Hydrophobically modified phosphogypsum and its application in polypropylene composites

Phosphogypsum (PG) is a solid waste residue in the production of phosphoric acid by the wet process, and many deposits of this waste pollute the environment. Anhydrous Phosphogypsum (APG) was prepared by pretreatment of PG, after which its surface was hydroxylated by NaOH solution. The surface hydrophobic modification of APG was achieved by grafting 3-(methacryloxy)propyltrimethoxysilane (KH570), alkoxytri (dioctyl pyrophosphate acyloxy) titanate (TCA-L38), and stearic acid (SA), respectively, on hydroxylated APG surfaces. The chemical surface structure and properties of the APG materials were determined, and the mechanism of the hydrophobic surface modification was discussed. Finally, the modified APG was used as polypropylene (PP) filler to prepare PP composites by melt blending. The results showed that the hydroxyl content on the surface of APG was significantly increased after hydroxylation, which significantly increased the grafting rate of KH570, SA, and TCA-L38 on the surface of APG. KH570, SA, and TCA-L38 could react with the hydroxyl group of APG, which were closely adsorbed on the surface of APG by chemical adsorption. The water contact angles of APG-OH-KH570, APG-OH-SA, and APG-OH-TCA were 80.52°, 124.99°, and 123.77°, respectively. The surface hydroxylation and hydrophobic modification of APG significantly improved the compatibility and interfacial interaction between APG and PP. The mechanical properties APG-OH-KH570/PP, APG-OH-TCA/PP, and APG-OH-SA/PP composites were better than those of pure PP.