Linear low density polyethylene
LLDPE aggregation methods mainly include low pressure gas phase method, liquid phase method and pressure method. Low pressure gas phase process short answer, mature. Short process flow, less energy consumption, equipment cover an area of an area small, the commonly used method is the production of LLDPE. In terms of molecular chain structure, LLDPE and HDPE are similar, with linear structure, but LLDPE molecular chains with a variety of short branched chain branching. Compared with LDPE, LLDPE is larger, the relative molecular mass of the distribution is relatively narrow. Macromolecular chain short branched chain, almost no long branches chain. These structural differences make LLDPE showed with LDPE different physical properties.
LLDPE melt viscosity is higher, if the LDPE is used to the mouth of the same mold, and make the pressure inside the head, the melt under high shear stress, the thin film surface is rough, even produce melt fracture phenomenon. At the same time, the high head pressure can also make production under certain influence. On body mold the easiest and most effective method is to widen the mouth mould clearance. Than LDPE LLDPE stretch viscosity and melt strength, easy to deformation after the melt extrusion die mold, sensitive to air, resulting in the bubble tube is not stable.
than LDPE LLDPE has higher tensile strength, tear strength, impact strength and rigidity and good resistance to environmental stress cracking resistance. At the same time, LLDPE crystallinity than LDPE, high melting point 10 - higher than LDPE 15 ℃ and heat in LDPE. In terms of processing performance, shear viscosity of LLDPE melt is larger, the sensitivity of viscosity to shear rate is a bit poor. LLDPE melt extension performance is good, but low melt strength, easy to produce tensile thinning phenomenon; LLDPE high melting point, forming temperature is higher than that of LDPE.
LLDPE extrusion products is given priority to with blown film. Compared with LDPE film, LLDPE film with high intensity, good toughness and high tear strength, durable sex good, heat resistant and cold resistant performance is superior, is widely used for packaging bags, frozen bags, cooking bags, shopping bags, garbage bags, industrial packaging and agricultural film. Compared with similar MFR of LDPE, LLDPE its melt viscosity less dependent on the shear rate, using general LLDPE film of LDPE blown film equipment production output it will be lower and the screw torque increases. Therefore, dealing with LDPE film production equipment of screw, cylinder structure is improved, make its can not only adapt to the rheological property of LLDPE, but more than the increase in power consumption.
LLDPE from the late 1970 s since industrial production development is rapid, PE new varieties, after the LDPE and HDPE was regarded as the third generation of PE. It is in the presence of organic metal catalysts, by anionic polymerization or radical polymerization, ethylene and a minus Olefin copolymerization and made of macromolecular main chain copolymerization monomer with short branched chain structure. Used for copolymerization monomer a minus Propylene, 1 - 1 - butylene, Has ene, 1 - Octene, commonly used is 1 Butene comonomer content is around 8%.
in LLDPE film production should be to improve the design of the wind ring, set up along the bubble surface flow tube laminar flow, reduce the impact of gas on the tube to keep the stability of the bubble tube. LLDPE film haze and glossiness are poor, the reason is that higher crystallinity made the film surface is rough. LLDPE with a small amount of LDPE blend can improve the transparency of LLDPE resin. Relative to LDPE, LLDPE injection molding processing plant products with high tensile strength and impact strength, hardness and rigidity, heat resistance and good environmental stress cracking performance, and vertical and horizontal contraction is not easy to warp, etc.
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