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An electron microscope investigation of films of synthetic polyisoprene rubber hydrochloride
AN ELECTRON MICROSCOPE INVESTIGATION OF FILMS OF SYNTHETIC POLYISOPRENE R U B B E R HYDROCHLORIDE V. Y~,. Gun' and E. IV[. I~OOOVXYA Moscow Technical I n s ti tu te for the Meat and Dairy I n d u s t r y
(Received 16 July
1965)
FILMS of natural rubber hydrochloride have found wide use as a packing material for the food industry. Attempts to obtain similar films from synthetic rubber hydroclflorides have frequently led to unsuccessful results [1]. The reason for this lack of success was the difficulty of obtaining a structure corresponding to the required set of properties. The appearance of a Soviet synthetic polyisoprene rubber with a regular structure, and also the wide development of structural investigations [2-5, 10] have made it possible to obtain, from synthetic polyisoprene rubber hydrochloride, a film which is not inferior in its properties to film from natural rubber hydrochloride [6]. In connection with what has been said, it is of great interest to study the structures of synthetic polyisoprene rubber hydrochloride (HC SKI) and to compare these with its properties. The work was carried out on EM-5 and J E M - 5 Y electron microscopes at electronoptical magnifications from 5000 up to 20,000. The following methods were used in the work: direct observation, ultra-thin sections, and replicas. With the direct observation method, the samples were prepared by placing a drop of the polymer solution (from 0"1 up to 2%) on a grid with a carbon or collodion substrate, or in the form of films, which were formed on the surface of water or on glass from an 0"1% solution. Methylene chloride and dichlorethane were used as solvents. The image contrast was increased by shadowing the samples with palladium, which was accomplished in an EVP-2 apparatus. The samples were prepared at room temperature and with annealing. The carbon replica method was used in the work. The replicas were taken from an etched surface of the polymer film and from a copy of a thick film (a few hundred microns). The carbon replica, shadowed with palladium, was removed by means of collodion and gelatin films which were then dissolved away. The ultra-thin sections were obtained on a microtome UMT-2 with the method described for biological objects [7]. Strips of the polymer (7 x 1 × 0"3 ram) were encapsulated by polymerization in a mixture of methyl metha~rylate (1 part by weight), butyl methacrylate (4 parts by weight) and benzoyl peroxide (1%) in gelatinous capsules and held in a thermostat at 50°C for 28 hr. * Vysokomol. soyed. 8: No. 9, 1539-1541, 1966. 1696
Synthetic polyisoprene rubber hydrochloride
1697
A m i c r o p h o t o g r a p h of a film o f the h y d r o c h l o r i d e o f s y n t h e t i c polyisoprene r u b b e r S K I - 3 is shown in Fig. 1. F r o m a careful consideration of the picture obtained, it m a y be seen t h a t it takes t h e f o r m o f a s y s t e m o f rods or fibres, consisting of fine grains. T r e a t m e n t of a large n u m b e r of h y d r o c h l o r i d e S K I - 3 films has shown t h a t such a s t r u c t u r e arises only in cases when stresses are created in t h e film during deposition on to the grid. I n the picture shown in ]~ig. 1,
FIG. 1. Sample of SKI-3 hydroehloride, prepared from a 1~o solution in methylene chloride at 20°C. Pd shadowed (× 15,000). FIG. 2. Ultra-thin section of SKI-3 hydrochloride (× 12,000). FIG. 3. Carbon replica taken from etched surface of SKI-3 hydrochloride (x 10,000). Fro. 4. Sample of SKI-3 hydrochloride, prepared from a 0"1~o solution in methylene chloride at 20°C and annealed for 6 hr at 104°C. Pd shadowed (× 12,000). t h e stresses are so great t h a t ellipsoidal tears h a v e been f o r m e d in the film, t h e m a j o r axes of which are o r i e n t a t e d along t h e line o f action of the deforming forces [8]. T h e grains, which f o r m t h e rods, are always observed a n d e v i d e n t l y represent crystalline f o r m a t i o n s of t h e spherulite t y p e . As will be shown, t h e crystalline n a t u r e o f the s t r u c t u r e was confirmed b y electron a n d X - r a y diffraction methods. The dimension of the grains was of the order of 0.1-0.5/~.
1698
V. YE. GI~L' and E. M. ROGOVAYA
Figure 2 shows an electron microscope picture o f an u l t r a - t h i n section o f S K I - 3 hydrochloride, in which the details of the film s t r u c t u r e are more clearly expressed. I n the same w a y as in Fig. 1, spherulites with a size of the order o f 0.1-0.5/~ can be seen. The carbon replica o b t a i n e d from an e t c h e d surface of SKI-3 h y d r o c h l o r i d e film (Fig. 3) also confirms the ideas p u t forward above.
FIG. 5a and b. Microdiffraetion picture of an SKI-3 hydrochloride sample obtained after annealing for 6 hr at 104°C. FIG. 6. Microstructure of an SKI-3 hydrochloride sample obtained from an 0"1~o solution in methylene chloride at 20°C and annealed for 6 hr at 104°C. Pd shadowed (× 12,000). FxG. 7. Stretched film of SKI-3 hydrochloride obtained from an 0"5~/osolution in methylene chloride. Pd shadowed (x 16,000). F r o m work carried out previoulsy on the g r o w t h of crystalline (in p a r t i c u l a r spherulitic) structures in isotactic p o l y p r o p y l e n e b y the annealing m e t h o d [9, 10] it is k n o w n t h a t during annealing it is possible to obtain more perfect crystalline structures. F o r this purpose, samples of S K I - 3 h y d r o c h l o r i d e on a carbon subs t r a t e were t a k e n a n d held in a t h e r m o s t a t at 104°C for 6-10 hr, after which t h e y were slowly cooled at a r a t e of l°C/hour. T h u s b o t h spherulites a n d also single crystals (one of the single crystals is pointed out b y the arrow in Fig. 4) were observed, the microdiffractibn p a t t e r n being evidence of this (Fig. 5 a n d 5a).
Synthetic polyisoprene rubber hydrochloride
1699
I n samples o b t a i n e d b y the annealing m e t h o d (Fig. 6), we observed r i b b o n s t r u c t u r e s t y p i c a l o f elastomers [2]. One m a y suppose t h a t t h e s t r u c t u r e of the actual p o l y m e r takes the form o f a c o m b i n a t i o n of a m o r p h o u s a n d crystalline structures. I t is also possible t h a t the a m o r p h o u s a n d crystalline p a r t s differ in their degree o f h y d r o e h l o r i n a t i o n . H o w e v e r , it is also posible t h a t the " m o i r e " picture is n o t a film structure, b u t is o b t a i n e d because of the film's rapid d r y i n g out a n d reflects t h e microrelief o f the film surface. W i t h the aim of explaining t h e s t r u c t u r e better, S K I - 3 h y d r o c h l o r i d e films were subjected to stretching on t h e surface o f water. ]~r o m the m i c r o p h o t o g r a p h o f the s t r e t c h e d sample, it m a y be seen (Fig. 7) t h a t a splitting u p of the film into separate fibres with t h e b r e a k - d o w n of the spherulitie s t r u c t u r e s takes place along the force field, t o g e t h e r w i t h a r e d u c t i o n in t h e cross-sectional area of the fibres a n d t h e n t h e i r r u p t u r e . CONCLUSIONS
An electron microscope investigation carried out into the s t r u c t u r e of S K I - 3 h y d r o c h l o r i d e has shown t h a t S K I - 3 h y d r o c h l o r i d e has a fine grain s t r u c t u r e of the spherulitic t y p e with spherulite dimensions o f a few t e n t h s o f a micron. The possibility has also been d e m o n s t r a t e d of obtaining single crystals o f S K I - 3 h y d r o c h l o r i d e u n d e r certain conditions. E l e c t r o n m i c r o g r a p h i e d a t a has been o b t a i n e d which is evidence o f the presence o f single a n d polycrystalline structures in S K I - 3 hydroehloride. W h e n t h i n films are s t r e t c h e d , s e p a r a t i o n of the film into individual fibres takes place w i t h b r e a k - d o w n o f the spherulites and s u b s e q u e n t r e d u c t i o n in r o d thickness. Translated by G. F. MODLE~ REFERENCES
1. G. S. WHITBY, Sinteticheskii kauchuk. (Synthetic Rubber.) (Russian translation) Leningrad, p. 611, 1957 2. V. G. KALASHNIKOVA, M. V. KAZHDAN, Z. Ya. BERESTNEVA and V. A. KARGIN, Vysokomol. soyed. 6: 906, 1964 (Translated in Polymer Science U.S.S.R. 6: 5, 998, 1965) 3. P. V. KOZLOV, N. F. BAKEYEV, LI PAN-TUN and A. S. KAFTANOVA, Vysokomol. soyed. 2: 421, 1960 (l~ot translated in Polymer Science U.S.S.R.) 4. V. A. KARGIN, T. I. SOGOLOVA and L. I. NADAREISHVILI, Vysokomol. soyed. 6: 1407, 1964 (Translated in Polymer Science U.S.S.R. 6: 8, 1554, 1965) 5. V. Ye. Gul', V. V. KOVRIGA and A. M. VASSERMAN, Dokl. Akad. Nauk SSSR, 146: 656, 1962 6. Yu. G. GORBACHEV, V. Ye. GUL', O. N. BELYATSKAYA and K. A. GORBATOVA, IX mendeleyevskii s'yezd po obshchei i prikladnoi khimii. Sektsiya khimii i tekhnologii pishehevykh produktov. (IXth Mendeleyev Conference on General and Applied Chemistry. Section on the Chemistry and Technology of Foodstuffs.) Kiev, p. 120, 1965 7. V. L BIRYUZOVA, V. L. BOROVYAGIN, V. P. GILEV, N. A. KISELEV, A. S. TIKHONENKO and Yu. S. CHENTSOV, Elektronnomikroskopicheskiye metody issledovaniya biologicheskikh ob'yektov. (Electron Microscope Methods of Investigating Biological Objects.) Moscow, p. 120, 1963. 8. V. Ye. GUL', Prochnost polimerov. (Strength of Polymers.) Moscow, 1964 9. G. P. ANDRIANOVA, Dissertation, Moscow, 1963 10. V. Ye. GUL', Y. V. KOVRIGA, E. M. ROGOVAYA and N. P. GROMOVA, Vysokomol. soyed. 6: 10, 1868, 1964 (Translated in Polymer Science U.S.S.R. 6: 10, 2668, 1965)
(Received 16 July
1965)
FILMS of natural rubber hydrochloride have found wide use as a packing material for the food industry. Attempts to obtain similar films from synthetic rubber hydroclflorides have frequently led to unsuccessful results [1]. The reason for this lack of success was the difficulty of obtaining a structure corresponding to the required set of properties. The appearance of a Soviet synthetic polyisoprene rubber with a regular structure, and also the wide development of structural investigations [2-5, 10] have made it possible to obtain, from synthetic polyisoprene rubber hydrochloride, a film which is not inferior in its properties to film from natural rubber hydrochloride [6]. In connection with what has been said, it is of great interest to study the structures of synthetic polyisoprene rubber hydrochloride (HC SKI) and to compare these with its properties. The work was carried out on EM-5 and J E M - 5 Y electron microscopes at electronoptical magnifications from 5000 up to 20,000. The following methods were used in the work: direct observation, ultra-thin sections, and replicas. With the direct observation method, the samples were prepared by placing a drop of the polymer solution (from 0"1 up to 2%) on a grid with a carbon or collodion substrate, or in the form of films, which were formed on the surface of water or on glass from an 0"1% solution. Methylene chloride and dichlorethane were used as solvents. The image contrast was increased by shadowing the samples with palladium, which was accomplished in an EVP-2 apparatus. The samples were prepared at room temperature and with annealing. The carbon replica method was used in the work. The replicas were taken from an etched surface of the polymer film and from a copy of a thick film (a few hundred microns). The carbon replica, shadowed with palladium, was removed by means of collodion and gelatin films which were then dissolved away. The ultra-thin sections were obtained on a microtome UMT-2 with the method described for biological objects [7]. Strips of the polymer (7 x 1 × 0"3 ram) were encapsulated by polymerization in a mixture of methyl metha~rylate (1 part by weight), butyl methacrylate (4 parts by weight) and benzoyl peroxide (1%) in gelatinous capsules and held in a thermostat at 50°C for 28 hr. * Vysokomol. soyed. 8: No. 9, 1539-1541, 1966. 1696
Synthetic polyisoprene rubber hydrochloride
1697
A m i c r o p h o t o g r a p h of a film o f the h y d r o c h l o r i d e o f s y n t h e t i c polyisoprene r u b b e r S K I - 3 is shown in Fig. 1. F r o m a careful consideration of the picture obtained, it m a y be seen t h a t it takes t h e f o r m o f a s y s t e m o f rods or fibres, consisting of fine grains. T r e a t m e n t of a large n u m b e r of h y d r o c h l o r i d e S K I - 3 films has shown t h a t such a s t r u c t u r e arises only in cases when stresses are created in t h e film during deposition on to the grid. I n the picture shown in ]~ig. 1,
FIG. 1. Sample of SKI-3 hydroehloride, prepared from a 1~o solution in methylene chloride at 20°C. Pd shadowed (× 15,000). FIG. 2. Ultra-thin section of SKI-3 hydrochloride (× 12,000). FIG. 3. Carbon replica taken from etched surface of SKI-3 hydrochloride (x 10,000). Fro. 4. Sample of SKI-3 hydrochloride, prepared from a 0"1~o solution in methylene chloride at 20°C and annealed for 6 hr at 104°C. Pd shadowed (× 12,000). t h e stresses are so great t h a t ellipsoidal tears h a v e been f o r m e d in the film, t h e m a j o r axes of which are o r i e n t a t e d along t h e line o f action of the deforming forces [8]. T h e grains, which f o r m t h e rods, are always observed a n d e v i d e n t l y represent crystalline f o r m a t i o n s of t h e spherulite t y p e . As will be shown, t h e crystalline n a t u r e o f the s t r u c t u r e was confirmed b y electron a n d X - r a y diffraction methods. The dimension of the grains was of the order of 0.1-0.5/~.
1698
V. YE. GI~L' and E. M. ROGOVAYA
Figure 2 shows an electron microscope picture o f an u l t r a - t h i n section o f S K I - 3 hydrochloride, in which the details of the film s t r u c t u r e are more clearly expressed. I n the same w a y as in Fig. 1, spherulites with a size of the order o f 0.1-0.5/~ can be seen. The carbon replica o b t a i n e d from an e t c h e d surface of SKI-3 h y d r o c h l o r i d e film (Fig. 3) also confirms the ideas p u t forward above.
FIG. 5a and b. Microdiffraetion picture of an SKI-3 hydrochloride sample obtained after annealing for 6 hr at 104°C. FIG. 6. Microstructure of an SKI-3 hydrochloride sample obtained from an 0"1~o solution in methylene chloride at 20°C and annealed for 6 hr at 104°C. Pd shadowed (× 12,000). FxG. 7. Stretched film of SKI-3 hydrochloride obtained from an 0"5~/osolution in methylene chloride. Pd shadowed (x 16,000). F r o m work carried out previoulsy on the g r o w t h of crystalline (in p a r t i c u l a r spherulitic) structures in isotactic p o l y p r o p y l e n e b y the annealing m e t h o d [9, 10] it is k n o w n t h a t during annealing it is possible to obtain more perfect crystalline structures. F o r this purpose, samples of S K I - 3 h y d r o c h l o r i d e on a carbon subs t r a t e were t a k e n a n d held in a t h e r m o s t a t at 104°C for 6-10 hr, after which t h e y were slowly cooled at a r a t e of l°C/hour. T h u s b o t h spherulites a n d also single crystals (one of the single crystals is pointed out b y the arrow in Fig. 4) were observed, the microdiffractibn p a t t e r n being evidence of this (Fig. 5 a n d 5a).
Synthetic polyisoprene rubber hydrochloride
1699
I n samples o b t a i n e d b y the annealing m e t h o d (Fig. 6), we observed r i b b o n s t r u c t u r e s t y p i c a l o f elastomers [2]. One m a y suppose t h a t t h e s t r u c t u r e of the actual p o l y m e r takes the form o f a c o m b i n a t i o n of a m o r p h o u s a n d crystalline structures. I t is also possible t h a t the a m o r p h o u s a n d crystalline p a r t s differ in their degree o f h y d r o e h l o r i n a t i o n . H o w e v e r , it is also posible t h a t the " m o i r e " picture is n o t a film structure, b u t is o b t a i n e d because of the film's rapid d r y i n g out a n d reflects t h e microrelief o f the film surface. W i t h the aim of explaining t h e s t r u c t u r e better, S K I - 3 h y d r o c h l o r i d e films were subjected to stretching on t h e surface o f water. ]~r o m the m i c r o p h o t o g r a p h o f the s t r e t c h e d sample, it m a y be seen (Fig. 7) t h a t a splitting u p of the film into separate fibres with t h e b r e a k - d o w n of the spherulitie s t r u c t u r e s takes place along the force field, t o g e t h e r w i t h a r e d u c t i o n in t h e cross-sectional area of the fibres a n d t h e n t h e i r r u p t u r e . CONCLUSIONS
An electron microscope investigation carried out into the s t r u c t u r e of S K I - 3 h y d r o c h l o r i d e has shown t h a t S K I - 3 h y d r o c h l o r i d e has a fine grain s t r u c t u r e of the spherulitic t y p e with spherulite dimensions o f a few t e n t h s o f a micron. The possibility has also been d e m o n s t r a t e d of obtaining single crystals o f S K I - 3 h y d r o c h l o r i d e u n d e r certain conditions. E l e c t r o n m i c r o g r a p h i e d a t a has been o b t a i n e d which is evidence o f the presence o f single a n d polycrystalline structures in S K I - 3 hydroehloride. W h e n t h i n films are s t r e t c h e d , s e p a r a t i o n of the film into individual fibres takes place w i t h b r e a k - d o w n o f the spherulites and s u b s e q u e n t r e d u c t i o n in r o d thickness. Translated by G. F. MODLE~ REFERENCES
1. G. S. WHITBY, Sinteticheskii kauchuk. (Synthetic Rubber.) (Russian translation) Leningrad, p. 611, 1957 2. V. G. KALASHNIKOVA, M. V. KAZHDAN, Z. Ya. BERESTNEVA and V. A. KARGIN, Vysokomol. soyed. 6: 906, 1964 (Translated in Polymer Science U.S.S.R. 6: 5, 998, 1965) 3. P. V. KOZLOV, N. F. BAKEYEV, LI PAN-TUN and A. S. KAFTANOVA, Vysokomol. soyed. 2: 421, 1960 (l~ot translated in Polymer Science U.S.S.R.) 4. V. A. KARGIN, T. I. SOGOLOVA and L. I. NADAREISHVILI, Vysokomol. soyed. 6: 1407, 1964 (Translated in Polymer Science U.S.S.R. 6: 8, 1554, 1965) 5. V. Ye. Gul', V. V. KOVRIGA and A. M. VASSERMAN, Dokl. Akad. Nauk SSSR, 146: 656, 1962 6. Yu. G. GORBACHEV, V. Ye. GUL', O. N. BELYATSKAYA and K. A. GORBATOVA, IX mendeleyevskii s'yezd po obshchei i prikladnoi khimii. Sektsiya khimii i tekhnologii pishehevykh produktov. (IXth Mendeleyev Conference on General and Applied Chemistry. Section on the Chemistry and Technology of Foodstuffs.) Kiev, p. 120, 1965 7. V. L BIRYUZOVA, V. L. BOROVYAGIN, V. P. GILEV, N. A. KISELEV, A. S. TIKHONENKO and Yu. S. CHENTSOV, Elektronnomikroskopicheskiye metody issledovaniya biologicheskikh ob'yektov. (Electron Microscope Methods of Investigating Biological Objects.) Moscow, p. 120, 1963. 8. V. Ye. GUL', Prochnost polimerov. (Strength of Polymers.) Moscow, 1964 9. G. P. ANDRIANOVA, Dissertation, Moscow, 1963 10. V. Ye. GUL', Y. V. KOVRIGA, E. M. ROGOVAYA and N. P. GROMOVA, Vysokomol. soyed. 6: 10, 1868, 1964 (Translated in Polymer Science U.S.S.R. 6: 10, 2668, 1965)