Preparation, properties and formation mechanism of hydroxyl-silicone oil coating on the surface of kaolin/TiO2 composites

A simple and effective preparation method of the powder surface coating was found. Namely, spraying hydroxyl-silicone oil (HSO) ethanol solution on the surface of calcined kaolin and nano-TiO2 composite (CKT) powder and formed the HSO layer due to the volatilization of ethanol. Subsequently, the samples were heated at 250 degrees C to form the HSO cure coating. The FT-IR, MAS NMR, XPS and SEM measure results indicate that the surface modification reaction occur between the OH groups in HSO molecules and HO-AlVI in the calcined kaolin. No any chemical reaction carry out on the Si, Ti sites on the surface of CKT composites. The performance testings show the HSO modification reaction dramatically improve the hydrophobicity of the CKT composites. The modifica-tion coating has no any negative effect on the whiteness, but the oil absorption values slightly reduce. Interestingly, it increases again after curing because the HSO layer releases a large great of lipophilic groups such as CH3 and CH2 during the curing process. The comparison of performances with nano-TiO2 and calcined kaolin shows that the CKT composites are expected to replace nano-TiO2 in many fields.