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Metallocene polyethylene

by:CSSSLD     2021-01-23
PE molecules by radiation and chemical methods, can form a mesh or described. properties of body structure. Described. properties of thermosetting material, the heat won't melt. Compared with ordinary injection molding processing PE, its mechanical strength, heat resistance, environmental stress cracking resistance, such as increased significantly, so as to expand the use of PE. PE into described. properties methods have radiation crosslinking, peroxide crosslinking method and silane crosslinking method.

due to the characteristics of metallocene catalyst and monomer, reactor, the role of the polymerization medium and other factors, makes the molecular structure of metallocene polyethylene has the following characteristics: relatively narrow molecular weight distribution, dispersion coefficient of 0. 2 - 2. 5, on the macromolecular main chain copolymerization monomer into uniform distribution, composition and structure of macromolecules is very uniform. From the point of view of form, metallocene polyethylene and LLDPE are similar, are ethylene with a - Olefin copolymer, but structural differences make the metallocene polyethylene with a series of unique performance.

because of reasons of cost and processing, the metallocene polyethylene often add a certain amount of LDPE or HDPE blending modification. At the same time, also can use metallocene polyethylene modified PE, such as adding a certain amount of metallocene polyethylene in LDPE blend, improves LDPE greenhouse film impact resistance, resistance to puncture strength, transparency is also improved. Of metallocene polyethylene industrialization production, only more than ten years since the time is in the stage of development and improvement, with the progress of metallocene catalytic polymerization technology and mature, the performance of metallocene polyethylene, variety and the cost will be further optimized, also will be more widely applied.

same density, the regularity of the molecular structure of metallocene polyethylene high, with a higher degree of crystallinity, the formation of crystal size uniform, has the high impact strength and puncture strength, excellent low temperature toughness. Compared with PE, although the metallocene polyethylene high crystallinity, but as a result of uniform chemical composition and structure, the formation of spherulite size and uniformity is good, has better transparency. The film made of fog degree is low, high resolution.

as a result of metallocene polyethylene crystal has the characteristics of small and uniform, and compared with the same density of ordinary PE, its melting point is lower, the initial heat sealing temperature is low, high heat sealing strength. With short branched chain of metallocene polyethylene narrow molecular weight distribution, melt to the sensitivity of the shear rate drop, melt viscosity is higher under the same shear rate, processing performance is poor. In general LLDPE and LDPE production line processing of metallocene polyethylene will encounter equipment higher torque, current increase, easy to melt fracture problems.

metallocene catalyst appeared in the 1950 s, but it was not until the mid - 80 - a breakthrough in the development and application. Metallocene catalyst is composed of metallocene compound and catalyst promoter of catalytic system, metallocene compounds is the main body. Characteristics of metallocene catalyst in only one polymerization activity, that is only one active center, polymerization is only allowed when the polymer monomer into the activity of catalyst, thus can accurately control the relative molecular mass and its distribution, comonomer content and distribution in the main chain of the molecule, and crystalline structure, etc.

in order to improve the processing properties of metallocene polyethylene, a kind of method is of long chain branched, or produce bimodal resins, namely the relative molecular mass distribution of the peak of more than 1, toughness and machinability of balance; Another way is to join processing AIDS, such as adding fluorine elastomer processing AIDS, amides lubricant to reduce the melt viscosity, increase liquidity. As a result of metallocene polyethylene in PE in the family has a unique performance, the application almost penetrate ordinary each injection molding processing and application field of PE, which is given priority to with all kinds of thin film.

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