According to Turnitin:
When an author publishes in a journal, the author often signs over rights to the publisher; thus, copyright infringement is possible if an author reuses portions of a previously published work.
Copyright law “protects original works of authorship” (www.copyright.gov). Authors can quote from portions of other works with proper citations, but large portions of text, even quoted and cited can infringe on copyright and would not fall under copyright exceptions or “fair use” guidelines. The amount of text one can borrow under “fair use” is not specified.
In addition to following fair use guidelines, authors need to recognize that copyright is not merely for published text. According to the U.S. Copyright Office (2010), a “work is under copyright protection the moment it is created and fixed in a tangible form that is perceptible either directly or with the aid of a machine or device.”