## 3 Results and Discussion
### Characterization of Main Spectral Regions
#### 3.1.2 Spectral Region 1200-1800 cm\({}^{-1}\)  
Within region 1244-1252 cm\({}^{-1}\), plant stem samples displayed a strong band that showed a very low intensity in the cellulose standard (Figure 5). According to the literature, the peak close to this range, at 1230 cm\({}^{-1}\), was attributed to methoxyl groups from the structure of lignin [43]. The peak occurring within a similar range was attributed to C-O stretching vibration of the acyl group of lignin [3; 8; 36; 43; 54; 56; 57]. The disappearance of the peak at 1239 cm\({}^{-1}\) from kenaf fibers [36] as well of the peak at 1243 cm\({}^{-1}\) from corn stem fibers [8] was attributed to the removal of lignin following chemical treatments. Considering that the peak within this region was missing in the standard sample, it can be assigned to other components than cellulose, such as lignin. Within region 1374-1384 cm\({}^{-1}\), a peak of varying intensity was observed in the four species analyzed as well as in the cellulose standard sample. Among samples and species, jute samples displayed the highest intensity of this peak, and showed a particular sharp shape compared to the other samples (Figure 5). This could be considered a species particularity, as it was observed in all three jute accessions. According to the literature,  
Figure 5: Detail of FT-IR spectral region 800–2000 cm\({}^{-1}\) for stems of flax, velvet leaf, hemp and jute compared to cellulose; cyan strips mark regions of high variability compared to standard. the peak in this region based on FT-IR analysis of bamboo samples was assigned to C-H deformation vibration [3; 53; 58] from cellulose and hemicellulose [58] (Table 3). Within range 1420-1428 cm\({}^{-1}\), a band displaying a peak and shoulder was observed in all samples, but was most prominent in the cellulose standard and least distinguishable in jute samples (Figure 5). The investigation of vegetal and wood fibers defined the band at 1420-1430 cm\({}^{-1}\) as representative for crystalline structural parameters of cellulose [40]. Since crystallinity has an influence on the fiber mechanical property [39], this region represents a good candidate as a marker region. Within the same range, a study of bamboo stems assigned the peaks of this region to CH\({}_{2}\) scissoring as well as bending vibration of olefin, as characteristics both for cellulose as well as hemicellulose [58]. In bamboo samples, the characteristic peak of lignin was detected at 1230 cm\({}^{-1}\) and 1506 cm\({}^{-1}\)[43]. In the case of _Epipremum aureus_ stem fibers, the lignin characteristic peaks were found at 1240 cm\({}^{-1}\) and caused by C-O stretching vibration, while the peak of low intensity around 1500 cm\({}^{-1}\) was determined to be due to C=C stretching vibration of the benzene ring of lignin [7]. In this study, the decrease in intensity of peaks between 1245-1252 cm\({}^{-1}\) and 1508-1509 cm\({}^{-1}\) can be attributed to a lower of lignin content, and could be used as a purity criterion for cellulose-based products and materials. A similar decrease in peaks at 1506 cm\({}^{-1}\) and 1230 cm\({}^{-1}\) was identified in bamboo samples after treatment for the isolation of the cellulose fraction, which was due to the dissociation of functional groups from components of lignin such as the dissolution of aromatic rings [43]. The peak situated within region 1620-1628 cm\({}^{-1}\) was identified in all four species analyzed, and could be attributed to both C=C vibration from lignin as assigned based on _Abutilon indicium_ fibers [10], superimposed with C=O vibration corresponding to amide I as assigned based on FT-IR analysis of cotton fibers [53] (Table 3). In jute plants from this study, the band of this region was situated at a lower wavenumber, but also displayed the highest intensity out of the species analyzed, particularly the accession from Hungary