Chemistry Reference
In-Depth Information
significantly (cf. Table 4). The allylalcohol homopolymer layer is soft; therefore,
the peel front propagates through the homopolymer layer at low peel strength.
The peeled surfaces were checked by XPS (Fig. 21). The C1s signals on both
peeled surfaces were identical and corresponded exactly to that of the allylalcohol
homopolymer. Increasing the percentage of ethylene in the respective copolymers
results in considerably increased peel forces (about 650 N/m). These high peel
values are due to the more crosslinked structure of the ethylene-rich copolymers
as also indicated by their insolubility. However, the peel front is shifted now par-
tially to the copolymer-PP interface. To avoid the adhesion failure the PP foils
were surface-oxidised in an O
2
plasma (10 s). Surprisingly, the measured peel
strengths after O
2
plasma pretreatment decrease strongly compared to those of
composites with untreated PP (cf. Table 4). The interpretation of this phenomenon
is the introduction of a new
Weak Boundary Layer
because of the too long pre-
treatment (10 s). Another possibility may be the higher input power (100 W in the
first series and 300 W in the second series). It is known that higher wattage pro-
duces more fragmentation of monomers in the plasma and the resulting plasma
polymer has an irregular and highly crosslinked structure. 50 : 50 and 75 : 25 eth-
ylene-allylalcohol copolymer interlayers show the largest adhesion-promoting ef-
fect. Ethylene-allylamine copolymers did not show an adhesion-promoting effect
as was expected from the possible chemical interactions between the metal and
functional groups. The investigations with carboxylic functionalities are in pro-
Table 4.
Types of interlayer and their influence on Al peel strength in the system Al-plasma polymerized in-
terlayer-PP (100 W and 300 W, duty cycle 0.1, 25 Pa)
%
ethylene
%
allylalcohol
OH
density
(per 100 C)
Peel strength
[N/m]
PP
pretreatment
Locus of peel front
100 W
0
100
29.5
60-100
no
in pp-polyallylalcohol
25
75
29.4
600-700
no
copolymer-PP interface
50
50
28.5
600-700
no
copolymer-PP interface
75
25
26.5
600-700
no
copolymer-PP interface
100
0
3.4
0-10
no
copolymer-PP interface
300 W
0
100
29.5
50-80
10 s O
2
plasma
in pp-polyallylalcohol
25
75
29.4
40-50
10 s O
2
plasma
copolymer-PP interface
50
50
28.5
90-110
10 s O
2
plasma
copolymer-PP interface
75
25
26.5
100-110
10 s O
2
plasma
copolymer-PP interface
90
10
14.5
50-70
10 s O
2
plasma
copolymer-PP interface
100
0
2.8
0
10 s O
2
plasma
copolymer-PP interface
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