Lynne Wong's PhD thesis

was still hot. Since the filter was used only as a cover for the fibre sample, it could be used
over and over again.
4.4.6.2.3 Comparison of the halogen drying method with the standard oven drying
method
About 3.5 g each of the fibres of nine sugar cane component parts were separately weighed
into pre-weighed 250 mL glass bottles with stoppers, and dried in a vacuum oven at 65 °C
and 875 mbar vacuum for 16 hours after a pre-heating period of one hour at 65 °C in an air
oven.
After drying, the bottles were cooled in desiccators. About 0.8 g of each sample was
quickly transferred into two small pre-weighed bottles, which were then weighed on the
analytical balance to four decimal places and dried by using the standard method of 105 °C
in an air oven to constant mass (about three hours). Two portions (about 0.6 g) of the same
sample were also examined by the halogen moisture analyser to yield duplicate moisture
content values of the sample.
Five replicates of nine fibre samples were examined. The results are shown in Table 4.11.
Statistical analysis by paired comparison of the averages of the duplicate results of residual
moisture content determined by the standard drying method and the halogen
thermogravimetric method showed that the difference was not significant; and for 45 data,
the standard error of the mean was 0.104% for a mean of 2.48% by the halogen drying
method compared with 0.096% for a mean of 2.36% by the standard oven drying method.
It was concluded that the method of moisture determination in fibre by halogen
thermogravimetry gives results comparable to the reference oven drying method at 105 °C
to constant mass, with a much shorter analysis time. The method was subsequently used
whenever it was required to check the moisture content in fibres.
Also, fibre which had been dried in a vacuum oven at 65 °C for 16 hours prior to Brix-free
water determination still contained about 1.1% moisture. As mentioned in Section 4.3.2,
Van der Pol et al. (1957) found a difference of five units in the Brix-free water values for
cane, dried at 60 °C over phosphorus pentoxide and under vacuum, compared to the higher
value for the same fibre dried at 125 °C. Since high temperature drying could have altered
the characteristics of the fibre (i.e. activating it), the method of drying in a vacuum oven at
65 °C for 16 hours was adopted for fibres in this study, and if required, the Brix-free water
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