tackifier

/ˈtækɪfaɪər/
noun
  1. A substance added to a material (such as glue, paint, or rubber) to make it stickier or more adhesive.
    • The manufacturer added a tackifier to the glue so it would hold better on smooth surfaces.
    • Without a tackifier, the rubber seal might not stick firmly to the window frame.
    • This paint contains a special tackifier that helps it adhere to plastic.