Enzymatic treatment of flax is gaining more interest as a promising alternative for dew retting, which is known for its dependence on weather and climate. Therefore, the effect of enzymatic treatments of flax on the effectiveness of fiber separation from each other and chemical fiber composition was investigated in this study. Chemical composition was determined by a gravimetric method, while ease of separation in the composites society, the process to obtain natural fibers from the plant is usually defined as extraction was determined based on the amount of long fibers obtained as well as total time needed to release this fiber fraction, providing necessary insights in the extent to which fibers are loosened from the stem. Besides these pectinases, xylanase activity also showed high potential for enzymatic retting. Hence, pectate lyase, polygalacturonase, and xylanase are promising enzymes to successfully replace the dew retting process.
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Enzymatic treatment of flax is gaining more interest as a promising alternative for dew retting, which is known for its dependence on weather and climate.
Therefore, the effect of enzymatic treatments of flax on the effectiveness of fiber separation from each other and chemical fiber composition was investigated in this study. Chemical composition was determined by a gravimetric method, while ease of separation in the composites society, the process to obtain natural fibers from the plant is usually defined as extraction was determined based on the amount of long fibers obtained as well as total time needed to release this fiber fraction, providing necessary insights in the extent to which fibers are loosened from the stem.
Besides these pectinases, xylanase activity also showed high potential for enzymatic retting. Hence, pectate lyase, polygalacturonase, and xylanase are promising enzymes to successfully replace the dew retting process. Natural fibers are gaining increased attention as an ecofriendly alternative for glass fibers as reinforcement in composite materials.
To use flax fibers as reinforcement, fibers need to be separated from the plant stem. Traditionally, dew retting followed by a mechanical separation is performed to release flax fiber bundles from the woody core of the stem. To ensure consistently high-quality flax fibers for demanding applications such as composites, a well-controlled and efficient retting process is necessary. The enzymatic treatment of flax can address the shortcomings of dew retting due to its high specificity of enzymes and the better controllability of the process.
Moreover, a less severe mechanical separation will be required afterwards, inducing less fiber damage. The reduced severity of the mechanical processing can increase the yield of long fibers and thus compensate for the extra cost of enzymatic retting.
During retting, flax fibers are loosened and partly separated from the woody stem. After retting, a mechanical separation is necessary to remove the woody parts left on the fiber. Traditionally, the mechanical separation consists of breaking, scutching, and hackling Bos With breaking, flax stems are led between fluted rollers to break the woody stem.
Scutching is a beating process to separate shives from fibers. Finally, hackling further enhances fineness through a combing process to obtain a higher degree of alignment of the fibers Bos However, the mechanical separation implies a lot of fiber damage due to the severity of the several individual processing steps. By the treatment of flax with targeted enzyme preparations, fibers can be removed more easily from the woody stem, implying that a less severe mechanical post-treatment will be necessary, and thus less fiber damage will be induced.
Additionally, a higher yield of long fibers will be achieved. Thus, enzymes show a great deal of potential to realize consistent high-quality natural fibers. The crystalline form of cellulose is accountable for the high mechanical properties of the natural fibers. Hemicellulose is another important polysaccharide present in the fiber and binds to cellulose. The most abundant forms of hemicellulose are xyloglucan and arabinoxylan, both are branched polysaccharides that are more easily degraded compared to cellulose Cosgrove Pectins are complex polysaccharides in the surrounding network of cellulose with an interconnecting purpose as well.
Examples of common pectic polysaccharides are homogalacturonan, xylogalacturonan, and rhamnogalacturonan I and II Cosgrove The loosening and separation of the fibers from the woody core can be realized by affecting the surrounding network of polysaccharides around the fibers with enzymes.
More specifically, the degradation of pectin and hemicellulose in the network can be accomplished by pectinases and hemicellulases, respectively. Hemicellulase activity, like endoxylanase, can degrade the hemicellulose polymers. Amorphous cellulose can also be present in the surrounding network. Therefore, cellulase activity, which is able to degrade cellulose, can be beneficial to enhance the separation process.
However, a too severe degradation of cellulose should be avoided, as it will result in cellulose fibrils of reduced fiber strength. Finally, the presence of laccase activity can be beneficial for degradation of the lignin present in the flax stem.
Enzymes result in a decreasing environmental impact and reduced overall production cost. A systematic research approach is needed starting from the individual pure enzyme activities. In this way, targeted enzyme blends can be defined as alternatives for the dew retting process. Within this study, flax was treated with various enzymes, and their efficiency was evaluated through the characterization of the chemical composition of the fibers separated after the enzymatic treatment, along with the determination of the separation efficiency.
Green flax GR of the Amina cultivar from Verhalle Zulte, Belgium was harvested in and kindly provided for this research. Different enzymes were tested for their retting effect on flax. Polygalacturonase activity was determined using the 3,5-dinitrosalicylic acid DNS method, based on the protocol of Miller As substrate, 0.
Standard references were prepared containing 0. Test tubes with standards or control were prepared containing 1 mL acetate buffer pH 5. Suitable enzyme dilutions were analyzed by adding 0. Approximately 0.
After cooling, 1 mL of the resulting solution was diluted with 2 mL of demineralized water, and the absorbance was measured spectrophotometrically at nm with a Thermo Scientific Nicolet Evolution spectrophotometer Thermo Fisher Scientific, Asse, Belgium. The total xylanase activity was characterized for all enzymes provided in accordance with the polygalacturonase assay. All above mentioned assays were repeated twice, and the samples were analyzed in triplicate. The cross section of a flax stem was visualized using scanning electron microscopy SEM.
Afterwards, the samples were stored under vacuum before SEM analysis. GR flax was used as starting material. After enzymatic treatment, flax stems were washed twice in water to remove enzymes and solubles. As stated earlier, in the composites society, the process to obtain natural fibers from the plant is usually defined as extraction.
Manual separation was chosen to exclude other possible side effects of mechanical separation and because of the scale of the experiment.
The factor 2 in Eq. The first step of the gravimetric method was the determination of the extractables content and consisted of a Soxhlet extraction for 5 h with an ethanol:toluene mixture ethanol Disolol from Chem-Lab, Zedelgem, Belgium; toluene from VWR International, Leuven, Belgium to remove solubles and waxes.
Then, 1 g of dried flax fiber was applied and weighed in an extraction thimble. Approximately 80 mg of residual fiber was subsequently utilized for lignin determination. After cooling, the content was filtered into crucibles, washed with 50 mL of demineralized water, and dried and weighed to determine the lignin content.
The residual fiber remaining after the extraction step was also subjected to the holocellulose determination. After adding mL of demineralized water, 0. After 1 h, 0. Then the flask was cooled in an ice bath. The resulting residue represents the holocellulose content. Incubation was continued for 1 more hour after adding 35 mL of demineralized water. The remaining residue was then washed on a Buchner funnel with subsequently mL NaOH solution of 8.
After drying and weighing, the cellulose content can be calculated from the remaining part. The hemicellulose content was calculated by subtracting the cellulose from the holocellulose content. The fibers were washed, and the filtrate was collected and diluted to mL. The 3-phenylphenol solution consisted of 0. Approximately 2. Absorbances were measured after exactly 3 min at nm with a Nicolet Evolution spectrophotometer Thermo Fisher Scientific, Asse, Belgium. The samples without the addition of 3-phenylphenol served as a blank for background correction.
All characterizations were repeated twice, and the samples were analyzed in triplicate. The enzymes are tested for their effectiveness as retting agents in this study. With enzymatic retting, polymers in the surrounding network of the fibers are degraded by specific activity of the enzymes, which could serve as an alternative for dew retting. In Fig. In Fig 1B, flax bundles are located within the sclerenchyma layer or the bast tissue 3 , underneath the epidermis 1 and cortex 2. The retting results in a partial to full detachment of fiber bundles from the phloem 4 and xylem tissue 5.
Because a systematic research approach is needed starting from the individual pure enzyme activities, as a first step of the research the enzymes were analyzed to gain clear insights into the activities present in the enzyme formulations.
This enabled the correlation of each enzyme activity with the characteristic properties of the separated flax fibers and retting efficiency. The activity determinations were mainly focused on the determination of polygalacturonase, xylanase, and cellulase activity to gather information about their possible presence as a main or side activity.
The results of the enzyme activity assays are presented in Table 1. The enzymes studied are listed according to their main activity. Other pectinase enzymes showed lower to almost no polygalacturonase activity. Moreover, a low xylanase and cellulase activity was observed, which was important for the enzymatic treatments. An exception to this was the PTE enzyme, exhibiting a xylanase activity of Polygalacturonase and cellulase activity in the hemicellulase preparations were rather limited.
Lac showed a polygalacturonase side activity of When looking at the activities of Cel, it contained mainly cellulase activity 1. All enzymes listed in Table 1 were then applied for enzymatic treatment of flax to unravel their potential behavior towards the retting process. Subsequently, the separated fibers were chemically characterized.
After treatment, fibers were manually separated from the stem for further characterization. Table 2. To evaluate the effect of the enzymes towards their retting behavior, the chemical composition of the separated flax fibers after enzymatic treatment of green flax was characterized.
For comparison, reference materials were included. The chemical composition was determined according to the gravimetric method. The cellulose, hemicellulose, and lignin contents of the reference materials and enzymatically separated fibers are shown in Table 2.
Effect of enzymatic treatment of flax on chemical composition and the extent of fiber separation
Calotropis procera , locally known as ankra, which is available as a wild shrub in the desert area of Rajasthan and Gujarat, has proved one such potential lignocellulosic raw material, finding usefulness for making specialty handmade paper and products. Extensive research carried out at the institute indicated a good possibility of extraction of good quality bast fiber with the application of identified enzymes bioretting process , making the process easier, productive, and less polluting while improving the yield and quality of the fiber obtained. The initiatives taken at KNHPI for utilization of Calotropis procera in the area of fiber extraction using bioretting process developed at the institute and utilization of the extracted fiber for making handmade paper and products should prove to be a potential employment-generating and income-generating opportunity among the rural masses. Proper utilization of the waste biomass, majority of which is presently utilized as a domestic fuel, could also improve the environmental status besides addressing the problem of global warming. Skip to main content.
Polygalacturonase Is the Key Component in Enzymatic Retting of Flax