The production and molding of the gypsum board is the bonding of gypsum board surface paper and gypsum slurry. The surface paper must be firmly bonded to the gypsum board core, so that the gypsum board has a specific strength. The effect and performance of the adhesive are significantly important in the gypsum board products.

1. GYPSUM BOARD ADHESIVE MODIFIED STARCH
1. The Function of Gypsum Board Adhesive
The production and molding of the gypsum board is the bonding of gypsum board surface paper and
gypsum slurry. The surface paper must be firmly bonded to the gypsum board core, so that the gypsum
board has a specific strength. The effect and performance of the adhesive are significantly important in
the gypsum board products.
When the gypsum board face paper is bonded with the gypsum slurry, the infiltration and diffusion of
water, the gypsum supersaturated liquid and the bonding agent penetrate the paper tissue together.
And the gypsum also generates needle-like crystals, which are combined with the bonding agent in the
vertical and horizontal directions of the face paper. It is tightly combined to form a network structure,
and the gypsum slurry is firmly bonded to the tissue through the adhesive.
The adhesive also acts as a protective film to prevent moisture in the air from immersing into the gypsum
board core, and to prevent the gypsum board core from getting damp and separating from the tissue.
The firm bonding between the tissue paper and the gypsum board core acts as a reinforcement in the
solidified gypsum, which enhances the compressive strength and flexural strength of the gypsum board.
2. Requirements for Gypsum Board Adhesive
Gypsum board adhesive should be rich in resources with low price. It is required that the gypsum board
surface paper and the gypsum board core have good bonding performance, and the relative amount of
bonding agent is small. It is required to have migration properties that can migrate from the gypsum
board core to the surface layer, so that the added bonding agent migrates to the board core bonding lay
er, and the bonding agent plays the role of bonding the board core and the facial paper. The gypsum
board bonding agent is easily soluble in water at room temperature. When the temperature rises, the
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2. viscosity does not rise fast, and when the temperature drops, the viscosity increases and also the
bonding force.
3. Selection of Gypsum Board Adhesive
In the process of research and test of gypsum board, a variety of adhesives, such as polyvinyl alcohol,
were used. In the production process of gypsum board, polyvinyl alcohol has a good bonding effect,
and the produced gypsum board is also powerful, but polyvinyl alcohol has no migration effect in the
gypsum board core, only bonding. It is relatively evenly distributed in the gypsum board core and does
not penetrate between the tissue paper and the gypsum board core, so the mixing amount is also large.
Besides, polyvinyl alcohol is expensive, resulting in high production costs for gypsum board.
but it has no mobility and is not suitable for use as a binding agent.
In the process of acid treatment, starch can undergo incomplete hydrolysis. The acid acts on the
glycosidic bond to hydrolyze the starch molecules, the starch molecular chains are broken, and the
starch molecules become smaller and become dextrin. Dextrin has fewer molecular chains, usually only
a few dozen starch sugar molecular chains. The migration of dextrin in the gypsum board core is
excellent, but it is easy to migrate to the outside of the tissue paper and affect the adhesion between
the tissue paper and the gypsum board core, and the bonding of dextrin itself is not strong. Tests show
that it is also not suitable as a gypsum board adhesive. Modified starch is also an incomplete hydrolysis
product of starch. Its starch sugar molecular chain number is less than that of natural starch, and more
than dextrin, usually between several hundred to several thousand. When the modified starch is heated,
its viscosity gradually rises. When it is cooled, the viscosity of the modified starch increases slowly, the
viscosity changes smoothly, and the final binding force is more remarkable.
The migration properties of modified starch can be well controlled. Most of the modified starch is
migrated to the interface between the gypsum board core and paper. There is very little modified starch
left in the gypsum board core. Similarly, it migrates into the paper. The amount of modified starch is also
small. In the production process of gypsum board, adding less modified starch can firmly bond the
gypsum board core and the surface paper together, which is an ideal gypsum board adhesive.
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They were taking tests for starches, acorn flour,
tapioca starch and corn starch. All the above
starch meets the requirements, but corn starch
has the best result. Starch is a carbohydrate
polysaccharide polymer, and the molecular
formula is (C6H10O5)n. The number of
monosaccharide chains is usually around
50,000, but some can reach millions. The natural
corn starch is gelatinized when heated to 60°C
and has a certain degree of binding power,
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3. 4. The Production Process of Modified Starch
Natural corn starch usually contains 10% to 12% moisture. In the modified starch factory, the corn starch
is slightly dried and all passed through a 120-mesh sieve. Spray 0.3% hydrochloric acid alcohol solution
as a catalyst, dilute the hydrochloric acid with an appropriate amount of anhydrous alcohol in advance,
stir it evenly in a sealed mixer, and age for 2 hours to fully acidify the corn starch. The starch added with
a hydrochloric acid alcohol solution is heated and acidified in an oil bath. The acidified starch in the oil
bath is slowly heated, and the heating rate is controlled at 1°C/min. When the temperature reaches
about 130°C, heat preservation and heating for 30 minutes, and then quickly cool to room temperature
to obtain modified starch. The modified starch oil bath equipment is shown in the figure. The modified
starch process is as follows:
Starch → drying → sieving → acidification → stirring → aging → heating → modification → cooling →
packaging → modified starch
Remark: Filled 38# cylinder oil into oil path pan, temperature 260℃，shaft rotation speed 31r/min.
5. Technical Indicators of Adhesive
Viscosity test conditions: The starch is formulated into a solution with a concentration of 12%, heated to
95°C while stirring, and then cooled to 25-30°C, and the viscosity is measured with a rotary viscometer.
Its technical indicators are shown in the table below:
Item Parameter Item Parameter
Starch Content ≥75% Ash Content 0.2%
Appearance White powder Solubility 73~78% @ 20~40℃ water
Protein 0.3% Viscosity 50~100Pa•s
pH 6.5~7.5 Moisture 8%~11%
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