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

linear full drawn curves due to the effect of porosity explained with αf. The data points
for hemp yarn, water retted hemp and P. radiata Cel 26 defibrated hemp followed the
dotted lines well due to the reduction of composite stiffness caused by porosity. The ratio
Ec/ρc reached 24.7 GPa/(g/cm 3 ) with P. radiata Cel 26 defibrated hemp and 17.4
GPa/(g/cm 3 ) with raw hemp bast due to the higher obtainable fibre content and the
higher fibre strength with P. radiata Cel 26 defibrated hemp. For barley straw, the
optimal fit was obtained using nE=0. The Norway spruce had the highest Ec/ρc value
(27.5 GPa/(g/cm 3 )) due to the very low density of wood (0.4 g/cm 3 ) compared with hemp
fibres and glass fibres.
Table 10. Composite and fibre strength and stiffness compared to the density. Data are
based on the highest obtained fibre content Vf,obt for composites and on fibres.
Fibre type and
defibration
ρc
g/cm 3
σcu
MPa
Εc
GPa
σcu/ρc
10 3 m 2 /s 2
Εc/ρc
10 6 m 2 /s 2
σfu/ρf
10 3 m 2 /s 2
Εf/ρf
10 6 m 2 /s 2
Epoxy matrix 1.136 64 2.93 56 2.6 - -
Raw hemp bast 1.18 122 20.4 104 17.4 339 49.4
Water retted hemp 1.19 153 26.4 129 22.2 370 55.7
C. sub. tr. hemp 1.22 130 24.3 107 19.9 340 55.7
P. rad. tr. hemp 1.22 174 30.1 143 24.7 407 59.5
Hemp yarn 1.23 230 21.3 187 17.3 428 38.6
Barley straw 3
0.67 19 4.0 28 6.0 160 14.7
E-glass 1.96 769 41.5 392 21.1 509 29.4
Norway spruce 1
0.40 88 11 220 27.5 220 27.5
1: Mechanical properties for dry Norway spruce (Picea abies), with a bulk density of 0.40 g/cm 3 and a
cell wall density of 1.50 g/cm 3 after correction of the bulk tensile strength (88 MPa) and stiffness (11
GPa) for porosity (Boutelje and Rydell, 1986; Klinke et al., 2001).
62 Risø-PhD-11