Thesis (M.Sc.) -- Chulalongkorn University, 2008

Slow released fertilizer was prepared by coating a fertilizer with polyurethane (PU) from the reaction of methylene diphenyl diisocyanate (MDI) and polyol. The polyols synthesized by glycerolysis reaction of glycerol and epoxidized palm oil, palm oil, and castor oil were used as starting material for preparing polyurethane used for slow releasing of nutrient. The PU was coated on the urea fertilizer for 1-5 layer and the coated fertilizer was studied the releasing rate by UV-Visible spectrophotometry technique. It was found that the coated fertilizer exhibited the slow released properties. When thickness of the PU coating was increased, the releasing rate of urea decreased and increasing ambient temperature resulted in increasing of releasing rate. Furthermore, basic condition decreased releasing rate of urea. For 1-3 layer coated fertilizer, urea completely released within 30 days while the 5 layer coated fertilizer gave a slower and constant releasing rate. Furthermore, it was found that the urea of 5 layers coated with epoxidized palm oil polyol based, palm oil polyol based and castor oil based polyurethane was released within 30 days by 85, 90 and 94% respectively.