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

Figure 9. Hemp stem shown at increasing magnification using different transverse
sections in SEM: A: Xylem + cambium + cortex + epidermis; B: Primary and secondary
single fibres; C: Major layers in primary single fibre; D: Thin lamellae within the S2
layer (Paper II).
The microfibril angle through the fibre wall was investigated by polarised light
microscopy and scanning electron microscopy. It was found that the microfibrils in
fibres of Felina hemp had a main orientation of 0-5° in the S2-layer. The presence of Zhelical
angles in the range 25-30° was observed (Figure 11A), but with variation
between the fibres (Paper II). Difference in microfibril angle is also present between
early wood and late wood (Table 2). Superficial attack of hemp fibres (Figure 11C) and
polarization light microscopy showed the S1 layer with microfibril angles in the range of
70-90° (Paper II). The average MFA in hemp fibres of 4° that is measured by X-ray
diffraction (Fink et al., 1999) is thereby confirmed with more detailed information. The
low overall MFA in hemp fibres explains the high stiffness in the range 50-80 MPa
compared with sisal (6-22 GPa) with similar cellulose content and higher MFA i.e. 10-
25° (Table 2,Table 3).
Figure 10. Single fibres partially decayed by fungi (transverse sections). A: P. mutabilis
decay of the thick layers in S2. B: P. radiata (wild) decay of the cell wall from the lumen
side. C: P. radiata Cel 26 decay of the thin layers between the thick concentric S2 layers
(Paper II).
22 Risø-PhD-11