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appliedsurface science
Applied Surface Science 72 (1993) 143-147
North-Holland
UV ozone modification of wool fibre surfaces
R.H. Bradley *, I.L. Clackson and D.E. Sykes
Institute of Surface Science and Technology, University of Technology, Loughborough, Leicestershire, LEll 3TU, UK
Received 21 February 1993; accepted for publication 2 June 1993
An ultraviolet (UV) ozone treatment has been used to oxidise the surfaces of batches of natural wool fibres. The changes in
surface composition and chemistry induced by this treatment have been followed using X-ray photoelectron spectroscopy (XPS).Oxidation of surface di-sulphide sulphur to sulphonic acid groups (-SO,H) containing S6+ is observed at levels of approxi-
mately 90% conversion. This is significantly higher than levels previously achieved using oxygen plasmas. The treatment also
appears to cause reaction of the proteinaceous carbon, leading to an increase in carbon-oxygen, particularly carbonyl, functional-
ity. The data presented indicate that the treatment used is capable of producing surface sulphur and carbon chemistry of the type
usually obtained by wet chlorination.
1. Introduction
The commercial shrink proofing of natural
wool is normally carried out by the deposition,
from solution, of cationic polymers such as
epichlorohydrin polyamide (known commercially
as Hercosett). The successful adsorption of such
polymers requires a surface oxidative pre-treat-
ment which increases the surface polarity of the
wool fibres by the introduction of anionic func-
tional groups. This is usually done using solutions
of chlorinated compounds which oxidise sulphur,
present in the di-sulphide linkages -S-S- of the
protein structure, to S6+ in the form of sulphonic
acid groups -SO,H. This process gives effectively
100% oxidation of the S2+ [1,2] but produces
large quantities of chlorinated waste water. It istherefore desirable to identify alternative effluent
free treatments on environmental grounds.
In previous work [3] we have shown that oxy-
gen plasma treatment can be used to increase the
levels of surface oxygen present in natural wool
fibres from N 10 to N 20 at%, this latter level
being commensurate with that achieved by com-
plete oxidation of di-sulphide linkages by the wet
* To whom correspondence should be addressed.
chlorination technique presently used commer-
cially. However, when oxygen plasmas are used
results indicate that only about 30% of this oxy-
gen increase is due to the oxidation of di-sulphide
to sulphonic acid sulphur whilst the remainder is
attributable to oxidation of surface proteinaceous
carbon which leads to the formation of hydroxyl/
ether (C-O) and carbonyl (C=O) functionalities.
In this paper we report the use of a UV ozone
treatment for the oxidation of natural wool fibre
surfaces. XPS has been used to characterise the
changes in surface composition and chemistry.
This technique is firmly established for surface
chemical studies of this type [l] and is shown here
to give quantitative information reflecting the ef-
fects of fibre oxidation. Data are presented which
indicate modification of both surface sulphur andcarbon species.
2. Experimental details
2.1. Samples
Results are presented for untreated natural
wool fibre surfaces and for similar surfaces after
exposure to UV ozone. For treatment, natural
0169-4332/93/$06.00 0 1993 - Elsevier Science Publishers B.V. All rights reserved
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1 4 4 R.H. Bradley et al. / CJV ozon e modif icatio n of w ool fibre surfaces
wool fibres, carded and washed, were exposed in
a static apparatus for 5 or 10 min periods (sam-
ples designated 5 min UVO or 10 min UVO).
Ozone was generated from atmospheric oxygen at
ambient pressure using a UV light source. Nosample degradation was observed after 5 min
exposure but samples treated for 10 min showed
signs of discolouration (yellowing).
using double-sided adhesive and held in place
using a copper frame which helped to minimise
sample charging. No Al or Cu peaks were de-
tected in spectra from any of the samples, indicat-
ing that only the wool surface was being analysed.
2.2. XPS analysis
For XPS experiments rafts of fibres (20 X 20 XPS experiments were carried out on a VG
mm> were affixed to aluminium sample stubs ESCALAB Mk 1 using AlKa X-rays of energy
0 IS
r- 1 0 mi n . UVO
N IS
I
0 200 400
Binding Energy (eV)
Fig. 1. Broad-scan spectra.
1
600
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R.H. Bradley et al. / UV ozone modification of wool fibre surfaces 145
1486.6 eV, at a residual pressure of 10-s Torr.
Measurements were made using fixed analyser
transmission and with the analyser normal to the
plane of the sample at pass energies of 85 eV for
broad-scan spectra and 25 eV for high-resolutionscans of S 2p and C 1s peaks. All peaks have been
charge referenced to the major C-C/C-H Is
peak at 284.6 eV. Surface compositions have been
calculated using the areas of the respective pho-
toelectron peaks after subtraction of a Shirley-
type background. Absolute concentrations must
be regarded as approximate ( + 10 at%) but accu-
rate comparisons can be made between like sam-
ples (*OS at%,>. Correction has been made for
the angular asymmetry of photoemissions [41,
transmission of the energy analyser [.51, photoioni-
sation cross-section [6] and the inelastic mean
free path of the photoelectrons [7]. Photoelec-
tron-peak-broadening components due to the X-
ray line shape have been removed from the high-resolution Cls spectra using in-house software on
an IBM-AT computer [S].
3. Results and discussion
3.1. Compositional effects of UV ozone t reatm ent
Broad-scan spectra from untreated, 5 min
UVO and 10 min UVO treated natural wool
Fig. 2. High-resolution S 2p spectra.
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146 R. H. Bradley et al. / W ozone modification of wool fibre surfaces
fibres are compared in fig. 1. All show photoelec-
tron peaks due to the presence of carbon, oxygen,
sulphur and nitrogen in their surfaces, which is
consistent with the proteinaceous nature of the
wool fibres. Similar spectra as that shown for theuntreated wool surface have resulted from a
number of earlier XPS studies of natural wool
fibres [9]. The intensities of the 01s peaks in the
spectra from the ozone-treated samples are no-
ticeably higher than for the untreated surface
and, as shown in table 1, which contains surface
compositional data derived from the three spec-
tra, the UV ozone treatment leads to levels of
surface oxygen which are more than a factor of 2
higher than those recorded for the untreated
surface. Indeed, the value shown for the 10 min
UVO sample (27.5 at%) is higher than that gen-
erally achieved by the wet chlorination process
(N 24%) which has been shown to oxidise all
di-sulphide sulphur to S6+.
3.2. Sulphur chemistry
Fig. 2 shows high-resolution S2p spectra from
the three surfaces studied. The curve from the
untreated wool shows only one peak at a binding
energy of 164 eV, which is consistent with the
presence of sulphur as di-sulphide linkages. Thecurves for the treated samples both show a minor
peak at N 164 eV and a peak of much greater
intensity at N 168 eV and are consistent with the
presence of sulphur in at least 2 oxidation states.
Again the peak at 164 eV is attributable to di-
sulphide whilst the peak at - 168 eV has been
shown to be characteristic of S”+ in the form of
sulphonic acid [l]. The most noticeable feature of
the curves is the much higher intensity of the
peaks due to sulphonic acid sulphur for both of
the UV-ozone-treated samples. Measurement of
relative peak areas and use of a relative sensitiv-
Table 1
Compositions (in at%) of wool surfaces from XPS experi-
ments
Untreated
uvo 5
uvo 10
C 0 S N
19.3 11.8 2.7 6.2
67.0 24.7 2.3 6.0
61.9 27.5 2.8 7.8
5 mi n . UVO
Fig. 3. High-resolution C Is spectra.
ity factor of 1.0 for both oxidation states of sul-
phur indicates that about 90% of the total surface
sulphur is oxidised to the (+ 6) state by the UV
ozone treatment. This level approaches that
achieved by the wet chlorination process cur-rently used in industry and is a significant im-
provement of the levels of oxidation previously
measured by the authors for samples treated us-
ing oxygen plasmas. However, as shown in table 1
the total increases in surface oxygen for the
treated samples appear to be at least as high as
those which might be expected for 100% oxida-
tion of all of the sulphur present. It is therefore
likely that, as has already been reported for the
oxygen plasma oxidation of wool surfaces, oxygen
is also being introduced at proteinaceous carbon
sites on the wool surface. This aspect of the
surface chemistry is considered below.
3.3. Carbon chemistry
Inspection of the high-resolution Cls curves
shown in fig. 3 reveals a considerable shoulder to
the higher binding energy side of the main C-
C/C-H peak (284.6 eV> for the UV ozone sam-
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R.H. Bradley et al. / W ozone modification of wool fibre surfaces 147
ples. The curve shown for the untreated sample
indicates the presence of hydroxyl/ether (C-O)
and carbonyl (C=O) oxygen but the carbonyl peak
is much less pronounced than those shown for
the UV-ozone-treated surfaces and it is clearfrom these spectra that some oxidation of the
surface carbon of the protein structure is brought
about by the UV ozone treatment in addition to
the di-sulphide oxidation discussed earlier. From
the curves shown it appears that the treatment
leads to the formation of surface carbonyl groups
which are detected as a marked shoulder in the
C 1s curves at a binding energy of N 288 eV. No
clear evidence is observed in these curves for a
significant increase in the surface concentrations
of hydroxyl or ether functionalities which would
give structure centred at a binding energy of
N 286 eV. Clear interpretation of this region of
these spectra is complicated by peak broadening
due to differential charging of the sample surface
and also the possible presence of an additional
peak due to C-N bonding at a binding energy of
285.3 eV which has been partially resolved in C 1s
spectra from similar wool surfaces during another
part of this study [lo]. Considerable development
of hydroxyl/ether peaks have been observed for
woven wool samples treated with oxygen plasmas.
It would appear, on the evidence presented here,that the UV ozone treatment leads to the forma-
tion of a much higher proportion of carbonyl
functionalities where as for the oxygen plasma
systems marked increases in both hydroxyl/ ether
and carbonyl groups are observed. Thus the reac-
tivity of the wool surface and the resulting car-
bon-oxygen functionalities differs for the two
types of oxidative treatments. In principle, this
gives some control over the type of functionalities
introduced at these surfaces.
4. Conclusions
The use of a UV ozone oxidation treatment is
shown to give a high degree of oxidation of sur-
face di-sulphide linkages to sulphonic acid groups
(S6’> for the natural wool fibre samples studied.
The conversion rate appears to be approximately
90% of all surface sulphur. This gives an increase
in surface anionicity which is comparable to pre-
sent wet industrial methods but without the highlevels of chlorinated effluent associated with such
processes. Further, this method is more effective
than previously studied oxygen plasma oxidation
treatments which only give - 20%-30% oxida-
tion of S2+ to S6+.
Oxidation of proteinaceous carbon by the in-
troduction of carbonyl oxygen is also observed
using this treatment. Little change in the hy-
droxyl/ether concentration of the surfaces is de-
tected, this is in marked contrast to results from
oxygen plasma treatments already reported which
show significant increases in both hydroxyl/ ether
and carbonyl oxygen.
The changes in wool surface chemistry ob-
served after the UV ozone treatment are suffi-
ciently similar to those achieved by wet chlorina-
tion to make the former process of further inter-
est. Work is currently underway to develop an
alternative, effluent free, technique for wool sur-
face oxidation based on the method described
and a patent has been applied for.
References
[l] C.N. Carr, SF. Ho, D.M. Lewis, E.D. Owen and M.W.
Roberts, J. Text. Inst. 6 (1985) 419.
[2] R.H. Bradley, I.L. Clackson, J.A. Crompton, M.A. Rush-
forth and 1. Sutherland, unpublished results.
[3] R.H. Bradley, I.L. Clackson, J.A. Crompton, M.A. Rush-
forth and 1. Sutherland, J. Chem. Tech. Biotechnol. 53
(1992) 221.
[4] R.F. Reilmann, A. Msezane and S.T. Manson, J. Elec-
tron Spectrosc. 8 (1976) 389.
[5] M.P. Seah, Surf. Interf. Anal. 2 (1980) 232.[6] J.H. Schofield, J. Electron Spectrosc. 8 (1976) 129.
[7] M.P. Seah and W.A. Dench, Surf. Interf. Anal. 1 (1979)
[8] P.H. Van Cittert, Z. Phys. 69 (1931) 298;
P.A. Jansson, J. Opt. Sot. Am. 59 (1968) 1665.
[9] For instance, ref. [l], p. 420.
[lo] R.H. Bradley and I.L. Clackson, unpublished results.