Effect of surface treatments on rheological ...

Effect of Surface Treatments on Rheological, Mechanical and Magnetic Properties of Ferrite-Filled Polymeric Systems D. R. SAINI, A. V. SHENOY, and V. M. NADKARNI Polymer Science and Engineering Group Chemical Engineering Division National Chemical Laboratory Pune 41 1 008, India Experimental data on the effect of the type and amount of surface treating agents on the rheological and mechanical properties of the ferrite-filled styrene-isoprene-styrene systems at high levels of loading has been presented. The viscosities of the treated ferrite systems are found to be lower than the untreated systems, with the extent in reduction depending upon the type and amount of surface treatment. It is also found that surface treatment decreases the tensile strength and percentage elongation in the present filler-matrix system, and the extent of the decrease in viscosity as well as mechanical properties is more in the presence of titanates than with silanes. INTRODUCTION

S

urface treatment of fillers to improve polymerfiller interaction has become common during the last decade (1) and a number of publications have recently appeared (2-1 1) dealing with the effect of surface modifiers such as silanes, titanates, phosphates, etc. on the rheological and mechanical properties of composites. Filled polymeric systems are no longer novelty materials as they have been used in a wide variety of applications for more than two decades. However, in most applications, the filler level is not usually greater than 50 percent by volume. Recently, there have been attempts to obtain specialized properties through the use of fillers with very high levels of loading in excess of 50 percent. One use of very high levels of filler loading is in the preparation of magnetic polymer composites (12-15). Ferrite loadings in the range of 60 to 70 percent by volume (87 to 92 percent by weight) are known to give desirable magnetic properties. Highly filled polymers often exhibit poor dispersion and reduced processibility. Improvement in the dispersion level and processibility can be attempted through the use of surface treatment of the fillers. The present paper deals with a study of the effect of type and amount of surface treating agents on the rheological and mechanical properties of 85 percent by weight barium ferrite filled styreneisoprene-styrene (SIS) composites. The polymer matrix (SIS) used in the present study is a thermoplastic elastomer which has not yet been commercially exploited for the preparation of magnetic polymer composites but shows considerable prom-

ise because of its ease of processibilitv, abrasion resistance, and toughness. The essential'features of the present work include the effect of surface treatment of ferrites on the rheological and mechanical properties of the composite at very high loadings and in a novel elastomeric matrix that would hold great promise for the manufacture of flexible magnets. EXPERIMENTAL Materials Filler-Platelet-shaped barium ferrite (BaFelzsupplied by Morris-Electronics, Pune, India, having a specific gravity of 4.0 and average particle size of 3 microns. Matrix-Styrene-isoprene-styrene Kraton 1107 supplied by Shell Chemie, Switzerland. Surface Treating Agents-The silane and titanate surface modifiers used are given in Table 1 . The silanes were supplied by Dow Chemical and the titanates were made available through the agent of Kenrich Petrochemicals in India (Technical Works & Industrial Link Ltd., D.N. Road, Bombay). 019)

Method of Barium Ferrite Surface Treatment Slurry treatment techniques were employed for surface treating the barium ferrites. The slurries were prepared by procedures recommended by Dow Chemical for silanes and by Kenrich Petrochemicals for titanates. A solution of 95 parts methanol and 5 parts water by volume was prepared for the silanes whereas the titanate solution was pre-

POLYMER ENGINEERING AND SCIENCE, SEPTEMBER, 1985, Vol. 25, No. 13

807

D. R. Saini, A. V. Shenoy, and V. M . Nadkarni

pared using xylene. The surface modifier amount equal to 1 percent by weight of barium ferrites was dispersed in the solvents. The slurry was formed by wetting the required quantity of barium ferrites with the prepared solution and stirring with a glass rod for about 30 min. It was allowed to stand overnight and then the solvent removed in an oven at 105°C for silanes and 130°C for titanates. A similar treatment procedure was used for KR TTS titanate with varying amounts, such as to get different levels of treatment of 0.5, 1.5, and 2.0 percent by weight of barium ferrite.

in a room conditioned at 22°C. The tensile strengths at yield and break, and the secant modulus at 1 percent strain were calculated from the stress-strain curves. The percentage elongation was obtained through the use of the 10 percent incremental extensometer. The above mechanical testing was done as per ASTM D638. The hardness of the composite specimens was measured using a ShoreDurometer as per ASTM D2240.

Compounding and Preparation of Test Specimens

Figure 1 shows the changes in the viscosity vs. shear rate behavior of 85 percent by weight ferritefilled SIS system with different types of surface treatment. The viscosity of the treated ferrite system in all cases is lower than the untreated ferrite composite and the reduction in viscosity is dependent upon the type of surface treatment. Silanes

The treated barium ferrite along with the required quantity of SIS Kraton 1107 to form an 85 percent by weight filled system was fed into the 70 cc mixing chamber of a C.W. Brabender Plasticorder PLE 330. The blending was done at 180°C with the help of roller type mixing blades at 125 rpm. The blending was continued till the recorded torque reached an equilibrium value. For mechanical property measurements, dumbbell-shaped specimens were compression molded at 180°C as per ASTM D638.

RESULTS AND DISCUSSION Rheological Behavior

A

- F L I R l T E TREATED

WITH S L I M E - 2 6 0 7 6

II - F E R R I T E TREATED WITH SIl.ANE-26OTI

Testing Methods

Rheological Measurements Viscosity vs. shear rate data at 220°C for the composites studied were generated using an Instron Capillary Rheometer Model 3211 fitted with a 0.1.52 cm diameter and 2.55 cm length capillary. The procedure as given in the Instron Capillary Rheometer Manual was followed in order to obtain this data.

Mechanical Property Measurements Tensile strength and percentage elongation measurements were performed on an Instron universal testing machine model 1122 in the extension mode at 10 mm/min extension rate using a 50 kg load cell

It1 A P P A R E N T S H E A R R A T E . S d '

Fig 1 Apparent vascosity vs apparent shear rate curves for unfilled, 85 percent untreated ferrite-jilled and 85 percent treated ferrite-filled SIS block copolymer systems at 220°C

Table 1. Summary of the Surface Modifiers Investigated

Trade Codes

Chemical Description

Chemical Structure

0 Z 6075

II

Vinyltriacetoxy silane

Z 6076

Chloropropyltrimethoxy silane

CH;F----CH Si(OCCH3)3 CI(CH2)3Si(OCH3)2 CH3 I

KR 38s

lsopropyl tri(diocty1pyrophosphato)-titanate

CHAH-0-Ti

O\O-C8Hi,\ II /

0-PaOH

P O-CsHi7

3

0

II KR 138s

Titanium di(dioctylpyrophosphate)-oxyacetate

KR TTS

lsopropyl triisostearoyl titanate

0

CH3 CH5-CH-O-Ti 808

0-C-CI7Hs


Rheology, Mechanical and Magnetic Properties of Ferrite-Filled Polymeric Systems

show only a marginal effect in decreasing the viscosity while titanates have a far more profound effect. There exists no convincing explanation for the observed drastic decrease in viscosity by titanate surface modifiers though it has been postulated (5, 16-19) that they have a tendency of producing a plasticizing effect due to the modification of the interfacial characteristics of the filled system. Titanates may be acting as dispersing agents in the present case instead of providing a chemical bridge between the polymer and filler particle. This is evident from the scanning electron microscope pictures shown in Fig. 2 . Titanates are found to provide a better dispersion as can be seen from Figs. 2e to 2g in comparison with silanes from Figs. 2c and d . In order to find the optimum amount of surface treating agent to get maximum benefits in processing of such highly filled systems, a rheological study was carried out at 720°C with SIS matrix filled with 85 percent barium ferrite treated with KR TTS. The results of this study are shown in Fig. 3. The viscosity ratio qcA/qwcA, namely, the viscosity of the

system with the surface modifier totthe viscosity of the system without the surface modifier at a shear rate level of 100 sec-' was used for generating the curve shown in Fig. 3. It is seen that about 0.8 to 1.0 percent of the surface modifier KR TTS provides the most efficient use of the material for reduction in viscosity. Increasing the quantity beyond 1 percent would not provide any further significant benefits to ease processing.

Mechanical Behavior

Table 2 summarizes the effect of surface modifiers on the mechanical properties of the ferritefilled SIS systems in terms of tensile strength at break and yield, percentage elongation at break and yield, and the hardness. Surface treatment has been found to decrease the tensile strength at break and yield; the maximum decrease in the tensile strength at break of the order of 60 percent and in the tensile strength at yield of the order of 80 percent was found to be in the case of KR TTS. The

(C)

.-.c

~~

(d)

Fig. 2 SEM micrograph of fracture surfaces for SIS matrices-unfilled (a), 85 percent ferrite-filled untreated (b), silane (Z 6076) treated (c), silanv (26075) treated (d), titanate (KR 38s) treated (e), titanate (KR 138s) treated ( f ) , titanate (KR TTS) treated (g).


809

D. R. Saini, A. V. Shenoy, and V. M . Nadkarni

(el

i

0 4 L DO

0 5

I .o Y.

TTS

1,s

2.0

I

4

Fig. 3. Variation of the viscosity ratio at shear rate = 100 sec-' of treated to untreated 85 percent ferritefilled SIS with percentage of K R TTS, for determining the optimum treatment level.

percentage elongation at break decreased by about 45 percent and that at yield by about 75 percent in the case of KR 138s treated systems. The effects on the mechanical properties are more adverse in the case of titanates than silanes. This behavior can 810

be explained on the basis of the plasticizing effect produced by the presence of certain surface modifiers as has been observed by earlier workers (5). The results of the present work are in general agreement with a number of investigations available in the literature (4,5, 11).As regards the hardness of the samples, the final reading after firm contact with the specimen was measured and the range of values shown in Table 2 represent the obtained values at various points of each sample. It is seen that titanates reduce the hardness of the 85 percent filled systems to a very significant extent. This again is due to the improved dispersion of filler and the plasticizing effect of the surface modifier. CONCLUSIONS The effect of type and amount of surface treating agents on the rheological and mechanical properties of 85 percent by weight barium ferrite filled SIS block copolymer has been elucidated. It has been found that the surface modifiers used in the present work helped in decreasing the viscosity of

POLYMER ENGlNEERlNG AND SCIENCE, SEPTEMBER, 7985, Yo/. 25, No. 13

Rheology, Mechanical and Magnetic Properties of Ferrite-Filled Polymeric Systems Table 2. Summary of the Effect of Surface Modifiers on Mechanical Properties

SIS content (YOby weight) by /. Barium ferrite content (“ weight) Amount of surface modifier (“/o by wt. of ferrite) Type of surface modifier Tensile strength at Break fMPa) Tensile strength at yield (MPa) O/O Elongation at break o/o Elongation at yield Secant modulus (MPa) at strain = 0.01 Hardness-Shore-A ~

100 0

15 85

15 85

15 85

15 85

15 85

15 85

0

0

1

1

1

1

1

-

1.01

0.275

Z 6075 0.48

0.97

Z 6076 0.54

0.235

KR 38s 0.49

0.255

0.275

KR 138s 0.5 0.235

KR TTS 0.38

0.196

38.0 4.41

27.5 20.0 0.83

20.8 6.3 0.32

23.7 5.4 0.304

21.8 8.5 0.245

14.8 4.9 0.44

20.9 7.0 0.265

30-33

55.59

55-62

60-65

30-45

35-45

30-35

~~

* Sample did not break

these highly loaded composite systems, thus implying that their use could improve processibility. However, there would essentially be a trade-off in the mechanical properties. Titanates were found to show more drastic effects than silanes. It has been postulated by earlier workers and confirmed by the present study that certain surface modifiers act as mere dispersing agents rather than coupling agents and provide a plasticizing effect. The level of dispersion achieved by the addition of titanates has been more than by the silanes as can be seen through the SEM micrographs (Figs. 2a to 2g). Nevertheless, with the developments of newer surface modifiers such as neoalkoxyl titanates (20, 21), there is certainly a possibility of achieving increases in tensile strength as well as elongation and these may be tested in future for the present filler-matrix system.

REFERENCES 1 . S. H. Morrell, Plust. Rubber Proc. A p p l . , 1, 179 (1981). 2. E. P. Plueddemann, in “Interfaces in Polymer Matrix ComDosites”. (E. P. Plueddemann, Ed.) Ch. 6, Academic Press, h e w York (1974). 3. S. J. Monte, Mod. plastic.^ Ency., 54, 168 (1977). 4. M. S. Boaira and C. E . Chaffey, Polym. Eng. Sci., 17, 715 (1977). 5. C. D. Han, C. Sandford, and H. J. Yoo, Polym. Eng. Sci., 18, 849 (1978).

6. S. J. Monte and G. Sugerman, Polym. Plast. Technol. Eng., 13. 11.5 (1979). 7. M.’HancOck, P. Tremayne, and J. Rosevear, J. Polym. Sci., Pslym. Chem. Ed., 18, 3211 (1980). 8. C. D. Han, T. Van den Weghe, P. Shete, and J. R. Haw, Polym. Eng. Sci., 21, 198 (1981). 9. T. Nakatsuka, H. Kawasaki, K. Itadani, and S. Yamashita, J . Appl. Polym. Sci., 27, 259 (1982). 10. A. Carton, S. W. Kim, and D. M. Wiles,]. Appl. Polym. Sci., 27, 4179 (1982). 11. V. P. Juskey and C. E. Chaffey, Can. J . Chem. Eng., 60,334 (1982). 12. Z. E. Kerekes, “Magnetic Fillers” in Handbook of Fillers and Reinforcements for Plastics, Ed. H. S. Katz and J. V. Milewski, Ch. 12, p. 205, Van Nostrand Reinhold, New York (1978). 13. Y. Fukuyama, S. Habu, and T . Hayashi, Int. Polym. Sci. Technol., 6, T/78 (1979). 14. J. E. Theberge, Polym. Plust. Technol. Eng., 16, 41 (1981). 15. H. L. Dickstein and W. H. Dickstein, U.S. Pat. 4,397,751 (Aug. 9, 1983). 16. Bulletin KR-0975.2, Kenrich Petrochemicals, Inc., Bayonne, N.J. (1975). 17. Bulletins KR-0376-4 and KR-1076-5, Kenrich Petrochemicals, Inc., Bayonne, N.J. (1976). 18. Bulletin KR-0278-7, Kenrich Petrochemicals Inc., Bayonne, N.J. (1980). 19. D. M . Bigg, Polym. Eng. Sci., 22, 512 (1982). 20. S. J. Monte and G. Sugerman, ACS 12Fjth Meeting Paper No. 61, Indianapolis, Indiana (May 8-11, 1984). 21. S. J. Monte and G . Sugerman, presentation at 1st International Conference Additives, Blends and Composites, Luxembourg (April 10-11, 1984).


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