Fraunhofer Institute for Structural Durability and System Reliability LBFWear caused by plastic compounds in melt processing
Wear in plastics processing
During melt processing, some plastic compounds have a strong wear effect on the machine components exposed to the melt, such as extruder and injection moulding screws, non-return valves and injection moulding tools. The wear effect is based on abrasion, corrosion or both.
Abrasive wear in glass fiber and hard material compounds
Purely abrasive wear is found, for example, in formulations with a high glass fibre content (at least 40-50%) or a high content of hard materials such as boron nitride or aluminium oxide. The latter serve to increase thermal conductivity so that the compounds in question are suitable to produce lights with high-performance LEDs, for example, without the need for additional metallic heat sinks.
Corrosive wear in halogen-free flame-retardant polyamides
Typical representatives of formulations with highly corrosive wear are polyamide compounds that are halogen-free flame retardant based on diethyl phosphinate (DEPAL). The additives in question can react directly with the steel materials in the melt or form corrosive compounds, such as inorganic acids, through thermal decomposition. Nevertheless, DEPAL has proven to be one of the most important halogen-free flame retardant components, especially for polyamides.
Combined wear mechanisms: synergy of abrasion and corrosion
The screw elements shown in the illustration are an example of corrosively damaged machine components. They originate from the processing of halogen-free (DEPAL system) flame-retardant polyamides with a glass fibre (GF) content of 30% in the LBF pilot plant. Compounds that contain both corrosive (here: DEPAL) and abrasive components (here: GF) lead to a mutually reinforcing wear effect, in that oxide layers acting as a barrier or the resulting corrosion products are removed by abrasion and thus the "fresh" steel surface is constantly exposed to corrosive attack.
New challenges posed by bio-based and recycled plastics
Corrosive susceptibility also arises in connection with plastics based on renewable raw materials and natural fibres used to reinforce plastic compounds. The economic importance of these materials has increased considerably in recent years. Corrosive damage during the processing of recycled plastics is also becoming increasingly important.
Support from the LBF in compound optimization
As the optimisation of plastic formulations and additives, including research into new additives, is a key area of work at the LBF, we are happy to support you in the development of compounds with minimal wear - while maintaining the target properties.