Crystallization Property, Thermal Resistance, Thermal And Thermal Oxidative Stabilities Of LLDPE Filled With Nano-SiO₂

In this paper, nano-SiO2 was pre-treated with a silane coupling agent or combination of a coupling agent and a dispersant under ultrasonic and LLDPE filled with nano-SiO2 were prepared by melt-blending. The influence of nano-SiO2 content and surface-treatment methods on the crystallization property and its kinetics, relaxation feature , thermal degradation property and its kinetics, thermal oxidative degradation property and its kinetics of the filled system were investigated systematically. The effects of nano-SiO2 content and surface-treatment methods on the isothermal crystallization behavior and its kinetics of filled LLDPE were investigated by DSC method. Results show that the crystallization rate of the system firstly increases then decreases abnormally with increase of nano-SiO2 content, which could be explained by adsorption effect of nano-SiO2 particles. Simultaneously, compared to the surface-treatment of coupling agents with same nano-SiO2 content, using a dispersant in the process of surface treatment by above coupling agent lead to more obvious heterogeneous nucleation of nano-SiO2 on LLDPE, as a result the crystallization rate of the system increases.The study of non-isothermal crystallization of the filled system and its kinetics shows that the content of nano-SiO2 has no obvious influence on the crystallization temperature. At the same cooling rate, the crystallization temperature of the system containing macromolecular compatibilizer is higher than that of the system without compatibilizer , demonstrating that nano-SiO2 has a nucleating effect on matrix in the former system. A study of the non-isothermal crystallization kinetics shows that the Avrami index n of the filled system containing compatibilizer or high content of nano-SiO2 decreases compared with that of LLDPE matrix, which also indicates the nucleating effect of the filler.The relaxation property of LLDPE filled with nano-SiO2 was investigated by DMTA, The results show that the ( relaxation peak shifts to lower temperature and peak strength decreases; meanwhile, (,( relaxation peaks remain with increase of nano-SiO2 content or with the addition of a macromolecular compatibilizer.The study of the melt property of the filled system indicates that Tm2 remains and Tm1 decreases with increase of nano-SiO2 content. Tm2 and Tm1 of the system with macromolecular compatibilizer decrease and melting peak widens compared with those of the system without compatibilizer. Tm0 of the system firstly decreases then increases with an increase of the nano-SiO2 content. Compared to the system filled with nano-SiO2 treated with a silane coupling agent, Tm0 of the system filled with nano-SiO2 co-surface-treated increase. The study of thermal deformation demonstrates that both HDT and Ts increases with increase of SiO2 content . Compared to the LLDPE filled with nano-SiO2 without surface treatment, HDT of LLDPE with nano-SiO2 treated with silane coupling agents increases and HDT of the system with macromolecular compatibilizer is more higher.The effect of nano-SiO2 content and interfacial feature on the thermal degradation and thermal oxidative degradation of LLDPE filled with nano-SiO2 were studied by TG firstly, and thermal degradation kinetic of the system were made by Dole-Ozawa method .The results show that both thermal degradation temperature and thermal oxidative degradation temperature of the filled system increase with increase of the nano-SiO2 content, and the increase of the later is significant ,which are thought to be due to controlled release effect of nano-SiO2 on antioxidant. After introduction of macromolecular compatibilizer, both thermal stability and thermal oxidative stability of the filled LLDPE increase. Nano- SiO2 content has a great influence on thermal degradation apparent activation energy Ea of the filled system. Compared with matrix , Ea of the filled system increases obviously and increases with increase of the nano-SiO2 content. The effect of interfacial feature on Ea is slight.