Plastics Polymer additives as key components

Processors of plastics and compounds know the limits of the application spectrum of their materials and processes and rely on established processes and many years of experience. Polymer additives can now shift these limitations.

When one thinks of the multitude of additives and processing aids used for different applications in plastic processing, it is easy to lose track. Stabilizers, plasticizers, fillers, flame retardants, pigments, etc., generally have one thing in common: They differ molecularly, physically and often also in their state of aggregation significantly from the plastic to which they are added. Only under these technological compromises is it usually possible to give the final product the desired properties using the additives.

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But what if, in the future, processing aids are similar to or "chemically identical" to the target polymer and still bring about the desired changes in properties? This idea has been pursued by Polytives GmbH from Rudolstadt in Thuringia. They have developed polymeric additives and have been marketing them since 2020. The multi-award-winning young company is playing a pioneering role with its bFI (Flow Improver) product family in making polymeric additives available for every type of plastic and user. The team from Thuringia refers to themselves as polymer architects, who, with their additive toolbox, have solutions ready for plastic raw material producers, plastic recyclers, masterbatchers, plastic processors and recyclers, as well as compounders. In individual cases, these solutions can also be individually adapted.

Compatible with petrochemical or biologically based plastics

The auxiliary substances of the polymeric additives used are themselves polymers. This way, their chemical, physical, and macroscopic behavior approaches that of the target polymer. These additives only differ in the structure of their internal architecture, the so-called molecular architecture, from the target plastic. What's more, the use of such additives greatly expands their application possibilities. They are compatible with most known plastics based on petrochemicals or biological materials—whether it's new material or quality from post-industrial or post-consumer cycles.

Altered molecular architecture provides additive effects

The polymer additives can be added to most types of plastic and polymer systems, both pure and in blends, without any problems and in a way that is customary in the industry. The additives can be used universally: they show high compatibility in resin and thermoset applications.

In summary: A plastic is treated with a plastic additive. The additive has a modified structure, which ensures that it behaves similarly to the target plastic chemically, physically and macroscopically, but can specifically influence desired process and/or product properties to a considerable extent. The simple secret of the additive effects is the already mentioned, altered molecular architecture.

Polymer additives increase performance

Various studies have shown that adding polymeric additives results in significantly lower melt viscosities. This improved flow behavior: the Melt-Flow-Index (MFI or MVR) has more than doubled in some cases. Thus, polymeric additives can be used for bulk materials with different viscosity profiles. These can be subjected to rheological homogenization without affecting the other material properties. Extrusion goods can be upgraded to injection molding goods. This activates recyclates qualitatively for the injection molding market, which has so far been largely closed to them, without their generally lower rheological quality resulting in a loss of attractiveness.

Better implementation of filigree injection molding components

The reduced viscosity also scores points in another part of the processing process: Delicate injection molded components can be better realized, as the shaping is facilitated by better mold filling. The additive integrates evenly into the polymer matrix within the molding compound. This effect stems from the chemically very large similarity and the associated relationship between the additive and the material. The base polymer thus possesses the added effect over its entire lifespan.

By adding polymeric additives, the original property of the material is retained, only the plastic-specific processing and product properties change. The type of modification depends on the type of the base polymer and also the type and amount of additive added. A performance comparison is exemplary for PMMA 7N and a corresponding blend of PMMA 7N and 10 wt .-% of a polymeric additive. While the MVR is significantly increased, the pure additive shown here of acrylic glass leads to no loss in transparency.

Process aids for more sustainable production

When the polymeric additive is added to the plastic, processing temperatures can be significantly reduced. This effect is made possible by the described decrease in melt viscosity. Thus, the plastics can be processed at lower plasticizing temperatures. Components and fillers, which thermally decompose at elevated temperatures, can now be used in the gentler process environment and enable new products for the portfolio of plastic processors.

The energy needed to maintain the temperature zones can also be reduced. Polytives demonstrated this using the example of polycarbonate: here, the temperatures could be lowered from over 280°C to 230°C, a reduction of about 20%. This makes it easier to demold the components at the end of the processing line: cooling times and cycle times can be reduced.

In addition to energy savings due to lower temperatures, injection molding pressures can also be reduced. The pressure reduction also results from the rheological influence on the polymer melt. When processing PMMA in an injection molding machine, a pressure reduction of up to over 30% was observed.

This allows the fleet of injection molding machines to be used much more broadly and flexibly for a part of the product ranges, where previously locking forces were limiting factors. With lower injection pressures, less internal stress remains in the component—component qualities improve. Processors can thus save energy and thus CO₂ at different or even several points in their workflow and get closer to their optimization goals.