Cyanoacrylate bonding EPDM

Cyanoacrylates can be used to bond many materials, including most thermoplastics and even the more difficult ones like polyethylene, polypropylene, and ethylene-propylene-diene ( EPDM ) rubber. The best results are obtained with close contact and narrow bonds (some formulations have limited ability to bridge large or irregular gaps between the surfaces). 

Polyolefin bonding has been advanced using cyanoacrylates through the use of surface primers. These primers promote adhesion to untreated polyethylene (PE), polypropylene (PP), and EPDM rubber. Table 7 shows comparison bonds using standard industrial-grade cyanoacrylates. 

Cyanoacrylate adhesives will bond most substrates to themselves and to each other. The few adherends which do not bond well with standard adhesives are polyethylene, polypropylene, EPDM rubber, plasticized PVC, teflon, and acidic surfaces. A few manufacturers sell modified adhesives which will bond some of these materials, such as EPDM and flexible PVC. Adhesion to low surface energy plastics like polyolefins and Teflon can be improved by an etching or oxidizing treatment. 

Polychloroprene, nitrile, natural rubber (polyisoprene), styrene butadiene rubber (SBR) and butyl are amongst the types of rubber that can be readily bonded with cyanoacrylates. Ethylene propylene diene monomer (EPDM) and fluroelastomers (Viton, registered trade mark of DuPont) can also be bonded, although only with specific grades of cyanoacrylate. Silicone rubber and thermoplastic rubber (Santoprene, registered trade mark of Advanced Elastomer Systems) can be bonded with the aid of a primer. Typical applications and techniques for bonding different grades of rubber are discussed in Section 10.11. 

Standard cyanoacrylates do not bond particularly well to EPDM but certain grades of ethyl-based cyanoacrylates have been specially developed for bonding to EPDM. One such grade is Loctite 406, an ethyl cyanoacrylate and this is used to attach an EPDM rubber edge strip to an EPDM conveyor belt to prevent potash from falling off the production line. 

The same product is used for mitre bonding of EPDM rubber seals for automotive doors and windows. The cyanoacrylate produces high strength invisible bonds in seconds. 

For fixing an EPDM rubber seal to a polyvinyl chloride (PVC) beer pump mechanism the cyanoacrylate must not only produce a reliable bond but also be approved for use with potable water. The cyanoacrylate, once fully cured, is essentially an inert plastic and many grades are approved for potable water as well as for medical applications (see Section 10.11.4). 

EPDM can be difficult to bond (Table 4.4) and many cyanoacrylates will not show particularly good adhesion to EPDM. However, some speciality grades of cyanoacrylate will show good adhesion to EPDM without the use of primer. The silicones, UV acrylics and two-part acrylics all show relatively poor performance on EPDM. 

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