1-Naphthylacetic-acid (NAA) has been reported to be a plant growth
regulator (PGR) for the rooting of cuttings, fruit-set inhibition, fruit
shedding, and the initiation of flowering [43]. In2012,Qiu[43] prepared
CRCU with dual attributions of controlled release and PGR. To prepare
the coating material, the monomers N-butyl methacrylate (BMA),
methyl methacrylate (MMA) and 2-hydroxyethl acrylate (HEA) were
added to a four-necked flask equipped with a stirrer, nitrogen supply,
and condenser. Benzoyl peroxide (BPO) (0.45%) dissolved in 5 ml of
ethyl acetate was then added to the monomers and the mix was
agitated under nitrogen with ethyl acetate for ~6 h until a non-sticky
material was produced. The non-reacted monomers were then precipitated
by n-hexane and separated. The final poly(BMA-MMA-HEA) was
air dried at 80 °C. The solid coating material (PBMHs-NAA) thus obtained,
along with the paraffin wax, was dissolved in ethyl acetate and the
solution was then sprayed onto a fluidized bed of urea granules at 75 °C
for 25 min. The controlled release property of the coated fertilizer was
determined by water dissolution followed by a urea concentration assay
via UV spectrophotometry. The initial release rate was high (100% in
eight days) due to the sticky adhesion of the granules which caused a
rough surface. The addition of 10% paraffin wax, however, prolonged
the dissolution: 1.54% at 24 h, and 78.77% at 28 days.