Linear Low-Density Polyethylene

Linear low-density polyethylene (LLDPE) is produced in the gas phase under low pressure. Catalysts used are either Ziegler type or new generation metallocenes. The Union Carbide process used to produce

HDPE could be used to produce the two polymer grades. Terminal olefins (C4–C6) are the usual comonomers to effect branching.

Developments in the gas-fluidized-bed polymerization reduced investments for high pressure processes used for LDPE. The new technology lowers capital and operating costs and reduces reactor purge/waste streams. Specific designed nozzles are located within the fluidized bed to disperse the hydrocarbons within the bed. The liquid injected through the nozzles quickly evaporates, hence removing the heat of polymerization.

These processes can produce a wide range of polymers with different melt flow indices (MFI of <0.01 to >100) and densities of 890–970 Kg/m3. Types of reactors and catalysts used for HDPE and LLDPE have been reviewed by Chinh and Power.9 LLDPE has properties between HDPE and LDPE. It has fewer branches, higher density, and higher crystallinity than LDPE.