Organic contaminants in recycled paper: a model study of the adsorbent properties of talc for idealised component suspensions

Transcription

1 Sida 219 Recycling Organic contaminants in recycled paper: a model study of the adsorbent properties of talc for idealised component suspensions Falko Benecke, University of Applied Sciences, Munich, Daniel Gantenbein, Joachim Schoelkopf, Patrick A.C. Gane and Thoralf Gliese, Omya Development AG, Switzerland KEYWORDS: Talc, adsorption of stickies, Stickies, Deposition, Papermaking, Stickies control, Recycled paper SUMMARY: The paper industry continues to increase the consumption of recycled paper in response to ecological and economic pressure. Additionally, water circuits become increasingly closed. A major challenge is being faced by this trend due to the increase of unwanted trash in the process. This trash can to some degree be removed successfully by mechanical and chemo-mechanical means, such as screening and flotation. However, a remaining part of this trash, so-called stickies, i.e. residues from glues, adhesives and other organic constituents of the recycled stock can form agglomerates and deposits in the paper machine and cause serious problems associated with paper quality and machine runnability. Talc is often used successfully to control unwanted deposition of wood resin and wood processing derivatives in the wet end circuit of a paper mill. The effectiveness of talc to control stickies, is, however, not undisputed in the industry. This work makes an initial evaluation of this controversy by using well-defined chemical families of polymeric compounds, frequently found in stickies, in the form of aqueous suspensions, and the ability of a commercial talc to adsorb and to detackify them is evaluated. The results show that talc acts specifically depending on the chemistry of the polymer. Good performance was seen for polyacrylate, polyvinyl acetate, colophonium (resin) and styrene-butadiene, whereas adsorption was less effective in the cases of fatty acid ester and mineral oil/silicone based defoamers. ADDRESSES OF THE AUTHORS: Falko Benecke 1 (falko.benecke@upm-kymmene.com): Hochschule München, University of Applied Sciences Munich, Lothstr. 34, D München, Germany. Daniel Gantenbein (daniel.gantenbein@ omya.com), Joachim Schoelkopf (joachim.schoelkopf@ omya.com), Patrick A.C. Gane 2 (patrick.gane@omya.com) and Thoralf Gliese 3 (thoralf.gliese@omya.com): Omya Development AG, Baslerstr. 42, CH-4665 Oftringen, Switzerland. 1 Current address: UPM-Kymmene GmbH & Co, D Schwedt/Oder, Germany. 2 Professor of Printing Technology, Department of Forest Products Technology, Faculty of Chemistry and Materials Science, Helsinki University of Technology, P.O. Box 6300, FI TKK, Finland. 3 Professor, Hochschule München, Univeristy of Applied Sciences Munich, Lothstr. 34, D München, Germany. Corresponding author: Daniel Gantenbein During the last decades ecological awareness has increased, and, consequently in parallel, the expectation from society for environmentally friendly production of paper has also grown. This has boosted the demand for recycled paper, which availability on the market is strongly regionally influenced and commands high rates. Nevertheless, the use of recycled paper brings some not inconsiderable disadvantages. The physical properties can reach critical limits, the amount of trash and fines are greater and the application in the food industry is problematic. The removal of trash from recycled stock requires extensive treatment. The most harmful problems evolve due to the influence of adhesives, developing from hot melt glues, binders and other thermoplastic materials, for example from book-backs and adhesive tape or from silicone based defoamers. These mostly exhibit varying degrees of hydrophobicity. They tend to be pliable organic materials, such as styrene-butadiene binders, latex in general, rubber, vinyl acrylates, polyisoprene, polybutadiene, hot melts etc. (Jones, Fitzhenry 2003; Doshi, Dyer 1998; Doshi 1991; Douek, Guo 1997). Under certain conditions, these compounds can become tacky and deposit in the paper machine. The deposits can lead to breaks in the paper or appear as visible spots, often darkened by heat, in the final product, resulting in loss of paper quality and downtime to clean the paper machine. Stickies can be classified based on their size as either macrostickies, the reject or retains on a 0.15 mm or 0.10 mm laboratory slotted screen, or microstickies, the accept through those screens (Doshi, Dyer 1998). Methods used to quantify stickies generally lack the accuracy and precision of methods used to evaluate other pulp properties. However, there are several established methods for quantifying stickies, which involve a number of techniques based on adsorption onto a defined surface, image analysis, reaction to heat, spectroscopic analysis and response to chemical agents. Doshi and Dyer (Doshi, Dyer 1998) provide a summary of such methods. In the work of Doshi (Doshi, Dyer 1998) the appearance of poly acrylate, poly vinylacetate, ethylene vinylyacetate, resin and styrene-butadiene latex in the different paper mill areas is shown. Often deposition occurs in parts of the paper machine where temperature, ph or conductivity is changing, or at concentrating steps. Another substance class which will be investigated in this work is that of defoamers. Amide based defoamers compete strongly with tall oil (Allen et al. 1993). Amide based defoamer adsorbs stronger on talc under the applied conditions, than tall oil, which is a compound derived from wood constituents. Because oil-based amide or silica defoamers were found to increase deposition (Dunlop- Jones, Allen 1989) it is important, that if too much defoamer was used, an effective adsorbent is available in the process. Nordic Pulp and Paper Research Journal Vol 24 no. 2/

2 Sida 220 Talc is widely used as a collector for detrimental lipophilic compounds, collectively termed pitch and stickies. To distinguish, the term pitch describes particles formed from colloidal resin components present in wood pulp, and covers a wide range of substances, such as fats and fatty acids, steryl esters and sterols and terpenoids including terpenes, whereas stickies derive from additional compounds and material brought into the life-cycle of paper production and usage, as described above. The general action of talc is understood to be due to hydrophobic interaction forces deriving from the low surface energy nature of the talc platelet structure, acting to attract colloidal particles or destabilised aggregates with subsequent adsorption (Wallqvist et al. 2006) or to deposit upon flocs of organic compounds. This results in a detackification of the organic surface and avoids ongoing agglomeration and deposition, and so favours their harmless removal from the system within the paper itself. In an example of this type of application (Biza et al. 2002; Holton, Williams 1994; Holton, Moebus 1982), the removal efficiency in the high density cleaner was increased from nearly 0 to 50%. While the positive action of talc in adsorbing and detackifying pitch is well documented in the literature (Douek, Guo 1997; Biza et al. 2002; Holton, Williams 1994; Baak, Gill 1971; Hamilton, Lloyd 1984; Hassler 1988) its usefulness in adsorbing sticky compounds from adhesives on recycled paper, such as polyisoprenes and waxes (Doshi 1991), but also residues of defoamers, is often disputed in the industry, whereas in the literature systematic studies are rare. A good review about the control of tacky deposits in paper machines is given by Hubbe et al. (2006). Putz et al. (2003) describe the potential of talc for reducing macrostickies, but also up to 18% of microstickies. Maat and Yordan (Maat, Yordan 1998) tested the detackification of hot melts containing polyvinyl acetate, which led to a reduction of up to 95% of tacky stickies by applying 2.5% talc (% based on pulp). As talc is not only used to reduce the tacky behaviour of the stickies, but also to improve the removal of stickies from the process, talc is often added just before the forward cleaner. Another publication describes the reduction of deposits when talc is added to a pulp/adhesive suspension. Polyvinylacetate adhesive, polyacrylate adhesive, a redispersable adhesive and a styrol-butadiene latex were investigated. Talc showed the potential to detackify the adhesives in certain ratios between talc and adhesive (Biza 1999). The mechanism of talc is described as a detackification of the stickies (Yordan, Williams 1997). As this might be true for large sticky particles the situation can be different for colloidal stickies (Holton, Moebus 1982). Besides the hydrophobic interactions of talc and organic contaminants it is also possible to use cationised talc qualities in order to create coulombic interactions between the cationic talc and the often anionic organic particles typical in stickies (Biza 1999). However, in this study the investigated talc grade did not contain cationic dispersants so as to identify the dominant hydrophobic interactions. An obvious problem in understanding the interactions with talc and other minerals is the extreme chemical heterogeneity of stickies. So it may well be that in one industrial situation talc works well against stickies but in another it seems to fail. We try in this work to dissect the problem by understanding in more detail what some common industrial stickies are composed off and then making clearly defined synthetic suspensions of each sticky family so as to test them individually in respect to their interaction with talc. In this work the method developed by Guéra et al. (2005) is applied, which has been shown to work well for assessing the adsorption of colloidal pitch species on talc. Materials and Methods Preparation of the test sticky suspensions A first step was to define some expected typical compounds to be found in stickies, particularly concentrating on those anticipated from recycled coated broke and coating colour, the second step being to bring these pure sticky polymers into a colloidal stable form, and thirdly to measure the adsorption efficiency of talc for these colloidal polymer species. The respective polymers are listed according to the abbreviations used subsequently, together with their source of supply, in Table 1. Table 1. Investigated polymers with their corresponding abbreviation, their product name and the supplier. Polymer Abbreviation Product name Source Styrene polyacrylic latex SA Acronal V 212 BASF Polyvinyl acetate PVAc Vinnapas B 17 Wacker Resin Col Colophonium Resina AG Styrene-butadiene latex SB Styronal D 809 BASF Fatty acid ester defoamer FED Afranil RS BASF Mineral oil / silicone defoamer MOD AGITAN 700 Münzing Chemie In the case of those polymers that were not directly available in aqueous suspension, a sample preparation was undertaken as follows: Polyvinylacetate: 0.1 g PVAc was dissolved in 2 cm 3 acetone. The solution was added under vigorous stirring to a solution of 0.1 g polyvinyl alcohol and 200 cm 3 distilled water. The acetone was evaporated at 60 C overnight to give a colloidal stable suspension with a turbidity of 64 NTU and a COD of 1280 mg O 2 per dm 3. Colophonium: 0.05 g Col was saponified in 100 g distilled water by the addition of 0.05 g sodium hydroxide. The ph was afterwards adjusted back to 7.5 by the addition of Hydrochloric acid with a resulting turbidity of 130 NTU and a COD of 813 mg O 2 per dm 3. The remaining polymers available as aqueous suspensions had their solid content adjusted with distilled water to 0.05%, with a ph adjusted to , representing the most relevant wet-end conditions of a paper mill. Conductivity was further adjusted to µscm -1 with 220 Nordic Pulp and Paper Research Journal Vol 24 no. 2/2009

3 Sida 221 Table 2. Average particle diameter measured on a Malvern Master Sizer S given in µm and the surface charge density measured on a Mütek PCD-02 and given in µeqg -1 for the investigated chemicals. Chemical Weight median equivalent spherical Surface Charge Density diffusional particle diameter (streaming current detector) (dynamic light scattering) (SCD) / µeqg -1 d 50 / µm (Mütek PCD-02) (Master Sizer S) Styrene polyacrylic latex Polyvinyl acetate ) Colophonium soap < Styrene-butadiene Fatty acid ester defoamer Mineral oil / silicone defoamer 3.9 < ) It was not possible to measure this suspension due to the inapplicable properties of the suspensions, meaning that the PVAc deposited uncontrollably on the apparatus sodium chloride as the ionic strength is a key factor influencing deposition and adsorption (Gruber et al. 2000; Hassler 1988; Holmbom, Sundberg 2003; Kekkonen, Stenius 2001). The properties of all the resulting suspensions are shown in Table 2. As can be seen from the actions taken to facilitate colloidal suspensions, the materials per se have either surfactants and/or carboxylation (latices and other binders) as a means of ensuring stability, or form naturally stabilised emulsions from solvent exchange. This undoubtedly limits the relevance, especially regarding the latices, only to the expected fresh form of these polymers, i.e. as anticipated, for example, from coated broke or waste coating colour, rather than from externally recycled sources, where the organic stickies are more likely to be stripped of their original emulsion stabilising additives, and probably would have undergone polymer inter diffusion and film forming. Furthermore, the list is far from comprehensive, as it ignores, for example, the typical glue materials to be expected from recycled fibre. However, this starting point is intended for later comparison with actually retrieved stickies from practical applications of recycled materials in paper mills, as part of ongoing work. Mineral characterisation The talc used in these experiments was an undispersed commercially available talc in powder form from Finland (Mondo Minerals Oy) (FT). The talc suspension was prepared by adding the dry talc to water under vigorous stirring. The slurry was checked for the absence of agglomerates in order to guarantee as far as possible the availability of the full talc surface area for adsorption. The specific surface area was determined by BET (Brunauer et al. 1938) to be 9 m 2 g -1. The particle size distribution was determined by two methods, namely by laser light scattering (Malvern Master Sizer) and by sedimentation (Micromeritics Sedigraph 5100). The light scattering measurement gave an ensemble average diffraction defined diameter of 5.99 µm, and the sedimentation method gave a weight median hydrodynamic equivalent diameter of 2.2 µm. The zeta potential of the talc was measured with a PenKem 500 device giving a value of 17 mv at the natural exposed ph of the talc which was determined to be 7.4. The total charge was determined by a streaming current detector (SCD) titration (Mütek PCD-02) and was found to be 1.9 µeqg -1, where 1 Eq (equivalent) is the weight in grams of that substance, which would react with or replace one gram of hydrogen. The mineral powder of the present study was analysed both by X-ray fluorescence (XRF) and X-ray diffraction (XRD) [from θ Bragg diffraction using a Bruker AXS D8 Advanced XRD system with CuKα radiation, automated divergence slits and a linear position-sensitive detector. The tube current and voltage were 50 ma and 35 kv, respectively: the step size was θ and the counting time 0.5 s*step -1 ]. The talc grade used was shown to contain the minerals talc, chlorite and magnesite, which were also confirmed by FTIR [Perkin Elmer Spectrum One Spectrometer] analysis, and XRF [ARL 9400 Sequential XRF] gave a talc content of ~ 94%. Test procedure and analysis The polymer suspensions were distributed into glass bottles: 200 g of suspension in each bottle and 0.5 w/w % of the mineral (10 g chemical-free slurry of 10 w/w %) was added to each. Then the bottles were closed and agitated for 2 hours. The suspension was then centrifuged for 15 minutes (Jouan C 312, by IG Instruments) at a rotational speed of min -1. Two phases are collected: an upper aqueous phase and a lower sedimented mineral-containing phase. A reference sample without mineral addition but with the same dilution was used as a comparison. As already described above, the sticky/mineral ratio was chosen to be 1:10. All measurements were repeated three times and the averaged values are shown in the figures. Upper aqueous phase chemical oxygen demand, turbidity and gravimetry A 100 cm 3 sample of the upper aqueous phase, obtained after centrifugation, was placed into a pre-weighed aluminium beaker and dried in an oven (90 C, 24 hours) to get a total amount of non-volatile residue in the aqueous phase. A further 45 cm 3 sample was taken to analyse for turbidity (NOVASINA 155 MODELL NTM-S (152)). This instrument transmits light in the near infrared spectrum through an optical fibre probe where the emerging beam is scattered by small particles in suspension. Light scattered back at 180 to the incident beam is collected by parallel optical fibres in the probe and focused onto a photo-diode. The resulting signal is amplified and displayed directly in Nephelometric Turbidity Units (NTU), defined as the intensity of light at a specified wavelength scattered, attenuated or absorbed by suspended particles at a method-specified angle, from the path of the incident light compared to a synthetic chemically prepared standard. Interference from ambient light is eliminated by using a modulated transmitting signal, removing the need for light-tight sample handling systems. A yet further 2 cm 3 sample was taken for chemical oxygen demand (COD) analysis, providing a value for the total organic content. The COD analysis expresses the quantity of oxygen necessary for the oxidation of organic materials Nordic Pulp and Paper Research Journal Vol 24 no. 2/

4 Sida 222 into CO 2 and was measured using a Lange CSB LCK 014, range mg dm -3, with a LASA 1/Plus cuvette). Lower sedimented mineral-rich phase thermogravimetric analysis Thermogravimetric analysis of the lower mineral-containing layer was made with a scanning differential thermal analyser (SDTA) 851 e by Mettler Toledo, under constant heating rate of 20 C min -1 from 30 C up to C. gravimetry During the first experiments it was observed that some polymers became extremely tacky in combination with, but also without, talc. These polymers even deposited on the glass surface. Therefore, the utilised glass bottles where weighed before and after the measurement (reemptied) to give a gravimetric value of deposits on the glass surface. Obviously, a glass surface cannot be compared with the surfaces present in a paper mill, and therefore this deposition test is not able to describe deposition potentials of the polymers in a paper mill. However, this test gives a first indication if the tackiness of a polymer is increased or decreased during the treatment with talc. Results and Discussion The ph after the mineral treatment was found to be between 7.3 and 7.4 for all samples. Conductivity was not affected by the mineral treatment. The values given in the figures for turbidity, chemical oxygen demand (COD) and gravimetry are normalised to 100% in respect to the corresponding untreated reference samples (Table 3). The results are presented in the following order: first the weighed deposits on the inner glass bottle surface, second the analyses of the upper liquid phase and finally the analyses of the lower sedimented mineral-rich phase. Fig 1 shows the amount of material stuck to the glass bottle. The grey bar shows the deposit upon exposure to polymer alone, while the black bar shows the deposit upon exposure to the polymer/talc mixture. The styrene poly acrylic latex (SA) shows only a small amount of deposits but the addition of talc was disadvantageous and the amount of deposits was increased. This can be explained in various ways by the incorporation of talc into the polymer suspension. On the one hand, talc may tend to steal stabilisers away from the polymer forcing it into coagulation and rendering the surface tacky by exposure of the polymer itself. This observation can have important implications for the inclusion of undispersed talc in papermaking. In such a case the addition of more talc would be needed to come once more into the detackification regime, thus indicating a critical dose relationship. In the case of polyvinyl acetate (PVAc), it is obvious that the talc amount used was sufficient to detackify this polymer. The pure polymer suspension showed about 25 mg of material on the glass surface, and after the talc treatment the deposits were reduced to nearly zero. It is always important to keep in mind that only 100 mg polymer per 200 g sticky suspension is present and potentially Fig 1. Amount of deposits on the glass bottles in mg per 100 mg polymer sample for styrene poly acrylic latex (SA), polyvinyl acetate (PVAc), colophonium (Col), styrene-butadiene (SB), mineral oil/silicone based defoamer (MOD) and fatty acid ester defoamer (FED). Table 3. Values for the untreated polymer suspensions used for normalising the analyses of the upper liquid phase after treatment. Chemical Gravimetry Turbidity COD /mg residue per 100 cm 3 /NTU /mg O 2 per dm 3 Styrene poly acrylic latex (SA) Polyvinyl acetate (PVAc) Resin (colophonium) (Col) Styrene-butadiene latex (SB) Fatty acid ester defoamer (FED) Mineral oil / silicone defoamer (MOD) Fig 2. Analyses of the upper liquid phase for styrene poly acrylic latex (SA), polyvinyl acetate (PVAc), colophonium (Col), styrene-butadiene (SB), mineral oil/silicone based defoamer (MOD) and fatty acid ester defoamer (FED). Gravimetry is given as grey bars, turbidity as the solid black and COD as the dotted. The values are normalised to 100% with the corresponding untreated reference polymer suspension. available to deposit in the glass bottle. The Colophonium (Col) compound did not show any attraction to the glass surface, with or without talc present. Addition of talc did not affect styrene-butadiene (SB), either, but unlike colophonium, there were measurable deposits in both cases. The mineral oil/silicone based defoamer (MOD) showed a strong deposition potential on the glass surface. About 37 mg of the original 100 mg defoamer deposited without the talc treatment, and talc seemed to detackify successfully. The fatty acid ester based defoamer (FED) did not show any attraction to glass. The addition of talc to the defoamer suspension, however, increased its deposition behaviour a little. Of course an increased amount of deposition on the glass surface would decrease the values found in the upper liquid phase, because the measurements reflect only stable colloidal particles, which remain in the upper 222 Nordic Pulp and Paper Research Journal Vol 24 no. 2/2009

5 Sida 223 phase during the centrifugation. Therefore, the interpretations of the liquid phase analyses have to be made carefully by constantly taking the deposition results into account (Fig 2). Table 3 gives the values used to form the reference levels, corresponding to 100% in Fig 2, for the normalisation. The talc treatment seems to adsorb certain components of styrene poly acrylic latex (SA) very efficiently. As shown in Fig 2, the turbidity is strongly reduced, as is the total amount of organics (COD). According to gravimetry the total amount of the material in the sample is also generally reduced. Concerning the liquid phase analyses, then, talc is perfectly capable of adsorbing a sticky suspension of styrene poly acrylic latex, though the tendency to induce deposits under a regime of under dosing is to be noted. The turbidity of a polyvinyl acetate suspension (Fig 2) is reduced to nearly zero, which indicates that this talc adsorbs strongly the colloidal particles from the PVAc. Also the amount of organics is reduced, but the rather moderate reduction to 73% only is most probably caused by the presence of non-adsorbed polyvinyl alcohol. The same effect is observed for the gravimetric analysis of the PVAc suspension. It seems also from the deposition data (Fig 1) that talc moreover acts well to detackify the polymer. It remains, however, unclear which polymer is the dominant driving force for the adsorption onto the talc surface. The trial to produce a stable PVAc suspension without the use of PVOH was not successful but also the addition of PVOH did not create a fully stable suspension (see deposition data in Fig 1). The PVOH is not properly stabilising the particle by steric interaction but still adsorbed to some degree on the PVAc surface. However, the addition of talc fully detackifies the particles and removes nearly all colloids in the suspension. Only dissolved organic matter is left after the talc treatment that corresponds to dissolved PVOH. Thus, the interaction of PVAc particles covered with PVOH and talc seems to be stronger than the interaction of the PVOH alone and talc. The adsorption of colophonium resin (Col) on this talc is very efficient, as might be expected from the literature (Guera et al. 2005), in which the adsorption of pitch was investigated. The removal efficiency for styrene-butadiene latex (SB) is quite impressive. The colloidal particles, and also the total amount of organics, were nearly totally removed. Also the gravimetric analysis shows a large reduction. Additionally, the tendency of the polymer to deposit was seen to be very low, and not altered with the addition of talc. In the case of the mineral oil/silicone based defoamer (MOD) talc was not very efficient in adsorption. The turbidity was only reduced to 74%, but, having said this, the original level of the colloidal species was very low with only 13 NTU, such that perhaps the additional removal of colloidal species could not occur. A similar trend is found for the fatty acid ester based defoamer (FED). This is given by all three analyses of the upper liquid phase. However, it might be that coagulation of defoamers forming coagulates of size similar to that of talc (Table 2), such that the interaction with talc is minimised and so what interaction, if any, occurs can be considered as being only weak heterocoagulation. Furthermore, defoamers, which are often added in huge excess, are known to destroy the pitch and sticky adsorbing potential of talc, and thus defoamer addition needs to be controlled properly for an effective pitch and sticky control (Allen et al. 1993). The thermo-gravimetric analyses of the lower sedimented mineral phase (Fig 3) confirm the findings for the upper liquid phase. The amount of the adsorbed polymer on the mineral correlates in general well with the turbidity and COD under the assumption that the weight loss is only produced by the loss of the polymer. For SA the turbidity is reduced to 5% and the COD to 12% whereas on the talc surface 83% of the total used polymer (SA) is to be found. The missing part (difference between the two measurements) can be explained by the fact that some material has stuck to the glass and was not measured. Similarly, for PVAc the reduction in turbidity was 100% and in the TGA 88% of the polymer was to be found. Due to the inclusion of polyvinyl alcohol to form this suspension, the COD cannot be taken into account. For the colophonium (Col) the turbidity was reduced to 12% and the COD to 46%, whereas in the TGA 57% of the total added resin is found. This suggests that some of the colophonium was also dissolved and not only present in a colloidal form, because most of the colloidal species are removed whilst still 50% of the total organics were left in the upper liquid phase. Also for the SB the reduction of the turbidity and COD was > 90%, and in the TGA 91% were to be found. The MOD showed a reduced turbidity with 74%, and the COD with 90%, and, consequently, only 20% of the original added defoamer is recoverable as deposit on talc. Fig 3. Thermogravimetric analysis of the lower sedimented mineral phase given as weight loss when heated to C per mg talc. Conclusions The effectiveness of talc in adsorbing and detackifying some selected stickies, introduced as stabilised colloidal suspensions, has been studied with the aim to assist the wet end engineer to anticipate the impact of talc on the removal and prevention of deposition of stickies. Nordic Pulp and Paper Research Journal Vol 24 no. 2/

6 Sida 224 The talc tested in this work was found to be an efficient adsorbent for styrene poly acrylic latex, though the results suggest the existence of a critical dose level, below which one might expect increased deposition. Similar efficiencies were seen for polyvinyl acetate and styrene-butadiene latex, but with no such signs of criticality. Talc worked efficiently also for colophonium, but in the case of two defoamers, the talc had nearly no adsorbing effect at the applied amounts. It is suspected that micelle formation may render the defoamers strongly hydrophilic, with their hydrophobic parts shielded from the talc. Talc was able, however, to prevent deposition of a mineral oil/silicone based defoamer. The greatest antideposition effect was observed for the polyvinyl acetate suspension. Acknowledgments The authors would like to thank Dr. J. Boettger, Dr. H. Praast. G. Stankewitz, A. Scherer and C. Haias from StoraEnso in Maxau for fruitful discussions with the necessary practical inputs. Literature Allen, L.H., Cavanagh, W.A., Holton, J.E. and Williams, G.R. (1993): New Understanding of Talc Addition May Help Improve Control of Pitch, Pulp & Paper, 67 (13), 89. Baak, T. and Gill, G.J. (1971): The Adsorptive Property of Talc and its Application to Pitch Control, Paperi Puu, 53 (8), 449. Biza, P. (1999): Selective Detackification of Stickies with Selected Talc Grades, 2. PTS-Symposium Stickies, München, Germany, November 2, 1999, PTS, München, Germany, 14/11-14/16. Biza, P., Gaksch, E. and Kaiser, P. (2002): Verbesserter Austrag von Stickys durch den Einsatz von Talkum, Wochenbl. Papierfabr. 11 (12), 759. Brunauer, St., Emmett, P.H. and Teller, E. (1938): Adsorption of Gases in Multimolecular Layers, J. Am. Chem. Soc., 60 (2), 309. Doshi, M.R. (1991): Properties and Control of Stickies, Progress in Paper Recycling, 1, 54. Doshi, M.R. and Dyer, J.M. (1998): Management and Control of Stickies, Paper Recycling Challenge, III, 195. Douek, M. and Guo, X.-Y. (1997): An Overview of the Chemical Nature of Deposits/Stickies in Mills Using Recycled Fibre, 1997 TAPPI Recycling Symposium, Chicago, Tappi Press, Atlanta, Dunlop-Jones, N. and Allen, L.H. (1989): The Influences of Washing, Defoamers and Dispersants on Pitch Deposition from Unbleached Kraft Pulps, J. Pulp Paper Sci. 15 (6), 235. Gruber, E., Gattermayer, J. and Paetzhold, R. (2000): Zur Adsorption Fein Dispergierter Polymere mit Klebendem Potential (Mikrostickies) 2, IPW das Papier, (5), 74. Guera, N., Schoelkopf, J., Gane, P.A.C. and Rauatma, I. (2005): Comparing Colloidal Pitch to Adsorption on Different Talcs, Nord. Pulp Paper Res. J. 20 (2), 156. Hamilton, K.A. and Lloyd, J.A. (1984): Measuring the Effectiveness of Talc for Pitch Control, Appita, 37 (9), 733. Hassler, T. (1988): Pitch Deposition in Papermaking and the Function of Pitch- Control Agents, Tappi J. 71 (6), 195. Holmbom, B. and Sundberg, A. (2003): Dissolved and Colloidal Substances Accumulating in Papermaking Process Water, Wochenbl. Papierfabr. 131 (21), Holton, J.E. and Moebus, C.R. (1982): Control of Pitch, Stickies, Gunk and Tramp Organics in Pulp and Paper Mills, Pulp Paper Can. 83 (4), 52. Holton, J.E. and Williams, G.R. (1994): The use of Talc to Control Stickies in Deinked Newsprint, 80th Annual Meeting of CPPA (Technical Section), Montreal, Canada, CPPA, Montreal, Canada, A151-A153. Hubbe, M.A., Rojas, Orlando, J.and Richard, A.V. (2006): Control of Tacky Deposits on Paper Machines A Review, Nord. Pulp Paper Res. J. 21(2), 154. Jones, D.R. and Fitzhenry, J.W. (2003): Esterase-Type Enzymes Offer Recycled Mills an Alternative Approach to Stickies Control, Pulp & Paper, 77 (2), 28. Kekkonen, J. and Stenius, P. (2001): Adsorption of Wood Materials on Silica Surface with a Wettability Gradient, Nord Pulp Pap Res J. 16 (1), 4. Maat, P. and Yordan, J.L. (1998): Use of the Microfoam (doshi) Method for Assessing the Effectiveness of Talc in Controlling Stickies, TAPPI 1998 Recycling Symposium, New Orleans, Tappi Press, Atlanta, Putz, H.-J., Hamann, A. and Gruber, E. (2003): Untersuchungen zur Stickybildung und Stickybekämpfung, Wochenbl. Papierfabr. 131 (14-15), 883. Wallqvist, V., Claesson, P.M., Swerin, A., Schoelkopf, J. and Gane, P.A.C. (2006): Interaction Forces between Talc and Hydrophobic Particles Probed by AFM, Colloids Surf. A, 277 (1-3), 183. Yordan, J.L. and Williams, G.R. (1997): Talc for Contaminant Control in Recycled Fiber, Paper Recycling Challenge, 1, 76. Manuscript received December 19, 2008 Accepted February 24, Nordic Pulp and Paper Research Journal Vol 24 no. 2/2009