uv ozone modification of wool fibre surfaces

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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



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



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.



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-



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.

uv ozone modification of wool fibre surfaces

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