Cyanoacrylate bonding silicone rubbers

Polychloroprene, nitrile, natural rubber, styrene butadiene rubber and butyl rubber can all be readily bonded with cyanoacrylates. EPDM and fluoroelastomers (such as Viton) can also be bonded, although only with specific grades of cyanoacrylate. The silicone rubbers and thermoplastic elastomers will usually require a primer but will also bond with cyanoacrylates. 

Silicone rubber is difficult to bond with cyanoacrylates. The adhesive does not wet the surface properly without special surface treatment, due to the very low surface energy, and therefore will not bond. Polypropylene (PP), polyethylene (PE), polytetrafluoro ethylene (PTFE) and acetal plastics and Santoprene rubber also fall into this category and cannot be bonded without prior surface preparation. 

These grades of rubber require priming prior to bonding (see also Section 10.6). Although this makes it a two-stage operation cyanoacrylates are used for bonding Santoprene and silicone rubbers. 

Examples in industry include attaching a silicone rubber seal to an aluminium parachute container. A primer is brushed on to the silicone rubber and the cyanoacrylate is applied to the aluminium. Once fully cured the bonded seal assembly prevents dust or moisture entering the safety critical box. 

Due to the high operating temperatures of silicone rubber, cyanoacrylates are not always suitable and RTV silicones may be the only adhesive option if the operating temperature is >150 °C. Silicones have a low surface energy and so will benefit hugely from surface treatment prior to bonding (Table 4.12). 

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