Study of monolith formation of polyvinylchloride

Study of monolith formation of polyvinylchloride

840 I . M . MONICt{ et al. REFERENCES 1. P. DEBYE and T. ZAKK, Theory of Electric Properties of Molecules, For. Lit. Publ. House, 1936 2. T. M. BIRS...

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840

I . M . MONICt{ et al. REFERENCES

1. P. DEBYE and T. ZAKK, Theory of Electric Properties of Molecules, For. Lit. Publ. House, 1936 2. T. M. BIRSHTEIN and O. B. PTITSYN, Zh. tekh. fiz. 24: 1998, 1954 3. O. B. PTITSYN and Yu. A. SHARONOV, Zh. tekh. fiz. 27: 2744, 1957 4. O. B. PTITSYN and Yu. A. SHARONOV, Zh. tekh. fiz. 27: 2762, 1957 5. L. L. BURSHTEIN and G. P. MIKItAILOV, Zh. tekh. fiz 27: 688, 1957 6. L. L. BURSHTEIN and G. P. M I ~ I L O V , Zh. tekh. fiz 27: 694, 1957 7. L. ONSANGER, J. Amer. Chem. Soc. 58: 486, 1936 8. S. T. BARSAMYAN, L. S. TOLAPCHYAN and B. N. PIKALOVA, Dokl. Akad. Nauk Arm. SSR 40: 1Ol, 1965 9. N. M. KOCHARYAN, S. T. BARSAMYAN, S. G. MATSOYAN, V. N. PIKALOVA, L. S. TOLAPCHYAN and M. G. VOSKANYAN, Izv. Akad. Nauk Arm. SSR, Chem. Sci. series 18: 441, 1965 10. U. DOBEN and K. PITUER, Conformational Analysis, Steric Effects in Organic Chemistry, For. Lit. Publ. House, 1960 11. M. V. VOL'KENSttTEIN, Stroyenie i fizicheskie svoistva molekul (Structure and Physical Properties of Molecules). Izd. Akad. Nauk SSSR, 1957 12. K. D. NENITSESKU, Organic Chemistry, vol. I, For. Lit. Publ. House, 1962 13. N. M. KOCItARYAN, S. T. BARSAMYAN and V. N. PIKALOVA, Dok. Akad. Nauk Arm. SSR 38: 295, 1964 14. N. M. KOCHARYAN, S. G. MATSOYAN, S. T. BARSAMYAN, L. S. TOLAPCHYAN and N. M. MORLYAN, Dokl. Akad. Iqauk Arm. SSR 37: 7, 1963 15. K, Z. FATTAKHOV, Zh. tekh. fiz. 24: 1401, 1954 16. P. DEBYE and F. BUCHE, J. Chem. Phys. 19: 589, 1951 17. A. KATERA, J. Chem. Soc. Japan, Pure Chem. Soc. 70: 118, 1949 18. R. J. W. LE FEVRE and K. M. S. SUNDARAM, J. Chem. Soc., 1494, 1962 19. G. P. MIKHAILOV, Uspekhi khimii 24: 875, 1955

STUDY OF MONOLITH FORMATION OF POLYVINYLCHLORIDE* I. M. M o ~ I c H , L. I. VIDYAIKII~'A, S. A. ARZHAKOV, •. a n d I. I~. RAZlI~SKAYA

A. OKLADI~'OV

Institute of Chlororganic Products and Acrylates (Received 8 January 1966) IN PREVIOUS p a p e r s [1-3] s e v e r a l p o l y m e r s were s t u d i e d i n c o n n e c t i o n w i t h m o n o l i t h f o r m a t i o n m e c h a n i s m s , t h e processes w h e r e b y a p o w d e r f o r m p o l y m e r is c o n v e r t e d i n t o a solid. A n u p p e r p r e s s u r e l i m i t w a s f o u n d o n t h e c u r v e o f log p vs. T; t h i s c u r v e l i m i t s t h e r e g i o n i n w h i c h t r a n s p a r e n t s a m p l e s o f all t h e p o l y m e r s u n d e r i n v e s t i g a t i o n are o b t a i n a b l e . M o r e o v e r i n t h e case o f p o l y m c t h y l l n e t h a c * Vysokomol. soyed. A9: No. 4, 754-758, 1967.

Monolith formation of polyvinylchloride

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r y l a t e (PMMA) it is possible to distinguish a region of t e m p e r a t u r e s and pressures of m o n o l i t h f o r m a t i o n in which solid p o l y m e r s possessing the o p t i m u m properties m a y be o b t a i n e d [4]. T h e presence of this region was c o n n e c t e d with transition of the p o l y m e r into the state of viscous flow, b u t it r e m a i n e d u n c e r t a i n w h e t h e r the existence of such a region was a general p h e n o m e n o n . Because of this the present research was u n d e r t a k e n to d e t e r m i n e m o n o l i t h f o r m a t i o n mechanisms for a p o l y m e r such as polyvinylchloride (PVC) with which t r a n s i t i o n to the viscous flow state practically coincides w i t h a region of r a p i d t h e r m a l d e g r a d a t i o n of the p o l y m e r . The substance investigated was commercial suspension PVC with a Fichentcher constant of 62-3 and the following powder properties: true density 1.3073 g/cm 3, bulk density 0.57 g/cm 3, homogeneity index 197 samples/0.1 cm 3, plasticizer (dibutyl phthalate) absorption time, 35 min. The method of sample preparation and of plotting annealing curves was described in [2]. The light-transmission coefficients of the samples were determined on a Pulfrich photometer; the density of the samples was estimated from the flotation temperatures in a mixture of sulphuric acid and water [5]. DISCUSSION OF RESULTS

E x a m i n a t i o n of the PVC annealing curves for several m o n o l i t h f o r m a t i o n pressures (Fig. 1) shows t h a t at pressures below 400 kg/cm 2 samples are o b t a i n a b l e in which, judging b y the m i n i m u m values of relative r e c o v e r y of height b y the ah/h,

\

O0

2

1

3

20

0

J

I

I

]

80

I/0

120

/50

I

Tm , °0

FIG. 1. PVC annealing curves (Ah/h, °~o-- change in sample thickness during annealing; Tm--moulding temperature, °C). Moulding pressure (kg/cm~): •--25, 2--50, 3--125, 4--225, 5--500, 6--1200, 7--3250. samples during m o n o l i t h formation, there is complete r e l a x a t i o n of t h e i n t e r n a l stresses. T h e d e p e n d e n c e of the annealing curves on pressure which coincides with a pressure rise from 25 to 400 kg/cm ~ is similar to t h a t f o u n d [4] for poly-

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I . M . MORTICE et al.

methylmethacrylate, and is apparently due to increased contaot between the polymer grains which facilitates monolith formation. A further rise in pressure (Fig. 1) results not in gradual displacement of the annealing curves into the high temperature region as in the case of :PMMA, but changes the position of the annealing curves. In the high temperature region the annealing curves have higher values relative to height recovery than the above-mentioned curves; moreover pressure rises are proportional to increasbs in the minimv:m value of Ah/h. :Plots of transparency loss by :PVC samples during annealing vs. moulding temperature (Fig. 2) are in complete agreement with the annealing curves and A~

5

I00

80 100

I

I

1

120

I~,0

16"0

I

180 T,,"C

FIG. 2. Plots of transparency loss vs. moulding temperature (AS~S, ~o--transparency loss; Tin--moulding temperature, °C). Moulding pressure (kg/cm2): 1--12.5, 2--25, 3--50, 4--125, 5--500 and above. indicate that the samples suffer complete loss of transparency when the monolith formation pressure exceeds 400 kg/cm 2. On comparing the experimental results one m a y conclude that within strictly limited pressure limits, at temperatures starting from 140 ° (i.e. below the temperature at which PVC undergoes transition into a state of viscous flow), truly monolithic samples are obtainable. Figure 3 shows the region of true monolith formation obtained from the annealing curves. The data on change in the flotation temperatures of the samples and in the relative recovery of thickness during the subsequent action of temperature and pressure on the samples (see Table) indicates that at the same time irreversible coalescence of the polymer grains does in fact take place. An interesting feature of the region of true PVC monolith formation is the presence of a certain critical pressure (Per) above which truly monolithic samples are unobtainable at any temperature. This is why this region was not detected in [9]. Further study of PVC monolith formation showed that with pressures exceeding Per a marked change occurs in several of the properties of transparent samples. :Plots of pressure versus inverse flotation temperatures and light-transmission coefficients of the samples show that there is a pressure region together with a lower limit of Per where a pressure rise is accompanied by a rapid increase in the density of the samples and in their degree of colouring.

Monolith formation of polyvinylehloride FLOTATIOI~" TEMPERATURE

AND RELATIVE

TION TO CONDITIONS

HEIGHT

RECOVERY

OF PRODUCTION

843

DURING

OF PVC

ANlhrEALING IN RELA-

SAMPLES

(Annealing temperature 110°, annealing time, 1 hr) Relative recovery of thickness I I during annealing temperature, of samples, oC %

Production conditions for samples Sample marking pressure,

kg/cm ~ A B A* A*-sample

lO0 1000 1000

140 140 140

i i

5.5 11 6

Flotation temperature of samples, oC before annealing

after annealing

36 22 22

37 70 37

A, r e m o u l d e d u n d e r the conditions indicated.

The authors attempted to elucidate the nature of Per during PVC monolith formation. Figure 6 shows applied pressure plotted against minimum values of height recovery taken from Fig. 1, and glass temperatures Tg of the polymer. To determine the relation of Tg to pressure the method described in [10] was used. /t, rp J 2 x

I

I

I

90

110

/3O

FIG. 3

I

ZSO ~ °C

I

I

e

I

3 ~;

FIG. 4

FIG. 3. Log P vs. T (P--pressure, kg/cm2; T - - m o u l d i n g temperature, °C): / - - r e g i o n of production of transparent samples, 2--region of true PVC monolith formation, 3--conditions of production of samples used in electron microscopic examinations. FIG. 4. Inverse flotation temperatures (Tfl) of PVC samples vs. applied pressure (P, kg/cm~).

In our view the good agreement between these curves shows that the impairment of monolith formation is due to increased rigidity of the PVC chains, while the critical pressure is that above which a rapid rise in Tg commences. Thus it appears from this study of PVC monolith formation that the production of truly monolithic samples is possible only within a definite temperature and pressure region, and that it is not connected with transition of the polymer to the state of viscous flow.

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Mo~IoH et al.

There is at present no lack of published data on PVC, in particular with regard to its supermolecular structures. Thus in [6-7] it was shown that bulk and suspension PVC have a globular structure due the nature of the interaction of the polymer with its own monomer. It is also known [8] that in the processing of PVC b y milling, i.e. in th3 application of shearing forces and heating, the initial globular structure is broken down and a fibrillar structure is formed. Because of this it was suggested that the special features of PVC in the process of monolith formation are also connected with transformation of the supermoleeular structures. To verify this suggestion electron microscopic examination of the structure of PVC samples with different degrees of monolith formation was carried out. 0

A h/h, "/.

~0

20 /6

30

x/ 02

[2 25 10

/

t26

8 I

2

3 FIG. 5

[#

K~X

I

z loop

z

Fro. 6

FIG. 5. Coefficients of light-transmission (0) of PVC samples vs. moulding pressure (P, kg/cm2). FIG. 6. Relative recovery in height of samples Ah/h (1) and Tg of PVC (2) vs. pressure (P). Single-stage angular replicas were used shaded with Mn or Pt/Pd, where P t / P d denotes a mixture of platinum and palladium. Before splitting the samples were cooled down to the temperature of liquid nitrogen. The peeling off of the replicas was effected in cyclohexanone. The samples investigated were produced under pressures of 100 and 400 kg/cm 2 and above, and at temperatures of 100, 115, 150 and 160 °. Thus the selected samples were obtained both in the region of true monolith formation, and beyond its limits, and it was possible b y means of electron microscopy to trace changes occurring in the PVC structure, and from this point of view to explain the monolith formation process. In the samples produced at 100 and 115 ° (P----100 kg/cm 2) the break generally occurs on the surfaces of separate particles of the initial PVC powder. Deformed grains of the powder and the interfaces between them are clearly visible (Fig. 7a). This pattern found under conditions far removed from those of true monolith formation agrees well with data obtained from plots of relative height recovery b y samples during annealing vs. monolith formation temperature. Certainly the high value of Ah/h shows that there is practically no irreversible coalescence of

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Monolith formation of polyvinylchloride

~he PVC grains in these samples. H o w e v e r , even at a m o n o l i t h f o r m a t i o n t e m p e r a t u r e of 115 ° in separate places where t h e b o n d s t r e n g t h b e t w e e n particles is g r e a t e s t and approaches the cohesive s t r e n g t h of the particles themselves a b r e a k

i

:FIG. 7. Replicas of breaks in samples moulded under a pressure 100 kg/cm 2 and at temperatures (°C) of: a-- 100; b-- 115; c-- 130; d-- 140; e-- 150;f-- 150, after annealing at 110° for 3 hr. occurs within the grain, m a k i n g it possible to observe its globular s t r u c t u r e (Fig. 7b). W i t h rise in the t e m p e r a t u r e of m o n o l i t h f o r m a t i o n the degree of irreversible coalescence of t h e grain is increased, and at the same time the likelihood

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I.M. Mo~rmH et al.

of a crack occurring at the time of the break within the grain. Therefore the number of opened grains is much greater at 130 ° than at 115 ° . When the temperature approaches nearer to the region of true monolith formation, greater changes are observed in the PVC structure. Thus at 130 ° fibrillar formations begin to appear in the replicas (Fig. 7c), and at 140 ° and above the fibrillar structure of the PVC begins to predominate (Fig. 7d, e). The fibrillar formations are most frequently gathered into bundle having a fan-like shape, and this arrangement of the fibrils is evidently due to the stress distribution in the PVC sample during its moulding, while the fibrillization of the initial globular structure indicates that shearing stresses develop in the sample with the application of pressure. The presence in the samples of segments in which globular and fibrillar structures coexist (Fig. 7c, d) is due to the fact that under the given conditions the sample as a whole is not subjected to the same internal stress conditions so t h a t transformation of the structure is not uniform through the whole volume of the sample. Under pressures higher than 400 kg/cm ~ fibrillar structures are not found in the samples whatever the temperature of monolith formation. Comparison of the electron microscopic data with the results of investigating the properties of PVC samples prepared in various regions of monolith formation indicates that true monolith formation is connected with structural changes resulting in the formation of fibrillar supermolecular structures in the region of true monolith formation. Moreover these structures are very stable; for instance, annealing at 100 ° for 3 hr does not cause any noticeable changes in it (Fig. 7f). It m a y be assumed that this peculiar behaviour is characteristic of PVC when instead of melting it readjusts its supermolecular structure according to the conditions. The authors are deeply grateful to V. A. Kargin for valuable advice and observations during discussion of these experiments. CONCLUSIONS

(1) The main mechanisms in the process of monolith formation from PVC powder have been studied. The possibility of distinguishing the range of pressures and temperatures in which truly monolithic samples are obtained by press-moulding has been demonstrated. (2 l It has been established that the region of true monolith formation of PVC is not connected with transition of the polymer into a state of viscous flow. (3) A critical pressure (400 kg/cm ~) above which no true PVC monoliths are obtainable at any temperature has been determined. (4) Electron microscopic examination of the structure of samples with different degrees of monolith formation shows that the process of true PVC monolith formation is connected with structural changes. Translated by R. J. A. HENDRY

Calculation of volume effects in macromolecules

847

REFERENCES 1. L. A. IGONIN, Yu. V. OVCHINNIKOV and S. A. ARZHAKOV, Dokl. Akad. Nauk SSSR 120: 1062, 1958 2. S.A. ARZHAKOV, Ye. Ye. RYLOV and B. P. SHTARKMAN, Vysokomol. soyed. 1: 1351, 1959 (Not translated in Polymer Sci. U.S.S.R.) 3. S. A. ARZHAKOV, Ye. Ye. RYLOV, G.L. SLONIMSKII and B. P. SHTARKMAN, Vysokomol. soyed. 5: 1513, 1963 (Translated in Polymer Sei. U.S.S.R. 5: 4, 614, 1964) 4. S. A. ARZHAKOV, Ye. Ye. RYLOV and B. P. SHTARKMAN, Vysokomol. soyed. 1: 1357, 1959 (Not translated in Polymer Sci. U.S.S.R.) 5. Yu. V. OVCHINNIKOV, Thesis, 1961 6. D.N. BORT, Ye. Ye. RYLOV, N. A. OKLADNOV, B. P. SHTARKMAN and V. A. KARGIN, Vysokomol. soyed. 7: 50, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 1, 50, 1965) 7. D. N. BORT, Thesis, 1965 8. L. I. VIDYAIKINA, N. A. OKLADNOV and B. P. SHTARKMAN, Vysokomol. soyed. 8: 390, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 3, 425, 1966) 9. Yu. V. OVCHINNIKOV, S. A. ARZHAKOV and L. A. IGONIN, Chem. Trans. (Gorkii) vol. I, 203, 1959 10. S. A. ARZHAKOV, G. L .SLONIMSKII, B. P. SHTARKMAN and V. A. KARGIN, Vysokotool. soyed. 5: 1854, 1963 (Translated in Polymer Sci. U.S.S.R. 5: 6, 986, 1964)

CALCULATION OF VOLUME EFFECTS IN MACROMOLECULES BY MEANS OF A MONTE CARLO METHOD: NON-SELF-INTERSECTING CHAINS ON A CUBIC LATTICE * A. K. K a o ~ and O. B. :PTITSY~ Institute of High-Molecular Compounds, U.S.S.R. Academy of Sciences

(Received 10 January 1966) MACROMOLECULES in solution generally have the shape of statistically rolled

coils. Where there is no interaction between different segments of the coils we have the so-called Gaussian coil, the average dimensions and shape of which have often figured in theoretical investigations. However, if all the chain segments interact with one another (the so-called volume effects) the average dimensions of the macromoleeule will differ from those of a Gaussian coil. Considerable difficulties are involved in theoretical investigation of these chains: in this connection there are the approximate formulae of Flory [1] and of one of the present authors [2]~ and of Kurata, Stockmayer and Roig [4] which were obtained by * Vysokomol. soyed. A9: No. 4, 759-764, 1967. ¢ A similar formula was afterwards suggested by F i x m a n [3].