산소플라즈마를 이용한 폴리우레탄의 표면 개질

장 얀, 명성운, 최호석, 김인호, ．최재혁

충남대학교 공과대학 화학공학과, ．유렉셀테크놀러지(주)

Surface Modification of Polyurethane by Oxygen Plasma Treatment

Yan Zhang, Sung-Woon Myung, Ho-Suk Choi, Inho Kim, ．Jae-Hyuk Choi

Department of Chemical Engineering, Chungnam National University

220 Kung-dong, Yusong-gu, Taejon 305-764, Korea

．Urecel Technology Co., LTD., Kongdo-Myun, Ansung City, Kunggi-Do, 456-820, Korea

1.Introduction

The modification of polymer surfaces by exposure to glow discharge has become common in recent years. The thickness of the modified layer may be as much as several micrometers, depending on the parameters of the plasma (pressure, power, gas, flow rate, treatment time, etc.); However, the surface characteristics of the material are determined solely by the composition of the outermost few monolayer. The plasma surface modification technique is a dry gas-solid process usually free of secondary reactive species causing undesirable side effects.

So far, several studies have been reported on this kind of surface modification with plasma treatment. Iwata and his coworkers studied graft polymerization of acrylamide onto a polyethylene film[1] treated with an oxidative plasmas. Kang et al. [2] reported the surface modification of polyetherurethaneureas and their antithrombogenicity. Lee and his coworkers grafted acrylic acid onto a porous poly(vinylidene fluoride) membrane for its riboflavin permeation.[3]

In this study, polyurethane film was treated by O2 plasma. After plasma  treatment, polyurethane film was exposed to air to generate peroxide. As known for further grafting monomer by plasma initiation method, the more active functional groups we got the more grafting sides existed. We change different parameters of plasma treatment to get optimum conditions for maximum functional group grafting. Peroxides were confirmed by DPPH method.

2. Experiments

2. 1. Experimental Materials

Polyol, catalyst, silicon, and TDI offered by Urecel Technology Co., Ltd. Korea. 1,1-Diphenyl-2-picrylhydrazine (DPPH) purchased from Alrdrich.

2. 2. Experimental Apparatus and Methods

Preparation of PU films

Polyol (100g) was degassed for 24 hours. The degassed polyol, silicon and catalyst were put into a beaker mixing 5 min at 500rpm in the nitrogen environment. Then change the speed at 1000rpm mixing 1 min. Put TDI (46.34g) into the mixture and stir again. After 5 seconds the solution was spread on a clean glass plate and kept overnight. The polymer film was separated from the glass plate. After washed by distilled water it was subjected to the surface modification experiments.

Surface Modification of PU films by Oxygen Plasma Discharge

A schematic diagram of the apparatus used in this study is represented in Figure 1. A reactor for plasma modification consists of four main sections; reaction column, gas inlet part, vacuum system and RF (radio frequency) plasma matching system. Gas flow rate is regulated and measured with a regulator and micro needle valve, respectively. The reduced pressure in the reactor is maintained using both mechanical rotary vacuum pump (Woosung vacuum Co., 200 □/min) and diffusion pump (KODIVAC Co., 360 □/sec). TC gauge (Varian Co., 801, analog type) is used to measure pressure in the reactor. A trap captures entrained particles from the reactor. An inductively coupled electrode (4 mm-OD copper tube, 2 turn) for glow discharge at 13.56 MHz frequencies was coiled at a distance of 30 mm from gas inlet and was connected to an auto matching network and a RF power generator (YOUNGSIN Engineering Co., 0∼300W). To prevent overheating of the electrode and diffusion pump, cooling system (mechanical fan) is installed at both electrode and diffusion pump. The reactor is made of high Pyrex glass column (90 mm ID ⅹ 110 mm high ). The whole system was initially evacuated up to 10 mtorr after a PU film (2ⅹ2 cm) was placed on the holder in the reactor chamber. The pressure of the plasma chamber was adjusted by controlling micro needle valve of oxygen container and kept for 5 min. Then the plasma is generated at a given power and the film was exposed to the plasma for given times. After the chamber was degassed again for 20 min, followed by introduction of Ar for 20 min. The surface treated film was taken out of the chamber and was exposed to air to generate peroxide.

Quantitative Analysis of Peroxide

For plasma treated film, the amount of peroxide formed on the PU surface was determined using a 1,1-diphenyl-2-picryl-hydrazyl (DPPH) method. [4] Mixing 254ml benzene (Bz) with 0.01g 1,1-diphenyl-2-picryl-hydrazyl (DPPH) to make 1.0ⅹ10-4 mol/l DPPH-Bz solution, followed by degassing and nitrogen purging. The plasma treated film was exposed to the air for 5 min. The unstable radical reacted with the moisture in the air to become peroxide. Then the film was inserted 4 ml DPPH-Bz solution and kept at   70□C for sometime to decompose the peroxides formed on and near the film surface. The DPPH molecules consumed were checked from the spectrophotometer at 520 nm.

The concentration of the peroxide can be got from the calibration curve in which UV absorbance of DPPH in benzene at 520 nm was as a function of DPPH concentration. Checking the absorbance of different diluted DPPH solution can get the calibration curve.

3. Results and Discussions

Polyurethane film was subjected to the oxygen plasma treatment for the generation of free radicals on the film surface and exposed to air for 5 min. The DPPH method was found to be effective for determining the concentration of peroxides formed. The principle of this method is to measure the consumption of DPPH when the plasma-treated film is put in a tolene solution containing a given amount of DPPH and kept at 70□C to decompose the peroxides.

The decomposed peroxide concentration calculated from the DPPH consumption as a function of the incubation time at 70□C for the film exposed to oxygen plasma for 60s at 100W can be seen in fig 2.

We found that the dependence of the peroxide formation on the glow discharge time shows a maximum. It was difficult to give a clear explanation for the appearance of a maximum. The long time oxygen plasma exposure doesn't help generating more peroxide, so it is possible the peroxides have been produced during film exposing to air after plasma treatment. The peroxides formation mechanism was well proposed by Iwata and his coworkers.[1]

4. Conclusions

In this study, we know that, since our polyurethane foam is very stable in solvent, it can't cast in casual film casting method. So we directly cast film after synthesizing polyurethane prepolymer. Since the sizes of film and the quantity of DPPH solution affect the incubation time, we found the fitful size film to shorten incubation time. Functionalized polyurethane surface can be prepared by plasma treatment. We got much more times peroxide on the surface comparing with other researchers results. It will be capable of generating high densities of a single functional group suitable for subsequent derivatization.

5. Reference

1. M. Suzuki, A. Kishida, H. Iwata, Y. Hata, and Y. Ikada, Macromolecules, 19, 1804, (1986).

2. K. Kang, O. H. Kwon, K. H. Byun, J. Materials Science: Materials in Medicine, 7, 135, (1996).

3.Y. M. Lee, J. K. Shim, J. Appl. Polym. Sci., 61, 1245-1250, (1996).

4. S. R. Palit, J. Polym. Sci., 58, 1225-1232, (1962).

Figure 1.Reactor of plasma treatment.

Fig.2 Effect of incubation time on the concentration of peroxide

plasma condition: 100W, 60s, 200mtorr.