Stuty On Elongational Deformation Effects Of The Melt Conveying In An Eccentric Rotor Extruder

Eccentric rotor extruder?ERE?based on volume pulsation is a novel polymer processing device.The extrusion system of a uniaxial ERE can be divided into straight section,uniform pitch helical section and non-uniform pitch helical section according to the size and variation of pitch.The traditional melt conveying theory is usually based on shear flow which neglects the effects of elongation deformation.The structure of the ERE extrusion system is complex and the working mechanism of ERE is different from that of screw extruders.Although many studies have shown that the performance of the uniaxial ERE is superior to that of other screw extruders,the elongation deformation mechanism of the flow field in the uniaxial ERE has not been reported.In this paper,the kinematics mechanisms of the straight section,the uniform pitch helical section and the non-uniform pitch helical section of the ERE are studied.It is found that the resultant motion of the eccentric rotation and reverse revolution at the same speed of the rotor can be equivalent to a motion that arbitrary section rotates around its own center of the corresponding section and reciprocating pulsates in the corresponding cavity of the stator.The basic governing equations of the melt conveying in the uniaxial ERE is established by modifying Newtonian melt constitutive equations through using Trouton viscosity.The elongation deformation is considered in the governing equations in the first time.The elongation deformation effect on the melt of the straight section was studied by a numerical method based on the method of separation of variables and non-slipping hypothesis.An approximate analytical method is also proposed.The straight section has the maximum elongation deformation index??_m?.?_m increases at smaller ratio of the length to the eccentricity of the straight part.Rotational speed and viscosity have great effects on pressure.The ERE was used to prepare polypropylene?PP?/3wt%titanium dioxide?TiO₂?nanocomposites.The effects of rotational speed on the TiO₂ aggregates size was studied and the experimental results were compared with theoretical results.The flow fields of the modified Newtonian fluid in the uniform and the non-uniform helical section of a uniaxial ERE were studied by a numerical method based on least-squares generalized inverse and an approximate analytical method.The elongation deformation index?_m of the melt in the uniform helical section increases first and then decreases with the increase of the stator pitch.The order of the pitches has no effects on?_m of the non-uniform pitch helical section.The incremental length of the stator pitch causes?_m decreases,and the rise of pressure.The pressure of both the uniform and the non-uniform pitch helical section increase with the increase of rotational speed and material viscosity.The low density polyethylene?LDPE?/polylactic acid?PLA?were prepared by the ERE to verify the theoretical result.Results show that numerical method and approximate analytical solutions are consistent.The elongation deformation plays a leading role in the melt conveying process of the ERE,and the elongation deformation effect of the straight section is the strongest.The uniform pitch helical section has a positive displacement characteristic,and the non-uniform pitch helical section is stronger than that of the uniform pitch helical section.The experimental results show that the aggregate sizes of TiO₂ nanoparticles in PP matrix decrease with the increase of the rotor speed,and the resultant aggregate sizes are consistent with theoretical results.The polylactic acid?PLA?phase forms fibers in the low density polyethylene?LDPE?/PLA blends extruded by ERE,which is consistent with the elongation deformation analysis in the non-uniform pitch helical section of the ERE.The crystallinity of PLA,tensile strength and bending properties of LDPE/PLA blends have been improved due to the formation of PLA fibers.