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INTRODUCTION
Dextrins are normally prepared by roasting starch in the
presence of acid which materially change the character and
properties of starch. Chemically they are intermediate between
starch and sugars derived from starch.
PROPERTIES
Unlike starch, dextrins are soluble in water. The severity
of the heat and acid treatment determines the degree of solubility,
which is the basis for classifying or grading dextrins. Finished
dextrins are very fine, powder varying in colour from pure
white to light yellow.
APPLICATIONS
As dextrins do not easily react with chemicals, they are
specially suitable for applications in the textile field.
In textiles printing, they are used as thickeners. Free of
grit and other impurities, which usually accompany lower grades
of starch, they ensure that the copper rolls (used in printing)
do not suffer from abrasion. In sizing, they are used with
starch for increased adhesiveness. In finishing, they give
desired feel and handle to the fabric.
The tack or stickiness of dextrins is increased by adding
caustic soda or borax. The adhesive thus formed is widely
used in various industries . In the adhesive industry itself,
dextrins are preferred to glue which - unpleasant odour and
is subject to rapid bacterial decomposition. They are also
preferred to starch, as they need less or no cooking and much
less water to form the paste. This means reducing drying
time and little likelihood of mould infection in warm climates.
As adhesives, dextrins are thus used with greater advantage
in book binding, carton sealing, cigarette pasting, label
pasting of all kinds, paper box making, gum tapes, spiral
tube winding etc. In dyestuff industry it is used as extenders.
The role of dextrins in foundries is well-known. Here the
main function is to give good green strength to moulds and
to prevent deformation of the core, which is considerably
handled before being fired in the oven. Another important
point is that dextrins do not make the core too dense, so
that there are no trapped gases which cause blow holes. All
these advantages make dextrins very good as core binding materials.
TECHNICAL DATA
| |
White |
Yellow |
| Moisture
(max.) |
10% |
10% |
| Ash (max.) |
0.40% |
0.05% |
| Ph |
2.5 to
3.5 |
2.5 to
3.5 |
| Cold Water |
45 |
85 |
| Soluble
min. |
|
|
| Reducing
sugar |
6 to 8% |
3 to 5% |
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