Thesis (M.Sc.)--Chulalongkorn University, 2001

Chitosan, a biopolymer, was used for controlled release of auxin hormones, 2,4-dichlorophenoxyacetic acid (2,4-D) and 3-indoleacetic acid (IAA). Polyphosphoric acid and glutaraldehyde were utilized as crosslinking agents in the preparation of beads from chitosan and 2,4-D (or IAA) mixtures. Our results indicated that the significant amount of 2,4-D was lost (only 20% recovery) during the preparation of beads containing chitosan:2,4-D ratio of 1:1 (w/w). Increase of chitosan contents and the use of polyphosphoric acid as crosslinking agent increased percent recovery of 2,4-D to about 69%, while the use of glutaraldehyde as crosslinking agent increased percent recovery of IAA to about 33%. The soil column leaching test indicated that polyphosphoric acid-crosslinked beads sustained the irrigation numbers of over 250% for 2,4-D and over 117% for IAA of the pure active compounds.