Problem definition and objectives: The Non-woody plant fibers such as Flax, Hemp, and Kenaf are always investigated due to their morphological similarities and sometimes variable values ​​obtained from microchemical tests. This study aims to evaluate the chemical composition ratio between the amounts of lignin, cellulose, and organic compounds and to investigate the differences between wood and bast fibers, bast fibers, and lignin extracted from flax, hemp, and kenaf and cotton fibers.
Methodology: For this purpose, in addition to library studies, laboratory and instrumental methods were also used. Four flax, hemp, kenaf, and cotton plants were collected from different regions of Iran and were classified and tested in four groups: a) stem (total wood and bast fibers), b) bast fibers, c) lignin, and d) cotton fibers. To obtain lignin from three flax, hemp, and kenaf plants, wood flour was prepared using the MWL method. These flours were extracted separately with a dioxane:water solution (V/V 1:9, mL/g 10) containing 0.2 M/L HCL in 3 stages for 24h by immersion method at 40 °C in a shaker. The solution was concentrated after filtration in a vacuum environment at 60 °C to a volume of 20 mL. The precipitated lignin was washed several times with distilled water, first in an oven at 60 °C and then in a freeze dryer. Finally, all four groups were examined using FTIR-ATR spectroscopy method and compared with the Garside diagram.
Results: The findings from the FTIR-ATR method have shown the same structures for the four plants above. But there is only the intensity factor in these compounds that shows their difference. Therefore, the ratio of the intensity values ​​of the aromatic vibrations of the C=C bonds of lignin in the region of 1595 cm -1 to the intensity values ​​of the vibrations of the ether glyoxyde bonds C-O-C in the region of 1105 cm -1, which are representative of polysaccharides (abundant amount of cellulose), and the intensity of the C-H stretching vibrations in the region of 2900 cm -1, which is representative of all organic materials, was evaluated. The study of the ratio of lignin to the amount of cellulose and the same amount of lignin to the amount of organic compounds in the fibers of flax, hemp, kenaf and cotton plants determines unique points for each plant that are separate even with the amounts of bast fibers separated from the stems of flax, hemp and kenaf plants and have an upper trend along the diagonal axis. So that the fibers with the lowest amount of lignin are closer to the center of intersection of the two axes and have a lower height from the two horizontal and vertical axes and are observed among cotton fibers and flax bast fibers. On the other hand, with increasing height from the two axes, the amount of lignin increases and the plant fibers move more towards lignification, which is observed in the kenaf stem and its bast fibers. The points on the graph show that the decrease in the amount of lignin of the bast fibers is relative to the total stem fibers (wood fiber + skin + companion cells) of each plant, and only the bast fibers of the kenaf plant do not follow this rule and show a higher amount of lignin compared to the small amounts of cellulose and organic compounds equal to this plant. Also, the amounts of lignin-rich extracts in each plant produce specific and distinct points from each plant, which are in order from the lowest to the highest amount of lignin for cotton, flax, hemp, and finally kenaf.
Conclusion: The results show that there are few differences between cellulose fibers of flax, hemp, and kenaf in these two destructive and non-destructive methods. however, the comparison between the ratio of lignin absorption intensity to organic compounds and the ratio of lignin absorption intensity to cellulose in the ATR method for each plant, including the total stem fibers, bast fibers, fiber from the seed (cotton), and lignin-rich extract belonging to each plant gives a separate point that is distinct from each other. Therefore, this non-destructive spectroscopic method can be used to identify and separate fibers of flax, hemp, kenaf, and cotton plants.