Typical tissue products include two or three paper plies with porous structure and low layer densities of around 15 to 30 g/cm2. They are made by conventional papermaking methods, with the addition of wet and dry strength agents, surfactants and other chemicals to impart the required mix of special characteristics. This process requires a large volume of water that is recycled as far as possible - the process chemicals are the limiting factor.
Some attempts have been to resolve these problems by employing vacuum plasma techniques to modify the surface of the lignocellulosic paper fibres. However, such treatment is costly and tends to reduce the absorbency of the material. Furthermore, it is restricted to batch throughput, which is incompatible with the high-speed continuous operation of a paper mill. Plasma treatment in air has also been examined, but this causes oxidation ageing and, again, a loss of absorption.
The ECOTISSUE team has therefore set out to explore the use of glow discharges in appropriate controlled gaseous mixtures at atmospheric pressure. As a result of earlier collaboration between some of the partner companies, a sound foundation of knowledge was already available, while an existing pilot plant is available for trials. With Commission support, the new research is expected to deliver, by the end of the funded period, the basis for a commercially viable solution.

The effects of gas plasma techniques (as used in the plastics industry today) are confined to the upper surface of the treated substrate, whereas it is desirable to modify the whole fibre network in a tissue matrix. This requires the development of a suitable large-area homogeneous glow discharge device, with special cathode design to prevent reversion to an arc discharge at ambient pressure.
A further task to be accomplished is the continuing study of the surface chemistry of the fibres, including advanced analytical examination to establish the physical and compositional changes taking place, and the uniformity of treatment that can be achieved.
Comparative testing will also be carried out, to determine the possibility of adapting established dielectric barrier discharge (DBD) methods to three-dimensional tissue materials, and to evaluate these against the new technology proposed by the consortium itself.
Treatment in an atmosphere consisting of inert nitrogen dosed with small amounts of, for example, carbon dioxide (CO2) or nitrous oxide (N2O), permits oxidation to be controlled, while the addition of precise amounts of silane (SiH4) results in the deposition of a thin silica layer that promotes permanent hydrophilic - water absorbing - properties.
The quantities of chemicals used in this process will be extremely low. In most cases they will react totally in the discharge area, giving rise to zero emissions - and any excesses due to imbalance can easily be extracted by gas purifier systems. Reduction or elimination of wet strength chemical additives will also facilitate water recycling, contributing to the drive for a totally closed loop water system in tissue paper manufacturing.

At present, gas plasma treatment could be incorporated either in the converting stage or in the tissue paper making process without requiring major plant modifications.
Significant economic benefit is likely to derive from the project, in terms of equipment and product sales within the EU and, ultimately, throughout the world. Exploitation of the results will strengthen the market position of the partners vis-à-vis US and Asian competition, as well as contributing to the sum of knowledge in the European scientific community. Derivative technologies can also be expected to find application in other product sectors - from packaging film and board to medical materials and textiles.