Study On The Properties And Morphological Structure Of The Polyolefin Sheets Solid-State Extruded In Complex Stress Field

Biaxial self-reinforced high density and metallocene linear low density polyethylene sheets were prepared by the die with complex stress field designed by us in solid state. Detailed research was made on the solid-state extrusion behavior, mechanical properties, crystallization behavior and morphology of these two kinds of polyolefines, the affects of the extrusion temperature and deformation ratio on the sheet were also studied. The main work and conclusions were listed as following:1) Longitudinal tensile strength of the HDPE6098 self-reinforced sheet was increased to 173.9 Mpa by 5 times, and the maximum transverse tensile strength was 51.3 Mpa, improved by 90%. The strength in the two directions was increased markedly.2) The metallocene linear low density polyethylene could be extruded accomplished, the longitudinal yield strength and the transverse yield strength were increased markedly, which there are 5-fold increase in the extrusion directionand the 57% increase in transverse direction, while the tensile strength has littleimprovement. The longitudinal yield strength increased with the draw ratio. The Young's modulus increased slowly with the temperature. The extrusion temperature has little effect on the samples tensile strength.3) SEM, DSC, WAXD tests were made on the solid-state extrusion sheet, the results showed that the typical oriented microfibril structure was formed in HDPE6098 and SP1520 sheets, and the obvious lateral Interfibrillar connection structure was not founded. The oriented microfibril endowed the great strength increase in the extrusion direction, while to the improvement in the transverse, we thought it was the result of the orientation of the amorphous chains in the transverse elongational flow field. As to the high temperature extrusion sheet of the HDPE6098, we presumed that there existed shish-kebab structure in the skin. The particular molecular structure, molecular weight distribution of the metallocene polyethylene affected the crystallization behavior, chains orientation and morphology, which differed clear with the HDPE.4) The surface quality and die swell were affected by the extrusion temperature and deformation ratio. With the decrease of the temperature, the sheets become transparent and smooth with few surface defectives. The die swell in the thickness of the SP1520 was higher than that of the HDPE6098, which was related to the high amorphous content in the former.