Properties of hemp fibre polymer composites -An optimisation of ...
Properties of hemp fibre polymer composites -An optimisation of ...
Properties of hemp fibre polymer composites -An optimisation of ...
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10 Conclusions and future work<br />
Hemp stems could be defibrated with the white rot fungus Phlebia radiata Cel 26 on at<br />
least the 100 g scale to make <strong>fibre</strong>s for reinforcement <strong>of</strong> <strong>composites</strong>, since the pectin and<br />
wax rich epidermis was degraded. The <strong>fibre</strong>s retained parallel orientation during the<br />
fungal defibration and water retting and are thereby useful for <strong>composites</strong> with aligned<br />
<strong>fibre</strong>s. Lignin located in the middle lamellae between the single fibers made pectinase<br />
defibration difficult. Lignin degradation in the <strong>hemp</strong> <strong>fibre</strong>s by cultivation <strong>of</strong> P. radiata<br />
Cel 26 resulted in more cellulose rich <strong>fibre</strong>s (78%) than treatment with pectin degrading<br />
enzymes. Even though the <strong>hemp</strong> <strong>fibre</strong>s were handled with mild methods like hand<br />
peeling and fungal defibration, <strong>fibre</strong> strength higher than 643 MPa was not obtained,<br />
which is similar to the strength <strong>of</strong> traditionally produced <strong>hemp</strong> yarn (677 MPa).<br />
Furthermore the <strong>fibre</strong> strength appeared to be linearly dependent on cellulose content and<br />
independent on cellulose crystallinity and micr<strong>of</strong>ibril angle. Pure cellulose had the<br />
estimated effective strength <strong>of</strong> 850 MPa that is about 10% <strong>of</strong> the strength on the<br />
molecular level. The plant <strong>fibre</strong> stiffness appeared to increase linearly with cellulose<br />
content, decrease with micr<strong>of</strong>ibril angle and increase with cellulose crystallinity. Pure<br />
crystalline cellulose had an estimated stiffness <strong>of</strong> 125 GPa.<br />
Future investigations could be to investigate the fracture mechanics in plant <strong>fibre</strong><br />
reinforced <strong>composites</strong>. That will potentially explain if the obtained composite strength is<br />
lower than determined based on the <strong>fibre</strong> strength or if the reduction in strength is only<br />
due to the effect <strong>of</strong> the Weibull distribution. Such investigations should be performed at<br />
varied <strong>fibre</strong> content and will in addition reveal further information about the effect <strong>of</strong><br />
<strong>fibre</strong> content on the resulting porosity content. Composites with various biodegradable<br />
matrix materials like starch or lignin could be tested to get a completely biodegradable<br />
material. This investigation should focus on the matrix properties and on how to get a<br />
good interface with the <strong>fibre</strong>s. The fungal defibration method could be replaced with<br />
constructed enzyme mixtures by genetic engineering or a designed and stable bacterial<br />
strain could be applied in the retting procedure.<br />
66 Risø-PhD-11
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