Despite being almost 30 times more sturdy than glass and extremely resilient to damage, you cannot simply adhere two pieces of Polycarbonate together using regular solvents, as this will cause the material to craze. Crazing occurs when the bonds that hold the material together at a microscopic level are damaged or broken, causing the material to appear as though it has hundreds of tiny little cracks both on and underneath its surface; these cracks cannot be felt however, and it is important to note that the material will still be capable of bearing a load.
There are two methods of bonding pieces of polycarbonate effectively, one being the use of an epoxide glue (Epoxy), which is relatively straightforward and not at all dissimilar to glueing any other two materials together; and the other being fusing the two together. Fusing is superior to using Epoxy as the end results tend to look seamless, almost invisible, and the bond itself is actually stronger and more resilient.
To fuse the material all you need are your polycarbonate sheets and some Methylene Chloride, which can easily be bought online; once you have these two things you can get started with bonding your sheets together.
Your best first step would be to thoroughly clean the areas that will be adhered to. This is best done by rinsing the sheets with lukewarm water before washing them in soapy water of the same temperature; use a gentle cloth or sponge and wipe it, preferably in the direction of the grain. It is important that you do not scrub or use anything with a rough surface, as the sheet will blemish. Rinse it one last time and then dry it off with another cloth.
Once dried you can start the process of fusing the sheets together by applying a small trail of your methylene chloride along the edge of the sheet that you intend to fuse; be sure to carry this out in a well-ventilated area, as methylene chloride is toxic and the fumes can be harmful. It should only take a moment but give the adhesive some time to soak into the sheet and become slightly sticky before placing the edge directly onto the surface of the other sheet where you would like it to bond.
Hold the sheets carefully in place, ensuring that the two surfaces that are being fused remain in constant contact. To this end it is also a good idea to apply a small amount of pressure on the sheets, encouraging a stronger bond to form. Once they are capable of supporting themselves, leave them to dry for a minimum of a full 48 hours; we recommend that you put as little strain on either of the pieces as possible; as doing so before the bond has fully formed may result in a weaker bond, or cause the two sheets to come apart.
This exact same process can also be used to glue sheets of Plexiglass or Perspex to one another, but it will not work on other plastics. Acrylic can also be bonded using a different method, one that involves specifically designed acrylic glue; if you would like to find out how to glue acrylic edges then please follow the link ‘here‘.