Nondestructive testing of defects in adhesive joints

commonly used to chemically modify silica surfaces and promote interactions between
hydrophilic silica surfaces and the hydrophobic rubber phase 3-5 . In the conventional technology,
the reaction between silica and the silane coupling agent takes place in the rubber-filler blend
during mixing. This in-situ modification requires a number of precautions regarding the mixing
sequence and the mixing temperature, as well as careful adjustment of mixing conditions for
every silane containing compound.
Recently, plasma polymerization has emerged as a surface modification technique for
polymers, metals and powders. Van Ooij et al. 6 have reported plasma modification of silica,
which changes the surface chemistry of the filler.
In the previous work 7,8 , the effect of plasma-acetylene coated silica on the properties of S-SBR,
EPDM, NBR compounds and their blends have been studied. In this study, the silica is modified
with plasma-thiophene, which has a sulphur moiety in its cyclic structure. The effect on
processing behavior and properties of EPDM, SBR and NBR compounds containing plasmathiophene
(PTh) coated silica will be evaluated.
Experimental
For the surface modification of silica powders, a radiofrequency (13.56 MHz)
electrodeless tumbler plasma reactor is used, based on a horizontally mixing principle and with a
capacity of 350 g/batch. The plasma polymerization was carried out after charging 100 g of dried
silica (Ultrasil VN3) into the reactor, evacuating the reactor to 13 Pa and introducing thiophene
gas. The operating pressure, which was determined by the thiophene vapour flow, was 20 Pa. The
power and treatment time were 100 Watts and 90 minutes.
The general characterization techniques used for treated silica powders are an immersion
test, water penetration measurements 9 , Thermo-Gravimetric Analysis (TGA), Time-of-Flight
Secondary Ion Mass Spectroscopy (ToF-SIMS) and Energy Dispersive X-ray Spectrometry
(EDX).
Mixing of the filler-rubber compounds was done in an internal mixer; the curatives were
added on a two roll mill. The compounds were characterized by measuring the Payne effect (RPA
2000) and bound rubber content 10,11 . The cure characteristics (RPA 2000) were measured, and the
reinforcement parameter (αF) 12 as well as the mechanical properties (ISO-37) were determined.
As references, untreated and silane-treated silica were used.
2