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Application of microwave energy in degumming of hemp stems for the processing of fibres
Abstract
Microwave assisted-degumming/retting of hemp stems was established and the changes in the components like cellulose, hemicellulose and lignin during microwave treatment were studied by near infrared (NIR) analysis of the fibres processed from the treated hemp stems. Pre-soaked hemp stems subjected to microwave assisted degumming/retting at various power levels showed significant increase in the cellulose content from 72.1% to 79.8% when compared with the control samples. The percentage of hemicellulose and
lignin were the key factors in binding the fibres together, which showed significant decrease when subjected to microwave treatment. Hemicellulose decreased from 14.5% to 12.1% and lignin from 8% to 5.5%. These compositional changes proved the effect of microwave energy in fibre separation. Measurements of diameter distribution and tensile strength, and colorimetric analysis, were performed to verify the effect on the physical
properties. Thirty five percent of control sample hemp fibre diameters were <23 mm whereas the microwave-assisted retted samples contained more than 50% of fibre diameter were <23 mm. Colorimetric tests and tensile strength tests did not show any specific trends but the results confirmed that the microwave energy did not have any significant influence in the changes of the physical qualities during the process. The above studies showed the efficiency of microwave treatments for the degumming of hemp fibres.
... This treatment attacks the middle lamella holding the fibres together. According to Nair et al. [16] or Cheng et al. [17], microwaves degrades the polar molecules created in the material during the soaking of the samples mentioned above. Pectin being a more polar molecule than cellulose, it is primarily degraded by the degumming treatment with microwave energy. ...
... The tests were conducted on a microwave oven of adjustable power and processing time. The processing power used is the same as that chosen by Nair in its study, i.e. 2 W per gram of material [16]. ...
Fibres from hemp stems can be extracted through different mechanical processes following dew or water retting etc. Extraction processes generally have a significant impact on mechanical and morphological properties of the fibres. In this study, hemp fibres are extracted following three different ways. In the first route hemp fibres are extracted from FUTURA 75 variety stems by performing scutching, hackling and microwave degumming. A second batch of fibres of the same variety was extracted by scutching and hackling after an initial microwave degumming treatment. In the third route, the same variety of hemp fibres are extracted from dew retted stems grown at Piacenza (Italy). Finally, the mechanical properties of single fibres as well as the fineness of technical fibres of all types of extracted fibres are evaluated and compared and the interest of the microwave degumming for hemp stem is evaluated.
... A treatment process defined as "degumming" is necessarily required to remove the gummy non-cellulosic materials closely adhered on the surface of bast fibers, the aim of this procedure is to eliminate the gummy non-cellulosic compounds with keeping the integrality of chemical structures or physical properties of ramie fibers . Degumming is the vital and critical method to isolate cellulosic fibers and prepare bast fibers in the textile industry (J. H. Liu, Guan, and Li 2018;Nair et al. 2015). Degumming technology has been extensively explored and widely used in extraction of cellulose fibers from ramie, which could be classified as chemical, physical, and biological techniques (Mishra et al. 2021;Wu et al. 2022;Yang et al. 2021). ...
Cellulose fibers from ramie is a kind of functional biological material with multipurpose in the textile industry, which called as “China grass.” The degumming of ramie fibers performed with Bacillus subtilis were regulated by response regulator CitT from CitS/CitT two-component system through specifically functioning on the degradation of component pectin. In this study, comparative proteomic analysis was executed to obtain insights into the sensitivity by which the metabolic network induced by the absence of CitT protein, and to further explore the regulatory mechanism during bio-degumming process of ramie fibers. Results showed that 29 differentially expressed proteins were detected from original strain and mutant strain, which were mainly involved in transmembrane transport system, two-component system, and amino acid metabolism. This study demonstrated that the lack of CitT protein could result in the down-regulation of enzymes in histidine biosynthesis pathway, and the up-regulation of enzyme in arginine degradation pathway. This study is the first time to reveal comprehensive information about the regulatory function of CitT protein in bio-degumming of ramie fibers, and may provide important scientific and technological basis for targeted constructing engineering strains in degumming of ramie fibers.
... An interesting solution for obtaining fibers is the use of microwaves in the retting process. For this purpose, flax [35] and hemp [36] straws were retted in water (at different times) and then microwaved, determining the effect of the applied power and exposure time on the quality of the fibers. The authors showed that retting helps loosen the bonds of pectin bonds connecting the fibers to the woody parts of the plant stalk in the plant. ...
This study presents the quantity and quality of flax (Linum usitatissimum L.) and hemp (Cannabis sativa L.) fibers obtained depending on the fiber extraction method. The extraction methods used in this study were osmotic degumming, dew retting, and water retting. The degummed straw was analyzed for fiber content, while the metrological, chemical, and physical properties were determined for the fibers obtained. It was shown that these properties change based on the method of fiber extraction used. The highest fiber content in the straw was obtained using the osmotic degumming method. These fibers are characterized by a light color, no unpleasant odor, low linear mass, good tenacity, lowest hygroscopicity, and reduced flammability compared to fibers obtained via the dew and water retting of straw.
... The retting experiment lasted for 120 h at 30 °C (Zhao et al. 2016). The microwave-assisted/natural hot water degumming (retting) (Nair et al. 2015) was performed immediately after the pre-soaking for all samples . The pre-soaked flax stems were subjected to microwave treatment in a microwave generator (Midea M1-L213C; Midea Group, Beijing, China). ...
Microwave-assistance was used to increase the degumming efficiency in flax water retting. Different pre-soaking times, microwave times, and microwave power were investigated in this study. The relationships between degumming rate and process parameters were established via response surface methodology (RSM). The optimum process parameters were a pre-soaking time of 25.5 h, a microwave time of 18.5 min, and a microwave power setting of 570 W. Under these optimal conditions, the degumming rate was 83.85% ± 1.13%, which was 1.33 times higher than that of natural hot water retting (P < 0.05). Moreover, the tensile properties and color of the resulting fibers showed that they had tensile properties similar to those of the natural hot water retting fibers. However, the color values for the natural hot water retting fibers were higher than those of the fibers treated with microwave-assisted flax water retting.
... Moreover, hemp grows 2 times faster, has 3 times higher fiber yield, has between 2-3 times lower carbon emissions compared to cotton (Ahirwar and Behera 2022;Duque Schumacher et al. 2020), and has a positive effect on biodiversity when assessing for biodiversity friendliness, while cotton has a negative score (Piotrowski and Carus 2011). Although the current industrial hemp degumming process is not yet sustainable, reducing hemp's advantage over cotton in overall production sustainability (Duque Schumacher et al. 2020), significant progress is being made toward sustainable degumming (Kalia et al. 2013;Kozłowski and Rózańska 2020;Nair et al. 2015). Moreover, the quality of hemp as a textile fabric, known to be quite stiff and ruff compared to cotton, has improved over the years thanks to adapted fiber treatment and spinning, making hemp fabric's aesthetic value comparable to that of cotton Vandepitte et al. 2020). ...
This paper evaluates the valorization potential of industrial hemp (Cannabis sativa L.) fibers produced on HM-contaminated soil as a safe feedstock for the textile industry. The chosen strategy was phytoattenuation, which combines the progressive soil quality improvement of contaminated land using phytoremediation techniques with the production of safe non-food biomass. A field experiment was set up with two hemp cultivars on a site contaminated with Cd, Pb, and Zn and on a nearby site containing clean soil as a control. Stem height and diameter were analyzed, as well as stem and fiber yield and the HM concentrations in the fibers, which were compared to legal safety standards and toxicity thresholds used in the textile industry. The hemp cultivar Carmagnola Selected (CS) had a significantly higher stem and bigger stem diameter compared to cultivar USO 31 on both sites. Stem yields showed a decrease of 30% and 50%, respectively, for both hemp cultivars grown on the contaminated site. However, the stem yield of CS growing on the contaminated site was similar to the stem yield of USO 31 growing on the control site, indicating that hemp cultivation on contaminated soil can be economically viable. Total and extractable Cd, Pb, and Zn fiber concentrations were far below the toxicity standards for textile production purposes. These results are promising in terms of the potential valorization of contaminated land with hemp cultivation and the development of a non-food value chain within a phytoattenuation strategy.
... Due to the electromagnetic treatment from MWE, the fibers act as a non-homogeneous material with increased polarity and absorb the MWE through the formation of hotspots within the fibers. Nair et al. (Nair et al., 2015) produced high-quality fibers using a microwave-assisted hot water degumming, evidenced by the near infrared (NIR) analysis of the degummed hemp fibers. The degumming performance of natural fibers mainly hinges upon the effective breakage of lignin-carbohydrate complex bonds. ...
Hemp bast fibers were degummed using combined microwave energy (MWE) and deep eutectic solvent (DES) to generate pure hemp cellulose fibers for potential textile applications. The properties of the degummed fibers were investigated and compared with those of the alkali-treated fibers using several analytical techniques. Results revealed that hemp fiber surface underwent dramatic structural disruption during the pretreatment, due to the removal of “gummy” compounds (i.e., pectin, oil, wax, etc.), lignin, and amorphous cellulose. The treated fibers had much enhanced thermal stability due to the removal of the gummy materials. The reduced enthalpy (171.34 J/g) of MWE-DES treated fibers at 1:20 fiber-DES ratio as compared to that of raw hemp fibers (272.09 J/g) also confirmed the higher thermal stability of MWE-DES treated fibers. Chemical composition analysis showed that the holocellulose content in the treated fiber samples at 1:20 fiber-DES ratio increased to 98.63% which was comparable with the holocellulose content (98.87%) of the alkali-treated fibers. The Ultraviolet (UV) protection factor (UPF) of MWE-DES treated fibers at 1:10 and 1:20 fiber-DES ratio was, respectively, 118.11 and 114.19, meeting the requirement of UV resistant textile fibers. The study demonstrates a potentially effective, less time-consuming, and environmentally sustainable protocol for manufacturing purified hemp cellulose fibers using combined MWE-DES treatment.
... Due to the electromagnetic treatment from MWE, the fibers act as a non-homogeneous material with increased polarity and absorb the MWE through the formation of hotspots within the fibers. Nair et al. (Nair et al., 2015) produced high-quality fibers using a microwave-assisted hot water degumming, evidenced by the near infrared (NIR) analysis of the degummed hemp fibers. The degumming performance of natural fibers mainly hinges upon the effective breakage of lignin-carbohydrate complex bonds. ...
Hemp bast fibers were degummed using combined microwave energy (MWE) and deep eutectic solvent (DES) to generate pure hemp cellulose fibers for potential textile applications. The properties of the obtained fibers were investigated and compared with those from the traditional alkali-based process using several analytical techniques. Results revealed that hemp fiber surface underwent dramatic structural disruption during the pretreatment, due to the removal of “gummy” compounds (i.e., lignin, pectin, oil, and wax) and amorphous cellulose. Ultraviolet (UV) protection factor (UPF) of DES-treated fibers with 1:20 fiber-DES ratio (i.e., 183.67) were significantly higher than those from the traditional alkali-treated (140.75) and untreated raw hemp fibers (127.47). The treated fibers also had higher thermal stability. Chemical composition analysis showed that the cellulose content in the treated fiber samples increased to 49.95% which was comparable with the cellulose content of the alkali-treated fibers (49.49%). The study demonstrates a potentially effective, less time-consuming, and environmentally sustainable protocol for manufacturing purified hemp cellulose fibers using combined MWE-DES treatment.
... Polar molecules interact with oscillating microwave and radio frequency radiation by undergoing rapid rotations, which generates thermal energy (termed dielectric heating) in proportion to the level of interaction. That enables a degree of selectivity as pectin is more polar than cellulose and thus heats up and is degraded at greater rates (Gregoire et al. 2019;Nair et al. 2015). Physical separations of the pectin from the cellulose are also likely. ...
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.
... Overall, the redness (a*) and yellowness (b*) values showed decreasing trends with increasing NaOH-urea loading and sonication time. These results are in accordance with the results reported for flax straw (Nair et al., 2012), corn stover (Karp et al., 2014) and hemp stem (Nair et al., 2015). ...
Selection and characterization of biomass feedstocks with the maximum biomaterial or biofuel yields need the accessibility of reliable and efficient methods for structural and compositional characterization of plant material. Understanding microstructure of lignocellulosic fibre is required to evaluate the heat and mass transfer phenomena, bond formation, fibre alignment and orientation, structural architecture and modelling of structure-property relationship, which are necessary for designing and developing cellulose-based products. Furthermore, the microstructural and compositional information can determine distributionof lignin, hemicellulose and cellulose in the biomass, interaction of reinforced fillers and polymer matrix in the bio-composites.Many conventional standard analytical methods for biomass study are laborious, slow and use harsh chemical reagents that need certain remediation. This paper reviews the microstructural and compositional analyses of lignocellulosic materials through imaging and spectroscopic techniques (I&ST) such as X-ray micro-computed tomography (X-ray μCT), scanning electronmicroscope (SEM), confocal laser scanning microscopy (CLSM), Fourier transform infrared (FTIR) spectroscopy and near infrared spectroscopy (NIRS). This review attempts to provide fundamental backgrounds, basic working principles, applications and technical limitations and possible solutions of I&ST for analysing lignocellulosic biomass, their products and changes acquired during processing.
... 24-hoursoaked samples treated at 2 W/g for 20 min showed maximum retting efficiency. A mathematical model for compositional changes (rate of change of lignin content, hemicellulose content, and cellulose content) during the microwave-assisted retting of the flax stem [108] and method optimization [109,110] were established in previous papers. Another gel-retting method has been introduced with four hours of retting period, which resulted in high fibre yield [62]. ...
Natural fibres are a gift from nature that we still underutilise. They can be classified into several groups, and bast natural fibre reinforcement in polymer composites has the most promising performance, among others. However, numerous factors have reported influences on mechanical properties of the fibre-reinforced composite, including natural fibre retting processes. In this review, bast fibre retting process and the effect of enzymatic retting on the fibre and fibre-reinforced polymer composites have been discussed and reviewed for the latest research studies. All retting methods except chemical and mechanical retting processes are involving secretion of enzymes by bacteria or fungi under controlled (enzymatic retting) or random conditions (water and dew retting). Besides, enzymatic retting is claimed to have more environmentally friendly wastewater products, shorter retting period, and controllable fibre biochemical components under mild incubation conditions. This review comprehensively assesses the enzymatic retting process for producing high-quality bast fibre and will become a reference for future development on bast fibre-reinforced polymer composites.
... Overall, the redness (a*) and yellowness (b*) values showed decreasing trends with increasing NaOH-urea loading and sonication time. These results are in accordance with the results reported for flax straw (Nair et al., 2012), corn stover (Karp et al., 2014) and hemp stem (Nair et al., 2015). ...
Ultrasound-assisted-alkali-urea (UAAU) pre-treatment of miscanthus biomass was investigated for enhanced delignification and extraction of cellulose fiber. The effect of pre-treatment conditions, sonication time (10.0, 15.0 and 20.0 min), alkali (NaOH) concentration (2.0, 3.5 and 5.0%, w/v) and urea-concentration (1.0, 1.75 and 2.5%, w/v) on the delignification and cellulose content was studied and optimized using a response surface methodology (RSM) based on the Box Behnken Design (BBD). The optimized pre-treatment conditions were 2.1%NaOH, 1.7%urea and 15.5-min sonication time with the corresponding cellulose and lignin content of 47.8% (w/w) and 27.5% (w/w) respectively. The pre-treated samples were characterized by FTIR, colorimeter, SEM, XRD, and TGA analyses. The UAAU pre-treated samples have a higher delignification and cellulose contents than the AU pre-treatment without sonication. Furthermore, selective removal of lignin occurred without degrading the functionalities of cellulose fiber. The UAAU pre-treated samples exhibited higher thermal stability, fibrillation, crystallinity index and smaller crystallite size.
... The coloration of the fibers was evaluated by CIE L*a*b* on a Hunterlab ColourFlex EZ spectrophotometer. The total color difference (ΔE) between treated and untreated materials was calculated according to a published methodology [14]. The hydrophobicity of the fiber was estimated through a wettability measurement, by applying drops of water to the fiber surface and measuring the contact angle between the droplet and the surface. ...
Bast flax fibers were treated, with or without ultrasound assistance, using a low melting mixture (LMM) composed of lactic acid, d-glucose and water. This LMM treatment affected both lignin and hemicelluloses contents and modified the fibers properties identified as crucial parameters in an industrial context, i.e. coloration, wettability, crystallinity, fibers diameter and chemical composition. Surface chemistry of the fibers were investigated through fluorescent tagged carbohydrates binding modules revealing macromolecular rearrangements responsible of both a fibers crystallinity enhancement and an unexpected hydrophobicity. It has been found that LMM treatments bleach fibers, which is considered a beneficial effect independent of the treatments.
... Due to the stiffness of the hemp fiber, it is not suitable for direct use, and it should be treated to remove lignin content and to obtain soft and good separated fibers [12]. The degumming processes like alkali, enzymatic, microwave-assisted [13][14][15] are required to achieve well-defined separation of the industrial hemp fibers with high quality fibers for textile use. Alkali and enzymatic are quite commercialized methods as compared to microwave and ultrasound methods which are not much known. ...
In this study, a comparison between alkaline and enzymatic degumming process of hemp fibers has been carried out. Degumming of hemp fibers is essential to remove the lignin content and to segregate the individual fibers for textile grade applications. In this research, optimization of degumming process parameters was carried out to reduce the strength loss in fibers. The percentage weight loss of hemp fibers after the degumming process was studied. Two approaches comprising alkaline and enzymatic methods were used. Hemp fiber diameter was determined along with the single fiber strength before and after the degumming process. Stiffness is directly linked to fiber diameter. Therefore, the fiber diameter was also taken into consideration for optimization of the degumming process. The chemicals used in alkali degumming were sodium hydroxide, magnesium sulfate, hydrogen peroxide, and magnesium chloride. Alkali degumming was the best-suited degumming method for segregating the individual hemp fibers. The optimized parameters obtained for alkali degumming method were heating time 50 min and heating temperature 75 °C. Enzymatic degumming is an eco-friendly method, but the result obtained does not provide a better separation of fibers and fine fiber diameter.
... Degumming has significant effects on spinning quality, fabric style, and comfort. There is a direct relationship between the degumming quality and fiber properties (Sreenath et al. 1996;Nair et al. 2015). ...
This bio-chemical study focuses on obtaining high-quality hemp fiber. The effects of the structures and properties of hemp fibers in different treatment periods were studied. Moreover, the changes of the surface morphology, chemical composition, and breaking tenacity of hemp fibers were researched by scanning-electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), fluorescence microscopy, and fiber tensile testing. The results showed that by virtue of the enzyme scouring process, alkali refining process, and bleaching process, the pectin, lignin, and hemicellulose and other impurities were removed. Through the single factor experiment, the optimal process conditions for the bio-chemical combination of the degumming process were obtained. These conditions included 10 g of dried hemp fibers, 15% (v/v) pectinase solution, a temperature of 50 °C, a duration of 120 min, pH 8.0 (phosphate buffer), a liquor ratio (w/v) of 1:10, and 0.0625 mol/L NaOH. In these conditions, the residual gum content and breaking tenacity were 4.8% and 49.8 cN/tex, respectively, indicating that the treated hemp fibers met the requirements of the spinning process.
Aiming at the problems of heavy environmental pollution, high energy consumption, and process complexity for current degumming techniques, three types of deep eutectic solvent (DES) systems as eco‐friendly sustainable solutions including choline chloride/urea (CU), ethylenediamine hydrochloride/ethylene glycol (EE) and choline chloride/imidazole (CI) were prepared and applied to the degumming of seed hemp. It was clearly showed that all three DES systems exhibit excellent degumming efficiency on seed hemp to remove noncellulosic components involving in pectin, hemicellulose, and lignin in amorphous region without damage to the structure and crystalline morphology of cellulose, leading to an increase of cellulose portion from 54% to about 80%. CI with the molar ratio of 3:8 at 175°C for 2.5 h give the best removal performance for hemicellulose and pectin while EE with molar ratio of 1:2 at 175°C for 3 h can remove lignin with highest efficiency. However, CU with the lowest cost reveals a balanced removal of three noncellulosic components, which may be the optimal choice for industrial production. Furthermore, density functional theory analysis disclosed the essential information of configuration stability for three DES systems.
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
Miscanthus, a high yield and low maintenance perennial plant with a high cellulose fiber contents, is a potential feedstock for pulp production. In this study, a binary enzyme cocktail of cellulase and laccase was employed for the extraction of cellulose microfibers from miscanthus biomass. The effect of enzyme concentrations (0.10%, 0.15%, 0.20%, and 0.25%, w/w) for the binary enzymes (cellulase-laccase: 1:1 ratio) pre-treatments on pulp and hand-sheet materials were studied and compared with those prepared from the single enzyme (cellulase or laccase) pre-treatment. The binary enzymes concentration at 0.25% (w/w) showed the maximum extraction yield of cellulose (47.2%, w/w) and lignin (27.9%, w/w). The resulting fibers had 43.7% crystallinity, a degree of polymerization of 1435, a water retention value of 312.7%, and a crystallite size of 23.4 nm. Furthermore, the resulting fibers from binary enzymes concentration at 0.25% (w/w) exhibited a higher thermal stability and fibrillated strands than those obtained from the single enzyme pre-treatment. Hand-sheets developed from the cellulose microfibers extracted by the enzyme cocktail at 0.25% (w/w) enzyme concentration showed higher mechanical properties and water absorption capacity than those prepared from the single enzyme pre-treatment.
The optimization of the alkaline degumming process of the hemp fibers was carried out in this study. The degumming parameters were optimized in such a way that the minimum strength loss of hemp fibers and elementary fibers was achieved. The main aim of this research work was to individualize and segregate the fibers uniformly by the removal of lignin content. Hemp single fiber tensile strength was carried out before and after the degumming process to determine the strength loss. It was carried out using a padding mangle and steamer technique. The best-suited alkali degumming method was investigated with the optimized parameters of heating time 45 min and heating temperature 120°C. The chemicals that provided the finest results were sodium hydroxide, wetting agent and hydrogen peroxide.
Cotton is the most popular natural fiber used in apparel industry world over. Although cotton is cultivated in approximately 2.4% of the world’s arable land, it accounts for 24% of the world’s insecticide market. Industrial hemp is considered as the most sustainable raw material as substitute of cotton in textile industry. However, there are several challenges associated with hemp processing as the fiber is coarse, stiff and it has comparatively poor spinnability particularly when 100% hemp is processed in ring spinning system. The purpose of this paper is to investigate the aesthetic and low-stress mechanical properties, and handle value of the plain woven hemp-blended cotton fabrics. The 16Ne and 30Ne linear density compact and ring yarns were produced and were used to manufacture plain woven suiting and shirting fabrics, respectively. Crease recovery angle, pilling, tear and tensile strength, and handle value of the fabrics were determined.
Within the commercially available materials, composites are a class of hybrid material constituted of at least two components. Used for structural and semi-structural applications, glass-fibers composites are widely spread. Due to environmental concerns regarding the final glass-fibers reinforced composites, natural plant fibers have been identified as a potential ersatz. Natural fibers are selected on the base of their intrinsic mechanical resistance, similar nay enhanced than glass-fibers. Local fibers suitable for such application could be found all around the world.
In Europe, natural fibers market is singularly different from the rest of the world. Instead of being ruled by cotton cultivation and trade, flax and hemp represent the main part of the fibers culture and market in Europe. Their physico-chemical properties turn them suitable for use as reinforcement agent in plastic matrix.
To elaborate composite, many steps are required from fibers harvesting to the obtaining of a final functional material. Each step includes multiple parameters to control which affect the resulting composite mechanical properties. Different parameters of the composite elaboration were evaluated to determine which affect the most the final material mechanical properties. Constitutive biopolymers of the fibers were found to play a crucial role in the improvement of the polypropylene and thermoplastic starch reinforcement.
In heterogeneous materials such as composites, an optimal load transfer is researched to fully exploit the properties of both initial components.
Interface quality between fibers and matrix determine this load transfer. In order to improve the fibers-matrices compatibility, fibers treatments exist such as chemical modification or enzymatic functionalization. The effects of these treatments were evaluated at the fibers level and the resulting composite. This manuscript describes and studies the design of functional natural fibers as plastic reinforcement agent.
Keywords : Natural plant fibers, biocomposites, laccase, fibers’ surface, lignocellulose
Microwave-assisted one-step degumming and modification of hemp fiber with graphene oxide (GO) have been studied. The results showed that the residual gum content of the hemp using GO bath is lower than that obtained using water bath, and the hemp fiber possessed electrical conductivity, better breaking strength, thermal conductivity, and good UV protection ability. Raman spectrum indicated that GO turned into reduced graphene oxide during the degumming process, and it was found on the surface of the fibers seen from SEM images. One-step degumming, reduction of GO, and modification of hemp fiber can be achieved with the microwave-assisting.
Flax fiber is an important textile material with excellent antibacterial activity and moisture wicking. Degumming of flax roving is essential in determining flax-fiber quality. Traditional degumming requires a large amount of chemicals to process flax roving. This study aimed to reduce the chemical usage and achieve cleaner production during this process by applying microbial treatment to degum flax roving. Microbial degumming instead of acid pickling and NaClO2-bleaching steps can no longer use H2SO4 and NaClO2, and the amount of alkali can be reduced by 50%. By analyzing the compositional changes of the main steps in traditional degumming processes and microbial-treatment sample, the application of Bacillus subtilis HR5 can achieve a good degumming effect. Results of environmental scanning electron microscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffractometry analyses showed that the gum was remarkably reduced, which can be confirmed by the gum components. Overall, the breaking tenacity and antibacterial activity of fibers degummed by microbial treatment were better than those treated by traditional degumming. These findings demonstrated the feasibility of microbial treatment as a solution for flax roving degumming.
Sustainable production defines an environmental friendly production that we produce without changing the balance of the nature. Processes and the utilized materials should be renewable, and our whole production should be harmless so that nature can recover itself in an indigenous way. All natural fibers are biodegradable and sustainable, and consequently, they are commonly called as biofibers. Providing a sustainable production chain for textile processes requires individual attention for each input in the first place. One of the most important parts of these inputs is raw material selection and therefore fiber supply. Right at this point, hemp fiber step forwards and shines out with its huge sustainable production potential for textile industry. In this chapter, sustainable and biodegradable hemp fiber, which is an alternative to cotton and petroleum-based synthetic fibers, for textile raw material sourcing is reviewed in detail. The parameters that make this fiber sustainable are also investigated. Present common and special uses and possible future innovative alternatives of hemp fibers for technical textiles production are also stated. Mainly, composite material production with this sustainable fiber is reviewed for a replacement of nonsustainable synthetic competitors. When sustainable composite materials are produced not only ecofriendly textile production is carried out but also other materials can be produced with an ecofriendly path leading to more sustainable world.
The mulberry fiber is extracted from the mulberry bast by biochemical degumming method. Based on the single factor experiment, the orthogonal experiment is further designed. The optimal process parameters for biochemical combined degumming are as follows: pretreatment stage, sulfuric acid solution concentration 2.5g/L, time 1h, temperature 60°C, bath ratio 1:20; alkaline pectinase treatment stage, alkaline pectinase solution concentration 46g/L, time 8h, temperature 50°C, bath ratio 1:20, solution pH = 9; alkali boiling stage, sodium hydroxide solution concentration 10g/L, alkali boiling time 3h, sodium silicate 30g/L, temperature 100°C, bath ratio 1:20; xylanase treatment stage, the concentration of xylanase solution 9g/L, the time 4h, the temperature 50°C, the bath ratio 1:20, and the solution pH = 4.8. By comparing the properties of mulberry fiber obtained by biochemical degumming and chemical degumming, it is found that the biochemical degumming process has less damage to fibers and more effective removal of lignin and hemicellulose.
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.
Flax fibers used for various applications are obtained from flax stems. Retting followed by drying and mechanical separation leads to the production of fibers. This review article discusses the application of electro-technologies in the production of bast fibers from the flax stem. In these technologies, flax stems harvested from the field are subjected to microwave assisted retting, followed by electro–osmotic dewatering which reduces the water content of the stems. Dewatered stems are transferred to a microwave chamber for further drying, thus retted stems are obtained for further processing.
Drying is essential for the production of fibre after retting process. Flax fibre was subjected to microwave drying at controlled temperatures to study the change in drying rate and qualities. The rate of drying was then compared with conventional hot air drying. The product temperature was maintained at 40 °C, 60 °C or 80 °C for both microwave and hot air drying. The initial moisture content of flax fibre was about 60% (wet basis). The microwave drying was conducted in a microwave apparatus which recorded mass, product temperature, incident microwave power, reflected microwave power and inlet/outlet air temperature. The final moisture content was set to 9% (wet basis). Microwave-convective drying ensured about 30% to 70% reduction of drying time for drying flax fibre as compared to hot air drying. Curve fitting with different mathematical models were carried out. While a significant difference in colorimeter-assessed colour existed between microwave-convective dried flax fibre and hot air dried flax fibre. The tensile strength of flax fibre, measured with an Instron apparatus, increased with an increase in the processing temperature of both processes. Hot air dried flax fibre showed the greatest tensile strength and modulus of elasticity at processing temperatures of 60 °C and 80 °C.
Flax stems were subjected to microwave drying at controlled temperatures. The rate of drying was then compared with conventional hot air drying. The product temperature was maintained at 40°C, 60°C and 80°C for both microwave and hot air drying. The moisture content of flax stem was about 70% (wet basis). The microwave drying was conducted in a microwave apparatus which recorded mass, product temperature, incident microwave power, reflected microwave power and inlet/outlet air temperature. The final moisture content for experiment was set to 9% (wet basis). Microwaveconvective drying ensured about 30% to 70% reduction of drying time for drying flax straw as compared to hot air drying. Curve fitting with different mathematical models were carried out and all the models were fitted well for both hot air and microwave drying. The tensile strength of flax straw, measured with an Instron apparatus, increased with an increase in the processing temperature of both processes. Hot air dried flax straw showed the greatest tensile strength and modulus of elasticity at processing temperatures of 60°C and 80°C with a significant difference.
Bethune seed flax was collected from Canada with seed removed using a stripper header and straw pulled and left in field for several weeks. Unretted straw was decorticated providing a coarse fiber bundle feedstock for enzyme treatments. Enzyme treatments using a bacterial pectinolytic enzyme with lyase activity were conducted in lab-scale reactors. Four fiber specimens were created: no retting, minimal retting, moderate retting, and full retting. Fiber characterization tests: strength, elongation, diameter, metal content, wax content, and pH were conducted with significant differences between fibers. Thermosetting vinyl ester resin was used to produce composite panels via vacuum-assisted infusion. Composite performance was evaluated using fiber bundle pull-out, tensile, impact, and interlaminar shear tests. Composite tests indicate that composite panels are largely unchanged among fiber samples. Variation in composite performance might not be realized due to poor interfacial bonding being of larger impact than the more subtle changes incurred by the enzyme treatment.
Natural fibre based polymer composite is developed by using high density polyethylene (HDPE) as matrix and Saskatchewan-grown flax oilseed flax fibre as reinforcement to develop a value-added product by using Compression molding processing technology. This is general process use to develop polymer composite product. This technique produces products which are less consistent due to poor dispersion of fibre in polymer matrix. Extrusion process was used for thermo-chemical fibre and polymer blend for better fibre dispersion for manufacturing compression molding product. This research has investigated the effect of flax fibre diameter on physical and mechanical properties of compression molded flax fibre based composites. The compression molded developed composite board could be used for automotive parts, construction industries and other commercial applications. This will help in developing new industries and provide some direction for value-added utilization of flax.
New methods for retting flax are sought to overcome problems in the current method of dew-retting of flax. Published data are reviewed and new data presented on the development and testing of a method to ret flax using pectinase-rich enzyme mixtures plus chelators based on cost and fiber yield and properties. In spray enzyme retting (SER), flax stems are crimped to physically disrupt the plant's protective barrier and then sprayed until soaked with, or briefly immersed in, an enzyme/chelator formulation. Flax is then incubated at temperatures optimal for enzyme activity, washed, and dried. Pilot scale tests, conducted with 10 kg samples of flax retted with a series of formulations, showed that this method effectively retted flax stems from a variety of sources, including fiber flax, mature fiber flax, and linseed straw. Fiber yield, strength, and fineness were significantly influenced by variations in enzyme-chelator amounts. Cellulases inpectinase mixtures appeared to preferentially attack dislocations in fibers and fiber bundles resulting in loss of fiber strength. Polygalacturonases alone effectively separated fiber from non-fiber components. The SER method proved to be an effective framework for further tests on enzyme-chelator formulations that now must be integrated with physical processing to optimize the extraction of flax fibers based on cost and fiber yield and properties.
The thermal degradation behaviour of hemp (Cannabis sativa L.) fibres under a nitrogen atmosphere was investigated by using thermogravimetry (TGA). The kinetic activation energy of treated fibres was calculated from TGA data by using a varied heating rate from 2.5 to 30 °C/min. The greater activation energy of treated hemp fibre compared with untreated fibre represented an increase of purity and improvement in structural order. A hydrophobic solvent affected the degree of non-cellulosic removal. Mercerisation and enzyme scouring removed non-cellulosic components from the fibre; however, structural disruption was observed after higher alkaline concentration, 20 %wt/v and longer scouring time, respectively. Structural disruption was observed by X-ray measurement. The FTIR results indicated an elimination of the non-cellulosic components by the mercerisation treatment and a specific removal of low methoxy pectin by use of pectate lyase enzyme (EC 4.2.2.2). An increase of temperature at the maximum rate of degradation and the rate of weight loss was characteristic of the purity and structure of treated hemp fibre.
To examine evidence on three claims that: 1) the THC content of Australian cannabis plants has increased up to 30 times; 2) problems experienced by cannabis users have increased in Australia in recent years; and 3) an increase in THC content is the most likely explanation of any increase in cannabis-related problems.
These claims were assessed by examining data: 1) on THC potency in Australia, the United States and New Zealand; 2) on cannabis-related problems; and 3) from the 1998 National Drug Strategy Household Survey on patterns of cannabis use.
1) Published data do not show a 30-fold increase in THC potency of cannabis but show a more modest increase in the US. 2) There is suggestive evidence of an increase in cannabis-related problems among people seeking treatment for alcohol and drug problems, juvenile offenders and young adults with psychosis. 3) There are two other more plausible explanations for these reportedly higher rates of cannabis-related problems among adolescents and young adults: (i) more potent forms of cannabis ('heads') are more widely used; and (ii) cannabis users are initiating cannabis at an earlier age, thereby increasing the prevalence of harmful patterns of use.
There has probably been a modest increase in the THC content of cannabis, but changing patterns of cannabis use have probably made a larger contribution to any increase in rates of cannabis-related problems among young Australian adults.
Better data on the THC content of cannabis, the extent of cannabis-related problems and the ability of users to titrate the dose of cannabis would contribute to more informed debate.
Microwave irradiation has been successfully applied in organic chemistry. Spectacular accelerations, higher yields under milder reaction conditions and higher product purities have all been reported. Indeed, a number of authors have described success in reactions that do not occur by conventional heating and even modifications of selectivity (chemo-, regio- and stereoselectivity). The effect of microwave irradiation in organic synthesis is a combination of thermal effects, arising from the heating rate, superheating or "hot spots" and the selective absorption of radiation by polar substances. Such phenomena are not usually accessible by classical heating and the existence of non-thermal effects of highly polarizing radiation--the "specific microwave effect"--is still a controversial topic. An overview of the thermal effects and the current state of non-thermal microwave effects is presented in this critical review along with a view on how these phenomena can be effectively used in organic synthesis.
Samples of flax (Linum usitatissimum) stems from the cultivars ‘Natasja’ and ‘Ariane’ were separated into fibre and core fractions and analysed by gas–liquid chromatographic methods, ¹³C CPMAS NMR spectrometry, histochemistry, electron microscopy and UV absorption microspectrophotometry to assist in determining the structure and composition of these cell walls in relation to quality and utilisation. Analyses from chromatography and NMR gave similar results for carbohydrate and phenolic constituents in various samples and in the lower, more mature regions of the stem. Amounts of uronic acids and xylose were lower while amounts of mannose, galactose and glucose were higher in fibre vs core fractions. Quantities of phenolic constituents were significantly higher in the core than the fibre, with groups representative of both guaiacyl and syringyl lignins; amounts of phenolic acids were low. NMR showed a low intensity signal for aromatics in fibre, and it is possible that such signals arise from compounds in the cuticle rather than the fibre. Microscopic studies indicated that aromatic constituents were present in core cell walls, cuticle of the epidermis, and cell corners and middle lamellae of some regions within the fibre tissues. The lignin in fibre appeared to be of the guaiacyl type and may be too low in concentration to be unambiguously detected by NMR. Aromatic compounds were not observed in the epidermis or parenchyma cell walls. Similar analyses of dew‐retted (unscutched) samples indicated that core tissues were mostly unchanged from unretted samples. Retted fibre tissues still contained lignified cell corners and middle lamellae in some regions. The cuticle, which was associated with retted fibres, was not degraded by dew‐retting fungi. Fungi removed interfibre materials in some places and at times degraded the secondary wall near the cell lumen of fibre cells. Results indicate that microspectrophotometry and histochemistry are useful to identify the location and type of aromatics in fibre cell walls.
The short fibre of oil-flax was studied by IR spectroscopy after fats, waxes and pectins were removed. The changes in the morphology of the fibre after various treatments were studied using SEM.
Up to the middle of 1980s, microwave oven was used only for defrosting frozen food and cooking. Microwave oven has now found an important utility value for carrying out chemical reactions in organic synthesis of compounds. Commercial microwave oven has found its way into India only recently. Microwave irradiation catalyses various chemical reactions efficiently. The main reason for this acceleration in the rate of chemical reactions is the rapid superheating of solvents. Many of the reactions which are conventionally run by thermal process; except for the reactions which require necessary precautions such as the use of dry nitrogen atmosphere, lachrymatric and fuming substances or the substances which may corrode the interior of the oven; can be conducted inside a microwave oven at a much faster rate. Commercial microwave ovens are sufficient for carrying out these reactions. Nevertheless, for carrying out certain reactions specially designed microwave ovens at the laboratory have to be used.
A new method for retting of flax stem was introduced by using microwave energy. The combined effect of pre-soaking, microwave volumetric heating and the non-thermal effect of microwave energy were applied in the retting of flax stem. Effective retting was observed in various combinations of pre-soaking, Microwave treatment times and microwave energy. The samples soaked for 24 and 36 h with microwave treatments of 20 min showed better retting efficiency. Fried tests, Near Infrared analysis and fibre diameter analysis were done to find out the retting efficiency. The effect of non-thermal effect of microwave in flax retting was proved experimentally. Colourimetric tests and tensile strength tests were conducted to compare the quality of fibres after microwave retting and no significant changes in the physical qualities were observed. The water released after pre-soaking was not contaminated because of less microbial activity in short duration of the entire process. In industrial point of view, this method is acceptable because of the ease of recyclability of the pre-soaked water and comparably short duration of the process.
Flax must be retted, in which bast fibres are separated from non-fibre components, and then mechanically processed to clean the fibres before industrial application. In the USDA Flax Fiber Pilot Plant, flax is first cleaned through four separate modules and then passed through a Shirley Analyzer to further clean fibres for high-value applications such as textiles. Often, multiple passages through the Shirley Analyzer are employed to obtain higher quality fibres, but it is difficult to determine when the limit for cleanliness is reached by this method. Further, it is clear that materials other than the woody shive components are being removed by Shirley-cleaning, and a method is needed to assess cleanliness beyond the measure for shives. In this study, we attempted to establish an index to determine the degree of purity of flax fibre during the secondary cleaning stage for high quality fibre. Dew-retted (DR) flax and enzyme-retted (ER) flax, which had been first processed through the USDA Flax Fiber Pilot Plant and assessed for shive content, were processed with 10 repetitions of cleaning through the Shirley Analyzer. For both flax samples, absorbances at 1730, 1766, 2312 and 2350 nm decreased with successive Shirley-cleaning steps. These wavelengths appeared to originate from the epidermal layer (EL) that was associated with the flax fibre, an index was calculated using 11 training samples and validated using 10 independent test samples from the same flax samples. Index values gradually decreased with successive Shirley-cleaning steps for both retted flax samples; a lower index value indicated cleaner fibre. Different curves were apparent for the two flax samples, suggesting variations in the cleanliness of the starting material or perhaps differencess in fibre composition. The results suggest it is possible to determine the extent of cleaning of flax fibre using NIR spectroscopy beyond that for shive content based on the epidermal layer of the plant.
An elementary plant fiber could be assimilated to a laminate, mainly constituted of the secondary wall S2 layer, made of a few non-crystalline polysaccharides reinforced by cellulose fibrils organized in a helix, with a microfibrillar angle (MFA) around 10° relative to the longitudinal fiber axis. This paper investigates the relationships between the MFA, the mechanical properties and the biochemical composition of different varieties of flax. To conduct this study, tensile tests on elementary flax fibers, X-ray diffraction, and solvent extractions have been carried out. Within the different varieties of flax, Young's modulus was found to be negatively correlated with the MFA. The results showed that the ratio between hemicelluloses (matter extracted with alkali) and pectins (hydrolyzed with acids) is highly correlated with the tensile properties; concurrently, we showed the great influence of pectic acids on the fiber’ Young's modulus, and on the orientation of the microfibrils.
Samples of flax (Linum usitatissimum) stems from the cultivars ‘Natasja’ and ‘Ariane’ were separated into fibre and core fractions and analysed by gas–liquid chromatographic methods, 13C CPMAS NMR spectrometry, histochemistry, electron microscopy and UV absorption microspectrophotometry to assist in determining the structure and composition of these cell walls in relation to quality and utilisation. Analyses from chromatography and NMR gave similar results for carbohydrate and phenolic constituents in various samples and in the lower, more mature regions of the stem. Amounts of uronic acids and xylose were lower while amounts of mannose, galactose and glucose were higher in fibre vs core fractions. Quantities of phenolic constituents were significantly higher in the core than the fibre, with groups representative of both guaiacyl and syringyl lignins; amounts of phenolic acids were low. NMR showed a low intensity signal for aromatics in fibre, and it is possible that such signals arise from compounds in the cuticle rather than the fibre. Microscopic studies indicated that aromatic constituents were present in core cell walls, cuticle of the epidermis, and cell corners and middle lamellae of some regions within the fibre tissues. The lignin in fibre appeared to be of the guaiacyl type and may be too low in concentration to be unambiguously detected by NMR. Aromatic compounds were not observed in the epidermis or parenchyma cell walls. Similar analyses of dew-retted (unscutched) samples indicated that core tissues were mostly unchanged from unretted samples. Retted fibre tissues still contained lignified cell corners and middle lamellae in some regions. The cuticle, which was associated with retted fibres, was not degraded by dew-retting fungi. Fungi removed interfibre materials in some places and at times degraded the secondary wall near the cell lumen of fibre cells. Results indicate that microspectrophotometry and histochemistry are useful to identify the location and type of aromatics in fibre cell walls.
Subjective and objective methods were compared for the assessment of the quality of unretted and retted straw, and the fibres obtained after dew-retting of four flax cultivars, Ariane, Evelin, Laura and Viola. Maturity of straw, degree of retting, ease of decortication after retting, divisibility, handle, cleanliness and colour were assessed as subjective factors and of these, degree of retting and handle appear to be useful for assessing quality. The samples were also analysed for physical and chemical differences using a range of objective methods. Straw quality could not be graded using height and maturity, although stem diameter and technical length could indicate quality. Changes in N, lipid and ash content, as a result of retting, were observed. The increase in the proportions of fibre fractions present in retted compared with unretted straw, due to microbial degradation of pectin, could be identified by thermal analysis. Analyses of the fibre samples to determine fineness, strength, cellulose, hemicellulose, lignin and minerals were carried out and significant differences in some of the parameters were identified. Cultivar Laura produced the best fibre. Fibre fineness, ash, lipid, caustic weight loss and fibre fractions as determined by thermal analysis were found to be important objective parameters for quality assessment. The assessment of fibre samples performed subjectively by an expert grader and by selected objective methods gave similar quality rankings.
Hemp (Cannabis sativa), is an annual plant used in the pulp and paper industry. It consists of two main morphological regions, the fibre cells which are bound by the middle lamellae and arranged in bundles, themselves separated by the cortex parenchyma cells with pectic and hemicellulosic rich cell walls, and the woody core with lignified cells. Any industrial utilisation of hemp requires the separation of the fibres from the rest of the plant, which is traditionally achieved by undertaking a dew retting in the field followed by several mechanical treatments. Our objective was to substitute the slow and difficult to control retting process by a fast and well controlled process, i.e. steam explosion treatment (STEX) of semi-retted decorticated hemp bundles. During the STEX treatment the pectins and hemicelluloses are hydrolysed and rendered water- or alkali-soluble, the fibres being more easily degummed. We optimised the treatment parameters (temperature/pressure, time and pH of impregnation) and found that impregnation in alkali and steaming for 90 s at 200°C (1.5 MPa) were among the best conditions for the degumming and individualisation of the elementary fibres. After washing of the steamed material a carding mechanical treatment is necessary to separate the single fibres. The steam exploded samples were observed by scanning electron microscopy (SEM), and the morphological aspects of the steam exploded hemp fibres are discussed.
This paper establishes a new method for estimating the single flax fibre diameter using the LaserScan instrument. The method is based on the mathematical modelling of the experimental fibre and fibre bundle width distribution and enables the flax fibre sample composition to be analysed in terms of proportions of single fibre and fibre bundles. The method can also be applied for the analysis of flax fibre fineness distribution produced by the Optical Fibre Diameter Analyser (OFDA) instrument. This method can be used as a tool for classification of flax accessions according to the estimated single fibre diameter, for evaluation of the efficiency of chemical and biochemical treatments aimed at the modification of flax fibre, and for evaluation of the suitability of flax fibre for spinning and manufacture of composites. The method was applied for the characterisation of 83 accessions from the Linum core collection produced by CGN at Wageningen, The Netherlands. The mean and standard deviation of single fibre diameter and proportion of single fibre and fibre bundles in the sample was estimated. Experimental results were in good agreement with theoretically expected relationships between the estimated mean diameter of single fibre and characteristics of fibre width distribution such as the mode and the overall average.
Information is needed to optimize enzymatic-retting of flax (Linum usitatissimum L.) based on a pectinase-rich mixture and chelators. Seed flax straw from North Dakota in 1998, ‘Natasja’ fiber flax straw from South Carolina in 1993, ‘Ariane’ fiber flax straw field-aged and dried from South Carolina in 1999, ‘Ariane’ fiber flax straw shed-dried from South Carolina in 1999, and Canadian seed flax straw in 1997 comprised diverse samples that were subjected to various tests to improve absorption of enzyme formulation by stems or to evaluate clean fiber yield. Mechanical disruption by crimping stems through fluted rollers at about 80 Newtons gave optimum fiber yield in conjunction with enzymatic-retting and was, therefore, used in further tests to evaluate enzyme absorption. Enzyme absorption was increased significantly for uncrimped flax stems with increased pressure of about 310 kPa or with a vacuum around 88 kPa. Increased pressure was effective more than the vacuum treatment. Samples with minimal post harvest handling were affected more by pressure alterations than samples that had considerable disruptions, such as seed flax straw or field-aged straw. Crimped stems showed little increase in enzyme absorption with alterations in applied pressure. Mechanical treatment of stems by crimping gave the largest increase in enzyme absorption and increased significantly the fiber yields. Based on a variety of sample types, the results suggest that normal atmospheric conditions are satisfactory for penetration of enzyme formulation into crimped stems, and that extraordinary measures are not required to expedite the enzyme-retting process.
Enzyme-retting offers an alternative to the current method of dew-retting to extract fibers from flax (Linum usitatissimum L.). Additional steps could improve the efficiency of enzyme-retting and modify the properties of the resulting fibers. Samples of ‘Ariane’ flax, which were grown in South Carolina during the winter and harvested early for quality fiber or late for both fiber and seed, were presoaked with distilled water before enzyme-retting. Soaked, enzyme-retted, and air-dried fibers were compared with unsoaked, control samples for yield and properties, and the water extract (or a freeze-dried portion) was tested in various methods for its influence on enzyme-retting. Presoaking increased fine fiber yield in some cases, but fiber strength at times was reduced. Analyses of the freeze-dried residue from soaking showed a mixture of sugars (128.6 and 101 mg g−1 for early and late harvest, respectively) and aromatic components including p-coumaric and ferulic acids and guaiacyl and syringyl units (3.51 and 3.05 mg g−1 total aromatics for early and late harvest, respectively). Water extracts from presoaking treatments at 1.0–2.0% (w/v) were not inhibitory to the retting fungus Rhizopus oryzae sb or to Viscozyme used for enzyme-retting, based on the Fried test and enzyme activities. Turbidity tests showed slight growth inhibition for Eschericia coli and Streptococcus sp. in the presence of water extracts from early versus late harvest flax at 0.5% (w/v), with those from late harvest flax more inhibitory. Benefits on the efficiency of water presoaking prior to enzyme-retting were moderate and not uniform in this study, and modifications may depend upon particular flax harvests.
The objective of the review is to provide fundamental knowledge on the chemical composition and structural characteristics of flax fibres. These are long and multinucleate cells without septum or partition (average length 2–5 cm) and have a secondary wall of very large thickness (5–15 μm). Fibres are gathered in bundles of one to three dozen cells that encircle the vascular cylinder. The bundle cohesion is insured by pectins, accumulating in the primary wall and cell junctions. In contrast, lignin, which is present in very low amount, does not seem to play a major role in bundle cohesion. At maturity, secondary wall is characterised by (i) a high level of cellulose with microfibrils locked into an almost axial direction and (ii) 5–15% non-cellulosic polysaccharides (NCPs). The chemical composition of NCPs depends on growth stage, indicating important cell wall remodelling, fibre position and variety. Despite the large disparity of the results reported in the literature, galactose appears to be the predominant sugar of NCPs, and β-1-4-galactan together with rhamnogalacturonan of type I (RG-I) and polygalacturonic acid (PGA) become, with fibre maturity, the most abundant tightly bound NCPs. Glycine-rich proteins (GRPs) and arabinogalactan-proteins (AGPs), also present in flax fibres, are both characterised by appreciable levels of glycine and acidic amino acid and are deficient in hydroxyproline, and may contribute to the cross-linking of pectins. (Galacto)glucomanans/glucans rather than xylans consist of cross-linking polymers in fibre secondary wall. A model is proposed where cellulose microfibrils, tethered by cross-linking (galacto)glucomanans/glucans, are embedded in a pectic matrix.
Pectin and hemicellulose contents were proportionally lower in the seawater-retted fibers compared with the raw hemp fiber according to the Fourier-transform infrared spectroscopy (FTIR) and chemical analyses. Also, the scanning electron microscopy (SEM) observation revealed the non-cellulosic gummy materials in hemp fibers could be removed to a considerable extent by the seawater-retting treatment. Cultivable bacteria involved in this retting process were isolated, and three of purified strains (SW-1, SW-2, and S-SW1) produced relatively high levels of pectinase activities and had good retting ability. The ERIC-PCR fingerprints of stains SW-1, SW-2, and S-SW1 were different, and should be further identified for each isolate. Strains SW-1 and SW-2 were identified as Stenotrophomnas maltophilia, while strain S-SW1 was assigned to Ochrobactrum anthropi by BIOLOG system. These two species represented rhizosphere bacterial genera, and were possibly introduced by the hemp plants. These organisms seemed potentially capable of producing pectinase, and thus effectively degrading pectin substances in this retting process.
It was demonstrated that pulsed microwave irradiation is a more effective method to accelerate the esterification of free fatty acid with a heterogeneous catalyst than continuous microwave irradiation. A square-pulsed microwave with a 400 Hz repetition rate and a 10-20% duty cycle with the same energy as the continuous microwave were used in this study. The pulsed microwaves improved the esterification conversion from 39.9% to 66.1% after 15 min in comparison with the continuous microwave under the same reaction conditions. These results indicated that pulsed microwaves with repetitive strong power could enhance the efficiency of biodiesel production relative to the use of continuous microwave with mild power.
Since the 18th century scientists have been intrigued by the interaction of electromagnetic fields (EMFs) and various life processes. Attention has been focussed on EMFs in different frequency ranges, of which microwave frequency range forms an important part. Microwaves are part of the electromagnetic spectrum and are considered to be that radiation ranging in frequency from 300 million cycles per second (300 MHz) to 300 billion cycles per second (300 GHz), which correspond to a wavelength range of 1 m down to 1 mm. This nonionising electromagnetic radiation is absorbed at molecular level and manifests as changes in vibrational energy of the molecules or heat (Microwaves irradiating the community, Hidden hazards, Bantan Books publisher, Australia, 1991). Identifying and evaluating the biological effects of microwaves have been complex and controversial. Because of the paucity of information on the mechanism of interaction between microwave and biological systems, there has been a persistent view in physical and engineering sciences, that microwave fields are incapable of inducing bioeffects other than by heating (Health Physics 61 (1991) 3). Of late, the nonthermal effects of microwaves on tissue responses are being documented (Physiol. Rev. 61 (1981) 435; Annals of New York Acad. Sci. 247 (1975) 232; J. Microwave Power 14 (1979) 351; Bioelectromagnetics 7 (1986a) 45; Bioelectromagnetics 7 (1986b) 315; Biologic Effects and Health Hazards of Microwave Radiation, Warsaw, Polish Medical Publication (1974) 289; Biologic Effects and Health hazards of the microwave Radiation, Warsaw, Polish Medical Publication (1974) 22; Multidisciplinory perspectives in event-related brain potential research, Washington DC, US Environmental Protection Agency, (1978) 444). The present article is an attempt to familiarise the reader with pertinent information regarding the effects, mainly athermal, of microwave irradiation on biologic systems, especially microorganisms.
Influence of water pre-soak on enzyme-retting of flax Bioeffects of microwaveeea brief review
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A method of estimating the single flax fiber fineness using data from the LaserScan system Chemical and strength difference in the dew retted hemp fiber Microwaves in organic synthesis. Thermal and non-thermal microwave effects
- S A Grishanov
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Impact of fiber diameter on mechanical properties of hemp based composite. ASABE Meeting Presentation
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STEX treated and un-treated hemp fiber comparative analysis An investigation of structural changes in short flax fibers in chemical treatment. Fibers and Textiles in Eastern Europe Comparison of subjective and objective methods to assess flax straw cultivars and fibre quality after dew-retting
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A new approach for estimating purity of processed hemp fiber by NIR spectroscopy Microwave radiation as a catalyst for chemical reactions
- M Sohn
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- W H Morrison
Sohn, M., Barton, F. E., Akin, D. E., & Morrison, W. H. (2004). A new approach for estimating purity of processed hemp fiber by NIR spectroscopy. Journal of Near Infrared Spectroscopy, 12(4), 259e262. Sridar, V. (1998). Microwave radiation as a catalyst for chemical reactions. Current Science, 74(5), 446e450.
Application of microwave technology for utilization of recalcitrant biomass Advances in induction and microwave heating of mineral and organic materials (pp. 697e722) InTech
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