22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Crystal structure changes of polypropylene films during surface modification by
atmospheric pressure dielectric barrier discharge
D.A.G. Sawtell1, Z. Abd Allah2, L. Simmons3, J.W. Bradley2, G.T. West1 and P.J. Kelly1
1
2
Surface Engineering Group, Manchester Metropolitan University, Manchester, U.K.
Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool, U.K.
3
School of Engineering, Manchester Metropolitan University, Manchester, U.K.
Abstract: Atmospheric pressure plasma treatment of polypropylene films is an industrially
significant process. Work presented here aims to further understanding of the mechanisms
occurring during the plasma modification process, in particular the effects of the plasma on
the crystal structure of the polypropylene films. This is supported by comprehensive XRD
and FTIR studies of treated films.
Keywords: surface modification, atmospheric pressure plasma, polypropylene
1. Introduction
Efficient plasma modification of polymeric web at
atmospheric pressure is of great industrial interest, due to
the environmental benefits and cost savings such a
process route provides. Atmospheric pressure plasma
systems used for this purpose are characterised by high
throughputs of polymeric web, and wide electrodes
perpendicular to the direction of web transfer. Although
some work has been carried out to elucidate the
mechanisms occurring on the surface of the
polypropylene during plasma treatment, they have been
under a limited set of conditions, and do not take into
account the crystal structure of the polymer [1, 2].
Understanding mechanisms and the structural changes
that occur to the polypropylene when plasma treatments
are made is key to improving the surface treatment
process.
This suggests that there is a structural change in the
polypropylene film caused by the plasma treatment.
2. Methodology
A series of treatments have been made to polypropylene
films using a dielectric barrier discharge reactor.
Nitrogen, both on its own, and with small concentrations
of acetylene, nitrous oxide and carbon dioxide, were used
as the process gases. XRD was then used to assess crystal
structure changes of the polypropylene due to the
treatment process, whilst FTIR spectroscopy was used to
corroborate these measurements as well as examine the
functional groups that have been formed on the surface of
the treated polypropylene. White light profilometry was
used to assess changes in surface topology, whilst surface
energy calculations were made from contact angle
measurements.
Fig. 1.
XRD patterns of treated and untreated
polypropylene films.
3. Results
XRD results are shown in Fig. 1. The shift to higher
angles exhibited in the diffraction patterns by the nitrogen
plasma treated polypropylene samples indicates a
decrease in the lattice parameters of the crystal structure.
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Fig. 2 represents example FTIR spectra for untreated
and plasma treated polypropylene. The peaks at 997 cm-1,
973 cm-1 and 840 cm-1 all exhibit changes after plasma
treatment, and this is due to changes in crystalline
structure of the polypropylene samples [3]. Fig. 3 shows
the ratios of these peaks with increasing plasma treatment
time, and they all exhibit an increase in crystallinity after
plasma treatment. This is perhaps due to preferential
etching of the amorphous regions in between the
crystalline lamella within the polypropylene.
4. Conclusions
Polypropylene films treated by atmospheric pressure
dielectric barrier discharge exhibit crystallinity changes
that appear to be due to the preferential etching of
amorphous regions during the plasma treatment process.
1
Fig. 2.
FTIR spectra of treated and untreated
polypropylene films.
Fig. 3. Infrared peak ratios at 997 and 973 cm-1 for
different treatment times and powers.
5. References
[1] R. Dorai and M. Kushner. J. Phys. D: Appl. Phys.,
36, 6 (2003)
[2] C. Klages, et al. J. Adhesion Sci. Technol., 24, 6
(2010)
[3] R.G. Quynn, et al. J. Appl. Polymer Sci., 2, 5 (1959)
2
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