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

a: Water retted hemp b: Hemp yarn
c: C. subvermispora treated hemp
e: Barley straw
d: P. radiata Cel 26 treated hemp
f: Glass fibres
Figure 33. SEM microscopy photos of transverse composite sections recorded at low
and high magnification with the applied fibres. The small inset pictures have a scale bar
length of 200 μm and the background pictures 20 μm (Paper IV; unpublished data).
9.2.1 Fibre content in relation to fibre size and fibre type
The obtainable fibre content in the composites decreased versus the fibre bundles
transverse section area from 35% v/v with hemp yarn of 1×10 3 μm 2 to 26% v/v with raw
hemp bast of 160×10 3 μm 2 . The obtainable fibre content appeared to decrease linearly
versus the logarithm to the fibre transverse section area (Figure 34). This area was
determined by image analysis on SEM photos as described in Paper II.
The compaction level increased due to the more uniform fibres of small size, which were
easier to compact. The large fibres were very irregular in structure and therefore difficult
to compact (Paper IV). In the composites reinforced with barley straw, a fibre content of
only 10% v/v could be obtained since the fibres had large fibre lumens and surface
porosities (Figure 33e). The glass fibres have smooth surfaces, no lumens and uniform
52 Risø-PhD-11