Regarding the origin of the improved anti-felting behaviour, contradictive explanations are proposed. According to us the anti-felting behaviour is due to an increase in fibre/fibre friction. This reduces the slipping of the fibres one to another that causes the shrinkage and felting of the wool material. The increased friction offers also an explanation for the increased yarn tenacity and elongation at break. It was indeed shown that fibre/fibre friction can be increased with more than 50 % after plasma treatment of wool sliver.

Treatment of cotton

Similar effects can be observed after treatment of cotton fabrics or yarns in oxygen plasma. In general the effects such as improved wettability, increased strength or fibre/fibre friction are less pronounced if compared to wool materials.

Much depends upon the level of pre treatment already applied to the material. For instance regarding wettability the improvements are not significant if the plasma treatment is applied to full bleached cotton. If intensive oxygen plasma treatments are applied to cotton fabric also negative effects can be observed namely a reduced tear and abrasion resistance. The negative impact can be minimised by selecting appropriate treatment conditions.

Treatment of PP

PP is a very interesting material for plasma treatment. PP is a very hydrophobic material with extreme low surface tension. On the other hand PP is used in a large number of technical applications were an improved wettabillity or adhesion properties are advantageous. This is also the case for PP technical textile applications such as filters, medical or hygiene applications etc.

Using an oxidative plasma important improvements in surface tension can be obtained within a very short plasma treatment. In order to obtain an optimisation of the plasma effects, a systematic approach (factorial experimental design) was followed for the evaluation of the plasma parameters upon the obtained effects.

PP non-woven filter webs were used as test samples. The treated samples were tested for wettability using liquids with a range of surface tensions and also the filtration time for fixed amounts of water was determined. Reference materials without plasma treatment can only be wetted with liquids with surface tension < 35 mN/m.

Without treatment, no water can pass trough the PP-web without applying a high pressure.

Treatments were performed with two different plasma generators: a kHz and a GHz system. In both cases a 64 I. plasma chamber is used. Parameters varied were: treatment time, vacuum level, treatment power. In addition some tests were performed with an adapted gas composition in stead of using 02.

The obtained effects were somewhat surprising. As expected we could observe for all plasma treatments an increase in surface tension. However the Increase in surface tension is not in correlation with the intensity of the plasma treatments. We expected an increase in the Improvement in the wettability properties the higher the plasma power and the treatment time is and the lower the vacuum pressure is. Once an optimum level is reached we expected the wettability would become constant and independent from the treatment intensity.

The results showed that an increase in wettability can indeed be observed but only at relatively low treatment intensities. Once the optimum is reached a sharp drop in wettability is obtained if the plasma treatment intensity is raised further. For instance a treatment in the kHz apparatus at 250 mTorr, 200 Watt and 120 sec. gives far better results than a treatment at 150 mTorr, 800 Watt and 240 sec. Especially the vacuum pressure and the applied plasma power have a large influence upon the observed over-treatment.

Also for the GHz plasma treatments similar effects are observed, although in general the treatment parameters are less critical. Using the GHz instrument it was observed that efficient plasma treatments still can be obtained at a relatively high vacuum pressure level of 1500 mTorr and higher. This can offer advantages since a high vacuum is difficult to maintain especially during continuous processes.

Most trials were performed with O2 as plasma gas, since it was thought this gas would offer the best results for an oxidative treatment in order to obtain wettability.