Analysis of the interactions between additives and fillers using the example of flame-retardant cable sheaths

Plastics used in cable sheaths must meet high requirements over a long period. The properties that are required, like flame retardancy, are specif-ically adjusted using additives. As a result of standard EN 50575:2017 coming into force, the more stringent fire requirements can only be met by adding phyllosilicates depending on the composition of the cable formulation. However, doing so would sig-nificantly reduce the cable sheath’s long-term stability, an issue that the researchers at Fraunhofer LBF have taken a closer look at as part of the “NanoFlame” project.

The cable sheaths being analyzed are made not only from the polymers poly-ethylene (PE) and ethylene-vinyl acetate (EVA), but also from a high proportion of the filler aluminum trihydrate (ATH) and nano-scale phyllosilicates that have been modified with an intermediate layer. Various additives, such as antioxidants and compatibilizers are used to complete these formulations. The project identified addi-tive-filler interactions that are responsible for the lack of sufficient long-term stability. 

The damage analysis was carried out using ATR-IR spectroscopy, with the data being evaluated using non-negative matrix fac-torization (NMF).

A method was also developed to allow fail-ure behavior under the influencing factors mentioned to be recognized at an early stage. This can be incorporated into the development of new materials which need to be both flame-retardant and possess suitable long-term properties. The new tool can be used to accelerate the develop-ment of cable sheath formulations and can be adapted to other systems.