Print on Demand Conundrum

So here's a question. In the name of research, I spend a lot of time either reading articles online or printing them out to read offline. Since I spend too much of my life staring at screens, I'd rather read them offline - but stapled-together printouts aren't a great format, either, particularly for longer articles. This afternoon, I thought: what if I could use a print-on-demand service to have whole sets of articles bound as one-off books for my use?

Now, the copyright status of these articles varies, but all have been freely published online - often in PDF or on sites which offer a "Print" version with most of the non-text content stripped out. So they have been made available for me to print a personal copy. If I compile a PDF of a dozen articles and order a single copy of it from a print-on-demand service, bound as a paperback, it doesn't feel like I'd be crossing a line in terms of my use of the material. But I suspect the print-on-demand provider wouldn't see it as acceptable use of their service.

Any thoughts, anyone?