- Email: [email protected]
Waste cement dusts as fillers for rubber compounds
CEMENT and CONCRETE RESEARCH. VoI. 14, pp. 776-784, 1984. Printed in the USA. 0008-8846/84 53.00+00. Copyright (c) 1984 Pergamon Press, Ltd.
WASTE CEMENT DUSTS AS FILLERS FOR RUBBER COMPOUNDS Andrzej K r y s z t a f k i e w i c z and Marek Maik I n s t i t u t e of Chemical and Engineering Technology P o l i t e c h n i k a Pozna6ska 60-965 Pozna~, Poland (Communicated by D.M. Roy) (Received May 13, 1983; in f i n a l form March 15, 1984)
ABSTRACT The p o s s i b i l i t y of s u b s t i t u t i o n of expensive a c t i v e f i l l e r s , e.g. carbon black, f o r the waste products which can play the r o l e of these filllers, e.g. the waste cement dusts or the waste post-HF s i l i c a , were i n v e s t i g a t e d . The physico-chemical p r o p e r t i e s of the i n v e s t i gated waste cement dusts and the waste post-HF s i l i c a , as well as the s t r e n g t h p r o p e r t i e s of the rubber compounds containing these as fillers, were determined. To increase the a c t i v i t y and chemical a f f i n i t y w i t h the rubber, the waste cement dusts and the waste post-HF s i l i c a were modified by the use of adhesion promoters, that is alkoxysilanes. I t was found t h a t i t would be possible to p a r t l y s u b s t i t u t e carbon black f o r the waste cement dusts and the waste post-HF s i l i c a . The mixture r a t i o of a compound which had these wastes and showed the optimum s t r e n g t h p r o p e r t i e s was proposed. Introduction The world energy c r i s i s forces a deep and precise analysis of used f i l l e r s upon the producers of rubber. These analysis should not be r e s t r i c t e d to the prices of p l a s t i c s , rubbers and f i l l e r s , but they must consider energy consumpt i o n and wearing out of processing machines. Kinds of f i l l e r s and methods of t h e i r a p p l i c a t i o n are usually kept secret by the producers and f o r t h i s reason, the i n f o r m a t i o n on f i l l e r s are very o f t e n not precise. There are four basic phases which can c o e x i s t in cements. These are: 3CaO.SiO 2, 2CaO.SiO 2, 3CaO.AI203 and 4CaO.AI203.Fe203. I t is the calcium s i l i cates t h a t can i n f l u e n c e the a p p l i c a t i o n of cement as the f i l l e r s of rubber compounds. The increase of chemical a f f i n i t y of the i n v e s t i g a t e d cement dust to polymer chains of rubber networks is of great importance, and at present, the i n v e s t i g a t i o n of t h i s increase towards more p l a s t i c s , before t h e i r p l a s t i c i z a t ion, is thoroughly c a r r i e d out. The mixing of cement with styrene-butadiene l a t e x is of considerable importance in the preparation of some new types of building materials. To achieve t h a t , the anionic s u r f a c e - a c t i v e agents are used which are introduced in order to obtain the desired d i s p e r s i o n and e m u l s i f i c a t i o n f o r the preparation of a co-polymer, as well as non-ionic surface a c t i v e agents which are added in order to s t a b i l i z e a polymer in a cement composition. 776
Vol. 14, No. 6
777 WASTE CEMENT DUSTS, FILLERS, RUBBER
The surface of cement dusts can be modified by the use of polyorganosiloxane compounds ( I ) , as well as alkoxysilane (2-6) and organotitanate (7,8) adhesion promoters. In our i n v e s t i g a t i o n s , we p a r t l y used the silane coupling agents to increase chemical a f f i n i t y of cement dusts towards a polymer (rubber). Experimental The i n v e s t i g a t i o n s of the waste cement dusts, dedusted by multicyclones in "Nowiny" cement p l a n t , together with the i n v e s t i g a t i o n s of the pretreated waste s i l i c a coming from the production of h y d r o f l u o r i c acid (post-HF s i l i c a ) , were carried out. The l a t t e r was used with the former as f i l l e r s in rubber compounds PM-75 commercially pure carbon black, produced in the USSR, was also used as a substitute for silica. The chemical c o n s t i t u t i o n of the investigated samples, the pH of water ext r a c t s and moisture content were determined. Specific surfaces were measured chromatographically ( I 0 ) . The whiteness degree of the waste cement dusts and s i l i c a were determined leucometrically. The Zeiss leucometer, with a 6V and 30W mercury lamp as a l i g h t source, and blue, 459 m~, as well as red, 614 my, were used. As a standard we used a f r e s h l y roasted barium sulphate. The a c t i v i t y of cement dust and waste s i l i c a were regulated througha change of h y d r o p h i l i c surfaces, p a r t l y or t o t a l l y , f o r hydrophobic ones. To do t h i s , some silanes were used to modify surfaces of these f i l l e r s . The modifications were c a r r i e d out in the semi-commercial scale ~y the use of a mixer of our own c o n s t r u c t i o n , which had the capacity of 3.5 dm3 ( I I ) . The following s i l a n e s , as the m o d i f i e r s , produced by Union Carbide Corporation (4), were used: A-189 A-172 A-IIO0
gamma-mercaptopropyltrimethoxysilane vinyl-tris(beta-methoxyethoxy)silane gamma-aminopropyltriethoxysilane
The silanes were added in the amounts of 0.5 - 3.0 parts by weight for a I00 parts by weight of f i l l e r . Because of the low e f f i c i e n c y of silane as a modifer of waste cement dusts, we t r i e d to mix cement with the post-HF waste s i l i c a , which is characterized by a considerably greater degree of i n t e r a c t i o n with the silane alkoxy groups. The choice of t h i s s i l i c a was dictated by i t s physico-chemical parameters, mainly p a r t i c l e diameters and s p e c i f i c surfaces, which are s i m i l a r to those of cement dust. Bulk density and packing density were determined by the use of a WE-5 electromagnetic volume i n d i c a t o r (12). Shaking down c o e f f i c i e n t as packing density and bulk d e n s i t y , the r a t i o of a loosely poured material was also calculated. To obtain a f u l l e r c h a r a c t e r i s t i c of the investigated f i l l e r s , the water and d i b u t y l p t h a l a t e absorbing capacities were determined. The amount of absorbed water depends on the surface development and on the degree of agglomeration of a f i l l e r . The end point of the investigated water absorbing capacity was taken the one in which one drop of water causes a clear f l u x i n g of the formeo paste. In terms of d i b u t y l p t h a l a t e , the end Doint was chosen as the one in which the consistency of paste changes rapidly and makes i t s t i c k to a glass plate. Heat of immersion was determined in a KRM d i f f e r e n t i a l calorimeter (13), using the e l e c t r i c method of the calorimeter capacity determination. Water and benzene immersion heat of modified and non-modified samples of waste s i l i c a and cement dust were measured. The observations of samples were carried out by the use of the intermediate s i n g l e - s t a g e r e p l i c a method (14) and a JEM-7A (Jeolco-
778
Vol. 14, No. 6 A. Krysztafkiewicz and M. Maik
Japan) over-exposure electron microscope. The next step was to i n v e s t i g a t e the Ker 1500 butadiene-styrene rubber compounds which contained waste cement dust. The mixture r a t i o is shown in Table I . TABLE 1 Mixture Ratio of the Ker 1500 Rubber Compound Based on Cement Dust Ingredient
A
Ker 1500 Stearin Accelerant M Sulphur Cement dust Zinc oxide
lO0 1 2 2 I00 -
Compound B (part by weight ) I00 1 2 2 I00 1
C I00 1 2 2 I00 2
Within each of the above A, B, and C compounds, the f o l l o w i n g samples of cement dust were introduced: (0) non-modified cement dust; ( I ) cement dust + 2 parts by weight of A-IIO0 s i l a n e ; (2) cement dust + 2 parts by weight of A-189 silane; and (3) cement dust + 2 parts by weight of A-172 s i l a n e . Cement dusts were also used to s u b s t i t u t e , p a r t l y or t o t a l l y , some r e i n f o r c i n g or semi-reinforcing f i l l e r s such as the PM-75 commercial carbon black and the waste post-HF silica. The compound r a t i o was as follows: Ker 1500 Stearin Cement Carbon black or s i l i c a Zinc oxide Benzothiazole disulphide Diphenyloguanidine Sulphur
I00 2 0-50 0-50 5 2.2 1.4 2
parts parts parts parts parts parts parts parts
by by by by by by by by
weight weight weight weight weight weight weight weight
The strength tests of the rubber vuncanizates were c a r r i e d out. In t h i s paper, we show the results of them for the v u l c a n i z a t i o n at 143°C f o r 30 minutes. Results Table 2 i l l u s t r a t e s the chemical analysis r e s u l t s of the "Nowiny" cement dust and the waste post-HF s i l i c a . Table 3 shows some physico-chemical fillers.
properties data of the non-modified
The results of immersion heat tests are shown in Table 4. I t shows that data for s i l i c a and cement dust modified by 3 parts by weight of the used s i lanes. The comparison of water and benzene immersion heat of the investigated f i l l e r samples modified by the A-189 s i l a n e , is shown in Figure I. Figure 2 shows the electron microscope photograph of cement dust, post-HF s i l i c a and the I : I mixture of them. The strength t e s t r e s u l t s of the compounds in Table I , f i l l e d with non-modified and alkoxysilane modified cement dusts, are shown in Table 5. Physico-mechanical indexes for the Ker 1500 rubbers, which have various amounts of the cement dust and the waste s i l i c a , are given in Table 6. Table 7 shows the same indexes for the Ker 1500 rubbers containing various amounts of
Vol. 14, No. 6
WASTE CEMENT DUSTS, FILLERS, RUBBER
779
TABLE 2 Chemical Constitution of the Investigated Cement Dusts and Semi-Reinforcing Post-HF Silica (average % by weight) "Nowiny" waste Dried waste Ingredient cement dust post-HF s i l i c a ~ SiO 2
24.58
88.42
AI203 CaO
4.58 57.80
2.20 1.63
FeO+Fe203 MgO F-
0.90 2.88 -
0.45 2.42
moisture
1.15
2.30
TABLE 3 Physico-ChemicalPropertiesData of the "Nowiny"Cement Dust and the Waste Post-HFSilica "Nowiny" Wastepost-HF Property
cement dust
silica
Water suspension pH 10.2 Specific gravity (g/cm 3) 5.42 Bulk density (g/dm3) ~ 634 Packing density (g/dm ~) 865 Shaking down coefficient 1.36 Water absorption (g/lOOg) Dibutyl pthalate absorption (g/lOOg) 62 Whiteness degree (!~) 32.1 Specific surface (m2/g) 10.5
2°~ [h FIih I~ Ce m ~ n t
25
dust
~ Io 5
Industr~oL b c ) -
,5
p, OCiuCt
/
o 5 ~r~r
~ p~,
2ph~
The influence of A-189 mercaptosilane quantity upon the immersion heat of modified waste silica and cement dust.
;.~..~...~
~~
,
Be"zene immersion
i
heat
'° s ~-~ T-~ ~-~q ~o .~,~l~
FiG. 1
~it]cc]
,
20
6.2 2.05 245 380 1.55 I00 90 70.7 42.1
~
Water immersion heat
:///~'.-/j./'.4
780
VoI. 14, No. 6 A. Krysztafkiewicz and M. Maik
TABLE 4 Water and Benzene Immersion Heat of Cement Dust and Waste Post-HF S i l i c a Kind of Sample • Waste post-HF silica Waste post-HF ÷ 3 parts by of A-189 Waste post-HF + 3 parts by of A-IIO0
Water Immersion Heat cal/g 'J/g
Benzene Immersion Heat c~I/~ J/g
2.42
10.13
2.45
10.23
silica weight
1.03
4.31
3.80
15.89
silica weight
2.86
11.95
3.40
14.31
5.63
23.52
1.94
8.13
4.55
19.02
2.25
9.41
5.80
24.24
2.15
8.99
IVaste cement dust Waste cement dust + 3 parts by weight of A-189 Waste cement dust + 3 parts by weight of A-IIO0
TABLE 5 Physico-Mechanical Properties of the Ker 1500 Rubber Vulcanizates F i l l e d with Non-Modified and Alkoxysilane Modified Cement Dusts Tensile strength (MPa)
Relative elongation (%)
Tensile set (%)
Hardness
a/o A/I A/2 A/3
2.72 3.24 4.14 3.80
680 720 760 520
40 44 36 32
61 60 68 67
B/O B/I B/2 B/3
3.30 4.25 4.58 4.45
580 600 540 540
24 24 28 28
66 65 68 65
C/O C/I C/2 C/3
3.67 4.80 5.73 5.30
550 600 560 420
28 28 28 28
65 65 65 65
Compound
(°SN)
the dust and the PM-75 commercial carbon black. Figure 3 shows the t e n s i l e strengths for rubbers f i l l e d with l : l mixture of the cement dust and the postHF s i l i c a modified by various silanes as a function of the silane amounts. Discussion Cement dust and post-HF s i l i c a have badly developed surfaces and as a res u l t of t h i s they belong to l i t t l e active f i l l e r s . In order to increase t h e i r
Vol. 14, No. 6
781
WASTE CEMENT DUSTS, FILLERS, RUBBER
(a)
(b)
(c)
FIG. 2 Electron-microscope photograph of the i n v e s t i g a t e d f i l l e r s . Magnification x 30.000. (a) cement dust; (b) Dos:-HF silica; (c) ] : ] mixture of cement dust and DOSt-HF s i l i c a .
782
Vol. 14,
No.
A. Krysztafkiewicz and M. Maik
TABLE 6 Physico-Mechanical Indexes for the Ker 1500 Rubbers Containing Various Amounts of the Non-Modified Cement Dust and the Post-HF S i l i c a . Vulcanization Parameters: Time - 30 minutes; Temperature - 143°C. Index
Tensile strength (MPa) Relative elongation (%) Tensile set (%) Modulus 300 (MPa)
Amount 0 Amount 5O
of cement dust (parts by weight) I0 20 30 40 50 of waste s i l i c a (parts by weight) 4O 3O 2O I0 0
5.6
5.0
4.2
3.9
3.4
2.8
310 I0 4.8
330 12 4.5
400 12 3.6
400 18 3.4
520 24 2.9
540 26 2.3
TABLE 7 Physico-Mechanical Indexes for the Ker 1500 Rubbers Containing Non-Modified Cement Dust and PM-75 Commercial Carbon Black. Vulcanization Parameters: Time - 30 minutes; Temperature - 143°C. Filler
Tensile strength (MPa)
Relative elongation (%)
Tensile set ,, (%)
Flexibility (%)
18.4
460
8
50
16.2
540
12
50
13.4
620
16
50
Commercial Carbon black (50 parts by weight) Carbon black + cement dust (I0 parts by weight) Carbon black (25 parts by weight) + cement dust (25 parts by weight)
~FIG. 3 The influence of the amount of silanes upon the tensile strength of rubbers f i l l e d with the I : I mixture of cement dust and post-HF si I i ca.
1~,o
I
/
,
~
/
~
~p -~ "~ ~
A- ~5c3 A - ~L A- ~
~),o 8,0 / ~ 6,o
~
/
"
:
o
~,o
2,0
,
3~ ~
, p~
r
6
VoI. 14, No. 6
783 WASTE CEMENT DUSTS, FILLERS, RUBBER
a c t i v i t y and chemical a f f i n i t y towards rubbers, i t is necessary to modify t h e i r surfaces. In our investigations, we used alkoxysilane adhesion promoters. We found that cement dusts undergo the influence of these silanes only s l i g h t l y , so we mixed them with s i l i c a which can be modified by the silanes very easily. When choosing the appropriate s i l i c a , we took into account p a r t i c l e sizes, so that the difference between the dust ones and the s i l i c a ones would be the smallest. For this reason, we used the post-HF s i l i c a , which is the waste s i l i c a from the HF production. Figure 3 confirms the s i m i l a r i t y of the p a r t i c l e sizes and shows that the dust and the s i l i c a were as thoroughly mixed as possible. Cement dusts are characterized by a low, s l i g h t l y about 30~ whiteness degree. S i l i c a , also, because of i t s impurities, e.g. AIF 3, CaF2, obtained during the production process, has a low, ca 70%, whiteness degree. The bulk density of cement dusts is high, over 600 g/dm3, while that of s i l ica is lower and amounts to about 250 g/dm3. The high values of bulk densities are the r e s u l t of considerably larger p a r t i c l e sizes which are, on the average, 80-100 nm and 100-150 nm for the s i l i c a and the dust, respectively. They are also the r e s u l t , as can be seen in the photographs, of badly developed external surfaces, The water and the dibutyl pthalate absorbing capacity is very low for both the cement dust and the waste s i l i c a . In terms of the dust, the water absorbing capacity can not be measured because of the cement setting. The dibutyl pthalate absorbing capacity of the dust and of the s i l i c a are 62 g/lOOg and 90 g/lOOg, respectively. I t must be said here that the dibutyl pthalate absorbing capacity values for the generally used s i l i c a and s l i c a t e f i l l e r s , in most cases exceed 200 g/lOOg and 300 g/lOOg. The very low dibutyl pthalate absorbing capacities prove once more the necessity of modification by the use of substances which increase the chemical a f f i n i t y towards hydrocarbon chains of a rubber. The hydrophobic properties of the investigated preparations can be calculated from the heat of the immersion results obtained by the KRM d i f f e r e n t i a l calorimeter method. The above data show that the water immersion heats decrease and the benzene immersion heats increase, when the dust and the s i l i c a surfaces are immersed in the A-189 mercaptosilane, as shown in Table 4. I t must be stressed that the modified cement dusts, contrary to the s i l i c a , change t h e i r water and benzene immersion heats only s l i g h t l y , which can be explained by a very weak i n t e r a c t i o n between silanes and the surface groups of cement dusts. Although the A-IIO0 aminosilane modification of the surfaces causes an increase of the water immersion heat, the benzene immersion heat is close to that of a surface modified by the use of A-189 silane. The increase of the water immersion heat is caused by the creation of hydrogen bonds between amine groups of the introduced silane and water molecules. The low immersion heat values of cement dust surfaces, even a f t e r t h e i r modification by the use of silanes, show the passive character of this rubber f i l l e r and confirms the proper usage of the waste s i l i c a together with the dust, as the rubber compound f i l l e r s . While introducing the waste cement dust and post-HF s i l i c a into the examined rubbers and mixing them on mixing r o l l s , no anomaly was observed. The physico-mechanical properties of the vulcanizates, f i r s t of a l l , depend on the size of the dust and the s i l i c a p a r t i c l e s , as well as the specific surfaces and the bulk densities of the dust and the s i l i c a . The character of a surface also exerts a considerable influence. Chemical a f f i n i t y , and what comes out of i t , strength parameters, depend to a great degree uDon the hydrophobic properties. In the Ker 1500 butadiene-styrene rubber vulcanizates, using an appropriate modification and a constant of 50 parts by weiaht, contents of a
784
Vol. 14, No. 6 A. Krysztafkiewicz and M. Maik
filler,
the following average tensile strengths were obtained:
Kind of F i l l e r
Rr(MPa)
Rubber industry l i m i t Ker 1500 rubber without f i l l e r s (with all the other components) Non-modified cement dust Cement dust + 2 parts by weight of A-llO0 Cement dust + post-HF s i l i c a (3:1) Cement dust + post-HF s i l i c a ( l : l ) Cement dust + post-HF s i l i c a ( l : l ) + 3 parts by weight of A-189 Cement dust + PM-75 carbon black ( l : l )
90 - lO0 20 40 60 60 70 llO 135
The above data prove the advantage of the last two systems which can, to a certain extent, eliminate carbon black. Conclusions The investigations proved that cement dust can be a cheap, low-active f i l ler and can be recommended, partly, as a substitute for commercial carbon black and s i l i c a in the recipe for the Ker 1500 butadiene-styrene rubber compounds. The system consisting of 25 parts by weight of the post-HF s i l i c a and 25 parts by weight of the dust modified, in terms of the butadiene-styrene rubbers, by A-189 mercaptosilane, or even a better one consisting of 25 parts by weight of the dust and 25 parts by weight of commercial carbon black, can be proposed. The later one allows eliminating the high energy-consuming carbon black by up to 50%. Apart from the satisfying results of tensile strengths and modulus, the above investigations proved nearly the same values of tension set for both samples and only s l i g h t increase of t h e i r e l a s t i c i t y . References I. 2. 3. 4. 5. 6. 7. 8. 9. lO. II. 12. 13. 14.
R. Bode, H. Ferch and H. Tvatzscher, Kautschuk und Gummi 20, 578 (1967). M. Kranz, L. Domka, A. Krysztafkiewicz and M. Maik, Polimery 24, 86 (1979). F. Thurn and S. Wolff, Kaut. u. Gum. Kunstst. 2~8, 733 (1975) - Union Carbide-Akzo-Symp. "Stomil" Zakopane, 1974 (Poland). Wacker Silanes f~r i n d u s t r i e l l e Anwendungen, M~nchen, July 1975. Chwan-HwaChiang, Nan-I-liu and J.L. Koenig, J. Colloid Inter.Sci. 8~6, 26 (1982). S.J. Monte, "Coupling Agents-Titanate" Modern Plastics Encyclopedia, October 1977, Vol. 54, Number lO A. S.J. I~onte, G. Sugerman and D.J. Seeman, "Titanate Coupling Agents - Current Applications," Kenrich Petrochemicals, Inc., American Chemical Society, Rubber Division, Chicago, I~ay 1977. A. Krysztafkiewicz, L. Domka and W. Wieczorek, Polimery 2~6, 221 (1981). T. Paryjczak "Chromatografia gazowa w badaniach adsorpcji i katalizy" PlaN Warszawa, 1975o L. Domka and A. Krysztafkiewicz, Polish pat. l l 9 358 (1982). Polish pat. 45 878 20-1V (1957). W. Zielenkiewicz and K. Kurek, Przem. Chem. 45, 247 (1966). D.E. Bradley, B r i t . J. Appl. Phys. 2, 65 (19~'7[).
WASTE CEMENT DUSTS AS FILLERS FOR RUBBER COMPOUNDS Andrzej K r y s z t a f k i e w i c z and Marek Maik I n s t i t u t e of Chemical and Engineering Technology P o l i t e c h n i k a Pozna6ska 60-965 Pozna~, Poland (Communicated by D.M. Roy) (Received May 13, 1983; in f i n a l form March 15, 1984)
ABSTRACT The p o s s i b i l i t y of s u b s t i t u t i o n of expensive a c t i v e f i l l e r s , e.g. carbon black, f o r the waste products which can play the r o l e of these filllers, e.g. the waste cement dusts or the waste post-HF s i l i c a , were i n v e s t i g a t e d . The physico-chemical p r o p e r t i e s of the i n v e s t i gated waste cement dusts and the waste post-HF s i l i c a , as well as the s t r e n g t h p r o p e r t i e s of the rubber compounds containing these as fillers, were determined. To increase the a c t i v i t y and chemical a f f i n i t y w i t h the rubber, the waste cement dusts and the waste post-HF s i l i c a were modified by the use of adhesion promoters, that is alkoxysilanes. I t was found t h a t i t would be possible to p a r t l y s u b s t i t u t e carbon black f o r the waste cement dusts and the waste post-HF s i l i c a . The mixture r a t i o of a compound which had these wastes and showed the optimum s t r e n g t h p r o p e r t i e s was proposed. Introduction The world energy c r i s i s forces a deep and precise analysis of used f i l l e r s upon the producers of rubber. These analysis should not be r e s t r i c t e d to the prices of p l a s t i c s , rubbers and f i l l e r s , but they must consider energy consumpt i o n and wearing out of processing machines. Kinds of f i l l e r s and methods of t h e i r a p p l i c a t i o n are usually kept secret by the producers and f o r t h i s reason, the i n f o r m a t i o n on f i l l e r s are very o f t e n not precise. There are four basic phases which can c o e x i s t in cements. These are: 3CaO.SiO 2, 2CaO.SiO 2, 3CaO.AI203 and 4CaO.AI203.Fe203. I t is the calcium s i l i cates t h a t can i n f l u e n c e the a p p l i c a t i o n of cement as the f i l l e r s of rubber compounds. The increase of chemical a f f i n i t y of the i n v e s t i g a t e d cement dust to polymer chains of rubber networks is of great importance, and at present, the i n v e s t i g a t i o n of t h i s increase towards more p l a s t i c s , before t h e i r p l a s t i c i z a t ion, is thoroughly c a r r i e d out. The mixing of cement with styrene-butadiene l a t e x is of considerable importance in the preparation of some new types of building materials. To achieve t h a t , the anionic s u r f a c e - a c t i v e agents are used which are introduced in order to obtain the desired d i s p e r s i o n and e m u l s i f i c a t i o n f o r the preparation of a co-polymer, as well as non-ionic surface a c t i v e agents which are added in order to s t a b i l i z e a polymer in a cement composition. 776
Vol. 14, No. 6
777 WASTE CEMENT DUSTS, FILLERS, RUBBER
The surface of cement dusts can be modified by the use of polyorganosiloxane compounds ( I ) , as well as alkoxysilane (2-6) and organotitanate (7,8) adhesion promoters. In our i n v e s t i g a t i o n s , we p a r t l y used the silane coupling agents to increase chemical a f f i n i t y of cement dusts towards a polymer (rubber). Experimental The i n v e s t i g a t i o n s of the waste cement dusts, dedusted by multicyclones in "Nowiny" cement p l a n t , together with the i n v e s t i g a t i o n s of the pretreated waste s i l i c a coming from the production of h y d r o f l u o r i c acid (post-HF s i l i c a ) , were carried out. The l a t t e r was used with the former as f i l l e r s in rubber compounds PM-75 commercially pure carbon black, produced in the USSR, was also used as a substitute for silica. The chemical c o n s t i t u t i o n of the investigated samples, the pH of water ext r a c t s and moisture content were determined. Specific surfaces were measured chromatographically ( I 0 ) . The whiteness degree of the waste cement dusts and s i l i c a were determined leucometrically. The Zeiss leucometer, with a 6V and 30W mercury lamp as a l i g h t source, and blue, 459 m~, as well as red, 614 my, were used. As a standard we used a f r e s h l y roasted barium sulphate. The a c t i v i t y of cement dust and waste s i l i c a were regulated througha change of h y d r o p h i l i c surfaces, p a r t l y or t o t a l l y , f o r hydrophobic ones. To do t h i s , some silanes were used to modify surfaces of these f i l l e r s . The modifications were c a r r i e d out in the semi-commercial scale ~y the use of a mixer of our own c o n s t r u c t i o n , which had the capacity of 3.5 dm3 ( I I ) . The following s i l a n e s , as the m o d i f i e r s , produced by Union Carbide Corporation (4), were used: A-189 A-172 A-IIO0
gamma-mercaptopropyltrimethoxysilane vinyl-tris(beta-methoxyethoxy)silane gamma-aminopropyltriethoxysilane
The silanes were added in the amounts of 0.5 - 3.0 parts by weight for a I00 parts by weight of f i l l e r . Because of the low e f f i c i e n c y of silane as a modifer of waste cement dusts, we t r i e d to mix cement with the post-HF waste s i l i c a , which is characterized by a considerably greater degree of i n t e r a c t i o n with the silane alkoxy groups. The choice of t h i s s i l i c a was dictated by i t s physico-chemical parameters, mainly p a r t i c l e diameters and s p e c i f i c surfaces, which are s i m i l a r to those of cement dust. Bulk density and packing density were determined by the use of a WE-5 electromagnetic volume i n d i c a t o r (12). Shaking down c o e f f i c i e n t as packing density and bulk d e n s i t y , the r a t i o of a loosely poured material was also calculated. To obtain a f u l l e r c h a r a c t e r i s t i c of the investigated f i l l e r s , the water and d i b u t y l p t h a l a t e absorbing capacities were determined. The amount of absorbed water depends on the surface development and on the degree of agglomeration of a f i l l e r . The end point of the investigated water absorbing capacity was taken the one in which one drop of water causes a clear f l u x i n g of the formeo paste. In terms of d i b u t y l p t h a l a t e , the end Doint was chosen as the one in which the consistency of paste changes rapidly and makes i t s t i c k to a glass plate. Heat of immersion was determined in a KRM d i f f e r e n t i a l calorimeter (13), using the e l e c t r i c method of the calorimeter capacity determination. Water and benzene immersion heat of modified and non-modified samples of waste s i l i c a and cement dust were measured. The observations of samples were carried out by the use of the intermediate s i n g l e - s t a g e r e p l i c a method (14) and a JEM-7A (Jeolco-
778
Vol. 14, No. 6 A. Krysztafkiewicz and M. Maik
Japan) over-exposure electron microscope. The next step was to i n v e s t i g a t e the Ker 1500 butadiene-styrene rubber compounds which contained waste cement dust. The mixture r a t i o is shown in Table I . TABLE 1 Mixture Ratio of the Ker 1500 Rubber Compound Based on Cement Dust Ingredient
A
Ker 1500 Stearin Accelerant M Sulphur Cement dust Zinc oxide
lO0 1 2 2 I00 -
Compound B (part by weight ) I00 1 2 2 I00 1
C I00 1 2 2 I00 2
Within each of the above A, B, and C compounds, the f o l l o w i n g samples of cement dust were introduced: (0) non-modified cement dust; ( I ) cement dust + 2 parts by weight of A-IIO0 s i l a n e ; (2) cement dust + 2 parts by weight of A-189 silane; and (3) cement dust + 2 parts by weight of A-172 s i l a n e . Cement dusts were also used to s u b s t i t u t e , p a r t l y or t o t a l l y , some r e i n f o r c i n g or semi-reinforcing f i l l e r s such as the PM-75 commercial carbon black and the waste post-HF silica. The compound r a t i o was as follows: Ker 1500 Stearin Cement Carbon black or s i l i c a Zinc oxide Benzothiazole disulphide Diphenyloguanidine Sulphur
I00 2 0-50 0-50 5 2.2 1.4 2
parts parts parts parts parts parts parts parts
by by by by by by by by
weight weight weight weight weight weight weight weight
The strength tests of the rubber vuncanizates were c a r r i e d out. In t h i s paper, we show the results of them for the v u l c a n i z a t i o n at 143°C f o r 30 minutes. Results Table 2 i l l u s t r a t e s the chemical analysis r e s u l t s of the "Nowiny" cement dust and the waste post-HF s i l i c a . Table 3 shows some physico-chemical fillers.
properties data of the non-modified
The results of immersion heat tests are shown in Table 4. I t shows that data for s i l i c a and cement dust modified by 3 parts by weight of the used s i lanes. The comparison of water and benzene immersion heat of the investigated f i l l e r samples modified by the A-189 s i l a n e , is shown in Figure I. Figure 2 shows the electron microscope photograph of cement dust, post-HF s i l i c a and the I : I mixture of them. The strength t e s t r e s u l t s of the compounds in Table I , f i l l e d with non-modified and alkoxysilane modified cement dusts, are shown in Table 5. Physico-mechanical indexes for the Ker 1500 rubbers, which have various amounts of the cement dust and the waste s i l i c a , are given in Table 6. Table 7 shows the same indexes for the Ker 1500 rubbers containing various amounts of
Vol. 14, No. 6
WASTE CEMENT DUSTS, FILLERS, RUBBER
779
TABLE 2 Chemical Constitution of the Investigated Cement Dusts and Semi-Reinforcing Post-HF Silica (average % by weight) "Nowiny" waste Dried waste Ingredient cement dust post-HF s i l i c a ~ SiO 2
24.58
88.42
AI203 CaO
4.58 57.80
2.20 1.63
FeO+Fe203 MgO F-
0.90 2.88 -
0.45 2.42
moisture
1.15
2.30
TABLE 3 Physico-ChemicalPropertiesData of the "Nowiny"Cement Dust and the Waste Post-HFSilica "Nowiny" Wastepost-HF Property
cement dust
silica
Water suspension pH 10.2 Specific gravity (g/cm 3) 5.42 Bulk density (g/dm3) ~ 634 Packing density (g/dm ~) 865 Shaking down coefficient 1.36 Water absorption (g/lOOg) Dibutyl pthalate absorption (g/lOOg) 62 Whiteness degree (!~) 32.1 Specific surface (m2/g) 10.5
2°~ [h FIih I~ Ce m ~ n t
25
dust
~ Io 5
Industr~oL b c ) -
,5
p, OCiuCt
/
o 5 ~r~r
~ p~,
2ph~
The influence of A-189 mercaptosilane quantity upon the immersion heat of modified waste silica and cement dust.
;.~..~...~
~~
,
Be"zene immersion
i
heat
'° s ~-~ T-~ ~-~q ~o .~,~l~
FiG. 1
~it]cc]
,
20
6.2 2.05 245 380 1.55 I00 90 70.7 42.1
~
Water immersion heat
:///~'.-/j./'.4
780
VoI. 14, No. 6 A. Krysztafkiewicz and M. Maik
TABLE 4 Water and Benzene Immersion Heat of Cement Dust and Waste Post-HF S i l i c a Kind of Sample • Waste post-HF silica Waste post-HF ÷ 3 parts by of A-189 Waste post-HF + 3 parts by of A-IIO0
Water Immersion Heat cal/g 'J/g
Benzene Immersion Heat c~I/~ J/g
2.42
10.13
2.45
10.23
silica weight
1.03
4.31
3.80
15.89
silica weight
2.86
11.95
3.40
14.31
5.63
23.52
1.94
8.13
4.55
19.02
2.25
9.41
5.80
24.24
2.15
8.99
IVaste cement dust Waste cement dust + 3 parts by weight of A-189 Waste cement dust + 3 parts by weight of A-IIO0
TABLE 5 Physico-Mechanical Properties of the Ker 1500 Rubber Vulcanizates F i l l e d with Non-Modified and Alkoxysilane Modified Cement Dusts Tensile strength (MPa)
Relative elongation (%)
Tensile set (%)
Hardness
a/o A/I A/2 A/3
2.72 3.24 4.14 3.80
680 720 760 520
40 44 36 32
61 60 68 67
B/O B/I B/2 B/3
3.30 4.25 4.58 4.45
580 600 540 540
24 24 28 28
66 65 68 65
C/O C/I C/2 C/3
3.67 4.80 5.73 5.30
550 600 560 420
28 28 28 28
65 65 65 65
Compound
(°SN)
the dust and the PM-75 commercial carbon black. Figure 3 shows the t e n s i l e strengths for rubbers f i l l e d with l : l mixture of the cement dust and the postHF s i l i c a modified by various silanes as a function of the silane amounts. Discussion Cement dust and post-HF s i l i c a have badly developed surfaces and as a res u l t of t h i s they belong to l i t t l e active f i l l e r s . In order to increase t h e i r
Vol. 14, No. 6
781
WASTE CEMENT DUSTS, FILLERS, RUBBER
(a)
(b)
(c)
FIG. 2 Electron-microscope photograph of the i n v e s t i g a t e d f i l l e r s . Magnification x 30.000. (a) cement dust; (b) Dos:-HF silica; (c) ] : ] mixture of cement dust and DOSt-HF s i l i c a .
782
Vol. 14,
No.
A. Krysztafkiewicz and M. Maik
TABLE 6 Physico-Mechanical Indexes for the Ker 1500 Rubbers Containing Various Amounts of the Non-Modified Cement Dust and the Post-HF S i l i c a . Vulcanization Parameters: Time - 30 minutes; Temperature - 143°C. Index
Tensile strength (MPa) Relative elongation (%) Tensile set (%) Modulus 300 (MPa)
Amount 0 Amount 5O
of cement dust (parts by weight) I0 20 30 40 50 of waste s i l i c a (parts by weight) 4O 3O 2O I0 0
5.6
5.0
4.2
3.9
3.4
2.8
310 I0 4.8
330 12 4.5
400 12 3.6
400 18 3.4
520 24 2.9
540 26 2.3
TABLE 7 Physico-Mechanical Indexes for the Ker 1500 Rubbers Containing Non-Modified Cement Dust and PM-75 Commercial Carbon Black. Vulcanization Parameters: Time - 30 minutes; Temperature - 143°C. Filler
Tensile strength (MPa)
Relative elongation (%)
Tensile set ,, (%)
Flexibility (%)
18.4
460
8
50
16.2
540
12
50
13.4
620
16
50
Commercial Carbon black (50 parts by weight) Carbon black + cement dust (I0 parts by weight) Carbon black (25 parts by weight) + cement dust (25 parts by weight)
~FIG. 3 The influence of the amount of silanes upon the tensile strength of rubbers f i l l e d with the I : I mixture of cement dust and post-HF si I i ca.
1~,o
I
/
,
~
/
~
~p -~ "~ ~
A- ~5c3 A - ~L A- ~
~),o 8,0 / ~ 6,o
~
/
"
:
o
~,o
2,0
,
3~ ~
, p~
r
6
VoI. 14, No. 6
783 WASTE CEMENT DUSTS, FILLERS, RUBBER
a c t i v i t y and chemical a f f i n i t y towards rubbers, i t is necessary to modify t h e i r surfaces. In our investigations, we used alkoxysilane adhesion promoters. We found that cement dusts undergo the influence of these silanes only s l i g h t l y , so we mixed them with s i l i c a which can be modified by the silanes very easily. When choosing the appropriate s i l i c a , we took into account p a r t i c l e sizes, so that the difference between the dust ones and the s i l i c a ones would be the smallest. For this reason, we used the post-HF s i l i c a , which is the waste s i l i c a from the HF production. Figure 3 confirms the s i m i l a r i t y of the p a r t i c l e sizes and shows that the dust and the s i l i c a were as thoroughly mixed as possible. Cement dusts are characterized by a low, s l i g h t l y about 30~ whiteness degree. S i l i c a , also, because of i t s impurities, e.g. AIF 3, CaF2, obtained during the production process, has a low, ca 70%, whiteness degree. The bulk density of cement dusts is high, over 600 g/dm3, while that of s i l ica is lower and amounts to about 250 g/dm3. The high values of bulk densities are the r e s u l t of considerably larger p a r t i c l e sizes which are, on the average, 80-100 nm and 100-150 nm for the s i l i c a and the dust, respectively. They are also the r e s u l t , as can be seen in the photographs, of badly developed external surfaces, The water and the dibutyl pthalate absorbing capacity is very low for both the cement dust and the waste s i l i c a . In terms of the dust, the water absorbing capacity can not be measured because of the cement setting. The dibutyl pthalate absorbing capacity of the dust and of the s i l i c a are 62 g/lOOg and 90 g/lOOg, respectively. I t must be said here that the dibutyl pthalate absorbing capacity values for the generally used s i l i c a and s l i c a t e f i l l e r s , in most cases exceed 200 g/lOOg and 300 g/lOOg. The very low dibutyl pthalate absorbing capacities prove once more the necessity of modification by the use of substances which increase the chemical a f f i n i t y towards hydrocarbon chains of a rubber. The hydrophobic properties of the investigated preparations can be calculated from the heat of the immersion results obtained by the KRM d i f f e r e n t i a l calorimeter method. The above data show that the water immersion heats decrease and the benzene immersion heats increase, when the dust and the s i l i c a surfaces are immersed in the A-189 mercaptosilane, as shown in Table 4. I t must be stressed that the modified cement dusts, contrary to the s i l i c a , change t h e i r water and benzene immersion heats only s l i g h t l y , which can be explained by a very weak i n t e r a c t i o n between silanes and the surface groups of cement dusts. Although the A-IIO0 aminosilane modification of the surfaces causes an increase of the water immersion heat, the benzene immersion heat is close to that of a surface modified by the use of A-189 silane. The increase of the water immersion heat is caused by the creation of hydrogen bonds between amine groups of the introduced silane and water molecules. The low immersion heat values of cement dust surfaces, even a f t e r t h e i r modification by the use of silanes, show the passive character of this rubber f i l l e r and confirms the proper usage of the waste s i l i c a together with the dust, as the rubber compound f i l l e r s . While introducing the waste cement dust and post-HF s i l i c a into the examined rubbers and mixing them on mixing r o l l s , no anomaly was observed. The physico-mechanical properties of the vulcanizates, f i r s t of a l l , depend on the size of the dust and the s i l i c a p a r t i c l e s , as well as the specific surfaces and the bulk densities of the dust and the s i l i c a . The character of a surface also exerts a considerable influence. Chemical a f f i n i t y , and what comes out of i t , strength parameters, depend to a great degree uDon the hydrophobic properties. In the Ker 1500 butadiene-styrene rubber vulcanizates, using an appropriate modification and a constant of 50 parts by weiaht, contents of a
784
Vol. 14, No. 6 A. Krysztafkiewicz and M. Maik
filler,
the following average tensile strengths were obtained:
Kind of F i l l e r
Rr(MPa)
Rubber industry l i m i t Ker 1500 rubber without f i l l e r s (with all the other components) Non-modified cement dust Cement dust + 2 parts by weight of A-llO0 Cement dust + post-HF s i l i c a (3:1) Cement dust + post-HF s i l i c a ( l : l ) Cement dust + post-HF s i l i c a ( l : l ) + 3 parts by weight of A-189 Cement dust + PM-75 carbon black ( l : l )
90 - lO0 20 40 60 60 70 llO 135
The above data prove the advantage of the last two systems which can, to a certain extent, eliminate carbon black. Conclusions The investigations proved that cement dust can be a cheap, low-active f i l ler and can be recommended, partly, as a substitute for commercial carbon black and s i l i c a in the recipe for the Ker 1500 butadiene-styrene rubber compounds. The system consisting of 25 parts by weight of the post-HF s i l i c a and 25 parts by weight of the dust modified, in terms of the butadiene-styrene rubbers, by A-189 mercaptosilane, or even a better one consisting of 25 parts by weight of the dust and 25 parts by weight of commercial carbon black, can be proposed. The later one allows eliminating the high energy-consuming carbon black by up to 50%. Apart from the satisfying results of tensile strengths and modulus, the above investigations proved nearly the same values of tension set for both samples and only s l i g h t increase of t h e i r e l a s t i c i t y . References I. 2. 3. 4. 5. 6. 7. 8. 9. lO. II. 12. 13. 14.
R. Bode, H. Ferch and H. Tvatzscher, Kautschuk und Gummi 20, 578 (1967). M. Kranz, L. Domka, A. Krysztafkiewicz and M. Maik, Polimery 24, 86 (1979). F. Thurn and S. Wolff, Kaut. u. Gum. Kunstst. 2~8, 733 (1975) - Union Carbide-Akzo-Symp. "Stomil" Zakopane, 1974 (Poland). Wacker Silanes f~r i n d u s t r i e l l e Anwendungen, M~nchen, July 1975. Chwan-HwaChiang, Nan-I-liu and J.L. Koenig, J. Colloid Inter.Sci. 8~6, 26 (1982). S.J. Monte, "Coupling Agents-Titanate" Modern Plastics Encyclopedia, October 1977, Vol. 54, Number lO A. S.J. I~onte, G. Sugerman and D.J. Seeman, "Titanate Coupling Agents - Current Applications," Kenrich Petrochemicals, Inc., American Chemical Society, Rubber Division, Chicago, I~ay 1977. A. Krysztafkiewicz, L. Domka and W. Wieczorek, Polimery 2~6, 221 (1981). T. Paryjczak "Chromatografia gazowa w badaniach adsorpcji i katalizy" PlaN Warszawa, 1975o L. Domka and A. Krysztafkiewicz, Polish pat. l l 9 358 (1982). Polish pat. 45 878 20-1V (1957). W. Zielenkiewicz and K. Kurek, Przem. Chem. 45, 247 (1966). D.E. Bradley, B r i t . J. Appl. Phys. 2, 65 (19~'7[).