Drying induced aggregation of halloysite nanotubes in polyvinyl alcohol/halloysite nanotubes solution and its effect on properties of composite film

The polyvinyl alcohol (PVA)/halloysite nanotubes (HNTs) solution were prepared with the aid of ultrasonic treatment. The composite films were prepared through casting or coagulating the PVA/HNTs solution. The coagulation process was employed to obtain a composite film without aggregation of HNTs. It is shown that the particle size and distribution of HNTs in the PVA/HNTs solution is independent of the ratio between HNTs and PVA. It is also revealed that the aggregation of HNTs takes place during the drying process of the as cast film. Compared with the film by coagulation method, the HNTs in the as cast film show less profound effect on the nucleation of the crystallization of the PVA. The crystallization temperature initially increases with HNTs loading and overloading of HNTs tend to depress the improvement in the crystallization temperature. The glass transition temperature (Tg) of the composite film decreases with HNTs loading and the aggregation process shows practically no effect on the Tg. Inclusion of HNTs greatly depresses the decomposition of the PVA backbone, while it is not effective for improving the resistance to the abstraction of the side groups. The aggregation process at low concentration of HNTs has more significant effect on the thermal decomposition of composite films compared with that at high concentration.