Plasticization method of studying the structural features of polyvinyl chloride

Plasticization method of studying the structural features of polyvinyl chloride

Structural features of polyvinyl chloride 473 CONCLUSIONS (1) It is shown that it is possible to determine the softening point of amorphous polymer...

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Structural features of polyvinyl chloride

473

CONCLUSIONS

(1) It is shown that it is possible to determine the softening point of amorphous polymers by recording the thermomechanical curves of specimens formed from powders. (2) The melting points of monolithic and powder specimens of crystalline polymers coincide under identical test conditions. (3) By recording the thermomechanical curves of specimens formed from powders it is easy to detect low-temperature transitions in polyamides. Translated by E. O. PHILLIPS REFERENCES 1. B. Ya. TEITEL'BAUM, T. I. SOGOLOVA and G. L. SLONIMSKII, Vysokomol. soyed. 4: 1879, 1962 2. B. Ya. TEITEL'BAUM and M. P. DIANOV, Vysokomol. soyed. 3: 594, 1961 3. V. D. GERASIMOV, G. A. KUZNETSOV and L. N. FOMENKO, Zavod. lab. No. 8, 996, 1963 4. R. H. BOYD, J. Chem. Phys. 30: 1276, 1959 5. A. E. WOODWARD, J. M. CRISSMAN and J. A. SAUER, J. Polymer Sci. 42: 23, 1960 6. A. E. WOODWARD, R. E. GLICK, J. A. SAUER and R. P. GUPTA, J. Polymer Sci. 45: 367, 1 9 6 0 7. F. RYBNIKAR, J. Polymer Sci. 28: 533, 1958 8. A. Mt~LLER and P. PFLYUGER, K h i m i y a i tekhnol, polimerov, No. 1, 67, 1961 9. J. H. WAKELIN, A. SUTHERLAND and L. R. BECK, J. Polymer Sci. 42: 278, 1960 10. R. P. GUPTA, J. Phys. Chem. 65: 1128, 196l

PLASTICIZATION METHOD OF STUDYING THE STRUCTURAL FEATURES OF POLYVINYL CHLORIDE* I. N. RAZINSKAYA,

B. P. SHTARKMAN

and P. V. KOZLOV

(Received 19 February 1963)

IT HAS been found [1-3] that with increasing slight quantities of plasticizer the strength, elasticity modulus and hardness of polyvinyl chloride (PVC) not only are not reduced, but even increase and pass through a maximum, the corresponding elongation and impact resistance passing through a minimum. Slight concentrations of plasticizer, up to 20~o by weight for instance, not only do not soften PVC, but make it stiffer and more brittle. This kind of effect has been found on a number of vulcanizates [4]. Volkova and Vol'lkenshtein, who carried * Vysokomol. soyed. 6: No. 3, 427-431, 1964.

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I. N. RAZINSKAYA e$ al.

out an X-ray diffraction study of the swelling of natural rubber [5], found that its degree of crystallinity passed through a maximum at a concentration of 3 - 4 % plasticizer. Also b y the X-ray diffraction method Horsley [1], using the example of the copolymer of vinyl chloride and vinylidine chloride, found that the increased rigidity was accompanied b y an increase in the ordering of the polymer structure. The brittleness of this kind of rigid specimen can be increased b y heating to above the glass temperature (T~) followed b y rapid cooling, and restored b y heating a specimen quenched in this way to below the Tg. An increase in the degree of ordering of PVC due to the addition of a plasticizer, has also been noticed in [6]. This abnormal behaviour of the properties after the polymer has swelled in a plasticizer, m a y be due to two competing and opposite processes: the flexibility of the chain increases and this makes additional structural ordering possible on the one hand, while on the other the molecular interaction becomes weaker and this is accompanied b y a reduction in the strength, elasticity modulus and so on. In a general case the superposition of these two processes produces extremely close dependence of the strength, elongation, elasticity modulus etc., on the amount of plasticizer in the mixture. The greater the state of ordering in the original polymer, the smaller will be the degree of ordering in the process of swelling. In [7] it is suggested that PVC produced b y different polymerization methods will have different supermolecular structures. This m a y be the reason for the difference in the plasticization effect of ethyl stearate on PVC produced b y different methods of polymerization. We decided it would be interesting to study the effect of small amounts of plasticizer on the properties of PVC prepared in different ways, in order to study the features of the supermolecular structure. The current methods of studying the structure of PVC, electron, X-ray diffraction analysis and electron microscopy, only give very general ideas regarding the nature of its ordering. Up till now at any rate, these methods have not been able to show the difference in the structures of PVC specimens prepared b y different polymerization processes. It m a y therefore be found that the study of the effect of small concentrations of plasticizer on the properties of the polymer could be a valuable method of revealing the different structural features of PVC specimens produced in different ways. EXPERIMENTAL

Latex (LPVC) and suspension (SPVC) PVC specimens were used for the study. The plasticizer was dioetylphthalate (DO]?). The PVC-plastieizer mixture was prepared as follows: the DOP was dissolved in ethyl alcohol and the PVC was softened with this solution. The alcohol was evaporated off and after this the mixture was heated for 1 hr at 100°. Blocks 70 mm in diameter were made from this mixture to determine the physicomechanical properties. As found in [8], the preparation of an optically transparent specimen does not necessarily indicate that the powder polymer is a monolith. For real cohesion strength the blocks must be compacted in the range of true compressibility. The extent to

Structural features of polyvinyl chloride

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which the polymer has become solid can be assessed from the relative change in the depth of the compacted specimen as a result of annealing, the lower the increase in depth after annealing showing a higher degree of solidity due to compaction. The blocks were compacted at 65 kg/em 2 between 150 and 165 ° depending on the composition of the mix. Specimens were cut from each block, annealed at 130 ° and the relative change in depth measured. The compacting conditions were chosen in such a way that the increase in depth should not be greater than 5~o. On blocks produced in this way dumb-bell specimens were made with an overall length of 60 ram, with 2 × 2 mm depth and width in the test part. The tensile strength and elongation, and also the elasticity modulus, were determined on a Polyani tester at 20 ° on a loading rate of 0.1 nxm/sec. The Tg of the mixture was determined thermomechanically on an apparatus based on the IZP-1 length meter with periodic loading and programmed temperature adjustment at the rate of 0'8°/rain. The viscosity of a melt of this mixture was determined on a slightly modified Heppler consistometer in which the heating was electrical with automatic temperature control having an accuracy of ± 1°. To prevent decomposition of the PVC on contact with the metal the indenter cone was repeatedly coated with VF-2 glue, while the polymer was placed in a glass container which was then inserted in a copper sheath. RESULTS AND DISCUSSION

F i g u r e 1 shows t h e s t r e n g t h , elasticity m o d u l u s a n d elongation as a f u n c t i o n o f t h e a m o u n t of D O P in t h e m i x t u r e for S P V C a n d L P V C . As c a n be seen f r o m these curves, t h e s t r e n g t h a n d e l a s t i c i t y m o d u l u s of t h e S P V C pass t h r o u g h a p e a k a t a p p r o x i m a t e l y 5 - 8 % D O P . I n this r a n g e t h e elongation passes t h r o u g h a p o o r l y defined m i n i m u m , a n d n o t until 1 5 % D O P does it begin to rise a p p r e ciably. I n L P V C t h e s t r e n g t h a n d e l a s t i c i t y m o d u l u s a t first fall slowly as t h e D O P is a d d e d (up t o 1 0 - 1 2 % D O P ) , t h e n t h e y fall quite r a p i d l y . U p to 1 5 % D O P t h e e l o n g a t i o n increases v e r y slowly, t h e n m o r e r a p i d l y to higher D O P concentrations. This shows t h a t as small a m o u n t s of D O P are a d d e d SPVC n o t only does n o t b e c o m e softer, b u t e v e n b e c o m e s slightly m o r e rigid t h a n t h e original. A t t h e s a m e t i m e , e v e n a f t e r t h e first small a m o u n t s of plasticizer h a v e b e e n added, L P V C begins to soften a t first v e r y slowly, a n d t h e n m o r e r a p i d l y . This is still f u r t h e r i l l u s t r a t e d b y t h e d e p e n d e n c e of t h e height of t h e h i g h - e l a s t i c i t y s t a t e p l a t e a u on t h e t h e r m o - m e c h a n i c a l curves, on t h e a m o u n t of D O P for this t y p e of P V C (Fig. 2). T h e height of t h e p l a t e a u d e p e n d s on t h e e l a s t i c i t y of t h e s y s t e m . This is clear f r o m t h e c u r v e t h a t L P V C b e c o m e s m o r e elastic as D O P is added. I n S P V C it r e m a i n s t h e s a m e u p to 1 2 % D O P a n d t h e n begins to rise as t h e a m o u n t of plasticizer increases. As S P V C a n d L P V C are c h e m i c a l l y no different f r o m one a n o t h e r a n d t h e y h a v e here b e e n m i x e d w i t h e x a c t l y t h e s a m e plasticizer, t h e difference in t h e i r p r o p e r t i e s on t h e swelling m u s t be a t t r i b u t e d to t h e difference in t h e n a t u r e of t h e i r s t r u c t u r e s . T h e S P V C s t r u c t u r e s should be less p e r f e c t t h a n in L P V C w i t h a n a d d i t i o n of u p t o 12% D O P p e r m i t s f u r t h e r s t r u c t u r a l ordering in t h e former. Our conclusions r e g a r d i n g t h e m a x i m u m degree of ordering in L P V C are in c o m p l e t e a g r e e m e n t w i t h t h e d a t a of [9].

476

I. N. RAZZNSKAYAet a/. ~, kg/cmz Q

E,kg/crn2 E,~

b

"/

~OOaO

500

:lJ)O0~

400

200 4000

40

20 DOP, °/o

.0

0i

I

I

40

20

DOP, °/o

FIG. 1. a--Tensile strength (curves I and 2) and elasticity modulus E (curves 1' and 2') versus the amount of DOP in PVC: 1 and /'--for SPVC; 2 and 2'--for LPVC; b--elongation versus the amount of DOP in PVC: 1--SPVC, 2--LPVC. I t is interesting to c o m p a r e these results with the T J a m o u n t of e t h y l s t e a r a t e (ES), which occupies an i n t e r m e d i a t e position b e t w e e n intro- a n d inter-bundling plasticizers, for PVC [7]. F i g u r e 3 shows these figures for SPVC a n d LPVC. This k i n d of p r o c e d u r e for similar e x p e r i m e n t s has been described in [7]. F o r SPVC t h e m a x i m u m r e d u c t i o n in the T~ of E S is 22 °, while for L P V C it is 15 °. According t o [7], we can t a k e it t h a t the supermolecular s t r u c t u r e s of SPVC are less perfect t h a n in LPVC. This conclusion is obviously in complete agreeh,IJ

2

200 -

4

"/20-

40

o

o

I

DOP, °/o

FIO. 2. Height of high-elasticity plateau on the thermo-mechanical curves versus the amount of DOP in PVC. 1--SPVC, 9--LPVC.

Structural features of polyvinyl chloride

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m e n t with the d a t a o b t a i n e d on the influence of slight a m o u n t s of D O P on the properties of PVC. I n conclusion we m u s t dwell slightly on certain figures o b t a i n e d in the measurem e n t of the viscosity of plasticized SPVC melts. Figure 4 shows log viscosity

To,~ go

9

I

I

40

0

L

20

FIG. 3. T g v e r s u s E S a m o u n t :

1--SPVC,

ES, % 2--LPVC.

of the melts as a f u n c t i o n o f t h e a m o u n t s of D O P a t different t e m p e r a t u r e s . All these curves pass t h r o u g h a deflection point between 10 a n d 15% D O P . T h e log viscosity versus reciprocal t e m p e r a t u r e (160-195 ° ) d e p e n d e n c e is linear for all m i x t u r e s studied. T h e a p p a r e n t a c t i v a t i o n e n e r g y of viscous flow (U) can be f o u n d from the slope ot these curves [10]. 70 X

o o

o

6.O

0

20

40

D-OP, °/o

FIG. 4. Log melt viscosity versus amount of DOP in SPVC at 170° (1), i80 ° (2), and 190° (3).

478

I.N. RAZI~SKAYAetal.

/%, 40

o

20

DOP, O/o

FIG. 5. Apparent activation energy of viscous flow U versus the amount of DOP in SPVC.

Variation in U is associated with a variation in the molecular interaction energy [11]. Figure 5 shows U as a function of the amount of DOP. The curve passes through a maximum at 15% DOP. The rise in U seems to be connected with an increase in the size of the section which corresponds to the act of irreversible flow. This can only occur where the PVC flow is due not only to the shifting of individual sections of flexible molecules, but of actual elements of supermolecular structures which are strengthened when slight concentrations of DOP are added to the mixture. The structural changes o f SPVC due to the addition of slight amounts of plasticizer seem to remain to some extent even in a melt. I t is suggested t h a t this m a y be the reason for the deflections on the viscosity versus DOP content curve. CONCLUSIONS

(1) I t has been demonstrated t h a t for SPVC the addition of slight amounts of plasticizer (DOP) leads to an increase in the rigidity of the polymer as well as the expected softening. Softening of LPVC starts immediately after the first amount of DOP has been added. (2) I t has been suggested t h a t LPVC has a higher degree of ordering t h a n SPVC. (3) At 10-15% DOP the viscosity versus DOP curves pass through a point of inflection. The apparent activation energy of viscous flow has a m a x i m u m of 15% DOP. (4) I t has been suggested t h a t in PVC flow units of the elements of supermolecular structures are displaced, and t h a t these m a y become strengthened by the addition of slight amounts of plasticizer. T r a n s l a t e d by V. AL~ORD REFERENCES

1. 2. 3. 4.

R. P. O. B.

A. HORSLEY, Plastics Progress, 77, 1957 E. CHERSA, Mod. Plast. 86: 135, 1958 FUgHS and P. P. FREY, Kunststoffe 49- 213, 1959 A. DOGADKIN, D. L. FEDYUKIN and V. Ye. GUL', Kolloidn. zh. 19" 287, 1957

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5. L. A. VOLKOVA and M. V. VOL'KENSHTEIN, Fiz. tverd, tela 1: 1272, 1959 6. L. A. IGONIN, A. V. YERMOLINA, Yu. V. OV[~HINNIKOV and V. A. KARGIN, Vysokotool. soyed. 1: 1327, 1959 7. I. N. RAZINSKAYA, P. V. KOZLOV, B. P. SHTARKMAN and L. P. IGNAT'YEVA, Vysokomol. soyed. 5: 1850, 1963 8. S. A. ARZHAKOV, Ye. Ye. RYLOV and B. P. SHTARKMAN, Vysokomol. soyed. 1: 1351, 1357, 1959 9. D. N. BORT, Yu. V. OVCHINNIKOV and Ye. Ye. RYLOV, Vysokomol. soyed. 4: 935, 1962 10. I. N. RAZINSKAYA and B. P. SHTARKMAN, Vysokomol. soyed. 5: 393, 1963 11. P. P. KOBEKO, Amorfnye veshehestva, Izd. Akad. Nauk SSSR, 1952

SALTING OUT AS A METHOD OF DETERMINING THE MOLECULAR WEIGHT DISTRIBUTION OF POLY-e.CAPRAMIDE* V. M. POLYAKOVA, A. YE. FAINERMAN and R. V. V O I T S E K H O V S K I I Institute of Polymer and Monomer Chemistry, Ukr. S.S.R. Academy of Sciences

(Received 23 February 1962)

THE turbidimetric method of determining the molecular weight distribution is preferable to the various different preparative methods due to its rapidity and to the possibility of analyzing small amounts of material. But a disadvantage is that equilibrium between the solid phase and the environment cannot be established at any precipitation addition rate which can be achieved in practice [1]. The results obtained in a turbidimetrie titration do not show any definite dependence on the concentration of the polymer which has gone over to the solid phase; they are affected by the time processes of desolvation, coallescence and flocculation. Directly the precipitator is added zones of excess concentration are created, which causes the co-precipitation of poiymer fractions. Although reproducibilility of the relative but not absolute optical density can be obtained by strictly observing the conditions of experiment, there is no certainty that the turbidimetric curves do accurately reflect the molecular weight distribution of the polymer. For the above reasons, when taking turbidimetrie curves it is best to use the principle of diffusion salting-out first applied by Zelenskii [2] to analyse the aminoacid composition of the proteins. According to our observations this principle can be successfully used, not only to distinguish materials of different chemical composition, but also to distinguish the different molecular weight fractions of polymers. * Vysokomol. soyed. 6: No. 3, 432-433, 1964.

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