ARTICLE pubs.acs.org/IECR
What Does LiOH Treatment Offer for Lyocell Fibers? Investigation of Structural Changes € urk,† Bill MacNaughtan,‡ John R. Mitchell,‡ and Thomas Bechtold*,† Hale Bahar Ozt€ †
Christian-Doppler-Laboratory for Textile and Fiber Chemistry in Cellulosics, Research Institute for Textile Chemistry and Textile Physics, University of Innsbruck, Hoechsterstrasse 73, A-6850 Dornbirn, Austria ‡ Division of Food Sciences, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, U.K. ABSTRACT: Lyocell fibers, regenerated cellulosic fibers spun from cellulose/N-methylmorpholine-N-oxide hydrate solution by wet spinning, were treated with LiOH aqueous solution at concentrations of up to 7.5 M to study the inter- and intrafibrillar changes. Wide-angle X-ray diffraction analyses were applied to identify the crystallinity index and crystallite size. Inverse size-exclusion chromatography was applied to study the pore structure of the swollen fibers. The mean pore diameter was found to increase after the LiOH treatment. The carboxyl content, measured by methylene blue sorption, decreased slightly. The water retention value, depth of color measured after dyeing with CI Direct Red 81, and weight loss of fibers changed gradually after LiOH treatment at concentrations up to ca. 5 M. The treated fibers became brittle as a result of both inter- and intrafibrillar swelling and the deep penetration ability of LiOH treatments above 5 M.
’ INTRODUCTION Lyocell is a type of regenerated cellulosic fiber obtained by the wet spinning process where N-methylmorpholine-N-oxide monohydrate solution is used as the dissolving agent.1 Lyocell fiber differs from other regenerated cellulosic fibers by its high crystallinity, high longitudinal orientation of crystallites, high amorphous orientation, low lateral cohesion between fibrils, low extent of clustering, and relatively large void (pore) volume.25 Hence, these peculiar features prevent the distortion of the high longitudinal stability of lyocell fiber by the penetration of swelling agents.6,7 Alkali treatment of cellulose types (cellulose I, II, III, IV, etc.) and natural (cotton, flax, etc.) and regenerated (lyocell, viscose, modal, etc.) cellulosic materials has always been an attraction for research to understand the effects of alkali (type, concentration, temperature) and material type (fiber, yarn, fabric) on the material properties. To improve dyeability, softness, and dimensional stability, alkali pretreatments are conducted before or after crosslinking to grant durable press properties to cellulosic fibers.8,9 Alkali treatments change the pore structure, crystallinity, unit-cell structure, orientation, and mechanical and thermal properties of fibers.1012 The effects of alkali treatments on materials can be investigated during or after the treatment: During the alkali treatment, swelling degree (alkali retention value, fiber diameter), fibrillation, and splitting tests can be conducted.1315 In interfibrillar swelling, fibrils move apart, and no penetration of swelling agent into the fibrils occurs, whereas intrafibrillar swelling results in penetration of swelling agent into the fibrils.16 Fibrillation is the breakage of fibrils from the surface of a swollen fiber, whereas splitting of a swollen fiber is the separation of fibrils from each other under mechanical force. Split numbers, which are counted under optical microscope,17 indicate the numbers of fibrils split from each other. The threshold concentration where intrafibrillar swelling starts together with interfibrillar swelling was suggested to be 2, 2.5, and 5 M for KOH, NaOH, and LiOH treatments, respectively, according to splitting tests.13,18 r 2011 American Chemical Society
After alkali treatment (i.e., after the removal of alkali from the cellulosic material by washing), fiber properties such as crystallinity, swelling, pore structure, dyeing, mechanical properties, and fibrillation tendency can be investigated.9,1925 As compared to the conventional NaOH treatment of cellulosic materials, LiOH, KOH, and TMAH (tetramethylammonium hydroxide) treatments are mostly reported in the literature. LiOH is not capable of penetrating the crystalline regions of highest order and mainly causes intercrystalline swelling. The crystallite lengths and crystallinity index of cotton were found to be reduced most by KOH treatment and least by LiOH when compared with NaOH treatment.19,24 In technical processing, NaOH is commonly used and KOH is rarely used for the alkali pretreatment of cellulosic materials. LiOH, which is more expensive than NaOH and KOH, is not used industrially but is researched academically to understand the effects of different cations of alkali solutions on cellulosic materials. Apart from the academic interest in LiOH solutions, Li is a highvalue metal in electronic devices. Therefore, recycling of LiOH is of interest. Ultrafiltration through a ceramic membrane can be used to remove LiOH from dispersed cellulose material, which can be followed by reconcentration of LiOH by evaporation of water in technical distillation.26 Judging from the behaviors of NaOH and KOH,27,28 one can expect complete removal of LiOH during the rinsing steps that have to be applied to achieve the production of alkali hydroxide free fibers. In the literature, the effect of LiOH treatment on lyocell fibers has not been investigated in the wide range from 0 to 7.5 M. The aim of this work was to study the effect of LiOH treatment on lyocell fiber properties. The threshold concentration where intrafibrillar swelling together with interfibrillar swelling begins Received: July 22, 2010 Accepted: June 22, 2011 Revised: June 17, 2011 Published: June 22, 2011 9087
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Figure 1. (Δ) Weight loss during LiOH treatment and ([) carboxyl content and (0) WRV of LiOH-treated lyocell fibers.
for lyocell fibers in LiOH was also of interest. Tensile tests; inverse size-exclusion chromatography (ISEC); dyeing with CI Direct Red 81; and measurements of carboxyl content using methylene blue method, weight loss, water retention value, moisture content, and wide-angle X-ray diffraction (WAXD) were performed to characterize fiber properties.
’ EXPERIMENTAL DETAILS Materials. Lyocell staple fiber (Tencel Standard) without spin finishing was kindly supplied by Lenzing AG (Lenzing, Austria). The titer and the length of the fibers were 1.3 dtex and 38 mm, respectively. Analytical-grade lithium hydroxide (LiOH, >99%) was obtained from Fluka (Buchs, Switzerland). NaCl (99.5%) from Merck (Darmstadt, Germany), CI Direct Red 81 (50%) from Sigma-Aldrich, acetic acid (100%) from Merck, sodium acetate (g98.5%) from Fluka, methylene blue CI 52015 from Merck, boric acid (g99%) from Merck, and poly(ethylene glycol) (PEG) and dextran (DEX) probes from Fluka for ISEC (inverse size-exclusion chromatography) were used. Methods. Fiber samples in slack form were immersed in an aqueous LiOH solution for 2 h and then washed, neutralized, and dried according to the method reported in the literature.29 The moisture content30 of fiber samples was measured gravimetrically after they had been conditioned at 20 °C and 65% relative humidity for at least 24 h. The water- and ethanol retention values (WRVs)21,31 of the samples were determined by a centrifugal method after the fibers had been swelled in water for 2 h. Moisture content assesses the sum of freezing bound water (Wf), nonfreezing bound water (Wnf), and bulk water (Wb) in the fibers, whereas WRV assesses the sum of Wf, Wnf, and Wb in the fibers and bulk water between the fibers. The weight loss (%)29 of the fibers was assessed by a centrifugal method after the fibers had been swelled in LiOH solutions of various concentrations. The carboxyl contents of the samples were determined by spectrophotometric analyses after methylene blue sorption of the fibers.32 Pore characteristics (size, volume, surface area) of wet fibers were studied by inverse size-exclusion chromatography (ISEC)33 in which molecules such as DEX and PEG of known molecular weight and diameter were used as probes and eluted in a mobile phase (distilled water) through a column packed with the fiber sample of interest. The ISEC instrument was made up of a
collection of Jasco products [CMA/260 degasser, oven, PU-1580 high-performance liquid chromatography (HPLC) pump, RI1531 detector, LC-Net II/ADC interface, AS-1555 sampler]. Relative color strengths (K/S values) of fiber samples dyed with CI Direct Red 81 were calculated by the KubelkaMunk function.29 Wide-angle X-ray diffraction (WAXD)27,34 analyses were conducted with a Bruker D5005 diffractometer using Cu KR radiation with a wavelength of 1.5418 Å for crystallinity determinations, and Gaussian functions for the 110, 110, and 020 crystallographic planes and one broad Gaussian feature for the amorphous component were taken into consideration. The tenacity and elongation at break27 of single fibers were measured with a Vibrodyn F120 instrument (Lenzing Technik Instruments) after the fibers had been conditioned at 20 °C and 65% relative humidity for at least 24 h.
’ RESULTS AND DISCUSSION Swelling, Carboxyl Content, and Weight Loss. Figure 1 shows the WRV, weight loss, and carboxyl content results for LiOH-treated lyocell fibers. WRV and weight loss showed similar trends in that they increased with increasing LiOH concentration up to ca. 5 M, above which they leveled off. LiOH treatments at concentrations of up to ca. 7.5 M caused a slight decrease in the carboxyl content. In the current study, the WRV and weight loss of LiOHtreated lyocell fibers showed gradual changes up to 5 M LiOH, above which they leveled off. The split number of lyocell fibers also showed a gradual change in LiOH solution up to 5 M.13 Therefore, we suggest 5 M to be the threshold concentration for intrafibrillar swelling (crystalline parts) together with interfibrillar swelling (amorphous parts) of lyocell fibers in LiOH solution. In the literature, gradual changes in WRV, weight loss, carboxyl content, and splitting tendency were reported to occur up to 2.5 3 M for NaOH and 2 M for KOH because of sole interfibrillar swelling of lyocell fibers.13,27,28 In interfibrillar swelling, the fibrils of a fiber move apart because of filling of the swelling agent into spaces. Interfibrillar swelling causes macroscopic changes in fiber affecting WRV, weight loss, carboxyl content, and split number. In intrafibrillar swelling, swelling agent penetrates into the fibrils of a fiber causing micro- and nanosized changes in the fiber. Hence, the effect of intrafibrillar swelling is not measurable by WRV, weight loss, carboxyl content, or splitting tests. The swelling degrees of 9088
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Figure 2. Difference between retention time of each probe (Te) and average of completely excluded probes (To) as a function of probe diameter from ISEC results [([) untreated and (0) 1, (2) 2, () 3, (]) 5, and (Δ) 7.5 M LiOH-treated lyocell fibers].
alkali-treated cotton fiber were reported to level off at treatment concentrations above 5.05 M LiOH, 4 M NaOH, and 3 M KOH.11 The threshold concentration at which intrafibrillar swelling starts was found to become lower (for lyocell fibers, 5 M LiOH, 2.53 M NaOH, 2 M KOH) as the size of the hydrated cations decreased because of easier penetration of the alkali solution into the cellulose structure. The hydrated cation size decreases in the order Li+ > Na+ > K+, according to measurements by column size-exclusion or conducting polymer insertion reported in the literature.35 The WRV order of lyocell fibers treated with LiOH, NaOH, and KOH was found to be LiOH-treated ≈ NaOH-treated27 > KOH-treated.28 In the literature, the WRVs of alkali-treated cotton fibers were reported to decrease in the order LiOH > NaOH > KOH.24,36 The difference in cellulose fiber type caused different impacts of alkali type on swelling degree (WRV). Pore Structure. The difference between the retention time of each probe (Te) and the average of completely excluded probes (DEX 4500000, PEG 511000, and PEG 182000) (To), that is, (Te To), is shown as a function of probe size in Figure 2 according to ISEC results. A higher probe diameter results in a lower Te To value. For 15 M LiOH-treated samples, changes in Te To value were not significant (i.e., less than 1 min) above a probe diameter of 3236 Å. The upper limits on the pore size of untreated, 15 M LiOH-treated, and 7.5 M LiOH-treated samples were found to be 2732, 3236, and 3643 Å respectively. KOH was reported to decrease the upper limit of pore size, whereas NaOH treatments was reported not to change it.27,28 In the current work, LiOH treatments were found to increase it. This can be attributed to the larger hydrated size of LiOH compared to NaOH and KOH, enlarging the pores during the treatment. Even after washing and drying of the fibers, the increased pore size persisted. Swelling changed the packing of intervening cavities, which also prevailed after washing and drying of the fibers.37 The accessible pore volume (APV) of the fibers corresponds to the pore volume of the fibers for each DEX or PEG probe able to access the fibers. Hence, for each DEX or PEG probe, the APV
of the fibers differs. Demonstration of the probe-dependent APV values gives the pore volume distribution of the fibers. APV was calculated for each probe using the equation APV ¼
ðTe To Þ F w
ð1Þ
where F is the flow rate (0.1 mL/min) and w is the weight of dried sample (g).33 APV is a probe-specific value, whereas Vp is an average of various APV values of a given sample type. The APVs of untreated and LiOH-treated lyocell fibers in relation to various DEX/PEG probe sizes are shown in Figure 3 as a function of LiOH treatment concentration. There was a slight increase in APV up to ca. 5 M LiOH, above which the APV increased by ca. 3050% for the 7.5 M LiOH treatment depending on the probe diameter. Values of the average pore volume (Vp), average pore area (Op), and mean pore diameter (Dp) obtained from ISEC are reported in Table 1. The Op values did not change significantly upon LiOH treatment. Only 7.5 M LiOH treatment increased Dp and Vp by ca. 25%, whereas other treatments did not change these values significantly. No correlation between the WRV and APV of LiOH-treated samples was found. In the literature, a correlation between WRV and APV was found for NaOH- and KOHtreated lyocell fibers. The Op values did not change significantly after NaOH and KOH treatments.27,28 Our results are consistent with the literature results, where Vp, Op, and Dp values obtained from ISEC were found to be 0.53 cm3/g, 411 m2/g, and 26 Å, respectively, for lyocell Lenzing fibers having a linear density of 1.3 dtex.38 The Vp, Op, and Dp values of lyocell fibers were reported as 0.53 cm3/g, 417 m2/g, and 25.5 Å, respectively.39 Crystallinity and Moisture Content. Figure 4 shows X-ray diffraction traces for untreated and 7.5 M LiOH-treated lyocell fibers, resolved into three sharp peaks corresponding to the 110, 110, and 020 diffraction planes of cellulose II, as well as a broad amorphous background. These three peaks were at the 2θ angular positions of approximately 12°, 20°, and 21.7°, respectively.40 The crystallinity index of lyocell fibers was found to decrease by around 14% for 1 and 7.5 M LiOH treatments, but a slight 9089
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Figure 3. Accessible pore volume of lyocell fibers as a function of concentration of LiOH treatment from ISEC results [probe diameter: () 6, (+) 9.6, (9) 12.84, (2) 14.23, ([) 17.62, () 19.01, (Δ) 22.05, (0) 26.75, and (]) 31.99 Å].
Table 1. Accessible Total Pore Volume (Vp), Average Total Pore Area (Op), and Average Pore Diameter (Dp) of Untreated and LiOH-Treated Lyocell Fibers Obtained from ISEC; Crystallinity Index (%) and Crystallite Size Values Obtained from WAXD; and Moisture Content (%) pore volume, Vp (mL/g)
pore area, Op (m2/g)
0
0.58 ( 0.04
369 ( 33
32 ( 1
12 ( 0.2
50.5
1 2
0.59 ( 0.01 0.62 ( 0.05
369 ( 1 410 ( 3
32 ( 1 30 ( 2
9.7 ( 0.5 9.0 ( 0.2
43.4 49.0
LiOH concentration (mol/L)
mean pore diameter, Dp (Å)
moisture content (%)
crystallinity index (%)
3
0.64 ( 0.03
408 ( 28
31 ( 1
11 ( 0.1
48.1
5
0.56 ( 0.02
337 ( 52
34 ( 4
12 ( 0.1
49.5
7.5
0.73 ( 0.01
367 ( 16
40 ( 1
9.0 ( 0.3
44.5
decrease for other treatments was observed as measured by WAXD (Table 1). The crystallinity index of lyocell fibers was reported to increase by ca. 1220% after NaOH and KOH treatments, except for 1 and 2 M KOH treatments, which decreased it.27,28 The current study shows that the effect of LiOH treatment on the crystallinity index of lyocell fibers differs from that of other alkali treatments by decreasing it. Lenz et al. mentioned that swelling decreases the crystallinity of regenerated cellulosic fibers through the cleavage of hydrogen bonds, but after rinsing and drying, crystallinity becomes higher than before.41 It is expected that, after LiOH treatment (i.e., because of a larger hydrated size), lyocell fibers could not recrystallize as much as before, even after being rinsed and dried. In addition to changes in the APV, an increase in the amount of amorphous parts (i.e., a decrease in the overall crystallinity) by LiOH treatments can also result in higher WRV. In the literature, the crystallinity of LiOH-treated cotton fibers was reported to decrease with increasing concentration up to 3.9 M, whereas above 3.9 M, it increased slightly up to 4.5 M. LiOH was reported not to be capable of penetrating the crystalline regions, that is, to cause mainly interfibrillar swelling. The crystallite lengths in cotton were reduced the least by LiOH treatment, whereas they were reduced the most by KOH treatment.11,19 Changes in crystallite size along the longitudinal direction of the fibers, changes across the cross section of the fibers, and changes at an angle between these planes refer to the 110, 110, and 020 planes, respectively. Sodium hydroxide causes swelling and separation
of the 110 planes, causing this peak to move to lower angles, as also happens to a lesser degree in the case of the 020 peak.34,42 The crystallite size normal to the 110 and 020 planes increased gradually as the LiOH concentration increased up to ca. 5 M (Figure 5), above which it leveled off in a trend analogous to those of the WRV, carboxyl content, and weight loss. Interfibrillar swelling at LiOH concentrations of up to ca. 5 M causes mainly reorganization of the amorphous parts of the fibers, increasing the crystallite size. The crystallite size normal to the 110 planes did not change upon LiOH treatment (Figure 5), similarly to NaOH treatment,27 whereas it was affected by KOH treatment.28 The moisture contents of untreated and LiOH-treated lyocell fibers are listed in Table 1. A maximum decrease of around 25% in moisture content was found for LiOH-treated samples depending on the treatment concentration, which is considerably higher than the standard deviation of the method used. The decrease in moisture content of LiOH-treated samples can be attributed to the increased crystallite size. This is in agreement with the effects of NaOH and KOH treatments reported in the literature.27,28 Cellulose that regains a high moisture content is not necessarily highly amorphous, but it could also be obtained from crystalline cellulose with a small crystal size.43,44 The moisture content of LiOH-treated samples was found to be comparable to the values of NaOH- and KOH-treated samples.27,28 The increase in overall crystallinity is assumed to be responsible for the decreased moisture content (i.e., the decrease 9090
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Industrial & Engineering Chemistry Research in easily accessible amorphous region).37,45 The cellulose II structure forms a hydrate (C6H10O5 3 1/3H2O or C6H10O5 3 1/2H2O) upon sorption of water vapor, whereas crystalline regions of cellulose I do not form hydrates.46,47 The first strong sorption of water to cellulose is caused by hydrogen bonding of water molecules to the accessible hydroxyl groups, which act as sorption sites.43
Figure 4. WAXD of (a) untreated lyocell fiber and (b) 7.5 M LiOHtreated lyocell fiber.
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These accessible hydroxyl groups can be either in the amorphous areas or in the surface of crystalline regions. The percentage of hydroxyl groups in the crystalline regions would increase with decreasing crystal sizes because of the increased surface area of the crystalline regions. When two cellulosic materials with equal amounts of amorphous regions are compared, the sample with smaller crystallite size will exhibit a higher sorptive capacity.43,44 CI Direct Red 81 Dye Uptake. The color strengths (K/S) of dyed samples are shown in Figure 6. Up to ca. 3 M treatment, K/S of LiOH-treated fibers did not change significantly. Only 5 and 7.5 M LiOH-treated samples showed higher color strengths (K/S). The inter- and intrafibrillar (crystalline parts) reorganization of lyocell fiber after 5 and 7.5 M LiOH treatments led to higher Direct Dye 81 uptake compared to other treatments, which were able to reorganize the fiber structure only interfibrillarly (amorphous parts). Correlation between Color Strength and Carboxyl Content. Figure 7 shows the linear relation between the color strength (K/S) and carboxyl content of LiOH-treated fibers. As the carboxyl content decreased, the color strength increased. This trend was also observed for NaOH-treated lyocell fibers and attributed to the repulsion forces between the anionic functional groups of direct dyes and the anionic groups of cellulosic fibers during the dyeing process.27,48,49 This relation was not observed for KOH-treated lyocell fibers,28 which was attributed to the shallow (superficial, i.e., lacking depth) penetration ability of KOH compared to the deep penetration abilities of NaOH and LiOH into lyocell fiber. Deeper penetration of alkali into a fiber increases the accessibility of the fiber through its cross section. Tensile Mechanical Properties. LiOH treatments did not change the elongation at break of lyocell fibers significantly. One molar LiOH treatment did not change the tensile strength of the fibers significantly. Tensile strength decreased gradually at concentrations between 1 and 5 M. At concentrations above ca. 5 M, the fibers were too brittle to conduct the tensile test (Figure 8). In the literature, tensile tests of lyocell fibers could not be conducted after NaOH treatments at concentrations of above 3 M. This was attributed to the intrafibrillar swelling of fibers during treatments causing brittleness of the fibers after treatments. Although intrafibrillar swelling occurred at concentrations above 2 M in KOH, tensile tests could be conducted for lyocell fibers. This shows that the brittleness of fibers occurs not only because
Figure 5. Crystallite sizes normal to the ([) 110, (0) 110, and (Δ) 020 planes of LiOH-treated lyocell fibers. 9091
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Figure 6. Color strength of untreated and LiOH-treated samples.
Figure 7. Plot of color strength versus carboxyl content measured by the methylene blue sorption method for LiOH-treated lyocell fibers.
Figure 8. ([) Tensile strength and (0) elongation at break values of untreated and LiOH-treated lyocell fibers. 9092
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Industrial & Engineering Chemistry Research of intrafibrillar swelling but also because of the deep penetration ability of the alkali type. KOH can penetrate only outer regions (shallow penetration) of the fibers, whereas NaOH can penetrate into the fiber core (i.e., NaOH has a deep penetration ability).27,28 Higher swelling degree (measured by alkali retention value) was obtained in the order NaOH > LiOH > KOH for lyocell fibers,13 which explains the loss in tensile strength in the reverse order. The higher the swelling during the alkali treatment, the weaker the fiber structure after the alkali treatment. Bhama-Iyer et al. mentioned that the higher degree of hydration of LiOH caused excessive swelling, which reduced the tenacity of cotton fibers considerably compared to NaOH and KOH solutions.9 During swelling, hydrogen bonds of cellulose are broken to form new hydrogen bonds between water molecules and the hydroxyl groups of cellulose.50 A reduction in strength due to the breakage of hydrogen bonds has been found in regenerated cellulose.51,52 In the intercrystalline region (amorphous parts) of cellulose, the orientation of chain molecules in relation to the fiber axis is irregular, and the density of interchain H-bonds is low; therefore, swelling is limited to this region and does not appreciably change the physical properties of cotton fibers. On the other hand, some swelling agents are able to break the interchain H-bonds in the crystalline region of the fiber, which results in the intracrystalline swelling and a lowered orientation, a loss of strength, and an increase in moisture uptake and accessibility.53 Orientation is an important parameter for the tensile properties of cellulose II fibers in that both the ultimate strength and initial modulus increase with increasing orientation.54 The tensile properties of untreated lyocell fibers depend on their crystallite orientation factor, whereas the tensile strength of lyocell fibers treated with NaOH depend on their amorphous orientation factor.6 Elongation at break was found to be inversely proportional to the amorphous orientation factor.41,55
’ CONCLUSIONS The effects of LiOH treatments on lyocell fiber properties at concentrations from 0 to 7.5 M were studied. The WRV, APV, and weight loss of LiOH-treated lyocell fibers changed gradually up to 5 M LiOH treatment concentration owing to interfibrillar (amorphous parts) swelling of fibers. Above 5 M, the WRV, APV, and weight loss values leveled off. Removal of easily dissoluble parts of cellulose from amorphous parts of the fibers caused the weight loss. The amount of the water kept in the amorphous parts and pores (APV) of lyocell fibers was demonstrated by WRV. Inter- and intrafibrillar swelling, together with the deep penetration ability of LiOH solution above 5 M, decreased the tensile strength of the lyocell fibers and caused brittleness. The large hydrated size of the Li+ cation in solution during alkali treatment resulted in a larger pore diameter size and a higher amount of amorphous parts in lyocell fibers after alkali treatment. ’ AUTHOR INFORMATION Corresponding Author
*Tel.: ++43-5572-28533. E-mail:
[email protected].
’ ACKNOWLEDGMENT The authors gratefully acknowledge the Christian-Doppler Research Society and Lenzing AG-Austria for financial and material support, Versuchsanstalt HTL-Dornbirn for equipment, and
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EPNOE for the Ph.D. student exchange program. We are grateful to Edith Winder and D.Ing. Margit Lenninger for assistance in sample preparation and data analyses for ISEC, respectively. The institutions where this work was performed, University of Innsbruck and University of Nottingham, are members of the European Polysaccharide Network of Excellence (EPNOE), www.epnoe.eu.
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