It is not definitively knowable whether such printing is allowed in the US. There is no specific statutory permission by way of a "private use" exception to copyright law. Copyright law would generally say that making any copy without permission is illegal; but we have the murky zone of "fair use". The way you would, in principle, get a more definitive answer would be to look at the case law, and see how courts have treated similar cases. "Fair use" means that non-infringing use is based on "balancing"
(1) the purpose and character of the use, including whether such use
is of a commercial nature or is for nonprofit educational purposes;
(2) the nature of the copyrighted work;
(3) the amount and substantiality of the portion used in relation to
the copyrighted work as a whole; and
(4) the effect of the use upon the potential market for or value of
the copyrighted work.
Printing a book is not fair use per (3), it tends somewhat to not be fair use per (4). Point (2) is supposed to be about "commentary", so simple re-printing does not add anything (derivative works are "more fair" than exact reproductions). It might make it under point (1). So maybe it's fair, maybe it's unfair.
Then by consulting all of the case law, you can see if there are decisions on point. There are none: there is no precedent as to the fairness or unfairness of printing out a copy of an online textbook which fails to grant or deny permission to print. The reason for that lack of case law is that it would be very expensive for the rights-holder to litigate the matter to the point of getting a definitive judgment. Most case law is about a large organization that makes a fair amount of money off of an act of copying. This unfair use case is more unfair than what you describe, and is not sufficiently analogous (the distributor is a university; the work was unpublished). Another somewhat informative case is Richards v. Merriam-Webster, where the guy wanted to create a version of a dictionary. He apparently decided to ask the courts first rather than do and then apologize, and the court said "No, that's not fair". Although the use was highly transformative, the extent of copying was complete, and the effect on market (which is where this is not parallel to your case) would be devastating.
There is a very weak further defense that might be mounted, that it is reasonable to believe that you have permission. Many online works are set up to be unprintable (barring the page my page screen shot approach). If the work is not crippled, and it is put out on the web for everyone to see, then it is reasonable to assume that you have implicit permission, since if permission was denied, the file would have been secured to make it unprintable (not a technically difficult thing to do). Fair use presupposes good faith. Everyone knows you should get written permission, to avoid doubt, but I do not know of any case law where "implicit permission" is (un)successfully invoked.