Surface modification of polymer fibre by the new atmospheric pressure cold plasma jet

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Abstract

A new cold plasma jet has been developed for surface modification of materials at atmospheric pressure. This new cold plasma jet generator is composed of two concentric cylindrical all-metal tube electrodes. The argon is fed into the inner-grounded electrode, the outer electrode is connected to the high-voltage power supply and covered with a layer of dielectric, and then a stable cold plasma jet is formed and blown out into air. The plasma gas temperature is only 25–30 °C. Preliminary results are presented on the modification of polypropylene (PP) and polyethylene terephthalate (PET) fibres by this cold plasma jet. The water contact angle of these materials is found to decrease after plasma treatment and it will recover a little in two months. The chemical changes on the surface of polymers are studied by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) is used to study the changes in surface feature of polymers due to plasma treatment. The hydrophilicity and surface structure of these materials after plasma treatment are discussed. The results show that such a plasma jet is effective.

Introduction

Polypropylene (PP) and polyethylene terephthalate (PET) fibres are used for a wide variety of applications in many technological fields because they have some excellent bulk properties, such as high strength-to-weight ratio, good resistance to corrosion and relatively inexpensive to produce [1]. However, polymers are innately hydrophobic, low-surface energy materials, and thus do not adhere well to other materials. It is necessary to modify their surfaces to increase the surface free energy while keeping their bulk properties for many commercial applications. Traditional methods of surface treatment are mostly chemical processes [2]; however the ecological requirements force the industry to search alternative environmental safety methods. The application of cold plasmas to the treatment of polymeric materials has become increasingly important in recent times [3], and it can improve the surface properties of polymers without affecting their bulk properties.

Many plasma applications in the field of surface modification are made at reduced pressures in the order of 1–10 Pa, and many kinds of low-pressure plasma systems have been developed up to now. These systems need vacuum equipments, which make complexity and cost for materials processing. Atmospheric pressure plasma devices can provide an advantage over low-pressure plasma systems because they do not need vacuum equipment and they have been shown to be of prospect for a number of industrial. Recently, a few novel atmospheric pressure plasma sources have been developed, such as the one atmosphere uniform glow discharge plasma (OAUGDP) [4], the atmospheric pressure surface discharge [4], the cold plasma torch [5], and the atmospheric pressure plasma jet (APPJ) [6]. The discharge regions of these plasmas are so limited that they are not suitable to treat bulky or complex objects except APPJ and the cold plasma torch. The gas temperatures of APPJ and the cold plasma torch are about 50–300 °C, thus thermal damage to treated materials can be easily avoided. For these reasons, they can be easily employed in commercial run. Atmospheric pressure plasma have shown great promise when applied to change the surface properties of polymers, and the better hydrophilicity of polymers is achieved [1], [7], [8], [9], [10].

In this paper, we will show a new atmospheric pressure cold plasma jet (APCPJ) generator which is excited by a low-frequency (6–20 kHz) AC power supply. Compared with APPJ and the cold plasma torch, the gas temperature of the APCPJ is lower, which is about 25–30 °C, so the cold plasma jet is more suitable for treating vulnerable objects. We have used it for sterilization because of its low temperature [11]. Polypropylene (PP) and polyethylene terephthalate (PET) fibres are treated with the APCPJ and the hydrophilicity and surface structure of the treated surface is examined.

Section snippets

Experimental set-up

Fig. 1 schematically shows the experimental set-up for the APCPJ. An all-metal tube electrode is placed inside another all-metal tube electrode covered with a layer of dielectric Teflon. The inner tube electrode is connected to the ground and the outer one is connected to a low-frequency AC supply (6–20 kHz). Feed gas (Ar) flow through the inner tube at the gas flow rate of 50–2500 l/h, and the plasma jet form at the nozzle. We can obtain steady and homogenous plasma, when the peak-to-peak

Results and discussion

PP and PET fibres are treated by the APCPJ, and the results of hydrophilic modification achieved by the APCPJ are investigated by water contact angle measurement. The water contact angle of the APCPJ-treated PP and PET fibres vs. the treatment time is shown in Fig. 4. The original water contact angles of PP and PET fibres are 120° and 150°, respectively. The decrease of water contact angle of PET is more than that of PP after they are treated by the APCPJ under the same condition. The water

Conclusions

A new plasma generator has been developed, which can produce a stable cold plasma jet at atmospheric pressure using pure argon. The size of the cold plasma jet is varied with the diameter of the nozzle and the gas flow rate, and its gas temperature is only 25–30 °C. This cold plasma source is used for polymer surface modification and the water contact angle of polymers decrease evidently. The analysis of FTIR and XPS show that the oxygen functional groups, such as –C6-point double bondO, –OH, and COO–, are

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