Bonding the un-bondable: Polyolefin Adhesives

Polyolefin plastics such as polypropylene have excellent chemical and physical properties so are used for a wide variety of applications such as; piping systems, medical and laboratory equipment and food containers amongst others. However, polyolefins are notoriously difficult to bond.

For an adhesive to successfully bond a substrate it must be able to wet (or otherwise penetrate) the surface. Adhesives are only able to wet the surface of a substrate if the surface energy of the adhesive is equal to, or lower than the surface energy of the substrate. Adhesives with a higher surface energy than the substrate will form beads on the surface, leading to very poor coverage and thus poor adhesion. Polyolefins have very low surface energy and so cannot be bonded with general adhesives. Some other methods of joining are also not possible for polyolefins. For example, polyolefins have very good chemical resistance so solvent welding is not an option.

Engineers often have to result to treating the surface of the polyolefin to increase the surface energy so that an adhesive can be used for bonding. Some examples of surface treatments are; chemical etching, electrical/corona discharge, gas plasma treatment and flame treatment. Surface treatment is far from ideal as it is costly financially and for the environment and also takes up a lot of time. Additionally, some forms of surface treatment require the use of hazardous chemicals. Furthermore, there are some applications where surface treatment is not possible due to space constrictions on products.

Structural Adhesives Ltd have recently re-opened a historic project surrounding the development of an adhesive to bond polyolefin plastics. In the last few months the research and development team have had a remarkable breakthrough and have devised an adhesive that successfully bonds untreated polypropylene. This will mean a greatly reduced environmental impact as well as financial savings for customers.

Here at Structural Adhesives Ltd we are confident that our polypropylene adhesive will solve problems for our customers as it has already begun to do so. Recently, a local business had a polypropylene fan case on a vacuum pump that was cracked and was subsequently repaired this using our new polypropylene adhesive which worked a treat.