods have been used for centuries for removal of non-cellulosic components from fibrous plant stems including from hemp, but carries a risk of reducing the mechanical properties of the fibres via damaging the cellulose. For NFCs new targeted fibre pre-treatment methods are needed to selectively and effectively remove non-cellulosic components from the plant fibres to produce cellulose rich fibres without introducing any damage to the fibres. A key feature for successful use of natural fibres such as hemp fibres in composite materials is optimal interfacial contact between the fibres and the hydrophobic composite matrix material. Targeted modification of natural fibres for NFCs must also be targeted to optimize the fibre surface properties. Consequently, improved interfacial bonding between fibres and hydrophobic polymers, reduced moisture uptake, increased microbial degradation resistance, and prolonged durability of NFCs can be achieved. This review, using hemp bast fibres as an example, critically and comprehensively assesses the targeted pretreatment technologies and data available for producing well separated cellulose bast fibres having optimal chemical and physical properties for maximizing the mechanical performance and durability of NFCs.
... Las fibras de cáñamo se presentan como haces tan largos como los tallos. Un tallo fresco de cáñamo consiste en un cilindro hueco de xilema de 1-5 mm de grosor cubierto por 10-50 µm de cambium, 100-300 µm de corteza, 20-100 µm de epidermis y 2-5 µm de cutícula (Ilustración 12) (Garcia-Jaldon, Dupeyre, & Vignon, 1998). El lumen es un espacio vacío en los tallos secos. ...
... La tecnología de explosión de vapor (STEX) ha demostrado ser de las mejores para maximizar la resistencia, longitud y limpieza de la fibra (Vignon, 1998). Es una tecnología que utiliza energía y productos químicos muy potentes (hidróxido sódico y acido sulfúrico) para conseguir los resultados deseados. ...
El clima del sudeste peninsular español proporciona las condiciones idóneas para el cultivo de diversas especies que proporcionan una gran variedad de fibras naturales. En la campaña 2012/2013 se sembraron en nuestro país 69.900 ha, de las cuales, el 99,8% de la superficie se localiza en Andalucía, y el resto en Murcia. Sin embargo, desde el año 2005, como consecuencia de la reforma del régimen de ayudas, se produjo un descenso de la superficie y de la producción, pasando de 343.000 t a 55.000 t en la campaña 2008/2009. A partir de 2009, tras el cambio del régimen de ayudas al algodón en la UE, se produjo un aumento de la superficie y de la producción, propiciada además por el fuerte incremento de los precios en el mercado mundial durante 2010 y parte de 2011. En el contexto europeo, Grecia es el mayor productor de algodón, con 270.000 ha cultivadas en 2012/2013, seguida de España y Bulgaria. Por tanto, la importancia del cultivo de plantas para la producción de fibras es tal que hoy día España es considerada como uno de los países productores potenciales a escala mundial. En este sentido, la capacitación de los agricultores de estas especies a través de la información técnica es uno de los elementos básicos en los que se apoya una sólida y moderna agricultura, en un contexto sostenible. El presente trabajo tiene como objetivo primordial poner a disposición de los técnicos, agricultores y todas aquellas personas relacionadas o interesadas en el cultivo de fibras naturales, procesamiento e información acerca de los diferentes aspectos culturales que les permitan mejorar su nivel tecnológico. Se proporciona una información resumida acerca de las generalidades respecto a los tipos de especies industriales, producción y características de las diversos tipos de fibra, lo cual sirve de base en el establecimiento de criterios para la selección material vegetal.
... This is consistent with the water resistance test results. There are two reasons for the increase in relative lignin content in PPAL-HP: (1) poplar underwent self-hydrolysis in aqueous medium, with the cellulose and hemicellulose were partially hydrolyzed into water-soluble sugars and oligomers (Vignon et al., 1996); (2) pretreatment with black liquor allowed additional lignin to be loaded onto the poplar powder.The PP spectrum featured an absorption band at 1038 cm − 1 , which shifts to 1027 cm − 1 in the PPAL-HP spectrum (this band corresponded to the C-O stretching vibration of the carboxyl group in cellulose and hemicellulose that are involved in C-H.O formation). This indicates that PPAL-HP displayed a higher bonding strength between cellulose and lignin (Wróbel-Kwiatkowska et al., 2012). ...
... Examples of complexing agents include EDTA, diethylenetriaminepentaacetic acid, oxalic acid, tetrasodium pyrophosphate and sodium tripolyphosphate; the alkalis commonly employed are NaOH, KOH or Na 2 CO 3 ; and sodium dodecyl sulfate (SDS) is widely used as detergent (Adamsen et al. 2002b;Beltran et al. 2002;Henriksson et al. 1998;Keller et al. 2001;Rognes et al. 2000;Sharma 1988). Such formulations have also been investigated as impregnation media for steam explosion processes, where the treated stems are subject to steam under high pressure followed by a rapid decompression (Garcia-Jaldon et al. 1998;Kessler et al. 1998;Vignon et al. 1996). Treatments of harvested flax with sulfur dioxide aid in preservation of moist plant material for longer durations and increase the retting rate in subsequent enzymatic treatments, but the resulting fiber bundles are coarse and prone to contain residues of inorganic salts (Easson et al. 1998;Sharma et al. 1999). ...
The paper is a review on the extraction processes of cellulosic fibers from flax and hemp. The two lignocellulosic crops have a long history of use by humans for extraction of the bast fibers among other purposes. The utility of bast fibers declined over time with industrial advances and changes to the economy, but of late, with an increase of focus on environmental impact and sustainability, there is a renewed interest in these resources. The use of biomass-based resource requires an appreciation of plant anatomy and the agronomical variables in their cultivation and harvesting. This review provides an overview of these aspects as well as of the processes of retting for initial weakening of the plant structure in preparation for fiber extraction, degumming to isolate fiber bundles, and delignification.
... Sustainability 2019, 11, 3163 2 of 12 found that composites prepared by extrusion followed by injection molding exhibited high flexural strength and stiffness [6]. ...
In recent years there has been a substantial growth in the use of natural fiber reinforced composite in more advanced applications. However, high strength applications require high mechanical properties. Hybridization of natural fibers with synthetic fibers is an effective method of increasing the field of application and mechanical properties. The effects of hybridizing hemp (Cannabis sativa L.) fiber with recycled-carbon fiber were investigated in this study to determine the trends in mechanical properties resulting from varied weight fractions. Characterization of void content was accomplished using micro computed tomography (micro-CT). Through hybridizing hemp fiber and recycled carbon fiber in a polypropylene thermoplastic, a new class of high performance, low cost composites were demonstrated for injection molding applications. This study showcased a 10–15% increase in tensile strength after the reinforcement of recycled-carbon fiber with hemp fiber. A 30–35% increase was observed in the flexure strength after the reinforcement of recycled-carbon fiber with hemp fiber. Impact strength also had an increase of 35–40% for hemp fiber reinforced recycled-carbon fiber polypropylene composites.
... For this aim, many pre-treatments of the fibres have been developed in order to improve the intrinsic properties of the fibre and the adhesion between the fibre and matrix: i) Chemical treatment, using silane, alkaline, acetylation ethylenediaminetetraacetic acid (EDTA) and ethylene diamine tetra (methylene phosphonic acid) (EDTMPA) increases the compatibility between fibres and matrix (Bledzki et al., 2008;Cantero et al., 2003;Islam et al., 2010;Liu et al., 2016), ii) Enzymatic treatment, (e.g. endo-polygalacturonase, hemicellulases) (Liu et al., 2016;Nykter et al., 2008) inducing a cleaner fibre's surface, helps to improve the mechanical properties of fibre reinforced composites and iii) steam explosion (Kukle et al., 2011;Thomsen et al., 2006;Vignon et al., 1997). Although these methods are reported in literature, the most widely used pretreatment in the hemp industry is field retting (also known as dew-retting) thanks to its low cost and ease of use (application) (Sisti et al., 2018). ...
Lignocellulosic fibres such as hemp fibres have emerged as an attractive alternative to nonrenewable fibers in the reinforcements in polymer composites. These fibres are subjected to pretreatment prior fibre extraction. In hemp industry, the retting is the first treatment applied to the plant after harvesting in order to separate the fibres from the central woody part of the stem. This treatment is needed to be more understood because of its importance for the development of high-performance hemp biocomposites. In this study, the influence of field retting treatment and lab-scale retting treatment of hemp fibres harvested at the end of flowering (EF) and at the seed maturity (SM) respectively, on hemp fibres /polypropylene biocomposites was investigated. The results highlight that, regardless the harvest period (initial state of the fibres) and type of retting, the thermal stability of biocomposite increased gradually with retting duration due to the increase of thermal stability of the fibres. The decomposition temperature of the fibres harvested at EF and SM increased from 335 °C and 352 °C, respectively to 350 °C and 368 °C for fibres that retted during five weeks. Tensile strength and Young's modulus of the biocomposites reinforced with fibres harvested at EF increase gradually until reaching a maximum (5 weeks) (46.0 ± 1.9 MPa and 4072 ± 196 MPa respectively), and then tends to decrease with a prolonged field retting (42.9 ± 1.6 MPa and 3627 ± 188 MPa respectively). In contrast, for biocomposites reinforced with fibres harvested at SM and retted in accelerated conditions, the tensile strength and Young's modulus decreased rapidly from 44.9 ± 2.2 MPa and 3732 ± 291 MPa for unretted fibres to 39.9 ± 2.6 MPa and 3327 ± 183 MPa for five week retted fibres.
... Pour résoudre ces problèmes, différents traitements surtout au niveau des fibres sont utilisés afin d'améliorer leurs adhésion avec la matrice et d'augmenter leur stabilité thermique (Vignon et al., 1996 ;Joffe et al., 2003). Il s'agit de traitements physiques comme le corona, le plasma et thermique de rétification ou bien chimiques comme le traitement alcalin et le greffage par du silane, de l'acide acétique, ou encore de molécules à base de benzoyl, d'isocyanate ou de triazin Zafeiropoulos et al., 2001 ;Xie et al., 2010 ;Zafeiropoulos et Baillie, 2007 ;Karmarkar et al. 2007). ...
Cette étude constitue une contribution à la recherche de nouveau matériau composite originaire des ressources naturelles végétales. Elle vise alors à l’exploitation des fibres naturelles extraites de la plante d’Alfa avec une matrice biopolymère thermoplastique de type Mater-Bi® afin d’élaborer des biocomposites. Trois types de fibres courtes extraites de la plante d’Alfa sont préparés ; non traitées et traitées par un traitement alcalin à 1 et 5%. Les diverses techniques utilisées pour la caractérisation des fibres ont révélé une augmentation de la rugosité, du taux de cellulose, de l’indice de cristallinité ainsi de la stabilité thermique après le traitement alcalin. Les matériaux composites sont préparés par extrusion bivis suivi d’une opération d’injection en faisant varier le pourcentage des fibres de 0 à 25%. Les analyses thermiques des biocomposites ont montré un accroissement significatif de la vitesse de cristallisation suite à l'incorporation des fibres d’Alfa ainsi une amélioration de la stabilité thermique pour les matériaux à base de fibres traitées. La résistance à la traction et le module de Young des biocomposites ont augmenté alors que la ténacité et l’allongement à la rupture ont diminué avec l'augmentation du taux de fibres. Les micrographies MEB des surfaces fracturées indiquent une bonne adhésion entre la matrice et les fibres d’Alfa traitées ou non. L’étude de la cinétique de cristallisation des différents biocomposites a prouvé le fort effet nucléant des fibres d’Alfa traitées ou non
... Vignon et al. [52] studied the properties of hemp bast fibers purified by steam treatment compounded with polypropylene (PP), either directly or after surface treatment with polypropylene-maleic anhydride co-polymer. The treatment increased the mechanical properties, tensile modulus, and tensile strength at yield of the resulting PP composites due to a better adhesion between the matrix and the fibers. ...
... Field retting is empirically carried out because of its very environmental-dependent conditions (temperature, humidity and duration) which results many problems of the inconsistency of the hemp fibres quality. For this reason, many efforts are nowadays directed for offering alternative methods of extraction of the fibres such as thermal and enzymatic treatment (Nykter et al., 2008), steam explosion (Vignon et al., 1997) and chemical treatment (Obendorf and Kyung, 2006). These methods are well-controlled, but economic viability for industrial upscaling still remains difficult because they are expensive and need more energy or specific enzymes, contrary to the field retting that is cheaper and easier to be applied (Tahir et al., 2011). ...
The use of hemp fibres as reinforcements in polymer composites requires a thorough understanding of the hemp fibres transformation processes to obtain a constant quality. In this context, the upstream processing termed field retting is considered. Retting allows a subsequent fibre separation from the plant stems by degradation of cementing compounds by microorganisms. This operation depends on weather conditions and is currently empirically carried out in fields, so that a large variability in the hemp fibres quality (color, morphology, biochemical composition, thermal properties and mechanical properties) is resulting. Therefore, the present study aims to investigate the influence of different retting durations (up to 9 weeks) on hemp fibres properties when harvested at the beginning of flowering growth stage to survey their temporal dynamic. Various assessments were applied on fibres: color observations, morphological (optical microscope), surface (ESEM) and biochemical (gravimetry) analyses, spectrocolorimetric measurements (pectins content), thermogravimetric (TGA) analysis, and mechanical in tensile mode testings. The results reveal that increasing the field retting duration leads to a change of color characteristics from light green to grey due to the development of microbial communities (most probably fungal and bacteria) at the stem surface. A separation of the fibres bundle to elementary fibres occurs with the degradation of pectins during retting. An increase of thermal stability of the fibres is also observed. Both increase of cellulose fraction and crystallinity induce an enhancement in tensile properties.
... Cellulose nano-fibrils were successfully produced from pineapple leaf, banana stem, jute and hemp by successive SE techniques combined with chemical treatments. [26][27][28] Vignon et al. 29 studied the production of fibers from chenevotte by SE after acid impregnation. It was shown that temperatures around 220-230 C were required. ...
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.
... These are non-structural applications where modest mechanical properties are not an issue, but there are technical and environmental benefits to using such fibres (Nadji et al. 2009). However, when dealing with natural fibres it is important to remember that different cultivars and growing techniques (Sankari 2000; Defoirdt et al. 2010;Keller et al. 2001), fibre isolation methods (Vignon et al. 1996;Garcia-Jaldon et al. 1998;Morrison et al. 2000;Mooney et al. 2001) and other treatments (Beckermann and Pickering 2008;Tserki et al. 2005;Troedec et al. 2008;Kostic et al. 2008;Pickering et al. 2007), may impact on ''sustainability'' (Chard et al. 2013(Chard et al. , 2015. ...
This study was conducted to determine and analyse the influence of production process on the mechanical properties of bleached alfa pulpboard. Scanning electron microscopy showed that the industrial process currently used to produce the pulpboard causes small-scale and large-scale deformations in the alfa fibres. The same process results in a preferred orientation of the alfa fibres, leading to alignment in the rolling direction and hence there is some variation in the mechanical performance of the pulpboard in the different directions. Indeed, the mechanical properties show that the pulpboard loses its isotropic nature, mainly in the high-deformation regions. The pulpboard does not have the same mechanical characteristics in the longitudinal, 45°, and transverse directions. The samples taken in a longitudinal direction, which corresponds to the rolling direction, have better mechanical performance than in samples taken in the other two directions. Furthermore, the alkali (NaOH) treatment that is used to extract the alfa fibres from the alfa stems did not succeed in removing all of the non-cellulosic materials initially present in the alfa stems.
... It is not hydrolyzed by acids, but soluble in hot alkali, readily oxidized, and easily condensable with phenol. Hemicellulose, pectins and lignin are not thermally stable and tend to degrade at low temperatures (below 250 ºC) [2][3][4][5][6][7]. The degradation of cellulose also begins under 500ºC, but for lower molar mass components as hemicelluloses, thermal decompositions begin at much lower temperature. ...
This work aims to prepare composites of polyamide 66 with vegetal fibers from curauá, jute and flax. Alkaline-treatment was conducted followed by silanization, improving the thermal properties of treated natural fibers. To reduce the processing temperature of PA 66, a combination of LiCl and N-butyl benzene sulphonamide was added to pure polyamide 66. It is shown that plasticizing PA 66 is one way to prepare composites with natural fibers using this high temperature polymer. The increasing of elastic modulus of PA 66 and the decrease of strain at break were observed.
... Water-soluble substances, pectin and waxes existing in water insoluble forms are present in low contents. Amorphous components such as hemicelluloses, pectin and lignin have a low thermal stability and tend to degradation at relatively low temperatures (below 500°C) [15,16]. The changes in hemp fiber/hurds during heating were investigated in some papers [5,[17][18][19]. ...
Sustainability goals are essential driving principles for the development of innovative materials in the construction industry. Natural fibers represent an attractive alternative as reinforcing material due to good mechanical properties and sustainability prerequisites. The study has been focused on the comparative investigation of chemical and physical treatments of hemp hurds and their influence on the thermal behavior of main hemp constituents in air and nitrogen atmosphere. Thermal decomposition of hemp hurds involves several parallel reactions related to heat and mass transfer processes. A comparison of DSC and TG/DTG results of hemp hurds samples before and after treatments demonstrates a better thermal stability for treated samples. It is caused by changes in chemical composition due to a partial removal of non-cellulosic components from hemp hurds structure, an increase in cellulose content and decrease in its degree of polymerization. The results show different thermal behavior of the hurds samples heated under nitrogen and air atmosphere. Based on DTG records, several-stage process of mass loss has been found for the samples under air, whereas only two-stage process under nitrogen.
... One possible way of reusing waste disposable cups and developing new applications for PP from WEEE is to produce PPL reinforced PP composites. Similar PP composites have been investigated using cellulose fibres from a range of natural materials including wood fibre, flax and hemp (Aranberri-Askargorta et al., 2003;Bengtsson et al., 2007;Vignon et al., 1996). In addition to pristine cellulose fibre the use of waste materials such as wood pulp, newspapers and vegetable fibres from agricultural residues has been reported (Thumm and Dickson 2013;Bullions et al., 2006;Ardanuy et al., 2012). ...
The majority of disposable cups are made from paper plastic laminates (PPL) which consist of high quality cellulose fibre with a thin internal polyethylene coating. There are limited recycling options for PPLs which has contributed to disposable cups becoming a high profile, problematic waste. In this work disposable cups have been shredded to form PPL flakes and these have been used to reinforce polypropylene to form novel paper plastic composites (PPCs). Samples were characterised using mechanical analysis and fhermogravimetric analysis (TGA). The work demonstrates that PPL disposable cups have potential to be beneficially reused as reinforcement in novel polypropylene composites.
... Research into the effect of the steam explosion technique on the properties of the fibers is not a new phenomenon. Vignon and coworkers 18 showed that high pressure steam explosion is an effective method to degrade the pectin contained in the fiber and improve the mechanical properties of the fiber-reinforced polypropylene (PP) composite. This technique also enhances the crystallinity of the fiber. ...
Kenaf bast fibers were treated by combined methods with steam (steam-chemical-ultrasonic treatment) and without it (chemical-ultrasonic treatment). The crystallinity and morphological properties of these treated fibers were compared with the untreated ones. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were employed to appraise crystallinity. Morphological features were examined by scanning (SEM) and transmission (TEM) electron microscopies. The fibers treated with steam had a higher degree of crystallinity than those without steam treatments and the untreated fibers. However, steam pre-treatment tended to reduce the fiber surface roughness. The fibers treated without steam showed surprising morphology, which is characterized by the formation of nanofibers on the surface of microfibers. Such morphology should enhance surface roughness and improve the performance of the corresponding composite.
... Research into the effect of the steam explosion technique on the properties of the fibers is not a new phenomenon. Vignon and coworkers 18 showed that high pressure steam explosion is an effective method to degrade the pectin contained in the fiber and improve the mechanical properties of the fiber-reinforced polypropylene (PP) composite. This technique also enhances the crystallinity of the fiber. ...
In order to characterize the morphology and size distribution of the cellulose fibers, natural cellulose from kenaf bast fibers was extracted using two chemical treatments; (1) alkali-bleaching-ultrasonic treatment and (2) alkali-bleaching-hydrolysis. Solutions of NaOH, H2O2 and H2SO4 were used for alkalization, bleaching and hydrolysis, respectively. The hydrolyzed fibers were centrifuged at a rotation speed of 10000 rpm for 10 min to separate the nanofibers from the microfibers. The separation was repeated in 7 steps by controlling pH of the solution in each step until neutrality was reached. Fourier transform infrared (FTIR) spectroscopy was performed on the fibers at the final step of each treatment: i.e. either ultrasonic treated- or hydrolyzed microfibers. Their FTIR spectra were compared with FTIR spectrum of a reference commercial α-cellulose. Changes in morphology and size distribution of the treated fibers were examined by scanning electron microscopy (SEM). FTIR spectra of ultrasonic treated- and hydrolyzed microfibers nearly coincided with the FTIR spectrum of commercial α-cellulose, suggesting successful extraction of cellulose. Ultrasonic treatment for 6 h resulted in a specific morphology in which cellulose nanofibers (=100 nm) were distributed across the entire surface of cellulose microfibers (∼5 μm). Constant magnetic stirring combined with acid hydrolysis resulted in an inhomogeneous size distribution of both cellulose rods (500 nm-3 μm length, 100-200 nm diameter) and particles 100-200 nm in size. Changes in morphology of the cellulose fibers depended upon the stirring time; longer stirring time resulted in shorter fiber lengths.
... Microbiological degumming is preferred because of the relative controllability of the resulting fiber quality (Ramaswamy et al. 1995), but high cost is one concern for kenaf production. As a physical degumming method, steam explosion (STEX) treatment has received increasing attention and has been developed because it is less time-consuming, more environmentally friendly, offers good repeatability (Vignon et al. 1996), and, most importantly, the degradation of hemicellulose and lignin during the STEX treatment is helpful to the subsequent degumming process. As a well-known method for separating lignocellulosic material into its three main components (cellulose, lignin, and hemicelluloses) (Josefsson et al. 2002), steam explosion of lignocellulosic material has been studied at length in recent years . ...
Kenaf is an economically viable and ecologically friendly cellulose source. It can be used in the textile, paper, and bio-energy industries, but it has not been effectively developed and utilized because of degumming problems. To effectively take advantage of kenaf resources, to satisfy the growing demand for natural fiber, and to provide support for other fiber material degumming, steam explosion (STEX) pretreatment followed by alkali-oxygen treatment was studied. The effect of pressure on the properties of kenaf during the STEX treatment was studied, and the optimal degumming process for kenaf was selected. Results showed that STEX pretreatment removed pectin and part of the hemicellulose. Carbohydrates (cellulose and hemicellulose) could be degraded via high pressure treatment. The residual gum content and the fineness of the kenaf fiber after the alkali-oxygen treatment were good enough for textile production. High pressure was found not to be a key factor influencing the degumming process. Low pressure STEX (0.5 MPa) and alkali-oxygen treatment was judged to be an efficient method for degumming kenaf fibers.
... The principle of steam explosion pretreatment is using the high temperature and high pressure steam to process the plant fiber raw materials in order to make the hemicellulose degradation and lignin softening, and decrease the lateral connection strength between the fibers (Shao et al. 2008). After a period of high temperature and high pressure treatment, the steam is released in a short time to achieve the effect of the chemical composition separation and the structural change (Vignon et al. 1996). Hence, processing parameters such as steam temperature and pressure, retention time, and pre-soaking in water, are important for the materials processing (Han et al. 2010). ...
The objective of this investigation was to evaluate the properties of binderless manufactured from bamboo (Phyllostachys heterocycla cv. pubescens) processing residues by steam explosion treatment. In particular, the effect of steam explosion retention time on fiber morphology, chemical composition and the properties of the boards was studied. The bamboo fibers were separated by steam explosion fully, and the hemicellulose degradation products and lignin were liberated from the fibers by steam explosion treatment and accumulated on the surface of the fibers, which contributed to the bond formation in the boards. The board properties evaluated were modulus of rupture (MOR), internal bond strength (TB), thickness swelling (TS) and water absorption (WA). The boards made from fibers treated under 180 s retention time exhibited the highest MOR value of 15.9 MPa. All boards passed the Japanese Industrial Standard A 59052003 for TB values except for the board made with fibers underwent extraction with hot water and hot-grind bamboo fibers. By increasing the retention time from 60 to 180 s, the thickness swelling was reduced by 73 %, and the water absorption decreased by 44 % respectively. In accordance with BS EN 622-5-2006, only the boards 3.0/120 and 3.0/180 matched the all requirementsfor ultra-light medium density (MDF) boards for use in dry conditions.
... Boiling or steaming of wood prior to grinding for mechanical pulping or production of coarse fibers has become common practice since then (Harris 1952). Although wet thermal methods have been carried out to remove hemicelluloses from lignocellulosic materials other than wood and, in some cases, some composites have been manufactured with those materials after thermal pretreatment (see for example Vignon et al. 1996;Focher et al. 1998;Suzuki et al. 1998;Laemsak and Okuma 2000;Keller 2003;Velasquez et al. 2003;Mosier et al. 2005b;Widyorini et al. 2005;Mohebby et al. 2008;Shao et al. 2009;Quintana et al. 2009;Mancera et al. 2011;Luo and Yang 2011; and other fifteen works referred by Youngquist et al. 1994), this review is focused on studies that have involved wood. Tiemann (1915) (referred by Hill 2006) reported that pre-dried wood subjected to steam at 150°C and 4 h reduced moisture sorption by up to 25 %, with low negative effects on mechanical properties. ...
The objective of this paper is to review the published literature on improving properties of wood composites through thermal pretreatment of wood. Thermal pretreatment has been conducted in moist environments using hot water or steam at temperatures up to 180 and 230 °C, respectively, or in dry environments using inert gases at temperatures up to 240 °C. In these conditions, hemicelluloses are removed, crystallinity index of cellulose is increased, and cellulose degree of polymerization is reduced, while lignin is not considerably affected. Thermally modified wood has been used to manufacture wood–plastic composites, particleboard, oriented strand board, binderless panels, fiberboard, waferboard, and flakeboard. Thermal pretreatment considerably reduced water absorption and thickness swelling of wood composites, which has been attributed mainly to the removal of hemicelluloses. Mechanical properties have been increased or sometimes reduced, depending on the product and the conditions of the pretreatment. Thermal pretreatment has also shown to improve the resistance of composites to decay.
The interest and thus the number of publications on the supply chains of bast fiber plants has steadily increased in recent years. A number of specific technical terms related to methods and their use for individual areas of the supply chain are often interpreted and used in very different ways. Therefore, the aim of this publication is to increase the clarity of the description of the operations and to improve the understanding of the sequence and the purpose of the process steps. This is based on a selected review of the relevant literature as well as on suggestions for their classification
Among the naturally available biodegradable materials, bast fibres (BF) play a significant role in engineering applications. The key attributes of BFs are dielectric, hygroscopic and surface properties, insulation properties and mechanical strength. The properties are variable based on chemical composition and environmental conditions. This study exhibits the extraction of BFs and the effect of physical modification of BFs and their effects. BFs can be extracted from herbs such as flax, hemp, ramie and other wild plants. The common extraction processes are microbial retting, mechanical extraction and alkali extraction techniques. The outer bark or phloem of jute, kenaf flax and hemp plants are called cellulose fibres and it is annually renewable crops growing in 9–100 days. The modifications of these BFs through biodegradable and eco-friendly techniques such as plasma treatment, fungi, microbial and biochemical reactions of enzymes. The treatment of BFs using these techniques varies the properties of the material. In the textile industries, natural fibres extracted from the plants play a vital role in the production of cloths, fabrics and mats that are ecologically sound. Cultivators involved in the growth of the herbs, as well as the extraction and treatment of the fibres, may benefit from the BFs. Hence, researchers show interest in discovering novel fibre and focusing on the various techniques to modify the surface of the already-discovered fibre for industrial requirements. These modifications can be accomplished by various eco-friendly methods such as physical, chemical and physicochemical treatments. In this paper, we have discussed and reviewed the various physical, chemical and surface behaviours of BFs and various surface treatments to modify the surface behaviour of the extracted BFs.
KeywordsBast fibresCelluloseBiodegradableSurface treatmentBark layerVegetable fibre
A poorly water soluble polar and non-polar bioactive complexes encapsulated in a nanocellulose-based polymeric network are the focus of this research. Ascorbic acid, resveratrol, holy basil extract, pomegranate extract, and niacin are all microencapsulated bioactive complexes that make up Zetalife®, a nutritional ingredient. It uses an interpenetrating polymeric network (IPN) with more dispersed nanocellulose and phospholipids to increase Zetalife® s bioavailability. Field Emission Scanning Electron Microscopic (FESEM) images were used in studying the morphology of encapsulated bioactive molecules. The average microbead size was determined to be 244.2 nm. After each month of storage, the sample’s microbial content was measured to assess stability. In vitro release followed a first-order kinetic model with high R2.
Bast fiber has gained momentum due to its renewable, biodegradable, multipurpose, and affordable features. After harvest, bast fiber plants are require to undergo a processing phase known as retting or degumming. It involves the separation of cellulosic bast fibers from heterogeneous inherent gummy substances, mainly hemicellulose, pectin, and lignin. While bast fibers are biocompatible, the current retting process involves environmental pollutants and is a complicated traditional or artificial process. Traditional retting processes, that is, water retting and dew retting, have been implemented for bast fiber production since its inception. With the augmented process, traditional retting processes are currently facing many difficulties, such as pollution, inefficiency, and the deficit of inputs. Traditionally, retting is achieved by naturally growing microbial mixtures and maceration in open field conditions. Currently, the demand for freshwater bodies is in competition with other agricultural sectors. Therefore the unavailability of sufficient retting niches, many bast mass has been concentrated on the same place, halting the biological oxygen supply to aquatic flora and fauna. Due to global climate change, uneven and low precipitation has increased the entire bast industry’s instability. Hence, the alternative retting process by manipulating retting elements with potential microbial agents has gained attention in this sector. The inoculation of potential bacterial agents as an initial starter is considered in many studies, giving upscaling insights into triggering the retting process, but its success depends on some crucial factors. This study discusses bast fiber retting processes, both bacterial formulations and enzymes, focused on selection criteria, separation efficiency, and the interaction with other retting factors.
Bast fiber plants require a post-harvest process to yield useable natural cellulosic fibers, denoted as retting or degumming. It encompasses the degradation of the cell wall’s non-cellulosic gummy substances (NCGs), facilitating fibers separations, setting the fiber’s quality, and determining downstream usages. Due to the inconvenience of traditional retting practices, bacterial inoculum and enzyme applications for retting gained attention. Therefore, concurrent changes of agroclimatic and socioeconomic conditions, the conventional water retting confront multiple difficulties, bast industries become vulnerable, and bacterial agents mediated augmented bio-retting processes trying to adapt to sustainability. However, this process’s success demands a delicate balance among substrates and retting-related biotic and abiotic factors. These critical factors were coupled to degrade bast fibers NCGs in bacterial retting while holistically disregarded in basic research. In this study, a set of factors were defined that critically regulates the process and requires to be comprehended to achieve optimum retting without failure. This review presents the bacterial strain characteristics, enzyme potentials, specific bast plant cell wall’s structure, compositions, solvents, and interactions relating to the maximum NCGs removal. Among plants, associated factors pectin is the primary biding material that determines the process’s dynamics, while its degree of esterification has a proficient effect through bacterial enzymatic degradation. The accomplished bast plant cell wall’s structure, macerating solvents pH, and temperature greatly influence the bacterial retting process. This article also highlights the remediation process of water retting pollution in a biocompatible manner concerning the bast fiber industry’s endurance.
The ongoing degradation of the environment along with the necessity to fabricate the reasonable finished goods, the intellectuals are switching their interest towards the prevarication of polymeric composites, generated by using vegetable fibers as their raw materials, which are entirely biodegradable in nature. Howbeit, these vegetable fibers interact with water molecules with the aid of hydroxyl (–OH) groups present over their superficial area and thus possess hydrophilic nature. This trait of fiber leads to poor bonding between the water repelling matrix, and therefore disturbing the consonance of the polymeric composites. As a consequence, it is an attire need for the treatment of plant fiber for better adhesion between the fiber and the matrix. Several researches had been carried out on the varied approaches for the modification of vegetable fiber and the reinforced polymer composites, to ameliorate their physiochemical properties. Multifarious surface treatment methodologies like Physical, Chemical and Biological are surveyed for the effectiveness of the finished product. Chemical Treatment like Alkylation, Silane, and Acetylation etc. are compiled and presented in this chapter. But with need for less harmful and eco-sustainable process, the demand for using the chemical treatment is diminishing day-by-day and scientist are shifting towards biological and physical treatments, which are also discussed briefly. Accentuation is laid upon the future scope for employing the sustainable and green treatment for the surface modification.
Green composites are materials having eco-friendly attributes that are technically and economically feasible while minimizing the generation of pollution. In this context, it refers to the combination of fully degradable fibers mostly cellulosic materials and natural resins to develop green composite materials. In the past decade, overdependence on petroleum products (synthetic polymers, resins, etc.) has consistently increased, and on account of this the researchers are now focusing more on green materials specially cellulosic. Green composites do not harm the environment much and could be satisfactory alternatives to petroleum-based polymers and polymer composites. The developing anxiety toward prevention of ecological destruction and the unfilled requirement for more adaptable environmental friendly materials has prompted expanding interest about polymer composites, originating from sustainable sources and biodegradable plant materials, particularly from forests. These have widened the utilization of plant fibers as reinforcements and have increased the possibility for sustainable and “biodegradable” composites, which can be called “green” composites as they satisfy the criteria of “green materials.” Thus the challenge to obtain “green” composite involves obtaining “green” polymers functioning as matrices in the production of composite materials. This chapter considers the materials and methods utilized for the fabrication and particularly the utilization of green composites in different technological fields.
Natural fiber-reinforced polymer composites (NFRPC) offer numerous advantages over the widely used nonrenewable materials sources in terms of recyclability, lower pollutant and greenhouse gas emissions, and enhanced energy recovery. Also, these materials are relatively cheap and have low density, low machine wear, good thermal insulation, and acoustic properties, high flexural strength, and abundance in quantity. Utilizing the synergetic effect, currently, hybrid composites are fabricated through a combination of multiple interfacial additives to overcome certain drawbacks like high moisture absorbing property and poor wettability often noticed in NFRPCs. In this chapter, the synergistic effect of NFRPC obtained through hybridization technique with multiple natural fiber fillers, the effect of nanofillers and synthetic hybridization are discussed.
Ce travail de thèse porte sur l’élaboration et la caractérisation de nouveaux matériaux composites à base de fibres naturelles. Cette étude consiste à exploiter des renforts végétaux résultant du travail du bois d’olivier introduit sous forme de farine de bois d’olivier (FBO) dans une matrice polymère en polypropylène (PP). Ainsi, deux types de bio-composites PP/FBO ont été fabriqués : les combinaisons polypropylène avec les fibres de farine de bois d’olivier non traitées ou traitées avec de l’amino-silane avec un taux de charge massique de 3%. Suite au traitement chimique, les caractérisations des fibres traitées ont montré une augmentation de taux de cellulose, de la rugosité, de la stabilité thermique et aussi de la cristallinité. Les échantillons de matériaux composites étudiés ont été fabriqués à partir des matières premières PP et FBO, par extrusion bi-vis suivie d’une injection en variant le taux de charge en FBO de 0 à 30%. Les micrographies des facettes de rupture réaliséesau microscope électronique à balayage (MEB) montrent une meilleure adhésion entre la matrice et les fibres traitées par rapport à celles non traitées. Dans l’objectif d’une caractérisation des propriétés élastiques, des méthodes de caractérisation destructive par essais mécanique et non destructive par ultrasons, sont confrontées afin d’en établir la correspondance, mais aussi les limites. Il en résulte que la rigidité des bio-composites PP/FBO a été améliorée avec l'augmentation du taux de fibres et l'ajout d'un agent de couplage. Un facteur de corrélation entre les modules de Young estimés est établi entre les valeurs ultrasonores et les valeurs mécaniques. Les vitesses longitudinale et transversaleaugmentent dans les mêmes proportions que la teneur en fibres et que l’ajout d’un agent de couplage. Enfin, la structure interne des échantillons de bio-composites PP/FBO a été évaluée par réflectométrie ultrasonore et la tomographie par rayons X.
In recent years, ecological awareness and other environmental issues led to the development of composite materials based on renewable resources such as natural fibers. These materials are environmentally friendly and low-cost alternatives to replace synthetic fibers. However, despite all those advantages, vegetable fibers have certain limits which can be reduced by using the natural fiber hybridization technique. Indeed, the combination of two or more different types of natural reinforcements in a common matrix leads to the improvement in composite mechanical properties. The only condition required to obtain a hybrid effect is that the two reinforcements must be different in terms of mechanical property and the type of interaction with the matrix. The aim of this chapter is to present the recent advances in manufacturing hybrid natural fiber composites and highlight their importance. First, it gives a complete presentation about the hybrid biocomposites in the case of thermoplastic and thermosetting materials, followed by their implementation process. Then, it explains how fiber hybridization is a promising strategy to toughen composite materials and to offer a better balance in mechanical properties than nonhybrid composites. Finally, despite all this technique's advantages, it has been concluded that any microstructural changes in the material can cause irreversible damages, which are listed at the end of the chapter.
The raising use of fiber composites is leading to a growing demand for understanding and mastering the damages and failures during the in-service of composite components.
This chapter aims to provide a relatively detailed description of defects and damages that occur in fiber composite structures especially the defects related to the fiber and the matrix. An understanding of the criticality of the defects and damages leads to determine the failure mechanisms and the failure modes that range from simple failure modes to complex failure modes occurring in bidimensional laminates. Conclusively, methods of detecting the defects and damages using nondestructive testing methods have also been described.
New energy-efficient materials are increasingly used in architecture and civil engineering today. Many of these are based on the reuse of plants and plant residues from industry and agriculture for the production of bio-sustainable insulation materials, and as aggregates in concretes. This paper presents the results of our study of research into hemp concrete, an emerging material in the green building sector, since it first appeared about twenty-five years ago to the present day. The study centres on a growing bibliography over this period, emphasizing some fundamental parameters of hemp raw materials and related building materials, the binders used in the production of hemp aggregate concretes and assessments of different aspects of their performance. The most important properties of hemp concrete vary according to the quality of the plant aggregates, the choice of binders (typically aerial or hydraulic lime), the proportions of the raw materials and the application techniques. Organic aggregates are less stable than inorganic aggregates and are therefore more difficult to use in a concrete mix with both inorganic and organic binders. Among other reasons, this is due to the disproportionate amount of water required in the mixing of plant-based concretes and to the release of organic compounds, which can have serious effects on the hardening process. This problem was identified in scientific studies on the use of hemp concrete in sustainable, bioclimatic construction, whether applied as a semi-liquid mass or as a precast element. This new biomaterial offers excellent results in terms of its application on site and has important physical properties, such as high durability and easy conservation. This study seeks to provide a useful tool for future research into sustainable building materials, better use of available energy and plant-based resources and more efficient recycling of the waste produced by human activities.
Natural fiber composites have experienced a renaissance in the last two decades as a response to societal demands for developing eco‐friendly, biodegradable and recyclable materials. They are now being extensively used in everyday products as well as in automotive, packaging, sports and construction industries. Hemp fiber is being used in most of these products because of its superior mechanical properties. Like other natural fibers, hemp fibers require modifications in order to improve their properties and interfacial bonding with polymer matrices, and to reduce their hydrophilic character. These modification methods can be grouped into three major categories: chemical, physical and biological. Chemical methods use chemical reagents to reduce fibers' hydrophilic tendency and thus improve compatibility with the matrix. They also expose more reactive groups on the fiber surface to facilitate efficient coupling with the matrix. Physical methods change structural and surface properties of the fiber and thereby influence the interfacial bonding with matrices, without extensively changing the chemical composition of the fibers. They are cleaner and simpler than the chemical methods. Biological methods use biological agents like fungi, enzymes and bacteria to modify the fiber surface properties. These methods are not toxic like chemical methods and are not energy‐intensive like physical methods. This paper presents an overview of recent developments in these methods. It is concluded that these methods almost invariably result in improvement in fiber/matrix interfacial bonding, resulting in increase in mechanical properties of the composites.
Ces travaux de thèse constituent une contribution au développement de composites chanvre/époxy 100% bio-sourcés. Les enjeux environnementaux actuels favorisent l'émergence de matériaux issus de ressources renouvelables telles que les fibres végétales mais conduisant aussi à une large gamme de synthons bio-sourcés, notamment à l'origine de prépolymères époxydiques. Une étude approfondie des deux constituants (fibres de chanvre et matrices polyépoxydiques) est réalisée avant l'étape d'élaboration des composites. Un traitement au CO2 supercritique est appliqué sur les fibres de chanvre utilisées comme renfort dans les matériaux composites. Le résultat de ce traitement mène à une meilleure individualisation ainsi qu'à une baisse du pouvoir hygroscopique des fibres. Ces aspects, décisifs pour garantir de bonnes propriétés pour le composite final, sont néanmoins nuancés par une baisse des propriétés ultimes en traction à l'échelle des fibres mais également à l'échelle du composite. De la même façon, la diminution du pouvoir hygroscopique des fibres après traitement se répercute à l'échelle du composite, permettant ainsi d'améliorer la durabilité du composite. La synthèse des résines époxydiques utilisées dans cette étude est réalisée à partir de ressources renouvelables et abondantes telles que la lignine. Les polyépoxydes thermodurcissables ainsi préparés présentent de bonnes performances, compatibles avec le cahier des charges pour des applications composites à renfort végétal. Au regard des résultats obtenus, les composites 100% bio-sourcés sont des matériaux d'avenir. Leur développement nécessite néanmoins une étude approfondie de leur durabilité.
Les réelles opportunités de croissance dont bénéficient les marchés liés à l'utilisation de fibres végétales en tant que renfort dans les matériaux composites sont intimement liées aux performances concurrentielles de ces fibres par rapport à celles de fibres de verre en particulier l’allégement, l’amortissement et l’isolation thermique. Dans l'industrie de la fibre de chanvre, le rouissage est le premier traitement appliqué aux plantes afin de faciliter la séparation des fibres de la partie ligneuse centrale de la tige. Ce traitement est actuellement réalisé de manière empirique en champ conduisant à l’obtention de fibres de qualité variable (couleur, morphologie, microstructure, composition biochimique, propriétés thermiques et mécaniques) ce qui constitue un frein à leur utilisation plus large dans des composites hautes performances. Par conséquent, la maîtrise du rouissage est primordiale. L’objectif de ce travail de thèse est de développer une approche globale de cette étape-clé de la production des fibres de chanvre en combinant à la fois l’étude du mécanisme biologique du rouissage, celle des caractéristiques intrinsèques des fibres et celle des émissions gazeuses et des odeurs associées à l’étape de rouissage. Différents items ont été particulièrement examinés :- L’influence de la durée du rouissage et de la période de récolte sur les caractéristiques intrinsèques des fibres de chanvre (couleur, morphologie, composition biochimique, microstructure, propriétés mécaniques, propriétés thermiques).- L’évolution des émissions de composés organiques volatils (COV) et de l'odeur lors du rouissage en champ.- La dynamique temporelle des densités de population des communautés bactériennes et fongiques pendant le rouissage- L'impact du rouissage en champ (climat méditerranéen) et du rouissage accéléré (conditions contrôlées en laboratoire) sur les propriétés microstructurales, thermiques et mécaniques d’un biocomposite polypropylène/fibre de chanvre
The development of high-performance materials made from natural resources is increasing worldwide. Within this framework, natural fiber reinforced polymeric composites now experience great expansion and applications in many fields, ranging from the automotive to the construction sector. The great challenge in producing composites containing natural fibers and with controlled features is connected to the great variation in properties and characteristics of fibers. The quality of the natural fibers is largely determined by the efficiency of the treatment process and can dramatically influence the properties of the final composites. The overall fiber extraction processes, applied to vegetable fibers, is called retting and consists in the separation of fiber bundles from the cuticularized epidermis and the woody core cells. Today, many efforts are being made to optimize the retting methods in terms of fiber quality production, reduction of environmental issues and production costs. This chapter aims to provide a classification and an overview of the retting procedures that have been developed during years and are applied to extract mainly bast fibers.
Wheat bran, abundant but underutilized, was investigated for its potential as a reinforcement in biocomposites through different pretreatment methods. Pretreatment methods included were dilute sodium hydroxide (NaOH), dilute sulfuric acid (H2SO4), liquid hot water (LHW), calcium hydroxide (CaOH), organosolv such as aqueous ethanol (EtOH), and methyl isobutyl ketone (MIBK). Changes in chemical composition and fiber characteristics of the treated bran were studied using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Cellulose content increased to 35.1% and 29.6% in brans treated with H2SO4 and NaOH, respectively. The SEM micrographs showed surface cleaning of treated bran while maintaining sufficient surface roughness for the H2SO4, NaOH, and MIBK treated brans. Crystallinity index increased slightly for all treatments except H2SO4. NaOH and H2SO4 pretreated brans achieved important fiber characteristics, which could be useful for making thermoplastic biocomposites. Innovative use of bran in thermoplastic will create more opportunities for growers while enhancing biodegradability.
Expanding the use of low-environmental impact materials in the field of building materials is a major aim in a context of sustainable development. These alternative materials should be non-polluting, eventually recycled, and locally available. Bioresources are already used in some building materials but few studies have investigated their relevance in such applications. The aim of this paper is to evaluate the suitability of three kinds of vegetal aggregates: barley straw, hemp shiv and corn cob. The availability of these bioresources, extracted from a French database, is discussed, as are their physical properties and chemical compositions. Their microstructure is described with SEM images and their particle size distributions are provided through image analysis. Sorption–desorption isotherms are measured by a Dynamic Vapour Sorption system. Bulk density, thermal conductivity and water absorption are also quantified. The results highlight a tubular structure for the three different aggregates, with low bulk density and thermal conductivity (0.044, 0.051 and 0.096 W m−1 K−1 respectively for straw, hemp shiv and corn cob) and high water absorption, especially for barley straw and hemp shiv (414 and 380% vs. 123% for corn cob). Their hygric regulation capacity is also sufficiently good, with a water sorption of between 20 and 26% at 95% of relative humidity. These plant aggregates could therefore be used as additions in an earth matrix, or a hydraulic, pozzolanic, air lime or gypsum binder, or just as loose-fill insulation material. However, future research should focus on their resistance to fire and bacterial growth to validate this approach.
This chapter gives the state of the art on the chemical composition of bio-aggregates and their interactions with mineral binders from the standpoint of bio-aggregate based building materials. The chemical composition of various bioresources included in bio-aggregate based building materials has been reviewed by comparing the results of 24 published references. This comparison highlights a large dispersion among the results of different references for the same bioresource, reflecting not only the effective variability of chemical composition due to agronomic, environmental and processing parameters but also the strong disparities in the results of common indirect gravimetric methods of biomass compositional analysis. However, the chemical composition of lignocellulosic particles can strongly impact their properties as bio-aggregates included in a mineral matrix. At early age, they can disturb the setting and hardening mechanisms of mineral binders; in the hardened state, they can modify the properties of the composite; and, finally, in the long term, they can influence durability.
The hemp (Cannabis Sativa L), traditionally applied in the paper and textile industries, is now used as a natural alternative for reinforcing composite materials. In this work the capacity of hemp as material for reinforcing polypropylene (PP) as polymer matrix has been evaluated. Mechanical properties under tensile, flexural and impact strengths have been studied, for materials reinforced with 20, 30 and 40 wt% of hemp strands. Moreover, the effect in the use of maleated polypropylene (MAPP) as coupling agent has been analysed with the aim of optimising the mechanical properties of these materials. The matrix-reinforcement adhesion has been examined by scanning electron microscopy (SEM). The formation of covalent bonds between the matrix and the strands as well as the determination of functional groups has been evaluated by FTIR spectroscopy. The obtained results inform that the hemp strands have enough capacity to be used as reinforcement of composite materials based on PP due to their intrinsic properties. The addition of MAPP leads to composite materials with tensile and flexural strengths which amount up 70% the values of PP composite materials reinforced with glass fiber.
The effects of cotton bast (CB) content and steam explosion parameters (including steam pressure, holdup time, and moisture content) on the mechanical properties of low density polyethylene (LDPE)/CB composites were investigated. The results show that LDPE/steam exploded cotton bast (SECB) composites show superior tensile and flexural properties compared with pure LDPE and LDPE/unmodified CB composites. The superficial area of CB is increased by steam explosion pretreatment, thus enhancing the mechanical properties of composites.
This chapter introduces the mechanism, key parameters, and operation mode of steam explosion, and emphasizes the recent investigations in biorefinery as a pretreatment or fractionation process. Although many kinds of pretreatment processes have been explored and developed, none of them has been employed industrially for second-generation bioethanol production in view of the cost and economical efficiency. Steam explosion, as a physicochemical treatment, has specific characteristic advantages over the others and has been considered extensively as a promising pretreatment for improving the enzymatic bioconversion. The biorefinery concept designates that the total utilization of lignocellulosic biomass and high-value-added production from main components is forward direction. This review summarizes the basic theoretic issues of steam explosion and provides the latest data of its applications on the production of ethanol or sugars.
This chapter mainly reviews the concept, properties and processing, and design method of the eco-friendly polymer nanocomposite (EPN), which is generally biodegradable and renewable. The major attractions of EPN are that they are environmentally friendly, sustainable, and degradable. These polymer composites can be easily composted or disposed without harming the environment. Some efforts have been made on attaining biodegradable reinforcing fillers giving improved performance of composites. Another concern is focused on employing recyclable synthetic fibers with thermoplastic composites to reduce the waste of fillers, and also some research is devoted to reusing or recycling the whole composites for the similar purpose. Simultaneously, people also would like to make composites manufactured with traditional production process become eco-friendly by extra reprocessing. Throughout the stages of development—design, appraisal, manufacture, use, reuse–recycling, and disposal—researchers are supposed to be fully engaged in reducing waste as much as possible, keeping in mind the environment all the time. A series of natural or synthetic materials have been used, such as cellulose, thermoplastic starch, etc. The challenge posed by eco-friendly composites also needs considerable attention in terms of poor bonding between matrix and fillers, loose control of fiber orientation, and difficulty in shaping nanoscale particles.
With the thermal gravity analysis and relative breaking strength test, both crystallization variability and the important temperature is determined in heating process of hemp fibers. Meanwhile, the critical time and temperature is got which have a effect on relative breaking strength of hemp fibres and the hemp fabric appearance. Those data about thermal stability is helpful for hemp manufacturing and processing.
With increasing environmental awareness and ecological risk, green composites have gained more and more research attention, as they have the potential to be attractive than the traditional petroleum-based composites which are toxic and nonbiodegradable. Because of their lightweight, friendly processing and acoustic insulation, green composites have been used widely ranging from aerospace sector to household applications. The end-of-life concern with many polymeric composites has also limited their application spectrum. The green composites not only replace the traditional materials such as steel and wood but also challenge certain nonbiodegradable polymer composites. The present research initiative aims at highlighting the issues and challenges in the development and characterization of poly lactic acid-based green composites. A few of these important composites and their mechanical properties (tensile, compressive, flexural, and impact strength) have been reported in this study. The focus is the identification of the possible areas for their novel applications. A study has been conducted to categorize the various types of green composites on the basis of their physical, chemical, and mechanical characteristics.
Polypropylene (PP) was reinforced with different wood fibers, chemithermomechani-cal (CTMP) aspen and commercial pulps (Tempure and Temalfa-A). Various chemical treatments on the fiber was carried out to improve the bonding at the interface. Fibres coated with Silane coupling agents Silane A-172 and A-174 (with vinyl and methacryloxy functional groups respectively) upon reinforcement showed poor tensile strength. PP filled with Pre-coated fibers containing maleated propylene wax, polymer and polymethylene polyphenyl isocyanate produced higher tensile strength and modulus. The use of dicummyl peroxide and cummine hydro peroxide as initiators during the coating of the fiber was not effective. Polypropylene reinforced with fibers of lower mesh size gave better tensile properties.
The study of biomass liquefaction has demonstrated that, under a variety of conditions and for several different substrates, it is possible to obtain oil yields in the range of 30 to 50% with oxygen contents of 10–30%. Economic analysis of these processes shows that it is desirable to have a low severity process and to define this, one requires some kinetic and mechanistic insight in order to optimize the process. The purpose of this article is to note that the rate determining step (i.e. that which controls the kinetics) appears to be the dissolution of the solid substrate and that the severity of this step controls the rate of liquefaction. Later reaction steps result in increasing fragmentation and deoxygenation of the material, leading to the production of “oil”.
Steam explosion treatment was carried out on almost pure natural celluloses (wood pulps and purified cotton linter) to obtain alkali-soluble cellulose and to clarify the effect of cellulose resources on the changes in morphology, viscosity-average degree of polymerisation Pv, solubility towards aqueous alkali solution Sa, and supermolecular structure of the celluloses. Soft wood pulp was most effectively treated in view of the changes in morphology and Pv, but cotton linter was found to be resistant to the treatment. The degree of breakdown of intramolecular hydrogen bonding at C3 and C6 (Xam(C3) and Xam(C6), respectively), as determined by solid-state cross-polarisation/magic angle sample spinning (CP/MAS) NMR, had a tendency to increase for soft wood pulp by the steam treatment employed here. Contrary to this, the crystallinity and the average crystal size estimated by X-ray diffraction increased. Solubility of the treated wood pulps towards aqueous alkali solution can be improved to 100% when suitable conditions for the steam explosion are chosen to give Pv less than 400 and Xam(C3) greater than 44% and Xam(C6) greater than 33%. Solid-state NMR analysis may suggest that hydrogen bond formation at the C2 hydroxyl group may first take place in the structural change of cellulose during the steam explosion.
An attempt was made to clarify the effect of steam explosion conditions on the changes in morphology, degree of polymerisation Pv, solubility towards aqueous alkali solution Sa, and supermolecular structure of a soft wood pulp and to elucidate the mechanism by which the steam explosion treatment makes natural cellulose completely soluble in aqueous alkali solution. For this purpose, scanning electron microscopic (SEM) observation and X-ray diffraction, solid-state cross-polarisation/magic-angle sample-spinning (CP/MAS) 13C nuclear magnetic resonance (NMR), Sa and Pv measurements were carried out on a series of soft wood pulps treated systematically by the steam explosion method. It was found that (1) the maximum Sa (c. 100%) was obtained when the soft wood pulp was treated under the conditions of steam pressure P = 2.9MPa and treatment time t = 30s, (2) the decrease in Pv of the pulp by the steam explosion resembled conventional acid hydrolysis of cellulose, (3) a higher water content in the sample to be treated gave a lower degree of decrease in Pv, (4) the repeated steam explosion method gave more fibrillated sample with higher Sa than the corresponding batch steam explosion, (5) the amorphous content of the samples as estimated by X-ray analysis decreased by the steam explosion, in spite of an increase in Sa, and (6) the structural parameters expressing the degree of breakdown in the intramolecular hydrogen bonds at the C3 and C6 positions, Xam(C3) and Xam(C6), of the samples as estimated by CP/MAS 13C NMR changed as functions of P and t, being almost parallel to Sa. This suggests that these parameters may be more closely correlated with Sa than with Xam(X) from X-ray analysis.
Cellulose fibers were surface modified with polypropylene–maleic anhydride copolymer. The physical properties of such fibers were characterized by contact angle measurements, and the chemical structure was identified with ESCA and FTIR. ESCA showed that the modifying agent was localized at the surface of the fibers. The modified fibers were compounded with polypropylene, and composites with various amount of fibers were manufactured by injection molding. All mechanical properties were improved when treated fibers were used. SEM showed improved dispersion, wetting of fibers, and adhesion. The nature of adhesion was studied using FTIR. It was found that the surface modifying agent is covalently bonded to the fibers through esterification. The degree of esterification is enhanced by activating the modifying agent before fiber treatment. This study has shown the effects of treatment conditions on activation of reactive species and chemical reaction between fiber and modifying agent. Moreover, a better understanding has been achieved of the nature of adhesion for the system.
Polypropylene (PP) was reinforced with chemi-thermomechanical (CTMP) pulp and wood flour. Different chemical treatment of the fiber a) polyethylene-poly-(phenyl isocyanate), b) silane A-172 and c) epolene was carried out to improve the bonding between the polymer and fiber. PP reinforced with CTMP pulp and wood flour showed a decrease in stress values as the concentration of fiber increased in the composite. Tensile modulus generally increased with filler loading and was not much affected by fiber treatment. Experimental results of the composites were compared with theoretically predicted values.
The ultrastructure of steam-exploded wood from the softwood Pinus radiata D. Don was examined by electron microscopy in order to determine the reasons for increased porosity and enhanced susceptibility to enzymatic hydrolysis. Ultrastructural changes were observed in the form of lignin redistribution and swelling of the cellulose framework. Lignin showed evidence of melting, having contracted into well defined agglomerates suspended in a web of cellulose. Using lanthanum and gold tracers of known particle size the pores in the microfibrillar cell wall have been examined. Cellulose regions were shown to contain numerous pores greater than 2 nm, while lignin agglomerates did not contain such pores. Treatment with NaOH resulted in lignin being smeared over the porous cell wall material — hence blocking pores and reducing digestibility.
この論文は国立情報学研究所の学術雑誌公開支援事業により電子化されました。 Wood chips of Shirakaba (Betula platiphilla Skatchev var, Japonica Hara) and Karamatsu (Larix leptolepis Gordon) were treated with a high pressure steam (12-28 kg/cm^2) for 1-16 min., and the steam pressure was released instantaneously to result in explosion wood. When the treating time was longer more fibrillation of cell walls of Shirakaba occurred. However, Karamatsu chips gave small non-fibrillated block fragments. Fibers of the explosion wood of both woods were observed to be vigorously ruptured. Glycosidic linkage of hemicelluloses and alkyl-aryl linkages of lignin were hydrolyzed to give low molecular weight fragments. Cellulose, on the other hand, remained apparently intact. The crystallinity and micelle width were found to be increased by explosion.
この論文は国立情報学研究所の学術雑誌公開支援事業により電子化されました。
The factors affecting the stability, hydrolysis, reduction, acetylation, quantitation, and identification of the neutral sugars from vegetable fiber preparations have been studied critically and optimized. The recommended method offers a consolidation of the recent modifications of the alditol acetate procedure for the estimation of neutral sugars. The recovery of the sugars was tested by glc and ion-exchange chromatography. Also, the modified carbazole method of Bitter and Muir was adapted to make it applicable for the estimation of uronic acid content of fiber because uronic acid cannot be estimated quantitatively by the acetylation procedure. It is emphasized that the proposed method is applicable only to highly purified fiber preparations which are free of coprecipitated intracellular compounds. Also, the levels of pentoses and hexoses in the fiber must be well defined and a suitable correction made for their interference in the assay.
Effects of time, temperature, and pH during the steam explosion of poplar wood were studied with the aim of optimize both pentoses recovery and enzymatic hydrolysis efficiency. Steam explosion of acid impregnated wood chips allowed the recovery of 70% of potential xylose as monomers (217 degrees C, 120 s) Enzymatic hydrolysis of pretreated fiber with Trichoderma reesei CL-847 cellulase system increased progressively with the severity of the steam treatment conditions. The best yield in term of glucose recovery after 24 h of enzymatic hydrolysis was 70% of potential glucose (225 degrees C, 120 s). Deactivation by adsorption on lignin of Trichoderma reesei cellulases and inhibition of these enzymes by low-molecular-weight phenols and trihydroxybutyric acids were noticed.
Optic micrograph of individualized woody core cells. (a) Wood fiber (scale bar: 10 /~m); (b) pith parenchyma cells (scale bar: 10 /zm); (c) ray cells
- M R Vignon
- D Dupeyre
- C Garcia
M. R. Vignon, D. Dupeyre, C. Garcia-Jaldon Fig. 3. Optic micrograph of individualized woody core cells. (a) Wood fiber (scale bar: 10 /~m); (b) pith parenchyma cells (scale bar: 10 /zm); (c) ray cells (scale bar: 10 /tin).
Garcia-Jaldon Fig. 1. Optic micrographs of thin Sections of hemp stem. (a) Transverse section of a hemp stem (scale bar: 10 ~tm); (b) transverse section of the cortex zone (scale bar: 10 /tm); (c) transverse section of the woody core
- M R Vignon
- D Dupeyre
M. R. Vignon, D. Dupeyre, C. Garcia-Jaldon Fig. 1. Optic micrographs of thin Sections of hemp stem. (a) Transverse section of a hemp stem (scale bar: 10 ~tm); (b) transverse section of the cortex zone (scale bar: 10 /tm); (c) transverse section of the woody core (scale bar: 10 jura).
Leaves, stem and wood in relation to taxonomy
- Metcalfe
Metcalfe, C. R. & Chalk, L. (1950). Leaves, stem and
wood in relation to taxonomy. In Anatomy of the Dicoty-&dons, ed. G. Cumberlege. Oxford University Press,
London, Volume II, pp. 1244-1278.
Examination of the bast fibre of Cannabis sativa, Linn (wild variety). The Textile Manufacturer
- B K Lohani
- B Biswas
Lohani, B. K. & Biswas, B. (1953). Examination of the
bast fibre of Cannabis sativa, Linn (wild variety). The
Textile Manufacturer, June, 329-332.
- T Yamashiki
- T Matsui
- M Saitoh
- K Okajima
- K Kamide
- T Sawada
Yamashiki, T., Matsui, T., Saitoh, M., Okajima, K.,
Kamide, K. & Sawada, T. (1990). Brit. Polymer J., 2,
121-128.
Autohydrolyse rapide de copeaux de bois de peuplier
- D Barnet
- G Excoffier
- M R Vignon
Barnet, D., Excoffier, G. & Vignon, M. R. (1989). Valorisation de la biomasse lignocellulosique. Autohydrolyse
rapide de copeaux de bois de peuplier. Bull. Soc. Chim.
Fr., 836-843.
P~,te h tr~s haut rendement: mise en p~te-V et blanchiment h partir de tremble. Pulp and Paper Canada
- B V Kokta
- R Chen
- H Y Zhan
- D Barrette
- R Vit
Kokta, B. V., Chen, R., Zhan, H. Y., Barrette, D. & Vit,
R. (1988). P~,te h tr~s haut rendement: mise en p~te-V
et blanchiment h partir de tremble. Pulp and Paper Canada, 89, T91-T97.
The structure of textiles fibers. VIII. The long vegetable fibers
- A J Turner
- M R Vignon
- C Garcia-Jaldon
- D Dupeyre
Turner, A. J. (1949). The structure of textiles fibers. VIII.
The long vegetable fibers. J. Textile hzst., 40, 972.
Vignon, M. R., Garcia-Jaldon, C. & Dupeyre, D. (1996).
Fibers from semi-retted hemp bundles by steam explosion treatment. Biomass and Bioenergy (in press).
Examination of the bast fibre of Cannabis sativa, Linn (wild variety)
- Lohani
Characterization of cellulose treated by the steam explosion method. Part I: influence of the cellulose resources on the changes in morphology, degree of polymerization, solubility and solid structure
- Yamashiki
Valorisation de la biomasse lignocellulosique
- Barnet