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Understanding the Mobilization of a Nitrification Inhibitor from Novel Slow Release Pellets, Fabricated through Extrusion Processing with PHBV Biopolymer
journal contribution
posted on 2019-02-06, 00:00 authored by Ian Levett, Steven Pratt, Bogdan C. Donose, Richard Brackin, Chris Pratt, Matthew Redding, Bronwyn LaycockDicyandiamide
(DCD) has been studied as a stabilizer for nitrogen
fertilizers for over 50 years. Its efficacy is limited at elevated
temperatures, but this could be addressed by encapsulation to delay
exposure. Here, poly(3-hydroxybutyrate-co-3-hydroxyvalerate)
(PHBV) was investigated as a biodegradable matrix for the encapsulation
of DCD. Cylindrical ∼3 mm × 3 mm pellets were fabricated
through extrusion processing with 23 wt % DCD. Release kinetics were
monitored in water, sand, and both active and γ-irradiated agricultural
clay loam soils. Raman maps showed a wide particle size distribution
of DCD crystals and indicated that Hitachi’s classic moving
front theory did not hold for this formulation. The inhibitor release
kinetics were mediated by four distinct mechanisms: (i) initial rapid
dissolution of surface DCD, (ii) channeling of water through voids
and pores in the PHBV matrix, (iii) gradual diffusion of water and
DCD through layers of PHBV, and (iv) biodegradation of the PHBV matrix.
After ∼6 months, 45–100% release occurred, depending
on the release media. PHBV is shown to be an effective, biodegradable
matrix for the long-term slow release of nitrification inhibitors.