Ind. Eng. Chem. Res. 2005, 44, 4599-4604
4599
Ionic Liquids and Paper Kazimierz Przybysz, Ewa Drzewin ´ ska, Anna Stanisławska, and Agnieszka Wysocka-Robak Institute of Papermaking and Printing, Ło´ dz´ University of Technology, ul. Wo´ łczan´ ska 223, 90-924 Ło´ dz´ , Poland
Anna Cieniecka-Rosłonkiewicz Institute of Industrial Organic Chemistry, ul. Annopol 6, 03-236 Warsaw, Poland
Joanna Foksowicz-Flaczyk and Juliusz Pernak* Faculty of Chemical Technology, Poznan´ University of Technology, pl. Skłodowskiej-Curie 2, 60-965 Poznan´ , Poland
The continuing increase of interest in ionic liquids prompts us to search both for new compounds and for their new potential application. The aim of this study was to examine the influence of ionic liquids (ILs) on the cellulose product, paper. In the studies, commercially available 3-alkyl1-methylimidazolium tetrafluoroborates and prepared 3-alkoxymethyl-1-methylimidazolium tetrafluoroborates and 3-alkoxymethyl-1-methylimidazolium bis(trifluoromethanesulfonyl)imides were used. Obtained salts with bis(trifluoromethanesulfonyl)imide anion are new compounds. ILs were found to impregnate paper, affecting its strength and other physical parameters. Various properties of paper were distinctly altered after treatment with ILs of varying anions. In general, IL-treated paper had decreased strength, which resulted from weakening of cellulose hydrogen bonds. On the other hand, paper wettability improved. Paper treated with 1-methyl-3octyloxymethylimidazolium tetrafluoroborate proved to be fully resistant to activity of moulds and fungi, inducing the blue discoloration of the paper. Introduction Ionic liquids (ILs) are a class of compounds composed of organic cations and organic or inorganic anions. Broadly speaking, such organic compounds which melt at or below 100 °C are considered ionic liquids. Salts which are liquid at room temperature are called room temperature ionic liquids (RTILs). In recent years, the number of possible cation and anion combinations has increased significantly as to make possible the existence of 106 ILs.1 Since 1997 RTILs have been the subject of intense focus due to their lack of volatility. Since they are nonvolatile and nonflammable, the risk of worker exposure and the loss of solvent into the atmosphere are diminished. This nonvolatile nature suggests that ILs might potentially be the “green solvents”, alternatives to the conventional volatile organic solvents. RTILs are highly solvating, yet noncoordinating, with a large liquid range. They dissolve many metals complexes, catalysts, organic compounds, and gases and can also be immiscible with many organic solvents and water. ILs also have a number of properties that make them suitable media for use as electrolytes in batteries, photoelectrochemical cells, solvents for a variety of chemical reactions, separation applications, lubricants,2 liquid crystals,3 and even embalming fluids.4 Their unique properties have already been demonstrated and many of the publications about the synthesis and potential application are covered in numerous excellent reviews.5-12 The most common ILs in use are those containing alkylammonium, alkylphosphonium, 1-alky* To whom correspondence should be addressed. E-mail:
[email protected].
lpyridinium, and 1,3-dialkylimidazolium cations. Actually, the imidazolium salts, in which an important role is played by the acidic proton of the imidazolium ring, are the dominant ones. Anions such as BF4-, PF6-, NO3-, CF3SO3-, [(CF3SO2)2N- ) Tf2N-], CF3COO-, (CN)2N-, AlCl4-, Al2Cl7-, Al3Cl10-, CuCl2-, CuCl3-, etc. can be used in combination with the above cations to form low melting temperature liquids. The nature of the anion is largely responsible for the chemical properties of ILs. The chloroaluminate ionic liquids are very sensitive to contact with oxygen and water. Hexafluorophosphates are unstable and will hydrolyze in contact with moisture, forming volatiles, including HF, POF3 etc.13 ILs which have anions such as BF4-, NO3-, CF3SO3-, Tf2N-, CF3COO-, and (CN)2N- are stable in air, water, and other common organic solvents. The interactions between water and ionic liquids and their degree of hydroscopic character are strongly dependent on anions of the ionic liquids. In a given time, the amount of absorbed water is highest in BF4- and lowest in PF6-.14 However, Tf2N- is much more stable in water, as well as having the advantage of an increased hydrophobic character. ILs are most easily obtained by metathesis, starting from the precursor chloride salts. ILs containing “noncoordinating” anions, including BF4- and PF6-, are not suitable solvents for cellulose15 but are suitable wood preservatives16 and effective antielectrostatic agents for pine and maple.17 On the other hand, 1-butyl-3-methylimidazolium chloride (IL) dissolves unmodified cellulose. Therefore chloride disrupts and breaks the hydrogen bonding present between the cellulose chains.15,18,19 High-resolution 13C NMR studies of cellulose and cellulose oligomers dissolved in 1-butyl-
10.1021/ie0402315 CCC: $30.25 © 2005 American Chemical Society Published on Web 05/26/2005
4600
Ind. Eng. Chem. Res., Vol. 44, No. 13, 2005
Scheme 1
3-methylimidazolium chloride (IL) show that the β-(1 f 4)-linked glucose oligomers are disordered in this medium and have a conformational behavior which parallels the one observed in water, and thus, reveal that the polymer is disordered in IL solution as well.20 In this study we will present the influence of ILs on cellulose product such as paper. Experimental Section 3-Alkoxymethyl-1-methylimidazolium tetrafluoroborates [CnOmim][BF4], bis(trifluoromethanesulfonyl)imides [CnOmim][Tf2N], and commercially available ILs 3-alkyl-1-methylimidazolium tetrafluoroborates [Cnmim][BF4] were selected (see Scheme 1). Obtained salts with bis(trifluoromethanesulfonyl)imide anion are new ionic liquids. 1H NMR spectra were recorded on a Varian Model XL 300 spectrometer at 300 MHz with tetramethylsilane as the standard. 13C NMR spectra were recorded on the same instrument at 75 MHz. A Melter Toledo DA-110M scale was used for the mass/density measurement. Refractive index of ILs was measured using Abbe’s refractometer, RL1 (PZO, Warsaw, Poland). Preparation of 3-Alkoxymethyl-1-methylimidazolium Chloride [CnOmim][Cl]. To a stirred solution of 1-methylimidazole (0.1 mol, freshly distilled) in anhydrous hexane (30 mL), the corresponding chloromethyl alkyl ether (0.1 mol) was added dropwise at r.t. The solution was stirred at r.t. for 1 h. The obtained chloride [CnOmim][Cl] was washed with hot hexane (30 mL). The final product was obtained as a hygroscopic compound and required rotary evaporation at 50 °C/8 mmHg for 8 h. 3-Hexyloxymethyl-1-methylimidazolium Chloride [C6Omim][Cl]. 1H NMR (DMSO-d6) δ [ppm]: 9.79 (s, 1H), 8.01 (t, J ) 2 Hz, 1H), 7.95 (t, J ) 2 Hz, 1H), 5.68 (s, 2H), 3.96 (s, 3H), 3.54 (t, J ) 6 Hz, 2H), 1.51 (m, 2H), 1.29 (m, 6H), 0.87 (t, J ) 7 Hz, 3H). 13C NMR (DMSO-d6) δ [ppm]: 137.2, 123.8, 121.7, 77.9, 69.1, 35.9, 30.9, 28.7, 25.0, 22.0, 13.9. Preparation of 3-Alkoxymethyl-1-methylimidazolium Tetrafluoroborate [CnOmim][BF4] was prepared following the reported procedure.21 3-Heptyloxymethyl-1-methylimidazolium tetrafluoroborate [C7Omim][BF4]. 1H NMR (DMSO-d6) δ ppm: 9.24 (s, 1H), 7.84 (t, J ) 2 Hz, 1H), 7.75 (t, J ) 2 Hz, 1H), 5.55 (s, 2H), 3.89 (s, 3H), 3.51 (t, J ) 7 Hz, 2H), 1.52 (m, 2H), 1.46 (m, 8H), 0.88 (t, J ) 7 Hz, 3H). 13C NMR (DMSO-d6) δ ppm: 136.9, 123.9, 121.7, 78.1, 69.2, 35.9, 31.2, 28.7, 28.4, 25.3, 22.1, 13.9. Preparation of 3-Alkoxymethyl-1-methylimidazolium Bis(trifluoromethanesulfonyl)imide [CnOmim][Tf2N]. A saturated aqueous solution of LiNTf2 was added to stoichiometric amounts of a saturated hot water solution of [CnOmim][Cl]. The reaction mixture was stirred at r.t. for 2 h. After phase separation, the water phase was decanted and the obtained IL was washed 3 times with water (30 mL).
The obtained IL was dried for 8 h at 40 °C in a vacuum. [CnOmim][Tf2N] were obtained with 79-94% yield. 3-Hexyloxymethyl-1-methylimidazolium bis(trifluoromethanesulfonyl)imide [C6Omim] [Tf2N]. 1H NMR (DMSO-d6) δ ppm: 9.27 (s, 1H), 7.85 (t, J ) 2 Hz, 1H), 7.76 (t, J ) 2 Hz, 1H), 5.55 (s, 2H), 3.89 (s, 3H), 3.50 (t, J ) 7 Hz, 2H), 1.52 (m, 2H), 1.27 (m, 6H), 0.88 (t, J ) 7 Hz, 3H). 13C NMR (DMSO-d6) δ ppm: 136.9, 123.9, 121.7, 78.1, 69.1, 35.9, 30.9, 28.6, 25.0, 22.0, 13.9. Signals of carbon from Tf2N- anion: 125.7, 121.5, 117.2, 113.0. Preparation of 3-Alkyl-1-methylimidazolium Tetrafluoroborate [Cnmim][BF4]. [Cnmim][BF4] was prepared following the reported procedures.22 Properties of ILs. Properties of 3-alkoxymethyl-1methylimidazolium bis(trifluoromethanesulfonyl)imides [CnOmim][Tf2N], 3-alkoxymethyl-1-methylimidazolium tetrafluoroborates [CnOmim][BF4], and 3-alkyl-1-methylimidazolium tetrafluoroborates [Cnmim][BF4] are presented in Table 1. All of the tetrafluoroborates and bis(trifluoromethanesulfonyl)imides which were prepared were liquids at r.t. Additionally, all the purchased ionic liquids were heavier than water. [CnOmim][Tf2N] did not dissolve in water. On the other hand, [CnOmim][BF4] with butoxymethyl substituent dissolved completely in water while those with pentyloxymethyl and hexyloxymethyl substituents dissolved only partially and those with heptyloxymethyl and octyloxymethyl substituent were immiscible with water at r.t. The commercially available [Cnmim][BF4], either with octyl or decyl substituent, were not miscible with water at r.t. Paper. Printing paper without surface sizing, having a basic weight of 90 g/m2, was used in the investigations. Measurements were conducted on untreated paper and paper impregnated with IL. At the equilibrium with the surrounding air, the untreated paper moisture content ranged from 5 to 10%. The investigated ILs were applied onto the surface of paper by a drawn-down technique, using a thin glass baguette. The treated paper samples contained 14-24 g of IL per m2 of paper, as shown in Table 1. The samples were stored at a constant temperature of 23 ( 1 °C, in a constant relative humidity (50 ( 2%) room, according to the ISO standard.23 The first measurement was performed after 24 h. Then, to determine the effect of time on the investigated properties, the measurement was conducted after 30 days. Water-Paper Interactions. Water penetration dynamics and water absorption were determined using a PDA device (Penetration Dynamics Analyzer, Emtec Electronic, Germany). The PDA is an analytical instrument designed for investigating the penetration dynamics of solid material samples, such as paper, by liquids. Data acquisition commences with initial contact, and results are displayed on the screen of a PC monitor in the form of curves of degree of penetration versus time. The results of this analytical technique are based on recording the changes of the intensity of ultrasonic signals transmitted through solid samples while one of their surfaces was in contact with a liquid.24,25 At least three measurements were conducted for each paper sample. Water Absorption. (Cobb30 - PDA) was computed by PDA software based on the volume of water that penetrated the solid during 30 s; i.e., the extent of paper saturation with water was determined for a period of 30 s.24,25 At least three measurements were conducted
Ind. Eng. Chem. Res., Vol. 44, No. 13, 2005 4601 Table 1. Ionic Liquids Prepared
salta
R
molar volumeb (mL/mol)
[C4Omim][Tf2N]* [C5Omim][Tf2N]* [C6Omim][Tf2N]* [C7Omim][Tf2N]* [C8Omim][Tf2N]* [C9Omim][Tf2N]* [C4Omim][BF4] [C5Omim][BF4] [C6Omim][BF4] [C7Omim][BF4] [C8Omim][BF4] [C8mim][BF4] [C10mim][BF4]
C4H9 C5H11 C6H13 C7H15 C8H17 C9H19 C4H9 C5H11 C6H13 C7H15 C8H17 C7H15 C9H19
314.06 323.62 333.02 342.58 351.97 361.56 179.82 189.44 198.77 208.29 217.72 257.65 291.52
a
densityb (g/mL)
Tdd (°C)
refractive indexb
amount of IL in paper [g/m2]
1.422 1.391 1.359 1.329 1.316 1.290 1.189 1.155 1.141 1.133 1.113 1.095 (1.08)c 1.064 (1.04)c
220 220 215 210 220 210 210 195 205 205 210 360 390
1.4309 1.4320 1.4337 1.4346 1.4362 1.4369 1.4239 1.4257 1.4293 1.4313 1.4338 1.4322 1.4367
14 20 18 16 14 18 19 20 22 23 24 18 20
The asterisk “*” indicates new ionic liquids. b At 25 °C. c Reference 29.
for each paper sample. The coefficient of variation was less than 0.3%. Surface Receptivity. Surface receptivity was measured using the xylene drop method, according to Polish standard.26 The time between the moment the glossy stain has been made by a drop of xylene (dyed with Sudan B) and the disappearance of glossy surface is a measure of surface receptivity, expressed in seconds. The longer the time needed for the sudden drop in gloss, the lower the surface receptivity. The coefficient of variation was less than 4%. Opacity. Opacity was measured by reflectance and determined according to the ISO standard.27 The measurements were conducted in a spectrophotometer (SpectroEye, Gretag Macbeth). The coefficient of variation was less than 1.2%. Breaking Length and Elongation. Breaking length and elongation at break were established according to the ISO standard,28 for clamping length of 100 mm. The coefficients of variation were less than 4%. Paper Resistance to Moulds and to the Fungi Which Induces Blue Discoloration of Paper. Resistance of paper impregnated with IL due to the effects of moulds and of fungi inducing blue discoloration of paper was examined. The two ionic liquids selected for this experiment were [C8Omim][BF4] and [C9Omim][Tf2N]. In this study the ionic liquids were applied to the paper using two techniques, including (1) application onto the surface of paper using a thin glass baguette (14-24 g of IL per 1 m2 of paper) and (2) full infiltration method, mimicking the development of paper chromatography spots 55-64 g of IL per 1 m2 of paper). The studies were conducted using two spores mixtures of moulds which attack paper. Mixture I: Aspergillus amstelodami [(Mangin) Thom and Church], Aspergillus terreus (Thom), Aureobasidium pullulans [(de Barry)Arnaud], Penicillium brevicompactum (Dierck), Penicillium funiculosum (Thom), Stachybotrys atra (Corda), Penicillium ochrochloron (Biourge), Scopulariopsis brevicalis [(Sacc.) Bain var. Glabra Thom]. Mixture II: Aspergillus niger (van Tieghem), Alternaria tenuis (Nees), Chaetomium globosum (Kunze), Cladosporium herbarum (Presoon Link), Trichoderma viride (Pers. ex Fries), Paecilomyces varioti (Bainier). Paper samples, 60 × 60 mm, were placed on CzapekDox medium supplemented with sucrose and infected with a suspension of spore mixture, containing 107 spores per mL. The infected samples were incubated in conditions promoting fungus development, i.e., at 29 (
d
Thermal degradation temperature.
Scheme 2
1 °C and 95% relative air humidity for a period of 35 days. In this period after 2 and 5 weeks the extent of sample overgrowth by the fungi was examined twice. The extent of sample overgrowth by fungi was expressed in percents. The control sample involved a paper infiltrated with water and infected with fungal spores. Results and Discussion ILs were made in a two-stage procedure shown in Scheme 2. In the first step 1-methylimidazole was quaternized with ROCH2Cl. This Menschutkin reaction, taking place by a SN1 mechanism, formed [CnOmim][Cl] with 80-96% yields. The resulting chloride salts were employed as synthetic precursors of ILs. During the second stage, the metathesis reaction was conducted in an aqueous solution. Obtained 3-alkoxymethyl-1methylimidazolium bis(trifluoromethanesulfonyl)imides are new compounds. All ILs, except for [C4Omim][BF4], were decanted from a reaction mixture. [C4Omim][BF4] was isolated by extraction with ethyl acetate. ILs were then washed with water until no chloride ion was detectable using AgNO3. The densities of the homologous series of ILs in Table 1 decreased with an increasing number of carbon atoms in the alkyl chain and approached that of water. Correspondingly, the calculated values of molar volume increased with increasing carbon chain length. Impregnation of paper with ILs did not result in any deformation of the paper and the paper manifested no tendency for undulation. The penetration curves, demonstrated in Figure 1, indicated water penetration rate in the course of 30 s for both untreated paper and paper impregnated with IL. The latter penetration rapidly reached equilibrium. For [C8Omim][BF4] and [C8Omim][Tf2N] this occurred by 10 and 20 s, respectively. The amount of water absorbed by 1 m2 of paper in 30 s was also measured and the Cobb30 index was established. As shown previously in Table 1, values of density and molar volume of ILs changed linearly in the homologous series. Therefore, the established values of
4602
Ind. Eng. Chem. Res., Vol. 44, No. 13, 2005
Figure 1. Penetration curves of water into clean paper and paper impregnated with [C8Omim][Tf2N] (1) and [C8Omim][BF4] (2). Figure 3. Absorptiveness of the surface using method of xylene drop of paper impregnated with [CnOmim][Tf2N] (1), [CnOmim][BF4] (2), and [Cnmim][BF4] (3) as a function of molar volume.
Figure 2. Graph of values of Cobb30 of paper impregnated with [CnOmim][Tf2N] (1), [CnOmim][BF4] (2), and [Cnmim][BF4] (3) as a function of molar volume.
Cobb30 could be related either to molar mass, length of alkyl substituent, density, or molar volume of ILs. The most clear-cut relations were obtained selecting molar volume. The straight lines in Figure 2 present the relationship of Cobb30 value and molar volume. The strong effect of anion was evident. The curve fit for [CnOmim][BF4] and [Cnmim][BF4] was characterized by the low gradient of alterations. On the other hand, the fit was entirely different for [CnOmim][Tf2N]. Differences in curves are due to different characteristics of used ILs. [Tf2N] salts are definitely more hydrophobic than [BF4] salts. Values of Cobb30 for a paper impregnated with the ILs strongly depended on their molar volume. The greater molar volume, the smaller density of ILs, better paper penetration, and higher values of Cobb30. But in the case of [Tf2N] salts values strongly depend on hydrophobicity, and decrease with increase of hydrophobicity and molar volume. The lowest value of Cobb30 equal to 28 g/m2 was obtained for [C9Omim][Tf2N], demonstrating that the paper treated with the IL was most hydrophobic. Moreover, the [CnOmim][Tf2N]treated paper was characterized by significantly lower values of Cobb30 than papers impregnated with [CnOmim][BF4] and [Cnmim][BF4]. In general, [BF4] salts penetrated paper fibers and augmented wettability of the paper more than [CnOmim][NTf2] did. After 30 days the Cobb30 index did not decrease. The use of IL induced a marked decrease in the surface absorption potential of the paper as established by the xylene technique. The results are presented in Figure 3 as paper surface absorption potential as a function of molar volume. The anion has a significant effect on the measured value of absorptive potential. For [BF4] salts, the larger molar volumes resulted in a
Figure 4. Absorptiveness of the surface using method of xylene drop of clean paper and paper impregnated with [C8Omim][Tf2N] (1), [C8Omim][BF4] (2), and [C8mim][BF4] (3).
greater extent of sizing, thus, the lower the surface absorption ability. The most pronounced surface sizing was observed in the case of paper impregnated with [C10mim][BF4], for which the time of xylene spot mirror decay reached the highest value of 54 s. On the other hand, appearance of the maximum for [Tf2N] salts was associated with their solubility in xylene. [C4Omim][Tf2N], [C5Omim][Tf2N], [C6Omim][Tf2N], and [C7Omim][Tf2N] are insoluble in xylene, [C8Omim][Tf2N] is soluble in high temperatures while [C9Omim][Tf2N] can be dissolved already at room temperature. All of the [BF4] salts are insoluble in xylene. A comparison of the paper impregnated with ILs with an alkyl substituent of 8 carbon atoms with untreated paper (see Figure 4) demonstrated a marked decrease in the surface absorption potential. On the other hand, after 30 days the absorption potential of IL impregnated paper increased. Nevertheless, the potential still remained lower than that of the untreated paper. The penetration of the ILs from the surface to the interior was reflected by the augmented surface absorption potential after 30 days. The time of xylene spot disappearance from paper impregnated with [BF4] salts decreased by 40%, while in the case of [C8Omim][Tf2N] it decreased only slightly, by 9%. This would indicate that [BF4] salts better penetrated the paper interior. ILs evidently decreased paper opacity or increased its transparency, as compared to the untreated paper, for which the measured opacity value was 94% (see Figure 5). The paper samples were treated with ILs which had
Ind. Eng. Chem. Res., Vol. 44, No. 13, 2005 4603 Table 2. Extent of Mould Overgrowth of Clean Paper and Paper Impregnated with ILs mould mixture I salt [C8Omim][BF4]a [C8Omim][BF4]b [C9Omim][Tf2N]a [C9Omim][Tf2N]b control a
2 weeks [%] 75 0 65 50
60 0 60 60 100
mould mixture II
5 weeks [%] 75 0 50 70
80 0 80 90
80 0 80 90 100
2 weeks [%] 80 0 80 90
60 0 80 95
30 0 80 95 100
5 weeks [%] 30 0 80 90
80 0 90 100
80 0 90 100 100
80 0 90 100
Paper impregnated with 14-24 g/m2. b Paper impregnated with 55-64 g/m2.
Figure 5. Opacity of paper impregnated with [CnOmim][Tf2N] (1), [CnOmim][BF4] (2), and [Cnmim][BF4] (3) dependent on refractive index.
a refractive index ranging from 1.4239 to 1.4369 as compared to 1.000 for air. Thus, paper impregnation with IL resulted in a reduced difference between the refractive index of cellulose fiber (1.5) and that of IL, as well as between the refractive index of the filler (approximately1.6) and that of IL, which resulted in a decreased opacity. The values of the IL refractive indices listed in Table 1 are linearly related to the length of alkyl substituent in a given homologous series. As evident from the curves in Figure 5, [BF4] salts decreased the opacity of paper with increasing length of the alkyl substituent, although no such relationship was noted for the [Tf2N] salts. After 30 days no significant changes could be detected in opacity of paper impregnated with IL. Paper impregnated with ILs resulted in deterioration of respective resistance parameters, as compared to those of untreated paper for which the measured breaking length amounted to 4600 m. As shown in Figure 6, a linear relation existed between the breaking length of the impregnated paper and a molar volume of ILs. We can observe here a relation that is similar to the relationship of Cobb30 value and anion. [BF4] salts with increasing values of molar volume were observed to be associated with a decrease of breaking length. On the other hand, in the cases of [Tf2N] salts a reciprocal relationship was noted: values of breaking length for paper treated with the compounds increased with their rising molar volume. Values strongly depend on hydrophobicity of [Tf2N] salts. The lowest value of the breaking length was documented for paper treated with [C4Omim][Tf2N]. Elapsing time was found to have an affect on the value of breaking length of the impregnated paper. The differences were significant, as presented in Figure 6. In the case of [CnOmim][BF4] and [Cnmim][BF4] the values deteriorated after 30 days, indicating that the compounds penetrated the paper fibers and significantly weakened the hydrogen bonds.
Figure 6. Breaking length of paper impregnated with [CnOmim][Tf2N] (1), [CnOmim][BF4] (2), and [Cnmim][BF4] (3 as a function of molar volume and time, where I is first day and II after 30 days).
According to literature data, ILs influence hydrogen bonding present between the cellulose chains.15,18,19,20 Carried studies show that impregnating paper with ILs worsens its strength properties, and thus it confirms literature data. On the other hand, the paper impregnated with [CnOmim][Tf2N] manifested with elapsing time the augmented values of breaking length and, thus, demonstrated that [BF4] salts bound to cellulose fibers. In this case a significant role of anion was demonstrated. In Tf2N anion delocalization of negative charge was proven within the S-N-S core.30 Also the elongation at rupture of paper manifested changes following impregnation with ILs. As compared to untreated paper, the ILs decreased the paper elongation: the untreated paper showed elongation of 0.6% as compared to 0.5% for the IL-impregnated paper. The value was identical for all of the examined ILs regardless of the length of alkyl chain and the type of anion. In the course of the subsequent time period of 30 days, the values remained the same. In general, [CnOmim][BF4] penetrated the paper better and induced a more pronounced decrease in its resistance than did [CnOmim][Tf2N]. Biological properties of imidazolium chlorides are generally known: they manifest activity against bacteria and fungi.31,32 ILs, which were applied to the paper, also belong to the same class of imidazolium salts. The results obtained for two ILs, [C9Omim][Tf2N] and [C8Omim][BF4], are presented in Table 2. Full preservation of the paper was achieved when [C8Omim][BF4] was used in the amount of 55-64 g per 1 m2 of paper. On the other hand, [C9Omim][Tf2N] proved ineffective. Conclusion The above studies indicated an altered resistance, optical parameters, surface sizing, and surface absorptive potential for ILs-impregnated paper. In general,
4604
Ind. Eng. Chem. Res., Vol. 44, No. 13, 2005
resistance parameters of the impregnated paper deteriorated and opacity as well as surface absorptiveness decreased. The extent of the observed changes depended on the applied IL (both on the anion type and size of the cation). The type of anion exerted a more pronounced effect on the measured variables. Tests performed 30 days after treatment indicated that ILs with noncoordinating anions such as [BF4] penetration of the paper. Weakening of hydrogen bonding in the cellulose leads to the deteriorated resistance properties of the treated paper. On the other hand, the [Tf2N] anion, in which delocalization of negative charge takes place, at first significantly deteriorates resistance parameters but then subsequently improves it over time. In this case, an equilibrium is slowly reached between IL and cellulose fibers. The potential for full protection against action of moulds and the blue color-inducing fungi is of key importance for the impregnation of paper with ILs. The performed tests have unequivocally indicated the need for continuation of the studies. The tested ILs represent only a small fraction of the enormous group of compounds from which the most effective should be selected for further studies. Major changes in the cation, for instance to phosphonium or ammonium, can have a significant impact on the properties of the treated paper. The proper selection will significantly affect properties of the paper and its preservation. Acknowledgment We are grateful for the financial support received from Poznan˜ University of Technology DS-32/007/2004. Literature Cited (1) Holbrey, J. D.; Seddon, K. R. Ionic Liquids. Clean Prod. Processes 1999, 1, 223-236. (2) Wang, H.; Lu, Q.; Ye, C.; Liu, W.; Cui, Z. Friction and Wear Behaviours of Ionic Liquid of Alkylimidazolium Hexafluorophosphates as Lubricants for Steel/Steel Contact. Wear 2004, 256, 44. (3) Abdallah, D. J.; Robertson, A.; Hsu, H. F.; Weiss, R. G. Smectic Liquid-Crystalline Phases of Quaternary Group VA (Especially Phosphonium) Salts with Three Equivalent Long n-Alkyl Chains. How do Layered Assemblies Form in LiquidCrystalline and Crystalline Phases. J. Am. Chem. Soc. 2000, 122, 3053. (4) Majewski, P.; Pernak, A.; Grzymisławski, M.; Iwanik, K.; Pernak, J. Ionic Liquids in Embalming and Tissue Preservation. Acta Histochem. 2003, 105 (2), 135. (5) Welton, T. Room-Temperature Ionic Liquids. Solvents for Synthesis and Catalysis. Chem. Rev. 1999, 99, 2071. (6) Wasserscheid, P.; Keim, W. Ionic Liquids - New “Solutions” for Transition Metal Catalysis. Angew. Chem., Int. Ed. 2000, 39, 3772. (7) Sheldon, R. Catalytic Reactions in Ionic Liquids. Chem. Commun. 2001, 2399. (8) Olivier-Bourbigou, H.; Magna, L. Ionic Liquids: Perspectives for Organic and Catalytic Reactions. J. Mol. Catal. A-Chem. 2002, 182-3, 419. (9) Dupont, J.; De Souza, R. F.; Suarez, P. A. Z. Ionic Liquid (Molten Salt) Phase Organometallic Catalysis. Chem. Rev. 2002, 102, 3667. (10) Wasserscheid, P.; Welton, T. Ionic Liquids in Synthesis; John Wiley & Sons: New York, 2002. (11) Van Rantwijk, F.; Lau, R. M.; Sheldon, R. A. Biocatalytic Transformation in Ionic Liquids. Trends Biotechnol. 2003, 21, 131. (12) Kubisa, P. Application of Ionic Liquids as Solvents for Polymerisation Processes. Prog. Polym. Sci. 2004, 29, 3.
(13) Swatloski, R. P.; Holbrey, J. D.; Rogers, R. D. Ionic Liquids are not Always Green: Hydrolysis of 1-Butyl-3-methylimidazolium Hexafluorophosphate. Green Chem. 2003, 5 (4), 361. (14) Tran, C. D.; De Paoli Lacerda, S. H.; Oliveira, D. Absorption of Water be Room-Temperature Ionic Liquids: Effect of Anions on Concentration and State of Water. Soc. Appl. Spectrosc. 2003, 57 (2), 152. (15) Swatloski, R. P.; Spear, S. K.; Holbrey, J. D.; Rogers, R. D. Dissolution of Cellulose with Ionic Liquids. J. Am. Chem. Soc. 2002, 124, 4974. (16) Pernak, J.; Zabielska-Matejuk, J.; Kropacz A.; FoksowiczFlaczyk, J. Ionic Liquids in Wood Preservation. Holzforschung 2004, 58, 286. (17) Li, X.; Geng, Y.; Simonsen, J.; Li, K. Application of Ionic Liquids for Electrostatic Control in Wood. Holzforschung 2004, 58, 280. (18) Turner, M. B.; Spear, S. K.; Huddleston, J. G.; Holbrey, J. D.; Rogers, R. D. Ionic Liquid Salt-Induced Inactivation and Unfolding of Cellulose from Trichoderma reesei. Green Chem. 2003, 5, 443. (19) Phillips, D. M.; Drummy, L. F.; Conrady, D. G.; Fox, D. M.; Naik, R. R.; Stone, M. O.; Trulove, P. C.; De Long, H. C.; Mantz, R. A. Dissolution and Regeneration of Bombyx mori Silk Fibroin Using Ionic Liquids. J. Am. Chem. Soc. 2004, 126, 14350. (20) Moulthrop, J. S.; Swatloski, R. P.; Moyna, G.; Rogers, R. D. High-resolution 13C NMR studies of cellulose and cellulose oligomers in ionic liquid solutions. Chem. Commun. 2005, 1557. (21) Varma, R. S.; Namboodiri, V. V. An Expeditious Solventfree Route to Ionic Liquids Using Microwaves. Chem. Commun. 2001, 643. (22) Pernak, J.; Czepukowicz, A.; Poz´niak, R. New Ionic Liquids and Their Antielectrostatic Properties. Ind. Eng. Chem. Res. 2001, 40, 2379. (23) ISO standard 187:1990, Paper, board and pulps. Standard atmosphere for conditioning and testing and procedure for monitoring the atmosphere and conditioning of samples. (24) Baumeister, M.; Gru¨ner, G. Wochenbl. Papierfabr. 1999, 127 (16), 1023. (25) Gru¨ner, G., Emtec Penetration-Dynamics Analyser; Materials of Emtec Electronic GmbH: Leipzig, 1996. (26) Polish standard: PN-76/P-50156. Paper and board. Paper industry products. Determination of surface receptivity. (27) ISO standard 2471:1998. Paper and board. Determination of opacity (paper backing). Diffuse reflectance method. (28) ISO standard 1924-1:1992. Paper and board. Determination of tensile properties. Part 1: Constant rate of loading method; 1924-2:1994. Paper and board. Determination of tensile properties. Part 2: Constant rate of elongation method. (29) Branco, L. C.; Rosa, N. R.; Ramos, J. J. M.; Afonso, C. A. M. Preparation and Characterization of New Room-Temperature Ionic Liquids. Chem. Eur. J. 2002, 16, 3671. (30) Oldham, W. J.; Costa, D. A.; Smith, W. H. Development of Room-Temperature Ionic Liquids for Applications in Actinide Chemistry. Ionic Liquids; Rogers, R. D., Seddon, K. R., Eds.; American Chemical Society: Washington, DC, 2002; ISBN: 0-84123789-1. (31) Urbanik, E.; Zabielska-Matejuk, J.; Skrzypczak, A.; Pernak, J. Antifungal Properties of New Imidazolium Chlorides Against Coniophora puteana (Schum.:Fr.) Karst., Trametes versicolor (L.:Fr.) Pilat and Chaetomium globosum (Kunze:Fr.). Mater. Org. 1997, 31 (4), 247. (32) Pernak, J.; Krysin´ski, J.; Skrzypczak, A. Wirkung neuer Iminiumverbindungen gegen Bakterien und Pilze. Pharmazie 1992, 47, 623.
Received for review September 7, 2004 Revised manuscript received March 23, 2005 Accepted April 20, 2005 IE0402315
