A new coated slow-release triple superphosphate (TSP) fertilizer was developed using formulations based on lignin (L) derived from olive pomace (OP) and a ic-carrageenan (C) biopolymer, and different plasticizers were added: glycerol (G) and polyethylene glycol 200 (P200) and 2000 (P2000). The effect of the type and molecular weight of the plasticizer on the physicochemical properties of the composites and phosphorus (P) release was investigated. The results showed a slight improvement in the thermal stability of the LC composite upon the addition of polyethylene glycol, while the hydrophobicity decreased. The addition of the plasticizers also decreased the elasticity of all the films except for P2000. The coating materials decreased the P release from 100% within 3 days for uncoated TSP to 55-69% within 30 days for coated TSP. However, the LC plasticizer formulations did not decrease P release compared to the LC formulations.