The Surface Treatment Of Nano-SiO₂ And The Structure And Properties Of LLDPE/Nano-SiO₂ Composites

Studies of common polymer materials with high performance and multiple functions have been the focus of much recent research. Compared with traditional modification methods, the incorporation of nano-particles into polymers provides a novel way for the modification of the polymer due to the particular properties of nano-particles. The surface modification method, surface nature and the content of nano-particles govern the structure and performance of the resulting polymer composites. Therefore, it`s very important to systematically study the surface modification methods of nano-SiO2 and the relationship between the properties and structure of the composites.In this work, nano-SiO2 was surface-treated with a silane coupling agent alone or combination of coupling agent and dispersant via ultrasonic dispersion. LLDPE/nano-SiO2 composites were prepared using a reactive two-screw extruder. The influence of surface treatment methods and content of nano-SiO2 on the mechanical properties, crystallization property, thermal stability, optical and rheological properties was systematically investigated.The effect of treating nano-SiO2 with a silane coupling agent in a ball mill was compared with treatment via ultrasonic dispersion. The dispersion-stabilization mechanism of the novel surface treatment of nano-SiO2 with both silane coupling agent and dispersant were also studied. The results showed that the treatment time via ultrasonic dispersion had an optimum value. The treatment methods had a significant influence on the dispersability of nano-SiO2 in LLDPE matrix. For example, at the same content of nano-SiO2, the average particle size of nano-SiO2 treated with the silane coupling agent in ball mill was 97 nm, while the average particle size of nano-SiO2 treated via ultrasonic dispersion reached 90 nm. Nano-SiO2 treated with both silane coupling agent and dispersant together exhibited the best dispersity.The influence of SiO2 content and interfacial structure on the static mechanical properties of LLDPE/nano-SiO2 was studied. The results showed that the elastic modulus of the composites increased with increasing nano-SiO2 content. The tensile and impact strength reached a maximum value at a content of 3 phr SiO2. Breaking elongation almost remained unchanged at lower SiO2 content. The influence of nano-SiO2 without surface treatment on the static mechanical properties of the composites was similar to that of the nono-SiO2 surface-treated with silane coupling agent in a ball mill. The introduction of a macromolecular compatibilizer into the LLDPE composites filled with nano-SiO2 surface-treated with amino silane coupling agent resulted in an obvious increase in the elastic modulus of the composites. On the basis of the Guth Equation, the mathematical relationship between modulus of the composites and filler volume fraction for our system has been described using experimental values of the elastic modulus of LLDPE composites filled with silane coupling agent-treated nano-SiO2. The resulting equation was also found to be applicable to LLDPE composites filled with untreated SiO2. The influence of nano-SiO2 content on the dynamic mechanical properties of LLDPE composites was also studied. The storage modulus E' and loss modulus E'' of the composites increased with increasing content of untreated SiO2. The α relaxation peak shifted to lower temperature and the β, γ relaxation peaks remained unchanged compared with pure LLDPE. Below room temperature, the storage modulus of LLDPE composites filled with silane coupling agent-treated SiO2 was lower than that of the composites filled with untreated SiO2. In a higher temperature range, this trend was reversed. With the addition of a macromolecular compatibilizer, the storage modulus E' of the composites in the higher temperature range exhibited a remarkable increase and the α relaxation peak continued to shift toward lower temperature. The LLDPE composites filled with SiO2 treated with an unsaturated silane coupling agent exhibited higher E' and E''...