Article pubs.acs.org/IECR
Bondable and Biodegradable Cellulosic Opacifiers Yung Bum Seo,*,† Yoon Woo Lee,‡ Young Gyu Park,‡ and Min Woo Lee† †
Department of Bio-based materials, College of Agriculture and Life Science, Chungnam National University, Daejun, Republic of Korea ‡ Pegasus Research Inc., Daejun, Republic of Korea S Supporting Information *
ABSTRACT: Fibers extracted from red algae produced a comparable increase in paper opacity to that produced by experimented inorganic fillers, calcium carbonate. Red algae fibers consist predominantly of cellulose and contain less than 1% inorganic ash. They are comparable to wood fibers in terms of their bonding, combustion, recycling, and biodegradation. While the bonding strength properties of paper decreased with an increase of inorganic fillers in the amount added to the paper, the red algae fibers maintained their bonding properties. These special characteristics seem to stem from the relatively large specific surface areas of the red algae fibers, which are relatively short (0.4−0.8 mm) and narrow (2−4 μm). Moreover, the addition of red algae fibers to the paper increased the paper stretch and folding endurance in proportion to their added amount. These special properties of red algae fibers may find application in low-basis weight printing paper grades that require high opacity and strength.
1. INTRODUCTION Red algae pulp fibers were first introduced by Seo et al.1 as raw materials for papermaking. A pulping and bleaching process simpler than that required for bleached wood pulp produces red algae pulp of high brightness. Previous reports briefly discuss the exceptionally high smoothness and opacity of the papers prepared from red algae pulp fibers.2,3 Moreover, red algae pulp fibers were also used as reinforcements for biocomposites.4,5 In recent times, there has been a need for combustible, biodegradable, completely recyclable, and environmentally friendly renewable organic fillers.6 Sometimes, waste paper containing fillers has to be burned to recover heat or to reduce the net volume of solid disposed in landfills. Researchers in Korea recently developed lignocellulosic fillers for papermaking using waste wood. However, the fillers were not sufficiently bright, and their size distribution was difficult to control.7 Alince8 used cationic latex to increase the tensile strength of wood fibers without losing opacity. Though the cationic latex indeed increased the tensile strength and maintained the opacity, it did not enhance the opacity.8 We found that red algae pulp fibers could be used as bondable fillers or opacifiers because they offer high opacity and develop strong interfiber bonding in white paper. Of the over 10 000 species of red algae,9 we used the red algae species, Gelidium corneum (Hudson) J. V. Lamouroux in this study. We focused on the unique high opacity of papers made from the red algae pulp fibers. In this study, we investigated the possible use of red algae pulp fibers as bondable, combustible, recyclable, and biodegradable opacifiers instead of inorganic fillers such as calcium carbonate.
mucilaginous carbohydrates were extracted from the red algae by heating at 120 °C for 3 h. No chemicals were used in the extraction process. The role of this simple extraction process in red algae is that of a chemical pulping process used in manufacturing wood chemical pulp. However, the absence of lignin in red algae rules out the need for strong chemicals.11 In the bleaching process, we used two bleaching chemicals: chlorine dioxide in the first stage and hydrogen peroxide in the second stage. In the first stage, we used 5% active chlorine dioxide by dry weight of the material to be bleached at pH 3.5. The temperature, duration, and initial pH were 80 °C, 60 min, and 3.5, respectively. The pH was controlled by adding sulfuric acid. In the second stage, we used 5% active hydrogen peroxide by dry weight of the material. The temperature, duration, and initial pH were 80 °C, 60 min, and 12, respectively. The pH was controlled by adding sodium hydroxide. The second stage was repeated two times to obtain the target brightness of over 85%. The details of the pulping and the bleaching processes are provided elsewhere.1 2.2. Handsheet Preparation and Testing. We made 60 g/m2 handsheets out of never-dried red algae pulp, according to the TAPPI test method (T205 sp-95). To compare the physical properties of red algae pulp to those of market wood pulp, we used a mixture (50:50) of commercial SwBKP (softwood bleached kraft pulp; a mixture of Hemlock, Douglas Fir, and Cedar) and HwBKP (hardwood bleached kraft pulp. a mixture of Aspen and Poplar), both of which are from Canada. The mixture was refined by a valley beater to 514 csf and handsheets of about 60 g/m2 were prepared. The opacifier should impart as much opacity to the paper as inorganic fillers without compromising the bonding strength
2. EXPERIMENT 2.1. Preparation of Red Algae Pulp. Red algae pulp was prepared from Gelidium corneum imported from Morocco. The
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© 2013 American Chemical Society
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calcium carbonates. Figure 2 indicates that red algae fibers offered opacity comparable to that offered by calcium
(or paper strength). To study the development of opacity and strength in the handsheets, we prepared samples (listed in Supporting Information Table 1), by adding predetermined amounts of calcium carbonate or red algae fibers to a wood pulp mixture. It was assumed that all of the red algae fibers were retained on the handsheets without any retention aids. The size and the International Organization for Standardization (ISO) brightness of the precipitated calcium carbonate (PCC) was 2− 3 μm, and 94.0%, respectively. The PCC was donated from M paper company located in Republic of Korea. It was delivered in emulsion with solid content of 18.3% (150 cP in viscosity). For retention of the fillers, cationic PAM of 6 × 106 molecular weight, and +20 meq (milimol equivalent) charge density was used in 0.1% concentration based on dry weight of what was furnished. The properties of the handsheets derived from the samples were listed in Supporting Information Table 2, where each value listed was the average of 10 measurements. The density (T410 om-98, T411 om-97); breaking length, which is a measure of tensile strength (ISO 1924); double folds (ISO 5626); tear index (ISO 1974); and drainage (T221 cm-99) of the handsheets were measured. The brightness (ISO 2470) and the opacity (ISO 2471) were measured using the Color Touch device manufactured by Technidyne Co. The void volumes and void specific surface areas of sample handsheet papers were measured using a mercury porosimeter (Autopore IV 9500, Micromeritics, USA) for pore diameters of ≥3 nm (equivalent to 60 000 psi).
Figure 2. Opacity development by the addition of red algae fibers and CaCO3.
carbonate, although calcium carbonate imparted a slightly higher opacity for equal addition levels. Figure 3 indicates that
3. RESULTS AND DISCUSSIONS Micrographs of the papers containing calcium carbonates and red algae fibers are shown in Figure 1. The ash content of 100% red algae fibers was 0.57% while that of 100% wood fibers was 0.65%. Red algae fibers were distributed more evenly than
Figure 3. Breaking length development by the addition of red algae fibers and CaCO3.
with increased addition, the sheets with red algae fibers developed a much higher breaking length than those with calcium carbonate. As expected, the breaking lengths of the sample sheets decreased with an increase in the amount of calcium carbonate; however, the addition of the red algae fibers did not affect the breaking length. This is because calcium carbonate cannot have bonding with wood fibers. The more calcium carbonate there is in the paper, the lower is the bonding properties. Red algae fibers are composed of cellulose and have hydroxyl groups, which can have hydrogen bonding with wood fibers. The effect of the addition of red algae fibers to the paper should be the simple replacement of wood fibers without changing the amount of interfiber bonding. Figure 4 shows the combined effect on the opacity and breaking length of the sample sheets. As the opacity increased, greater differences were seen in the breaking length of the sample sheets with red algae fibers and calcium carbonate. Red algae fibers, like wood fiber,1 consist of cellulose and hemicellulose and contain as many hydroxyl groups as wood pulp fibers. Thus, both wood pulp fibers and red algae fibers
Figure 1. Micrographs of the samples (SEM). 9813
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Figure 6. Increase of brightness by the addition of calcium carbonates and red algae fibers.
Figure 4. Breaking length comparison on the axis of opacities for the handsheets containing red algae fibers and CaCO3.
calcium carbonate used in this study was 94.9%. The more calcium carbonate is added, the higher the brightness difference will be. The stretch of the handsheets decreased according to the addition levels of calcium carbonate and increased with red algae fibers, as shown in Figure 7. The calcium carbonate was
certainly develop interfiber bonding. Seo et al. explained why the red algae fibers impart high opacity by showing the difference in the accumulated void specific surface area measured by mercury intrusion for paper with a pore diameter of 250 nm2. In ref 2, Seo et al. showed that the larger is the accumulated void specific surface area over the pore diameter of 250 nm, the higher is the paper’s opacity and the addition of red algae fibers increased proportionally to that accumulated void specific surface area. The cumulative specific surface areas of the samples measured by the mercury intrusion method were listed in Supporting Information Table 3, where the values increased with the addition of red algae fibers and calcium carbonates increased at 250 nm pore diameter. The average width of red algae fibers was 2−4 μm as shown in Figure 1 and in ref 2, while that of wood fibers was 10−50 μm. The size of PCC used in this experiment was 2−3 μm, which is very close to the width of red algae fibers. We believe this similar dimension resulted in similar light scattering effects. Furthermore, the specific surface area of red algae fibers will be much greater than that of wood fibers. Figure 5 shows the
Figure 7. Stretch changes of the handsheets by the addition of red algae fibers and CaCO3.
added to the handsheets to replace wood fibers for opacity improvement, but the inorganic material such as calcium carbonate could not respond to tension stretching, and gave lower stretch values in proportion to its addition level. In contrast, red algae fibers as shown in the micrographs in Figure 1, showed curled morphologies, and might have stretched more under tension than wood fibers. Page et al. showed a positive relationship between paper stretch and fiber curl index.10 We believe that was why there were so many different stretch behaviors as shown in Figure 7. Double folds were quite different between red algae fibers and calcium carbonate as shown in Figure 8. We believe that was because of the combined effects of high breaking lengths and high stretches of the handsheets containing red algae fibers.
Figure 5. Relationship between opacities and cumulative specific surface areas at 250 nm pore diameter of the samples.
opacities of the samples containing red algae fibers and calcium carbonate plotted against the accumulated specific surface areas over the pore diameter of 250 nm; the regression coefficient (R2) was found to be 0.931. Figure 6 shows noticeable differences in the brightness of the sample sheets for the samples containing calcium carbonates and red algae fibers used in this study. Brightness of the handsheet with 100% red algae fibers was 87.9%, but that of
4. CONCLUSIONS Red algae fibers can increase paper opacity as much as calcium carbonates can, but without decreasing the breaking length. Red algae fibers can be used as bondable, combustible, recyclable, and biodegradable fillers in white paper. A few conclusions can be drawn from the results of this study. 9814
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(7) Kim, C. H.; Lee, J. Y.; Lee, Y. R.; Chung, H. K.; Back, K. K.; Lee, H. J.; Gwak, H. J.; Gang, H. R.; Kim, S. H. Fundamental study on developing lignocellulosic fillers for papermaking (II)Effect of lignocellulosic fillers on paper properties. J. Korea Tappi 2009, 42 (2), 1−6. (8) Alince, B. Increasing tensile strength without losing opacity. Tappi J. 1991, 74 (8), 221−223. (9) Woelkerling, W. M. J. An introduction. In Biology of the Red Algae; Cole, K. M., Sheath, R. G., Eds.; Cambridge Univ. Press, UK, 1990; p 2. (10) Page, D. H., Seth, R. S., Jordan, B. D., Barbe, M. C., Curl, crimps, kinks, and microcompressions in pulp fibers-their origin, measurement and significance. In Papermaking Raw Materials; Punton, V. Ed.; Transactions of the 8th fundamental research symposium held at oxford, Vol. 1; Mechanical Engineering Publications Ltd.: London, 1985; pp 183−227. (11) Yoon, M. H.; Lee, Y. W.; Lee, C. H.; Seo, Y. B. Simultaneous production of bio-ethanol and bleached pulp from red algae. Bioresour. Technol. 2012, 126, 198−201.
Figure 8. Double folds of the handsheets by the addition of red algae fibers and CaCO3.
• Red algae fibers impart opacity as much as inorganic fillers while conserving the interfiber bonding in paper. • Red algae fibers increase the paper stretch. The stretch improvement is attributed to the severely curled shapes of the red algae fibers embedded in the paper structure. • Red algae fibers increased the folding endurance of the paper greatly at high opacity. • Red algae fibers are made of cellulose; they are bondable, combustible, recyclable, and biodegradable. The red algae fibers can be best utilized for manufacturing premium grade, high strength, high folding resistance, lightweight printing papers and high quality filter papers that need high specific surface areas.
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ASSOCIATED CONTENT
* Supporting Information S
Additional tables as described in the text. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Fax: 82-42-821-6159. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Seo, Y. B.; Lee, Y. Y.; Lee, C. H.; You, H. C. Red algae and their use in papermaking. Bioresour. Technol. 2010, 101, 2549−2553. (2) Seo, Y. B.; Lee, Y. Y.; Lee, C. H.; Lee, M. W. Optical properties of red algae fibers. Ind. Eng. Chem. Res. 2010, 49, 9830−9833. (3) Seo, Y. B.; Kim, Y. W.; Lee, M. W.; Chung, S. Y. Improvements in the physical properties of Hanji by using red algae fibers. J. Korea Tappi 2009, 41 (5), 33−37. (4) Sim, K. J.; Han, S. O.; Seo, Y. B. Dynamic mechanical and thermal properties of red algae fiber reinforced poly(lactic acid) biocomposite. Macromol. Res. 2010, 18 (5), 489−495. (5) Lee, M. W.; Han, S. O.; Seo, Y. B. Red algae fibre/poly(butylenes succinate) biocomposite: The effect of fibre content on their mechanical and thermal properties. Compos. Sci. Technol. 2008, 68, 1266−1272. (6) Shen, J.; Song, Z.; Qian, X. Possible trends of renewable organic fillers and pigments derived from natural resources for sustainable development of papermaking industry. Bioresources 2010, 1 (5), 5−7. 9815
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