Studies On Rheolgical Behaviors And Crystalline Properties Of Pe/v-poss Nanocomposites

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 hybrid inorganic-organic compositions provide a novel way for the modification of the polymer due to the particular properties. In this work, vinyl-polyhedral oligomeric silsesquioxanes (V-POSS) was synthesized from vinyl-trimethoxysilane. PE/V-POSS nanocomposites were prepared using a two-roll mill respectively. The influence of content V-POSS and molecular structure of PE on the rheological properties, mechanical properties, crystallization property and thermal stability was systematically investigated.The rheological behaviors of the LLDPE/V-POSS blends were investigated. The results showed that the blends fluidity increased with increasing shear stress when the content was within 3% and under 160℃. But the pseudoplasticity was weakened with increasing the content or the experimental temperature when the content was beyond 3% and higher than 160℃. The fluidity of HDPE/V-POSS blends increased with increasing shear stress and the pseudoplasticity was enhanced while addition of V-POSS. The rheological behaviors of the MPE/V-POSS blends increased with increasing shear stress and the pseudoplasticity was enhanced while addition of V-POSS. The rheological behaviors of the the LDPE/V-POSS blends decreased with increasing shear stress and the pseudoplasticity was weakened while addition of V-POSS.The non-isothermal crystallization of LLDPE/V-POSS and its kinetics were investigated by DSC. The results showed that the V-POSS content had no obvious influence on the crystallization temperature of the composites, and that the nucleating and plasticizing effects of V-POSS coexisted. The analysis of Gupta, modified Avrami and combined Ozawa-Avrami approaches can successful describe the nonisothermal crystallization process of LLDPE and LLDPE/V-POSS nanocomposites at various cooling rates. The Ozawa model is failed to provide an adequate description of nonisothermal crystallization for these systems due to secondary crystallization. The higher contents of V-POSS imply that the secondary crystallization plays an important role. The value of Avrami exponent n is changing from 2.2 to 3.4. The results are attributed to spherulitic crystal growth mechanism with heterogeneous nucleation at low cooling rates and simultaneous occurrence of spherulitic and lamellar growth with heterogeneous nucleation at higher cooling rates.The non-isothermal crystallization of HDPE/V-POSS and its kinetics were investigated by DSC. The results showed that the analysis of Gupta, modified Avrami and combined Ozawa-Avrami approaches can successful describe the nonisothermal crystallization process of HDPE and HDPE/V-POSS nanocomposites. The phenomena of nanocomposites imply that the secondary crystallization plays an important role. At the primary crystallization stage, the value of Avrami exponent n is changing from 2.0 to 3.2 and decrease with increase of cooling rates and contents of V-POSS. The results are also attributed to simultaneous occurrence of tridimensional and two dimensional growth from heterogeneous nucleation or/and simultaneous occurrence of two dimensional growth from homogeneous and heterogeneous nucleation.The mechanical properties of the PE/V-POSS nanocomposites were investigated. The LLDPE/V-POSS blends had better mechanical properties when the mass fraction of V-POSS in the blend was up to 3%; The HDPE/V-POSS blends had better mechanical properties at the content of 2-6%; The MPE/V-POSS blends had better mechanical properties when the mass fraction of V-POSS in the blend was up to 2%.