Poly-acrylic acid grafted natural rubber for multi-coated slow release compound fertilizer: Preparation, properties and slow-release characteristics

In this study, a novel multi-coated slow release compound fertilizer based on natural rubber (NR) was prepared and characterized. Firstly, NR was grafted with poly-acrylic acid by in-situ radical solution polymerization to synthesize poly-acrylic acid grafted natural rubber (NR-g-PAA), the reaction conditions were optimized to increase the water absorption properties of NR-g-PAA. Through a series of characterization and test, the structure, morphology, thermal properties and biodegradability of NR-g-PAA were determined. Subsequently, a multi-nutrient fertilizer core was fabricated with urea, KH2PO4, and attapulgite by pan granulation. Then the fertilizer core was coated by NR as the inner layer and NR-g-PAA as the outer layer. Meanwhile, the slow release behavior of the compound fertilizer in soil was also studied. Results showed that the maximum water absorbency of NR-g-PAA is 744.00 ± 14.38%. The release rate of N, P and K in 30 days for NR/NR-g-PAA coated fertilizer was about 54.35 ± 1.49%, 51.18 ± 2.15% and 44.37 ± 1.38%, respectively, showing that the nutrient element release can last for >30 days. Overall, the novel method introduced in this study can inform the development of NR based controlled release fertilizers.