Effect of plasma treatment on hydrophobicity and barrier property of polylactic acid C. Chaiwong a,b, ⁎, P. Rachtanapun c , P. Wongchaiya c , R. Auras d , D. Boonyawan a,b a Plasma and Beam Physics Research Facility, Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand b ThEP Centre, 328 Sri Ayuddhaya Rd., Bangkok 14000, Thailand c Department of Packaging Technology, Faculty of Agro-Industry, Chiang Mai University, Chiang Mai 50200, Thailand d School of Packaging, Michigan State University, MI, United States abstract article info Available online 26 February 2010 Keywords: Plasma treatment Polylactic acid Hydrophobicity Barrier property In this work, we investigated the influence of SF 6 plasma generated by an inductively coupled discharge on the hydrophobicity and barrier properties of poly(lactic acid), PLA. It was found that SF 6 plasma enhanced the hydrophobicity of PLA as observed in the increase of the water contact angle. Water absorption time of the plasma-treated PLA was two-fold increased. However, the plasma treatment did not have significant influence on water vapor permeability of PLA. The differential scanning calorimetry results revealed that the bulk structure which controls transportation property of PLA remained unchanged after plasma treatment. Atomic force microscopy showed topographical modification after plasma treatment. Attenuated total reflectance Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy showed the bounding of fluorines in the PLA structure, which leads to the increase in hydrophobicity of PLA. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Petroleum-based polymers such as polystyrene, polyamide and polyethylene have been used as packaging materials extensively because they are available in large quantities at low costs. Recently, awareness towards environmental pollution resulting from the accumulation of waste disposal of these non-biodegradable polymers leads to the creation and development of packaging materials, which are biodegradable and compostable. Polylactic acid (PLA), an aliphatic polyester made up of lactic acid building blocks, is one of the biodegradable polymers that are increasingly being used due to their mechanical, thermal and barrier properties. PLA has been considered a promising polymer to alleviate the waste disposal problems and minimize the use of petroleum-based polymers. PLA is derived from renewable plant sources such as corn, cassava and sugarcane. Earlier, PLA has been used mainly in biomedical applications. However, new PLA process technologies have been studied and developed to mass production of PLA. Thus, new PLA applications have been developed [1,2]. Although PLA may offer a substitute for many non-biodegradable polymers, it has a number of drawbacks for some applications that may limit its broad application. Barrier properties of PLA are lower than some petroleum-based polymers such as poly(ethylene terephthalate), PET, which is used widely as food packaging material [3,4]. Therefore, for PLA to be used in some packaging applications, its barrier properties have to be improved. Recently, a number of techniques have been utilized for modifying the barrier properties of polymers including coating polymers with films [5,6], addition of inorganic/organic compounds [7,8], and co- extrusion [9]. However, these techniques present some disadvantages such as adhesion failure of coating films upon mechanical deforma- tion, deteriorated mechanical properties of polymers and changing of color of polymers. The process of co-extrusion and addition of compounds may increase the production cost associating with the processing facility. The use of plasma treatment appears to be suitable for industrial application as solvents are eliminated and the treatment time is short to achieve significant change in the properties governed by surface characteristics. Plasma treatment is one of the new technologies to achieve the modification of surface characteristics of polymeric materials. The interactions between the plasma and the surface molecules of polymers lead to the surface phenomena such as etching, cross- linking and activation [10,11]. Depending on the conditions and the plasma species, surface properties of polymer, such as morphology, hydrophobicity and adhesion can be altered [12–15]. It has been demonstrated that fluorination of polymer surface can be achieved through fluorine radicals generated in the fluorine containing plasmas. Fluorinated polymers have unique properties including good chemical stability and improved barrier properties [16–18]. To our knowledge, there is no work reported on SF 6 treatment of PLA. In this work, we investigated the effect of SF 6 plasma on the barrier characteristics of PLA films. SF 6 was chosen based on its low polymerization with respect to fluorocarbon compounds [19]. Surface morphology and mechanical as well as thermal properties of PLA were evaluated. Surface & Coatings Technology 204 (2010) 2933–2939 ⁎ Corresponding author. Plasma and Beam Physics Research Facility, Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand. Tel.: +66 53 943 379; fax: +66 53 222776. E-mail address: cchwng@gmail.com (C. Chaiwong). 0257-8972/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2010.02.048 Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat