Are these old flour sacks? If so, there are quilters who buy these to piece specialty quilt tops. Flour sacks wouldn't normally be used for a quilt backing because they are so highly prized and are becoming more rare as time goes by.
If these are new flour sacks, I'd like to find out who makes them!
No special seaming is required when piecing flour sacks, but you probably want to quilt rather than tie. One of the benefits of quilting is that it relieves stress on seams.