Lynne Wong's PhD thesis

It is evident that in some cases marked with asterisks, the fibre saturation point is not yet
reached. From Table 6.9, it can be seen that the bound water values estimated are much
higher than the Brix-free water results obtained at ambient temperature, and that the FSP
increases with increase in temperature from 30 ºC to 60 ºC in most cases, contrary to the
finding of Berry and Roderick (2005). The reason why cane fibres behave differently from
timber is not known.
As described in Section 5.6.4.5, the mass fraction of cane components (stalk fibre and pith,
rind fibre and fines) and the measured component EMC can help to calculate the EMC of
the reconstituted cane stalk (Igathinathane et al., 2005). By plotting the calculated EMC
against relative humidity, the fibre saturation point at 30, 45, 55 and 60 ºC can be
estimated. Similarly for the reconstituted dry leaf and green leaf of R 570 aged 52 weeks.
These values are compared in Table 6.9 to the Brix-free water value (corrected for residual
moisture) of the reconstituted cane stalk, dry leaf and green leaf of R 570 aged 52 weeks
extracted from Table 4.26.
Stamm (1967b) provides a mathematical treatment of the possible types of diffusion in
wood during drying, including diffusion of water vapour within the void structure, and
diffusion of water in the ‘solid solution’. If the water is chemically bound to materials in
the cell walls during adsorption, then a diffusion process would involve a series of discrete
jumps from one binding site to the next. The final equilibrium would equate to a
thermodynamic state of maximum entropy.
The fibre saturation point values, in a number of cases are similar to the total water, m, as
found with the Hailwood-Horrobin model, i.e. the sum of the dissolved and hydrated
water.
6.9.1 The accepted Brix-free water value of 25% for cane
The traditionally accepted value of 25% Brix-free water on cane fibre has been quoted by
Anon. (1970) and Anon. (1984), but no information is given on the source of the
information. A literature search revealed that Foster (1962) mentioned he had obtained: “a
value of 25% in an earlier work (Foster, 1956) on Q 50 cane fibre by measuring the water
adsorbed at 20 o C at relative humidities of 35 to 95% and extrapolating the values to 100%
relative humidity. This gave a value of 25% for hygroscopic water, which is the value
generally used in milling calculations and cane analysis in Queensland at the present time”.
22