聚丙烯接枝改性及其挤出发泡研究

以有机过氧化物为引发剂,以双螺杆挤出机为反应器,将线型不饱和聚酯(ULP)接枝到聚丙烯(PP)分子链上。通过FTIR、DSC及凝胶含量测试,对MPP的结构和性能进行了研究,表明PP发生了接枝反应;泷变性能和熔体流动速率(MFR)测定表明,接枝反应有效地改善了PP流变性能,用双螺杆挤出机对未接枝和接枝的PP进行了发泡研究,SEM分析表明接枝PP具有更好的发泡效果。     

Total Strain of Newtonian Fluids in a Vane Extruder

The vane extruder, which makes a polymer suffer elongation stress much larger than shearing stress, is an innovational equipment in polymer processing. A physical model and a mathematical model are established to analyze the mixing characteristics in polymer processing, namely, the two important functions of residence time distribution and strain distribution function are obtained. It is shown that the direction of total strain gradient is consistent with the orientation of the material flow. The results show that the vane extruder has an advantage over traditional screw extruders due to it being based on elongational rheology.     

Mechanical,thermal and rheological properties and morphology of poly (lactic acid)/poly (propylene carbonate) blends prepared by vane extruder

In this study, the poly (lactic acid) (PLA) and poly (propylene carbonate) (PPC) blends with different compositions were prepared by a novel vane extruder based on elongation rheology. The mechanical properties, morphologies, crystallization behavior, thermal stability, and rheological properties of the blends were investigated. Mechanical test showed that PLA could be toughened by PPC to some extent, and the impact strength of the PLA was maximized when PPC content was about 30%. Differential scanning calorimetry analysis revealed that PPC had little effect on the melting process, the crystallization behavior of PLA component in the blend was improved, and the cold crystallizability of PLA decreased with the increase of PPC content when the PPC content was less than 50%. Thermogravimetry analysis showed that the thermal stability of the blends was improved by compounding with PLA. Scanning electron microscope showed that the dispersion of PLA droplets in PPC matrix was better than that of PPC droplets in PLA matrix. Rheological test showed that the melt viscosity of the pure PLA and the blend with 10% PPC was insensitive to shear rate, and the blends melt appeared shear thinning phenomenon with the increase of PPC content. It also showed that the blends microstructure changed with the addition of PPC and the blends with PPC content in a certain range had similar stress relaxation mechanism. Copyright © 2016 John Wiley & Sons, Ltd.     

Adaptive non‐conformal mesh refinement and extended finite element method for viscous flow inside complex moving geometries

Two different techniques to analyze non‐Newtonian viscous flow in complex geometries with internal moving parts and narrow gaps are compared. The first technique is a non‐conforming mesh refinement approach based on the fictitious domain method (FDM), and the second one is the extended finite element method (XFEM). The refinement technique uses one fixed reference mesh, and to impose continuity across non‐conforming regions, constraints using Lagrangian multipliers are used. The size of elements locally in the high shear rate regions is reduced to increase accuracy. FDM is shown to have limitations; therefore, XFEM is applied to decouple the fluid from the internal moving rigid bodies. In XFEM, the discontinuous field variables are captured by using virtual degrees of freedom that serve as enrichment and by applying special integration over the intersected elements. The accuracy of the two methods is demonstrated by direct comparison with results of a boundary‐fitted mesh applied to a two‐dimensional cross section of a twin‐screw extruder. Compared with non‐conforming FDM, XFEM shows a considerable improvement in accuracy around the rigid body, especially in the narrow gap regions. Copyright © 2011 John Wiley & Sons, Ltd.     

Ram extrusion force for a frictional plastic material: model prediction and application to cement paste

We developed a model to predict the ram extrusion force of frictional plastic materials such as cement-based pastes. The extrusion of cement-based materials has already been studied, but the interaction between shaping force and paste behaviour still have to be understood. Our model is based on the plastic frictional behaviour of cement-based materials and integrates the physical mechanisms that govern material extrusion flow and extrusion force increase. When the process starts, a pressure gradient is created in the extruder due to wall friction of the paste that is submitted to plug flow. It induces a consolidation of the material. As a result, a large increase of extrusion force appears. A Coulomb law is used to model cement-based materials, which is considered as consolidating granular media. Such modelling is compared with experimental results. Tests were carried out on extrudible cement pastes. Modelling and experimental results are in good agreement.Paper presented at the Annual European Rheology Conference, Grenoble, April 2005     

Well‐posedness and exact controllability of the mass balance equations for an extrusion process

In this paper, we study the well‐posedness and exact controllability of a physical model for an extrusion process in the isothermal case. The model expresses the mass balance in the extruder chamber and consists of a hyperbolic partial differential equation (PDE) and a nonlinear ordinary differential equation (ODE) whose dynamics describes the evolution of a moving interface. By suitable change of coordinates and fixed point arguments, we prove the existence, uniqueness, and regularity of the solution and finally, the exact controllability of the coupled system. Copyright © 2015 John Wiley & Sons, Ltd.     

三维动态混合过程界面追踪模拟与表征

建立了振动力场作用下单螺杆挤出机计量段物理模型,在Stokes假设基础上,得到了螺槽内牛顿流体速度分布的解析解。采用自适应步长4阶Runge-Kutta方法,对动态混合过程进行三维数值模拟追踪,计算了示踪剂构形依时演变及界面拉伸速率,对动态混合过程进行了实时表征。结果表明,低频振动时,螺槽内的混合仍然是规则的层流混合,混合效果有待于进一步提高,指出了进一步提高混合效果的措施。