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

7.3 The treatment procedures effect on cellulose crystallinity
Wet oxidation of corn stover resulted in increased content of crystalline cellulose in the
fibres. The content of crystalline cellulose appeared to reach a level of 38-42% w/w for
obtained cellulose contents of 50-60% w/w. Crystalline cellulose is thereby converted
into its amorphous form at the high temperature applied during the treatment (190°C).
For the fungal defibrated hemp fibres, the cellulose crystallinity tended to decrease
versus the obtained cellulose content showing that some crystalline cellulose was
converted into amorphous form (Figure 27). Hemp yarn had even lower cellulose
crystallinity and a sample crystallinity similar to water retted hemp fibres. The cellulose
crystallinity remained constant during water retting of hemp, which was presumably due
to the low lignin degradation, compared with the lignin degradation during defibration
with P. radiata Cel 26 (Paper IV).
Sample crystallinity [% w/w]
100
80
60
40
20
0
Corn stover
Barley straw
Hemp fibres
WO corn stover
C.sub. treat hemp
P.rad. treat hemp
Water-rett. hemp
Hemp yarn
Norway spruce
0 20 40 60 80 100
Cellulose content [% w/w]
Figure 27. Sample crystallinity determined by Rietveld refinement versus the cellulose
content determined by the comprehensive fibre analysis. The full drawn line shows the
relationship for non-woody fibres. The grey line shows the effect of wet oxidation on
corn stover. The effect of fungal treatment is shown by the dotted line (Paper III; Paper
IV).
44 Risø-PhD-11