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

sections (Af,i, n = 50) using Image Pro software (Equation 1). The lumen size (al,i) was
calculated similarly by drawing a line around the lumen in the fibers. The lumen fraction
(L±ΔL) was calculated with Equation 2.
Af
, i
Equation 1 Af
=
n
∑
Equation 2
L =
∑
∑
a
A
l,
i
f , i
Tensile testing of hemp fiber bundles
Fiber bundles of 15 mm length (lspec) were strained to fracture at 3 mm span (lspan) at a
test speed of 0.30 mm min -1 using an Instron 5566 with pressley clamps [Type:
Stelometer 654 from Zellweger Uster] at 20°C and 66% relative humidity. Following
fracture the fiber pieces were weighed (mspec). Some pieces were separated into single
fibers and coated with gold and the brash-like fractured ends were examined using SEM.
The tensile strength (σ) was calculated based on the force of fracture (Fmax) and the
density of hemp yarn ρspec=1.56 g ml -1 .
Equation 3
σ
F
= max
l
spec
mspec
× ρ
spec
The elastic modulus (E) was calculated based on linear regression of force versus
elongation in the elongation range (Δl) from 0.030 mm to 0.045 mm.
Equation 4
⎛ dF ⎞
m
E = ⎜ ⎟ × l
⎝ dΔ l⎠ l ×
Δ= l 30−45μm span
spec
spec
ρspec
Histochemical reactions and microfibril angle
Cytochemical reactions were made on transverse hemp stem sections mounted on glass
slides in one drop of 50 % (v/v) glycerol in water and a cover slip placed on top. All the
experiments were performed in at least triplicates. Light microscopy was performed at
50-630 x magnifications using a Leica DMLS bright field microscope fitted with
polarized light filters with images recorded digitally. The following cytochemical
reactions were performed:
Lignin - hydroxycinnamyl aldehydes (Wiesner reaction): Sections were stained with two
drops of 10 g l -1 phloroglucinol in ethanol, followed by addition of 2 drops of 35 % (v/v)
HCl (Strivastava, 1966). Lignin - syringyl (Mäule reaction): Sections were stained with
one drop of 10 g l -1 KMnO4 for 5 min followed by three washes in water. Sections were
then immersed in 3 % (v/v) HCl for 1 min, washed in water, and immersed in 29 % (v/v)
NH3 for 1 min (Strivastava, 1966; Wu et al., 1992). Pectin: Sections were stained with 1
g l -1 Ruthenium Red [JMC Speciality Products] (Strivastava, 1966; Jensen, 1962). Wax:
Sections were immersed in 10 g l -1 Sudan IV in 70 % ethanol on a glass slide (Wu et al,
1992).
Microfibril angle: Cell wall cavities formed during P. mutabilis colonization and attack
before harvest by native colonizing fungi were seen as dark lines using polarized light
microscopy. These cavities were orientated parallel with the microfibrils (Khalili et al.,
94 Risø-PhD-11