Article pubs.acs.org/IECR
Improving Stability and Sizing Performance of Alkenylsuccinic Anhydride (ASA) Emulsion by Using Melamine-Modified Laponite Particles as Emulsion Stabilizer Wei Zhang,† Wenxia Liu,*,† Haidong Li,† Martin A. Hubbe,‡ Dehai Yu,† Guodong Li,† and Huili Wang† †
Shandong Provincial Key Laboratory of Fine Chemicals, Key Laboratory of Pulp & Paper Science and Technology (Qilu University of Technology), Ministry of Education, Jinan, Shandong 250353, China ‡ Department of Forest Biomaterials, North Carolina State University, Raleigh, North Carolina 27695-8005, United States S Supporting Information *
ABSTRACT: Alkenylsuccinic anhydride (ASA) is commonly applied as oil-in-water (o/w) emulsions in the papermaking industry. Herein Laponite mineral nanoparticles were employed as a stabilizer of the ASA emulsions after being modified with melamine just before emulsion preparation. The emulsion was prepared by homogenizing the mixture of ASA and melaminemodified Laponite aqueous dispersion. The modification of melamine on the Laponite was characterized by infrared spectroscopy and X-ray diffraction, whereas the impacts of the modification on the morphology, wettability and ζ-potential of the Laponite, as well as the interfacial tension between ASA and Laponite aqueous dispersion, were also analyzed. It is found that the adsorption of melamine on Laponite particles neither causes the aggregation nor significantly changes the charge properties of the Laponite particles. However, the adsorption of melamine can significantly increase the wettability of Laponite by the ASA liquid, and adequately lower the apparent interfacial tension between ASA and Laponite aqueous dispersion when the melamineto-Laponite mass ratio is less than 3%. This results in an improvement in emulsion stability, a reduction in emulsion droplet size and an enhancement in the sizing performance of the ASA emulsion when the emulsion is stabilized by melamine-modified Laponite particles. The ASA emulsion with the smallest droplet size and best sizing performance is produced at a melamine-toLaponite mass ratio of 3%. By monitoring the variations of the emulsion with time, it is discovered that the modification of Laponite with melamine can restrain the growth of emulsion droplets and the hydrolytic action of ASA substantially, thus decreasing the loss in sizing performance of the ASA emulsion with time. This is particularly important for the wide application of ASA emulsions in the papermaking industry.
1. INTRODUCTION In papermaking, internal sizing is a process used to make the end product more resistant to water or other fluids. A small amount of sizing agent should be able to overcome the inherent hydrophilicity of cellulose fibers, which are the main structural component of ordinary papers.1,2 Efficient hydrophobization of paper requires that the sizing agent contains a hydrophobic group, can be efficiently retained on fiber surfaces, gets well distributed on a molecular scale during the papermaking process and becomes fixed at the surface.1 Alkenylsuccinic anhydride (ASA) is a highly efficient internal sizing agent. It is usually applied in papermaking systems as an ASA-in-water emulsion.1−7 ASA has the advantages of quick sizing development and high aluminum tolerance.1,8,9 However, it also undergoes quick hydrolysis when the ASA emulsion is not properly stabilized.4,10 The hydrolysis product of ASA, a diacid, has adverse effects on paper sizing and machine runnability.11,12 Hence an ASA emulsion droplet needs to be sterically/mechanically segregated from the surrounding water, and the emulsion should be used immediately after its preparation. Usually, a high mass ratio of cationic starch (2−6 times the mass of ASA) has to be employed to achieve the most efficient sizing response by inhibiting the hydrolysis of ASA in an emulsion.5 The relatively high dosage of cationic starch is also © 2014 American Chemical Society
intended to contribute to the dry strength of the paper. However, the cationic starch stabilized ASA emulsions commonly have a very low concentration of ASA, e.g., 1 wt %,2,10 owing to the high mass ratio of cationic starch and the high viscosity of cooked cationic starch aqueous dispersions. This increases the energy input and decreases the production efficiency of emulsion preparation. In addition, a surfactant is commonly employed in order to promote emulsification.2 Such use of a surfactant is detrimental to the sizing development of ASA and may cause foaming problems. Therefore, how to prepare a high efficient ASA emulsion with a high concentration and low hydrolysis speed of ASA in the absence of a surfactant is becoming an imperative task. It has been well established that fine solid particles can stabilize emulsions by adsorbing to the oil−water interface when they are partly wetted by oil and water.13−15 The adsorbed particles form a mechanical barrier around emulsion droplets, resisting emulsion coalescence.14 Because of the high resistance to coalescence, solid particle stabilized emulsions, which are also called Pickering emulsions, can show many Received: Revised: Accepted: Published: 12330
April 3, 2014 July 11, 2014 July 14, 2014 July 14, 2014 dx.doi.org/10.1021/ie501381a | Ind. Eng. Chem. Res. 2014, 53, 12330−12338
Industrial & Engineering Chemistry Research
Article
and good sizing performances at a reduced amount of modifier for Laponite.
advantages over conventional emulsions, such as being able to prepare stable emulsions with a high internal phase fraction at a rather low particle concentration, enhancing emulsion coalescence stability and avoiding the adverse effects of a surfactant.14,16 When an ASA emulsion is stabilized by solid particles, the formation of particle barriers around ASA droplets is also expected to lessen the direct contact of ASA with water, reducing the hydrolysis reaction of ASA.17 Therefore, using particles to stabilize an ASA-in-water emulsion has attracted more and more attention.8,9,18−22 Of the solid particles used to stabilize ASA emulsions, clay particles such as kaolin clay, montmorillonite and Laponite have generated much interest due to their platelet structures with favorable charge properties, high hydrophilicity and easy modification by ion exchange and adsorption,8,21−26 which provide great opportunities for tailoring both the particle interactions and wettability to oil and water.27−29 Compared to kaolin clay and montmorillonite, Laponite has the merits of high purity and small and uniform particle size, which favor the preparation of oil-in-water (o/w) emulsions with droplet sizes less than 1 μm after its wettability is carefully tailored.30,31 When the Laponite is employed to stabilize ASA emulsions after being modified, the as-prepared emulsions possess higher stability, smaller drop diameter and better sizing performance than those stabilized by modified montmorillonite with the same modifier.25,32 Even a partly hydrolyzed ASA shows a considerable sizing effect after it is transformed into an emulsion stabilized by modified Laponite.9 Therefore, Laponite is a more competent particle stabilizer than montmorillonite for ASA emulsion after being modified. Laponite can be modified by adsorption of surfactants,33,34 or small surfactant-like molecules.8,21,35 However, the introduction of cationic surfactants with long hydrocarbon chains would inevitably induce either the flocculation of Laponite particles or the dramatic enhancement of particle wettability with oil. The former approach yields emulsions with larger droplets due to the enhancement of apparent particle size by flocculation,36 whereas the latter tends to reverse emulsion from o/w to w/o because oil-wetted particles prefer w/o emulsions.37 Compared to long-chain surfactants, small surfactant-like molecules hardly cause the flocculation of particles, and can moderately adjust the wetting behavior of the particles.38 This is especially important for tailoring the wettability of particles in preparing o/w emulsions of ASA. Our previous studies confirm that using small surfactant-like molecules such as n-butylamine, urea and alanine, to tailor the wettability of Laponite particles to ASA, significantly improves the creaming stability of ASA-in-water emulsions and reduces the emulsion droplet diameter, producing emulsions with enhanced sizing performances8,9,21 and hydrolysis resistance.8 Nevertheless, the modification efficiency of Laponite still needs to be improved. In this study, melamine, which is a trimer of cyanamide, was used to tailor the wettability of Laponite to ASA. Melamine possesses a lower solubility in water than n-butylamine, urea and alanine due to its 1,3,5-triazine skeleton, but carries more amino groups. The low solubility and the excess amino groups are expected to enhance the adsorption rate of melamine molecules on Laponite particle surfaces, hence improving the modification efficiency of Laponite and/or reducing the interference of free amphiphilic molecules on the sizing development of ASA. The purpose is to obtain ASA-in-water emulsions with improved stability, high hydrolysis resistance
2. EXPERIMENTAL SECTION 2.1. Materials. Laponite with a name Laponite RD was supplied as a white powder by Rockwood Additives Ltd. (UK). It is a synthetic hectorite with a molecular formula of Na0.7[(Si8Mg5.5Li0.4)O4(OH)20] and disk-shaped crystals in an average diameter of 25−30 nm and a thickness of about 1 nm. Melamine was purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Alkenylsuccinic anhydride (ASA) is an amber liquid at room temperature and provided by Dixie Chemical Co., Inc. It has a density of 0.947 g/cm3 at 25 °C. According to the supplier’s report, the ASA consisted of 94.9 wt % of octadecenylsuccinic anhydride (C22H38O3), 3.38 wt % of hexadecenylsuccinic anhydride (C20H34O3) and residual olefins. The pulp used in the study was alkaline peroxide mechanical pulp (APMP) supplied as a dry pulp board. It is a commercial product of Shandong ShengYuan Paper Co., Ltd. The dry APAM was torn to pieces and immerged in tap water for 24 h, then the pulp was disintegrated for 30000 revolutions at a concentration of 12 g/L with a pulp disintegrator (Lorentzen and Wettre), refined to 40 °SR with a laboratory Valley beater, dewatered in a machine washer to about 20 wt % dryness and stored in a refrigerator before use. The ζ-potential of the pulp was −26.2 mV. It was measured using a Mütek streaming potential analyzer (SZP04, Mütek Analytical GmbH, Herrsching, Germany), which works by forcing aqueous solutions through a pad of fibers at a known pressure drop. Cationic acrylamide copolymer (CPAM) with a relative molecular mass of 8 million was provided by Ciba Specialty Chemicals Ltd. Aluminum sulfate (Al2(SO4)3·18H2O, >99.0%) and the other chemicals are analytically pure reagents. 2.2. Preparation and Characterization of MelamineModified Laponite and Its Aqueous Dispersion. Laponite and melamine powder were dried in an oven at 105 °C for 3 h to remove adsorbed water. Dried Laponite powder was dispersed in deionized water at a rapid agitation to form an aqueous dispersion less than 20 g/L. When the Laponite particles swell completely after 1 week, the dispersion concentration was regulated to 20 g/L with deionized water. The Laponite was directly modified by blending its aqueous dispersion with melamine aqueous solution according to a predetermined melamine-to-Laponite mass ratio. After being dialyzed against deionized water for 48 h to remove free melamine, dried at 60 °C and ground to a powder, the melamine-modified Laponite without free melamine was obtained and used for infrared (IR) spectrum and X-ray diffraction (XRD) analyses. IR spectra were collected on a Nexus 670 Fourier transformation infrared-Raman spectrometer (Thermo Fisher Scientific Inc.) in the range of 400−4000 cm−1 using pressed KBr discs. XRD patterns were recorded on a Bruke D8 Advance powder X-ray diffractometer under a Nifiltered Cu Kα (λ= 0.154 06 nm) irradiation in a scan range of 2θ = 20−80° with a scanning resolution of 2θ = 0.01°. The wettability of the modified Laponite samples was evaluated by measuring their three phase contact angle using equally modified mica; this approach can be justified due to both the similarity of mica with Laponite in chemical composition and crystal structure, and the difficulty of contact angle measurement for particulate materials in an oil.18,31 According to Li et al.,31 the mica flakes were immersed in melamine aqueous solution for 24 h to allow the adsorption of melamine. Then the 12331
dx.doi.org/10.1021/ie501381a | Ind. Eng. Chem. Res. 2014, 53, 12330−12338
Industrial & Engineering Chemistry Research
Article
mica flakes were dried in a vacuum. The treated mica flake was placed at the bottom of an open, transparent glass vessel filled with ASA oil. A drop of water, which has a diameter of 2.2 ± 0.1 mm, was dripped from a height of 5 mm onto the mica surface (shown in Figure S1, Supporting Information). The appearance of the water drop was recorded using an optical contact angle measuring device (JC2000C1, Shanghai Powereach Co., Ltd.), and the value of the contact angle was determined by the photogoniometric method.18 The melaminemodified Laponite aqueous dispersion without removal of free melamine was diluted to a concentration of 0.67% with deionized water and directly used as an aqueous phase. The turbidity of the aqueous phase was determined with a WGZ800 scattering optical turbidity meter (Shanghai Xinrui Tester Co., Ltd.). The ζ-potential of the modified Laponite was measured with a Zetasizer 3000 (Malvern, UK). The interfacial tension between ASA and the aqueous phase was tested with a Krüss K100MK2 tensiometer (KRÜ SS GmbH, Germany) at 25 °C. 2.3. Preparation and Characterization of ASA Emulsions. ASA emulsions were prepared by adding 45 mL of melamine-modified Laponite aqueous dispersion without removal of free melamine into 15 mL of ASA oil followed by homogenizing the mixture using a FM200 high shear dispersing emulsifier (FLUKO Equipment Shanghai Co., Ltd.) with a 1.0 cm head at 5000 rpm for 3 min. The concentration of melamine-modified Laponite aqueous dispersion was predetermined according to the charge level of Laponite based on ASA. Immediately after the homogenization, emulsion viscosity was measured with a NDJ-8S digital display viscometer (Shanghai Precision & Scientific Instrument). Emulsion type was determined by conductivity measurement with a DDS-11A conductivity meter (Shanghai Pengshun Scientific Instrument Co., Ltd.).18 The stability of ASA emulsions was represented by the final emulsion volume fraction,26 which was the ratio of emulsion volume to the total volume of the emulsified system after being stored at room temperature (25 °C) for 24 h. The morphology of ASA emulsions without dilution was analyzed with a Rise-3002 optical biomicroscope (Jinan Runzhi Science and Technology Co., Ltd.). The average diameter of the emulsion droplets and the droplet size distribution were tested and calculated by using a microscopic image analysis software package.8,9,21 2.4. Chemical Stability of ASA Emulsion against Hydrolysis. The chemical stability of the ASA emulsion against hydrolysis was evaluated by the chemical variation of the ASA with time, which was characterized by IR spectroscopy.19 An ASA sample was prepared by extracting the emulsion with acetone followed by removing the water brought with the emulsion by anhydrous sodium sulfate.8,19 In a typical process, 1 mL of ASA emulsion, as described earlier, was dissolved in 10 mL of acetone followed by addition of 4 g of anhydrous sodium sulfate to absorb the water. After the water was completely absorbed, the sodium sulfate solids were removed by centrifugation, and the obtained acetone solution of ASA was directly used for infrared analysis. The IR spectrum was collected on a Nexus 670 Fourier transformation infraredRaman spectrometer (Thermo Fisher Scientific Inc.). 2.5. Handsheet Making and Sizing Degree Measurement. The internal sizing performances of the as-prepared ASA emulsions were tested by making sized handsheets on a PTI Rapid-Köthen Blattbildner-sheet Former, and measuring the sizing degree of the handsheets according to China
National Standard GB/T460-2008, which could be found in the Supporting Information and elsewhere.8,19,21,39 To prepare the sized handsheets, 2 wt % of aluminum sulfate (based on oven-dry APMP, the same below), which was used to either neutralize disturbing substances in APMP or reduce the adverse effect of hydrolyzed ASA on sizing, was added to 10 g/L APMP aqueous suspension with an initial pH of 7.50 at a stirring speed of 750 rpm, followed by addition of the ASA emulsion described earlier (addition levels are given later), and 0.03 wt % of CPAM in sequence. The final pH of the APAM suspension (which was influenced mainly by the aluminum sulfate addition) was 6.12. The stirring speed was then increased to 1250 rpm, having the mixture undergo 60 s of high shearing. After that, the stirring speed was returned to 750 rpm, and 0.3 wt % of Laponite, which constituted a nanoparticle retention aid system with the preadded CPAM for improving the retention of APMP and ASA species, was added and mixed for 60 s. Handsheets with a basis weight of approximately 60 g/m2 were made using the sheet former.
3. RESULTS AND DISCUSSION 3.1. Modification of Laponite by Melamine. The melamine molecule has three primary amino groups (pKa = 8)40 joined onto its rigid and planar triazine ring (pKa = 5.10),41 thus giving rise to a very weak positive ionic charge when it meets Laponite particle because the pH of Laponite aqueous dispersion is higher than 9 (shown in Figure S2, Supporting Information). It is expected to modify the Laponite in aqueous medium by hydrogen bonding or dipole−dipole interactions. Figure 1 compares the IR spectrum patterns of
Figure 1. IR spectra of melamine, Laponite and melamine-modified Laponite after free melamine being removed.
melamine, Laponite and melamine-modified Laponite. The mass ratio of melamine to Laponite is 20% before free melamine is removed by dialysis. As shown in Figure 1, the typical absorption bands of melamine at 814, 1551 and 1651 cm−1, which belong, respectively, to the deformation vibration of the triazine ring, the stretching vibration of the CN, and the bending vibration of the NH,42 do not appear in the IR spectrum of melamine-modified Laponite after the free melamine is removed. This indicates that the adsorbed amount of melamine on Laponite is too low to be detected. However, the absorption bands assigned to water of hydration/adsorption at 3400−3600 and 1630 cm−1 are significantly weakened, suggesting the dehydration of Laponite by melamine adsorption. 12332
dx.doi.org/10.1021/ie501381a | Ind. Eng. Chem. Res. 2014, 53, 12330−12338
Industrial & Engineering Chemistry Research
Article
The effects of melamine adsorption on the morphology, three phase contact angle, ζ-potential of the Laponite and the turbidity of its aqueous dispersion were also investigated, and the results are shown in Figure 3. Apparently, the negative ζpotential of Laponite particles is only slightly neutralized due to the weak protonation of melamine at a pH of higher than 9 and the very high surface charge density of the Laponite particles. Therefore, the modification does not induce the aggregation of Laponite particles, which can be judged from both the TEM images and variation of the turbidity. The turbidity of the Laponite aqueous dispersions is even slightly increased after the Laponite is modified by melamine because the adsorption of melamine results in dehydration of Laponite particles. The purpose of modifying Laponite with melamine is to improve the wettability of Laponite by the ASA liquid. However, it is hard to measure the contact angle of nanoparticles. Also, the ASA is viscous and has a high susceptibility to hydrolytic decomposition, resulting in variation of the tested three phase contact angles with time, even when using mica to mimic the Laponite, as represented in Figure 3c. Nevertheless, it can be found that the adsorption of melamine onto mica significantly increases the three phase contact angle of mica: the higher the concentration of melamine, the higher the three phase contact angle. The contact angle findings suggest that the adsorption of melamine onto Laponite renders the Laponite particles less hydrophilic, which suggests their greater wettability by ASA. 3.2. Effects of Laponite Modification by Melamine on Apparent Interfacial Tension between ASA and Aqueous Laponite Dispersion. When using solid particles to stabilize ASA emulsions, a decrease of the apparent ASA−water interfacial tension generally contributes to preparing emulsions
The adsorption of the melamine molecule on the Laponite surface can also be confirmed by X-ray diffraction (XRD) because the interlayer distance, i.e., the basal plane spacing d (001) (d-spacing) of Laponite crystal, is significantly affected by the adsorbed substances in the interlayer gallery,43 and can be calculated from the diffraction angle 2θ of the (001) plane based on Bragg’s Law. Figure 2 shows the XRD patterns of
Figure 2. X-ray diffraction patterns of Laponite and melaminemodified Laponite after free melamine being removed.
Laponite and melamine-modified Laponite. As shown, the broad (001) diffraction band of Laponite is centered at 2θ = 7.14°, corresponding to a d-spacing of 12.37 Å. With the introduction of melamine, the diffraction band appears at a smaller scattering angle at 2θ = 6.78°, corresponding to a dspacing of 13.03 Å. This provides additional evidence for the adsorption of melamine on Laponite surfaces.
Figure 3. TEM images of (a) Laponite particles, (b) melamine-modified Laponite particles with the melamine-to-Laponite mass ratio of 3%; effects of melamine-to-Laponite mass ratio on (c) three phase contact angle of mica after it is treated with the given concentrations of melamine, (d) ζpotential of melamine-modified Laponite, and turbidity of melamine-modified Laponite aqueous dispersion. The concentration of melaminemodified Laponite aqueous dispersion is 0.67%. The bars in the TEM images are 20 nm. The “0 min” and “30 min” in panel c present the contact time of water drop on mica in ASA. 12333
dx.doi.org/10.1021/ie501381a | Ind. Eng. Chem. Res. 2014, 53, 12330−12338
Industrial & Engineering Chemistry Research
Article
with high physical stability.21 Figure 4 shows the variation of ASA−water apparent interfacial tension with Laponite concen-
3.3. Effects of Laponite Modification by Melamine on Emulsion Stability and Properties. ASA emulsions stabilized by melamine-modified Laponite of different melamine-to-Laponite mass ratios were prepared at a fixed ASA volume fraction of 25%. By conductivity measurement, all the as-prepared emulsions are found to be ASA-in-water type.8 When the Laponite-to-ASA mass ratio is higher than 1%, no ASA oil is released from the as-prepared emulsions after being prepared and stored for 24 h due to the formation of particle barriers around the emulsion droplets (as shown by confocal fluorescence microscope images in Figure S4, Supporting Information), i.e., all the as-prepared emulsions are stable to coalescence.31 Therefore, the Laponite-to-ASA mass ratio was always not less than 1% in the subsequent emulsion preparation, and emulsion stability was characterized only by the emulsion volume fraction after the emulsion was prepared for 24 h. Figure 5 shows the variations of emulsion stability and viscosity with the melamine-to-Laponite mass ratio. The inset
Figure 4. Surface tension of Laponite aqueous dispersion (filled squares) and apparent interfacial tension between ASA liquid and Laponite aqueous dispersion (open squares) as a function of (a) Laponite concentration in the absence of melamine and (b) melamineto-Laponite mass ratio, while the concentration of Laponite is 0.67%.
tration and the melamine-to-Laponite mass ratio. As shown in Figure 4, neither the Laponite nor the melamine is able to change the measured surface tension of Laponite aqueous dispersions. However, the introduction and enhancing the concentration of Laponite markedly reduce the apparent interfacial tension between the ASA and the Laponite aqueous dispersion, as previously reported.8,21 This implies that the attachment of Laponite particles onto the ASA−water interface decreases the apparent interfacial tension. Similar to the other short-chain modifiers such as alanine and tetramethylammonium chloride,21,44 the melamine further reduces the measured interfacial tension due to its improvement on the wettability of Laponite particles to ASA when the melamine-to-Laponite mass ratio is less than 3%. When the melamine-to-Laponite mass ratio becomes higher than 3%, the measured interfacial tension starts to increase and does not change significantly as the melamine-to-Laponite mass ratio reaches 10%. This increase in the apparent interfacial tension is probably originated from the interference of free melamine molecules in the attachment of Laponite particles on the ASA−water interface. The occurrence of free melamine molecules in the modified Laponite aqueous dispersion is proved by the absorption bands assigned to melamine in the IR spectra of melamine-modified Laponite without dialysis before drying (shown in Figure S3, Supporting Information).
Figure 5. (a) Emulsion volume fraction and (b) viscosity of ASA− water emulsion systems as a function of melamine-to-Laponite mass ratio after being stored at room temperature (25 °C) for 24 h. The ASA volume fraction is 25%. The “Laponite/ASA” in the figures represents the Laponite-to-ASA mass ratio.
shows the appearances of corresponding ASA emulsions with a 2% Laponite-to-ASA mass ratio. As shown in Figure 5a, the pristine Laponite-stabilized emulsion is not stable to creaming.31 A considerable volume of water is released from the emulsion even when the Laponite-to-ASA mass ratio is as high as 2%. However, the emulsions become stable by modifying the Laponite with melamine at a melamine-to-Laponite mass ratio of as low as 1%, confirming the high modification efficiency of melamine on Laponite when compared with the other small surfactant-like substances such as n-butylamine, urea and 12334
dx.doi.org/10.1021/ie501381a | Ind. Eng. Chem. Res. 2014, 53, 12330−12338
Industrial & Engineering Chemistry Research
Article
alanine in our previous studies.8,9,21 Further increasing the melamine-to-Laponite mass ratio, all the emulsions remain stable. Nevertheless, the introduction of melamine significantly increases the viscosity of the emulsions, especially when the Laponite-to-ASA mass ratio is higher than 1.5% as shown in Figure 5b. This indicates that free Laponite particles exist in the continuous phase, especially when the Laponite-to-ASA mass ratio is higher than 1.5%.30 The free Laponite particles in the continuous phase have been confirmed with a laser scanning confocal microscope after they are labeled with Auramine O (Figure S4, Supporting Information). To readily compare the properties of the ASA emulsions, two Laponite-to-ASA mass ratios, which are 1% and 2%, respectively, are employed in the subsequent work. Figure 6 shows the effects of the melamine-to-Laponite mass ratio on the average droplet size of the as-prepared ASA
3.4. Sizing Performance of ASA Emulsions Stabilized by Melamine-Modified Laponite Particles. The effect of the melamine-to-Laponite mass ratio on sizing development of the as-prepared ASA emulsions and sizing performance of the ASA emulsions with an optimized melamine-to-Laponite ratio of 3% were evaluated and shown in Figure 7. The extent of sizing was expressed by sizing degree of sized handsheets, for which 30 s indicates a good sizing.
Figure 6. Effects of melamine-to-Laponite mass ratio on average droplet diameter of ASA emulsions. The inserts are corresponding optical microscope images. The “Laponite/ASA” in the figure represents the Laponite-to-ASA mass ratio. The scale bars in the optical microscope images are 50 μm.
emulsions. The inserts are corresponding optical microscope images. As shown, all the ASA emulsions possess spherical droplets and the droplet diameter is mostly in the range of 1 to 4 μm (Figure S5, Supporting Information). Emulsions with smaller average droplet diameters are formed by modifying the Laponite with melamine when the melamine-to-Laponite mass ratio is less than 3% due to both the increase in hydrophobicity of Laponite particles and the decrease in the apparent ASA− water interfacial tension, which are, respectively, shown in Figures 3c and 4a. The former promotes the adsorption of Laponite particles onto ASA droplet surfaces,45 whereas the latter promotes the breakup of ASA droplets in the presence of hydrodynamic shear.46 Further increasing the melamine-toLaponite mass ratio, the average droplet diameters of the two emulsions start to increase. The emulsions prepared at a 3% melamine-to-Laponite mass ratio, at which the interfacial tension between ASA and melamine-modified Laponite aqueous dispersion achieves its minimum value as shown in Figure 4b, possess the smallest average droplet diameters. This result is similar to that of ASA emulsions stabilized by tetramethylammonium chloride-modified Laponite.44 From Figure 6, it can be found that the average droplet diameter of the emulsion with a 2% Laponite-to-ASA mass ratio is affected less by introduction of melamine than that of the emulsion with a 1% Laponite-to-ASA mass ratio because the Laponite can also lower the apparent interfacial tension as shown in Figure 4a.
Figure 7. (a) Effect of melamine-to-Laponite mass ratio on sizing effect of ASA emulsions, where the amount of ASA is 0.1 wt % based on oven-dry pulp; (b) sizing performance of ASA emulsion stabilized by melamine-modified Laponite, where the melamine-to-Laponite mass ratio is fixed at 3%. The “Laponite/ASA” in the figures represents the Laponite-to-ASA mass ratio.
As shown in Figure 7a, the sizing degrees of the handsheets sized with the as-prepared ASA emulsions are greatly enhanced by the initial increasing of the melamine-to-Laponite mass ratio, and reach their maximum values at 3%, at which the emulsions have their smallest average droplet size and good stability, as shown in Figures 6 and 5, respectively. With further increasing of the mass ratio, the sizing degrees decrease significantly due to the increase of emulsion droplet size, demonstrating that the uniform distribution of ASA is important on the sizing development.8 Therefore, the optimized melamine-to-Laponite mass ratio is 3%. It can also be seen from Figure 7a that the emulsion with the 2% Laponite-to-ASA mass ratio exhibits higher sizing efficiency at all melamine-to-Laponite mass ratios, although its droplet size may not be always smaller than the emulsion with the 1% Laponite-to-ASA mass ratio. This suggests that the sizing performance may also be affected by stability of diluted ASA emulsions, because an emulsion 12335
dx.doi.org/10.1021/ie501381a | Ind. Eng. Chem. Res. 2014, 53, 12330−12338
Industrial & Engineering Chemistry Research
Article
Figure 8. IR spectra of ASA species separated from ASA emulsions with (a) 2% pristine Laponite-to-ASA mass ratio, (b) 2% melamine-modified Laponite-to-ASA mass ratio after the emulsions are stored for different time; effect of storage time on (c) average droplet diameter, (d) sizing effects of ASA emulsions stabilized by either pristine or melamine-modified Laponite; the melamine-to-Laponite mass ratio of modified Laponite is 3%. The added amount of ASA is 0.1 wt % based on APMP. The Laponite-to-ASA mass ratio in panel c is 2%. The “pristine Laponite/ASA” and “melaminemodified Laponite/ASA” in panel d represents the pristine Laponite-to-ASA mass ratio and melamine-modified Laponite-to-ASA mass ratio, respectively.
emulsions or by the hydrolysis of ASA, also affects the sizing performance of the prepared ASA emulsions. Therefore, the alterations of chemical composition, emulsion droplet size and sizing performance of the prepared ASA emulsions stabilized either by melamine-modified Laponite or by pristine Laponite were explored. The chemical composition of ASA species was analyzed with IR spectroscopy. In the IR spectra (shown in Figures 8a, b), the peaks assigned to ASA carbonyl stretching vibrations are located at approximately 1782 and 1863 cm−1 whereas the absorption band of carboxyl groups from the hydrolyzed ASA appears at about 1711 cm−1.8,21,48 The stronger absorption at 1711 cm−1 relative to the absorptions at 1782 and 1863 cm−1 suggests the higher hydrolysis extent of ASA in a sample.19,20 As shown in Figures 8a, b, the ASA in the two ASA emulsions stabilized either by pristine Laponite or by melamine-modified Laponite has already started to hydrolyze once the emulsion preparation is finished due to its contact with water, and the hydrolysis becomes more obvious with increasing the storage time. However, the hydrolysis of ASA in the emulsion stabilized by melamine-modified Laponite is slower than that in the emulsion stabilized by pristine Laponite, although the former has a smaller droplet size than the latter (Figure 8c). After the standing time attains 5 h, the absorption peak at 1711 cm−1 is still rather weak for the melamine-modified Laponite-stabilized ASA emulsion. This demonstrates that the melamine-modified Laponite particles can constitute stronger mechanical barriers for ASA droplets and can prevent the ASA from hydrolysis
stabilized by more particles generally shows higher stability after being diluted.47 From Figure 7b, it can be found that both of the two emulsions with the 1% and 2% melamine-modified Laponite-toASA mass ratios show good sizing performances. By adding emulsions of 0.05% ASA (based on APMP) to paper, the sizing degree can reach 80 and 115 s, respectively, which is higher than the sizing degree (66 s) produced by adding the same amount of traditional ASA emulsion stabilized by cationic starch with a starch-to-ASA mass ratio of 4:1 (shown in Figure S6, Supporting Information). Moreover, the melaminemodified Laponite-stabilized emulsions yield quicker increments in the sizing degree of handsheets with increasing the charge level of ASA emulsion than the traditional emulsion, especially as the dosage of ASA exceeds 0.15%. When the ASA dosage reaches 0.3%, the two emulsions stabilized by melamine-modified Laponite afford sizing degrees of 565 and 594 s, respectively, for the handsheets, while the traditional emulsion produces a sizing degree of 356 s (shown in Figure S6, Supporting Information). Therefore, using the melaminemodified Laponite to stabilize the ASA emulsion not only prepares emulsions with high ASA content but also significantly improves the sizing performance of ASA. 3.5. Alteration of ASA Emulsion with Standing Time. One of the expected benefits of using solid particles to stabilize ASA emulsions is to impede the hydrolysis of ASA, and thus reduce the loss in sizing performance of ASA emulsions with time. Meanwhile, the variation of emulsion droplets size with time, which is induced either by the Ostwald ripening of 12336
dx.doi.org/10.1021/ie501381a | Ind. Eng. Chem. Res. 2014, 53, 12330−12338
Industrial & Engineering Chemistry Research more evidently than the pristine Laponite when they are used as the stabilizers of ASA emulsions. As shown in Figure 8c, which illustrates the impact of standing time on the emulsion droplet diameter of the two emulsions, the emulsion droplets become larger with the increasing of storage time. The emulsion stabilized by the melamine-modified Laponite shows a slower increase in droplet diameter than the emulsion stabilized by pristine Laponite because the former has less ASA being hydrolyzed. The sizing performance of the emulsions stabilized by melamine-modified Laponite, therefore, decays slower than that of the emulsions stabilized by the pristine Laponite, as presented in Figure 8d. After being prepared for 2 h, for instance, the sizing degree of the handsheet sized by emulsion with a 1% melamine-modified Laponite-to-ASA ratio is only decreased by ca. 14%, whereas that sized by emulsion with a 1% pristine Laponite-to-ASA mass ratio is decreased by approximately 45%.
■
REFERENCES
(1) Hubbe, M. A. Paper’s resistance to wettingA review of internal sizing chemicals and their effects. BioResources 2007, 2 (1), 106−145. (2) Gess, J. M.; Rende, D. S. Alkenyl succinic anhydride (ASA). Tappi J. 2005, 4 (9), 25−30. (3) Isogai, A. The reason why the reactive chemical structure of alkenylsuccinic anhydride is necessary for efficient paper sizing. J. Soc. Fiber Sci. Technol., Jpn. 2000, 56 (7), 334−339. (4) Isogai, A.; Morimoto, S. Sizing performance and hydrolysis resistance of alkyl oleate succinic anhydrides. Tappi J. 2004, 3 (7), 8− 12. (5) Lee, H. L.; Kim, J. S.; Youn, H. Y. Improvement of ASA sizing efficiency using hydrophobically modified and acid-hydrolyzed starches. Tappi J. 2004, 3 (12), 3−6. (6) Martorana, E.; Belle, J.; Kleemann, S. ASA optimization Control of particle size, stability, and hydrolysis. Prof. Papermaking 2008, 5 (2), 34−42. (7) McCarthy, W. R.; Stratton, R. A. Effects of drying on ASA esterification and sizing. Tappi J. 1986, 70 (12), 117−121. (8) Qian, K.; Liu, W.; Zhang, J.; Li, H.; Wang, H.; Wang, Z. Using urea to improve stability, sizing performance and hydrolysis resistance of ASA emulsion stabilized by Laponite. Colloids and Surf., A 2013, 421 (1), 125−134. (9) Ding, P.; Liu, W.; Zhao, Z. Roles of short amine in preparation and sizing performance of partly hydrolyzed ASA emulsion stabilized by Laponite particles. Colloids and Surf., A 2011, 384 (1), 150−156. (10) Nishiyama, M.; Isogai, A.; Onabe, F. Roles of reactive alkenyl succinic anhydride (ASA) in paper sizing. J. Soc. Fiber Sci. Technol., Jpn. 1996, 52 (4), 189−194. (11) Hodgson, K. T. A review of paper sizing using alkyl ketene dimer versus alkenyl succinic anhydride. Appita J. 1994, 47 (5), 402− 406. (12) Wasser, R. B.; Brinen, J. S. Effect of hydrolyzed ASA on sizing in calcium carbonate filled paper. Tappi J. 1998, 81 (7), 139−144. (13) Sullivan, A. P.; Kilpatrick, P. K. The effects of inorganic solid particles on water and crude oil emulsion stability. Ind. Eng. Chem. Res. 2002, 41, 3389−3404. (14) Aveyard, R.; Binks, B. P.; Clint, J. H. Emulsions stabilized solely by colloidal particles. Adv. Colloid Interface Sci. 2003, 100, 503−546. (15) Frith, W. J.; Pichot, R.; Kirkland, M.; Wolf, B. Formation, stability, and rheology of particle stabilized emulsions: Influence of multivalent cations. Ind. Eng. Chem. Res. 2008, 47, 6434−6444. (16) Zhu, Y.; Zhang, S.; Hua, Y.; Zhang, H.; Chen, J. Synthesis of latex particles with a complex structure as an emulsifier of Pickering high internal phase emulsions. Ind. Eng. Chem. Res. 2014, 53, 4642− 4649. (17) Yu, D.; Liu, W. Preparation and sizing performance of inorganic particles-stabilized ASA emulsion. China Pulp Pap. 2009, 28 (6), 26− 29. (18) Zhao, Z.; Liu, W.; Liu, Z.; Ding, P.; Li, H. Phase inversion of TiO2 nanoparticle stabilized emulsions of alkenyl succinic anhydride. Chem. Eng. Sci. 2013, 87, 246−257. (19) Li, H.; Liu, W.; Zhang, W.; Qian, K.; Wang, H. Laponite and PAS costabilized ASA emulsion with high hydrolysis resistance and sizing efficiency. J. Appl. Polym. Sci. 2013, 129, 3209−3218. (20) Li, H.; Liu, W.; Zhang, W.; Yin, G.; Wang, H.; Wang, Z. Formation of particle coated fusiform droplets via lowering interfacial tension with polyaluminum sulfate. J. Dispersion Sci. Technol. 2013, 34 (10), 1316−1323.
ASSOCIATED CONTENT
S Supporting Information *
Pictures of three phase contact angle measurement; pH of melamine-modified Laponite aqueous dispersions and ASA emulsions stabilized by melamine-modified Laponite; IR spectra of melamine-modified Laponite without removal of free melamine; confocal fluorescence microscope images, optical microscope images and droplet size distribution of the particle stabilized ASA emulsions; the sizing curve of a traditional ASA emulsion and the sizing degree measurement method. This material is available free of charge via the Internet at http://pubs.acs.org.
■
ACKNOWLEDGMENTS
The project was funded by National Natural Science Foundation of China (No. 31270625, No. 21206086). The authors are grateful to Miss Hua Tang and Mr. Bei Gong for the help in preparation of handsheets and sizing degree measurement.
4. CONCLUSIONS Stable ASA-in-water emulsions with the ASA volume fraction of 25%, which is far higher than that of a traditional cationic starch stabilized ASA emulsion, can be prepared by using melaminemodified Laponite as a particle stabilizer at the Laponite-toASA mass ratio of 1−2%. Using melamine to modify Laponite increases the wettability of Laponite by the ASA liquid and adequately lowers the interfacial tension between ASA and Laponite aqueous dispersion when the melamine-to-Laponite mass ratio is less than 3%. As a consequence, the introduction of melamine improves the creaming stability, reduces the droplet diameter and greatly improves the sizing performance of Laponite-stabilized ASA emulsions. The ASA emulsions acquire their smallest droplet diameters and best sizing performances at the melamine-to-Laponite mass ratio of 3%, implying a high modification efficiency of melamine on Laponite. The ASA emulsions with a 3% melamine-to-Laponite mass ratio not only show higher sizing performances than the traditional cationic starch stabilized ASA emulsion but also have higher resistances to hydrolysis during storage than the ASA emulsion stabilized by pristine Laponite. Therefore, using melamine-modified Laponite to stabilize ASA emulsion is an attractive technique, and has good application prospects in the paper making industry.
■
■
Article
AUTHOR INFORMATION
Corresponding Author
*W. Liu. Phone: +86-531-89631168. Fax: +86-531-88574135. E-mail:
[email protected]. Notes
The authors declare no competing financial interest. 12337
dx.doi.org/10.1021/ie501381a | Ind. Eng. Chem. Res. 2014, 53, 12330−12338
Industrial & Engineering Chemistry Research
Article
(21) Wang, H.; Liu, W.; Zhou, X.; Li, H.; Qian, K. Stabilization of ASA-in-water emulsions by Laponite modified with alanine. Colloids Surf., A 2013, 436, 294−301. (22) Yu, D.; Lin, Z.; Li, Y. Octadecenylsuccinic anhydride Pickering emulsion stabilized by γ-methacryloxy propyl trimethoxysilane grafted montmorillonite. Colloids Surf., A 2013, 422, 100−109. (23) Yan, N.; Masliyah, J. H. Creaming behavior of solids-stabilized oil-in-water emulsions. Ind. Eng. Chem. Res. 1997, 36, 1122−1129. (24) Daniel, L. M.; Frost, R. L.; Zhu, H. Y. Edge-modification of Laponite with dimethyl-octylmethoxysilane. J. Colloid Interface Sci. 2008, 321 (2), 302−309. (25) Liu, Z.; Liu, W.; Wang, X. Preparation and sizing performance of ASA emulsion stabilized by n-butylamine/modified bentonite. Pap. Pap. Making 2012, 31 (5), 43−47. (26) Lu, P.; Liu, W.; Wang, H.; Wang, Z. Using chitosan as sizing promoter of ASA emulsion stabilized by montmorillonite. BioResources 2013, 8 (4), 4923−4936. (27) Madivala, B.; Vandebril, S.; Fransaerb, J. Exploiting particle shape in solid stabilized emulsions. Soft Matter 2009, 5, 1717−1727. (28) Lagaly, G.; Reese, M.; Abend, S. Smectites as colloidal stabilizers of emulsions I. Preparation and properties of emulsions with smectites and nonionic surfactants. Appl. Clay Sci. 1999, 14, 83−103. (29) Lagaly, G.; Reese, M.; Abend, S. Smectites as colloidal stabilizers of emulsions II. Rheological properties of smectite-laden emulsions. Appl. Clay Sci. 1999, 14, 279−298. (30) Chevalier, Y.; Bolzinger, M.-A. Emulsions stabilized with solid nanoparticles: Pickering emulsions. Colloids Surf., A 2013, 439, 23−34. (31) Li, W.; Yu, L.; Liu, G.; Tan, J.; Liu, S.; Sun, D. Oil-in-water emulsions stabilized by Laponite particles modified with short-chain aliphatic amines. Colloids Surf., A 2012, 400, 44−51. (32) Ding, P.; Liu, W. Preparation of ASA emulsions with butylamine modified Laponite and its sizing performance. China Pulp Pap. 2011, 30 (10), 1−6. (33) Liu, Q.; Zhang, S.; Sun, D.; Xu, J. Foams stabilized by Laponite nanoparticles and alkylammonium bromides with different alkyl chain lengths. Colloids Surf., A 2010, 355, 151−157. (34) Van den Dungen, E. T. A.; Hartmann, P. C. Synergistic effect of Laponite RD and oil soluble surfactant in stabilization of miniemulsions. Appl. Clay Sci. 2012, 55, 120−124. (35) Liu, Q.; Zhang, S.; Sun, D.; Xu, J. Aqueous foams stabilized by hexylamine-modified Laponite particles. Colloids Surf., A 2009, 338 (1), 40−46. (36) Cui, Z. G.; Yang, L. L.; Cui, Y. Z.; Binks, B. P. Effects of surfactant structure on the phase inversion of emulsions stabilized by mixtures of silica nanoparticles and cationic surfactant. Langmuir 2009, 26 (7), 4717−4724. (37) Zhang, S.; Lan, Q.; Liu, Q.; Xu, J.; Sun, D. Aqueous foams stabilized by Laponite and CTAB. Colloids Surf., A 2008, 317 (1), 406−413. (38) Akartuna, I.; Studart, A. R.; Tervoort, E.; Gonzenbach, U. T.; Gauckler, L. J. Stabilization of oil-in-water emulsions by colloidal particles modified with short amphiphiles. Langmuir 2008, 24, 7161− 7168. (39) Liu, W.; Liu, H.; Chen, M.; Xiao, H. Sizing performance and molecular orientation of dispersed cationic rosin-ester. Appita J. 2008, 61 (5), 387−390. (40) Sun, H.; Liu, N.; Wang, L.; He, P. Determination of melamine residue in liquid milk by capillary electrophoresis with solid-phase extraction. J. Chromatogr. Sci. 2010, 48, 848−853. (41) Weinstabl, A.; Binder, W. H.; Gruber, H.; Kantner, W. Melamine salts as hardeners for urea formaldehyde resins. J. Appl. Polym. Sci. 2001, 81, 1654−1661. (42) Costa, L.; Camino, G. Thermal behaviour of melamine. J. Therm. Anal. 1998, 34, 423−429. (43) Coche-Guérente, L.; Desprez, V.; Labbe, P. Characterization of organosilasesquioxane-intercalated-Laponite-clay modified electrodes and (bio)electrochemical applications. J. Electroanal. Chem. 1998, 458, 73−86.
(44) Tan, H.; Liu, W.; Yu, D.; Li, H.; Hubbe, M. A.; Gong, B.; Zhang, W.; Wang, H.; Li, G. ASA-in-water emulsions stabilized by Laponite nanoparticles modified with tetramethylammonium chloride. Chem. Eng. Sci. 2014, 116, 682−693. (45) Li, W.; Zhao, C.; Tan, J.; Jiang, J.; Xu, J.; Sun, D. Roles of methyl orange in preparation of emulsions stabilized by layered double hydroxide particles. Colloids Surf., A 2013, 421, 173−180. (46) Rallison, J. M. The deformation of small viscous drops and bubbles in shear flows. Annu. Rev. Fluid Mech. 1984, 16, 45−66. (47) Frelichowska, J.; Bolzinger, M. A.; Chevalier, Y. Effects of solid particle content on properties of o/w Pickering emulsions. J. Colloid Interface Sci. 2010, 351, 348−356. (48) Yano, T.; Ohtani, H.; Tsuge, S.; Obokata, T. Determination of neutral sizing agents in paper by pyrolysis−gas chromatography. Analyst 1992, 117 (5), 849−852.
12338
dx.doi.org/10.1021/ie501381a | Ind. Eng. Chem. Res. 2014, 53, 12330−12338
