Enhancement of Dry Strength in High Performance Linerboard Using a Dual Additive Approach

Transcription

1 Enhancement of Dry Strength in High Performance Linerboard Using a Dual Additive Approach Reprint R-1086 By Michael R. St. John, Research Associate, Nalco, an Ecolab Company An Ecolab Company ABSTRACT Dry strength is clearly a critical characteristic of board grades. Cationic starches have been the additive that has long dominated the dry strength market particularly in North America and Europe. Two industry trends have put a greater requirement on dry strength additives, namely the increased use of lower quality fiber sources and the increased closure of the mills water systems. These trends lead to the need to use larger amounts of starch and diminishing returns in the dose-dry strength relationship. Handsheet data obtained using recycle board furnishes from 2 mills will be presented in this paper and will show how the use of a dual additive approach of starch plus a synthetic polymer dry strength can be used to enhance the achievable dry strength in recycle high performance linerboard. These laboratory results were found to be consistent with the dry strength programs being run at the 2 mills. INTRODUCTION To say that dry strength is a critical property of board grades is to state the obvious. Developing the dry strength needed for a specific grade is a balance between fiber selection, basis weight, refining, press loading, and the use of chemical additives in order to meet the required specification at the lowest cost. The use of inexpensive fiber sources is naturally desired, and very clearly a conversion from virgin unbleached kraft to recycle fiber like OCC [old corrugated containers] and more and more to MW [mixed waste] has been occurring over the past years. This conversion is particularly extensive in Asia and continental Europe. Less expensive fiber sources virtually always lead to lower strength board because the fiber properties are poorer, e.g. fiber length, but also because the increased ash content acts as a debonder. Ash content in recycle board furnishes can be as high as 15 or 20%, and 10 wt% is relatively common. In this sense, recycled board is no longer an unfilled grade but has filler content comparable to fine paper in some cases simply because of the recycled fiber sources being used. A historical re- Table 1 Negative Effects of Refining Negative Impacts on End Product Properties Increased sheet density/ decrease sheet bulk Decreased tear Decreased porosity Slows Production Decreases drainage increased fines and fiber surface area Increases fiber moisture [e.g. WRV] sponse to this loss in dry strength is to increase refining, but the negative effects of refining listed in Table 1 are limiting its utility. In fact board mills are being built without refiners because some do not view refining as a viable option for increasing the strength of recycle board. Increasing press loads can be a viable approach to increase sheet strength through increased sheet consolidation, but presses have mechanical limitations manifested by such things as sheet crushing and result in the same negative sheet properties listed for refining in Table 1. Adding basis weight to increase the board strength can always be practiced, but this approach has the obvious disadvantages of the added cost, increased packaging weight, and environmental impact of using more fiber. The argument can be made based on these trends that the use of existing dry strength additives and the need for improved dry strength additives are increasing, as they are the remaining approach left. The use of chemical strength additives can be expected to provide the benefits listed in Table 2. Of course, the effective use of dry strength additives is always predicated on their cost being lower than alternatives, like increased Table 2 Benefits of Dry Strength Additives Substitution of less expensive fiber or filler Basis weight reduction [light weighting] at same dry strength Increased production through reduced refining [less refining energy also] and lower basis weight Maintain sheet properties lost by refining at desired strength Presented at PaperCon 2012

2 basis weight. In this report, information on starch efficacy in recycle board systems and the potential benefit of dual additive programs consisting of synthetic dry strength used in conjunction with starch is presented. WET END STARCH USE IN RECYCLE BOARD MILLS Historically, wet end starches have been the dominant chemical additive used to increase the dry strength of board, particularly in North America and Europe, and remain the cost effective approach in many instances. An insightful publication by van de Steeg, etal. from looked at the adsorption of polyelectrolytes in relation to the charge density of the polymer, the ionic strength [salt content] of the solution, and the charge density of the surface involved. In papermaking the last two are given properties of the white water and fiber system while the polymer additive charge density can be adjusted by the additive manufacturer. Although it is well known that charged polymers can be prevented from adsorbing or attaching on surfaces if the salt content is high enough, their research provided guidance on the salt level required to interfere with polymers of given charge densities. Coupling this information with the trend in the closure of board mill white water systems [some 100% closed] leading to conductivities in the range of 2.0 to 10.0 ms/cm indicates that polymers of low charge density can have trouble adsorbing under recycle board mill conditions, see for example references 2 and 3. Conductivity is used here as a simple measure of ionic strength or salt content as it also depends on the amount of ionized salts in the water. Table 3 provides some charge densities of polymers to be discussed in this report along with some comparative polymers. Starch A is a typical cationic potato starch having a charge level near the acceptable FDA limit. Lower charge density starches are desired to lower costs. Starch B is described as a high charge density potato starch, but as noted in Table 3, high only means a doubling of the typical Starch A. Both starches have significantly lower charge density compared to other cationic wet end additives considered to be low charge like the acrylamide based retention aid reported in Table 3. A commercial synthetic dry strength based on glyoxalated DADMAC/AcAm [GPAM] may have a charge density as shown in Table 3, which is over twice as large as the typical Starch A. The coagulant p-dadmac is provided as an example of a high charge additive and is seen to be over an order of magnitude larger than the even the high charge cationic starch. The importance of this information is that the cationic starches have the lowest charge density of the commonly used wet-end additives and as such are expected to be the first additive to have trouble adsorbing to the fibers as the conductivity of the papermachine s water system increases. Although starch adsorption studies on cellulose/fiber as a function of conductivity [ionic strength] have been conducted in the past 2-7, some additional data is reported here using 100% OCC pulp from a board mill with a 100% closed water system having a conductivity of 5 ms/cm. To conduct the adsorption experiments, the OCC pulp fiber was filtered and washed until the conductivity was reduced to 57 μs/cm. The OCC fibers were then reslurried to 1 wt% with DI water to which variable amounts of NaCl were added as a simple salt to vary the conductivity [ionic strength]. The experiments focused on the conductivity range important to recycle board manufacture from 1 to 10 ms/cm with a reference slurry at 57 μs/cm providing a system with essentially no ionic strength. Adsorption experiments were conducted by preparing 1 wt% fiber slurries containing the desired dosage of starch after which the slurries were mixed for 30 minutes and centrifuged to remove the solids. Unadsorbed starch was then measured using the KI/I 2 test for starch 12,13 with the concentrations being determined from calibration curves prepared with the starch of interest. The adsorbed starch was then just the difference between the amount added and the amount measured as unadsorbed. Table 3 Charge Densities of Selected Cationic Additives Product Nitrogen Content, Charge Density, wt% meq/g polymer Starch A; typical cationic potato starch with FDA limit cationic charge Starch B; high cationic charge potato starch mol% DMAEA*MCQ/AcAm copolymer; frequently used low charge density cationic retention aid 1.19 glyoxalated DADMAC/AcAm; synthetic dry strength 0.66 polydadmac, high charge density polymer used as coagulant

3 Figure 1 Adsorption Isotherms of Starch A on Washed OCC Fiber at Different Conductivities Adjusted with NaCl The adsorption isotherms for Starch A on the OCC fiber at the different conductivities are shown in Figure 1. Aspects of Figure 1 to note over this important range of conductivities are: 1) the maximum of amount starch adsorbed decreases as the conductivity increases and 2) the amount of starch adsorbed increases faster with the equilibrium concentration in solution at lower conductivity. The latter observation can be viewed as the adsorption being characterized by essentially a high affinity type isotherm at low conductivity where essentially all the starch is adsorbed until the surface is saturated to a more Langmuir type isotherm where only some fraction of the amount added is adsorbed even at the initial doses as the conductivity increases. The implication here is that in this conductivity range, some or even most of the starch is being adsorbed, and therefore can provide strength, but as the conductivity increases less and less of the starch sticks to the fiber. This result may be seen more easily if the data is re-plotted as in Figure 2 where the amount adsorbed is given as a function of the starch dose. The dosages in Figure 2 were selected to cover a range consistent with starch use in mill practice. As can be seen from this data, basically all the starch added is adsorbed at low conductivity but as the conductivity is increased, more has to be added to achieve a given level of adsorption. For example at 6.0 and 8.6 ms/cm, only 8 lb/ton starch is adsorbed when 10 lbs/ton are added and at 20 lb/ ton addition only 14 lbs/ton gets attached to fiber. This unadsorbed starch remains in the white water system, and the efficiency of the starch is reduced. A conclusion to be made here is that in current recycle board mills, the starch still provides strength but diminishing returns with dose can be expected for conventional wet-end starches. Maybe surprisingly, the results of starch adsorption on this OCC fiber are very similar to published results with bleached kraft furnishes 2,4 in regard to amounts adsorbed and Figure 2 Adsorption of Starch A as Function of Dose on Washed OCC Fiber at Different Conductivities Adjusted with NaCl the effect of salts. Such comparisons are dangerous without knowledge of the fiber s accessible surface area, which is dependent on the amount of refining and fines, but at least this OCC has not lost sites for adsorption as some have suggested. Based on the concepts of electrostatic adsorption 1, increased adsorption would be predicted if the polymer charge density was increased. Adsorption of Starch B from Table 3 identified as a so-called high charge starch was examined to explore this expectation. Although the charge density of this high charge starch is twice the value of Starch A, it is still rather low when compared to nearly all other cationic additives. However, the adsorption isotherms presented in Figure 3 show that it behaves noticeably different from Starch A. High affinity isotherms appear to be maintained up to conductivities of 3.33 ms/cm with this higher charge density starch, but reduction in adsorption efficiency still is observed at the higher conductivities.the result is consistent with the simple charge driven adsorption but contributions from Figure 3 Adsorption Isotherms of Starch B on Washed Linpac Fiber at Different Conductivities Adjusted with NaCl 3

4 other properties like molecular weight and polymer structure [e.g. amylose versus amylopectin] are also possible.examining the data as adsorbed starch versus dose, Figure 4, reveals that efficiency of the starch adsorption remains good up to 20 lb/ton dose with this high charge density starch. For the recycle mill where this fiber was obtained, the high charge density starch was not a solution to its strength needs as machine runnability issues were encountered with its use and the increased cost associated with higher charge starch was reported to be significant. Figure 5 General Formula for Glyoxalated DADMAC/ AcAm Dry Strengths Figure 4 Adsorption of Starch B as Function of Dose at Different Conductivities Adjusted with NaCl STARCH PLUS POLYACRYLAMIDE BASED DRY STRENGTH PROGRAM The previous section was intended to show that a diminishing return in starch adsorption is likely to occur with common wet-end starches at the conductivities [ionic strengths] currently found in recycle board mills based on the accepted theory of polyelectrolyte adsorption 1 and experimental adsorption results present in the literature 2-7 and preceding section. Synthetic dry strengths based on polyacrylamide have been known for a very long time with patents issued as early as the 1950 s 8,9. Although a given dry strength can normally be achieved with polyacrylamide base dry strengths at considerably lower does than starches, e.g. many suggest a ratio of 4 to 1 as rule of thumb, the lower dose has not been sufficient to offset the lower cost of the starch. The exception to this has been in Asia, particularly Japan, where acrylamide based dry strengths are commonly used. Although used extensively for temporary wet-strength for many years 10 in North America, glyoxalated DADMAC [diallyldimethyl ammonium chloride]/acam [acrylamide] polymers have become increasingly popular as dry strength additives in recent years. Figure 5 provides an empirical formula for this class of polymers often referred to as GPAMs. A wide variety of different products exist depending on the amounts of the various components shown, and additional monomers could certainly be introduced to increase the compositional variety further. The component listed as di-reacted glyoxal in Figure 5 is a cross-linking element formed by the reaction of the glyoxal with two AcAm units that not only generates higher molecular weights but also imparts molecular structure to the polymers as well. All off these factors can lead to polymers with different types of activities quantitatively and even qualitatively. The use of the GPAMs in conjunction with cationic starch as a dual-polymer strength additive program has been found to be useful in some recycle board mills in situations where the starch has reached the point of diminishing returns in dosage, and the dry strength results from handsheet testing with the dual programs that confirms the usage on two 100% recycle linerboard machines is presented here. Some pertinent details on the wet ends of the two mills are provided in Table 4. Table 4 Mill Wet End Description Mill A Linerboard Furnish: 100% OCC Sizing: ASA size Starch: Cationic waxy maize at 10 lb/ton Retention Program: Cationic flocculant Thin Stock Conductivity: ~2 ms/cm ph: 6.9 Mill B Linerboard Furnish: 100% OCC Sizing: Neutral rosin size Starch: Amphoteric waxy maize at ~27 lb/ton Retention Aid: Alum + anionic flocculant Thin Stock Conductivity: ~5 ms/cm ph: 6.7 4

5 EXPERIMENTAL PROCEDURES Furnishes for handsheet making were prepared by diluting mill thick stock, which was refined but without additives, with mill white water to the desired consistency. The resulting furnishes had the properties given in Table 5. As the table shows, the conductivities are in the 1 to 10 ms/cm range. Soluble cationic demands measured by colloid titration with a Mutek PCD02 endpoint are viewed as in the normal range for recycle board mills. Additive addition sequences and timing for furnishes from mills A and B are given in Tables 6 and 7, respectively. Handsheets were prepared using a semi-automatic British handsheet mold under TAPPI conditions and pressing. The sheets were dried in rings under constraint in a controlled humidity and temperature room under TAPPI standard conditions overnight, after which the test sheets were cut and tested for various dry strength properties.ten test specimens were cut from five sheets, and the mean values are reported. Table 8 provides statistics on the basis weights and apparent densities for all of the sheets made during the evaluation in each mill s furnish.the COVs for the apparent densities indicate that the sheet making was reasonably consistent and differences in sheet strength are not likely to arise from differences in sheet consolidation.the variation in strength could also arise through changes in retention caused by the dry strength additive, but the variation in basis weight observed and lack of correlation with the dry strength additive dose indicated that the sheet compositions were reasonably constant throughout the sheet making. Strength measurements were either indexed or normalized to a targeted basis weight to remove variation arising from basis weight variation. Table 5 Properties of Mill Furnishes Used in Handsheet Preparation Mill Measured Consistency wt% CSF, mls ph Conductivity, ms/cm Soluble Cationic Demand, meq/l Fines Fraction mesh, % of total solids Mill A Furnish Mill B Furnish Table 6 Additive Dosing Sequence for Mill A Sequence for Single Dry Strength Additive Time, sec Event 0 Start Mixing 10 Add GPAM or Starch 130 Add cationic retention aid, 0.5 lb/ton 170 Stop & Make Sheets Sequence for Dual Dry Strength Additive Time, sec Event 0 Start Mixing 10 Add Starch 40 Add GPAM 130 Add cationic retention aid, 0.5 lb/ton 170 Stop & Make Sheets Table 7 Additive Dosing Sequence for Mill B Time, sec Event 0 Start Mixing 10 Add GPAM, if added 30 Add alum, 18 lb/ton 40 Add Starch, if added 100 Add anionic retention aid, 0.4 lb/ton 170 Stop & Make Sheets Table 8 Sheet Basis Weight and Apparent Density Statistics for All Sheets Mill Mean Basis Weight, gsm Mean Basis Weight, lb/1000 ft 2 Basis Weight COV, % Mean Apparent Density, g/cc Apparent Density COV, % A B

6 DRY STRENGTH RESULTS AND DISCUSSION Mill A The burst values obtained in the furnish from Mill A as a function of dose for GPAM 1 and the mill s cationic waxy maize are present in Figure 6 along with the curve for GPAM 1 in the presence of 10 lb/ton of the starch. 10 lb/ton of the starch was selected as this is the dose currently used at Mill A. In this case, the GPAM 1 and the Mill A starch dosed individually have essentially the same dosage profile making the starch preferred on a cost basis. However, the starch has clearly reached a diminishing return in dosage at the 10 lb/ton dose and maybe even before this. Consequently, increased dry strength, burst in this case, can not be achieved by further increases in the starch dose. In this sense, the mill has done a good job in selecting their optimum starch dose. Figure 6 also shows that further increases in burst beyond the starch optimum can be achieved by the addition GPAM 1 in conjunction with the optimum starch dose. This result was thought to be somewhat surprising because dry strength additives are viewed as functioning in the same way by increasing the bond strength between fibers and perhaps increasing the real bond area. On this basis a reasonable expectation might be that the addition of the GPAM 1 to the optimum starch dose would follow the same curve as the starch, i.e. behave as if additional starch was added. The data indicates that this expectation is not true and suggests that the GPAM 1 and the cationic starch function in different ways, at least in part. Nanko 11 found evidence for polyacrylamide dry strengths adsorbing in a different way than starch, which might support a different mode of action. GPAMs also have a chemically reactive functionality 10 that starches do not have, which is the mono-reacted glyoxal functionality identified in Figure 5. This reactive functionality Figure 6 Burst (Normalized to 26 lb BW) Dosage Curves in Mill A Furnish for GPAM 1 with and without Starch and Starch Alone 6 Figure 7 Dosage Curves of Burst Increase (Normalized to 26 lb BW) over Initial Value in Mill A Furnish for GPAM 1 with and without Starch and Starch Alone could also provide a mode action not available to the starch. In Figure 7, the burst increase above the initial value is plotted for the same curves in Figure 6. If the function of the GPAM 1 was totally independent of the starch s function, the increase obtained with and without starch would be expected to be the same. Figure 7 shows that it is not, and the burst increase with GPAM 1dosage is not as great with the starch as without. Consequently, the two additives do not function totally independently. However, if increased burst is needed or can be converted to a production benefit of the types listed in Table 2, then this dual strength additive program can be useful as it has been at Mill A. Examination of other strength properties is always useful in establishing the reliability of strength additive trends and providing information on their quantitative improvements. To this end, the dosage responses for STFI [short span compressive strength] and STFI increases are provided in Figures 8 and 9, respectively. The results are similar to the burst in that the starch also reaches diminishing returns with dose and the use of GPAM 1 in conjunction with starch is capable of achieving STFI values not achievable by the starch alone. Clearly, the increases of about 1 point of STFI are commercially significant. A difference between the STFI and burst results can be found in the GPAM 1 increases with and without starch. In the case of STFI, the GPAM 1 dosage response is greater with starch than without [Figure 9], which is the opposite of the burst results [Figure 7]. Such a result could suggest that the GPAM 1 and starch are synergistic for STFI, but such a conclusion is thought to be unreliable without further evaluations considering the error in the STFI measurements and the discrepancy with the burst testing. The equivalent data for tensile index is provided in Figures 10 and 11. Not surprisingly, the tensile index results are comparable

7 Figure 8 STFI (Normalized to 26 lb BW) Dosage Curves in Mill A Furnish for GPAM 1 with and without Starch and Starch Alone Figure 10 Tensile Index Dosage Curves in Mill A Furnish for GPAM 1 with and without Starch and Starch Alone Figure 9 Dosage Curves of STFI Increase (Normalized to 26 lb BW) over Initial Value in Mill A Furnish for GPAM 1 with and without Starch and Starch Alone Figure 11 Tensile Index Increase Dosage Curves in Mill A Furnish for GPAM 1 with and without Starch and Starch Alone to those obtained in burst. So for all three strength measurements made in Mill A s furnish, the addition of GPAM 1 in conjunction with the optimum starch dose was able to provide useful increases that were not achievable by further increases in starch dose. Mill B The dual strength additive evaluation in Mill B s furnish was conducted with a GPAM of different composition than in Mill A, and it is designated as GPAM 2. As indicated in Table 4, the starch, sizing, and retention aid were also different. The burst data for Mill B is presented in Figure 12 and exhibits behavior similar but not exactly like the data from Mill A s furnish. Again the starch demonstrates diminishing returns in strength as a function of dose, but the dose of 27 lb/ton at which this happens is much higher than observed in Mill A s testing. The starch provides an excellent result even though the dose is 7 very high. Like Mill A, the dose used by the mill is 27 lb/ton, so again the mill has done a good job in optimizing the starch dose. Figure 12 also shows that addition of GPAM 2 in conjunction with the starch optimum dose can continue to increase the burst when further additions of starch can not. Examining the increases in burst given in Figure 13 reveals that at the early doses the GPAM 2 is more efficient than the starch in generating strength but then it too exhibits diminishing returns at the higher dose. However, the 5 point burst improvement is viewed as respectable. The GPAM 2 also appears to yield the same result with or without the starch suggesting a mechanism of action that is largely independent of the starch. Turning now to the STFI results presented in Figures 14 and 15 shows the now expected result that diminishing returns in dose occurs for the starch at Mill B s usage dose and addition of GPAM 2 on top of the starch provides a healthy increase in the STFI.

8 Figure 12 Burst (Normalized to 35 lb BW) Dosage Curves in Mill B Furnish for GPAM 2 with and without Starch and Starch Alone Figure 14 STFI (Normalized to 35 lb BW) Dosage Curves in Mill B Furnish for GPAM 2 with and without Starch and Starch Alone Figure 13 Burst Increase (Normalized to 35 lb BW) Dosage Curves in Mill B Furnish for GPAM 2 with and without Starch and Starch Alone Figure 15 STFI Increase (Normalized to 35 lb BW) Dosage Curves in Mill B Furnish for GPAM 2 with and without Starch and Starch Alone The GPAM 2 activity on its own only yields strength increases comparable to the starch at equivalent doses, but when coupled with the starch, it provides much more dramatic STFI improvement, see Figure 15. Again like the STFI result obtained in Mill A s furnish, a synergistic effect is suggested by the data, but the fact that it manifests its affect only with the STFI is viewed as suspicious. Lastly, ring crush was also measured with Mill B s sheets, and these results are given in Figures 16 and 17. Ring crush is also a compressive test, and the results obtained mirror qualitatively the STFI compressive test results. In this regard, the diminishing returns in starch dose were the same and GPAM 2 responses were the same: 1) similar dosage profile to starch when used alone and 2) a dramatic in ring crush when used in conjunction with the optimum starch dose with an apparent synergy. CONCLUSIONS 1. Experimental data supported by theoretical analyses of polyelectrolyte adsorption at different conductivities [ionic strengths] onto fibers indicates that the low charge densities of cationic starches will lead to difficulties in their adsorption at the conductivities found in recycle board machines, i.e ms/cm. 2. The effect of increasing conductivity on the starch adsorption is to reduce the maximum amount adsorbed and, more importantly in the conductivity range of interest, causes diminishing returns in adsorption as the starch dose is increased to achieve greater strength. This means excess unadsorbed starch in the white water system with its accompanying problems. 8

9 Figure 16 Ring Crush (Normalized to 35 lb BW) Dosage Curves in Mill B Furnish for GPAM 2 with and without Starch and Starch Alone 3. Handsheet evaluation of starch dry strength activities in two recycle linerboard furnishes with conductivities in the 1-10 ms/cm range demonstrated diminishing returns in starch dosage with the optimum doses in the handsheet work corresponding to the actual doses used on the commercial board machines. 4. The addition of GPAM dry strength polymers at the starches optimum dose was capable of increasing dry strength further when increased doses of starch could not. Such dual strength additive programs were being practiced in the two mills whose furnishes were examined. The fact that the GPAM provides additional strength suggests that the two additive function in a different manner at least to some extent. In compressive strength testing [STFI & ring crush], a synergistic effect of the GPAM seemed to occur, i.e. the effect of the GPAM addition was much larger in the presence of the optimum starch dose than with no starch. 5. Examining the addition of GPAM to an existing starch strength program may be worthwhile if the starch program appears to have reached its limit and additional dry strength can be utilized. Figure 17 Ring Crush Increase (Normalized to 35 lb BW) Dosage Curves in Mill B Furnish for GPAM 2 with and without Starch and Starch Alone 9

10 REFERENCES 1. van de Steeg, H.G.M., Cohen-Stuart, M.A., de Keizer, A., and Bijsterbosch, B.H., Polyelectrolyte Adsorption: A Subtle Balance of Forces, Langmuir, 1992, 8, Hedborg, F. and Lindström, T., Adsorption of Cationic Starch on Bleached Softwood Cellulosic Fibres, Nordic Pulp Pap. Res. J., 1993, 8(2), Mendes, P., Costa, C.A.V., Silvy, J., and Belgacem, M.N., Adsorption Behavior of Cationic Starch on Bleached Eucalyptus Globulus Kraft Pulp, Appita J., 2001, 54(1), Gaiolas, C., Costa, A.P., Silva, M.S., and Belgacem, M.N., Adsorption of Cationic Starch on Typical Furnishes Used in the Portugese Paper Industry, Appita J., 2004, 57(2), van de Steeg, H.G.M., de Keizer, A., Cohen-Stuart, M.A., and Bijsterbosch, B.H., Adsorption of Cationic Amylopectin on Microcrystalline Cellulose, Colloids Surfaces A: PhysicoChem. Eng. Aspects, 1993, 70, van de Steeg, H.G.M., de Keizer, A., Cohen-Stuart, M.A., and Bijsterbosch, B.H., Adsorption of Cationic Potato Starch on Microcrystalline Cellulose, Colloids Surfaces A: PhysicoChem. Eng. Aspects, 1993, 70, van de Steeg, H.G.M., de Keizer, A., Cohen-Stuart, M.A., and Bijsterbosch, B.H., Adsorption of Cationic Starches on Microcrystalline Cellulose, Nordic Pulp Pap. Res. J., 1993, 8(1), Woodberry, N.T., Moore, S.T., and Jen, Y., Paper of High Dry Strength and Low Wet Strength, US Patent 2,890,978, June 16, Wilson, L.H., Thomas, W.M., and Padbury, J.J., Paper of Improved Dry Strength and Method of Making Same, US Patent 2,884,057, April 28, Farley, C.E., Glyoxalated Polyacrylamide Resin Ch. 3 in Wet-Strength Resins and Their Application, L.L. Chan, Ed., TAPPI Press: Atlanta, Nanko, H., Bond Strength Enhancement Mechanisms of Cationic Starch and Cationic Polyacrylamide, pp , Proc International Physics Conf., Victoria, BC, Williams, P.C., Kuzina, F.D., and Hlynka, I., "A Rapid Colorimetric Procedure for Estimating the Amylose Content of Starches and Flours", Cereal Chem., 47(4), (1970). 13. Magel, E., "Qualitative and Quantitative Determination of Starch by a Colorimetric Method", Stärke, 43(10), (1991). NALCO COMPANY Locations North America: Headquarters 1601 West Diehl Road Naperville, Illinois USA Energy Services Division 7705 Highway 90-A Sugar Land, Texas USA Europe: A-One Business Center Z.A. La Pièce 1 Route de l Etraz 1180-Rolle Switzerland Asia Pacific: 2 International Business Park #02-20 The Strategy Tower 2 Singapore Latin America: Av. das Nações Unidas Andar São Paulo SP Brazil Nalco and the logo are Trademarks of Nalco Company Ecolab is a trademark of Ecolab USA, Inc Ecolab USA Inc. All Rights Reserved 9/12