Tearing sewed items and separating items that were glued together?
See Volume 2 “The Laws of Cutting and Tearing items on Shabbos” for the full elaboration on this subject.
Below [in the gray table] is a brief summary which relates to the tearing prohibition that corresponds to the sewing prohibition. It does not relate to the cutting and fixing prohibition which may also apply.
Cutting and tearing sewn threads: The tearing prohibition applies when one tears or separates two entities from each other, even if one does not have intent to reattach them, if the attachment was meant to last. The tearing prohibition does not apply by tearing a single entity. If the sewn items were meant to be eventually torn then it may be torn not in the presence of an ignoramus.
In all cases that there is no tearing prohibition involved in tearing an item one must verify that there is likewise no cutting or fixing prohibition involved in doing so.
Separating glued items: It is forbidden to separate glued items if the items were glued to be permanently attached. If they are not meant to be attached and were accidently glued on their own, as at times occurs during book binding that glue or wax attaches pages together, than they may be separated on Shabbos. [See Q&A regarding if they were intentionally glued to last a very short time!]
May one separate items that were intentionally glued for temporary purpose?
This may be done not in the presence of an ignoramus.