Microwave drying and grinding characteristics of gum karaya (Sterculia urens).

Samples of gum karaya (Sterculia urens) of approximately 3.5 g each were dried
in a domestic microwave oven for different time periods ranging from 10 to
90 s. The samples showed an average moisture loss of 7.5 x 10-j kg of water/kg
of dy weight of solids per second. The dried samples were ground in a domestic
dy grinder and the ground samples were subjected to sieve analysis to calculate
the average final particle size. The grinding characteristics were evaluated bv
calculating the Bond’s work index. The microwave-dried samples were crisp and
consumed less energy for grinding compared to the control samples. This was
evident from the bulk dying of gum samples of 1.5 kg (initial moisture content
16%) for 20 min. The Bond’s work index for this sample was 0.4786 compared
to 0.7567 k Wh kg-’ for the control of the equal moisture content. Studies were
also made on the effect of the microwave power supply on dying and grinding,
and this was found to havIe no effect on the latter These studies have all
indicated that microwave dying is a good candidate for dying of gum samples.
The rheological studies were carried out with I % suspensions. They indicate
non-Newtonian pseudoplastic flow behaviour and the data fit well to the power
law fluid model. The effect of dying time on the ,flow behaviour index was
assessed.