Preparation And Properties Of Polysiloxane Grafting Multi-walled Carbon Nanotubes/Polymer Nanocomposites

Since Iijima discovered carbon nanotubes(CNTs), it has been drawn great attention. CNTs have excellent mechanical properties, predominant electrical, thermal stabilities and have the unique nano-effects of one dimensional nano-structure,which makes CNTs be the perfect reinforce for polymer materials, and give polymer materials many new functions. However, to effectively reinforce a matrix polymer with these outstanding properties of CNTs, two main issues have to be resolved:homogeneous dispersion of CNTs in matrix polymer; as well as strong interfacial adhesion between CNTs and matrix polymer. These requirements can be realized by improving the compatibility between CNTs and matrix polymer. In this regard, a key issue in development of polymer/CNTs composites is how to maximize the compatibility between CNTs and matrix polymer. Chemical functionalization technique is one of the methods for solving these problems.Siloxane(DMS) is composed by silicon and oxygen. Due to longer length and larger bond angle of Si-0 bond, it rotates easily. The intermolecular force gets weak, and the polymer is high elastic state. Polysiloxane has many outstanding physical, chemical performances, like oxidative resistance, the weathering resistance, hydrophobieity as well as physiological inert and so on.Various function groups are introduced into siloxane molecules to endow some new functions and retain DMS characteristics.In this study, functionalized MWNTs were fabricated through one-step condensation reaction of MWNTs-COOH with polysiloxane. Amino functionalization of the MWNTs was performed using diaminopropyl terminated dimethylpolysiloxane (DPD). DPD has a larger molecular weight and may form MWNT-MWNT network structure better. The FTIR, XPS and thermogravimetry analysis were used to study the surface chemical state of the modified multi-walled CNTs.Then PC/MWNTs-COOH and PC/MWNTs-DPD nanocomposites were prepared by the solution method and melt extrusion method. The mechanical properties, transmission electron microscopy (TEM), TGA, limiting oxygen index (LOI), UL-94 test, and permittivity test were used to evaluate the properties of the composites. The results showed that the MWNTs-DPD was dispersed well in the PC matrix; its tensile strength, flexual strength, flexural modulus, and flame retardancy were better than that of PC/MWNTs-COOH. However, the electrical properties of the PC/MWNTs-DPD nanocomposites based on pemittivity and dielectric loss result were worse than PC/MWNTs-COOH.The MWNTs-DPD were used in PP-IFR and to study their synergistic effect. The nanocomposites were prepared by the melt extrusion method. The mechanical properties, TGA, limiting oxygen index (LOI), UL-94 test were used to evaluate the properties of the composites. The experimental results discovered that the fire-retardant properties of PP-IFR/MWNTs-DPD was better than PP-IFR/MWNTs-COOH, but poor mechanical properties. TGA data show that the liquid DPD had macromolecular chain, which made the initial decomposition temperature and maximum decomposition temperature of PP-IFR advancing and carbon content decreasing. Therefore, the initial decomposition temperature and maximum decomposition temperature of PP-IFR/DPD were advanced and carbon content were decreased. But compared with PP-IFR, the initial decomposition temperature and maximum decomposition temperature of PP-IFR/ MWNTs-COOH were delayed and carbon content were also decreased.