'Surface photografting' onto polymers - a new method for adhesion control

Abstract

Surface photografting onto polymers is a new method for surface modification of sheet, film, filament and yarn. It was invented in our laboratories in 1985 and was developed as two processes: A batchwise process where photoinitiator and monomer are transferred to the substrate through vapor phase and the monomer is grafted to the surface of the substrate by UV irradiation; and a continuous process where photoinitiator and monomer in solution are transferred to the substrate in liquid phase by 'presoaking' a strip of film, a filament or a yarn in the solution and the monomer is grafted to the substrate surface by UV irradiation on line. The batch process has been applied to film, sheet and molded plates of various commercial polymers which have been surface photografted with acrylic acid (AA), acrylamide (AM), 4-vinyl pyridine (4-VP) and glycidyl acrylate (GA) using benzophenone (BP) as initiator. The grafted layers are analyzed by electron spectroscopy for chemical analysis (ESCA) and reflection IR spectroscopy, contact angle measurements with water, and dye adsorption measurements, and analyzed by microtitration to be maximum 10 nm thick. The epoxide groups of GA-grafted polymer surfaces were reacted with stabilizers, amines and proteins to secondary grafted layers. The effect of surface photografting on adhesion was studied for molded low density polyethylene (LDPE) plates which were surface photografted with AA, AM, 4-VP and GA using the batch process. The adhesion of Scotch tape to the LDPE plates increased 5 to 8 times after grafting of the plates with the four monomers, measured by 90° peel tests. Strips of polypropylene film and filaments and yarns of polyethylene, polypropylene and polyester (all commercial samples) were surface photografted with the four monomers mentioned using the continuous process. The measured adhesion of the substrates to epoxy resin, measured by pull-out tests from the cured resin, increased by a factor of 3 for AA-grafting and a factor of 6 to 7 for AM-grafting. The bulk tensile properties of high strength PE fibers are not affected by the grafting.

Keywords:

• Surface modification
• fiber and film
• polyethylene
• polypropylene
• poly(ethyleneterephthalate)
• acrylic monomers
• vinylpyridine
• benzophenone
• photoinitiated grafting
• adhesion
• peel test
• shear test
• pullout test