Polypropylene waxes are relatively low molecular weight polymers of proylene, produced via the polymerization of propene. This can be done using a Ziegler-Natta catalyst via the slurry, bulk or gas phase process, or by using a Metallocene catalyst which can also been done via these three processes.
Polypropylene can exsist in three basic chain structures dependent on the position of the methyl groups. Isotactic polypropylene has all the methyl groups oriented to the same side of the polymer backbone, where in syndiotactic PP the methyl groups have regular alternate positions along the chain. The third structure is called atactic where the methyl group positions are placed randomly along the chain. Perfectly isotactic polypropylene is highly chrystalline and has the highest melting point where atactic polypropylene is amorphous and has much lower melting points. Commercial polypropylene is a predominantly isotactic polymer containing 1-5% by mass of atactic material.
Propene can be co-polymerised with monomers like ethene or hexene. The simplest are random co-polymers but block co-polymers are produced as well.
Final properties like molecular weight, tacticity and crystallinity and therefore hardness, flexibility, melt viscosity and melting point differ with polymer design (tacticity and type of copolymer).
PP waxes can be functionalized through grafting with Maleic Anhydride (MAH). This is done to be able to “connect” dissimilar materials and to make these waxes emulsifyable.
The molecular weight (Mn) of PP waxes can vary roughly between 5000 and 30.000 with melting points starting at 90°C and going up to 160°C.
Grafting levels in these waxes range from 0,2% to 3% depending on the molecular weight of the polypropylene. The optimum grafting ratio is 1:1 which means that no molecule is left ungrafted and that no molecule gets multigrafted. Free MAH levels should be kept to an absolute minium because they cause an unacceptable odor, fogging, decolorisation and poor UV resistance.
Non-functionalised PP waxes are used in the following applications:
- Printing inks
Functionalised PP waxes are used in the following applications:
- Water based emulsions
- Glass fibre sizing