The hottest linear low density polyethylene

2022-08-14
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Linear low density polyethylene (LLDPE

linear low-density polyethylene is structurally different from general low-density polyethylene because there is no long branched chain. The linearity of LLDPE depends on the different production and processing processes of LLDPE and LDPE. LLDPE is usually formed by the copolymerization of ethylene and higher a olefins such as butene, hexene or octene at lower temperature and pressure. The LLDPE polymer produced in the copolymerization process has a narrower molecular weight distribution than general LDPE, and has The linear structure makes it have different rheological properties. The melting flow characteristics of LLDPE can meet the requirements of new processes, especially the film extrusion process, which can produce high-quality LLDPE products. LLDPE is used in all traditional markets of polyethylene. The properties of tensile resistance, penetration resistance, impact resistance and tear resistance are enhanced, making LLDPE suitable for thin films. Its excellent environmental stress cracking resistance, low temperature impact resistance and warpage resistance make LLDPE attractive for pipe, plate extrusion and all molding applications. The latest application of LLDPE is as a mulch film for waste landfill and the lining of waste liquid pool

production and characteristics

lldpe production starts with transition metal catalysts, especially Ziegler or Phillips types. The new process based on cycloolefin metal derivative catalyst is another option for LLDPE production. The actual polymerization reaction can be carried out in solution and gas phase reactors. Usually, octene and ethylene are copolymerized in a solution phase reactor, butene. Hexene and ethylene are polymerized in a gas phase reactor. The LLDPE resin generated in the gas phase reactor is in the form of particles, and can be sold as powder or further processed into particles

a new generation of super LLDPE based on hexene and octene has been developed by Mobier and union carbide. Novacor and Dow plastics. These materials have great toughness limit and have new potential in the application of automatic bag removal

very low density PE resin (density less than 0.910g/cc.) It has also appeared in recent years. Vldpes has flexibility that LLDPE cannot achieve

the properties of resin are generally reflected in melt index and density. The melt index can reflect the average molecular weight of the resin and is mainly controlled by the reaction temperature. The average molecular weight is independent of the molecular weight distribution (MWD). Catalyst selection affects MWD

density is determined by the concentration of comonomer in polyethylene chain. The monomer concentration for copolymerization controls the number of short branches (its length depends on the type of monomer for copolymerization) so as to control the resin density. The higher the monomer concentration for copolymerization, the lower the resin density

in structure, LLDPE is different from LDPE in the number and type of branches. High voltage LDPE has long branches, while linear LDPE only has short branches

in structure, LLDPE is different from HDPE only in the number of short branches. HDPE has fewer short branches, so it is a material with higher density

The physical properties of LLDPE are controlled by its molecular weight, MWD and density

lldpe is superior to LDPE, which ultimately depends on its use. Generally, LLDPE is used to produce products with stronger rigidity in all applications, although the density of LLDPE and LDPE is between 0.91-0.925 according to the ATSM standard for low density materials

lldpe forms a higher crystalline structure because there is no long branched chain. The greater crystallinity of LLDPE produces products with higher rigidity. This higher crystallinity also increases the melting point of LLDPE by 10 ~ 15 ℃ compared with LDPE

higher tensile strength, penetration resistance, tear resistance and increased elongation are the characteristics of LLDPE, which makes it particularly suitable for thin films. If hexene or octene is used as comonomer instead of butene, even the impact resistance and tear resistance can be greatly improved. For a given resin with the same melt index and density, the impact and tear properties of hexene and octene LLDPE resin are improved to 300%. The longer side chains of hexene and octene resins act as "knot" molecules between the chains, improving the toughness of the compounds

using cycloolefin metal derivative catalyst to produce resin will have unique properties. Narrower MWD, improved comonomer distribution, better film transparency, sealing and impact strength, which are similar to LLDPE produced with Ziegler catalyst. In terms of transparency, LLDPE has similar shortcomings with LDPE. The turbidity and gloss of O LLDPE film are poor, mainly because its higher crystallinity leads to the surface roughness of multi attack protective film. The transparency of LLDPE resin can be improved by blending with a small amount of LDPE

processing

ldpe and LLDPE have excellent rheology or melt fluidity. LLDPE has less shear sensitivity because of its narrow molecular weight distribution and short branched chains

in the shearing process (such as extrusion), LLDPE maintains a higher viscosity, so it is more difficult to process than LDPE with the same melt index. In extrusion, the lower shear sensitivity of LLDPE makes the stress relaxation of polymer molecular chain faster, and thus the sensitivity of physical properties to the change of inflation ratio is reduced

in melt elongation, LLDPE usually has low viscosity at various strain rates. That is to say, it will not produce strain hardening during stretching like LDPE. With the increase of the deformation rate of polyethylene, LDPE shows an amazing increase in viscosity, which is caused by molecular chain entanglement

this phenomenon cannot be observed in LLDPE, because the lack of long branched chains in LLDPE makes the polymer not entangled. This property is very important for thin film applications, because LLDPE films are easy to make thinner films while maintaining high strength and toughness. The rheology of nlldpe can be summarized as "rigid in shear" and "soft in extension"

when LLDPE is used to replace LDPE, the film extrusion equipment and conditions must be modified. The high viscosity of LLDPE requires that the extruder is also a material that integrates waterproof and thermal insulation. It has higher power and provides higher melt temperature and pressure

the die gap must be widened to avoid reducing production due to high back pressure and melt fracture. The general die gap dimensions of LDPE and LLDPE are 0.024 ~ 0.040 in. and 0.060 ~ 0.10in respectively

lldpe's "soft when extending" characteristic is a disadvantage in the film blowing process. The blown film bubble of LLDPE is not as stable as that of LDPE

the general single lip wind ring is stable enough for LDPE. The unique membrane bubble of LLDPE requires a more perfect double lip wind ring to stabilize. Cooling the internal bubbles with double lip air ring can increase the stability of the bubbles and improve the film production capacity at high productivity. In addition to better cooling of film bubbles, many film manufacturers use blending with LDPE to enhance LLDPE solubility. In principle, LLDPE extrusion can be completed on existing LDPE film equipment when the concentration of LLDPE in LDPE Blends reaches 50%. When processing 100% LLDPE or LDPE blended materials rich in LLDPE, the general LDPE extruder must be used, and the equipment must be improved

according to the service life of the extruder, the improvement may be to widen the die gap, improve the air ring, modify the screw design to better extrude, and increase the motor power and torque if necessary. For injection molding applications, the equipment generally does not need to be improved, but the processing conditions need to be optimized

rotational molding requires LLDPE to grind into uniform particles (35 mesh). The processing process includes filling the mold with powdered LLDPE, heating and biaxially rotating the mold to make LLDPE evenly distributed. After cooling, the product is removed from the mold

application

lldpe has penetrated into most traditional markets of polyethylene, including film, molding, pipe, wire and cable. Anti leakage film is a newly developed LLDPE market. Mulch film, a large extruded sheet, is used as a landfill and waste pool liner to prevent leakage or pollution of the surrounding area

some film markets of LLDPE, such as production bags, garbage bags, elastic packaging, industrial liners, towel liners and shopping bags, all take advantage of the secondary resin after improving strength and toughness. Transparent films, such as bread bags, have always been dominated by LDPE because of its better turbidity. However, the blend of LLDPE and LDPE will improve the strength. The penetration resistance and the stiffness of LDPE film do not significantly affect the transparency of the film

injection molding and rotational molding are the two largest molding applications of LLDPE. The superior toughness, low temperature and impact strength of this resin are theoretically suitable for waste containers, toys and refrigerators "for work, family, relatives and friends

in addition, LLDPE's high resistance to environmental stress cracking makes it suitable for injection molding molded covers in contact with oil foods, Roto plastic waste containers, fuel tanks and chemical tanks

there is a small market for its application in the coating of pipes, wires and cables, where the high rupture strength and environmental stress cracking resistance provided by LLDPE can meet the requirements. At present, 65% - 70% of LLDPE is used to make films

source: Jinshi Group

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