By Bob Lebeaux, President, The Plastics Group of America
October 7, 2009 in Polypropylene
Olefins, like polypropylene and polyethylene do not adhere to metals particularly well because of the non-polar nature of their base molecules. To significantly improve their ability to bond to metals, simply add polar copolymers. This can be done either in the reactor or by compounding with polymers with polar side-groups like acid copolymers such as EVA, EMA, and EMAA.
Polypropylene is available in maleated acid copolymer which has several percent maleic anhydride bonded onto the polymer chain.High temperatures and fast injection help to measurably enhance the bond. For other processes, such as coextrusion/lamination, the use of film-grade polar copolymers is well-established; they are often used to integrate a metallic component, such as aluminum foil barrier layers, into a multi-layer film structure.
Finally, the chances of bonding an already-formed PP to metal are not good – the best chance would involve utilizing a hot adhesive, likely an acid copolymer derivative.
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