Plasma Modification of Paper by Means of Surface Barrier Discharge

Plasma-enhanced chemical vapour deposition (PECVD) at atmospheric pressure becomes a promising technology. The objective of the present work is to develop technique for deposition of thin films with desired properties on paper surface by means of atmospheric pressure discharge. The depositions were carried out by the means of surface discharge at atmospheric pressure. The films were deposited from the mixtures of C4F8 with nitrogen. The properties of the thin films were investigated by means of the contact angle measurement and industrial permeability tests. The mechanical properties were studied by means of the depth sensing indentation test. Introduction Surface activation of polymeric materials by means of plasma has been extensively reported, including the surface treatment of paper, wood and other cellulose based materials [1 5]. The plasma treatment has the advantage of easy and ecological utilization and enables to modify the surface properties of polymeric materials in order to increase or decrease their surface free energy, while retaining their useful bulk properties unchanged. The most abundant functional group on the polymeric components of cellulose based materials is the hydroxyl group, followed by other oxygen containing functionalities. Due to the presence of hydroxyl and other polar groups, the cellulosic materials have a very high affinity for water. These characteristics can cause several disadvantages like: weathering degradation, biological degradation or swelling. Considerable work has been done in the last years in plasma treatment of cellulose based materials in order to protect their surface against water penetration. Most of the applications were taken at reduced pressure [1-3], where the spatially homogeneous plasma can be easily generated. However, the use of expensive vacuum systems that force batch processing has discouraged this application of low-pressure plasmas in larger industrial scale for treatment of low-cost materials. Thus it is apparent that such low-pressure plasma systems cannot be utilized for standard paper production lines. The atmospheric-pressure plasma processes offer several advantages for the modification of low-cost cellulosic based materials: costly vacuum equipment is not necessary, processing times are reduced and the plasma modification is simpler than in low pressure plasma reactor. Recently, mainly atmospheric corona or silent discharge devices are used for surface treatment of polymeric materials. In these cases the useful plasma conditions are achieved only in small volume plasma channels called "streamers", developing perpendicularly to the material surface. As a consequence, the plasma is in a very limited contact with the surface. This results in low processing speeds, typically in the order of 1 m/min. Moreover, the localised arcing may result in the formation of pinholes in the material being treated, because the plasma channels and arcing are an intrinsic phenomenon associated with this discharge type. The disadvantages of corona and silent discharges can be eliminated using atmospheric pressure glow discharge (APGD), however APGD is very sensitive to gas purity and to optimisation of electrode arrangement and these facts limit its applicability [7]. The objective of the present work is to develop technique for surface modification of cellulose (paper) using atmospheric pressure surface barrier discharge (SD) [8]. The SD is certain type of barrier discharges, which enables us to eliminate the above listed disadvantages of the standard barrier discharge treaters. WDS'05 Proceedings of Contributed Papers, Part II, 332–336, 2005. ISBN 80-86732-59-2 © MATFYZPRESS