Biodegradable polymer/clay systems for highly controlled release of NPK fertilizer

Abstract

The aim of this work was to obtain biodegradable polymeric systems based on poly(hydroxybutyrate) (PHB) for use in the controlled release of agrochemicals and to analyze the relationship between the properties of polymers and the rates of release of active compounds. Two types of systems were obtained: one using nitrogen, phosphorous, and potassium (NPK) fertilizer directly mixed within the polymer matrix and another with the fertilizer previously incorporated in bentonite (Bent) and mixed with the polymer. The systems were obtained by melt processing and then evaluated by their properties. The release of the active compounds was analyzed by conductometric analysis using an aqueous solution as release medium for 240 hours. The obtained results were correlated with the biodegradation process of PHB. All of the systems presented a significant reduction in the active compounds released to the environment as compared with the direct application of NPK. The PHB/NPK systems showed a release of up to 37% of the compounds, while the PHB/m‐Bent showed greater control, with a release between 4% and 11% after 240 hours. In addition, the properties of the polymer systems presented a direct relationship with the rate of active compounds released. The type of production process, properties, and biodegradability indicate interesting potential of these systems for application in the controlled release of active compounds.

Poly(hydroxybutyrate)‐based systems behavior on the controlled release of NPK fertilizers

“…This behavior is well known in such biopolyester‐based systems, where the presence of chemical groups capable of reacting with polymer chains leads to a reduction in the thermal stability of these materials 21 . As already shown in previous works, 13 NPK fertilizer has a great trend to carry out degradation of PHB structure during processing mainly due to the reaction between the nitrogen compounds, which in contact with carbonyl groups of the chains lead to degradation reactions. As a consequence, the more degraded samples presented a decrease of 30°C in T 5% , and the presence of free NPK and m‐Bent particles leaves reduction of about 10°C in the T m due to the structures formed.…”

“…The clay was then filtered, washed with deionized water and ethanol, and dried in a vacuum oven at 70°C for 8 hours until a constant weight was obtained. The resulting m‐Bent is composed of six‐times fewer active principles than pure NPK, as determined in our previous work by elemental analysis of carbon, hydrogen, and nitrogen, flame photometry and Rutherford backscatter spectroscopy 13 …”

“…The nanoparticle of Bent modified with NPK (m‐Bent) was obtained by a reaction performed using the protocol previously developed in the research group and published elsewhere 13,17 . First, a suspension of 3.0 g of Bent in 100 mL of deionized water was prepared to ensure a greater degree of swelling of the clay and to increase the efficiency of the cation exchange.…”

“…The release of the fertilizer was evaluated through conductometric analyses using an Ion DDS‐12DW equipment based on the methods described in the literature, where the increase in the ionic conductivity of the solution is directly related to the release of the soluble ionic active compounds 8,13,19 . The compounds were immersed in deionized water at three different pHs (5, 7, and 9) to simulate the action of water in the leaching of the active compounds from the polymer chains under different environments.…”

“…Recently, our research group developed controlled‐release systems based on poly(hydroxybutyrate) (PHB) that acts on the release of pure NPK fertilizers or NPK previously incorporated in nanoparticles 13 . Interesting results were obtained, achieving around 90% reductions in the release of active compounds.…”