Study of the viscous flow of dimethylsiloxane polymer and rubber solutions over a wide range of deformation rates

STUDY OF THE VISCOUS FLOW OF DIMETHYLSILOXANE POLYMER AND R U B B E R SOLUTIONS OVER A WIDE RANGE OF DEFORMATION RATES * N. A. IvA~ovA, A. ~ . PRIBYTKOand I. I. SKOROKHODOV Chemical and Organo-metallic Technology Research I n s t i t u t e

(Received 18 March 1968)

DIMETHYLSILOX/kN'E polymers (P)gS-liquids) and solutions of dimethylsiloxane rubber in low viscosity PlVIS-liquids are now widely used as fillers in shockabsorbing apparatus. To construct such equipment correctly it is essential to know the effect on the systems mentioned of deformation rates up to fairly large values. There is very little information contained in the literature on this question [1-3], although some studies were made on the flow behaviour of P1KS-liquids. The theological properties of dimethylsiloxane (D~S) rubber solutions had not been studied at all. We therefore decided to carry out such an investigation on the most characteristic properties of the above systems and to clarify the question of whether the two systems are exchangeable in shock absorbers. EXPERIMENTAL The study objects were four technical PMS-liquids produced by alkaline polycondensation, i.e. PMS-15,000, PMS-100,000, PMS-400,000 and PMS-1,000,000; in addition 4 solutions were prepared by dissolving the DMS rubber SKT, having an average reel. wt. S O M E OF T H E

PltOPERTIES

% w/w Sample code

PMS-15,000 r-r-30,000 PMS-100,000 r-r-250,000 PMS-400,000 r-r-600,000 PMS-1000,000 r-r-1800,000

rubber eontent in solution

OF T H E

EXAMINED

SAMPLES

Mol. wt. of liquid

inn viscosity at 20°C, cP

Viscosity at 20 ° and 103 sec -1 deformation, cP

10,700

16,000 30,000 100,000 250,OOO 420,000 625,000 1,000,000 1,850,000

10,000 3000 19,000 8000 55,000 14,000 60,000 22,000

~Towt On.

16.5 38,000 28.5 115,000 30.7 224,000 50.0

* Vysokomol. soyed. A l l : No. 5, 1012-1016, 1969. 1145

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N . A . IVA•OVA et al.

of 5"4 × 105, in PMS-liquid 400. The solution concentrations were chosen in such a manner t h a t the nominal viscosities were similar to those of the first 4 PMS-liquids. The concentrations of these solutions, the exact viscosities, and the mol. wt. of the PMS-liquids, were all determined b y osmometry b y the zero-velocity method [4], and are given in the Table. The flow curves were obtained in the range of deformation rates from 0-1 to 104 see -1 and at temperatures ranging from --30 to -~ 70°C. F o r the low deformation rates (up to 102 sec -1) the viscous flow curves were obtained with the aid of r o t a t o r y viscometer PB-8, as well as a constant pressure capillary viscometer for which the description was given elsewhere [5]. The results of both these methods agreed in the range of deformation rates mentioned. The flow curves for the higher range of deformation rates were obtained with the capillary viscometer. The open-type rotatory viscometer gave irreproducible results due to the Weissenberg effect, and this applied to all the studied samples; its intensity increased with the mol. wt. of the PMS-liquids, or the concentration of the rubber solutions. RESULTS T h e v i s c o u s flow c u r v e s a t 20°C o f t h e t r u e v i s c o s i t y l o g a r i t h m , p l o t t e d a g a i n s t t h e l o g a r i t h m o f t h e d e f o r m a t i o n r a t e , a r e s h o w n i n F i g . 1. T h e s a m e s h a p e of curve was also obtained at other temperatures.

tvq 6

-1

0

/

2

3

#

/ogD

FIG. 1. Flow curves of PMS-liquids (continuous lines) and of SKT rubber solutions in PMS-400 (lines of dashes) at 20°C. 1 -- PMS- 15,000, 2-- PMS- 100,000, 3 -- PMS-400,000, 4 -- PMS- 1,000,000 5--r-r-30,000, 6--r-r-250,000, 7--r-r-600,000, 8--r-r-l,800,000. The results showed the sample viscosity to be independent of deformation at l o w r a t e s , i.e. a N e w t o n i a n flow w a s o b t a i n e d . T h e c r i t i c a l d e f o r m a t i o n r a t e , at which the samples could be regarded as Newtonian liquids, depended on the mol. wt. of the polymer, or on the concentration of the rubber solution. An increase o f t h e s e v a l u e s c a u s e s t h e r a n g e o f N e w t o n i a n flow t o n a r r o w , b u t i t n e v e r d i s a p p e a r e d . I t w a s a l s o t y p i c a l t h a t t h e N e w t o n i a n flow r a n g e w a s n a r r o w e r in t h e

1147

Study of viscous flow of dimethylsiloxane polymer

case of the liquids than of the PlUS-liquids, and t h a t the deviation from the Iqewton rule could be observed at lower deformation rates in the former case. The viscosity of the systems decreased at high deformation rates with increase in the deformation rate, i.e. the systems then behaved like pseudo-plastic bodies. A point worth noting is t h a t a larger mol. wt, of the polymer, or a larger rubber /og% olx7 -1 -,', 2 " 8 u3 A -2 _ v ~ , I 0 ASV V8

-3

-4

i

3

1

5

i

7

9

I

II

FIG. 2. Flow curves of PMS-liquids and of SKT rubber solutions in PMS-400 in generalized coordinates: 1--PMS-15,000, 2--PMS-100..( 0, 3--PMS-400,000, 4 - - as 3 at 70°C, 5 - - as 3 at --30°C, 6--PMS-1,000,000, 7--results f ' ) m [1, 3], 8--r-r-30,000, 9--r-r-250,000, l O - r-r-600,000, 1 l -- r-r- 1,800,000.

concentration caused a stronger decrease of the true viscosity with increasing deformation rate, and the viscous flow curves of the two groups of system came closer together. A similar trend was observed earlier for PMS-liquids [3]. The substantial difference between rubber solutions and PMS-liquids was due to the much more rapid viscosity decrease in the pseudo-plastic range of flow with increasing deformation rate, when compared with the viscosities of polymers. This is easily seen in Fig. l, and also from the Table, in which the Newtonian viscosities are compared with those at a deformation rate of 10a sec-1; the latter coincide with the uses as shock absorber fluids. The true viscosity of rubber solutions at 10a sec -1 deformation is only a fraction of t h a t of the Pi~S-liquids having approximately the same nominal viscosity. The results described are very important from the practical aspect, because they show t h a t the possibility of exchange is not as simple as it appears (PI~[Sliquids to be exchanged for SKT rubber solutions in Pi~S-400). The true viscosity of the systems under conditions of use must be considered, and not the nominal viscosities, determined at low rates of deformation. For example, the given data, show polymer P1~S-400,000 and solution-600,000 not to be equivalent shock-absorbing fluids, since their viscosities differ by about a factor of 4 at larger deformation rates. Polymer P]¢[S-100,000 and solution-l,800,000, on the other hand, can be regarded as equivalent fluids, because their true viscosities will be similar under conditions of use. The possibility of presenting the viscous flow curves of one or more types o ~polymer system in a standard form is of considerable theoretical and practical

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N.A. IVA~OVAet al.

interest. This would firstly make it possible to give a general picture of the rheological behaviour of these systems, and secondly the standard viscous flow curves could be used to assess the viscous properties over a wide range of deformation rates without having to make a large number of tests. The analysis of the above question on 1)MS-liquids and rubber solutions showed the best results, amongst the numerous known methods, to be obtained by the temperature-constant viscosity characteristic of polymers, as proposed by Vinogradov et al., who established the viscosities of linear polymers of different type with sufficient accuracy (for most purposes) at different temperatures by one universal flow curve, provided that the reduced viscosity and reduced deformation rates are used [6, 7]. Our results in reduced coordinates are shown in Fig. 2. The same diagram also illustrates the appropriately calculated data for P~S-liquids with viscosity larger than 10,000 cP, taken from the work carried out by others [1, 3] (P~Sfluids with lower viscosity are characterized by Newtonian flow and the pseudoplastic flow range is non-existent, as shown by others [1, 3]). Figure 2 shows that all the experimental results with P~S-liquids, irrespective of the production method, mol. wt., and temperature of testing, fall on one curve for the whole range of deformation rates. This curve was found to apply generally for the temperature-constancy correlation, as established for linear polymers [6, 7], and the deviations of individual points, using organosilicon polymers, was no larger than that in other cases. The conclusion which apparently can be drawn from this is that the behaviour of these systems during flow is governed by the same general principles, although the properties of the P~S-liquids greatly differ from those of organic polymers of the same mol. wt. In other words, the cooperative nature of the deformation process of macromolecules during flow, the effect of deformation rate on the molecular interaction and the destruction of supermolecular structures in PlUS-liquids, and in linear polymers of different type, is qualitatively the same [7]. The behaviour of rubber solutions during flow (Fig. 2) is not described by the generalized flow curve, but it is similar to that of the solutions of other polymers [7]. It must not be overlooked, however, that their viscosities also fall on the general curve in reduced coordinates, although slightly below it, and that this fact does not depend on concentration. This position below the universal curve will be more pronounced the higher the reduced deformation rate. The separate course of the generalized flow curves of P~S-liquids and of rubber solutions is due to the viscosities of the rubber solutions being chiefly determined by the reaction between the larger rubber molecules and those of liquid PMS-400; these do not take place, or are less pronounced, in the case of polymers having a narrower mol. wt. distribution. In conclusion we draw attention to the fact that this universal representation of viscosities is of considerable practical importance. I t makes it possible to assess ~he enumerated true viscosities accurately enough for a wider range of deforma-

Study of viscous flow of dimothylsiloxane polymer

1149

t i o n r a t e s w h e n d e t e r m i n i n g only t h e v i s c o s i t y of t h e s y s t e m a t a given t e m p e r a t u r e in t h e N e w t o n i a n range; this p r o c e d u r e is m u c h simpler t h a n t h e flow c u r v e d e t e r m i n a t i o n . CONCLUSIONS

(1) T h e flow curves were p l o t t e d for a series of Pl~S-liquids a n d S K T r u b b e r solutions in PMS-400 in t h e r a n g e of d e f o r m a t i o n s f r o m 0.1 to 10 a sec -1 a t t e m peratures ranging from --30 to +70°C. (2) T h e flow of these s y s t e m s w a s f o u n d to follow t h e N e w t o n rule a t s m a l l e r d e f o r m a t i o n rates; t h e larger t h e mol. wt. of t h e p o l y m e r , or t h e c o n c e n t r a t i o n of t h e solution, t h e n a r r o w e r was the r a n g e of N e w t o n i a n flow. All t h e s t u d i e d s y s t e m s b e h a v e d like p s e u d o - p l a s t i c bodies a t larger d e f o r m a t i o n rates, a n d t h e r u b b e r solutions were typified b y a well defined t r u e v i s c o s i t y - d e f o r m a t i o n r a t e function, c o m p a r e d w i t h the P ~ S - l i q u i d . (3) Certain p r o p o s a l s for selecting PMS-liquids a n d S K T r u b b e r solutions in PMS-400 as s h o c k - a b s o r b i n g fluids are m a d e on t h e basis of t h e o b t a i n e d results. Translated by K. A. ALLEN

REFERENCES 1. J. G. GEORGIAN, Trans. ASME 71: 389, 1949 2. E. J. NESTOKIDES, A Handbook on Torsional Vibration, B.J.G.E.R.A., Cambridge, 1958 3. T. KATAOKA and S. VEDA, J. Polymer Sci. A3: 2947, 1965 4. D. B. BRUSS and F. H. STROSS, J. Polymer Sci. 55: 381, 1961 5. G. V. VINOGRADOV and N. V. PROZOROVSKAYA, Plast. massy, No. 5, 50, 1964 6. G. V. VINOGRADOV, A. Ya. MALKIN, N. V. PROZOROVSKAYA and V. A. KARGIN, Dokl. Akad. ~Tauk SSSR 150: 574, 1963 7. G. V. VINOGRADOV, A. Ya. MALKIN, N. V. PROZOROVSKAYA and V. A. KARGIN, Dokl. Akad. ~qauk SSSR 154: 890, 1964