Process of preparing a composite article

The present invention provides a method of preparing a composite article comprising: providing a first substrate having a surface comprising fluoropolymer; contacting the surface of the first substrate with a modifying composition preparable from components comprising a phase transfer catalyst, at least one of a sulfide or polysulfide salt or anionic conjugate acid thereof, and a liquid vehicle, wherein the fluoropolymer has a backbone comprising subunits having the structure -CH 2 CFX-, wherein X represents H, Cl, or F; and bonding the first substrate to a second substrate to provide a composite article, wherein the method is carried out in the substantial absence of actinic radiation.