Xue-Ping Gu

Crystallization behavior of functional polypropylene grafted graphene oxide nanocomposite

With an aim to understand the role of polymer grafted graphene oxide (GO) in crystallization processes, a functional polypropylene (PP) grafted GO nanocomposite, prepared by isocyanate group-contained polypropylene (PP-g-TMI) reacting with hydroxyl and carboxyl groups on GO, was investigated in terms of isothermal and non-isothermal crystallization by differential scanning calorimetry. Comparing with the PP-g-TMI/natural graphite (NG) nanocomposite, a fully exfoliated and uniformly dispersed GO in the PP-g-TMI matrix for the PP-g-TMI/GO nanocomposite was affirmed by transmission electron microscopy and a large enhancement of its storage modulus. For isothermal crystallization at 140 °C, the addition of GO into PP-g-TMI accelerates the crystallization rate dramatically more than that of NG, indicating the grafted GO can act as a very efficient heterogeneous nucleation agent to increase nucleation dramatically. However, for isothermal crystallization at 126 °C, the crystallization rate of PP-g-TMI accelerated by grafted GO is inferior to that by NG, which can deduce that the grafted GO can restrict migration and diffusion of polymer molecular chains to the surface of the nucleus for spherulitic growth due to strong covalent binding with PP-g-TMI, the formed highly viscous and dense GO layers. These two converse effects of the grafted GO on crystallization can also explain the interesting non-isothermal crystallization behavior that the grafted GO increases the crystallization rate of PP-g-TMI at a low cooling rate, while it decreases the crystallization rate at a high cooling rate.

Computational fluid dynamics simulation of hydrodynamics in an uncovered unbaffled tank agitated by pitched blade turbines

Computational fluid dynamics (CFD) simulations were applied for evaluating the hydrodynamics characteristics in an uncovered unbaffled tank agitated by pitched blade turbines. A volume of fluid (VOF) method along with a Reynolds stress model (RSM) was used to capture the gas-liquid interface and the turbulence flow in the tank. The reliability and accuracy of the simulations are verified. The simulation results show that the vortex can be divided into central zone and peripheral zone, and flow field in the tank can be divided into forced vortex flow region and free vortex flow region. With the increase of impeller speed, the vortex becomes deeper, while the critical radius of the two zones keeps almost unchanged. The impeller clearance and the rotational direction have little effect on the vortex shape. The vortex becomes deeper with increasing of the impeller diameter or the blade angles at the same rotational speed. Power number is little influenced by the impeller speed, and decreases by about 30% when impeller diameter varies from 0.25T to 0.5T. When blade angle varies from 30° to 90°, power number increases by about 2.32-times. Power number in uncovered unbaffled tank is much smaller than that in baffled tank, but is very close to that in a covered unbaffled tank. The discrepancy of power number in uncovered unbaffled tank and that in covered unbaffled tank is less than 10%.

Integration of CFD and polymerization for an industrial scale cis-polybutadiene reactor

ABSTRACT A computational fluid dynamics (CFD) approach, coupled with anionic polymerization kinetics, was used to investigate the solution polymerization in a 12 m3 industrial scale cis-polybutadiene reactor. The kinetic model with double catalytic active sites was integrated with CFD by a user-defined function. The coupled model was successfully validated by the plant data and then used to investigate the key operating variables. Also, predictions of CFD model were compared with those of continuous stirred tank reactor (CSTR) model. Although the reaction mixture is well mixed in the middle and at the top of the reactor, there exists a poor mixing feeding zone at the bottom, which leads to serious deviations from the ideal CSTR. The polymerization process with nonideal mixing is very sensitive to the inlet temperature and the feeding rate. Enhancing the mixing performance in the feeding zone could be an effective way to improve the product quality.

Steady-state optimization of an industrial high-density polyethylene slurry process based on an equation-oriented molecular weight distribution model

Abstract High-density polyethylene (HDPE) has been widely used as the main material in the film, pipe, and container industries. An equation-oriented molecular weight distribution (MWD) model is developed for an industrial HDPE slurry process using the method of moments and Flory`s distribution. The Kriging method is used to establish a surrogate model for the thermodynamic properties. A completely simultaneous approach is proposed to optimize the steady-state process and achieve products with expected MWDs. Two HDPE grades with different MWDs are discussed.