Tailoring the release of DCD from biopolymer matrices: The effect of DCD crystal size, loading, blends of PHBV and PCL and temperature on DCD release kinetic

Abstract

To increase the efficiency of nitrogen fertilizers, stabilized fertilizers have been developed by the fertilizer industry. These stabilized fertilizers can slow down the nitrification of ammonium using nitrification inhibitors (NI). Dicyandiamide (DCD) is a commonly used NI used in agriculture today, but its lifetime in soil exponentially declines with increasing temperature. Controlled-release of DCD can protect the molecule from bacterial degradation and prolong the duration of inhibition. This can be achieved by encapsulating it in a biodegradable polymer matrix. Biopolymer matrices include poly(3-hydroxybutyrate-co-3hydroxyvalerate) (PHBV) and polycaprolactone (PCL). In this research, DCD-PHBV pellets with DCD crystal sizes of 0-106 μm, 106-250 μm, >250 μm at DCD loadings of 20% (w/w), 40%, and 60% were produced by extrusion processing. In addition, an 80% loading with 0-106 μm DCD was fabricated. Further, 0-106 μm DCD was extruded at 40% loading with PHBV, PCL and 3:1, 1:1 and 1:3 PHBV/PCL blends. The release kinetics of DCD from these materials was monitored in water over eight weeks. Firstly, the effect of loading and DCD crystal size was investigated at 23℃. Following this, the effect of blends of PHBV and PCL were studied at 10℃, 23℃ and 40℃. The pellets were characterized using micro-computed tomography (µ-CT), Raman spectroscopy mapping and differential scanning calorimetry (DSC). The water release experiments confirm that the release profiles of DCD can be tailored by controlling the DCD loading, DCD crystal grind size, and the compositions of PHBV/PCL blends for specific applications and climatic conditions. Increasing loading increased the amount and rate of DCD release of DCD-PHBV pellets. This is due to a higher degree of connected channels to the outside, confirmed by the µ-CT results. For DCD-PHBV/PCL pellets, it is likely molten PCL filled the in voids/cracks forming in the PHBV matrix during production, which resulted in a diffusion controlled release mechanism. This is supported by Raman mapping and DSC results. The release profiles of DCD from DCD-PHBV pellets were modelled using a power law for the initial surface wash (0-5 h), modified first order model for II release via connected pathways (5 h-21 d) and a linear regression for the slow diffusion controlled release (21 d-56 d), based on which we predicted the release profile of DCD-PHBV pellets with other loadings. Our research indicated that DCD-loaded PHBV/PCL pellets is a practicable delivery system for the controlled release of DCD.

Understanding content placement strategies in smartrouter-based peer video CDN

“…To meet the skyrocketing growth of bandwidth requirement from the data-intensive video streaming and reduce the monetary cost for renting expensive resource in conventional content delivery networks (CDNs), video service providers are deploying their peer CDNs to make use of network and storage resources at individuals' homes for content delivery. Youku, one of the largest online video providers in China, has deployed over 300K smartrouters at their users' homes in less than one year [9], expecting to turn a large fraction of its users (250M) to such content delivery peer nodes.…”