Comparative Study of Aqueous Unbonded Filler Dispersions · of Aqueous Unbonded Filler Dispersions...

Author: Siegfried Heckl Translation: Wilhelm Bachmann Approval: May 2008

VM / Dr. Alexander Risch _____________________

Comparative Study

of Aqueous Unbonded

Filler Dispersions

R H E O L O G Y

VM

-3/0

5.2

00

8/0

61

389

80

HOFFMANN MINERAL GmbH · P.O. Box 14 60 · D-86619 Neuburg (Donau) · Phone (+49-84 31) 53-0 · Fax (+49-84 31) 53-3 30 Internet: www.hoffmann-mineral.com · eMail: [email protected]

Summary

In this study, the rheological behavior of the product groups Sillitin, Sillikolloid and Aktisil was compared with other common fillers used in the paints and lacquers industry. The study looked at isotropic and anisotropic fillers as well as Neuburg Siliceous Earth. All measurements were performed using a rotation viscometer with infinitely variable settings. The viscosity of the products was measured and depicted according to the concentration and shear rate. Viscosity characteristics (structure viscosity, dilatancy, thixotropy, rheopexy and yield point) were separately evaluated.

shear rate 500 1/s

15 20 25 30 35 40 45 50 55 60 65 70 75

filler concentration in %

1

10

100

1000

10000viscosity in mPas (log)

Sillitin Z 86

quartz powder

unground clay

ground clay

kieselguhr

Fig. 1

Despite its low kaolinite content (approx. 20 to 30 % depending on type), the rheological behavior of Neuburg Siliceous Earth is closer to that of anisotropic than isotropic fillers. The Sillitin types are similar in their flow behavior to unground clay (Fig. 1). It is interesting to note that the particle structure of fillers permits no prediction on their rheological behavior in water. Particle size distribution and the particle surface generally have a larger influence on rheological behavior than crystalline structure. Aktisil MM is a surface-treated (coated) Neuburg Siliceous Earth whose viscosity does not differ to the base material Sillitin Z 86 (see Figs. 9 and 10). Aktisil EM, on the other hand, exhibits considerably lower viscosity throughout, while Aktisil MM has the highest thixotropic factor of all fillers tested.

Contents

1. Preliminaries 2. Objectives 3. Methods 3.1 Raw material characteristics 3.2 Creation of dispersion 3.3 Apparatus and measurement methods 4. Rheological tests 4.1 Viscosity curves 4.1.1 Isotropic fillers 4.1.2 Anisotropic fillers 4.1.3 Neuburg Siliceous Earth 4.1.3.1 Sillitin and Sillikolloid 4.1.3.2 Aktisil 4.2 Rheological effects 4.2.1 Isotropic fillers 4.2.2 Anisotropic fillers 4.2.3 Neuburg Siliceous Earth 4.2.3.1 Sillitin and Sillikolloid 4.2.3.2 Aktisil

1 Preliminaries

Manufacturers of coatings, adhesives and sealing compounds are faced with an ever

increasing range of fillers for every type of application area. When paints, plastics and rubber were first developed, fillers were mainly used to

cheapen expensive polymers. This purely economic aspect is still of importance today. However, increased ecological and quality awareness has resulted in products of greater complexity, with increasing specialization and higher demands being placed on coatings, adhesives and sealing compounds. Consequently, the requirements placed on the fillers for these products have increased. Fillers are no longer used just to cheapen recipes, but also to improve their physical and/or optical characteristics. Fillers, when surface-treated with silanes or other substances, are now used specifically as a means of improving properties.

2 Objectives

During the course of this investigation, comparative studies have been carried out on

light-colored fillers in water. Our aim is to present research departments with a means of deciding which filler to use on the basis of its rheological behavior.

Typical representatives of individual fillers classes were chosen in order to study the

broadest possible spectrum of filler types. The shear range was adapted to the conditions normally encountered in practice.

The tests examined how Neuburg Siliceous Earth, with its particular structure (natural

combination of corpuscular, crypto-crystalline and amorphous silica and lamellar kaolinite), performed against various filler classes. The whole spectrum of Neuburg Siliceous Earth, from Sillitin V 85 to Sillikolloid P 87, including the puriss types and surface-treated Aktisil types was examined.

3 Methods

3.1 Raw Material Characteristics Tables 1 to 4 show the most important physical characteristics of fillers for paint manufacturers. The data are only guidelines values. The fillers have been classified according to structure groups in order to simplify presentation as follows:

Methods for Determination of Brightness The brightness values Y and Z were determined with a spectral photometer according to DIN 53 163,

illuminant D 65/10 at d/8 (Mini-Scan from Hunterlab). Furthermore the brightness Y was determined with a

l-a-d meter, illuminant C at 45/0 (D 25-9 from Hunterlab). Isotropic Fillers These fillers can be mainly characterized by their cubic to spherical structure. When combined with the polymer matrix, no process-related preferred structural planes are exhibited under operating conditions.

Oil absorpt-

Particle

Brightness

pH

Price index*

Filler ion value

g/100g

size

d50 in m Y

(45/0) Y

(DIN 53 163) Z

(DIN 53 163)

value Sillitin Z 86 = 1.0

chalk 18 2.0 88 85 85 9 0.2

calcite 18 1.5 94 92 95 9 0.8

barytes 12 1.1 95 93 99 --- 1.5

calcined clay 80 4.0 90 94 98 6.5 1.5

kieselguhr 132 6.0 88 94 100 10.0 5.1

quartz powder 31 3.0 90 88 93 7 0.9

Table 1 * based on German prices 1993

Isotropic Fillers (chalk, calcite, barytes, calcined clay, kieselgur, quartz powder) fillers with largely even three-dimensional particle structure. Anisotropic Fillers (talc, clay, mica, wollastonite) fillers with fibrous or plate-shaped (lamellar) structure. Neuburg Siliceous Earth (Sillitin, Sillikolloid, Aktisil) forms its own group, but can be broadly classified under the isotropic fillers as the plate-

shaped kaolinite cannot align due to interspersed silica particles.

Anisotropic Fillers Polymers filled with anisotropic minerals more or less exhibit directional dependence in terms of their physical properties where shear forces occur during processing.

Oil absorpt-

Particle

Brightness

pH

Price index*

Filler ion value

g/100g

size

d50 in m Y

(45/0) Y

(DIN 53 163) Z

(DIN 53 163)


coarse talc 32 87 87 86 92 9.3 2.0

fine talc 40 79 79 80 84 9.5 1.6

unground clay 55 - - 77 75 4.5 1.4

ground clay 39 87 87 89 90 4.0 2.6

mica 48 79 79 80 80 8.4 3.6

wollastonite 32 88 88 91 96 9.8 2.3


Neuburg Siliceous Earth Sillitin and Sillikolloid Neuburg Siliceous Earth is classified according to particle size and brightness. The letters in the product

name (V, N, Z and P) refer to the particle size distribution; the figures to the brightness Y (45/0).

Oil absorpt-

Particle

Brightness

pH

Price index*

Filler ion value

g/100g

size

d50 in m Y

(45/0) Y

(DIN 53 163) Z

(DIN 53 163)


Sillitin V 85 45 3.0 85 83 79 8.0 0.8

Sillitin N 82 45 2.3 82 80 71 8.0 0.8

Sillitin N 85 ** 45 2.3 85 84 79 8.0 0.9

Sillitin Z 86 ** 50 1.8 86 84 79 8.2 1.0

Sillitin Z 89 ** 50 1.8 89 89 89 8.5 1.2

Sillikolloid P 82 50 1.6 82 79 70 8.2 1.6

Sillikolloid P 87 ** 50 1.6 87 85 80 8.2 1.6


** also available as puriss version

Puriss Versions As a result of careful processing the grit content is maintained at an exceptionally low level. This considerably reduces the abrasive effect of this series of products, thereby protecting the manufacturer's processing equipment (e.g. airless sprayers). The remaining technical characteristics are identical to those of the base materials. The puriss versions are particularly recommended for very thin lacquer coatings. The results have not been included in the graphics as they are identical to the standard types. Aktisil The Aktisil types are activated Sillitins, produced by modifying the surface of the raw material by a variety of special coatings. In this study only those Aktisil types (based on Sillitin Z 86) suitable for aqueous systems free from binding agents have been considered: - Aktisil EM (coated with epoxy group silane) - Aktisil MM (coated with mercapto group silane)

Oil absorpt-

Particle

Brightness

pH

Price index*

Filler ion value

g/100g

size

d50 in m Y

(45/0) Y

(DIN 53 163) Z

(DIN 53 163)


Aktisil EM 50 1.8 86 84 78 8.5 2.5

Aktisil MM 50 1.8 86 84 78 7.3 2.3


3.2 Creation of Dispersion The filler was dispersed with a rotation speed of 10 to 15 m/s for 20 minutes using a laboratory mixer. The dispersion was then stored for 24 hours to enable it to recover its anomalous viscosity characteristics (thixotropy and structural viscosity). The flow curves were then recorded following a brief homogenization phase.

3.3 Apparatus and Methods The measurements were made with a rotation viscometer comprising the following components: Rheometer Measuring Apparatus Viscolab LM Rotation Rheometer Viscolab LC 10 Flow Curve Programmer Viscolab FP 10 x-y Recorder PM 8043 Manufacturer: Physica Meßtechnik GmbH &. Co. KG, Stuttgart (FRG) Different measurement systems were used, depending on the viscosity of the samples. Table 5 shows the measurement ranges determined.

Measurement system

recommended viscosity range

in Pas shear rate in 1/s

shear stress in Pa

MS-Z1 DIN (double slit measurement system)

0,001 - 1 4,97 - 3979 0,676 - 67

MS-Z2 DIN 0,02 - 15 1,291 - 1033 1,958 - 195

MS-Z3 DIN 0,118 - 100 1,291 - 1033 11,42 - 1140

MS-Z4 DIN 0,672 - 500 1,291 - 1033 65,01 - 6500

Table 5 The proportion of filler in the dispersion was increased until loss of flow occurred (breaking up of flow in measuring vessel). The filler amount was increased in 10% stages and at 5% stages where its proportion in the dispersion was higher.

The test temperature was (23 ± 0.1) C. The flow curves were plotted without pre-shearing (no incremental stages) with: increasing shear rate up to 500 s

-1

and

decreasing shear rate of 500 to 0 s

-1

with a linear change of 4.17 s-2

The viscosity curves were evaluated at a shear rate interval of 8.9 to 500 s

-1. The measurements were

performed twice with the measurement system being refilled each time. Only the flow curves with increasing shear rate (upward curve) were used to evaluate viscosity. The downward curve was used to determine hysteresis (thixotropy and rheopexy), as well as the yield value.

4. Rheological Tests

4.1 Viscosity Curves Sillitin Z 86 is used for comparison in all graphics. 4.1.1 Isotropic Fillers Fig. 2 clearly illustrates the special position of barytes due to its high specific gravity and low demands on bonding agents. Fluid dispersions with a filler concentration of greater than 85 percent by weight can be produced. However, as many paints are no longer sold by weight but by volume, the heavier filling ability of barytes is only an advantage in certain circumstances, since its use increases the specific gravity of the recipe. On the other hand, fillers of greater volume have a far greater influence on the pigment volume concentration than on the density of the formulation. Fig. 3 shows that the filler dispersions in the range of < 100 s

-1 have clear structural

viscosity. This is least pronounced in calcined clay and quartz powder. Kieselguhr was not taken into account as its max. filler concentration was 35 %. Sillitin Z 86 has a somewhat higher shear rate to viscosity ratio, probably due to the special structure of the Neuburg Siliceous Earth.

shear rate 500 1/s

15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90


1

10

100

1000


Sillitin Z 86 quartz powder

kieselguhr chalk

calcite barytes

calcined clay

Fig. 2

Fig. 3

fi l ler concentration 40 %

0 100 200 300 400 500

shear rate in 1/s

1

10

100

1000


Sillitin Z 86 quartz powder chalk calcite bary tes calcined clay

4.1.2 Anisotropic Fillers The measurements show clearly that the flow behavior of Sillitin Z 86 is closer to anisotropic than isotropic fillers. Comparison of the viscosity curves clearly show that needle-shaped wollastonite has a very high structural viscosity. On the other hand, the mica dispersion shows practically Newtonian flow behavior. The other fillers lie between these two extremes. As Fig. 5 shows, it is not possible to extrapolate a typical flow behavior from the structure.

Fig. 4

Fig. 5

shear rate 500 1/s

15 20 25 30 35 40 45 50 55 60 65 70

fi l ler concentration in %

1

10

100

1000


Sillitin Z 86

unground clay

ground clay

coarse talc

f ine talc

mica

wollastonite


0 100 200 300 400 500

shear rate in 1/s

10

100

1000


Sillitin Z 86 unground clay ground clay coarse talc

f ine talc mica wollastonite

4.1.3 Neuburg Siliceous Earth The particle structure of the Neuburg Siliceous Earth is a key factor in terms of its application characteristics. The Neuburg Siliceous Earth disperses very easily and, in contrast to purely lamellar fillers such as talc or clay, does not agglomerate. 4.1.3.1 Sillitin and Sillikolloid The concentration-related visco-sity curves of the different types of Neuburg Siliceous Earth are shown in the following diagrams (Figs. 6 and 7). Comparison of the individual curves reveals some unex-pected effects. Products of the same particle size range, but of different brightness, have clearly differing curves which are frequently closer to the next particle size fraction. The difference between Sillitin V 85 and Sillitin V 88 is particularly obvious.

Fig. 6

Fig. 7

shear rate 500 1/s

15 20 25 30 35 40 45 50 55 60 65 70


1

10

100

1000


Sillitin Z 86

Sillitin V 85

Sillitin V 88

Sillitin N 82

Sillitin N 85

shear rate 500 1/s

15 20 25 30 35 40 45 50 55 60 65


1

10

100

1000


Sillitin Z 86

Sillitin Z 89

Sillikolloid P 87

Sillikolloid P 82

Fig. 8 shows the different types of Neuburg Siliceous Earth at a filler concentration of 40 % relative to shear rate.

Fig. 8

As the kaolinite content was only 20 % to 30 %, the flow behavior of Neuburg Siliceous Earth was

hardly expected to be very similar to that of unground clay. This shows all the more clearly that, due to

its rheology, the Neuburg Siliceous Earth must be regarded as an independent filler group. The

Neuburg Siliceous Earth has its own characteristic profile!


0 100 200 300 400 500

shear rate in 1/s

1

10

100

1000

viscosity in mPas (log)

Sillitin Z 86 Sillitin V 85 Sillitin V 88 Sillitin N 82

Sillitin N 85 Sillitin Z 89 Sillikolloid P 82 Sillikolloid P 87

4.1.3.2 Aktisil Common to the Aktisil types is the fact that the silanes are chemically almost completely

bonded to the filler surface1,

with the result that any interaction or chemical reaction of the binder with the Aktisil is linked by the organic groups of the silane. If the silane were first added when formulating the coating the silane could then remain free to "roam" in the coating, leading to adhesion problems with the threshold surface (coating substrate). In addition to this, silane could lead to surface defects (e.g. fish-eyes). Figs. 9 and 10 show that Aktisil EM has a much lower viscosity level than Aktisil MM and Sillitin Z 86.

1 Albers and Lechner Kunststoffe 81 (1991) H.5. p. 420 ff

Fig. 9

Fig. 10

shear rate 500 1/s

15 20 25 30 35 40 45 50 55 60 65


1

10

100

1000


Sillitin Z 86

Aktisil EM

Aktisil MM


0 100 200 300 400 500

shear rate in 1/s

1

10

100

1000

viscosity in mPas (log)

Sillitin Z 86 Aktisil EM Aktisil MM

4.2 Rheological Effects In the following chapter, variations in flow behavior of the filler dispersions from Newtonian flow were quantified. The fillers were grouped according to particle structure, as in the case of the viscosity curves. The rotation test does not permit a (physically) exact description of thixotropy, rheopexy and the yield point. For that reason, auxiliary values were defined which permit a practical comparison of quantitative deviation from Newtonian flow.

Description of methods for anomalous viscosity values: 1. Structural viscosity factor As well as Newtonian flow, where viscosity is independent of the shear rate, some

systems exhibit shear rate dependent flow behavior. Where viscosity decreases at an increasing shear rate this is considered to be a structurally viscous or pseudo plastic flow. Where viscosity increases with an increasing shear rate, this is termed dilatancy.

For the following assessment the structural viscosity factor (SVF) as an auxiliary value was defined as follows:

SVF = relationship: viscosity at 50 s

-1 / viscosity at 500 s

-1 (upward curve)

SVF = 1 Newtonian flow SVF < 1 dilitancy flow SVF > 1 structural viscous flow 2. Yield point Substances with a yield point first start to flow when the external force is greater than the

internal structural forces affecting them. These substances exhibit plastic flow below the yield point.

The yield point is assessed from the shear stress at a shear rate of 5 s

-1 (from the

downward curve).

In this assessment it should be noted that the anomalous viscosity values cannot be regarded as

absolute, but must be considered individually in relation to the viscosity of a particular system.

3. Thixotropy / Rheopexy Thixotropy is understood to mean the breakdown of a structure measured as a reduction

of viscosity under external shear forces over time. The original structure recovers after a given relaxation period.

Rheopexy refers to structural reinforcement over time under the influence of external

shear forces (increase in viscosity). With the measurement method used, it was only possible to carry out a single point

evaluation of thixotropy, therefore not giving an ideal picture of thixotropic or rheopexic flow. However, the measurements do give some practical information with which to compare fillers.

A thixotropic factor (TF) was therefore defined as follows: TF = 100 -[(visc. downwards at 300 s-1 / visc. upwards at 300 s-1) - 100] TF > 0 ==> thixotropic flow TF < 0 ==> rheopexic flow. The thixotropic factor gives the percentage deviation in viscosity from the downward

curve (after shearing) against the viscosity of the upward curve (no shearing) at a shear rate of 300 s

-1.

Thixotropy has not been shown graphically, as the thixotropic values of the fillers

examined revealed no significant differences, with the exception of the Aktisils.

4.2.1 Isotropic Fillers The structural viscosity factors reveal very different concen-tration ratios. Sillitin Z 86 has the highest structural viscosity factors compared to the isotro-pic fillers. In the case of chalk, calcite and kieselguhr, the structural viscosity factor only changes insignificantly with increasing filler concentration. Quartz powder is the only sub-stance that has a dilatancy flow at higher filler concentrations. All fillers exhibited a clear drop in the structural viscosity factor at the highest filler concen-trations. Sillitin Z 86 has the highest yield point over the whole concentration range. In the case of kieselguhr a very large increase in the yield point can be seen, but this is limited by the low filler level. All the isotropic fillers tested exhibited thixotropic flow only when the highest filler level was reached. This particularly applies to chalk, with a clear rheopexic flow in the con-centration range 30 % to 60 %, a very unfavorable result in terms of rheology.

20 30 40 50 60 70 80


0

1

2

3

4

5

6

7

8

9

10structural viscosity factor (SVF)

Sillitin Z 86 quartz powder kieselguhr calcined clay

chalk calcite barytes

Fig. 11 Structural viscosity factors of isotropic fillers

20 30 40 50 60 70 80


0,001

0,01

0,1

1

10

100

yield point in Pa

Sillitin Z 86 quartz powder kieselguhr calcined clay

chalk calcite barytes

Fig. 12 Yield point of isotropic fillers

4.2.2 Anisotropic Fillers As with the isotropic fillers, the structural viscosity factors were not uniform. Apart from fillers with a low concentration ratio such as mica, fine and coarse talc, there were very large differences amongst the other fillers tested. As in the viscosity curves, unground clay shows almost the same rheological behavior as Sillitin Z 86. Like the isotropic fillers, the structural viscosity factors of nearly all fillers ease off distinctly at the highest filler concentration. Ground clay has the highest value over the whole range at the yield point. Sillitin Z 86 has nearly the same values as unground clay. Fine talc exhibits the steepest increase in the yield point, but is only fillable up to 45 % in water. Comparison of the thixotropic factors of the anisotropic fillers shows a very widely different-iated picture. Ground clay exhibits a slightly rheopexic flow over the whole filler range, whereas wollastonite has a slightly thixotropic flow. The other fillers only exhibit thixo-tropic flow at the highest filler level, as already observed with the isotropic fillers.

Fig. 13 Structural viscosity factors of anisotropic fillers

20 25 30 35 40 45 50 55 60 65 70


0,01

0,1

1

10

100

1000yield point in Pa

Sillitin Z 86 unground clay mica ground clay

wollastonite fine talc coarse talc

Fig. 14 Yield point of anisotropic fillers

20 30 40 50 60 70

f iller concentration in %

0

1

2

3

4

5

6

7

8

9

10

11


Sil l i tin Z 86 unground clay ground clay mica

wollastonite fine talc coarse talc

4.2.3 Neuburg Siliceous Earth 4.2.3.1 Sillitin and Sillikolloid In terms of yield value and structural viscosity factor, the fine grade Neuburg Siliceous Earth products Sillitin Z 89, Sillikolloid P 82 and Sillikolloid P 87 have almost the same values as Sillitin Z 86, the material used for comparison, and have not been included in the graphics for that reason. We also observed that the structural viscosity factor of the Neuburg Siliceous Earth tended to increase as particle size decreases. An exceptions to this is the newly developed product Sillitin V 88. Dependency of the rheological behavior to the particle size is also reflected in the yield point curve. As already mentioned for structural viscosity, Sillitin V 88 is also exceptional in terms of yield point. The value is markedly lower than the values determined for other types of the same particle size. As far as the thixotropic factor is concerned, the same patterns emerge for isotropic and anisotropic fillers: definite thixotropy is only apparent at the highest filler concentration (60 %) with the silica products. Sillitin Z 86 had the highest thixotropic factor of all the untreated types of Neuburg Siliceous Earth.

Fig. 15 Structural viscosity factors of Neuburg Siliceous Earth


20 30 40 50 60


0,01

0,1

1

10

100

yield point in Pa

Sillitin Z 86

Sillitin Z 89

Sillikolloid P 82

Sillikolloid P 87

Fig. 17 Yield point of Neuburg Siliceous Earth

20 30 40 50 60


0,01

0,1

1

10

100

yield point in Pa

Sillitin Z 86

Sillitin V 85

Sillitin V 88

Sillitin N 82

Sillitin N 85


20 30 40 50 60


0

1

2

3

4

5

6


Sillitin Z 86 Sillitin Z 89 Sillikolloid P 82 Sillikolloid P 87

20 30 40 50 60


0

1

2

3

4

5

6


Sillitin Z 86 Sillitin V 85 Sillitin V 88 Sillitin N 82 Sillitin N 85

4.2.3.2 Aktisil As already described for the viscosity curves, the surface treatment given to Aktisil EM has an effect on its viscosity characteristics. In terms of the structural viscosity factor and yield point, this product exhibits the least deviation to Newtonian flow, differing clearly from the starting material Sillitin Z 86. Aktisil EM exhibits definite thixotropy throughout the entire test range, as does Aktisil MM. Aktisil MM has the highest structural viscosity factor of all fillers examined. The yield point of Aktisil MM corresponds to the yield point of the starting material Sillitin Z 86.


20 30 40 50 60


0,01

0,1

1

10

100

yield point in Pa

Sillitin Z 86

Aktisil EM

Aktisil MM


Our technical service suggestions and the information contained in this report are based on experience and are made to the best of our knowledge and belief, but must nevertheless be regarded as non-binding advice subject to no guarantee. Working and employment conditions over which we have no control exclude any damage claims arising from the use of our data and recommendations. Furthermore, we cannot assume any responsibility for any patent infringements which might result from the use of our information.

Fig. 21 Thixotropic factors

20 30 40 50 60


0

1

2

3

4

5

6

7

8


Sillitin Z 86 Aktisil EM Aktisil MM

20 30 40 50 60 70


0

10

20

30

40

50thixotropic factor (TF)

Sillitin Z 86

Aktisil EM

Aktisil MM

Comparative Study of Aqueous Unbonded Filler Dispersions · of Aqueous Unbonded Filler Dispersions...

Documents

Transcript of Comparative Study of Aqueous Unbonded Filler Dispersions · of Aqueous Unbonded Filler Dispersions...