Low-density polyethylene (LDPE) was filled with blends of different proportions of two sizes of calcium carbonate (CaCO 3 ; 600 and 2500 mesh). The torque of the LDPE/CaCO 3 samples was measured with a torque rheometer. The results showed that the process torque values of the LDPE/CaCO 3 samples obviously decreased when LDPE was filled with a blend of two sizes of CaCO 3 (600-and 2500-mesh CaCO 3 blend) in comparison with samples filled with CaCO 3 of a single size (600 or 2500 mesh). When the ratio of 600-mesh CaCO 3 to the total CaCO 3 was in the range of 40-60 wt %, the lowest torque value of the LDPE/CaCO 3 samples was achieved. When the content of CaCO 3 in a sample was 30 wt %, LDPE filled with CaCO 3 of different size distributions showed the largest decrease in the torque ratio in comparison with the samples filled with CaCO 3 of a single size. The torques of LDPE samples filled with CaCO 3 of a single size and those filled with CaCO 3 of different size distributions at different temperatures were also studied. The results showed that the flow activation energy and flow activation entropy of LDPE samples filled with CaCO 3 of different size distributions increased obviously. The increase in the flow activation entropy was used to explain the phenomenon of the process torque decreasing for LDPE samples filled with CaCO 3 of different size distributions.
A new kind of polypropylene (PP)/CaCO 3 composites was prepared on a twin screw extruder with the nanoparticle content of 5 wt % and the 2500 mesh microparticle content of 15 wt %. The mechanical property of four different samples [pure PP (1), PP filled with 15 wt % microCaCO 3 particle composites (2), PP filled with 5 wt % nanoCaCO 3 particle composites (3) and PP filled with micro/nano-CaCO 3 complex size particle composites (4)] was investigated through tensile tests, notched Izod impact tests and SEM. The results indicated that the sample 4 had the best mechanical property. The proofs of SEM showed that the high impact energy could lead to debonding and creating microcavitation between the nanoparticle and polymer interface if the polymer was filled with the nanoparticles. This process could absorb a lot of mechanical failure energy, but too much mechanical failure energy would lead to the enlargement of microcavitation and the destruction of the composites in sample 3. In sample 4, the microparticle could be used to prevent the enlargement of microcavitation in the matrix polymer under the higher impact failure energy. In this article, the model of the impacting failure process of micro/nanoCaCO 3 /PP composites was established.
The thermoplastic filled with the different size distribution fillers was a new method for improving processability of thermoplastic composites. In our former study, we found that the melt torque of low-density polyethylene (LDPE) composites, which were filled with 30 wt % the effective size distribution CaCO 3 , evidently decreased. In this article, two sizes of CaCO 3 , 600 meshes and 2500 meshes, were blended by different proportions and were filled into LDPE matrix with 30 wt %. Crystal process, isothermal crystallization kinetics, and nonisothermal crystallization kinetics of a series of composites were characterized by differential scanning calorimeter (DSC). The results showed that composites filled with the effective size distribution CaCO 3 leaded to the lower melting and crystallization temperature, the more wide crystallization temperature area, while their the crystallization rate constant (k) of isothermal crystallization kinetics decreased and their Avrami exponents (n) and crystallization halflife (t 1/2 ) of isothermal crystallization kinetics increased compared with those of the composites filled with the single size CaCO 3 . Nonisothermal crystallization kinetics had the similar results.
Two kinds of different size calcium carbonates are blended and filled into polypropylene in 30 wt%. The melting viscosity of PP composites samples is measured by capillary extrusion rheometer at 2308C. The results show that the melt viscosity of PP composites evidently decreased when that was filled with the blending 325 and 1,500 mesh CaCO 3 and the 1,500 mesh proportion in fillers was from 20 to 60 wt%. The viscosity in the low shear velocity decreased more than that in the high shear velocity. The shear viscosity of single filler and filler samples with the size distribution at the different temperature was studied by capillary extrusion rheometer. The results show that the flow activation energy and the flow activation entropy of composites filled with the size distribution filler increased. The change of the flow activation entropy and the model of the efficient arrangement of the structure are used to explain the phenomenon in melting viscosity decrease of PP filled with the size distribution fillers. A structural model of composites that filled with the size distribution fillers was set up. OLYM.
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