Exploiting poly(ε-caprolactone) grafted from hydrohydroxymethylated sunflower oil as biodegradable coating material of water-soluble fertilizers

Abstract

In the present study, hyperbranched poly(ε-caprolactones) were prepared and used as coating materials to prepare slow release diammonium phosphate (DAP) fertilizer. Firstly, the sunflower oil was hydrohydroxymethylated by one-pot two-step process using Rh(acac)(CO)2 as catalyst, and triethylamine as ligand. Next, the bio-based hyperbranched poly(ɛ-caprolactone) (PCL) were prepared in open air by in-situ ring-opening polymerization of ε-caprolactone using hydrohydroxymethylated sunflower oil as macro-initiator and tetra(phenylethynyl)tin (Sn(C ≡ CPh)4) as catalyst. The structures of the prepared polymers (SFO-O-g-PCL) were confirmed by nuclear magnetic resonance (1H NMR) and the infrared spectroscopy (FTIR). Furthermore, molecular weight values around 20.000 g.mol−1 of PCL grafted in SFO-O-g-PCL were obtained, the thermal stability and morphology of the coated film were also evaluated using thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) respectively. The hydrophobic character of the films prepared from SFO-O-g-PCL was confirmed by measuring the contact angle of water droplets. In the second part, the DAP granular fertilizers were uniformly coated by the prepared material (SFO-O-g-PCL) using a laboratory rotary drum. Then the slow release performance in water of the coated and uncoated DAP fertilizer granules was evaluated by tracking the cumulative concentration of P2O5 released. Thus, it was found that only 10 % of P2O5 was released after 2 h of essay from the coated DAP compared to a total release of P2O5 from uncoated DAP (conventional fertilizer) during the same period. This finding opens a wide perspective to combine the advantages of hydrophobic polyesters and bio-based oils to produce biodegradable coating agents.