Acrylic vs. Polycarbonate?

[bcoons]

Can anyone here give a qucik tutorial on Acrylic vs. polycarbonate (PC)? I believe plexiglass is a brand name of acrylic, and lexan is a brand name of polycarbonate. I know acrylic is cheaper than PC, and (from making race car windows) that plexi breaks and cracks easier than PC. Other than the cost difference, is there a reason most aquarium equipment is acrylic rather than PC? It seems that almost all DIY reactors are built from acrylic.

Do the same glues/adhesives/sealers work on both? I believe it's Weld-on that is used for acrylic? Will it also work on polycarbonate? How about silicon sealant?

I was in Walmart today and in the housewares section saw a "poly" cutting board. I assume this is polyethelene? It looked like it would make a nice, thick base plate for some DIY projects. Is it aquarium safe? Does it use the same adhesives and techniques as acrylic or PC?

Now I wish I had paid more attention to the Materials classes back in engineering school. ('Course, that was before plastics were invented! ;) )

[Yak]

I know very little about the subject, but i do know that you can make things out of Lexan. Here's a pic of my new 4'x4' Lexan tank:

http://i7.photobucket.com/albums/y290/theyakuza/Picture274.jpg

I didn't go out looking for a Lexan tank, there just happened to be an LFS that makes them locally. It's supposed to be harder to get a good bond on Lexan than on acrylic, but it can be done. The seams aren't nice and clear like acrylic either. But the thing I do like about it is I got the MR10 coated Lexan, which is supposed to be pretty scratch resistant. The guy to talk to on here is "Acrylics", he can answer any questions you have on the subject. If he doesn't chime in maybe you could send him a message....

[MarkS]

OK, let's see...

1.) Polycarbonate is far more flexible than acrylic, which can actually be a very bad thing.
2.) Acrylic scratches badly. Polycarbonate scratches even worse, unless you get coated PC at a higher cost.
3.) PC is harder to solvent weld.
4.) PC is more expensive than acrylic.
5.) PC is not as clear as acrylic and has a bluish tint, especially with thicker sheets.

I'm not sure if you can use acrylic solvent on PC. I do know that you CANNOT use PVC cement on PC. I tried that once when I was making a small PVC CC skimmer. I used a 3/16" PC tube for the air inlet and tried to bond it to the PVC with PVC cement. The tube literally melted. It completely turned to goo where the cement touched.

As far as the polyethylene and polypropylene, neither can be solvent welded. Both are noted for their resistance to solvents. You can use a true cement to bond, but you are only getting the strength of the cement in the bond. In order to get a high strength bond with PP and PE, you must use a hot air welder and then only weld it to more PP or PE. You can use mechanical fasteners (screws), but that is not always a good idea in a marine environment.

[EdMiller]

I used Lexan to make my skimmer since it was easier to get in the size of tubing I wanted than cast acylic. It was actually a lot cheaper too. the tubing is 1/8" wall and is quite strong, I have not had any problems with it. I used Weldon #16 to glue it. I also glued the PVC fittings in with the #16.

[Acrylics]

I'd have to agree with MarkS on just about every point with the possible exception of using PVC cement. It may just depend on the type of PVC cement; THF (tetrahydrafuran) is a common solvent used with polycarbonate and if it's the primary solvent in the PVC cement - should be fine though the PVC monomer may inhibit some of the reaction as it, itself may not be compatable to "fill" any gaps effectively. You can use just about any acrylic solvent such as Weld-on 3, 4, 10, 16, etc on polycarbonate though actual joint strength may vary.

HTH,
James