Surface grafting stearic acid to the coupling agent on attapulgite: A reinforced filler in castor oil‐based polyurethane coating

Abstract

Developing economic controlled‐release fertilizers (CRFs) with superior performance is an ongoing and important research area. This work investigated the co‐modification of acid‐activated attapulgite (ac‐AT) to optimize its surface properties for polyurethane (PU) composite applications, specifically in the coatings of CRFs. The modified ac‐AT (MAT) rods were obtained through treatment with 2.0 wt.% KH‐560 coupling agent and in‐situ grafting with stearic acid (SA). Varying the addition amount of SA resulted in the synthesis of different MAT fillers. Along with the adjustment of the filling amount, the properties of the MAT/PU composites were controlled. Notably, applying 1.5 wt.% SA onto the KH‐560 treated ac‐AT produced MAT with a contact angle of 100.8°, enhancing hydrophobicity and dispersion within the PU matrix. Furthermore, at a filling amount of 9.0 wt.%, the MAT/PU composite exhibited the most favorable properties with a tensile strength of 2.37 MPa, making it the optimal coating for CRFs with 75% nutrient release within 46 days while the coating efficiency was 3.0 wt.%. This co‐modification approach shows great potential in enhancing filler properties and promoting their application in organic coatings.