Debonding Performance of Various Cationic Surfactants on Networks

Sep 28, 2010 - By applying AAS at levels of up to 20 mg/g, the tensile and burst indices of the networks were reduced by 18.6%, and 14.2%, respectivel...
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Ind. Eng. Chem. Res. 2010, 49, 11402–11407

Debonding Performance of Various Cationic Surfactants on Networks Made of Bleached Kraft Fibers Pedram Fatehi,* Kevin C. Outhouse, Huining Xiao,* and Yonghao Ni Department of Chemical Engineering and Limerick Pulp and Paper Centre, UniVersity of New Brunswick, Fredericton, NB, Canada E3B 5A3

Debonding agents are applied in the paper industry for various purposes, for example, to increase the softness of tissue paper. In this work, the debonding capacities of three cationic aliphatic ammonium surfactants and one alkoxylated amine surfactant on kraft fibers were determined. The results showed that the adsorption of the alkoxylated amine surfactant (AAS) was higher than that of others on the fibers, but a cationic cetyltrimethyl ammonium surfactant (cetyltrimethyl ammonium bromide, CAB) was the most effective debonding agent, probably because of its relatively long hydrophobic chain. By applying CAB at levels of up to 20 mg/g, the tensile and burst indices were reduced by 37% and 41%, respectively. By applying AAS at levels of up to 20 mg/g, the tensile and burst indices of the networks were reduced by 18.6%, and 14.2%, respectively. The tear index of the fiber networks negligibly changed upon application of AAS, but increased by 19% upon application of CAB. The strain of the fiber networks prior to rupturing increased upon application of AAS, whereas it decreased upon application of CAB, which implies that the surfactants have different debonding mechanisms. The debonding efficiency of CAB was independent of both the refining revolutions and basis weights of the fiber networks. 1. Introduction Some surfactants, known in the paper industry as debonding agents, are used in fluffing pulp productions to reduce interfiber bonding and energy consumption.1-3 They have also been applied as softeners in tissue paper manufacturing.1,3 In this case, by decreasing the fiber network strength, they increase the softness of the tissue paper.4 Cationic surfactants having a quaternary ammonium group with four aliphatic chains,5 ester-functional quaternary ammonium compounds,3 or dialkyl dimethyl quaternary ammonium compounds3 are used as debonding agents. However, they significantly increase the hydrophobicity of the fibers, thus impairing the water absorbency of the paper products,3 which might not be desired in the production of tissue paper products. The solution for this problem is to decrease the number of aliphatic chains in the cationic surfactant.3 Several studies have been reported on understanding the adsorption characteristics of cationic surfactants on cellulose fibers.6-10 The influence of benzyl dimethyl ammonium chloride and various alkyl methyl quaternary ammonium componds on the tensile strength of various recycled fiber networks has also been reported.1,3 We also investigated the application of a cationic alkoxylated amine surfactant as a rewetting or debonding agent for various paper products.11-13 It is known that the surface and strength properties of fibers significantly affect the mechanical and structural properties of fiber networks, as well as the performance of additives on the networks.14-16 Therefore, the efficiency of a debonding agent might be different on networks made from different fiber grades. As bleached kraft fibers are extensively used in tissue paper manufacturing in North America, one objective of this study was to investigate the adsorption performance and debonding capacity of various cationic surfactants on kraft fibers. Because bleached kraft fibers are more hydrophilic than recycled fibers, the changes in the * To whom correspondence should be addressed. E-mail: (P.F.) [email protected]. (H.X.) [email protected]. Tel.: 506-452-6084. Fax: 506453-4767.

hydrophilicity of fibers, which are due to the application of surfactants, might not significantly affect the water absorbency in the production of tissue paper products. Pulp refining is widely practiced in the paper industry to improve the fibrillation of fibers, resulting in increases in the surface area of the fibers, the fiber flexibility, and the strength of the fiber networks. Another objective of this study was to investigate the influence of mechanical refining on the performance of a selected cationic surfactant. In this work, the debonding affinities of various cationic surfactants were determined, and the performance of the most effective surfactant was compared with that found in our previous work.13 The influence of refining on the debonding capacity of the selected surfactant was also evaluated. 2. Materials and Methods 2.1. Materials. Bleached pine kraft pulp was received from a mill in Eastern United States. It was kept in a refrigerator prior to use. Cationic alkoxylated amine surfactant (AAS) was provided by Clariant Chemicals (Charlotte, NC), whereas cetyltrimethyl ammonium bromide (CAB), dodecyltrimethylammonium bromide (DAB), and tetrabutylammonium iodide (TAI) were purchased from Aldrich (Milwaukee, WI) and dissolved in water (1 wt %) prior to use. The moisture content of the pulp was measured in accordance with TAPPI standard test method T 412. The fiber characteristics were analyzed using a fiber quality analyzer from Optest Equipment Inc. (ON, Canada). Also, the refining of the pulp was carried out according to TAPPI test method T 248 in a PFI refiner, no. 158 (Norway). The freeness of the pulps was tested using a Canadian Standard Freeness (CSF) tester in accordance with TAPPI test method T 227. 2.2. Adsorption Analysis. About 1 g (oven-dried) of unrefined fibers was first dispersed in a 125 mL Erlenmeyer flask at a 3% consistency and 30 °C. In one set of experiments, 10 mg/g of various surfactants was added to the unrefined fibers, and the flasks were shaken at 200 rpm for various times. Afterward,

10.1021/ie101442p  2010 American Chemical Society Published on Web 09/28/2010

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Figure 1. Chemical structures of (a) AAS, (b) CAB, (c) DAB, and (d) TAI.

the supernatants and fibers were separated by vacuum filtering. In another set of experiments, various dosages of AAS or CAB were added to the unrefined fiber suspensions, the mixtures were shaken for 1 h under the conditions specified above, and the filtrates were collected. To reduce the impact of the colloidal substances on the analysis, the supernatants were centrifuged at 3000 rpm for 30 min.1-3 Then, samples were taken from the solutions of centrifuged supernatants for determining the concentration of surfactants by nitrogen analysis. The nitrogen analysis was conducted using a nitrogen/sulfur analyzer (9000 series, Antek, Houston, TX) at the temperature of 1075 °C. A calibration curve was prepared by plotting the predefined concentrations of AAS or CAB against the intensities of the nitrogen peak. The concentrations of AAS or CAB in the solutions were determined based on the calibration curve. A similar procedure was followed to determine the adsorption of CAB on the refined fibers. The adsorption analysis was repeated three times, and the standard deviation was determined and is presented. 2.3. Fiber Modification and Sheet Preparation. Pulp fibers were first dispersed in distilled water in a 2 L three-neck glass flask at a 3% consistency and 30 °C. First, various dosages of AAS or CAB were applied to the suspensions of unrefined fibers, and the suspensions were stirred for 1 h. Then, the fibers were washed thoroughly with distilled water to remove unadsorbed surfactants. The cellulosic fiber networks (handsheets) were prepared in accordance with TAPPI test method T 205 and dried in a conditioning room in accordance with TAPPI test method T 402. Second, 5 mg/g or 10 mg/g of CAB was mixed with various refined fiber suspensions, and the fiber networks were prepared as described above. Third, 5 mg/g of the CAB was added to the suspensions of unrefined fibers under the conditions explained above, and the fiber networks were prepared at various basis weights. 2.4. Fiber Network Analysis. The light scattering coefficient and brightness of the fiber networks were tested in accordance with TAPPI test methods T 425 and T 452, respectively, using a Techni-Brite Micro TB-1C optical tester (New Albany, IN). The finite-span tensile strength (simplified as tensile strength) and the tear strength were measured in accordance with TAPPI test methods T 494 and T 414, respectively, using Lorentzen & Wettre (L&W) tensile and tear testers (Kista, Sweden). The burst strength of the networks was also measured in accordance with TAPPI T 403, using a Burst-o-Matic, Lorentzen & Wetter (Kista, Sweden) burst tester. The zero-span tensile strength was measured using a Pulmac tester (Montreal, Quebec, Canada), model FQT-E2-110, in accordance with TAPPI test method T 494. The fiber network analysis was conducted twice, and the standard deviation was determined and is presented.

Figure 2. Adsorption of surfactants upon addition of 10 mg/g on kraft fibers.

3. Results and Discussion 3.1. Adsorption of Various Surfactants on Fibers. The adsorption of cationic surfactants onto pulp fibers is mainly achieved through electrostatic interactions between the cationic charges (quaternary ammonium groups) of surfactants and the anionic charges of fiber surface.2 Figure 1 shows the chemical structures of the surfactants used in this study. The hydrophile/ lipophile balance (HLB) of the surfactants was determined based on the Davies’ HLB theory,17 group number coefficients available in the literature,18-20 and the surfactant chemical structures (Figure 1). The HLBs of AAS, CAB, DAB, and TAI were found to be 41.58, 19.97, 21.87, and 21.4, respectively. It is well-known that the higher the HLB, the higher the hydrophilicity of a surfactant.17-20 Therefore, the hydrophobicity of the fiber surface would be the highest upon application of CAB. Upon adsorbing, the long-chain alkyl groups of surfactants extend from the fiber surface, causing an increase in the hydrophobicity of the fiber surface, which impairs the development of interfiber bonding.1-3,8 However, the presence of primary ammonium, quaternary ammonium, and carbonyl groups on the structure of AAS, which results in a very high HLB, increases the hydorphilicity of the fiber surface upon adsorption. In our previous work, we reported that the total moisture contents and rewetting abilities of the networks were increased upon adsorption of AAS on sulfite fibers.13 Figure 2 shows the adsorption of cationic surfactants on kraft fibers versus the time of adsorption. As can be seen, the adsorption of the surfactants reached a plateau level in 1 h, which is in agreement with the results reported in the literature.8,21 Therefore, further adsorption analysis and fiber modification were conducted at 1 h. Figure 3 shows the amount of each surfactant adsorbed on the fibers versus the concentration of surfactant remaining in

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Figure 3. Adsorption isotherms of surfactants on kraft fibers (adsorption time ) 1 h).

solution. It is evident that AAS adsorbed onto the fibers relatively more than the other surfactants. The development of hydrogen bonding might be one reason for the higher adsorption of AAS compared to the others. The higher AAS adsorption can also be attributed to its relatively smaller size (compared to the other surfactants), which promotes its diffusion into the fiber pores. However, it was previously reported that there were aggregations between the extended hydrophobic chains of the adsorbed surfactants and the surfactants approaching from the bulk to the fibers, which increased the adsorption amount of surfactants.8 In this case, the larger the alkyl chain, the higher the aggregation and adsorption of the surfactants on the fibers.8 The relatively higher adsorption of CAB compared to DAB and TAI (Figure 3) was probably due to the aggregation phenomenon. The S-shaped form of the adsorption isotherms in Figure 3 was also observed by others6-8 and attributed to the aggregation phenomenon described above. 3.2. Influence of Various Surfactants on Strength of Networks. The tensile and burst indices of networks made from kraft fibers modified with various surfactants (10 mg/g) are shown in Figure 4. Evidently, AAS, DAB, and TAI reduced the tensile and burst indices of the fiber networks by 4-7%, 3-8%, and 3-8%, respectively. In our previous work, the addition of AAS (10 mg/g) caused 12% and 15% reductions, respectively, in the tensile and burst indices of networks made from sulfite fibers.13 Because of the presence of more hemicelluloses on kraft fibers than on sulfite fibers, the fiber bonding is more greatly developed in the networks of kraft fibers. In other words, more hydrogen bonding presents in the networks of the kraft fibers that should be conquered by the surfactants (as a debonding agent). Therefore, the debonding capacity of the surfactants is less on the networks of kraft fibers than on those of sulfite fibers at the same dosage of surfactants adsorbed. Furthermore CAB reduced the tensile and burst indices of the networks by 19.5% and 27.3%, respectively (Figure 4). As described earlier, the HLB of CAB was significantly lower than that of AAS. Thus, the hydrophobicity of the fiber surface probably increased more significantly upon application of CAB, which was perhaps the reason for its higher debonding capacity. The higher debonding capacity of CAB compared to DAB and TAI might be largely due to its larger hydrophobic chain preventing fiber bonding development (Figure 1) and to its higher adsorption dosage (Figures 2 and 3). Because CAB was the most effective debonding agent in our study, we selected it for further analysis, and its debonding capacity was compared with that of AAS on kraft fibers, which was used on sulfite fibers in our previous study.13 3.3. Effect on Network Properties. The properties of networks made from fibers modified with various dosages of

Figure 4. Tensile and burst indices of networks made of fibers modified by addition of 10 mg/g of various surfactants at a basis weight of 60 g/m2.

AAS and CAB are listed in Table 1. Evidently, when the dosage of AAS was increased from 0 to 20 mg/g, the tensile and burst indices of the networks were reduced by 18.6%, and 14.2%, respectively, whereas the apparent density was marginally changed. More interestingly, when the CAB dosage was increased from 0 to 20 mg/g, the tensile and burst indices were reduced by 37% and 41%, respectively, whereas the apparent density was reduced by 3.5%. However, the tear index negligibly changed upon addition of AAS, but increased up to 19% upon addition of CAB. The zero-span tensile index of the fiber networks is well correlated with the fiber wall strength.13-16,22 In the literature, it was shown that small molecules, such as dyes23 and surfactants,24-26 could easily diffuse into the fiber pores and adsorb on the fiber wall. Once inside the fiber wall, surfactants can hamper the cross-linking of the fiber wall during drying because of the decreased hydrogen-bonding development. It is apparent in Table 1 that the zero-span tensile index of the fiber networks was reduced by 5.2% and 10.7% for AAS and CAB, respectively. In our previous work, we reported that the strength of sulfite fibers was insignificantly affected by AAS.13 The simplified form of Page’s tensile strength equation is given by 1 1 1 ) + T F B

(1)

where T, F, and B represent the tensile index, fiber wall index, and interfiber bonding index, respectively.27 Therefore, the interfiber bonding index in eq 1 can be estimated by determining the finite tensile and zero-span tensile strengths of the networks. Figure 5 shows the interfiber bonding index of the networks as a function of the dosages of AAS and CAB. As can be seen, upon application of AAS or CAB up to 20 mg/g, the interfiber bonding index was reduced by up to 17% or 41.5%, respectively. Because more AAS than CAB adsorbed (Figure 3), but the network strength was reduced more upon application of CAB than AAS (Table 1), it can be claimed that CAB was a more efficient debonding agent than AAS on kraft fibers.

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Table 1. Properties of Paper Networks Made from Fibers Modified with Various Dosages of AAS or CAB dosage/ sample ID 0 2.5 5 7.5 10 20

tensile index (N m/g)

tear index (N m2/kg)

burst index (kPa m2/g)

zero-span tensile index (N m/g)

apparent density (kg/m3)

AAS

CAB

AAS

CAB

AAS

CAB

AAS

CAB

AAS

CAB

32.3 ( 1.3 31.0 ( 1.1 31.1 ( 0.8 30.9 ( 0.9 30.5 ( 0.9 26.3 ( 1.0

32.3 ( 1.3 28.9 ( 0.8 27.6 ( 0.7 27.0 ( 1.1 26.0 ( 0.8 20.4 ( 0.9

26.0 ( 1.2 27.8 ( 1.8 28.6 ( 1.5 27.1 ( 1.6 27.8 ( 1.8 28.6 ( 1.5

26.0 ( 1.2 25.9 ( 1.6 26.8 ( 1.7 28.0 ( 1.9 29.1 ( 1.4 31.0 ( 1.3

2.38 ( 0.09 2.28 ( 0.11 2.29 ( 0.12 2.25 ( 0.11 2.20 ( 0.08 2.04 ( 0.10

2.38 ( 0.09 1.99 ( 0.07 1.87 ( 0.06 1.80 ( 0.12 1.73 ( 0.11 1.41 ( 0.11

153.7 ( 1.9 151.2 ( 1.8 150.6 ( 1.6 150.4 ( 1.5 148.1 ( 1.4 145.7 ( 0.7

153.7 ( 2.1 150.1 ( 1.8 146.5 ( 2.1 142.8 ( 2.2 140.1 ( 0.8 137.2 ( 1.6

591.0 ( 5.4 590.3 ( 2.1 587.6 ( 5.4 586.9 ( 2.4 584.9 ( 4.3 581.1 ( 3.3

591.0 ( 5.4 593.2 ( 3.2 582.7 ( 4.5 582.8 ( 3.5 579.1 ( 5.2 570.2 ( 3.2

Table 2. Properties of Fibers Refined under Various Revolutions refining revolutions

fiber length (LW) (mm)

fines (LW) content (%)

curl index

CSF (mL)

0 500 4000 9000

2.15 ( 0.12 2.28 ( 0.14 2.04 ( 0.08 1.95 ( 0.09

15.2 ( 4.1 17.1 ( 3.1 21.6 ( 2.3 24.2 ( 1.2

0.15 ( 0.03 0.13 ( 0.04 0.12 ( 0.02 0.10 ( 0.01

751 ( 11 723 ( 6 605 ( 8 438 ( 10

To gain insight into the debonding mechanisms of AAS and CAB, the final strain of the networks prior to rupturing in tensile strength testing was determined, as shown in Figure 6. Interestingly, the final strain of the networks increased with increasing dosage of AAS, whereas it decreased with increasing dosage of CAB. These results suggest that AAS can increase the plasticity of the fiber networks as a result of the increase in the moisture absorbance of fibers, as discussed in our previous work.11-13 However, the increase in the hydrophobicity of fibers upon addition of CAB leads to a decrease in the shear strength of interfiber bonding and, thus, a decrease in the strain of the fiber networks. 3.4. Fiber Refining Analysis. The properties of kraft fibers refined under various revolutions are listed in Table 2. Evidently, refining at 500 revolutions increased the fiber length and slightly increased the fines content. In the literature, the increase in the

fiber length was attributed to the straightening of fibers at a low refining revolution for kraft and sulfite fibers,13,28 which was supported by the decrease in the curl index in Table 2. However, a further increase in the refining revolutions decreased the fiber length, but increased the fines content. These results imply that fiber breakages dominated at high numbers of refining revolutions (>4000). The decrease in the curl index might also suggest that the curly fibers were straightened or broken by refining at high revolutions.13 The decrease in the Canadian standard freeness (CSF) obtained by increasing the refining revolutions is due to increases in the fibrillation (surface area), fiber flexibility, and fines content. 3.5. Adsorption of CAB on Refined Fibers and Its Corresponding Impact on Properties. Figure 7 shows the adsorption of CAB on various refined fibers. As can be seen, the higher the refining revolutions (the lower the CSF), the higher the adsorption of CAB, regardless of the surfactant dosage. This behavior is due to the increase in the surface area of fibers upon refining, thus favoring the surfactant adsorption process. The properties of networks made from various refined fibers modified with two different dosages of CAB are listed in Table 3. As expected, the burst index of the networks was increased, but the light scattering coefficient was reduced by increasing the refining revolution. This behavior is attributed to the increases in the interfiber bonding, obtained from the improved swelling ability; in the flexibility and fibrillation of the fibers; and in the fines content of fibers. Additionally, the zero-span tensile index of the networks was increased, which was attributed to an increase in fiber wall cross-linking as a result of the increase in fiber wall fibrillations and/or in fiber flexibility.24,25 It is evident in Table 3 that the burst index of the networks was reduced by up to 20-25%, whereas the light scattering coefficient was increased by up to 6-12% upon application of up to 10 mg/g CAB. The zero-span tensile index of the networks was reduced by 8%, regardless of the number of refining revolutions, which was probably due to the diffusion of CAB into the fiber pores, as described earlier.

Figure 5. Interfiber bonding index of networks made from fibers modified with various dosages of AAS or CAB.

Figure 6. Final strains of networks made of fibers modified with various dosages of AAS or CAB.

Figure 7. Adsorption of CAB on various refined fibers (addition dosage of 5 or 10 mg/g).

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Table 3. Properties of Networks Made from Fibers Refined under Various Revolutions and Modified with 5 or 10 mg/g of CAB burst index (kPa m2/g)

light scattering coefficient (m2/kg)

zero-span tensile index (N m/g)

refining revolutions

control

5 mg/g

10 mg/g

control

5 mg/g

10 mg/g

control

5 mg/g

10 mg/g

500 4000 9000

3.58 ( 0.05 5.39 ( 0.04 6.02 ( 0.06

2.97 ( 0.07 4.89 ( 0.08 5.22 ( 0.04

2.67 ( 0.05 4.20 ( 0.07 4.81 ( 0.04

161.2 ( 2.1 173.3 ( 3.2 185.0 ( 2.6

156.4 ( 2.4 172.3 ( 3.2 174.6 ( 4.2

146.8 ( 1.8 162.2 ( 2.6 170.4 ( 3.2

22.3 ( 0.1 15.9 ( 0.2 14.1 ( 0.1

23.4 ( 0.2 16.8 ( 0.1 14.7 ( 0.2

23.7 ( 0.1 17.3 ( 0.1 15.9 ( 0.2

Table 4. Properties of Fiber Networks Made from Fibers Modified with 5 mg/g of CAB at Various Basis Weights tensile index, Nm/g 2

tear index (N m2/kg)

burst index (kPa m2/g)

apparent density (kg/m3)

basis weight (g/m )

control

CAB

control

CAB

control

CAB

control

CAB

30 45

28.0 ( 1.2 31.4 ( 2.1

24.5 ( 3.1 27.9 ( 2.3

20.2 ( 2.4 23.9 ( 1.8

21.1 ( 2.2 25.2 ( 2.3

2.03 ( 0.06 2.14 ( 0.07

1.65 ( 0.06 1.78 ( 0.07

543.4 ( 6.8 575.8 ( 10.2

531.3 ( 7.6 564.9 ( 8.7

Figure 8 shows the relationship between the tear and tensile indices of the fiber networks made from refined fibers modified with 5 or 10 mg/g of CAB. When the number of refining revolutions was increased, the tear index of the networks generally decreased, whereas the tensile index increased. It was reported that, if the fiber bonding was not well developed in a network, the fiber breakages, which required a higher energy than fiber bonding breakages did, was dominant in tear strength determination.29,30 However, if the fiber bonding was well developed, the fiber bonding breakages, rather than fiber breakages, prevailed in the tear strength determination.29,30 The tear index of the networks made from fibers modified with CAB was found to be larger than that of the networks made from the control sample at a tensile index of lower than 45 N m/g (Figure 8). However, the tear index of the networks made from the fibers modified with CAB was lower than that of the networks made from the control sample when the tensile index was higher than

Figure 8. Tear index versus tensile index of networks made from refined fibers modified with 5 or 10 mg/g of CAB.

45 N m/g. We propose that, when CAB was applied to the unrefined fibers, the number of fiber breakages increased more than the number of fiber bonding breakages did in the tear strength determination, as a result of fiber bonding reduction. Upon application of CAB to well-refined fibers, the number of fiber bonding breakages was increased more than the number of fiber breakages, which decreased the tear index of the networks. It is also apparent that the tensile indexes of the networks made from the fibers modified with CAB were lower than those of the networks made from the control sample, regardless of the number of refining revolutions. To gain insight into the debonding capacity of CAB on various refined kraft fibers, the interfiber bonding index of the networks was plotted again the apparent density of the networks in Figure 9. This analysis implies the performance of the surfactant on fibers having various degrees of flexibility/ fibrillation. As can be seen, at a constant apparent density, the interfiber bonding index was reduced by the surfactant application at any number of refining revolutions. This is true at different apparent densities as a result of refining. The explanation is that, at a higher refining degree, the increase in the surfactant adsorption (Figure 7) can compensate for the surface area increase; therefore, the debonding capacity of CAB was not reduced by increasing the number of refining revolutions. 3.6. Influence of Basis Weight on Efficiency of CAB. When the basis weight is reduced, the number of fibers required for interfiber bonding is reduced. In this case, the ratio of fiber strength to interfiber bonding strength is changed, which might affect the surfactant’s debonding effectiveness. The results of the application of CAB (5 mg/g) on networks having various basis weights are listed in Table 4. It is apparent that the tensile and burst indices of the networks were reduced by 12-14% and 18-21%, respectively, upon application of CAB, regardless of the basis weight. It is also evident that the apparent density of the fiber networks was reduced by decreasing the basis weight, which principally contributed to the debonding capacity of CAB, as discussed earlier. 4. Conclusions

Figure 9. Interfiber bonding versus apparent density of networks made from refined fibers modified with 5 or 10 mg/g of CAB.

The results of this study on the debonding performance of various cationic surfactants on networks made of bleached kraft fibers showed that alkoxylated amine surfactant (AAS) had a higher adsorption than other cationic surfactants on kraft fibers and that the surfactants reached their maximum adsorption level in 1 h. By applying AAS up to 20 mg/g on unrefined fiber, the tensile and burst indices of the networks were reduced by 18.6% and 14.2%, respectively, whereas the apparent density, tear index, and zero-span tensile index were marginally changed. The strain of the networks increased prior to rupturing upon application of AAS. However, at the same addition level, the cationic cetyltrimethyl ammonium surfactant (CAB) was the

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most effective debonding agent compared to others tested. By adding CAB up to 20 mg/g, the tensile and burst indices were reduced by 37% and 41%, respectively, and the zero-span tensile index and apparent density was reduced by 3.5% and 10.7%, respectively. However, the tear index increased by 19%, whereas the strain of the networks decreased upon application of CAB. The debonding efficiency of CAB was independent of the number of refining revolutions and the basis weights of the fiber networks. Acknowledgment The authors thank Clariant Chemicals for providing the alkoxylated amine surfactant. Also, the Atlantic Innovation Fund (AIF) and NSERC CRD, Canada, are gratefully acknowledged for providing funding for this research. Literature Cited (1) Talaeipoor, M.; Imani, R. Effect of Debonding Agents and Refining on the Properties of Deinked Pulp. Tappi J. 2008, 7 (7), 12. (2) Liu, J.; Hsieh, J. Application of Debonding Agents in Tissue Manufacturing. In Proceedings of the TAPPI Papermakers Conference Trade Fair; TAPPI Press: Atlanta, GA, 2000; Vol. 1, p 71. (3) Poffenberger, C.; Jenny, N. Evaluation of Cationic Debonding Agents in Recycled Paper Feed Stock. TAPPI Recycl. Symp. 1996, 289. (4) Liu, J.; Hsieh, J. Characteristics of Facial Tissue Softness. Tappi J. 2004, 3 (4), 3. (5) Liu, J.; Hsieh, J. Improving Water Absorbency of Tissue Products. TAPPI Eng. Conf. 2000, 329. (6) Aloulou, F.; Boufl, S.; Beneventi, D. Adsorption of Organic Compounds onto Polyelectrolyte Immobilized-Surfactant Aggregates on Cellulosic Fibers. J. Colloid Interface Sci. 2004, 280 (2), 350. (7) Alila, S.; Aloulou, F.; Beneventi, D.; Boufi, S. Self-Aggregation of Cationic Surfactants onto Oxidized Cellulose Fibers and Coadsorption of Organic Compounds. Langmuir 2007, 23 (7), 3723. (8) Aloulou, F.; Boufi, S.; Belgacem, N.; Gandini, A. Adsorption of Cationic Surfactants and Subsequent Adsolubilization of Organic Compound onto Cellulose Fibers. Colloid Polym. Sci. 2004, 283 (3), 34. (9) Alila, S.; Boufi, S.; Belgacem, N.; Beneventi, D. Adsorption of a Cationic Surfactant onto Cellulosic Fibers I. Surface Charge Effects. Langmuir 2005, 21 (18), 8106. (10) Penfold, J.; Tucker, I.; Petkov, J.; Thomas, R. K. Surfactant Adsorption onto Cellulose Surfaces. Langmuir 2007, 23, 8357. (11) Shepherd, I.; Xiao, H. The Role of Surfactants as Rewetting Agents in Enhancing Paper Absorbency. Colloids Surf. A: Physicochem. Eng. Aspects 1999, 157 (1-3), 235. (12) Xiao, H.; Shepherd, I. Effect of Cationic Surfactant as Rewetting Agent on Paper Absorbency and Structures. J. Pulp Pap. Sci. 1999, 25 (5), 170. (13) Fatehi, P.; Outhouse, K.; Xiao, H. Cationic Alkoxylated Amine Surfactant as a Debonding Agent for Papers Made of Sulfite-Bleached Fibers. Ind. Eng. Chem. Res. 2009, 48, 749.

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ReceiVed for reView July 6, 2010 ReVised manuscript receiVed August 28, 2010 Accepted September 11, 2010 IE101442P