Is polyethylene wax a by-product or a high-quality polymer additive?

Polyethylene wax in all its variety is available on the market in the form of lumps, flakes, powder and granules. And increasingly, in communication with customers, we hear that wax is a by-product of ethylene polymerization, a waste product. Is this really the case? In what areas is it used? Let's figure it out. So, everything is in order.

Production technologies

There are several technologies for producing polyethylene wax, which leads to global differences in product quality, price and applications.

Polyethylene is produced by polymerization using an ethylene monomer and an added comonomer. Depending on the conditions of the polymerization process at high pressure or polymerization at low pressure, substances of different molecular weights are obtained. At the same time, polyethylene wax, characterized by a molecular weight of less than 10,000 and a carbon chain length of 50 to 700 carbon atoms, occupying an intermediate place between paraffins and branded polyethylene. It is this wax that is considered a by-product of polymerization. Low polymer wax contains residual catalysts, solvent, oligomers, water and other impurities and has a quality that makes it unsuitable and dangerous for most applications. Therefore, the pure by-product of ethylene polymerization is difficult to find on the market. This product requires further conversion, refining, hydrogenation, filtration, deactivation of catalysts and other technological processes. And this is no longer a by-product in its pure form, but a deeply processed high-quality product.

But there are other ways to obtain high-quality polyethylene wax - by thermal degradation of high molecular weight polyethylene, through the Fischer-Tropsch process and other less common methods. 

A well-known fact is that polyethylene wax can be obtained both from primary high-grade polyethylene and from secondary raw materials by thermal degradation. The quality of the raw materials made from a secondary polymer has a decisive influence on a number of wax characteristics and the consistency of its interparty properties. It is impossible to extend the results of the quality assessment of test samples and some batches of products to the products of other batches, they will differ.

As in the case of polyethylene, depending on the process conditions, several types of waxy polymers (such as linear, branched, oxidized, and others) with varying degrees of crystallinity can be obtained. Polyethylene wax can be conditionally attributed to soft (amorphous) or brittle (with a high proportion of the crystalline phase) materials depending on the degree of crystallinity at an equivalent molecular weight.

Such a variety of methods and methods for producing polyethylene wax gives a huge range of physico-chemical properties and applications. Therefore, it is important to test different types, brands and shapes of wax.

A variety of applications of polyethylene wax

One of the applications of polyethylene waxes is to use it as a lubricant in the processing of plastics. Numerous publications and studies in this field illustrate empirically determined relationships between the solubility of technological additives in the polymer and the rheological properties of the processed composition. In simple terms, technological additives soluble in a polymer composition are usually classified as internal lubricants that reduce viscosity and internal friction during processing of the mixture, while insoluble in polymer are external lubricants, the effect of which is fully revealed in reducing friction between polymer and metal walls of equipment in the production of film materials and work in thin the slots of the die tool. That is, the same polyethylene wax, depending on the percentage of input and the polarity of the polymer base being processed, can be an internal and external technological lubricant for the latter.

It is important to note that with an increase in the polarity of polyethylene wax, for example by inoculating oxygen-containing reaction groups in the middle or at the ends of the molecular chain, compatibility with polar polymers will increase, respectively, the functional load during processing on wax will change.

Thus, the physical characteristics of polyethylene wax determine its use as a technological additive for a wide range of plastics, such as PVC, PE, PS, ABS, PET, PA, and influence the behavior of the polymer during processing, consumer properties and competitive features of the product made from it.

• The effect of external lubrication during processing is realized by eliminating adhesion between the metal wall of the processing equipment and the melt flow of the polymer mass, i.e. sliding along the flow direction from the forming hole of the die tool and the flow gradient along its cross section is ensured.

• The effect of internal lubrication is manifested in reducing the viscosity and temperature dependence of the melt, homogenizing the components during processing and improving the dispersion of the filler.

For example, the prevention of melt rupture during leakage in thin crevices can be ensured by the introduction of polyethylene non-oxidized wax as an external lubricant into the PVC composition during processing, while the introduction of oxidized polyethylene wax as an internal lubricant, the so-called plasticization promoter, will ensure optimal, timely plasticization and melt uniformity quality, but will not solve the problem with an unbalanced expiration of it from the shaping tool. It is important that in certain processes, the irrational introduction of additives that affect the described phenomena, among other things, can be critical for the processor.

To achieve a balance of the properties of processing additives, complex combinations of technological additives are often necessary, representing an individual qualitative contribution to the formulation and the processing process as a whole, while the total effect is not always predictable and needs a series of tests.

Of the many applications of polyolefin waxes, an important one is their use as a carrier material or additive in the production of masterbatches, dye concentrates and chalk additives. At the same time, high-quality dispersion of powdery substances prone to agglomeration and sedimentation is realized in high concentrations in a polyethylene carrier wax. The ease of entry and high quality of the dispersed functional components of the masterbatches greatly simplifies the processes at the production site of the plastics processor, which gave rise to the spread of one-pack additives in plastic processing plants.

In addition, introducing polyethylene non-oxidized wax into a non-polar system of substances (for example, paraffins, petroleum waxes, bitumen, and much more) can introduce qualitative changes in the melting and softening temperature, and depending on the temperature properties of the main component system, change it in the desired direction.

Polyolefin waxes can serve as raw materials for the synthesis of oxidized and modified waxes, wax emulsions and other products, the scope of which is so extensive that it makes sense to consider them in another review.

In whatever application polyethylene wax is considered, the criteria of choice for the processor should be the quality level and consistency of its characteristics.