The Introduction about Polyacrylic Acid
Polyacrylic acid (PAA) is colorless or light yellow liquid. PAA can form stable compounds with metal ions, calcium, and magnesium. PAA has an excellent decomposition of calcium carbonate and calcium hydroxide in water. PAA can be miscible with water, also is soluble in ethanol, isopropanol etc. PAA belongs to weakly acidic. Polyacrylic acid can be made of polyacrylonitrile or polyacrylic ester under the temperature of 100 degrees to acidic hydrolysis and oxidation/reduction system composed of sodium sulfate as initiator to preparing aqueous solution polymerization method.
Polyacrylic acid monomers is acrylic acid, the industry mainly use acrylic or catalytic oxidation in acrolein production, its melting temperature is 12 ℃, boiling point is 142 ℃, and has similar smell with acetic acid. It is usually by water solution to polymerization. Its polymerization rate in the water is affected greatly by pH, it is faster than in alkaline medium when be in acidic medium. Polyacrylic acid aqueous solution of PAA for the polyelectrolyte, its viscosity due to pH changes, namely the abnormal viscosity increases when the pH > 7. This is because the polyacrylic acid carboxyl ionized form negative ions produce electrostatic repulsion; the conformation of polymer chain in solution is more relax. Polyacrylic acid, because of the large viscosity can be used as a thickener. Polyacrylic acid can be used as a crosslinking on ZnO etc, the so-called ionic crosslinking polymer, is a new type of fillings.
The production process is generally intermittent. Polymerization temperature control in 60 ~ 100 degrees, reactant ester ratio, the concentration of acrylic acid is commonly 10%~30%. Ammonium persulfate (NH4)2S2O8 is generally used in an amount of 8% to 15% of acrylic acid. Molecular weight modifier can be added. In the quality of products to control the molecular weight of polyacrylic acid; don’t add the molecular weight regulator. And molecular weight regulator, the formula of acrylic try preferable limit; should take the lower conversely. And in the molecular weight regulator, the amount of initiator in the formula should be limited, the opposite response to the lower limit. Acrylic initiator at the same time, according to the proportion respectively drops to the water or a combination of chain transfer agent and water injection in the polymerization reaction. In general, high molecular weight regulator, the dosage of initiator dosage, is beneficial to reduce the product molecular weight of polyacrylic acid. For preparation of high molecular weight polyacrylic acid, there must be an inert gas of oxygen in the reaction system quickly opposite approach.
