Study on the Rheological Behavior for Polymer Melts and Concentrated Solutions The Molecular Theory of Visco-elasticity for Recoverable Strain and Swelling Ratio of Homo-polymers Melts Extrudate

Based on the structural model of multiple entangled transient networks and the mechanism of multiple reptation by dynamic reorganization of entanglements，the probability distribution function of the end - to - end vector for entangled constituent chain，the conformation probability distribution function of entangled polymer chain，the visco - elastic free energy of deformation of polymeric melts under stress， and the recoverable visco - elastic free energy of deformation of extrudates without stress were calculated by the combined method of statistical mechanics and kinetics. A new molecular theory of visco - elasticity of recoverable strain for extrudates of polymers was proposed. The memory function and elastic modulus were derived from the molecular theory of visco - elasticity of recoverable strain for extrudates of polymers. When the memory function is introduced into the O - W - F type of constitutive equation with the Cauchy - Green and Finger tensors for simple strain shear fluid，then the dependence of viscosity and first normal - stress difference coefficient on shear rate was formulated. A new method for determining the visco- elastic parameters（η0，GN and ψ10）and the topologically constrained dimension numbers（ n' and a）was used to study on the relations of recoverable strains to the conditions of extrusion. It is well known that the total strain consists of elastic and visco - elastic strains，when the unified structure parameter of the fraction of trans - isomer conformation of polymer chains under elastic and viscoelastic strain state is introduced into above expressions of free energy of deformation. A new relationship between the recoverable strain and the swelling ratio for extrudates is obtained and a new equation of swelling ratio for extrudates was derived. At the same time，based on the material function a set of new relationships between the recoverable strain（ SR）with the condition of extrusion［temperature，rate of extrusion，extrusion die and length to diameter ratio（ L / D）］and the primary structure of resins was developed. These equations were verified by a great amount of experimental data. It shows that they are an excellent agreement between theese theoretical equations and experimental data.