Analytical Methods for Surface Grafts. - Analytical Chemistry (ACS

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Additional studies are needed on the kinetics and competitive processes of ion-exchange for various ions on a given membrane. These studies would best be performed with specific applications in mind so that the solution pH, possible interferences, etc. can be realistically matched to the conditions of the system to be monitored.

ACKNOWLEDGMENT The authors are grateful to Arthur Bradley, Surface Activation Corporation, Westbury, N.Y., for the acrylic acid graft samples and for helpful suggestions.

LITERATURE CITED (1)R . S. Swingle. Anal. Chem., 47, 21 (1975). (2)J. S.Brinen and J. E. McClure, J. Electron Spectrosc. Relat. Phenom.. 4, 243 (1974). (3)G.D. Nichols, D. M. Hercules, R. C. Peck, and D. J. Vaughn, Appl. Spectrosc., 28,219 (1974). (4)A. Bradley and J. D. Fales, Chem. Techno/., April 1971,p 232. (5)A. Bradley and M. Czuha, Anal. Chem., 47, 1838 (1975). (6) F. A. Cotton and G. Wilkinson, "Advanced Inorganic Chemistry." 3rd ed., Interscience,New York, 1972,p 52.

RECEIVEDfor review February 18, 1975. Accepted May 8, 1975.

Analytical Methods for Surface Grafts Arthur Bradley Surface Activation Corp., 1150 Shames Drive, Westbury, N. Y. 11590

Michael Czuha, Jr. DuPont lnstrument Products Division, Monrovia, Calif. 9 10 16

Surface modification of plastics, textile fibers, and other materials to improve serviceability may involve exposure to ionizing radiation, ultraviolet light, or corona discharge. Under suitable conditions, such excitation can result in free radical sites to initiate graft copolymerization. A radical change in surface properties of these materials is observed without modification of bulk behavior. Thus, various organic compounds have been grafted to wool fiber ( I ) , cellulose (2), and polyester ( 3 ) to enhance shrink-resistance, moisture retention, or launderability. Plasma-initiated polyacrylic acid grafts provide polymer films and sheets with a new dimension of surface polarity ( 4 , 5 ) . Potential applications include improved wettability for battery separators and better adhesion properties and printability for packaging films. The effects are more pronounced and more permanent than those obtained by exposure to corona (air) discharge, although the technology and apparatus bear some formal similarity and the cost of treatment is comparably small. This paper describes various techniques used in characterizing the surfaces of grafts on polypropylene, polyethylene, and polyester films.

EXPERIMENTAL AcryIic Acid Grafted Films. Samples used in this program were prepared by the gas discharge initiated surface grafting method previously described ( 5 ) . Free radical sites were created on 1-mil polypropylene film (Dow Chemical Co, Midland, Mich.) by exposure to argon plasma in the range 0.5 to 4 Torr and quenched with acrylic acid vapor close to its equilibrium vapor pressure, about 4 Torr a t room temperature. Barium Ash Determination. To 500 ml of an aqueous solution of barium chloride, saturated a t room temperature, was added 10 g of barium hydroxide. Grafted film specimens were immersed in this reagent for a t least 30 min a t 60-70°, then removed and given three successive 1-min rinses in fresh deionized water to remove excess barium salts. Dried specimens were ashed a t the Schwarzkopf Microanalytical Laboratory, Woodside, New York City. Conversions from % ash to mequiv acid/g were made on the assumption that the ash was BaO and that 1.53% ash corresponded to 0.100 mequiv/g of barium and 0.200 mequiv/g of acidic hydrogen. Titration. Weighed samples of film between 0.1 and 0.2 g were cut into slivers and placed in 125-m1 Erlenmeyer flasks. A 50-ml portion of 0.05N aqueous sodium chloride (technical grade) was added to each, followed by 1.00 ml of 0.1N NaOH. The flasks were stoppered and allowed to stand for a t least 4 hr, with frequent 1838

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