Lynne Wong's PhD thesis

The isotherm parameters of the Hailwood-Horrobin and GAB models were estimated by
the non-linear regression procedure of SigmaPlot (SPSS Inc.) for the calculated EMC data
of reconstituted R 570 cane stalk, dry leaf and green leaf aged 52 weeks (Tables 5.29 and
5.31) and aged 36 weeks (Tables 5.30 and 5.32). The values of the isotherm parameters,
together with the calculated regression criteria: coefficient of determination R 2 , the mean
deviation modulus P and the standard error of the estimate E s , for each model and for the
reconstituted cane stalk, dry leaf and green leaf aged 52 and 36 weeks are shown in Table
5.33. All R 2 values approach one and the P values are less than 10, except for reconstituted
green leaf aged 36 weeks as predicted by the Hailwood-Horrobin model, and the E s values
are also low. The good-fit of the Hailwood-Horrobin and GAB models to the calculated
EMC values of reconstituted cane and leaves is confirmed by inspection of the isotherm
plots (Fig 5.15).
5.7 CONCLUSIONS
The EMC of cane components of variety R 570 aged 52 and 36 weeks were determined at
30, 45, 55 and 60 °C for water activities ranging from 0.17 to 0.98. The resulting sorption
isotherms exhibit a type II sigmoid pattern. Three models were found to provide a good-fit
to the experimental data: the modified GAB, Hailwood-Horrobin and GAB models in this
order. However, the modified GAB model did not extend to water activity values greater
than 0.95, whereas the other two models covered the whole range of water activities
studied.
The EMC of sugar cane stalk of variety R 570 aged 36 and 52 weeks was estimated from
the dry mass fractions of cane stalk fibre, stalk pith, rind fibre and rind fines, and the
respective individual observed EMC values. Similarly, the EMC of dry leaf and green leaf
was calculated from the dry mass fractions of fibre and fines and their constituent
experimental EMC.
The GAB model was found to fit the calculated EMC values of the reconstituted cane
stalk, dry leaf and green leaf of R 570 aged 36 and 52 weeks well; similarly for the
Hailwood-Horrobin model except for green leaf aged 36 weeks.
The models of the sorption characteristics of the sugar cane component parts could now be
used to determine a number of thermodynamic parameters that enable the bound water to
be characterised. This work is described in Chapter 6.
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