Why Polypropylene is so difficult to Bond ? 1

[smitacowper]

I want to Bond PP to Brass,but not able to get suitable solution. Everybody knows PP is difficult to bond substrate due to inert nature.

Friends Can you please help me in understanding the chemistry why PP is difficult to bond and what are the best ways of bonding it.

Thanks
Smita

 

[aspearin1]

One suggestion. You can strive for mechanical bond by melting the PP to the brass piece. Drill some small holes in your brass piece on the side which you want the PP to be bound. Heat the brass piece to above the melting temperature of PP. Then just take the hot brass piece and press it down on the PP under pressure until it cools. Some of the Melted PP should get into the small holes, and the brass will then constrict around the PP sprews as it cools. All of this could be done with a blow torch and a drill press (depending on how sensitive your pieces are.) Hope it helps. If this is going to be a throughput product or product piece, I suggest using a commercially available heat stamper. Cheap, tight controls, and fast. More generally used for stamping of logos into polymer surfaces, using heat and pressure. If interested, check out

http://www.stampritemachine.com

aspearin1

 

[Compositepro]

Polypropylene is difficult to bond to because the polymer has no polar or chemically reactive groups. The surface is very low energy like parafin wax, which is chemically similar. The surface can be chemically etched with very reactive chemicals or treated with a flame or plasma (corona treatment). Bonds are still likely to be weak or unreliable.

The sugestion to get mechanical bonding is a good one. I have found that it is usually better to have raised barbs rather than holes. These melt and penetrate plastic with little flow being required. To get the polymer to melt at the surface and then flow though a hole is much more difficult.

A useful technique is to spot weld a woven or knitted wire mesh to the metal suface. Heat the metal object above the melting point of the plastic and press the plastic part onto the metal one. As the plastic melts the metal cools and the bonding is complete in ten or twenty seconds.