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

Table 5. Fibre yield and cellulose recovery for the hemp fibres treated as presented in
Figure 24 (Paper I; Thomsen et al., 2005).
Fibre yield
[% w/w]
Cellulose recovery
[% w/w]
Use of raw hemp bast
Wet oxidation (20 g batch) 78 90
Wet oxidation (40 g batch) 76 88
Wet oxidation (60 g batch) 83 97
Steam explosion (no alkali, 2 min) 74 90
Use of water retted hemp fibres
Hydrothermal treatment (no alkali) 83 100
Wet oxidation (no alkali) 85 100
Wet oxidation (with alkali) 71 88
Steam explosion (no alkali) 83 100
Retted-STEX (with alkali) 27 31
Note: Conditions are shown in Figure 24.
MONOMERIC PHENOLS
(from lignin)
R2
R1
OH
R3
R1= -H, , -CHO, -C(C=O)CH3 or -COOH
R2= -H or -OCH3
R3= -H or -OCH3
(oxidative cleavage)
WET OXIDATION
OF WHEAT STRAW
SOLUBLE FRACTION
hemicellulose &
degradation products
CARBOXYLIC ACIDS
(from lignin and sugars)
RCOOH
CO2
HO
SOLID FIBRE FRACTION
cellulose &
hemicellulose, lignin and NCWM residues
FURANS
(from sugars)
glucose xylose
O CHO
(oxidative cleavage)
O CHO
5-HMF 2-furfural
Figure 25. Principle of wet oxidation applied as pre-treatment of plant fibres. NCWM:
water-soluble compounds like proteins and pectin; 5-HMF = 5-hydroxymethyl-2furfural.
The plant fibres are fractionated into a solid fraction of cellulose and a liquid
fraction of hemicellulose and lignin. The intermediate phenols from lignin degradation
and furans from sugar degradation are further oxidized to carboxylic acids and CO2
(Klinke et al., 2002).
7.2 Biotechnological treatments
Treatment of Uso-hemp by combined field retting and exposure to frost during
wintertime (Pasila, 2000) resulted in moderate increase in the cellulose content of the
fibres (60→65% w/w) due to removal of water-soluble components and ash
(unpublished data). The water retting process resulted in addition in pectin degradation
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