Color-stable Superabsorbent Polymer Composition
Patent #: 7,504,551
Inventor(s): Norbert Herfert, Michael Azad, Peter Carrico, Guy Woodrum, Michael Mitchell and Ma-Ikay Kikama Miatudila
Company: BASF Aktiengesellschaft
A method of manufacturing color-stable superabsorbent polymer particles has been patented. The process comprising the steps of: (a) forming a monomer mixture comprising at least one monomer capable of forming a superabsorbent polymer, a crosslinking agent and an initiator system comprising a sulfinic acid derivative having a structure. In this method, M is hydrogen, an ammonium ion, or a monovalent or a divalent metal ion of groups Ia, IIa, IIb, IVa, and VIIIb of the Periodic Table of the Elements. R1 is OH or NR4R5, wherein R4 and R5, independently, are H or C1-C6alkyl. R2 is H or an alkyl, alkenyl, cycloalkyl, or aryl group, optionally having 1-3 substituents independently selected from the group consisting of C1-C6alkyl, OH, O—C1-C6alkyl, halogen and CF3. R3 is COOM, SO3M, COR4, CONR4R5, or COOR4, wherein M, R4, and R5 are as defined above, or, if R2 is unsubstituted or unsubstituted aryl, R3 is H; and the salts thereof or a mixture with an optional photoinitiator and water. The monomer is polymerized and the crosslinking agent in the monomer mixture forms a superabsorbent polymer hydrogel. Optionally, the superabsorbent polymer hydrogel is subjected to a low dose of UV radiation and the superabsorbent polymer hydrogel is committed to provide superabsorbent hydrogel particles. The superabsorbent polymer hydrogel particles are dried for a sufficient time at a sufficient temperature to provide the color-stable superabsorbent polymer particles, wherein the color-stable SAP particles, after storage for 30 days at 60°C and 90% relative humidity, exhibit an HC60 color value of at least 60 and a maximum b-value of 10.
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