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The processes for the manufacture of sodium alginate from brown seaweeds fall into two categories. This diagram is simplified to show their essential differences. The chemistry of the processes used to make sodium alginate from brown seaweeds is relatively simple. The difficulties of the processes arise from the physical separations which are required, such as the need to filter slimy residues from viscous solutions or to separate gelatinous precipitates which hold large amounts of liquid within the structure and which resist filtration and centrifugation.
To extract the alginate in the seaweed caustic soda is added to convert the seaweed to water-soluble sodium alginate.
The aqueous alginate solution is further processed through a clarification procedure. Since the aqueous alginate solution is very thick at this stage, the solution is diluted with large amount of water then clarified.
The seaweed extract is filtered to separate the sodium alginate solution from the cellulose contained in the fibrous seaweed residue.
An acid is added to isolate the alginic acid from the diluted sodium alginate solution.
This allows the insoluble alginic acid to be isolated. This method is known as the "Acid Precipitation Method". The "Acid Precipitation Method" provides the purest form of alginic acid as reduces contamination from calcium; calcium negatively alginic acid and its derivatives.
Precipitated alginic acid is dehydrated. The fibrous wet body (gel) is produced. The Fibrous wet body is dried and pulverized to make alginic acid powder which is the gelling ingredient in dental impression material.