How rough for gluing two surfaces

[Andy]

When I want to glue to surfaces togther then I am advised to roughen the surfaces first.

In this particular case I have two fairly soft hard plastics (about as soft as styrene but not as soft as polyethylene) which i wish to stick together.

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I have a choice of adhesive: (1) "super glue" - cyanoacrylate adhesive (2) Bostik or UHU - general purpose adhesive (3) Evostik - contact adhesive (4) Araldite - epoxy resin (5) hot melt adhesive from glue gun - various formulations

The cyanoacrylate super glues should be good for this application but too often I have tended to get disappointing results from this type of glue. I find the hot melts too can be problematic.

So I will probably use either (a) a Bostik/UHU type of general purpose adhesive or (b) a contact adhesive.

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The QUESTION is what sort of roughening is best to allow this sort of glue to bond strongly with each plastic surface. Each surface is currently smooth.

(ONE) Should the roughening be quite fine. Perhaps similar to using 300 grit glasspaper?

(TWO) Or should the roughening be almost visibly "streaky" as one might get using 40 grit glasspaper?

(THREE) Would you change your recommendation if I made a different choice of adhesive fro the range above?

Thank you.

[Kono imo!]

you should use a glue for that plastic, all the above will not work that well. The plastic glue will dissolve the plastic some, and bond it. Try pipe cement, for plastic piping, it is a great plastic glue.

[Marshall Dudley]

You need to identify the plastic. Styrene is a liquid, not a solid, so comparing hardnesses is not logical.

Marshall

Andy wrote:

[Andy]

Maybe drain pipe solvent cement could work. But different cement is used for different drain pipe plastics (styrene, ABS, PVC, CPV) and I can't identify what my surfaces are.

The two plastics I am joining do not dissolve even slightly with acetone or with ethyl acetate (both as nail varnish removers).

[Andy]

[Kono imo!]

try the plastic pipe cement, very cheap, works with many plastics, but not polycarbonate I think

[Roy L. Fuchs]

On Fri, 14 Apr 2006 22:57:20 +0100, Andy Gave us:

Liquid nails construction adhesive from home depot or the like. No surface pre-prep required.

[The Natural Philosopher]

This is good advice. CA and epoxy do not bond well to MOST plastics. Solvent based contact adhesive is good.

But it all depend on the type of joint, and the exact plastic.

Styrene and PVC solvent weld very well indeed. Polythene is almost impossible to glue to anything with anything - its just to greasy.

Thermoset plastics work well with epoxy and polyester glues.

Reasonable glue joints can be made to MANY but not ALL plastics with hot melt or no more nails type glues...

It would hep if you said exactly what you are trying to do.

[The Natural Philosopher]

Bad news. TRy petrol =- that may dissolve them.

[RadicalLibertarian]

There are lots of styrene based plastics. I think that Bondo is based on styrene, as well as the resin used for making fiberglass composite. It's some type of polyester -

Well, if you live in the US, there is a new type of glue on the market callet "Gorilla Glue". I think it's made in Norway or somewhere, and you can also get it from their website. It is a polyurethane, and would probably stick pretty good.

You could also try %100 silicone from hardware store.

But for this app, I think that a hot glue gun might work pretty good too. I think that the glue sticks these days are made from some kind of polypropylene formulation.

You might also consider welding somehow, most thermoplasts can be welded.

[RadicalLibertarian]

If I were you I'd hit it with various sandpapers, and then scrape it up a little with a razor blade.

Cyanocrylate will dissolve expanded polystyrene. If cyano softens your plastic, you may not need to rough it at all. I think that hobby models are made of styrene, and the glue is basically styrene dissolved in toluene.

I'd test the cyano - it wont cure at all on some substrates.

What is it you are building ? Where'd you find the plastic ?