It depends on how thick of acrylic you use and the size of the piece as well as the final presentation.
On a large piece, if the acrylic is 1/8th inch (typical frame grade acrylic) and you are not framing it, then you have to reinforce it with a sub frame as mentioned by Doug, or you can use diBond or a piece of Black 1/4" acrylic (my preference). If you are framing it, then the frame will add rigidity so sintra should work OK. (if it's very large and not a pano, such as a 40x60, then something stiffer than Sintra is best even if framed, otherwise there will be a noticeable "bulge" of the acrylic.
If the acrylic is 1/4", then sintra is a good option, although 1/8" black acrylic is also a good option. We just delivered a large number of pieces face mounted to 1/4" Optix, with 1/8" white Celtec (basically the same as Sintra), mounted to a 1/2" thick Celtec frame 3" inside the edge of the piece, the top cut at 45 degrees with a matching piece for the wall ... basically a french cleat. Sizes from 11x14 to 40x60. Everything looked great when it was installed. Typically the backer is black, but the architect firm chose white for the back, and it did look nice on the wall.