Control of release characteristics in pH‐sensitive poly(vinyl alcohol)/poly(acrylic acid) microcapsules containing chemically treated alumina core

The pH‐sensitive poly(vinyl alcohol)/poly(acrylic acid) hydrogel microcapsules containing vitamin B 12 ‐loaded Al 2 O 3 core were prepared with a three‐step emulsion polymerization. Al 2 O 3 was chemically treated with HCl or NaOH solutions at room temperature for 24 h to modify the binding properties with vitamin B 12 . The colon‐targeted release characteristics of vitamin B 12 from the microcapsules were evaluated at different pHs. These microcapsules showed the faster and larger release of vitamin B 12 due to the high swelling of microcapsule shell as the pH was changed into more basic condition. However, these microcapsules showed the slower and less release of vitamin B 12 as the acid value of Al 2 O 3 increased due to the strong binding interaction between Al 2 O 3 core and vitamin B 12 even though the initial loading of vitamin B 12 was higher. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010