The relationship between processing and fibre properties in hemp (Cannabis Sativa L.)

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Kemian tekniikan korkeakoulu |
Final Project. 30cr
Degree programme
BTT - Biotuotetekniikan koulutusohjelma
The goal of this study is to investigate how processing of hemp fibre bundles affects their mechanical properties. The mechanical properties of interest are the ultimate tensile strength and the stiffness. Therefore, tensile tests of seven differently processed fibre bundle types have been conducted. The fibre bundle types varied in the applied method of retting (field retted, unretted, winter retted) and in the processing method (decortication, rollercarding, refining). The values obtained from the tensile tests and the diameter measurements conducted with the optical microscope were used to calculate the strength and stiffness of in total 226 fibre bundles (30 – 35 specimen per fibre type). It was expected that the mechanical properties (strength and stiffness) decrease with further processing of the fibre. However, the values obtained from the tensile tests did not show a clear trend. This could be accounted to the fact that the diameter measured under the optical microscope was incorrect due to tissue still adhering to the fibre bundles. Especially with the unprocessed fibres a distinction between the bark and the actual fibre was not possible with the optical microscope. Therefore the measured diameter was not that of the fibre bundle but of the fibre bundle plus the surrounding tissue which does not have a load bearing function. Due to the (wrong) high diameter the resulting strength and stiffness properties were very low. Other means were taken into account to describe the relationship between processing and fibre properties such as the load at which the fibre bundles failed and the share of non-linear stress-strain curves per fibre bundle type. It can be concluded that processing adds defects to the fibre cell wall and thus the mechanical properties strength and stiffness decrease with further processing. Nevertheless, processing is not solely responsible for defects in fibres which cause weak fibre properties. Considering only processing methods as a reason for fibre bundle properties is not sufficient. Growth conditions can also influence the occurrence of defects. Furthermore, inaccurate and varying means of determining fibre properties make it challenging to compare the results with findings from other authors. It is therefore concluded to standardize fibre bundle tensile testing and to not only focus on processing with regard to defects in fibres but also on upstream processing steps.
Hughes, Mark
Thesis advisor
Hernandez Estrada, Albert
hemp, fibre bundles, processing, strength, stiffness, diameter
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