Investigation of the relaxation properties of filled polyarylates

Investlgatmn of the relaxation properties of polyarylates

1221

6 T. W CAMPBELL and D J LYMAN, J Polymer Sch 55 169, 1961 7 A I KITAIGORODSKII, Rentgenostrukturnyl anahz ( X - R a y Structure Analysis ) Gostekhlzdat, 1950 8 W SCHONIGER, Mlcrochlm acta 1 123, 1955 9. V P SHIBAYEV, N A PLATE, R K GRUSHINA a n d V A KARGIN, Vysokomolek. soyed 6 231, 1964 10 P SWAN, J Polymer Scl 56 409, 1962 11 Pohetflen i druglye poholefiny (Polyethylene and Other Polyolefins ), I z d "Mlr", Moscow. 1964, p 338 12 B A KRENTSEL', G Ye SEMENIDO and D Y e IL'YINA, Vysokomolek soyed 5: 558, 1963 13 R W KEYSER, B CLEGG and M DOLE, J Phys Chem 67 300, 1963 14 W SCHNABEL a n d M DOLE J Phys Chem 67 295, 1963 15 L BARISH, J Appl Polymer Scl 6 617, 1962 16 J VAN SCHOOTEN, J Appl Polymer Sc~ 4 122, 1960 17 K NUMBY, J Appl Polymer Scl 4 69, 1960 18 N A SLOVOKHOTOVA, Z F IL'YICHEVA, L A VASIL'YEV and V A KARGIN, Vysokomolek soyed 6 608, 1964

INVESTIGATION OF THE RELAXATION PROPERTIES OF FILLED POLYARYLATES* G

L

SL0~IMSKII, A

A ASKA.DSKII, V

V

KORSHAK, S V VII~'0GRADOVA,

I A GRIBOVA, A N C~MA~VSXAYA, A V KRASI~'OV and M K MOLDABAYEVA I n s t i t u t e for E l e m e n t a r y Orgamc Compounds, U S S R A c a d e m y of Sciences (Recewed 9 June 1965)

AT the present time there is extensive hterature on the study of various propertles of polymer-filler systems However, problems connected with the underlying structural changes which take place when sohd polymers are filled (m particular taking account of relaxation phenomena) have as yet been studied extremely inadequately In connection with this, we have carried out an investigation of stress relaxation m certain glassy polymer-filler systems at different temperatures b y the method described m reference [1] We have put forward this type of test as being of interest for several reasons Firstly, the way m whmh this investigation was carrmd out made it possible to determine numerical values of the parameters Upo and ? p m the equatmn for the temperature dependence of relaxation time [2-3] for the initial and for the * Vysokomol soyed 8 2qo 6, 1109-1112, 1966

G. L. SLO~MSK~ el a/.

1222

filled polymers, and to follow changes m these constants over a wide range of filler content Secondly, since the possible working regmns (according to hardness) of the polymer material are determined m the results of these experiments (that ]s, the regmns of stress and temperature m whmh the polymer material retains an adequate hardness and may be used m ngld constructions [1]), there was interest m following how these regmns change depending on the composltmn of the polymer-filler system, and to compare them with the possible working regmn of the initial polymer. Moreover, it should be noted t h a t m the majority of the data m the hterature, the softening temperature of filled polymers is determined at a partmular single load (most often small) In our case, this determmatmn was made over a wide range of stresses, and this has made it possible to find certain relatmns m this httle studmd field. EXPERIMENTAL

Polyarylate F-1 [4-5] was selected as the experimental material, together with compomtlons based on this mixed with varmus wmght concentratmns of copper powder This selectmn was made so t h a t samples based on these composltmns should have good mechamcal propertms and so t h a t it would be posmble to carry out stress relaxatmn tests with confidence. The results of tests on the lmtlal polyarylate F-1 are shown m l%g. 1. S]mflar relations were obtained for the filled polymers.

d, kg/cm 2

400

~,k/cm2 8OO ~ ! 400

....

.

\

200

N~.~ t......

140

ol ©2

-

"I-"

I

180

220

FIG 1

",

¢},,~L

2GOT,°C

300

e3

200 I00 0170

o5

x4 oG

I

I,

I

IBO

2"/0

230

I

250T,°C

Y'IG 2

FIG 1 Posmble working region (according to hardness) of polyarylate F-1. :FIG 2 Curves defimng the posmble working regions for samples based on polyarylate F-1 with various concentrations of copper powder /--F-I, 2--F-1+20 vet. % Cu, 3--F-1+40. wt. % Cu, 4--theoretmal points, calculated by means of equation (1), 5--F-1-t-60 wt % Cu, 6--F-lq-80 wt % Cu.

Investigation of the relaxation propertms of polyarylates

1223

I n order to show the effect of the amount of filler on the change in the possible working region of the filled polymer materials more graphically, we have plotted the curves which describe these regions on a single graph (Fig 2). From an analysis of these curves it may be noted t h a t for 20 weight % filler, the possible working region is shifted in the direction of lower temperatures when comparatively small stresses act on the sample Under the action of large stresses, the curves showing the possible working regions for the initial and filled polyarylate F-1 coincide With a filler concentration of 40°//o m the composition, a still greater shift in the direction of low temperatures is observed. With a further increase m the filler concentratlon, the possible working region begins to extend in the direction of higher, temperatures, and with 80 weight ~/o of filler, it exceeds the possible working region of the initial polyarylate both for temperatures and also for stresses One m a y draw the conclusion from this t h a t a small a m o u n t of filler exerts a plastlclzing action on the polymer, lowering its softening point With a large filler concentration, however, the softening point is raised, and exceeds the softening point of the initial polymer. To demonstrate this more graphically, we have plotted curves a t constant stress for the relation between the temperatures which define the possible working regions, and the filler concentration, and these are shown in Fig 3 I t is clearly evident from these curves t h a t the temperature defining the possible working region begins to fall until 40 weight ~o of filler is present in the composition, and then it begins to rise with a further increase in filler concentration (this appears especially clearly for comparatively small stresses).

F'°C

I

210 20

40 60 Cu,,% FIG 3

80

7FIG 4

FIG 3 Relation between the temperature, defining the possible worl~ng region, and the percentage filler concentration at various stresses, namely 1--100, 2--200, 3--300 kg/cm2 :Fio 4 Schematm representation of the curve defining the possible working region of a polymer materml

Calculation of the parameters U~o and ~,p in the equation for the temperature dependence of the stress relaxation t~me [2-3] As two of the authors have shown previously [1], a curve defining the possible working region (according to hardness) of a polymer material obeys the following equation

1224

G L

SLOI~UMS~rI~et al.

fir

In --=(U~o--~,~fi)/RT,

(1)

fi¢o

where a is a umaxial compression stress, T is the absolute temperature, R is the umversal gas constant, U~o , y~ and a~ are parameters of the polymer maternal, whmh determine its relaxation propertms Examination of equation (1) shows that a curve defimng the possible working region has the schematm form shown m Fig 4 The meaning of the symbols is also given m Fig. 4. ~ a v m g determined this relation expemmentally and having made use of equation (1), one m a y find the values of the constants U~o , 7, and a~. We have calculated the parameters U~o , ?~ and fi~ for the initial polyarylate F-1 and for the compositions based on it with different concentrations of copper powder. The values of stress and temperature were taken to correspond with Fig. 2. The results of calculations for the mltlal activation energy for the stress relaxation process U~o showed that it falls, as compared with the initial polymer, as the filler concentration rises to a certain hmlt, and then remains practically constant (Fig. 5a). Thin reduction m the initial activation energy for the stress relaxation process is evidently explained b y the fact that filler partmles hinder the natural development of supramolecular structures in the polyarylate F-1 [5], and thus facilitate their regrouping m the relaxation process. These results are m agreement with data m the literature about the determination of activation energies b y an independent method m other experimental materials [6], and also with data about the effect of filler on the development of supramolecular structures in polymobutylene [7]. Apart from the initial activation energy, there was great interest in following the change in the structure constant ?r with composition make-up. From the d a t a shown in Fig. 5b, it m a y be seen that ?v at first falls with an increase in filler concentration up to approximately 40 weight ~/o, and then starts to increase again. In this way, the overall activation energy for the relaxation process (U~o--Tva) for small filler concentrations is, on the one hand, reduced as compared with the initial polymer because of a reduction in U~o b u t on the other hand, it is increased because of the reduction in 7~ (and consequently in the value of Tva as well). However, it should be noted that for small values of a the contmbution of the quantity ?va in the overall activation energy is small, and because of this the quantity (Uro--7ra) is somewhat reduced for small filler concentrations. For large values of a, the quantity 7,fi begins to play a greater role, and in connection with this the total activation energy on the whole m increased as compared with the initial polymer, and the curves defining the possible working region for the filled polymers coincide with the curve for the initial polymer, as m a y be well seen from Fig. 2. This points to the fact that the slope of the curves for polymers with a small filler concentration will be greater than that for the imtial polymer. As m a y be seen from Fig. 4, the curve defining the possible working region for the polymer material cuts the stress axis at the point situated at a distance

1225

Investigation of the relaxation propertms of polyarylates

U~o/7~ f r o m t h e coordinate origin. W e h a v e p l o t t e d t h e relation b e t w e e n U~o/7~ a n d filler concentration, which is shown in l~ig. 5c. I t m a y be seen f r o m this F i g u r e t h a t initially (up to a filler c o n c e n t r a t i o n o f 40 weight %) t h e value o f U~o/7~ rmes, as was to be e x p e c t e d f r o m t h e discussion of Fig. 2, a n d t h e n starts to fall away. keG/ mmz ,m-~--k-~"

40

80

40

80

40

8g

Cu,% Cu,% Cu,% FIG 5 Relation between the percentage filler concentration and (a) the actlvatmn energy for the relaxation process, U~o; (b) the structure constant ?v, and (c) the ratio Uvo/?~ I n this way, the investigation which has been carried out has shown certain characteristic features of the r e l a x a t i o n b e h a v l o u r of filled glassy p o l y m e r materials o v e r a wide range o f stresses a n d t e m p e r a t u r e s . I t is o f i n t e r e s t to c a r r y o u t a similar investigation on o t h e r polymer-filler systems, m order to o b t a i n a m o r e complete picture of r e l a x a t l o n properties o f filled sohd polymers

CONCLUSIONS (1) B y a n i n v e s t i g a t i o n o f t h e stress r e l a x a t i o n a t various t e m p e r a t u r e s m filled sohd p o l y m e r s based on p o l y a r y l a t e F - l , the possible working regions (according to hardness) of these systems h a v e been d e t e r n n n e d [1]. (2) T h e p a r a m e t e r s Uro a n d ?r m t h e e q u a t i o n for the t e m p e r a t u r e d e p e n d e n c e o f t h e r e l a x a t i o n t i m e h a v e been d e t e r m i n e d , a n d t h e i r d e p e n d e n c e on filler conc e n t r a t m n has been d e m o n s t r a t e d . (3) T h e o b s e r v e d changes in properties c o n s e q u e n t u p o n t h e i n t r o d u c t i o n o f t h e filler p o i n t to t h e effect o f filler particles u p o n t h e f o r m a t i o n o f supramolecular s t r u c t u r e s in t h e sohd (glassy) polymer. Translated by G MODLEI~ 1. 2. 3 4 5 6 7

REFERENCES G. L. SLONIMSgII and A. A. ASKADSKII, Mekh~ml~a pohmerov 1 36, 1965 A. P. ALEKSANIDROV, Tr I i I I Konf. pc vysokomolekulyarnym soyedmemyam (Vol. I and II of Conference on High Molecular Weight Compounds ) p 49, 1945 G. I. GUREVICH, Zh tekh. fiz. 17 1491, 1947 V. V. KORSHAK, S. V. VINOGRADOVA and S. N. SALAZKIN, Vysokomolek. soyed. 4 339, 1962 G. L. SLONIMSKH, V. V. KORSHAK, S. V. VINOGRADOVA, A. I KITAIGORODSKII, A A. ASKADSgII, S. N. SALAZKIN and Ye. M BELAVTSEVA, Dokl Akad l~auk SSSR 156 924, 1964 Yu. S. LIPATOV and R. P. KI~OROSITIKO, Vysokomolek soyed. 4 37, 1962 V. A. KARGIN, T I. SO00LOVA and T. K METEL'SKAYA, Vysokomolek, ~oyed 4 601, 1962, 5 921, 1963