Lynne Wong's PhD thesis

5.6.3 Procedure to determine equilibrium moisture content of sugar cane
components
The nine cane component parts of the same age (1 g) were placed in separate pre-weighed
empty glass bottles, and dried in a vacuum oven (without applying vacuum) at 65 °C for
about two hours. During this period, the samples were stirred two or three times by using a
spatula. The vacuum was then applied and drying continued at 65 °C and 900 mbar
overnight. These conditions were used since it has been reported that drying under a harsh
regime could cause irreversible changes in the fibre which could lose its adsorptive power
(Nilsson et al., 2005). The next day, the glass bottles were removed from the oven,
stoppered, cooled in desiccators and weighed.
Aqueous sulfuric acid solution (500 mL) of known concentration (e.g. 5%) was poured
into a desiccator. The nine glass bottles containing the dried samples were placed with the
covers off onto a support with perforated holes above the sulfuric acid solution, the
desiccator was closed and placed in an air oven heated at 30 °C. Since the air oven could
accommodate two desiccators at a time, a second series of nine dried samples could be
examined in an atmosphere of 10% sulfuric acid at 30 °C. The masses of the samples were
checked daily and weighing was accomplished as fast as possible. The samples were
allowed to reach equilibrium which could take from one to five days depending on the acid
concentration and temperature used. Preliminary tests showed that the speed at which the
nine components reached equilibrium did not differ much, but it varied tremendously with
sulfuric acid concentration and temperature. The slowest was at low acid concentration
and high temperature, e.g. 5 days in 5% sulfuric acid at 60 °C, and the fastest was at high
acid strength and low temperature, about one day in 60% sulfuric acid at 30 °C (Table 5.6).
Equilibrium was considered to be attained when no discernible mass change (of < 0.005 g)
was detected between two consecutive measurements. Typical equilibration times are
indicated in Table 5.6.
After equilibrium was achieved, the glass bottles were removed from the desiccator,
stoppered firmly, cooled in desiccators and weighed. The moisture adsorbed was then
determined by drying at 105 °C in an air oven to constant mass (about three hours),
stoppering, cooling in desiccator and weighing. The sulfuric acid solution and the samples
were discarded after each determination.
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