“plasmamodifizierung von polyethylen” dissertation zur erlangung ...

Kapitel 4: Zusammenfassung und Schlußfolgerung 101
By the " acid index " a close relationship between process pressure and power could be shown. During
the parameter combination RF-50 W; 0.4 mbar the highest acid index (1,69) was achieved. Also here
the RF plasma was superior to the microwave.
A further meaningful method for the characterisation of surface functionalizations is the determination
of the surface tension from contact angel. A dependency of the surface tension on the used process
gas, the process time and slightly also of the frequency could be proven during the plasma activation.
The surface tension was increased most clearly by the plasma treatment with Nirogen, followed of the
treatment with Argon and Oxygen. A process time of 3 min is sufficient for an uniform surface
treatment under the given conditions. On the basis of the calculation of the polar and disperse proportions
of the surface tension was shown that by the plasma activation the polar proportions of the
surface tension are essentially increased, in the most favorable case around 10 - 20 drawer than the
basic material (e.g. A27 MA: from 1,20 mN/m to 21,77 mN/m). Similar predicates apply to the
plasma polymerization. The polar proportions of the surface tension were increased also here (from
1,4 mN/m to 25,0 mN/m). Against what the influence on the disperse proportions remains small. A
significant influence of the process parameters on the surface tension could not do proven.
By the plasma treatment the adhesion of the LDPE powder was influenced. This could be proven by
the modification of the adhesive strength. The used process gases possess the most significant
influence on the adhesion during the plasma activation. A max. adhesive strength of 6,49 N/mm²
could be achieved at the Oxygen-Plasma. Additionally easy rising of the adhesive strength with
increase of the process power and the gas flow were determined. The functional groups inserted by
plasma polymerization influenced the adhesion of the polyethylene powder on metallic background
likewise substantially. An improvement of the adhesive strength of 1,12 N/mm² on max. 6.92 N/mm²
was achieved. Also here a connection between process power and pressure could be proven. Whereby
already low acrylic acid quantities on the powder surface are sufficient, in order to achieve a clear
improvement of the adhesive strength.
The basic characteristics (melt and crystallization behavior) of the polyethylene powders were
changed neither by the plasma activation nor by the plasma polymerization.
The individual analysis methods (ESCA, FTIR, surface tension, adhesive strength) showed that they
are suitable by plasma processes for the problems of the proof caused by functional groups on powder
surfaces. The individual results of analysis are comparable well together and in itself conclusive. From
these investigations it follows that the incorporation of the functional groups and thus the adjustment
of the required surface properties can be controlled by the variation of the process parameters directly
and adapted to the application. Similar modification results are achieved by both procedures. A
comparison of the two plasma processes shows that the activation in the plasma is to be preferred
regarding the processing and time of the plasma polymerization.