Lynne Wong's PhD thesis

e any residual moisture in the sample, it would imply under-estimation in the subsequent
Brix-free water determination.
One gram each of the nine cane component fibres was placed in separate pre-weighed glass
bottles of 60 mm diameter and 70 mm height with snap-on metallic caps. The samples
were dried in an air oven at 65 °C for one hour with occasional stirring, followed by
vacuum oven drying at 65 °C for 16 hours under 875 mbar vacuum, and weighed when
cool. They were subjected to further drying in an air oven at 105 °C for three hours to
drive off any residual moisture present, and weighed when cool. The difference in the two
masses affords an estimation of the residual moisture in the samples after the vacuum oven
drying method. The experiment was performed eleven times, and the results (Table 4.10)
show that the average residual moisture in the samples varied from 0.63% for cane top
fibre to 1.42% for dry leaf fines, and the average for all fibre samples was 1.12%.
The drying method used by Mangion and Player (1991), i.e. vacuum oven drying at 80 °C
and 825 mbar vacuum for three hours, was also checked to see if it was sufficient to dry
the samples completely. The same samples were tested again eleven times and the results
thereof are presented in Table 4.10. They varied from 1.38% for rind fibre to 2.22% for
dry leaf fibre, and the average for all fibre samples was 1.72%.
Since the accepted standard method of moisture determination by drying at 105 °C to
constant mass takes a long time, i.e. at least three hours, it was thought useful to have a
rapid method for residual moisture determination in fibres.
4.4.6.1 Halogen thermogravimetry as a technique to determine residual moisture in
fibres
Wong Sak Hoi (1997) tested the suitability of a halogen moisture analyser for rapid
moisture determination in sugars. The method devised was found to give results
comparable to those of the reference oven drying method at 105 °C for three hours, with a
shorter analysis time ranging from two to twelve minutes depending on the moisture
content of the sugar. In addition, good precision and accuracy was obtained for moisture
levels in sugars as low as < 0.1% and as high as 4%.
133