Properties of hemp fibre polymer composites -An optimisation of ...

CONCLUSIONS
Cultivation of P. radiata Cel 26 on hemp stems resulted in fibres with higher cellulose
content than water retting of hemp due to more effective degradation of pectin and
lignin. The cellulose crystallinity tended to decrease with the cellulose content obtained
by the fungal treatments showing that during processing part of the crystalline cellulose
is converted into its amorphous form.
Even though the hemp fibres were handled with mild methods like hand peeling and
fungal defibration, a fibre strength higher than 643 MPa was not obtained, which is
similar to the strength of traditionally produced hemp yarn (677 MPa). The fibre strength
and stiffness properties were derived from composite data using the rule of mixtures
model.
The effective fibre stiffness was 94 GPa in the P. radiata defibrated hemp fibres which is
high compared to literature data on flax - (50-70 GPa) and glass fibres (72 GPa). The
high stiffness and low density of the defibrated hemp fibres compared with glass fibres
makes hemp a good alternative to glass fibres for material construction.
The calculated plant fibre strength appeared to be linearly dependent on cellulose content
and independent on cellulose crystallinity and microfibril angle. Pure cellulose had the
estimated effective strength 850 MPa that is about 10% of the strength on the molecular
level.
The calculated plant fibre stiffness appeared to increase linearly with cellulose content,
decrease with microfibril angle and increase with cellulose crystallinity. Pure crystalline
cellulose had an estimated stiffness of 125 GPa.
ACKNOWLEDGEMENTS
This work was part of the project “High performance hemp fibres and improved fibre
networks for composites” supported by the Danish Research Agency of the Ministry of
Science. Dr. Claus Felby (The Royal Veterinary and Agricultural University) is
acknowledged as supervisor for Ph.D. student Anders Thygesen. Senior scientist Poul
Flengmark (Danish Institute of Agricultural Sciences) is acknowledged for supplying the
hemp and Mrs. Ann-Sofie Hansen (WURC) for setting up the fungal cultivation
experiments. Mr. Henning K. Frederiksen (Risø National Laboratory) is acknowledged
for help in composite fabrication and Mr. Tomas Fernqvist (Risø National Laboratory)
for help in the chemical fibre analysis. Dr. Bo Madsen and Engineer Tom L. Andersen
(Risø National Laboratory) are acknowledged for discussion and inspiration. Lecturer
Kenny Ståhl is gratefully acknowledged for assistance in X-ray measurements and
allowing us to use the equipment.
REFERENCES
Akhtar, M., Attridge, M.C., Blanchette, R.A., Myers, G.C., Wall, M.B., Sykes, M.S.,
Koning, J.W., Burgess, R.R., Wegner, T.H., Kirk, T.K., 1992. The white-rot
fungus Ceriporiopsis subvermispora saves electrical energy and improves
strength properties during biomechanical pulping of wood. In: Kuwahara, M.,
Shimada, M. (Ed.), Biotechnology in pulp and paper industry, Uni Publishers
CO., Tokyo, Japan. 5, pp 3-8.
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