Study On Morphological Structure And Properties Of High-Performance Polyolefin Sheets Extruded In Complex Stress Fields

Polyolefme is a general plastics. But because of their low strength and modulus, it is difficult for structure material to use. hi order to meet the engineering needs of high strength and high modulus, more people are concerned of the self-reinforcement technology to make use of the self-latent ability.Until now, many people made research on the self-reinforcement technology to obtain high performance Polyolefine material. But among those researches on crystal in stress field, most were concentrated in morphology in simple stress field. The results showed that the properties were improved along the direction parallel to stress field, but properties decreased along the vertical direction of stress field. Those caused isotropical products.In order to decrease the isotropy of the products and improve the properties along all directions simultaneously, we made use of the die with complex stress field and succeeded in producing biaxially self-reinforced sheets. The research on Polyolefin crystal morphology in complex stress field has not been reported. This paper made detailed research on the change of Polyolefine crystallographic structure, melt behavior and morphology structure in complex stress field.m-LLDPE is a new material which developed in recently years. Because it has unique features, for example, single activated center, narrow molecular weight distribution, short chain, uniform chain distribution, low density, high transparency, and so on, many people are interested in its research. The research on crystal behavior of m-LLDPE in complex field has not been reported. The paper also maderesearch on change of double melting peak m-LLDPE crystallographic structure, melt behavior and morphology structure in complex stress field.We also made research on the fluence of different processing conditions on the structures and properties. These offered the basic data for its industrial application. The main work and conclusions were listed as following:1) Longitudinal direction stretch strength of HDPE self-reinforced sheets had been increased 6 times to 170MPa, and transverse stretch strength had been improved 63% to 44MPa. This all showed that longitudinal and transverse direction properties had been improved.2) Longitudinal yield strength of m-LLDPE sheets had been increased 5 times to 45.7Mpa, and transverse yield strength had been improved 51% to 14.7Mpa. Sheets show the phenomenon of strain stiffening.3) Vica soft points of HDPE self-reinforced sheets had been improved max to 37℃. This increased the heat-resistance.4) Melting peak of HDPE self-reinforced sheets drifted to high temperature, which showed wafer thickened. Melting distance decreased, which showed crystal sizes were homogeneous. Crystallinity increased. However micorlite sizes decreased.5) We made analysis and token on the sheets extruded at solid state in complex stress field. The results showed that the reason of improvement of properties of extruded sheets lied in the sheets with microfiber structure morphology.6) First, We also made research on crystallographic structure, melt behavior and morphology structure of sheets extruded at critical temperature state. Extruded sheets had better synthetical properties.7) There exist a great deal of shish-kebab morphology structure for HDPE material in sheets extruded at critical temperature state. But for m-LLDPE, there existed blend crystals of shish-kebab and folded chain lamellae.8) Strength of HDPE and m-LLDPE general sheets extruded at melt temperature state are lower, but tenacities are better. The testing results showed that there existed a great quantity of sperulites, but the sperulite size of m-LLDPE sheets were bigger than those of HDPE sheets.9) The results showed that with the increase of extruded temperature, strength and the degree of orientation decreased. But for crystallographic structure, unit cell parameters did not change and microlite size increased. Breaking elongation increased and modulus did not chan...