Alternatives to PMMA/Acrylic

[BenM68]

I am looking for polymer materials that can be used as an alternative to PMMA/Acrylic/Plexiglass. As with PMMA, the material must have a reasonably low density and good optical properties. Also, better elasticity than PMMA, which is the reason I am looking for an alernative.

Some background info - I have some components that I had made from PMMA/Acrylic/Plexiglass. The components are quite complicated and are mostly composed of components machined from flat sheet and tube that fit together and are then glued in place with Acrifix. The weight is the most critical aspect of the component.

The problem that I have has so far is that the glued jounts and even some of the tubes have developed stress fractures in service. The component undergoes some bending forces, and the glued joints are unable do suffer much deformation without cracking.

So does anyone have any alternatives which are close to the properties of acrylic but offers better elasticity? I had thought of polycarbonate??? Which appears to have better flexibility - but what about glued joints?

 

[CoryPad]

Polycarbonate is a good suggestion.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Eltron]

Yep, polycarbonate is what I would suggest. Also take a look at different solvent welds for your joints. Maybe that's part of the problem.

 

[BenM68]

Any tips on the best solvent to use (i.e. one that retains the most flexibility when cured)?

 

[Eltron]

Well, the idea of a solvent weld is that it melts the material to be joined then volatilizes leaving the parent material only behind. So you don't want a weld solvent to add a different material to your joint. Some of the solvent weld manufacturers do mix in the plastic (acrylic) monomer into their products to increase working time or make them a little more like a paste. I've always had luck with a product from IPS called Weld-On. You have to apply it with a glass syringe since it is liquid. If you don't want to use a pre-fab solvent weld, then you can just use dichloromethane in the same way. Just be sure to follow the proper handling guidelines for whatever you choose. It wouldn't be a bad idea to talk to a couple of the manufacturers for the plastics and the solvent welds. I'm sure they'll have some recommendations for you.

 

[Compositepro]

Solvent bonding can often lead to stress cracks because the polymer swells significantly as it absorbs solvent and shrinks when it dries. Narrow bonds will allow the solvent to evaporate more readily while wide bondlines tend to trap solvent and leads to more stress. Thermal bonding is also possible, as well as casting the part in one piece using acrylic monomer.