Study On Reological Properties And Crystallization Kinetics Of HA-CaCO₃/PP

Modification of PP by adding β nucleating agents can significantly improve the crystallization properties and impact resistance of PP resin, so as to achieve the high performance of polypropylene.Inorganic particles coated with pimelic acid has been proved to be excellent nucleating agents, which attract wide attention and has brode application prospects. In this dissertation, calcium carbonate coated with pimelic acid(HA-CaCO3) was adopted as β nucleating agent to modified PP. The steady and dynamic rheological properties of the HA-CaCO3/PP system were investigated systematically. PP-g-MA was added into PP/CaCO3 composites to increase the interfacial force between calcium carbonate particles and PP matrix. The effect of PP-g-MA on the HA-CaCO3/PP system, especially the crystallization kinetics was studied, to provide a theoretical basis for the processing of this nucleating agent. The main contents of this dissertation include the followings:(1) The factors of nucleation effect were discussed. When the mass ratio of HA/CaCO3 was 0.5/100 and the amount of modified CaCO3 was 5%, the nucleation effect was best. The excess of HA and modified CaCO3 would reduce the content of β-PP.(2) The rheological properties of HA-nCaCO3/PP were studied systematically, and compared with that of unmodified nCaCO3 and CaHA/nCaCO3. Shear stress, dynamic frequency, temperature and content of HA-CaCO3 had an effect on the rheological properties of HA-CaCO3/PP. On the condition of stbale rheological measurements, viscosity of HA-CaCO3/PP composites decreased with increase of shear rate and was non-Newtonian liquid. Viscosity curves of HA-CaCO3/PP composites were fitted by Ostwald-de Wale equation, and the non-Newtonian index n decreased with increase of calcium carbonate content.Under the condition of dynamic rheological measurements, with the increase of the frequency, the dynamic storage modulus G′ and the dynamic loss modulus G′′ increased, the complex viscosity η* decreased.Temperature also had a great influence on the rheological properties. The complex viscosity η* and relaxation time decreased when temperature rised. At a certain temperature and scanning frequency, the order of viscosity and relaxation time of different blending systems were : 5%nCaCO3/PP < 4.5%nCaCO3/0.5%CaHA/PP < 5%HA-nCaCO3/PP. Compatibility analysis show that 5%nCaCO3/PP and 5%HA-nCaCO3/PP exhibited phase-separated morphology at 200℃-260℃. And the compatibility between nCaCO3 and PP matrix was improved after coating treatment.(3) Polypropylene-graft-maleic anhydride(PP-g-MA) is used as interface compatibilizing agent, and its effect on HA-nCaCO3/PP was investigated. It was found that PP-g-MA content improves mechanical properties, heat resistance, flow properties and crystal properties. Crystallization kinetics of pure PP, HA-nCaCO3/PP, HA-nCaCO3/PP-g-MA/PP was investigated by differential sanning calorimeter(DSC). For isothermal crystallization process, the crystallization curves show that the crystallization temperature range of HA-nCaCO3/PP has greatly improved compared to pure PP, thus HA-nCaCO3 can increase the crystallization temperature and promote crystallization. Friedman equation and Arrhenius equation were adapted to analysis and calculate the apparent activation energy of isothermal crystallization.And the result was in consist with Avrami equation. It’s concluded that HA-nCaCO3 increased the total crystallization rate, while PP-g-MA slowed down the crystallization rate. Besides, along with the process of crystallization, the apparent activation energy increased, the crystallization became more and more difficult. For non-isothermal crystallization process, Jeziorny method and Mo method did well in interpreting isothermal crystallization behaviors, but Ozawa analysis failed to provide an adequate description of the non-isothermal crystallization process. The results of Jeziorny analysis showed that the crystallization rate Zc increased with the increase of cooling rate. For the same cooling rate, the order of Zc was: HA-nCaCO3 /PP-g-MA/PP > HA-nCaCO3/PP > PP. The Avrami index n changed little in the whole system. The results of Mo analysis showed that HA-nCaCO3 and PP-g-MA can promote the crystallization and accelerate the crystallization rate.The results of nucleation activity and activation energy ?E calculated by Friedman equation showed that the addition of HA-nCaCO3 and PP-g-MA had strong nucleation activity and accelerated the nucleation rate.(4) The crystallization process of the polymer is mainly divided into two stages: nucleation and crystal growth, so the total crystallization rate is determined by the two stages. The changes of induction time △tinc, crystallization time △tc and overall crystallization time ttotal show that both HA-CaCO3 and PP-g-MA had a heterogeneous nucleation effect on the polymer matrix, and HA-CaCO3 can promote the growth of crystals, but PP-g-MA cannot. By the total crystallization rate Z value, the addition of PP-g-MA made the crystallization rate of isothermal crystallization process slow down, and the crystallization rate of the non-isothermal crystallization process is increased. It reflected that for the isothermal crystallization process, crystal growth process is dominant. But nucleation formation process was dominant for the non-isothermal crystallization process.