Can’t Bond Polyprop?

In case I get run over by a herd of antelopes on the way to work tomorrow, here is the synopsis for my poster, to be presented at the Sheffield University LGBT STEMinar on Friday 15 Jan:

Can’t Bond Polyprop?

Background

Adhesive bonding is a valuable part of industrial design, allowing different materials to be joined so that their properties can be fully exploited.

Polypropylene is a fairly rigid thermoplastic which enables designers to achieve weight reduction in components and assemblies.

The inert, low-energy surface of PP helps to prevent staining, but also inhibits bonding and coating processes.

Conventional wisdom: ‘Polypropylene is impossible to bond, and can only be joined using heat-welding techniques.’ Numerous online message boards carry postings from disillusioned DIY enthusiasts who have arrived at this conclusion following their attempts to glue PP components.

Experimental work

Shear strength measurements on lap-joints showed that through-primer abrasion created stronger bonds than pre-primer abrasion. The technique has been used with three different grades of PP (brittle homopolymer, ethylene copolymer, and rubber-toughened PP copolymer) and two different adhesives (epoxy and polyurethane) giving strong, durable joints.

Options for future work

New variants of the primer system: water-borne and chlorine-free polymers, rather than traditional xylene solutions of chlorinated PP.

Advanced polymer substrates: glass-reinforced PP, non-woven textile systems.

Message to aspiring researchers

There are opportunities for exciting developments in seemingly established and unpromising fields of technology. The established views (‘you can’t bond PP so don’t bother trying’) need to be challenged using detailed programmes of experimental test results.

Tim Norris, PhD, ATSC

Leicester Polytechnic, Oxford Polytechnic, Open University

Carrs Paints, Mason Coatings, Newtown Industrial Paints, Sterling Technology,
EC Pigments, Kernow Coatings, Exova, Corrocoat, FBS Prestige

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