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Nondestructive testing of defects in adhesive joints

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Stress (MPa)<br />

26<br />

24<br />

22<br />

20<br />

18<br />

16<br />

14<br />

12<br />

10<br />

8<br />

6<br />

4<br />

2<br />

SU (S: S-SBR; U: Untreated silica)<br />

SPTh (S: S-SBR; PTh: Plasma-thiophene coated silica)<br />

ST (S: S-SBR; PTh: Silane-treated silica)<br />

0<br />

0 100 200 300 400 500 600 700 800<br />

Stra<strong>in</strong> (%)<br />

Fig. 3: Tensile properties <strong>of</strong> untreated, PTh- and silane-treated silica filled SBR<br />

In a PTh-silica filled EPDM, the material shows higher tensile strength and elongation at<br />

break values due to a better dispersion and compatibilization with the polymer. However,<br />

lower<strong>in</strong>g <strong>of</strong> the modulus <strong>in</strong> EPDM shows the formation <strong>of</strong> a less dense network due to a lower<br />

number <strong>of</strong> unsaturation sites <strong>in</strong> the polymer cha<strong>in</strong> structure. In NBR, the PTh-treated silica<br />

showed improved tensile properties result<strong>in</strong>g from an improved morphology and stronger<br />

network compared to untreated and silane-treated silica.<br />

Conclusions<br />

Silica as re<strong>in</strong>forc<strong>in</strong>g filler for elastomers can be plasma-coated under vacuum conditions.<br />

As a consequence, it shows a significant decrease <strong>in</strong> surface energy due to film deposition.<br />

It is possible to improve the dispersion <strong>of</strong> the filler <strong>in</strong> different polymers by match<strong>in</strong>g the<br />

surface energies. The properties <strong>of</strong> the silica surface can be tailored by deposit<strong>in</strong>g different<br />

functional groups by plasma-polymerization, which leads to an improvement <strong>of</strong> the f<strong>in</strong>al<br />

properties <strong>of</strong> filled polymers.<br />

Acknowledgements<br />

The support <strong>of</strong> STW, Hexagon Polymers and Timcal Graphite & Carbon is greatly<br />

acknowledged.<br />

5

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