The Surface Analysis Laboratory
Flame Treatment of Polypropylene:
A Study by Electron and Ion Spectroscopies
David F Williams, Marie-Laure Abel, Eddie Grant*, John F Watts
Department of Mechanical Engineering Sciences
Faculty of Engineering & Physical Sciences
Cagliari, Sardinia Italy
13th – 18th October 2013
*
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Flame Treatment Used for
Many Years
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Seminal Publications
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Automotive Flame Treatment
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Outline of Presentation
• Flame Treatment
• Industrial Examples
• Methods and Materials
• XPS Surface Composition as Function of
Treatment Parameters and Sample Type
• Valence Band Studies
• Treatment Layer Thickness
• ToF-SIMS: Oxygen Functionalisation
• ToF-SIMS: Additives
• Conclusions
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Flame treatment
• Increases the surface energy
• Ablative cleaning
• Improved adhesion
Active region
Main reaction zone
The Aerogen Company (2013)
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Industrial Examples of
Flame Treatment
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Flame treatment
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Polypropylene
Polymer All Filled with carbon Black
Designation
A homopolymer with no
additional filler A
A homopolymer with 40% talc
B
A copolymer with 20% talc C
A polymer with 20% long glass
fibre D
1 dyn cm-1 = 1 mN m-1
NB Plus unknown processing aids
Automotive Grade PP
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Flame Treatment Conditions
• Equivalence ratio 0.93 (stoichiometric amounts =1,
so slightly oxygen rich)
• Natural gas and filtered compressed air mixed in a
venturi 5 m up stream of burner
• Burner PP gap 18 -200 mm (Optimum 100 mm)
• Conveyor speed = 1 ms-1 (double pass)
• Dwell time in flame = 0.02 s
• Multiple passes; 90 s recovery allowed between
passes
• PP injection moulded plaques 3 mm thick
• Dyne pens immediately after flaming then wrapped
in Al foil
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Instrumentation Used
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XPS/Cluster Profiling
X-ray photoelectron spectroscopy performed
using the Thermo Scientific K-Alpha system
• Monochromated X-ray source
• Fully automated acquisition
MAGCIS (monatomic and gas cluster ion source)
used to produce craters
• Ar Cluster size up to 2000 atoms
• Ion energy = 2 - 8 keV
• Monatomic Ar ion beam
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Parameters Investigated
Parameters
• Burner to substrate distance
• Equivalence ratio = Ø
• Dwell time
mfuel/moxidiser
(mfuel/moxidiser)stoich
Effects
• Depth of treatment
• Ablation of surface material
• Ageing
• Chemical changes
• Topography changes
• Surface energy changes
Ø =
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Example XPS Spectra
XPS spectra for Sample A untreated
(lower) and treated (upper).
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As Received PP Samples
Sample B
Sample C
Sample A
Sample D
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Surface Composition vs
Contact Angle
Specimen
Surface Composition
Atomic %
Carbon Oxygen Sulphur O/C
ratio
Water Contact
Angle (°)
Dyne Ink
(mN m-1)
A 100.0 0 0.00 98 30
B 96.8 2.9 0.3 0.03 104
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Influence of Dwell Time
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Effect of Multiple
Passes on Surface
Properties Specimen C O S N
O/C
ratio
Contact
angle
Dyne
ink level
Sample A
Untreated 100.0 0.0 0.0 0.0 0.0 98 30
1 pass 89.6 10.0 0.4 0.0 0.11 70 52
2 passes 89.3 10.7 0.0 0.0 0.12 66 56
3 passes 85.1 14.9 0.0 0.0 0.18 62 56
5 passes 83.9 16.1 0.0 0.0 0.19 N/A N/A
7 passes 83.1 16.9 0.0 0.0 0.20 N/A N/A
Sample B
Untreated 96.8 2.9 0.3 0.0 0.03 104
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Dwell Time
(Passes Through
Flame) • Increased by using more passes 1,2 and 3 passes used (0.02, 0.04 and 0.06s respectively)
0.00
0.05
0.10
0.15
0.20
0.25
0 1 2 3 4
O/C
rat
io
Number of passes
O/C Ratio
60.0
62.0
64.0
66.0
68.0
70.0
72.0
74.0
0 1 2 3 4
Co
nta
ct a
ngl
e (
Degr
ees)
Number of passes
Contact Angle
Sample A X Sample B
Sample C
Sample D
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Burner Gap
0.00
0.05
0.10
0.15
0.20
0.25
0 20 40 60 80 100 120 140 160
O/C
rati
o
Burner gap (mm)
60.00
65.00
70.00
75.00
80.00
85.00
90.00
0 20 40 60 80 100 120 140 160
Wate
r c
on
tact
an
gle
(d
eg
rees)
Burner gap (mm)
Sample C X Sample D
Sample A
Sample B
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Equivalence Ratio
55.00
60.00
65.00
70.00
75.00
80.00
1.07 1.01 0.96 0.92 0.89
Wa
ter
Co
nta
ct
An
gle
(d
eg
rees
)
Equivalence Ratio
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
1.07 1.01 0.96 0.92 0.89
O/C
Rati
o
Equivalance Ratio
Sample A X Sample C
Sample B
Sample D
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Ageing Test
60.0
65.0
70.0
75.0
80.0
85.0
90.0
95.0
100.0
105.0
110.0
Untreated 0 Days 7 Days 14 Days 21 Days 26 Days 42 Days 49 DaysWate
r C
on
tact
an
gle
(D
eg
rees)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
Untreated 0 Days 7 Days 14 Days 21 Days 26 Days 42 Days 49 Days
O/C
Rati
o
Sample C X Sample B
Sample A
Sample D
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Valence Band
Valence band spectra
for Sample B
untreated
treated with 1 pass
treated with 2 passes
treated with 3 passes Briggs (1979)
polyethylene
polypropylene
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Mono XPS Valence Band
Untreated
1 Pass
3 Passes
7 Passes
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Depth of Treatment
• Angle Resolved XPS
• Mg-Al Source Comparison
• Depth profiling with cluster ions
0.04
0.06
0.08
0.1
0.12
0.14
0.16
25 29 32 36 40 44 47 51 55 59 62 66 70 74 77 81
O/C
Rati
o
Electron Take Off Angle (ETOA) (Degrees from the normal)
108MF treated
19T treated
STAMAX Treated
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Depth Profiling
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60
Ato
mic
perc
en
t (%
)
Etch Depth (nm)
C1s
O1s (5x)
Analysis on a K-Alpha using large cluster ions to etch (Ar1000)
Depth calculation using estimate from Irganox reference.
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ToF-SIMS Identification of
Oxygenation
C3H5O
C4H9
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mass / u69.00 69.05 69.10
4x10
2.0
4.0
Inte
nsit
y
4x10
1.0
2.0
Inte
nsit
y
4x10
0.5
1.0
1.5
Inte
nsit
y
4x10
1.0
2.0
Inte
nsit
y4x10
1.0
2.0
Inte
nsit
y
4x10
1.0
2.0
Inte
nsit
y
C3HO2
C4H5O C5H9
8 passes
6 passes
3 passes
2 passes
1 pass
Untreated
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Variation with Treatment
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Additives: ToF-SIMS Spectra
Additive Chemical structure Characteristic peaks
Ethylene Bis-steramide 282, 310
Irganox™ 1010 57, 203, 219, 259
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Ablation of Additives
C18H36NO
C20H40NO C15H23O
C17H23O
Ethylene Bis-steramide Irganox™ 1010
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Conclusions
• Increase of surface energy
• Level of treatment is most sensitive to
equivalence ratio
• Depth of treatment ≈ 20nm
• Ablation of detected additives
• Reduction of the methyl pendant group.