DFG Project “The Effect of Liquid Silicone Rubber Formulation on Adhesion to Thermoplastics”

The Department of Plastics Engineering will soon launch a new research project, funded by the German Research Foundation (DFG), to investigate the adhesion between liquid silicone rubber (LSR) and thermoplastics. The goal of the three-year project is to investigate the influence of LSR formulation and the compounding process on bond strength and to elucidate the adhesion mechanism between the two material groups, which has not yet been fully understood.

The research project focuses on the development and investigation of proprietary LSR formulations. While previous scientific studies have primarily relied on commercially available materials with unknown compositions, this project will systematically vary all relevant formulation components—including base polymers, fillers, crosslinkers, catalysts, inhibitors, and adhesion promoters. In addition, the effects of compounding and processing parameters in the injection molding process are being investigated. The resulting LSR-thermoplastic composites are comprehensively characterized in terms of their mechanical properties, their bond strength, and the interface between the two materials. Modern analytical methods such as atomic force microscopy (AFM), transmission electron microscopy (TEM), and thermal analysis provide detailed insights into the interfacial layer. In addition, machine learning methods will be used to identify correlations between material formulation, processing, and composite adhesion.

AFM analysis (phase image) of the boundary layer of a PP-LSR composite with a silicate layer formed by surface treatment via silicatization 

Although LSR-thermoplastic composites have been used industrially for many years, it remains unclear to this day what causes the adhesion between the two materials. Previous research has focused primarily on surface pretreatments of the thermoplastics or on commercial LSR systems whose exact composition is unknown. As a result, there is a lack of fundamental understanding regarding the contribution of individual formulation components to the formation of adhesion. This study, which examines LSR formulations developed in-house, aims to close this scientific gap. The project’s results will contribute to a better understanding of the fundamental adhesion mechanisms between liquid silicone rubber and thermoplastics. This will enable the targeted development of high-performance, durable multi-component parts for technical and industrial applications.