Study On The Mechanism Of Viscous Encapsulation In Multiphase-multilayer Flow Molding

Multiphase-multilayer flow molding (shortened as MMFM) is the common molding mode of the new advanced polymer multi-component molding techniques. Because of the interaction of stresses on the interfaces between adjacent melts, each one of MMFMs has its special transport rule of flow and dynamic characters, therefore, the MMFM has more rich and more complex content of research than traditional single phase flow molding. Because of viscous encapsulation always existing in multiphase-multilayer flow molding, the influencing rules of polymer melt rheological parameters and process parameters on viscous encapsulation for MMFM were studied by means of numerical simulation in this paper. At the same time, based on theories of rheology and hydrokinetics etc., the mechanism of viscous encapsulation was disclosed. The following main achievements are yielded:1,Based on technique characteristics of MMFM and theories of polymer rheology, hydrokinetics and thermodynamics etc., the full 3D, steady, isothermal viscoelastic theoretical models of describing MMFM process were established by means of reasonable assumption.2,On the basis of the mixed finite element stable discrete techniques of Galerkin method, penalty function method, EVSS, SUPG and Mini-Element method etc., a corresponding stable finite element numerical model with fast convergence was established for high non-linearity 3D viscoelastic theoretical models of MMFM. Finally, with above numerical model systems, direct finite element numerical simulations of viscous encapsulation for MMFM were implemented.3,By means of numerical simulation, the quantitative comparisons of the distributaries of flow field,the difference of flow characters and the interface patterns of viscous encapsulation under various rheological parameters and process parameters are presented. Therefore, the initiation of viscous encapsulation is disclosured by theoretical analysis, and dependence of viscous encapsulation on rheological parameters is studied for the polymer MMFM process.4,The viscous encapsulation for MMFM caused by melt secondary flow, and the degree of viscous encapsulation increases with increasing of the intensity for the melt secondary flow which is proportioned to the jump in the first normal stresses difference across the interface. The necessary condition of viscous encapsulation is that the melt secondary flow in cross section must have two flow centers of vortex.5,The degree of viscous encapsulation for MMFM increases with increasing of the melt relaxes time and flow rate, but decreases with increasing of material coefficientα.