 Many thermoplastics can also be welded using chemical solvents . When placed in contact with the plastic , the solvent will begin to soften it , bringing the surface into a thick , liquid solution . When two melted surfaces are pressed together , the molecules in the solution mix , joining them as one . Because the solvent can permeate the plastic , the solvent evaporates out through the surface of the plastic , causing the weld to drop out of solution and solidify . A common use for solvent welding is for joining PVC or ABS ( acrylonitrile butadiene styrene ) pipes during plumbing , or for welding styrene and polystyrene plastics in the construction of models . Solvent welding is especially effective on plastics like PVC which burn at or below their glass transition , but may be ineffective on plastics like Teflon or polyethylene that are resistant to chemical decomposition . 
