- Email: [email protected]
Structure investigation of lyocell fibres by in situ USANS measurements
ARTICLE IN PRESS
Physica B 350 (2004) e541–e544
Structure investigation of lyocell fibres by in situ USANS measurements E. Jerichaa,*, M. Villaa, M. Barona,b, R. Loidla,b, O. Biganskac, P. Navardc, S. Patlazhanc, P. Aldredd, H. Ruf . e, K.C. Schustere a
Atominstitut, Vienna University of Technology, Stadionallee 2, A-1020 Vienna, Austria b Institut Laue Langevin, F-38042 Grenoble, France c ! Centre de Mise en Forme des Mat!eriaux, Ecole des Mines de Paris, F-06904 Sofia Antipolis, France d Christian Doppler Laboratory for the Chemistry of Cellulosic Fibres and Textiles, Dornbirn A-6850, Austria e Lenzing AG, Research and Development Lyocell, A-4840 Lenzing, Austria
Abstract Lyocell fibres nowadays are widely used in textile production and have an enormous potential for various technical applications. The structure of these fibres, however, is a pending research issue. Particularly, the process of fibrillation is still to be understood and a major issue for the optimisation of the production process. Now, first experiments with neutrons using USANS technique have revealed indications about the fibre structure in the micrometer range. We observed clear ultra-small-angle scattering patterns from even small numbers of fibres after spinning and even from inside the spinning bath during the spinning process. The outer diameter of the fibres is well reproduced in the scattering patterns which also indicate the presence of smaller internal structure. First experimental results obtained at the S18 instrument at the ILL are presented. r 2004 Elsevier B.V. All rights reserved. PACS: 61.12.Ex; 81.05.Lg; 03.75.Be Keywords: Ultra-small-angle neutron scattering; Cellulose fibre structure; Industrial application
1. Introduction The structure of cellulose fibres is a pending research issue. Related investigations have mostly been performed by X-ray scattering [1] and resulted in a structure model for the nanometer range. Wide-angle X-ray scattering revealed the crystallite structure of cellulose II of which regenerated lyocell fibres are composed [2]. *Corresponding author. Fax: +43-1-58801-14199. Email-address: [email protected] (E. Jericha).
Small-angle X-ray [3] and neutron [4] scattering determined sizes and orientation of crystallites, and sizes and characteristics of voids between them. Lyocell fibres consist of elementary fibrils which are oriented essentially parallel to the fibre axis and which are formed by the cellulose crystallites separated by highly oriented amorphous regions. However, taking fibrillation (the splitting of the fibre into smaller fibrils which is a cause for textile deterioration) as example, it is found that knowledge of the fibre structure in the nanometer range
0921-4526/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.03.147
ARTICLE IN PRESS e542
E. Jericha et al. / Physica B 350 (2004) e541–e544
described by a convolution of the reflection curves of the two perfect crystals [6] as Z ð1Þ R3 ðQ0 ÞR3 ðQ Q0 Þ dQ0 ; IR ðQÞ ¼ I0
Fig. 1. Electron microscope image of a cellulose fibre after chemical and mechanical treatment.
is not sufficient for a complete explanation of the effect. Fibrils that split off the fibres have typical diameters from some tenths up to a few micrometres. Substructures in fibres in this size range can be made visible by swelling in special reagents or by severe squeezing. Fig. 1 shows an image taken by electron microscopy where the substructures of a fibre have been recorded after such treatment. The drawback of such methods is the destruction of the fibre before structure investigation. Therefore, we applied the ultrasmall-angle neutron scattering technique (USANS) as a candidate for non-destructive cellulose fibre characterisation.
2. Experimental Experiments were performed with the USANS option of the S18 instrument at the ILL, Grenoble [5]. The set-up is a double perfect crystal diffractometer in Bonse–Hart configuration with two triple-bounce channel-cut perfect silicon crystals serving as monochromator and analyser, which are mounted on a common optical bench. USANS patterns are recorded by rotating the analyser crystal with typical sub-mrad step widths. The rocking curve IR ðQÞ (scattering vector Q in horizontal direction perpendicular to the rotation axis of the analyser) of the empty instrument is
where RðQÞ is the reflection probability for a single reflection and I0 is the incoming neutron intensity. Due to inevitable background the measured instrument curve is given by IRm ðQÞ ¼ IR ðQÞ þ IB with the background intensity IB which usually amounts to a few neutrons per minute. A laboratory spinneret provided by Lenzing AG (Lenzing, Austria) was mounted above the optical bench near the analyser crystal for in situ measurements of cellulose fibres during the spinning process. Some experimental details are given in Fig. 2. The fibres are generated from cellulose dissolved in n-methyl morpholine oxide (NMMO) which is washed out afterwards in a water-filled spinning bath leaving a cellulose fibre bundle [7]. To minimise neutron losses, the spinning bath was filled with D2 O instead of normal water. The neutron beam through the spinning bath was limited vertically by a narrow Cd slit to allow for position sensitive measurements along the spinning line. A typical fibre bundle observed during measurements consisted of about 10–40 individual cellulose fibres.
spinning dye (nozzle) air gap bath entry cellulose fibre thread D22O spinning bath deflection rollers Fig. 2. Schematic of the spinning bath used for the measurements. A cellulose/NMMO-mixture is generated in the spinning dye and pressed through several openings of the nozzle into a 3 cm wide air gap where several fibres containing cellulose and NMMO solvent are formed. The thread enters a spinning bath where the NMMO is washed out. The bath container was made of 3 mm thick quartz glass windows and the path length through D2 O was 1:5 cm:
ARTICLE IN PRESS E. Jericha et al. / Physica B 350 (2004) e541–e544
3. Results and discussion Some USANS scattering patterns obtained from online measurements are shown in Fig. 3. The measured intensity Im ðQÞ follows as Z Im ðQÞ ¼ I0 PðQ0 ÞIR ðQ Q0 Þ dQ0 þ pIR ðQÞ þ IB ; ð2Þ where PðQÞ is the scattering function of the fibres which is convoluted with the instrumental rocking curve and p denotes the fraction of neutrons which pass the sample unscattered. To obtain a preliminary analysis we have assumed the fibres to be homogeneous monodisperse cylindrical scatterers. In this case the scattering function is given by 2J1 ðQRÞ 2 PðQÞ ¼ ðDNbc Þ2 p2 R2 ð3Þ QR with DNbc being the difference in scattering length densities between the fibre and its surrounding material, and the cylinder radius R: From this analysis we find that the fibre diameter increases in the spinning bath, goes through a maximum and then decreases again. The fibre size is usually characterised by the special unit dtex denoting their weight in grams over a length of 10 km: We followed the evolution of 1:3 dtex fibres along the spinning line. The fibres swell to a diameter of 22ð1Þ mm at bath entry which 4
neutron intensity / min.
10
air gap bath entry before 1st roller after bath exit instrument curve
3
10
2
10
1
10
0.0
0.5
1.0
1.5x10
-4
-1
Q [Å ] Fig. 3. USANS scattering patterns of 6:7 dtex cellulose fibres along the spinning bath. The curves represent fits according to the model (3) taking Eq. (2) into account. Deviations from the simple cylinder model indicate the more complex internal structure of the fibres.
e543
is increased to 30ð1Þ mm near the centre of the bath. At the first deflection roller, where all fibres come together, we find an outer diameter of about 130 mm: We assume that this corresponds to the whole fibre bundle rather than to the individual fibres, as they seem to form a homogeneous scattering object for the incident neutrons. Immediately after bath exit the size of the fibres is reduced to 10:5ð2Þ mm: It is speculated that the fibre swelling and de-swelling in the spinning bath leads to an instability in the formed fibre structure whose degree may eventually be responsible for the fibrillation effect. For 6:7 dtex fibres (whose diameter should be roughly twice the value of the 1:3 dtex fibres), we observed scattering patterns generated with the spinning bath at the measurement location (shown in Fig. 3), which indicate much smaller cylinders than found for the 1.3 dtex fibres at the corresponding location. Also, the diameter of the cylinders were found to be 12:0ð2Þ mm after bath entry and 10:8ð2Þ mm before the first deflection roller. This indicates a large internal cylindrical macro-fibril structure and may be compared to the large fibrils shown in Fig. 1. In air the total fibre diameter was resolved by the neutrons and amounts to 20ð10Þ mm in the gap (with large uncertainty) and to 18:8ð2Þ mm after bath exit which is reasonably consistent with the 1:3 dtex data. No scattered intensity was detected when the fibre bundle was running horizontally. Since the USANS camera is only sensitive to scattering in the horizontal plane it may be concluded that also large internal fibre structures are predominantly oriented along the fibre axis. To summarise, we have demonstrated the capability of the USANS technique to study the structure of different Lyocell cellulose fibres nondestructively. Additionally, fibres were produced offline under various conditions to account for different treatment after spinning. Reports on these measurements will be presented elsewhere. Next steps will include a refinement of the fibre model, especially by including internal structure which will enter the scattering function PðQÞ: High statistics experimental runs are needed for a better
ARTICLE IN PRESS e544
E. Jericha et al. / Physica B 350 (2004) e541–e544
understanding of the fibre structure development during the spinning process. A connection to the scattering range covered by conventional SANS is planned to access smaller structural components. These measurements also demonstrate the value of neutron scattering techniques for in situ studies of industry relevant material forming processes.
References [1] O. Glatter, O. Kratky (Eds.), Small-Angle X-Ray Scattering, Academic Press, New York (1982).
[2] J.F. Kadla, R.D. Gilbert, Cellulose Chem. Technol. 34 (2000) 197. [3] J. Lenz, J. Schurz, E. Wrentschur, Holzforschung 42 (2) (1988) 117. [4] J. Crawshaw, M.E. Vickers, N.P. Briggs, R.K. Heenan, R.E. Cameron, Polymer 41 (2000) 1873. [5] M. Hainbuchner, M. Villa, G. Kroupa, G. Bruckner, M. Baron, H. Amenitsch, E. Seidl, H. Rauch, J. Appl. Crystallorgr. 33 (2000) 851. [6] D. Schwahn, A. Miksovsky, H. Rauch, E. Seidl, G. Zugarek, Nucl. Instrum. Methods. A 239 (1985) 229. [7] W. Feilmair, Chem. Fibres Int. 46 (1996) 441.
Physica B 350 (2004) e541–e544
Structure investigation of lyocell fibres by in situ USANS measurements E. Jerichaa,*, M. Villaa, M. Barona,b, R. Loidla,b, O. Biganskac, P. Navardc, S. Patlazhanc, P. Aldredd, H. Ruf . e, K.C. Schustere a
Atominstitut, Vienna University of Technology, Stadionallee 2, A-1020 Vienna, Austria b Institut Laue Langevin, F-38042 Grenoble, France c ! Centre de Mise en Forme des Mat!eriaux, Ecole des Mines de Paris, F-06904 Sofia Antipolis, France d Christian Doppler Laboratory for the Chemistry of Cellulosic Fibres and Textiles, Dornbirn A-6850, Austria e Lenzing AG, Research and Development Lyocell, A-4840 Lenzing, Austria
Abstract Lyocell fibres nowadays are widely used in textile production and have an enormous potential for various technical applications. The structure of these fibres, however, is a pending research issue. Particularly, the process of fibrillation is still to be understood and a major issue for the optimisation of the production process. Now, first experiments with neutrons using USANS technique have revealed indications about the fibre structure in the micrometer range. We observed clear ultra-small-angle scattering patterns from even small numbers of fibres after spinning and even from inside the spinning bath during the spinning process. The outer diameter of the fibres is well reproduced in the scattering patterns which also indicate the presence of smaller internal structure. First experimental results obtained at the S18 instrument at the ILL are presented. r 2004 Elsevier B.V. All rights reserved. PACS: 61.12.Ex; 81.05.Lg; 03.75.Be Keywords: Ultra-small-angle neutron scattering; Cellulose fibre structure; Industrial application
1. Introduction The structure of cellulose fibres is a pending research issue. Related investigations have mostly been performed by X-ray scattering [1] and resulted in a structure model for the nanometer range. Wide-angle X-ray scattering revealed the crystallite structure of cellulose II of which regenerated lyocell fibres are composed [2]. *Corresponding author. Fax: +43-1-58801-14199. Email-address: [email protected] (E. Jericha).
Small-angle X-ray [3] and neutron [4] scattering determined sizes and orientation of crystallites, and sizes and characteristics of voids between them. Lyocell fibres consist of elementary fibrils which are oriented essentially parallel to the fibre axis and which are formed by the cellulose crystallites separated by highly oriented amorphous regions. However, taking fibrillation (the splitting of the fibre into smaller fibrils which is a cause for textile deterioration) as example, it is found that knowledge of the fibre structure in the nanometer range
0921-4526/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.03.147
ARTICLE IN PRESS e542
E. Jericha et al. / Physica B 350 (2004) e541–e544
described by a convolution of the reflection curves of the two perfect crystals [6] as Z ð1Þ R3 ðQ0 ÞR3 ðQ Q0 Þ dQ0 ; IR ðQÞ ¼ I0
Fig. 1. Electron microscope image of a cellulose fibre after chemical and mechanical treatment.
is not sufficient for a complete explanation of the effect. Fibrils that split off the fibres have typical diameters from some tenths up to a few micrometres. Substructures in fibres in this size range can be made visible by swelling in special reagents or by severe squeezing. Fig. 1 shows an image taken by electron microscopy where the substructures of a fibre have been recorded after such treatment. The drawback of such methods is the destruction of the fibre before structure investigation. Therefore, we applied the ultrasmall-angle neutron scattering technique (USANS) as a candidate for non-destructive cellulose fibre characterisation.
2. Experimental Experiments were performed with the USANS option of the S18 instrument at the ILL, Grenoble [5]. The set-up is a double perfect crystal diffractometer in Bonse–Hart configuration with two triple-bounce channel-cut perfect silicon crystals serving as monochromator and analyser, which are mounted on a common optical bench. USANS patterns are recorded by rotating the analyser crystal with typical sub-mrad step widths. The rocking curve IR ðQÞ (scattering vector Q in horizontal direction perpendicular to the rotation axis of the analyser) of the empty instrument is
where RðQÞ is the reflection probability for a single reflection and I0 is the incoming neutron intensity. Due to inevitable background the measured instrument curve is given by IRm ðQÞ ¼ IR ðQÞ þ IB with the background intensity IB which usually amounts to a few neutrons per minute. A laboratory spinneret provided by Lenzing AG (Lenzing, Austria) was mounted above the optical bench near the analyser crystal for in situ measurements of cellulose fibres during the spinning process. Some experimental details are given in Fig. 2. The fibres are generated from cellulose dissolved in n-methyl morpholine oxide (NMMO) which is washed out afterwards in a water-filled spinning bath leaving a cellulose fibre bundle [7]. To minimise neutron losses, the spinning bath was filled with D2 O instead of normal water. The neutron beam through the spinning bath was limited vertically by a narrow Cd slit to allow for position sensitive measurements along the spinning line. A typical fibre bundle observed during measurements consisted of about 10–40 individual cellulose fibres.
spinning dye (nozzle) air gap bath entry cellulose fibre thread D22O spinning bath deflection rollers Fig. 2. Schematic of the spinning bath used for the measurements. A cellulose/NMMO-mixture is generated in the spinning dye and pressed through several openings of the nozzle into a 3 cm wide air gap where several fibres containing cellulose and NMMO solvent are formed. The thread enters a spinning bath where the NMMO is washed out. The bath container was made of 3 mm thick quartz glass windows and the path length through D2 O was 1:5 cm:
ARTICLE IN PRESS E. Jericha et al. / Physica B 350 (2004) e541–e544
3. Results and discussion Some USANS scattering patterns obtained from online measurements are shown in Fig. 3. The measured intensity Im ðQÞ follows as Z Im ðQÞ ¼ I0 PðQ0 ÞIR ðQ Q0 Þ dQ0 þ pIR ðQÞ þ IB ; ð2Þ where PðQÞ is the scattering function of the fibres which is convoluted with the instrumental rocking curve and p denotes the fraction of neutrons which pass the sample unscattered. To obtain a preliminary analysis we have assumed the fibres to be homogeneous monodisperse cylindrical scatterers. In this case the scattering function is given by 2J1 ðQRÞ 2 PðQÞ ¼ ðDNbc Þ2 p2 R2 ð3Þ QR with DNbc being the difference in scattering length densities between the fibre and its surrounding material, and the cylinder radius R: From this analysis we find that the fibre diameter increases in the spinning bath, goes through a maximum and then decreases again. The fibre size is usually characterised by the special unit dtex denoting their weight in grams over a length of 10 km: We followed the evolution of 1:3 dtex fibres along the spinning line. The fibres swell to a diameter of 22ð1Þ mm at bath entry which 4
neutron intensity / min.
10
air gap bath entry before 1st roller after bath exit instrument curve
3
10
2
10
1
10
0.0
0.5
1.0
1.5x10
-4
-1
Q [Å ] Fig. 3. USANS scattering patterns of 6:7 dtex cellulose fibres along the spinning bath. The curves represent fits according to the model (3) taking Eq. (2) into account. Deviations from the simple cylinder model indicate the more complex internal structure of the fibres.
e543
is increased to 30ð1Þ mm near the centre of the bath. At the first deflection roller, where all fibres come together, we find an outer diameter of about 130 mm: We assume that this corresponds to the whole fibre bundle rather than to the individual fibres, as they seem to form a homogeneous scattering object for the incident neutrons. Immediately after bath exit the size of the fibres is reduced to 10:5ð2Þ mm: It is speculated that the fibre swelling and de-swelling in the spinning bath leads to an instability in the formed fibre structure whose degree may eventually be responsible for the fibrillation effect. For 6:7 dtex fibres (whose diameter should be roughly twice the value of the 1:3 dtex fibres), we observed scattering patterns generated with the spinning bath at the measurement location (shown in Fig. 3), which indicate much smaller cylinders than found for the 1.3 dtex fibres at the corresponding location. Also, the diameter of the cylinders were found to be 12:0ð2Þ mm after bath entry and 10:8ð2Þ mm before the first deflection roller. This indicates a large internal cylindrical macro-fibril structure and may be compared to the large fibrils shown in Fig. 1. In air the total fibre diameter was resolved by the neutrons and amounts to 20ð10Þ mm in the gap (with large uncertainty) and to 18:8ð2Þ mm after bath exit which is reasonably consistent with the 1:3 dtex data. No scattered intensity was detected when the fibre bundle was running horizontally. Since the USANS camera is only sensitive to scattering in the horizontal plane it may be concluded that also large internal fibre structures are predominantly oriented along the fibre axis. To summarise, we have demonstrated the capability of the USANS technique to study the structure of different Lyocell cellulose fibres nondestructively. Additionally, fibres were produced offline under various conditions to account for different treatment after spinning. Reports on these measurements will be presented elsewhere. Next steps will include a refinement of the fibre model, especially by including internal structure which will enter the scattering function PðQÞ: High statistics experimental runs are needed for a better
ARTICLE IN PRESS e544
E. Jericha et al. / Physica B 350 (2004) e541–e544
understanding of the fibre structure development during the spinning process. A connection to the scattering range covered by conventional SANS is planned to access smaller structural components. These measurements also demonstrate the value of neutron scattering techniques for in situ studies of industry relevant material forming processes.
References [1] O. Glatter, O. Kratky (Eds.), Small-Angle X-Ray Scattering, Academic Press, New York (1982).
[2] J.F. Kadla, R.D. Gilbert, Cellulose Chem. Technol. 34 (2000) 197. [3] J. Lenz, J. Schurz, E. Wrentschur, Holzforschung 42 (2) (1988) 117. [4] J. Crawshaw, M.E. Vickers, N.P. Briggs, R.K. Heenan, R.E. Cameron, Polymer 41 (2000) 1873. [5] M. Hainbuchner, M. Villa, G. Kroupa, G. Bruckner, M. Baron, H. Amenitsch, E. Seidl, H. Rauch, J. Appl. Crystallorgr. 33 (2000) 851. [6] D. Schwahn, A. Miksovsky, H. Rauch, E. Seidl, G. Zugarek, Nucl. Instrum. Methods. A 239 (1985) 229. [7] W. Feilmair, Chem. Fibres Int. 46 (1996) 441.