Glue and other adhesives cause substances to stick together by forming strong molecular bonds, so to separate items, you need to break the adhesive bonds that hold them together. Depending on the type and strength of the particular adhesive, you can usually use vinegar to safely remove adhesives from plastic, wood or glass.
You can remove most adhesives, such as price stickers or labels on new items, by peeling or scraping the sticker with your fingernail or dull knife. If the adhesive is still sticky, you can apply a nontoxic solution of warm water, vinegar and liquid dish detergent. Soak a paper towel in the warm vinegar solution and rub it over the adhesive. Let it sit for five minutes. Then remove the paper towel and scrape away the residue. You can use ammonia instead of vinegar in the solution; however, if you use ammonia, make sure to work in a well-ventilated area.
You need to make sure the liquids used for adhesive removal will not cause damage to the material’s surface; it’s best to test the liquid mixture by applying it to an inconspicuous area first. Removing adhesives with vinegar is most effective for surfaces made of plastic or glass, as opposed to paper, fabric or wood.
Another method you can try to break the molecular bonds that hold objects together without damaging the material is to freeze the material. This can be done either by placing the object with the adhesive in the freezer or by rubbing an ice cube encased in a plastic bag over the adhesive. This causes the adhesive to become stiff and crumble, allowing it to be scraped off easily. Similarly, steam is effective at releasing adhesive bonds without damaging the material, especially paper, fabric and wallpaper.