Dilek YAYLALI, Canan URAZ, Esat GÜMÜŞKAYA
diameter and wall thickness. In this study, a targeted raw hemp bast fibre size of 4 mm on average was attained using a fine cutting mill. The lengths of the hemp bast fibres ranged from 2.2 to 8.6 mm with an average length of 4.9 mm. The average value deviated by 22.5% from the targeted average value. The highest percentage (24%) of fibre lengths was within the 5 mm range. The length distribution was primarily found in the 5 – 6 mm range. These results and the average value indicate that despite processing the fibres twice, the targeted average length of hemp bast fibres was achieved using the fine cutting mill. For further studies, other size reduction methods can be considered for better precision. The diameters of the hemp bast fibres ranged from 11 to 39 μm with an average diameter of 23 μm. The highest percentage (24%) of the fibre diameter was in the 26 μm range. The cell wall thickness of the hemp bast fibres ranged from 3.2 to 9.2 μm , with an average wall thickness of 6 μm, and the highest percentage (24%) of fibre wall thickness was in t he 5 μm–7 μm range. The average cell wall thickness determined in this study was 10.4% lower than that in the results of Dutt et al. [2005] and 9.1% higher than that in the results of Danielewicz and Surma- Ś lusarska [2017]. These differences in diameter and cell wall thickness of hemp bast fibres could be due to the OM measurement methods or the nature of the raw materials. The results indicate that there may be some variations in hemp bast fibre cell wall thickness amongst different cultivars of hemp. The cultivation conditions, harvesting time, subgenre difference, etc. also affect this phenomenon. The method of producing pulp from hemp stalks is also effective in this difference. Figure 2 presents OM images of hemp bast fibres before and after treatments as well as the images of hemp bast fibres in (a) raw, (b) cooked and (c) beaten forms.
Fig. 2. Optical microscope images of (a) raw, (b) cooked and (c) beaten hemp bast fibres These figures show that cooking has no effect on fibre fibrillation, but it is apparent that beating has some fibrillation effect on the cooked hemp bast fibres. Since the low degree of external fibrillation after beating, it seems to be the main problem for the wide usage of hemp bast fibres.
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