Rheological Behavior, Crystallization Kinetics And Mechanical Properties Of Bimodal Polyethylene And Their Blends

1. Different composition blends of liner bimodal polyethylene (LBPE)/LDPE and bimodal medium density polyethylene (BMDPE)/LDPE are made by melt blending way. Melts rheological behavior of blends is studied. Influences of composition of the blends, shear ratio and shear stress on melt apparent viscosity are discussed. Non-Newtonian index (n), melting flow rate (MFR) and swell ratio of the blends with different proportions are measured. Processability of BMDPE and LBPE are apparently improved by LDPE. Conventional yield stress, breaking stress and breaking extensibility of the blends with different proportions are also measured. It is proved that mechanical properties of the blends are improved with BMDPE and LBPE content increasement.Nonisothermal crystallization kinetics of LBPE, BMDPE and theirblends with LDPE were studied using differential scanning calorimeter(DSC) at various scanning rates. The Avrami analysis modified by Jeziornyand a method developed by Mo were employed to describe thenonisothermal crystallization process of LBPE and BMDPE. The theory ofOzawa was also used to analyze the LBPE and BMDPE DSC data. Kineticparameters such as the Avrami exponent (n), the kinetic crystallization rateconstant (Zc), the peak temperatures (Tp) and the half-time of crystallization(t1/2) etc. were determined at various scanning rates. The appearance ofdouble melting peaks and double crystallization peaks in the heating andcooling DSC curves of blends indicated that different polyethylene inblends could crystallize respectively. As a result of these studies, thecrystallization rate constant (Zc) of LBPE and BMDPE increase with theincreasing of cooling rates. The Ozawa analysis failed to provide anadequate description of the nonisothermal crystallization of LBPE andBMDPE because of the comparisons of different stages of crystallization at different cooling rates. The Avrami analysis modified by Jeziorny and a method developed by Mo were successful in describing the nonisothermal crystallization process of LBPE and BMDPE. The nonisothermal crystallization of LBPE and BMDPE corresponds to a three-dimensional growth.2. Different composition of LBPE/LDPE/LLDPE and BMDPE/ LDPE/LLDPE blends are made by melt blending way. Melts rheological behavior and Mechanical Properties of blends is studied. Influences of composition of the blends, shear ratio, shear stress and different temperatures on swell ratio and melt apparent viscosity are discussed. Non-Newtonian index (n), melting flow rate (MFR), conventional yield stress, breaking stress and breaking extensibility of the blends with different composition are measured. It is proved that processability of BMDPE and LBPE are apparently improved with LDPE content increasement.3. Different composition of BMDPE/Nano-ZnO, BMDPE/nano-CaCO3 and nano-montmorillonite (MMT) composite materials are made by melt blending way. Melt rheological behavior of blends is studied. Influences of composition of the blends, shear ratio and shear stress on melt viscosity are discussed. Non-Newtonian index (n), melting flow rate (MFR) and mechanical properties of the blends are measured. SEM observes distribution circumstances of nano-particles in blends. As a result, the mechanical properties of BMDPE and LBPE are improved by nano-ZnO, nano-CaCO3 or nano-montmorillonite in different degrees.