STPP Chemical And Physical Properties Hydration performance With different sodium generation temperature, sodium tripolyphosphate has high temperature type and low temperature type, which has the differences between the two bond length and bond angle. After hydration, both high and low temperature products can produce hexahydrate. However, under the same conditions, the hydration of high temperature type is faster, which makes it produce high heat. But it is prone to agglomeration when it is soluble in water, which is due to the presence of sodium ions is in the tetra-ligand in the structure of high temperature type and the tetra-ligand has a strong affinity for water. Whereas the low temperature type produces hexahydrate at a very slow rate in water. STPP is quite stable at room temperature, but will slowly hydrolyze in moist air, and produce sodium orthophosphate eventually. Sodium triphosphate also has complexation with metal ions in water to form soluble complex compound. Buffer function The aqueous solution of sodium tripolyphosphate is weakly alkaline, and it can form suspension in water with PH value from 4.3 to 14. This can be called dispersion effect. It can also make liquid and solid particles be better dissolved in the liquid medium and make the appearance of the solution is completely transparent. This is solubilization. Because of its unique properties, sodium triphosphate is an important ideal material in detergents.

Sodium triphosphate contains two types, anhydride and hexahydrate. Anhydride are usually divided into high temperature type (Ⅰ) and low temperature type(Ⅱ). It is mostly white crystalline or crystalline powder in appearance. The relative molecular mass is 367.86, the relative density is 2.49 and the melting point is 662℃. It is gradually hydrolyzed in an aqueous solution to form pyrophosphate or orthophosphate. STPP chemical has complexation of alkali earth metal and heavy metal ions, and can soften water. It also has the ion exchange ability and strong dispersion, which can make the suspension into solution. Type Ⅰ has larger hydrolysis velocity than Ⅱ, so type Ⅱ is also known as slow hydrolysis type. Type Ⅱ can be transformed into type Ⅰ at 417 ℃.

Hexahydrate is white prismatic crystal of trisoclinal orthogonal crystal system, which can be weathered and has a relative density of 1.786. The melting point is 53℃. It can be decomposed during recrystallization. Even if sealed, it can still decompose to sodium diphosphate at room temperature. When heated to 100℃, it can be decomposed into sodium diphosphate and sodium phosphate. Therefore, hexadydrate type sodium tripolyphosphate are not easy to keep.

Industrial grade sodium tripolyphosphate is actually the mixture of type Ⅰ and type Ⅱ. For that, type Ⅰ has fast dissolution rate, and has large thermal effect when hydrated to form hexahydrate, which is easily absorbed in the atmosphere and clumped with moisture. Type Ⅱ is slower in moisture absorption and less prone to clumping. Therefore, the content of type Ⅰ sodium tripolyphosphate uses in detergents shouldn’t be too high, generally controlled at 10-30%.