Lubricants are added to the polymer for two reasons: internal lubrication and external lubrication. External lubrication reduces friction between the polymer and process equipment such as die. For example, lubricants eliminate melt fracture by reducing the stress applied to the melt that passes through the die. In addition, the seepage and accumulation of material at the die edge is reduced by these lubricants. Internal lubricants significantly reduce the friction between molecules during melt flow and viscosity. The use of these lubricants also reduces the power consumption required to process some polymers that are difficult to process. Common lubricants include stearic acid metal salts and paraffins
