Polypropylene film chemical and physical modifications by dielectric barrier discharge plasma treatment at atmospheric pressure

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Abstract

Dielectric barrier discharge (DBD) technologies have been used to treat a polypropylene film. Various parameters such as treatment speed or electrical power were changed in order to determine the treatment power impact at the polypropylene surface. Indeed, all the treatments were performed using ambient air as gas to oxidize the polypropylene surface. This oxidation level and the surface modifications during the ageing were studied by a wetting method and by X-ray photoelectron spectroscopy (XPS). Moreover polypropylene film surface topography was analyzed by atomic force microscopy (AFM) in order to observe the surface roughness modifications. These topographic modifications were correlated to the surface oxidation by measuring with a lateral force microscope (LFM) the surface heterogeneity. The low ageing effects and the surface reorganization are discussed.

Graphical abstract

This LFM figure shows that atmospheric plasma treatments oxidise (creation of polar groups) PP film at localised bumps. We suggest a dewetting process of the treated PP during the treatment.

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Introduction

The polypropylene is one of the most common polymers used in industry in spite of its lousy wetting and adhesion properties. Plasma treatments should enhance these properties. I. Novak et al. [1] and M. Sira et al. [2] showed that air atmospheric plasma treatments increased the polypropylene surface free energy and more precisely the polar component from 34 to 49 mN/m with a DBD plasma treatment during 10 s [2]. I. Novak et al. [1] showed that a corona treatment at atmospheric pressure increased the surface free energy from 34 to 39.2 mN/m but this treatment is not stable because the surface free energy goes down from to 39.2 to 37 mN/m after 30 ageing days.

Using XPS analyses a lot of studies [2], [3], [4] showed that there is an increase of the polypropylene surface oxygen amount after a plasma treatment. The O/C ratio changes either with the type of plasma discharge and gas used. Indeed, according to various publications, the O/C ratio goes from 0.14 (atmospheric pressure air plasma treatment) [2] to 0.29 (atmospheric pressure H2/O2 plasma treatment) [4]. This O/C ratio increase is due to the creation of oxidized groups such as hydroxyl, carbonyl and carboxyl groups at the polymer surface. Same results were obtained on many other polymers [5], [6], [7] like polyester, polyethylene, polyamide, etc.

DBD plasma treatments with air modify the surface roughness of polypropylene film. This modification depends on the treatment time and power [8]. By the way, the surface roughness modification depends also on the gas used for the treatment [9], [10]. Indeed the roughness modification is higher with gas like CO2, O2 or N2 than with argon. The plasma discharge type has also an impact on the surface roughness because a corona treatment gives an higher surface modification than a Atmospheric Plasma Glow Discharge (APGD) or DBD treatments [2].

With a plasma treatment the polar groups creation at the polymer surface and the surface roughness modification increase the coating adhesion between polypropylene materials and polyvinyl acetate as shown by I. Novak et al. [1]. Unfortunately this better adhesion behaviour decreases strongly within the 50 days following the treatment. This coating adhesion decrease is mainly due to the bad ageing behaviour of the treatment, indeed the surface oxidation decreases with time. This adhesion increase was also observed with many other polymers such as polyethylene terephthalate with rubber [11], carbon fibers with epoxy resin [12] or polyester fabric with fluoropolymers [13].

The main interest of this paper was to study the impact of an atmospheric plasma treatment with air using the dielectric barrier discharge technology (DBD) on a polypropylene film. We followed the oxidation ageing of these treatments. Moreover a correlation between the topographic and chemical surface modifications was made.

Section snippets

Material

One pure polypropylene film was used. Table 1 gives the characteristics of this film. The surface free energy of the polypropylene film is 33.7 mN/m and it has no polar component.

Plasma treatments

Atmospheric plasma treatments were carried with the “Coating Star” from Ahlbrandt System (Fig. 1). Plasma discharge was generated at atmospheric pressure by two electrodes and a counter-electrode both covered by a dielectric material (ceramic). The counter electrode was a roll shaped type. The reactive gas used with

Results

For this study, two treatment parameters were changed. The first one was the electrical power. Four values were chosen, from the lower to the higher one: 300, 500, 700 and 1000 W. The second parameter was the treatment velocity. For this parameter, four values were also chosen: 2, 5, 7 and 10 m/min. All results were given as a function of the treatment power (TP).

Discussion

DBD plasma treatments at atmospheric pressure increase the polypropylene film surface free energy (Fig. 3) very easily even with a low treatment power. Indeed a treatment with TP = 3.6 kJ/m2 increases the surface tension from 33.6 to 44.9 mN/m and with a TP = 60 kJ/m2 to 50.2 mN/m. This surface free energy increase is mainly due to an increase of its polar component. It is also very important to notice that the surface free energy obtained by these treatments is very stable in time as after one

Conclusion

Dielectric barrier discharge plasma treatments at atmospheric pressure using air as a plasma gas give a permanent oxidation of the polypropylene surface. This oxidation increases the polymer surface free energy from 33.6 to 47.7 nN/m by adding polar groups such as hydroxyl, carbonyl and carboxyl depending of the treatment power. The ageing has just a very low impact on the surface tension property but in this paper a gradient of reduction of the oxidized groups was highlighted as a function of

Acknowledgments

The authors acknowledge the French “Region Nord-pas-de-Calais” for their financial help. We acknowledge Christian Catel (GEMTEX—Roubaix) for his precious help. We also acknowledge Martine Frère (UCCS—University of Lille1/France) for her help concerning the XPS analyses, Denis Tondelier (IEMN—University of Lille1/France) for the AFM analyses and Loic Brunet (CCMIC—University of Lille1/France) for the MEB images and Marie France VALLAT (ICSI—Universite de Haute Alsace) for helpful discussions.

References (27)

  • G. Borcia et al.

    Appl. Surf. Sci.

    (2004)
  • G. Borcia et al.

    Appl. Surf. Sci.

    (2004)
  • C. Wang et al.

    Surf. Coat. Technol.

    (2006)
  • H. Krump et al.

    Appl. Surf. Sci.

    (2006)
  • F. Leroux et al.

    Appl. Surf. Sci.

    (2008)
  • C.M. Chan et al.

    Surf. Sci. Rep.

    (1996)
  • I. Karapanagiotis et al.

    Surf. Sci.

    (2005)
  • C. Luo et al.

    Surf. Sci.

    (2004)
  • I. Novak et al.

    J. Mater. Sci.

    (2004)
  • M. Sira et al.

    J. Phys. D Appl. Phys.

    (2005)
  • P.P. Tsai et al.

    Tex. Res. J.

    (1997)
  • M.G. McCord et al.

    Tex. Res. J.

    (2002)
  • F. Leroux et al.

    J. Adhes. Sci. Technol.

    (2006)
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