Oxidized polyethylene wax, used as an internal lubricant in PVC production.
The Role of Internal and External Lubrication in PVC Processing
In the polymer industry, PVC compounds are presented in a fairly large assortment. These are insulating cable compounds, pipe compositions, hoses and profiles, siding and panels, etc. Almost all PVC compounds are produced using polyethylene wax. Oxidized polyethylene wax is used as an internal lubricant as it combines well with the PVC matrix. Non-oxidized polyethylene wax is used as external lubricant. Its main purpose is to reduce shear loads during extrusion both on the outer layer and inside the composite.
Internal lubricants (oxidized PE wax)
Mostly oxidized polyethylene waxes are used as internal PVC lubricants. Internal PVC lubricants perform the function of heating the polymer mass, if the polymer mass is difficult to melt, for example, if there are problems with equipment (wear of the screw pair, increased gaps, etc.), then the effect of non-melting often appears. PVC processors use the term "heat up the system". This is achieved by introducing internal lubrication. Being a polar lubricant, it is fully compatible with PVC, increases the pressure on the screw and thus heats up the mass. In addition to heating the mass, the internal lubrication significantly reduces the kneading time. For example 0.5% INNOWAX 272 shortens the kneading time to 38 seconds,
Some manufacturers use stearic acid as an internal lubricant based on economic considerations. However, it should be noted that stearic acid can only act as a grease (shortening the plasticization time) and has no effect on the temperature state of the system (due to its low molecular weight structure). That is, it will not be able to eliminate either local underheating or partial melting. Stearic acid is not able to "warm up the system"
Comparative plastogram of PVC compositions on INNOWAX 272 and Viscowax 272 waxes
Influence of external and internal lubrication on the processing parameters of
rigid PVC
Parameter |
Internal lubrication |
External lubrication |
Reducing PVC adhesion to metal surfaces of equipment |
Does not affect |
Strongly affects |
Internal friction
|
declines
|
insignificantly |
Plasticizing time
|
shrinks
|
does not affect |
Bending effect
|
decreases
|
decreases |
Transparency
|
does not affect
|
Matte / glossy shade |
Surface gloss
|
improves
|
improves significantly |
Printability, adhesion, weldability
|
does not affect
|
Slightly affected |
Pigment distribution
|
improves
|
does not affect |
Melt viscosity
|
decreases
|
insignificantly |
|
IE Zakharova Elizaveta Nikolaevna is a contractor of Innovative Chemical Technologies LLC (the largest manufacturer of polyethylene waxes in Russia).
The method for producing polyethylene wax consists in thermal cleavage of high molecular weight polymers and ethylene copolymers in a hydrocarbon solvent medium.
The goal of the company is: export of polyethylene waxes from Russian manufacturers.