Characterization and evaluation of primer formulations for bonding silicone rubber to metal
PERRIN François-Xavier, BELEC Lénaïk, SOSSON Franck (SMAC)
The use of silicone rubbers (HCRs) as dampers or seals is growing in aeronautic and space fields because of their stability to environmental parameters (UV, temperature, ozone). Usually, HCRs are assembled to a metal part via the use of organosilanes based primers and/or polysiloxane additives. However, the role of primer compounds is not well understood. This work aims to improve the understanding of adhesion mechanisms between a HCR and a metal via the use of primers. Three commercial primer formulations covering a wide range of compositions and performances were selected from the available information. First, these formulations were analyzed in detail in order to better understand their chemistry. In the industrial conditions, kinetic reactivity of the primers was followed after their application on the surface alloy. HCR adhesion was measured by a 90° peel test, according to the primer and the roughness of the alloy. Results were completed by the analysis of the fracture zones. Results highlighted the key role played by the polysiloxane additives in primers on the adhesion of the assemblies. Polydimethylsiloxane (PDMS) based primers usually contain fumed silica fillers. The aim of the last part of the work is to improve our understanding of the role played by these fillers on adhesion. PDMS-silica mixtures were prepared varying the amount and the nature of the surface chemistry of the fillers. PDMS-silica interactions and dispersion of the fillers were determined by rheology and TEM respectively. Reinforced PDMS samples were then mixed with silanes to make primers. Reinforcement of the primers by silica was studied by atomic force microspcopy (AFM) in Peak Force mode. Results were correlated with the adhesion measurements of the assemblies via the use of these primers and with the observed fracture zones. Adhesion measurements and the characterization of the fracture surfaces revealed the existence of an optimal amount of silica, which varies according to its nature.
Adhesion, silicone rubber HCR, Adhesion primer, metal alloy, PDMS, fumed silica.