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

The curves for composite stiffness versus fibre volume fraction were also steeper for the
hemp fibres produced by cultivation of P. radiata (Figure a) than the curves for raw
hemp bast and water retted hemp (Figure b). The raw hemp bast and the water-retted
hemp fibres had therefore lower stiffness of 78 GPa and 88 GPa, respectively than the
hemp fibres produced by cultivation of P. radiata (94 GPa) (Table 4). The highest
composite stiffness obtained using raw hemp bast, water retted hemp or P. radiata
defibrated hemp, as reinforcement were 20 GPa, 26 GPa and 30 GPa, respectively
without consideration of porosity (Ec). Cultivation of P. radiata for defibration of hemp
fibres resulted thereby both in the highest composite strength and highest composite
stiffness. Based on obtainable composite strength and stiffness, the best defibration
method was cultivation of P. radiata followed by water retting and then by cultivation of
C. subvermispora. It was determined that the hemp fibres tensile strength and stiffness
were affected by the defibration methods at 90% probability using analysis of variance
(F-test with number of samples = 4 and number of repetitions = 23 for F0.1).
V p [% v/v]
10
5
0
Raw hemp bast
Water retted hemp
C.sub. treated hemp
Hemp yarn
P.rad. treated hemp
0 10 20 30
Vf [% v/v]
Figure 5. Porosity content in the composites versus fibre volume fraction.
134 Risø-PhD-11
40