Polymer Journal, Vol. 27, No. 6, pp 575~578 (1995)

Effect of 12 Plasma on the Properties of Polyethylene

Motoi FunsHIMA, Daigo KAWABATA, Chihiro FuNAKOSHI, Yasuhiko YOSHIDA,. Tad:;ttaka YAMASHITA, Kunihiro KASHIWAGI, and Kanto HIGASHIKATA*

Department of Applied Chemistry, Faculty of Engineering, Toyo University, Kawagoe, Saitama 350, Japan * C. Itoh Fine Chemical Co. Ltd., 3-29 Kioicho, Chiyoda-ku, Tokyo 102, Japan

(Received October 4, 1994)

ABSTRACT: Polyethylene surfaces were treated with 12 plasma. From ESCA analysis, it became apparent that iodine atoms were bound chemically to the surface of polyethylene substrate

by the treatment of 12 plasma. Also, iodine bonded chemically to polyethylene increased by the

exposure of 12 vapor after 12-plasma treatment of the substrate. The reaction of lz-plasma treated polyethylene with aminoalcohol made the polyethylene substrate hydrophilic. KEY WORDS Plasma / Iodine / Surface / Treatment / Polymer /

In glow-discharge low-temperature plasma, treatment of a polymer by fluorine derivatives atoms and/or molecules are activated to give such as tetrafluoromethane or fluorine is used ions, radicals or excited species. Plasma are for etching a material surface, and gives water expected to be applied in various fields, such repellency to polymer surface. 3 Also, plasma as forming thin films with high functionality, treatment of organic materials by chloroform etching a substrate surface, and treating the is reported.4 However, plasma treatment by surface of organic material substrates. Though iodine (I2) gas has not been reported, although plasma chemistry has been widely investigated, plasma polymerization using iodomethane was further studies on plasma chemistry are re­ carried out to form thin films containing iodine quired in order to create the various functional linked chemically. 5 This article reports that thin films or surfaces. lz-plasma treatment of polymer forms organic Recently, plasma treatment of polymer has materials linking chemically iodine atoms. The been done to introduce various functionalities functionality ofI2 -plasma-treated polyethylene onto the surface of organic materials. Func­ was investigated. tionalities, such as wettability, water repellency and adhesion, are attributed to chemical struc­ EXPERIMENTAL tures and functional groups on polymer sur­ face. Plasma treatment of a polymer is useful As shown in Figure 1, the plasma apparatus method for reforming a polymer surface, which is made of a pyrex glass, 5 cm in diameter and changes the surface properties of an organic 40 cm in length, fitted with an iodine (I2) gas material, such as hydrophobicity or hydro­ inlet, argon (Ar) gas inlet, pressure gauge and philicity . The treatment of the organic vacuum system. The plasma was generated by materials by 0 2 , N 2 , or Ar plasma produces application of a high voltage amplified by a the functional groups, such as hydroxyl, neon transformer to the tungsten (W) elec­ carbonyl, amino or nitrile groups, and adds trodes. The plasma power was controlled using various functionalities, such as hydrophilicity, a variable resistor. The plasma apparatus was wettability or adhesion property. 1•2 Plasma evacuated to about 200-400mTorr, and then

575 M. FUJISHIMA et al.

to vacuum pump Voltage Transformer t

Substrate t t h Ar

Figure 1. Schematic diagram of the apparatus for

12 -plasma treatment.

c) the vapor ofl2 sublimed at 0°C was introduced.

Before the plasma treatment by I2 vapor, the atmosphere was replaced with Ar gas. As a b) sample for ESCA analysis, polyethylene thin film (PE, 30 mm x 25 mm x 0.8 mm) was used. a) The polyethylene substrate (50mm x 25 mm x 2 mm) was used to measure the contact angle. The reaction of the treated polyethylene with 640 610 amine was carried out as follows. The Ir Binding energy (eV) plasma-treated polyethylene substrate was Figure 2. ESCA spectra of 12 -plasma, l 2-plasma/1 2- placed in a beaker containing a solution of vapor-treated polyethylene and untreated polyethylene. a) various amines (200 ml) for a specified period. polyethylene substrate without treatment; b) polyethylene substrate treated by 1,-plasma for I hour; c) polyethylene The substrate was washed by ethanol, and dried substrate treated by 1,-plasma for I hour and exposed to under reduced pressure. 12 vapor for I hour. ESCA spectra were recorded with a Shima­ dzu electron spectrometer, ESCA 750. Wet­ physically to the surface of the polyethylene tability of the treated polyethylene substrate substrate only by exposure of I2 vapor without was estimated by the contact angle with water. plasma generation.

Contact angles with water were measured at Polyethylene substrate was treated by I2 room temperature using a contact-angle meter plasma at 200 mTorr. The I2 -plasma-treated (ERMA Inc., Model G-I). polyethylene was analyzed by ESCA. As shown

in Figure 2b, I2 -plasma-treated polyethylene RES ULTS AND DISCUSSION showed peaks at 630.60eV and 619. l0eV, which were assigned to iodine atoms of 3d312 Ii-Plasma Treatment of Polyethylene and 3d512 respectively. These peaks are in­

Vapor of iodine (1 2) was introduced into the dicative of iodine bonded chemically to carbon reactor without generating plasma, and the by I2 plasma, since iodine was not detected on polyethylene substrate was exposed to I2 vapor. polyethylene exposed to 12 vapor. The polyethylene substrate was analyzed by The iodine in polyethylene surface depended

ESCA. The iodine doublet at 630 and 619eV on the time of 12 -plasma treatment. As shown was not detected, thus showing that iodine did in Figure 3, iodine became approximately not link chemically and was not adsorbed constant at 25% at an 1/C molar ratio over

576 Polym. J., Vol. 27, No. 6, 1995 Effect of 12 Plasma on the Properties of Polyethylene

0.3 Table I. Surface composition of I 2-plasma-treated and l 2-plasma/1 2-vapor-treated polyethylene 0.25 • 0 • 12 -plasma (I h)/ "§ 0.2 12 -plasma (I h) Plasma voltage Ii-vapor (1 h) ;;; • 0.15 (kV) 0 I/C E 1/C (.) 0.1 :::: 3.0 0.04 0.16 0.05 3.6 0.22 0.43 4.8 0.29 10 20 30 40 50 60

treatment time (min) Table II. Depth profile of 12-plasma-treated polyethylenes surface• Figure 3. Effects of 12-plasma treatment time on iodine bonded to polyethylene. (Plasma voltage, 3.6kV) 0° (d) 30° (0.87d) 45° (0.71d) 60° (0.5d)

20min. I/C 0.04 0.08 0.05 0.02 The ac voltage applied to the W electrodes • (d, escape depth of photoelectron m the range was set at 3.0 kV, 3.6 kV, and 4.8 kV, because -100A). iodine bonded to the polyethylene was very low below 3.0kV and 12 plasma was unstable over iodine vapor was introduced into the reactor 4.8 kV. At each plasma voltage, lz-plasma for I h without plasma generation. The surface treatment was carried out for I h. Iodine of polyethylene substrate after this treatment bonded to polyethylene surface is shown in was analyzed by ESCA. As shown in Figure 2 Table I. Iodine in polyethylene increased with and Table II, exposure to 12 vapor after plasma voltage. 12 -plasma treatment caused the introduction of The depth profile of iodine bonded to iodine more than that of iodine by 12-plasma polyethylene was measured by varying the treatment only. This suggests that lz-plasma incident angle of X-ray to the surface of the treatment of polyethylene forms carbon-iodine polyethylene film. From Table II, it was bonds and radical species on polymer surface, confirmed that iodine was present at a depth and thereafter that radical species surviving on of ca. 1ooA from the topmost layer of the the polymer surface react with 12 vapor polyethylene surface. It has been reported that introduced into the reactor without activation the escape depth of photoelectron is the by plasma, to form the additional carbon­ outermost few tens of Angstroms of the sample iodine bonds. (in the range IOOA). 6 Reactions of Polyethylene Containing Iodine

Treatment of Polyethylene by 12 Plasma and 12 with Amine Derivatives Vapor The hydrophobic/hydrophilic properties of Radical species are present at the surface of lz-plasma-treated polyethylene or 12-plasma/ organic material treated by plasma and the life Ii-vapor-treated polyethylene were determined span is very long in comparison with that of by measurement of the contact angle with the organic radical species. Halogen molecules water. The contact angle with water ranged are known to react easily with radical species. from 56 to 104°, because the contact angle The surface of the polyethylene substrate was depended on the amount of oxygen and iodine treated for I h with 12 plasma generated at bonded to the polymer surface. To import plasma voltages of 3.6kV, and thereafter, hydrophilicity to the polymer surface, the

Polym. J., Vol. 27, No. 6, 1995 577 M. FUJISHIMA et al. reaction of polyethylene contammg iodine Table III. Elemental composition of substrate with amine was carried out. Polyethylene surface treated by the reaction of containing iodine was prepared by lz-plasma l 2-plasma-/12 -vapor-treated polyethylene with various amines• treatment for 1 h at 3.6 kV and thereafter treatment with I vapor alone for another Element ratios 2 Contact Amines 1 h without plasma. Alkyl iodide easily reacts angles with amine to give the ammonium iodide salt, N/C 1/C as follows. I n-Propylamine 0.20 0.03 76° 2 Isopropylamine 0.31 0.06 58° I I I 1(±) e 3 Triethylamine 0.15 0.04 60° -C-1 + N- - -c-N- I 4 2-Methylaminoethanol 0.33 0.03 24° I I I I 5 2-Dimethylaminoethanol 0.40 0.04 27° 6 2-Ethylaminoethanol 0.33 0.05 21° After reactions with various amines, iodine in polyethylene containing iodine decreased, a 12-plasma/Irvapor treated polyethylene: 1/C; 0.43, and the introduction of nitrogen atoms to contact angle; 73°. polyethylene substrate was apparent from the results of ESCA measurement (Table III). CONCLUSIONS The nitrogen (N 1.) peak appeared at 403 eV, which was assigned to the nitrogen atoms of In this study, iodine was bonded chemically ammonium salts. It is considered that the to polyethylene surface by treatment of 12 decrease of iodine contents resulted from the plasma. By exposure of 12 vapor after 12 - exchange reaction of iodide ion (I-) with hy­ plasma treatment, more iodine than that by 12- droxide ion (OH-) and the elimination reac­ plasma treatment only became bound to the tion of hydrogen iodide (HI) from polyethylene surface of polyethylene. containing iodine by interaction of the amine. The 12 -plasma-treated polyethylene surface The contact angle with water decreased slightly, reacted with aminoalcohols, causing the sur­ after reactions of I2 -plasma-/Iz-vapor-treated face to become hydrophilic. polyethylene with amines (Table III, No. 1-3). Similarly, after reactions with aminoalcohol REFERENCES derivatives (No. 4-6), iodine in polyethylene containing iodine decreased and nitrogen I. H.K. Yasuda, "Plasma Polymerization and Plasma atoms were bound to polyethylene substrate. Treatment of Polymers," J. Appl. Polym. Sci., Appl. The contact angle with water decreased at all Polym. Symp., 42 (1988). 2. Y. Nakagawa, Y. Yoshida, and T. Yamashita, surfaces of the polyethylene substrate treated Kobunshi Ronbunsyu, 46,209 (1989); Y. Yoshida and by I 2-plasma-/Irvapor/aminoalcohol, causing Y. Nakagawa, "Proceedings of Japanese Symposium the surface to become hydrophilic. on Plasma Chemistry," Vol. 2, Organizing Com­ mittee Japanese Symosium on Plasma Chemistry, Treatment of polyethylene substrate by 1 - 2 Ed., Shinzansha Scitech Co. Ltd., Tokyo, 1989, p 225. plasma, Iz-plasma/12 -vapor, or 12 -plasma/Ir 3. M. Strobel, S. Corn, C. S. Lyons, and G. Korba, J. vapor/aminoalcohol makes it possible to Polym. Sci., A, Polym. Chem. Ed., 25, 1295 (1987). change the hydrophobicity/hydrophilicity of 4. N. Inagaki, S. Tasaka, Y. Suzuki, J. Appl. Polym. polyethylene. Sci., 13, 51 (I 994). 5. J. H. Dully, F. J. Wodarczyk, and J. J. Ratto, J. Polym. Sci., A, Polym. Chem. Ed., 25, 1187 (1987). 6. D. T. Clark, Adv. Polym. Sci., 24, 125 (1977).

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