An Investigation Of The Rheology And Morphology Of Polyethylene Prepared By Vibration-assisted Extrusion

The Polymer Dynamic Shaping Technologies which the physics field acts on the polymer melt directly; have already become one of the effectual new methods to strengthen the shaping course of the polymer processing. At present, investigation on the theory and experiment of the polymer dynamic shaping has already become a hot point in polymer processing engineering, high polymer physics and high polymer chemistry, etc.This work designed a set of hydraulic vibration device. Its frequency is adjustable within the range of 100Hz; the amplitude is adjustable from 0mm to 7mm. Using this vibration source, the high density polyethylene was successfully extruded with vibration-assisted extrusion which the vibration field was applied to the inner of the die. The influence of the frequency and amplitude to the apparent viscosity of HDPE was researched under various conditions during the vibration- assisted extrusion.During the study great changes of the HDPE extrudate were found experimentally by comparing the mechanical properties of HDPE products made by vibration-assisted extrusion with those made through optimized conventional extrusion .At the same time high molecular weight PE was blended to enhance this influence. The resins utilized during the studywere 6100M and DMDY1158. Then the microscopic structures and the morphologies of the products were investigated through modern analysis and test methods. The result of the study shows:1. Mechanical vibration may greatly reduce the apparent viscosity of HDPE when it is extruded . During the research, the biggest reduction of the apparent viscosity was 52.7%. The frequency and amplitude can influence the apparent viscosity. When frequency is low, with the increase of frequency, apparent viscosity drops rapidly, but when frequency increases further, the apparent viscosity goes up on the contrary, but the rise trend is milder. When using larger amplitude, the apparent viscosity reduces more obviously.2. The impact on HDPE' s apparent viscosity of vibration is different under different temperature, shearing rate or crystallization condition. It is greater when having a lower temperature or shearing rate, or having a lower crystallization degree or the crystals having more defects.3. The longitudinal and transverse tensile strength of 6100M products improved 11.9% and 6.9% respectively when made by vibration-assisted extrusion. After adding 4% of the high molecular weight PE DMDY1158 to 6100M, the influence that the vibration brought was much more remarkable. The maximum longitudinal tensile strength improved 27.9%, and the maximum transverse tensile strength improved 32. 9%.4. The DSC analyses result indicates, vibration raised the crystallinity degree of 6100M sample, while the melting point was reduced; to 6100M/1158 system, vibration raised its crystallinity degree greatly, and narrowed the melting dimension, but there was no obvious change with the melting point.5. SEM was used to study the crystal morphology of the samples made by vibration-assisted extrusion. Found that the vibration made the lamellar crystal of the pure 6100M and 6100M/1158 system obviouslyorientated, and the orientation direction kept the same with the vibration direction or had a certain slope.6. The wide angle X ray diffraction test result shows: The micocrystallite size of 6100M sample was diminished, and the perfection degree of the crystal was reduced, but its crystal and molecular chain appeared to be orientated; To the 6100M/1158 sample, vibration made the crystal become more perfect, and also diminished the micocrystallite size, at the same time the orientations of its crystal and molecular chain were obvious. Using WAXD to study the conformational structure, it indicated that the vibration had little impact on the cell parameter of 6100M or 6100M/1158.