Modification of Polyolefin Surfaces by Plasma-Induced Grafting K. JOHNSEN," S. KIRKHORN,' K. OLAFSEN,* K. REDFORD, and A. STORl zyxwvu SINTEF Materials Technology, P.O. Box 124 Blindern, N-0314 zyxwvuts Oslo, Norway SYNOPSIS Polar monomers have been grafted onto polyolefin surfaces with the aid zyxw of inert gas plasma. In the first stage, an inert gas plasma (argon plasma) was used to generate free radicals on the polyolefin surface. In the second stage, the plasma generator was turned off and a vinyl monomer introduced as a vapor. Monomer was surface grafted by free radical polymerization. After cleaning and drying, the samples were analyzed by XPS, IR, and contact angle. LD- PE was successfully grafted with acrylic acid, glycidyl methacrylate, methyl acrylate, and 2-hydroxy ethylacrylate. The grafting of acrylic acid was studied in more detail, and the rate of grafting was observed to increase with increasing monomer pressure and to decrease with time. The increasing of grafting temperature was found to reduce the degree of grafting. This last factor can be explained by the reduced concentration of monomer at the polymer surface or by a deactivation of surface radicals. zyxwvu 0 1996 John Wiley & Sons, Inc. I NTRO DU CTI 0 N Nonmodified polyolefin surfaces are difficult to paint or print on without prior surface treatment. A number of methods are employed to modify polyolefin surfaces. These methods include: corona treatment,' flame treatment,' and cold oxygen pla~ma.~ All three methods serve to add polar groups to the surface by oxidation. They add a poorly defined mixture of hydroxyl, ketone, alde- hyde, acid, peroxide, and ester groups to the sur- face of the polymer. It would be of interest to study the interactions of a lacquer system to a polyolefin surface with a better defined surface chemistry, preferably a sur- face with primarily one chemical group. Such a surface may be generated by the surface grafting of a polar monomer. Grafting has been reported initiated by peroxides4*'(either by swelling organic peroxides into the polyolefin surface or by per- oxides generated with corona treatment), UV ini- * Current address: JOTUN A/S, P.O. zyxwvutsr Box 2021, N-3235 San- ' Current address: Statoil Fou, N-7004 Trondheim, Norway. * T o whom correspondence should be addressed. Journal of Applied Polymer Science, Vol. 59, 1651-1657 (1996) zyxwvutsrq 0 1996 John Wiley & Sons, Inc. defjord, Norway. CCC 002 1-899S/96/1016S 1-07 tiation,6 or y-irradiati~n.~ In the present work, the use of inert gas plasma (argon) has been used to generate free radical sites for the grafting of polar vinyl monomers. The use of inert gas plasma to graft monomers on to a polymer surface from the vapor phase has been described earlier in the lit- erature.8-11The use of inert gas plasma for gen- erating free radicals and later exposure to oxygen or direct exposure to oxygen plasma (for formation of peroxide groups for initiating grafting from liq- uid phase monomer) has also been described in the literat~re.'~,'~ This article deals with the surface generation of radicals by inert gas plasma and the grafting of monomers from the vapor phase. Inert gas plasma was chosen in favor of corona or UV, as it enables the treatment of difficult geometries. The inside of a bottle can be easily activated by plasma but would prove difficult by the alternative techniques. Vapor phase grafting was chosen over liquid or solution grafting, as it offers the simplification that the same chamber can be used for the plasma gen- eration of radicals and the grafting. Although plasma-induced grafting using monomer in the vapor phase at the present probably is not an in- dustrial method, it may have a potential for further development. 1651