Application of cassava in nonfood uses
Dextrins
were accidentally discovered in 1821 when during a fire in a
Dublin (Ireland) textile mill one of the workmen noticed that
some of the starch had turned brown with the heat and dissolved
easily in water to form a thick adhesive paste.
Three primary groups of dextrins are now
known: British gums, white dextrins and yellow dextrins.
British gums are formed by heating the
starch alone or in the presence of small amounts of alkaline
buffer salts to a temperature range of about 180?220?C. The
final products range in color from light to very dark brown.
They give aqueous solutions with lower viscosities than starch.
White dextrins are prepared by mild heating
of the starch with a relatively large amount of added catalyst,
such as hydrochloric acid, at a low temperature of 80?-120?C
for short periods of time. The final product is almost white,
has very limited solubility in water and retains to varying
degrees the setback tendency of the original starch paste.
Yellow dextrins are formed when lower
acid or catalyst levels are used with higher temperatures
of conversion (150?-220?C) for longer conversion times. They
are soluble in water, form solutions of low viscosity and
are light yellow to brown in color.
The following are some of the major uses
of dextrins in nonfood industries.
Corrugated cardboard manufacture. One of the
large users of dextrins is the corrugated cardboard industry
for the manufacture of cartons, boxes and other packing materials.
The layers of board are glued together with a suspension of
raw starch in a solution of the gelatinized form. The board
is pressed between hot rollers, which effects a gelatinization
of the raw starch and results in a very strong bonding. Medium-quality
flours are suitable for this purpose provided the pulp content
is not too high.
Remoistening gums. These adhesives are coated and
dried on surfaces, such as postage stamps and envelope flaps,
for moistening by the user before application to another surface.
Cassava dextrins in aqueous solution are well suited for this
purpose as they give a high solids solution with clean machining
properties.
Wallpaper and other home uses. Various types of starch-based
products are used as adhesives for wallpaper and other domestic
uses.
Foundry. Starch is used as an adhesive
for coating the sand grains and binding them together in making
cores which are placed in moulds in the manufacture of castings
for metals.
Well drilling. Starches and modified starches
mixed with clay are used to give the correct viscosity and
water-holding capacity in bores for the exploratory drilling
of oil wells or water wells. These starch products are replacing
other commercial products for making the muddy materials which
are indispensable for drilling wells. For this purpose a coldwater-soluble
pregelatinized starch which can be made up to a paste of the
required concentration on the spot is desired.
Paper industry. In the paper and board
industries, starch is used in large quantities at three points
during the process:
(i) At the end of the wet treatment,
when the basic cellulose fiber is beaten to the desired pulp
in order to increase the strength of the finished paper and
to impart body and resistance to scuffing and folding;
(ii) At the size press, when the paper
sheet or board has been formed and partially dried, starch
(generally oxidized or modified) is usually added to one or
both sides of the paper sheet or board to improve the finish,
appearance, strength and printing properties;
(iii) In the coating operation, when
a pigment coating is required for the paper, starch acts as
a coating agent and as an adhesive.
Cassava starch has been widely used as
a tub size and beater size in the manufacture of paper, in
the past mainly on account of its low price. A high color
(whiteness), low dirt and fiber content, and, above all, uniformity
of lots are needed in this instance.
An important new application of starch
is in the machine coating of magazine paper, formerly done
exclusively with caseins. There are indications that cassava
is particularly well suited to the purpose; however, definite
specifications for the starch still have to be worked out.
Textile industry. In the textile industry, starches
occupy an important place in such operations as warp sizing,
cloth finishing and printing. Warp sizing is the application
of a protective coating to prevent the single yarns from disintegrating
during weaving. The size consists of an adhesive and a lubricant
and is generally removed after weaving. Cloth finishing alters
the "feel" of the fabric by making it firmer, stiffer
and heavier. Cassava starch is also used for cloth printing
or producing certain designs in various colors on the smooth
surface of a finished fabric. While cassava accounted for
about 20 percent of all starch for these purposes in 1937,
it has been largely replaced by other starches after the Second
World War.
An exception is the manufacture of felt,
where cassava continues to be used exclusively in the finishing
process.
Wood furniture. Before the Second World War
the manufacture of plywood and veneer relied mainly on cassava
as glue. The basic material in this case is gelatinized at
room temperature with about double the amount of a solution
of sodium hydroxide. After prolonged kneading of the very
stiff paste in order to give it the required stringy consistency,
the glue is applied to the wood with rollers. As the presence
of a certain amount of the pulp is useful, medium- to low-quality
flours are acceptable or even preferable, although the presence
of sand is objectionable.
Since 1945, however, the use of cassava
as glue has declined to second place owing to the increasing
success of water-resistant plastics.
Particle board from cassava stalks
As cassava cultivation increases, more stalks will
become available for disposal. The Tropical Products Institute,
London, has been working on the utilization of the cassava
plant. Particleboards could be made from cassava stalks by
cutting them into small sections and mixing them with certain
resins. The strength of the board can be varied by altering
the resin content or the density.
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