Polyethylene waxes are basically low molecular weight polymers of ethylene, produced via the polymerization of Ethylene. This can be high pressure or catalytic polymerization (Ziegler-Natta, Metallocene) . Final properties like molecular weight, branching and crystallinity and therefore hardness, flexibility, melt viscosity and melting point differ per production method.
A completely different production method for producing PE waxes is by thermal degradation of Polyethylene polymers. This results a well defined molecular weight distribution and therefore improved rheological properties. This method also allows for the recycling of Polyethylene polymers into waxes.
PE waxes can be functionalized through oxidation, maleic grafting or copolymerization, of which oxidation is by far the must used method. The reason for the controlled oxidation of PE waxes is to build in polar functionality in order to make them easier to emulsify. Maleic grafting and copolymerization with polar functional groups (Acrylic acid or Acetate) is mainly done to increase the adhesion on polar substrates like glass, metal or paper.
The molecular weight (Mn) of PE waxes can vary roughly between 300 and 10.000 with melting points starting at 90°C and going up to 140°C. Melt viscosities can also differ to a great extent starting from very low (<40 mPa.s) up to very high (around 90.000 mPas.).
Oxidized waxes have acid numbers starting at 14 going up to 30 and generally slightly lower melting points and melt viscosities due to the partial breakdown of the PE backbone during the oxidation process.
Non-oxidized PE waxes are water white, where oxidized PE waxes can be slightly off-white to light yellow.
The density of Polyethylene waxes can be controlled like this is done with high molecular weight polymers. LDPE waxes have densities ranging from 0.92 to 0.94 whereas HDPE waxes range from 0.95 to 0.98. HDPE waxes have higher melting points and melt viscosities than LDPE waxes.
Oxidized PE waxes are mainly used in water and solvent based emulsions and dispersions. For applications of wax emulsions please follow this link.
Non-oxidized PE waxes are used in the following applications:
- Hotmelt adhesives
- Cable industry
The best known producers of Polyethyele waxes are Honeywell (AC wax), Clariant (Licowax) and BASF (Luwax).