Adhesion enhancement of electrospun nanofiber mats to polypropylene nonwoven fabric by low-temperature oxygen plasma treatment Fabio Rombaldoni a, ⁎, Khalid Mahmood b , Alessio Varesano a , Michela Bianchetto Songia a , Annalisa Aluigi a , Claudia Vineis a , Giorgio Mazzuchetti a a National Research Council — Institute for Macromolecular Studies (CNR-ISMAC), Corso G. Pella 16, 13900 Biella, Italy b Politecnico di Torino — Biella Campus, Corso G. Pella 2/B, 13900 Biella, Italy abstract article info Article history: Received 17 September 2012 Accepted in revised form 20 November 2012 Available online 24 November 2012 Keywords: Electrospinning Nanofibers Plasma treatment Adhesion Polypropylene In this work, adhesion of different nanofiber mats to a polypropylene nonwoven was studied. In particular, low-temperature oxygen plasma treatment was investigated as a potential interface engineering tool to use for en- hancing adhesion between polypropylene nonwoven and nanofibers. Poly(ethylene oxide) (PEO) and polyamide-6 (PA6) nanofibrous mats were deposited onto a polypropylene nonwoven, both untreated and plasma-treated, by single-jet solution electrospinning, using the same process parameters (with the exception of flow rate) identified to be effective for coating the substrate with almost defect-free nanofiber mats. Electrospun PA6 nanofibers were finer (diameters lower than 300 nm) than PEO ones (mean diameter about 450 nm); consequently, webs in which nanofibers got closer to each other and formed smaller pores were produced with PA6, this implies that the final air permeability of the multilayered material formed by the nonwoven and the nanofibrous mat was lower when using PA6 than when using PEO (about 50 lm −2 s −1 for PA6 nanofiber-coated substrate and about 120 lm −2 s −1 for PEO nanofiber-coated one). The coated area of the nonwoven substrate by nanofiber coating was larger when PA6 was used (about 100 cm 2 ), while smaller coatings were obtained using PEO (coated area about 50 cm 2 ). All these properties were not influenced by the plasma treatment. On the contrary, the adhesion of nanofiber mats to polypropylene nonwoven, characterized by means of a customized 180° peeling test, was dras- tically enhanced by oxygen plasma treatment. In particular, PEO nanofibrous mats were proved to adhere to treated polypropylene substrate better than PA6 ones. Mean adhesion energy between untreated polypropylene nonwoven and nanofiber mat was 0.58 and 0.39 J/m 2 for PEO and PA6 nanofibers, respectively. After the plasma treatment of the substrate, the values significantly increased to 4.80 J/m 2 for PEO nanofibers, and to 0.89 J/m 2 for PA6 ones. © 2012 Elsevier B.V. All rights reserved. 1. Introduction It is well-known that solution electrospinning is a simple and versa- tile process for producing nanofibers having many potential applications (e.g. high-tech fibrous materials for filtration and phase separation, cata- lysts, sensors for chemical detection, individual protection and biomedi- cal devices). Despite some recent advances, the large-scale nanofiber production is still the major unresolved problem. Nevertheless, other challenges have to be faced on the basis of the final application of electrospun nanofibers, and new knowledge is required. In particular, for filtration [1,2], clothing [3] and protective textiles [4–7], electrospun nanofibers need to be deposited on a supporting substrate (usually textile materials such as woven or nonwoven fabrics, dielectric by nature) because of their limited mechanical properties and to enhance their handling and further transformation, such as, for example, pleating and assembly for filter production. For such applications, two key aspects need to be investigated: (1) the effect of a non-conducting textile placed between jet-emitting source and collector; and (2) the adhesion of electrospun nanofibers to the textile substrate onto which they are deposited. Very few works have dealt with such issues [8–10]. The first aspect was considered in our previous work [8], that reported on the effect of a polypropylene nonwoven placed between a multi- nozzle jet-emitting source and the metallic collector. The work highlight- ed how shielding the electric field changes the electrospinning conditions, nanofiber morphology, stability of jets and fiber deposition on the collecting surface, due to various perturbation phenomena of the electri- cally driven jets, namely switching off of the jet at nozzle, spraying and blowing up (the drop expands and splits into a multitude of jets/droplets flowing from its apex). The second aspect was preliminarily approached in this work, in which the adhesion of different electrospun nanofiber mats to the poly- propylene nonwoven fabric was studied. In particular, low-temperature plasma (LTP) treatment of the supporting fabric before nanofiber coating was used in an attempt to modify its surface structure and properties and enhance bonding and, consequently, adhesion (otherwise very poor) between it and nanofiber mats. Surface modification by cold plasma treat- ment has been widely used for textiles and polymeric materials [11], and Surface & Coatings Technology 216 (2013) 178–184 ⁎ Corresponding author. Tel.: +39 015 8493043; fax: +39 015 8408387. E-mail address: f.rombaldoni@bi.ismac.cnr.it (F. Rombaldoni). 0257-8972/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.surfcoat.2012.11.056 Contents lists available at SciVerse ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat