LLDPE Linear Low Density Polyethylene

LLDPE, with the full name of Linear Low Density Polyethylene, is a molecular structure with very short comonomer branches formed on the main chain of linear ethylene by copolymerization of ethylene and a small amount of α-olefin. It is a low-density polymer with a density between 0.915 ~ 0.930g/cm3 and a certain amount of short-chain branches. LLDPE is non-toxic, tasteless and odorless milky white particles in appearance. 

According to the types of comonomer, linear low density polyethylene is mainly divided into three types of copolymers, C4 (butene-1), C6 (hexene-1) and C8 (octene-1). Among them, butene copolymer is the LLDPE resin with the largest production volume in the world, while hexene copolymer is currently the fastest growting LLDPE granules variety. In LLDPE resin, the typical amount of comonomer is 5% to 10% by weight, and the average amount is about 7%.

1. Flexibility with high impact strength.
2. Good chemical resistance.
3. Good water vapor and alcohol barrier properties.
4. Good stress cracking and impact resistance.
5. It has excellent transparency and heat sealability, and can be widely used in the production of transparent low-temperature frozen packaging products.
6. Excellent moisture resistance. It is a high-quality raw material for making dry food or packaging for items that require good moisture resistance.
7. Linear low-density polyethylene resin has excellent heat-sealing properties. Although the melting temperature of LLDPE is about 5℃ higher than that of LDPE, the heat-sealing properties have good ion-like properties. As long as the heat sealing temperature is higher than the initial heat sealing temperature, high heat sealing strength can be obtained. If LLDPE is used as the heat-sealing material, only a lower heat-sealing temperature can be used to achieve highly reliable heat-sealing strength, which is suitable for high-speed heat-sealing machines.
8. The melt viscosity is quite large. Meanwhile, its melt viscosity is not sensitive to temperature, but very sensitive to processing stress.

Linear low-density polyethylene uses ethylene as the main raw material and a small amount of α-olefins (such as 1-butene-1, 1-octene, etc.) to carry out gas-phase fluidized bed polymerization under the action of a catalyst under high pressure or low pressure. Then the reacted materials are granulated, dried, and sent for packaging.

The production of LLDPE resin starts with transition metal catalysts. A new process based on cycloolefin metal derivative catalysts is another option for LLDPE production. The actual polymerization reaction can be carried out in solution and gas phase reactors. Typically, octene and ethylene are co-polymerized with butene in a solution phase reactor. Hexene is polymerized with ethylene in a gas phase reactor. The LLDPE resin produced in the gas phase reactor is in granular form. Linear low density polyethylene is usually characterized by 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. Catalyst choice affects molecular weight distribution. Density is determined by the concentration of comonomers in the polyethylene chains. The comonomer concentration controls the number of short chain branches and thus the resin density. The comonomer concentration controls the number of short chain branches and thus the resin density.

Low-density polyethylene (LDPE) is a colorless, translucent particle with long chain branches in the molecule, and the molecules are not tightly arranged. Linear low-density polyethylene (LLDPE) generally only has short branched chains in its molecules.

Traditional low-density polyethylene is obtained by using polymerization-grade ethylene with oxygen or peroxide as an initiator to stop free radical polymerization under high temperature and high pressure. Therefore, it is also called high-pressure polyethylene. LDPE is a waxy white resin with a non-linear layout.

The linearity of LLDPE depends on the different production and processing processes of LLDPE and LDPE. LLDPE is usually produced by the copolymerization of ethylene and higher α-olefins such as butene, hexene or octene at lower temperature and pressure. The LLDPE polymer produced by the copolymerization process has a narrower molecular weight distribution than ordinary LDPE.