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Lab Scale Preparation of Gypsum Wallboard

Paper Type: Free Essay Subject: Chemistry
Wordcount: 2758 words Published: 16th Jan 2018

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STATEMENT OF THE PROBLEM AND SIGNIFICANCE OF PROPOSED RESEARCH (State succinctly the problem which is to be addressed. Clearly outline the importance of the problem, the originality of the approach and the impact it may have on the field if successful. Give an overview of the broader significance as well as the immediate impact of this research.)

The main purpose of this research is to create a gypsum wallboard with enhanced fire resistant property. Gypsum owns a property of combined water content, is a noncombustible and acts as effective fire proofing material. When heat from fire comes in contact with a plaster wall (or gypsum wallboard), it begins to lose combined water as steam thus making the hemihydrate form of gypsum (stucco) rehydrated and it reverts back to dihydrate. Wide range requirements such as fire resistant, increase moisture resistant can be achieved by the use of different calcining methods and additives. The wide applicability of gypsum is in construction. It is also used in the chemical industries

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In producing the fire resistant gypsum wallboards, the various properties of GWB like thermal, physical, chemical and mechanical characteristics are to be studied which plays a major role in controlling the spread of fire in buildings. Gypsum wallboard consists mainly of gypsum i.e. calcium sulfate dihydrate, CaSO4.2H2O. Calcium sulfate in nature is mostly available in two forms: Calcium sulfate dihydrate is commonly referred as gypsum, which is one of the oldest construction materials. It naturally occurs in sedimentary deposits from ancient sea beds. The most distinguishing feature of Gypsum is that it is moderately soluble in water at room temperature and exhibits a special feature of retrograde solubility i.e. gypsum becomes less soluble at elevated temperatures. Another form of calcium sulfate is the calcium sulfate anhydrite. At a temperature of 58 ËšC Gypsum and Anhydrite coexist, also the anhydrite exhibits the strong retrograde property but it does not revert back to gypsum as its solubility decreases with increasing temperature. Gypsum wallboard is used to make interior walls and ceilings in residential and commercial applications that often require specific fire rated assemblies.

Various types of gypsum wallboard are manufactured, with the most common variety and specialized varieties such as fire resistant, water resistant, and plaster lath. Combination of beta hemihydrates stucco, water and other additives form slurry which is used in the manufacture of the gypsum wallboard. Additives such as asphalt emulsion, vermiculite, chopped fiberglass and paper fiber impart to the wallboard characteristics such as water resistance, fire resistance and strength.

The fire resistance property is mainly attributed to the absorption of energy related with the loss of hydrate water going from the dihydrate (CaSo4.2H2O) and from the hemihydrates to the anhydrous form (CaSo4). Impinging heat of gypsum wallboards initially operates to reverse the hydration reaction resulting in controlling the spread of fire and penetration of flame through set gypsum structures. Fire resistance can be achieved by using appropriate additives such as fiber, glass textile fibers, vermiculite, which expands when heated, which acts against the gypsum shrinkage.

Because of its worldwide occurrence and huge potential reserves, however its uses are not considered basic to survival in a national emergency, gypsum is not considered a strategic mineral. This has permitted natural economic factors to prevail in the development of the mineral worldwide, which overall is a healthy situation that should continue to prevail.

PLAN OF PROCEDURE (Outline the initial approach to the problem and its feasibility. Point out innovative features, relate it to previous work including pertinent references, and indicate how this plan may contribute to the solution of the broader problem proposed.)

Gypsum manufacturing process consists of three main steps (1) rock preparation, (2) calcining and (3) formulating and manufacturing. Though we start with buying the gypsum material from one of the providers so the next important step ahead is the calcination process. Gypsum is usually referred to be CaSO4.2H2O. Calcium sulfate dIiydrate undergoes calcination to form hemihydrate (CaSO41/2H2O) or anhydrous form (CaSO4). Initially the calcination process was achieved by heating the raw gypsum material in an open environment, later on with the development in science calcination was achieved by heating the gypsum material in a kiln. Kinetic studies of calcination process plays an important role in determining the gypsum product parameters. We are interested in knowing the time, temperature and rate at which the calcination process can be achieved. Initially a small amount of the gypsum material is taken and X- Ray diffraction studies are conducted on it to know its composition i.e. CaSO4.2H2O or CaSO41/2 H2O or CaSO4 .Later after determining the form of gypsum material, thermogravimetric studies (used for the determination of weight change at different temperatures and time) are conducted on the CaSO4.2H2O to determine the temperature and time required to convert from dihydrate form to hemihydrate and anhydrite form. Again the obtained product is first subjected to XRD and SEM studies to investigate the state of gypsum i.e. dihydrate, hemihydrate or anhydrous form. This can be studied by interpreting the obtained results with the earlier established results. Later gypsum powder is subjected to different temperatures at different time intervals to determine the time and temperature required for the calcination process to finish by using Thermogravimetric Analysis Instrument also Differential Scanning Calorimetry (which determines the melting and boiling temperatures) studies are also conducted to know the melting temperatures of the product Until now the calcination process is studied by using a very small amount of the sample in a laboratory environment, the obtained results from these experiments is used to correlate with the calcination process which is done in hot air oven by using a large amount of samples. The temperature obtained from the thermogravimetric studies is used as basis for the calcination process in hot air oven. These studies are done to know the reproducibility for large scale samples. This encompasses the first step in our research. The importance of these kinetic studies related to calcination is very useful to determine the conditions for achieving the hemi hydride from calcium sulfate which undergoes rehydration process i.e is addition of water molecules to the hemi hydride form to form the gypsum wallboard.

Calcium sulfate hemihydrate (CaSO41/2H2O) or Calcium sulfate anhydrite (CaSO4) undergoes rehydration in the presence of water. Rehydration plays an important role as it allows to add the additives such as glass material, vermiculite etc. to the slurry which is referred as stucco. Chemically stucco is referred as the hemihydrate form of CaSO4. These additives are added to increase the fire resistant property in addition to the strength of the wallboards. The kinetic studies related to the rehydration process are studied similar to the calcination step. These kinetic studies gives us scope for better understanding the process of gypsum wallboard. i.e the amount of water required for rehydration and also the amount of additives that can be added to the gypsum mixture to retain the chemical stability of the gypsum composition required for the wallboard manufacturing. Similar to the first step this step is studied for the time, temperature and rate of reaction in the open environment and later in the laboratory environment by using kettle. In the kettle the hemihydrate and hydride forms of calcium are reacted with the water and the obtained product is subjected to the XRD and SEM studies to determine the state of product. This is the second step in our research.

The final step in our research is the lab scale preparation of gypsum wallboard which involves the dihydrate form of calcium sulfate react with the sufficient amount of water to form slurry. Theoretically about 18.6 parts of water is required to react with the 100 parts of gypsum but to get a slurry, excess of water (about 80 to 85 parts) is reacted with 100 parts of gypsum. In this step water along with 10-30 wt. % of starch such as corn starch is added to obtain milk of starch. Next about 0.1 -1.5 wt.% of amolytic enzyme such as α amylase based on the starch is added and heated to the decomposition point of the starch with stirring. After the heating is stopped enzyme deactivating agent based on the starch is added in the range of 0.8 to 1.0 wt. % and mixed with water to obtain a starch paste. To the prepared starch material the calcination product is added along with water and vermiculite, glass materials which improve the fire resistance property of the gypsum wallboard. This mixture is agitated in slow motion to obtain a slurry. This slurry form of gypsum is poured into a paper sheets such as paper boards. The edges of the paper is folded upwards to retain the slurry form of gypsum. The other end of the product is covered with another paper material which helps to retain the structure of the gypsum board. This mixture is subjected to heating by using hot air press which is useful to remove the excess water and to obtain a specific structure of the gypsum board. This process is continued until all the excess water is removed. It is dried in the temperature range of 50 ËšC-200 ËšC.

Starch paste such as denatured starch and dextrin is used as an auxiliary adhesive to prevent calcination of the crystal of gypsum dihydrate and dehydrated to give a gypsum hemihydrate in drying at high temperatures. Also to prevent separation of the gypsum core member from both paper board, hardening modifier are added to the raw material of the gypsum core member. It is effective that starch paste along with water in the gypsum core member and both paper boards migrate during drying at high temperatures, and cover the crystal of gypsum dihydrate due to water retention capability of the starch paste which developed into the fiber of the paper boards so as to prevent the calcination and dehydration of the crystals. The obtained wallboard is subjected to different analytical techniques such as Thermogravimetric analysis, Thermomechanical analysis, XRD, SEM and Differential scanning calorimetry as discussed in the calcination and rehydration step.









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Materials and Supplies


Raw gypsum material ( 50 pounds)

$16.81 per 1 pound



Starch material (20 pounds)

7.53 per pound



Paper( 20 square meter)

$1.5 per square meter



Travel Expenses


National gypsum – North Carolina

transport+ stay+ food ( 2 days)




Materials and supplies:

A minimum of 50 pounds of raw gypsum is required to make the gypsum wallboard and test its fire resistant property by adding the additives such as starch, dextrose, glass fibers. Initially a wallboard is made without adding any additives and for that about 5 pounds of the powder is used and tested for its properties. Similarly by adding the additives wallboard are made and tested for its properties. If the properties observed are similar to the standard fire resistant properties, variations in the additives is done and another wallboard is made to test for its fire resistant property. This procedure is followed until a wallboard with improved fire resistance is observed.

Travel Grant :


A trip to National gypsum located in North Carolina, which is one of the leading producer of gypsum wallboard helps us to get the outline idea of the process of preparation of gypsum wallboard and also the trip gives us idea about the research being conducted by them.



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