Applied Clay Science 23 (2003) 257 – 264
`
`www.elsevier.com/locate/clay
`
`Influence of deagglomeration and carboxymethyl cellulose binders
`on rheological behaviour of kaolin suspensions
`
`S.I. Conceicßa˜o a,b, J.L. Velho a, J.M.F. Ferreira b,*
`
`a Department of Geosciences, University of Aveiro, 3810-193 Aveiro, Portugal
`b Department of Ceramics and Glass Engineering, University of Aveiro, CICECO, 3810-193 Aveiro, Portugal
`
`Received 31 May 2002; accepted 16 April 2003
`
`Abstract
`
`The influence of adding two carboxymethyl cellulose (CMC) binder/thickening agents with different molecular weights on
`the rheological behaviour of kaolin suspensions has been investigated in the presence of ammonium polycarbonate as
`dispersant.
`Ball milling performed deagglomeration of the kaolin. The suspensions were prepared at different solid contents from 20 to
`45 vol.%, and the rheological measurements were made on these suspensions (nondiluted systems) and compared with those
`performed on suspensions containing the same solid volume fractions but derived from a more concentrated one (45 vol.%) by
`adding the required amounts of water (diluted systems). The experimental results showed that at given solid loading, diluted
`systems are less viscous and pack better than nondiluted ones. This indicates that in the range of solid concentration studied,
`increasing the solid volume fraction enhances deagglomeration of kaolin particles.
`The rheological effects of adding CMC binder/thickening agents strongly depended on the amount added, molecular weight
`(MW), and the suspension preparation procedure. The strong thickening effect was generally observed for the higher MW CMC,
`followed by the mixture of both, although a different sequence has been observed for the more concentrated and nondiluted
`systems. Slip casting experiments were also performed in order to correlate the flow characteristics of the suspensions with their
`ability towards packing.
`D 2003 Elsevier B.V. All rights reserved.
`
`Keywords: Kaolin deagglomeration; CMC binders; Rheology; Particle packing; Paper coating
`
`1. Introduction
`
`Kaolin clay is a fine clay mass, usually white or
`near white in colour, containing the particulate min-
`eral kaolinite as the main constituent. Such clays have
`been formed in geological times by the weathering or
`
`* Corresponding author.
`E-mail address: jmf@cv.ua.pt (J.M.F. Ferreira).
`
`hydrothermal alteration and feldspar and mica min-
`erals in igneous or metamorphic rocks (Andrews et
`al., 2000). The term kaolin comes from Kauling
`(Gaolin) in the Jiang Xi Province, in China, where
`this type of raw material has long been used for the
`fabrication of porcelain tableware and art objects
`(Gomes, 1986).
`Kaolin clays are very useful raw materials for
`many industries,
`including painting, paper, rubber,
`plastics, fibreglass, cement, adhesives, enamels, phar-
`
`0169-1317/03/$ - see front matter D 2003 Elsevier B.V. All rights reserved.
`doi:10.1016/S0169-1317(03)00125-X
`
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`258
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`
`maceuticals, crayons, ceramic industries, and molec-
`ular sieves (Murray, 2000; Atkinson and Fleming,
`2001). They are a main component in formulations of
`porcelain, electrical
`insulators, sanitary, and white
`tableware. They possess and impart important proper-
`ties to the ceramic pastes and final products, such as
`plasticity and mouldability, mechanical resistance,
`refractoriness, and whiteness after sintering (Atkinson
`and Fleming, 2001). Water chemistry to a large extent
`controls plasticity. These industrial properties are
`controlled by mineralogical (presence of impurities,
`such as titania, various ferruginous minerals, mica
`and non-kaolinitic clays such as bentonite and atta-
`pulgite), chemical (pH, surface properties, etc.), and
`physical (particle size and shape, specific surface
`area) properties of the clay (Atkinson and Fleming,
`2001). These, along with colour and brightness, affect
`useful processing properties such as low and high
`shear viscosity, absorption, plasticity, green, dry and
`fired strength, casting rate, permeability, and bonding
`strength (Velho et al., 1998).
`In the paper industry, kaolin pigments impart
`excellent brightness, whiteness, smoothness, opacity,
`and gloss. Their excellent rheological properties and
`relative inertness allow high solid loads to be achieved
`(Murray, 2000). Previous studies have indicated that
`the rheological behaviour of kaolin suspensions is
`governed by the fundamental properties of kaolin
`particles: their particle size and distribution, morphol-
`ogy, and aggregation, in addition to mineralogical and
`chemical impurities (Bilimoria et al., 2001; Jonhs et
`al., 1990; Yuan and Murray, 1997).
`Water-soluble polymers, such as carboxymethyl
`cellulose (CMC) binders, greatly affect the colloidal
`forces by adsorbing on clay particles. The dissolved
`polymers also make the liquid phase of a coating more
`viscous. CMC binders are used in many different
`technical applications, such as thickeners in food,
`additives in washing powders, binders in the paper
`industry, co-binder, and water retention agent in paper
`coatings, and are available in a wide range of molec-
`ular weights (Willis et al., 1999; Davis, 1987; Sanda˚s
`and Salminem, 1993).
`The present work aims to investigate the influ-
`ence of the slip preparation procedure and the con-
`centration and molecular weight of CMC binders
`on the rheological behaviour of kaolin suspensions
`and particle packing ability, evaluated by slip cast-
`
`ing the slurries in plastic rings based on plaster
`plates.
`
`2. Experimental procedure
`
`2.1. Material and slip preparation
`
`The kaolin used in this work was the Standard
`Porcelain (ECC International, UK), a type of ‘‘china
`clay’’. Its average particle size (d50 = 4.95 Am) was
`measured by using a laser diffraction instrument
`(Coulter, LS230, UK). It is easily dispersed in aque-
`ous media and it forms stable suspensions for colloi-
`dal processing or paper coating.
`Well-deflocculated suspensions containing 20, 30,
`40, and 45 vol.% of solids were prepared by firstly
`dispersing the kaolin particles into distilled water
`containing a 0.4-wt.% (relative to dry solids) solution
`of an ammonium polycarbonate (Targon 1128, BK
`Ladenburg, Germany) as dispersing agent. Stirring for
`20 min accomplished the mixing. Then, the suspen-
`sions were transferred to a cylindrical polyethylene
`container and ball milled for 24 h using silicon nitrite
`balls as grinding media (diameter = 1.5 cm). The
`suspensions were then subjected to a de-airing step
`by rolling them in the milling container, without balls,
`for another 24-h period.
`Another set of suspensions containing the same
`solid volume fractions (20, 30, and 40 vol.%) was also
`prepared by taking portions of a ball milled 45 vol.%
`‘‘stock’’ suspension and adding the required amounts
`of distilled water. These suspensions will be referred
`to as ‘‘diluted’’ to distinguish them from those that
`have been prepared from the beginning with the
`required proportions of kaolin and water.
`To the as-prepared suspensions, two different
`molecular weight carboxymethyl cellulose binders
`(CMC35-MW = 35 000 g, CMC250-MW = 250 000 g)
`were added separately or mixed in a 1:1 ratio in total
`amounts of 0.1 or 0.2 wt.% relative to the solids. These
`binders were added to the suspensions after the 24-h
`deagglomeration step; the final mixtures were homo-
`genised during the following 24-h rolling and de-airing
`period. The influence of the suspension preparation
`procedure and of adding these carboxymethyl cellu-
`loses on the rheology of the suspensions and on particle
`packing performance was studied and correlated.
`
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`
`259
`
`2.2. Slip characterisation
`
`Rheological measurements allow one to obtain
`information on particle interactions in suspension
`and their macroscopic structure (Kislenko and Verlin-
`skaya, 2001). Rheological measurements were per-
`formed in a rotational controlled stress rheometer
`(Carri-med 500 CSL, UK) at a strictly controlled
`temperature of 20 jC, after the 24-h slip de-airing
`step. The measuring configuration adopted was a cone
`and plate (/ = 4 cm, 2j, gap = 53 Am), and stress
`sweep and multi-step shear measurements (10 points,
`maximum equilibrium time of 1 min) were performed
`in the shear rates range from 0.1 up to 1300 s 1.
`Before starting a measurement, pre-shearing was
`performed at high shear rate for 1 min followed by
`a rest of 2 min,
`in order to transmit
`the same
`rheological history to the whole portion of suspension
`being tested.
`
`2.3. Preparation and characterisation of green bodies
`
`The suspensions were poured into plastic rings
`with a 25-mm diameter based on an adsorbent plaster
`plate. Two cylindrical samples, with a thickness of
`about 8 mm, were prepared from each suspension.
`The green bodies were first dried at room temperature
`for 24 h, demoulded, and then put in an oven at 100
`jC for another 24-h period.
`The density of the green bodies was measured after
`the drying process according to the Archimedes’
`method by immersion in mercury. The relative density
`(percent of the theoretical density—%TD) of the
`green samples was calculated from the real density
`of kaolin (2.5 g cm 3) as determined by a helium
`multi-pycnometer (Quanta chrome, USA).
`
`3. Results and discussion
`
`3.1. Effects of solid volume fractions, slip preparation
`procedure, and CMC binders on rheology
`
`The flow curves of the diluted and nondiluted
`suspensions containing different volume fractions of
`kaolin (in the range of 20 – 40 vol.%) are displayed in
`Fig. 1. It can be seen that all suspensions exhibit
`shear thinning behaviour with shear stress and yield
`
`Fig. 1. Effects of solid load and suspension preparation procedure
`on the flow curves of kaolin suspensions.
`
`stress values increasing as the volume fraction of
`kaolin increases. The differences are much more
`pronounced when passing from 30 to 40 vol.% solids
`due to the closer proximity to the critical solid
`content for which viscosity becomes infinite (Berg-
`strom, 1996). It is interesting to note that for all solid
`volume fractions tested, diluted systems require lower
`shear stress values for flowing under stress sweep
`measurements.
`The same type of information can be drawn from
`Fig. 2, which shows the steady shear viscosity
`curves. Since diluted systems have been prepared
`from a stock suspension containing 45 vol.% solids,
`and the shear forces increase with increasing solid
`loads, these results suggests that (i) the best dispers-
`ing degree would be obtained for the more concen-
`trated suspension tested (45 vol.%); (ii) shear forces
`play a dominant role on deagglomerating kaolinite
`booklets. Whether further increments in solid volume
`fraction could lead to further dispersing improve-
`ments is uncertain because the high viscosity of this
`starting suspension demonstrates that more concen-
`trated suspensions would be difficult to prepare and
`to handle. These interpretations rely not only on the
`present results, but also on the results collected in
`previous works (Oliveira et al., 2002; Conceicßa˜o et
`al., submitted for publication; Laarz et al., 2000; Tarı`
`et al., 1998a,b; Ferreira, 2001; Velho and Gomes,
`1991). It is expected, however, that the optimal level
`of solids will be lower than those found for other
`systems containing more isometric particles, 50
`vol.% for silicon nitride-based powder suspensions
`
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`

`260
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`
`packing ability, compared with other two above-
`referred materials containing finer particles but with
`lower aspect ratio. Considering that
`the maximum
`solid volume fraction of a typical porcelain slurry for
`slip casting, which contains about 50% of isometric
`non-clay (quartz and feldspar) particles,
`is in the
`range of 44 – 45-vol.% (Olhero et al., 2001),
`it
`is
`possible to conclude that a good dispersion degree
`has been achieved in the present case, in which the
`same concentration level was achieved using 100%
`of plate-like kaolinite particles.
`If one considers that lightweight applications, such
`as coatings and fillings for papers and boards require
`delamination of kaolinite particles to enhance the
`brightness of the end products (Velho and Gomes,
`1991; Tarı` et al., 1998b), the results presented in Figs.
`1 and 2 might have a considerable industrial impact,
`since they allow selection of the most efficient con-
`ditions to perform deagglomeration. For the solid
`concentrations lower than the optimal one, the prob-
`ability for the agglomerates or even the coarser
`primary particles to be smashed between two milling
`elements decreases, while for concentrations higher
`than the optimal one, the viscosity increases too much
`for allowing a good dispersion efficiency.
`Figs. 3 and 4 show the influence of the molecular
`weight of CMCs added in a total amount of 0.1 wt.%
`relative to the mass of solids, on steady shear
`viscosity curves of nondiluted and diluted kaolin
`suspensions, respectively. The suspensions without
`
`Fig. 2. Effects of solid load and the suspension preparation
`procedure on the steady shear viscosity curves of kaolin
`suspensions. Open symbols: diluted systems; full symbols: non-
`diluted systems (n, 5: 20 vol.%; ., o: 30 vol.%; E, D: 40
`vol.%).
`
`with d50 c 0.4 Am (Oliveira et al., 2002) or 60-vol.%
`for a ground calcium carbonate (GCC) having a
`d50 = 1.8 Am (Conceicß a˜o et al., submitted for pub-
`lication). Although these differences might be also
`related to factors such as particle/agglomerate size
`and particle/agglomerate size distribution, specific
`surface area of the powder, and on the chemistry
`of solid/liquid interface (Laarz et al., 2000), type, and
`amount of dispersant, dispersion mechanism (Tarı` et
`al., 1998a; Ferreira, 2001), and so on, in the case of
`kaolin,
`the morphological aspects would play a
`dominant role. The typical plate-like morphology of
`the kaolinite particles confers to the kaolin a poorer
`
`Fig. 3. Influence of the molecular weight of CMC on steady shear
`viscosity curves of nondiluted kaolin suspensions (20 – 40 vol.%) in
`the presence of a total amount of 0.1 wt.% CMC. Open symbols: 20
`vol.%; full symbols: 30 and 40 vol.% (x, w: without CMC; ., o:
`CMC35; E, D: CMC35 – 250; n, 5: CMC250).
`
`Fig. 4. Influence of the molecular weight of CMC on steady shear
`viscosity curves of diluted kaolin suspensions (20 – 40 vol.%) in the
`presence of a total amount of 0.1 wt.% CMC. Open symbols: 20
`vol.%; full symbols: 30 and 40 vol.% (x, w: without CMC; ., o:
`CMC35; E, D: CMC35 – 250; n, 5: CMC250).
`
`

`

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`
`261
`
`CMCs and containing 20 vol.% solids show a near
`Newtonian fluid behaviour. Adding CMC binders
`and/or increasing solid volume fractions to 30
`vol.% conferred to the suspensions a shear thinning
`behaviour, especially in the lower shear rate range,
`followed by a trend to a Newtonian fluid behaviour.
`At
`the lower solid volume fractions (20 and 30
`vol.%),
`the steady shear viscosity curves of non-
`diluted and diluted systems seem very similar,
`although the diluted ones are slightly more fluid,
`according to the results presented in Figs. 1 and 2.
`The sequence of the curves is also the same at these
`two solid volume fractions, the less viscous being the
`suspension without CMC binders, followed succes-
`sively by those containing CMC35 alone, the mixture
`CMC35 – 250, and CMC250 alone. This sequence
`can be understood because it is known that CMC
`binders/thickeners might also have a dispersing role,
`which is enhanced as the molecular weight decreases,
`while the thickening abilities are improved with
`increasing molecular weight (Willis et al., 1999;
`Davis, 1987; Sanda˚s and Salminem, 1993). At the
`lower solid loading,
`the average distance between
`particles is larger, and the contribution of CMCs to
`dispersion is masked by their thickening effects and
`only becomes apparent for the nondiluted and less
`well-dispersed system at 30 vol.% solids and for
`shear rates >600 s 1. In fact, the thickening effects
`of these types of additives are mostly observed at low
`shear rates due to some structuration of water mole-
`cules around the hydrophilic polymeric chains. Under
`shear,
`this structure is gradually destroyed as the
`applied stress increases, accentuating the shear thin-
`ning characteristics of the suspensions.
`At 40 vol.% solids and for both nondiluted and
`diluted systems, a shear thickening behaviour along
`all the shear rate range is evident in absence of CMC
`binders. This flow behaviour is typical of well-
`dispersed and highly concentrated suspensions (Tar-
`ı`et al., 1998b). The possible presence of some
`remaining booklet-type hard agglomerates will also
`account for the accentuation of this behaviour. Add-
`ing 0.1 wt.% CMC binders to these suspensions
`increases the viscosity along all the shear rate range
`and changes the flow behaviour to shear thinning at
`low shear rates (up to c 400 s 1 where minimum
`viscosity values were measured), followed by the
`same shear thickening trend observed in absence of
`
`is generally
`binders. The strong thickening effect
`observed for the higher MW CMC, followed by the
`mixture of both, although a different sequence can be
`observed for the more concentrated and nondiluted
`suspension. In fact, Fig. 3 shows that the mixture
`(CMC35 + CMC250) has a higher thickening effi-
`ciency followed by the low molecular weight
`CMC35, when compared with the high molecular
`weight CMC250. This suggests that the nondiluted
`and less well-deagglomerated systems are less reli-
`able, probably due to a lower mixing efficiency of
`the additives and their consequent less homogeneous
`distribution in the suspension.
`Figs. 5 and 6 show that increasing the amount of
`added binders to 0.2 wt.% accentuated the thickening
`effect, as expected, shifting the steady shear viscosity
`curves upward. As a consequence, the suspensions at
`40 vol.% solids for the nondiluted system could not be
`prepared (Fig. 5), although the more well-deagglom-
`erated diluted one could still be obtained (Fig. 6).
`Three sets of curves can be clearly distinguished in
`Fig. 6, each one corresponding to given total solid
`concentration of 20, 30 and 40 vol.%. Concerning the
`effects of added binders, the sequence of the curves is
`generally the same already observed in Fig. 4, with
`the high molecular weight CMC250 showing as a
`higher thickening efficiency followed successively by
`the mixture of both and the low molecular weight
`CMC35; some differences were observed only for the
`more concentrated suspension. This also points to
`
`Fig. 5. Influence of the molecular weight of CMC on steady shear
`viscosity curves of nondiluted kaolin suspensions (20 – 30 vol.%) in
`the presence of a total amount of 0.2 wt.% CMC. Open symbols: 20
`vol.%; full symbols: 30 vol.% (x, w: without CMC; ., o: CMC35;
`E, D: CMC35 – 250; n, 5: CMC250).
`
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`

`262
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`
`Table 1 shows the relative density (%TD) of the green
`bodies of nondiluted and diluted kaolin suspensions,
`at different solid loads in absence of CMC binders. It
`can be seen that for both diluted and nondiluted
`suspensions,
`the density increases with increasing
`solid loading reaching a maximum value of 67% of
`the theoretical density at the highest solid volume
`fraction for both systems. However, significant differ-
`ences can be observed between the packing ability of
`nondiluted and diluted suspensions at 20 and 30
`vol.%. This can be clearly attributed to particle/
`agglomerate segregation phenomena (Ferreira, 1998;
`Olhero and Ferreira, 2002), which are favoured by the
`low viscosity of the suspensions at these lower solids
`concentrations and by the size differences among the
`suspended particles/agglomerates. These results prove
`that better dispersion and deagglomeration degrees
`have been achieved in the diluted systems, being in
`close agreement with a previous report on calcium
`carbonate (Conceicßa˜o et al., submitted for publication).
`Tables 2 and 3 show the effect of molecular weight
`of the binders on green density of slip cast bodies
`prepared from nondiluted and diluted suspensions, for
`total added amounts of 0.1 and 0.2 wt.%, respectively.
`It can be seen that the relative densities (%TD) of the
`green bodies derived from nondiluted systems tend to
`increase with increasing solid loading, reaching a
`maximum value of 61%, while for the diluted ones,
`the theoretical densities of the green bodies are mostly
`in the range of 61 – 62%. These differences are obvi-
`ously more mitigated than those observed in absence
`of the binders, which can be attributed to their
`thickening effects that tend to hinder particle segrega-
`tion, confirming again the better dispersion and deag-
`glomeration degrees achieved in the diluted systems.
`
`Fig. 6. Influence of the molecular weight of CMC on steady shear
`viscosity curves of diluted kaolin suspensions (20 – 40 vol.%) in the
`presence of a total amount of 0.2-wt.% CMC. Open symbols: 20
`vol.%; full symbols: 30 – 40 vol.% (x, w: without CMC; ., o:
`CMC35; E, D: CMC35 – 250; n, 5: CMC250).
`
`difficulties in obtaining a homogeneous distribution of
`the additives when the viscosity of the suspension is
`too high. Even though, Fig. 6 shows that the more
`accentuated thickening effect at low shear rates has
`been obtained for the CMC250, compared with the
`CMC35, the situation reverses at higher shear rates
`(c 550 s 1). A similar reversal at c 800 s 1 is
`observed between the suspension without binders and
`that containing the mixture of both.
`
`3.2. Effects of solid volume fraction, slip preparation
`procedure, and CMC binders on particle packing
`
`Slip casting experiments were carried out to get
`complementary information about the effects of the
`intensity of shear forces during slip preparation on the
`state of dispersion and deagglomeration of the kaolin.
`
`Table 1
`Effect of solids loading on green density of slip cast bodies of kaolin prepared from nondiluted and diluted suspensions
`
`Systems
`
`Nondiluted
`
`Solids (vol.%)
`Solids (wt.%)
`Green density
`q (g cm 3)
`
`%TD (average)
`
`1
`2
`Average
`
`Solid volume/weight fraction
`
`20
`38
`1.42
`1.41
`1.42
`57
`
`30
`52
`1.50
`1.48
`1.49
`60
`
`40
`63
`1.66
`1.66
`1.66
`66
`
`45
`67
`1.68
`1.67
`1.68
`67
`
`Diluted
`
`20
`38
`1.56
`1.55
`1.56
`62
`
`30
`52
`1.63
`1.63
`1.63
`65
`
`40
`63
`1.65
`1.64
`1.65
`66
`
`45
`67
`1.68
`1.67
`1.68
`67
`
`

`

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`
`263
`
`Table 2
`Effect of molecular weight of CMC on green density of slip cast bodies prepared from nondiluted and diluted kaolin suspensions containing a
`total amount of 0.1 wt.% CMC
`
`Additives
`
`CMC35
`
`CMC250
`
`CMC35 + CMC250
`
`Solids (vol.%)
`Solids (wt.%)
`
`20
`38
`
`30
`52
`
`40
`63
`
`20
`38
`
`30
`52
`
`40
`63
`
`20
`38
`
`30
`52
`
`40
`63
`
`Systems
`
`Samples
`
`Green density q (g cm 3)
`
`Nondiluted
`
`Diluted
`
`1
`2
`Average
`%TD (average)
`1
`2
`Average
`%TD (average)
`
`1.41
`1.43
`1.42
`57
`1.52
`1.52
`1.52
`61
`
`1.47
`1.50
`1.49
`60
`1.55
`1.55
`1.55
`62
`
`1.53
`1.53
`1.53
`61
`1.55
`1.54
`1.55
`62
`
`1.41
`1.43
`1.42
`57
`1.51
`1.50
`1.51
`61
`
`1.50
`1.50
`1.50
`60
`1.53
`1.52
`1.53
`62
`
`1.51
`1.52
`1.52
`60
`1.54
`1.56
`1.55
`62
`
`1.44
`1.43
`1.44
`58
`1.53
`1.52
`1.53
`62
`
`1.50
`1.51
`1.51
`60
`1.54
`1.54
`1.54
`62
`
`1.52
`1.53
`1.53
`61
`1.52
`1.52
`1.52
`61
`
`Increasing the total added amount of CMC bind-
`ers to 0.2 wt.% did not cause significant changes in
`terms of packing, although a slightly higher value of
`63% has been obtained for the diluted suspensions at
`40 vol.% in the presence of the lower molecular
`weight CMC (Table 3), attributable to the combined
`effects of the better dispersion ability of this binder,
`the less homogenous distribution of the binder in the
`high concentrated suspensions according to the
`rheological results discussed above, and the better
`deagglomeration degree of
`the kaolin in diluted
`systems.
`
`4. Conclusions
`
`The results presented in this work enable us to
`draw the following conclusions:
`
`(1) The delamination efficiency of kaolin agglomer-
`ates, the rheological characteristics of well de-
`flocculated suspensions, and their packing ability
`during slip casting were shown to be strongly
`dependent on the intensity of shear forces acting
`during slip preparation, as controlled by solids
`volume fraction. The delamination efficiency
`
`Table 3
`Effect of molecular weight of CMC on green density of slip cast bodies prepared from nondiluted and diluted kaolin suspensions containing a
`total amount of 0.2 wt.% CMC
`
`Additives
`
`CMC35
`
`CMC250
`
`CMC35 + CMC250
`
`Solids (vol.%)
`Solids (wt.%)
`
`20
`38
`
`30
`52
`
`40
`63
`
`20
`38
`
`30
`52
`
`40
`63
`
`20
`38
`
`30
`52
`
`40
`63
`
`Systems
`
`Samples
`
`Green density q (g cm 3)
`
`Nondiluted
`
`Diluted
`
`1
`2
`Aug
`%TD (average)
`1
`2
`Aug
`%TD (average)
`
`1.43
`1.42
`1.43
`57
`1.50
`1.51
`1.51
`61
`
`1.52
`1.52
`1.52
`60
`1.51
`1.52
`1.52
`61
`
`–
`–
`–
`–
`1.56
`1.56
`1.56
`63
`
`1.43
`1.43
`1.43
`57
`1.47
`1.48
`1.48
`59
`
`1.47
`1.48
`1.48
`59
`1.53
`1.52
`1.53
`62
`
`–
`–
`–
`–
`1.52
`1.53
`1.53
`62
`
`1.42
`1.42
`1.42
`57
`1.50
`1.48
`1.49
`60
`
`1.51
`1.51
`1.51
`60
`1.52
`1.49
`1.51
`60
`
`–
`–
`–
`–
`1.53
`1.53
`1.53
`62
`
`

`

`264
`
`S.I. Conceicßa˜o et al. / Applied Clay Science 23 (2003) 257–264
`
`always increased with increasing the solids con-
`centration along the whole solid volume fraction
`range tested. These results might have a high
`industrial impact, showing that when a high degree
`of delamination is desired to be achieved in low or
`moderate concentrated suspensions, it is advisable
`to start from a high concentrated one with an
`optimised solid load and then add the required
`amounts of suspending medium to set the final
`concentration.
`(2) The efficiency of delamination/dispersion can be
`accessed by rheological measurements and com-
`plemented by slip casting experiments. The green
`density of slip cast bodies seems even more
`reliable in evaluating the delamination/dispersing
`degree then rheology.
`(3) Adding CMC binders enhances the shear thinning
`or decreases the shear thickening characteristics of
`the suspensions while they tend to hinder particle
`segregation phenomena due to their thickening
`effects, which tend to increase with increasing
`molecular weight.
`
`Acknowledgements
`
`This work was supported by FCT (Portuguese
`Foundation for Science and Technology) contract No.
`POCTI/1999-CTM 36244.
`
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