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An electron microscope study of crystallization in thin polymer layers
2296
Yu. M. ]~AT.TI~'SKII¢A~al. REFERENCES
1. V. Ya. KABANOV, N. M. KAZIiKIROVA, A. A. NESTERENKO and V. I. SPITSYN,
Vysokomol. soyed. B10: 855, 1968 (Not translated is Polymer Sci. U.S.S.R.) 2. V. Ya. KABANOV, R. E. ALIEV and N. M. KAZIMIROVA, Vysokomol. soyed. BU: 834, 1969 (Not translated in Polymer Sci. U.S.S.R.) 3. K. Kh. RAZIKOV, Kh. U. USMANOV and U. A. AZIZOV, Vysokomol. soyed. 7: 1798, 1965 (Translated in Polymer Sei. U.S.S.R. 7: 10, 1980, 1965) 4. M. L. ROLLINS, A. M. CANNIZZARO, F. A. BLOUIN and G. C. ARTHUR, J. Appl. Polymer Sci. 12: 71, 1968 5. V. Ya. KABANOV, N. M. KAZIMIROVA and V. I. SPITSYN, Vysokomol. soyed. Ag: 1758, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 8, 1983, 1967) 6. M. R. KISELEV, E. L YEVKO and V. M. LUK'YANOVICH, Zavod. labor. 32: 201, 1966
AN ELECTRON MICROSCOPE STUDY 0F CRYSTALIJ~ATION IN THIN POLYMER LAYERS* Yu. M. ~AT,TWSKH,M. B. KONSTAlVTIlVOPOL'SKAYA,N. l~I. TITOVA and V. A. KARGnV (dec.) L. Ya. Karpov Scientific Research Institute of Physical Chemistry
(Received 8 February 1971) THE behaviour of polymers situated at t he b o u n d a r y of two phases is known to differ from t h a t in t he bulk [1, 2]. The mobility is reduced in t he boundary layers due to interaction with the surface of the other phase and t he geometrical restriction of the number of macromolecular conformations. Earlier studies had shown polypropylene with a 60% v / v glass powder cont e n t [3] to be almost incapable of crystallization; this was regarded as evidence of a v e r y substantial restriction of movement of t he structural elements. The influence of the solid surface on the crystallization kinetics of the polymers in thin layers has been established [4]. The object of this work was to study the influence of a hard surface on structure formation in polymers. Electron-microscopic observations were made of the crystallization of polymers on solid surfaces of different chemical compositions. We assumed th e surface energy of the material in contact with t he polymer surface to affect molecular motion at the phase boundary, which would affect the crystallization characteristics. EXPERIMENTAL
We studied isotactic polypropylene (Moplen). The structures produced on fiat, solid surfaces and in systems filled with a dispersed fine powder were studied. The polymer ~lms were produced from solutions with different thermal histories be* Vysokomol. soyed. A14: No. 9, 2048-2052, 1972.
Crystallization in thin polymer layers
2297
cause it is known [5, 6] that the temperature and the duration of heating the solution before pouring it on supports have an effect on the polymer structure in the solution and on the morphology of the resulting films. Electron photomierograms were produced to determine the state of phase of the polymer. Crystallization of pO~ypropylene (PP) on solid surfaces from solutions not subjected to heat treatment. Solutions of 0"001-0"lye concentration were used in the crystallization experi. ments. The original PP suspension in decalin was heated to the boiling point and the resulting solution was immediately poured on electron microscope grid supports with a carbon or quartz film base; the latter were at room temperature. The solvent was evaporated at room temperature and the amorphous samples (the state of phase was assessed from the morphological picture and the absence of crystal reflections) were tempered at 94 or 165°C for 2 hr. The samples were shadowed with palladium to increase the contrast. RESULTS
Tempering at 94°C yielded particles on both the supports which were amorphous according to electron-scattering (Fig. la). This was found in all the original solution concentrations. One could have assumed the amorphous state of P P under these conditions to be the result of an insufficiently high tempering temperature. To verify this and to create more favourable crystallization conditions, the films were tempered at 165°C. This temperature elevation did not produce a n y drastic morphological changes in P P films produced from 0.02% solution (Fig. lb), but the general electron diffraction picture showed reflections in the samples produced on both bases. These belonged to the a-modification of P P (Fig. lc). A 0.1% P P solution on a carbon base crystallized in typically dendritic crystals (Fig. 2a), while a quartz base did not give any morphologically typical structures at first (Fig. 2b). The tempering of films produced from 0.02% solutions on the quartz and carbon bases showed crystallization to be inhibited at 94°C regardless of the chemical nature of the bases, or retarded at 165°C; the crystal phase formed in the latter case, but the electron-microscope picture remained unchanged. However, the effect of the quartz base on crystallization spread further in depth during tempering t h a n t h a t of the carbon base. The experiments made so far had not led to the detection, in the majority of cases, of dendritic crystals typical for PP; the fact t h a t structures formed were evident only in the electron pictures, as there was only a slight morphological change during crystallization of the P P films. We were therefore interested to find conditions which would give rise to dendritic crystals. The solutions used for this purpose had a different thermal history. P P crystallization on solid surfaces from solutions subjected to heat treatment. The heat t r e a t m e n t of the solutions was t h a t described earlier [6]. The structure formation in dilute P P solutions was very slow. This agreed with earlier findings [5] on the formation kinetics of structures in polymer solutions. The original P P suspension in dec&lin was heated to its boiling point and placed in a thermostat at 94°C for 3-4 hr (such heating possibly produces some de-
2296
Y u . M. MALINSKII e$ al.
gradation of PP, but even if this is the case, it is not likely to interfere with the effect of the type of base on the crystallization which takes place in the polymer film). A droplet of the solution was then placed at t h a t temperature on the electron microscope grid, the solvent was evaporated and the sample tempered 2 hr at 94 or 165°C.
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N Fio. 1. A polypropylene film produced from a 0.02~ solution which was not heat-treated-" a--after crystallization at 94°C on carbon and quartz, b--ditto at 165°C, c--electron diffraction picture after crystallization at 185°C. Films produced from solutions with a 0.002-0.1% P P concentration showed typical dendritic crystals on both the bases even before tempering; these were like those shown in Fig. 2a and remained also afVer tempering. This means t h a t there was no further strueturation during tempering. The influence of the type of base on crystallization was detected on films produced from 0.001% solution; the films were amorphous on both the bases before
Crystallization in thin polymer layers
2299
tempering. Tempering on a quartz base at 94°C left the whole film amorphous (Fig. 2c), while dendritic crystalls appeared on the carbon base (Fig. 2d). The amorphous structure of the P P film on the quartz base, and the crystalline one on the carbon base was confirmed b y the electron diffraction picture, i.e. there were no reflections in the first case, typical for a crystalline polymer (Fig. 3a), b u t microdiffraction showed in the second case (Fig. 3b) the typical fibrils of P P spherulites [7].
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FIe. 2. A polypropylene film produced from: a, b--a 0"lye, c, d--a 0"00lYe solution not subjected to heat treatment after crystallization at: a, b - 165°C, c, d - - 9 4 ° C on: a, d - - c a r b o n , b, c-- quartz. More favourable crystallization conditions for films produced from 0.001% polymer solutions were created b y tempering at 165°C. The carbon base was found to give rise to well-defined facets which terminated in thinner needles (Fig. 4).
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FIG. 3. Electron diffraction pictures of polypropylene produced from a 0.001 Yo heat-treated solution after crystallization at 94°C on: a--quartz, b--carbon. (The observed d e p e n d e n c e o f t h e crystal m o r p h o l o g y on t h e crystallization t e m p e r a t u r e - d e n d r i t e s a t 94°C a n d facets a t 1 6 5 ° C - - a g r e e d w i t h t h a t f o u n d before [8]). No crystals t y p i c a l o f P P could be d e t e c t e d on quartz; t h e p o l y m e r r e m a i n e d a m o r p h o u s u n d e r these conditions.
FIG. 4. The structures present in polypropylene film produced from a 0.001 ~o heat-treated solution after crystallization at 165°C on a carbon base. FIG. 5. The structures present in polypropylene--glass powder filrnR after c r y s t a l l i z a t i o n on: a--quartz, b-- carbon.
T h e use o f h e a t - t r e a t e d solutions for P P film p r o d u c t i o n t h u s h a d a critical c o n c e n t r a t i o n ( 0 , 0 0 1 ~ ) below which t h e solid base can completely suppress crystallization.
Crystallization in thin polymer layers
2301
The structuration of P P in filled systems. The test series was carried out with a 0.001 solution, because the type of base had been found earlier to play a decisive part on crystallization in the polymer film. The filler was powdered glass with 1-2 g particle diameter. The original powdered glass suspension in the PP solution was heated 3 hr to 94°C, after which the solution was not shaken and the supernatant was transferred to another flask (this operation was carried out to remove traces of the atactie fraction and other admixtures which probably remained adsorbed on the glass), a new portion of glass was added and the whole kept another 3 hr at 94°C. The glass suspension in the PP solutions was then poured on the carbon or quartz base and tempered 2 hr at 94°C.
The P P was found to wrap the glass in a film on both types of bases, covering mostly all the particle surfaces, but sometimes only individual particles. All the glass particles were coated with amorphous P P on the quartz base (Fig. 5a). The P P crystallized dominantly at some distance from the glass surface when on the carbon base, and the thin polymer film adjacent to the latter was electron-optically blank; the polymer is probably amorphous in this layer (Fig. 5b). There were some cases, however, in which dendritic growth started immediately at the glass surface, and this was probably due to an activity difference between various particles on the glass surface. The literature contains numerous results indicating the physical and chemical heterogeneity of solid surfaces [9-11] and points out the extremely uneven surface distribution of adsorptive particles of varying activities, up to completely inactive ones. Our results fully agreed with these findings. EVALUATION OF RESULTS
This report describes the tests with solutions which had not been subjected to prolonged heating. The electron scattering studies showed the films produced from such solutions to be amorphous. Structures started to form in such films on the base during tempering, but this depended on the reaction between the solid surface and the macromolecules of the polymer. I t was actually proved t h a t the solid surface type plays a decisive part in structure formation, in the studied concentration range, i.e. in the layer in contact with the solid surface. Crystallization was either fully suppressed (at 94°C) or difficult (at 165°C), and the effect of the quartz base penetrated deeper t h a n t h a t of the carbon base. The bond between P P and quartz was thus stronger and this seems to be due to induction forces combining here with the dispersionary intermolecular ones. The effect of the base type on the behaviour of polymer crystals during tempering was also observed by others [12]. The authors explained this by referring to the theory of physieo-chemical reactions between the base and the polymer, and this was also the treatment given by us to our results. The influence of the type of adjacent phase on the polymer chain conformation in the surface layer was also pointed out elsewhere [13]. The use of a heat-treated P P solution for the film production showed the
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Yu. M. MA~NsYJIel a~.
solution concentration to affect the PP crystallization on the two bases. The quartz base, using a 0.001 ~ solution, was found to completely suppress crystallization while it occurred on the carbon base. From 0.002~ concentration onwards, the type of base had no effect, As the tempering of films made of greater than 0.002°~o solutions did not produce any structural changes on the bases, one can say that the reason for the lessening of the effect of the base, when increasing the solution concentration, is the existence of structuration in the solutions used. Heat-treated solutions of 0.002~/o and greater concentrations contained polymer already in an oriented state. The existence of a supermolecular structure in dilute solutions has already been reported in the literature [5, 14]. The film forming on the base retained the structure originally present in the solution. Both types of bases gave rise to typical dendritic structures of PP. Very dilute solutions (~0.001%) do not seem to contain orderly arranged structures, and the film produced from them will have a structure forming in it dependent on the type of interaction between the solid surface of the base and the polymer macromolecules; this also applied to untreated solutions. The observed suppression of crystallization on quartz seems to be connected with an almost complete lack of mobility in the polymer next to the quartz surface and this is due to strong intermolecular reactions. Raising the tempering temperature of polymer films produced from a 0.001% solution from 94 to 165°C resulted in a greater molecular mobility which sufficed for crystallization to take place on the carbon base, and for the formation of the higher order of crystals, but the picture remained unchanged in the case of the quartz base. The results of the electron microscopic study of PP crystallization in mixtures with glass powder on various solid bases showed that the structuration will depend in such systems on the total physical interaction of the polymer with the base and the filler; this confirmed the inference of there being a strong reaction between PP and quartz. All the polymer which had enveloped the glass particles was amorphous on the quartz base. Although the polymer crystallized on the carbon base, this only happened at some distance from the glass filler. This taken as evidence of glass delaying the crystallization in the boundary layer on the carbon surface. The examination of the above results showing the differing effects of different type surfaces on the crystallization and the morphology of the polymer in the boundary layers agreed with the findings published by a number of investigators [15-19]. CONCLUSIONS
(1) The formation of crystal structures will take place in polypropylene films on solid surfaces, but depends to a large extent on the physical reaction of the polymer with the base.
Crystallization in thin polymer layers
2803
(2) T h e c r y s t a l l i z a t i o n s t u d y of p o l y p r o p y l e n e in filled s y s t e m s on d i f f e r e n t solid b a s e s e s t a b l i s h e d t h a t t h e a c t i v i t y of t h e filler on c r y s t a l s t r u c t u r e f o r m a t i o n d e p e n d s on t h e t y p e of solid b a s e used. Translated by K. A. AT.T.~W
REFERENCES 1. Yu. S. L][PATOV, Fiziko-khimiya napolnonnykh polimerov (The Physical Chemistry of Polymer-Filler Systems). Izd. "Naukova dumka", 1967 2. Yu. M. MALINSKII, Uspekhi khim. 39: 1511, 1970 3. Yu. M. MAT,INSKII and L V. EPEL'BAUM, Vysokomol. soyed. B9: 500, 1967 (Not translated in Polymer Sci. U.S.S.R.) 4. Yu. M. MALINSKII, I. V. EPEL'BAUM, N. M. TITOVA and V. A. KARGIN, Vysokomol. soyed. A10: 786, 1968 (Translated in Polymer Sci. 1O: 4, 913, 1968) 5. N. I. NIKANOROVA, N. F. BAKEYEV, S. Kh. FAKIROV and V. A. KARGIN, Vysokoreel. soyed. A l l : 2197, 1969 (Translated in Polymer Sci. 11: 10, 2503, 1969) 6. I. I. GORINA, Dissertation, 1966 7. H. D. KEITH, F. J. PADDEN, N. M. WALTER and H. W. WIJKOFF, J. Appl. Phys. 30: 1485, 1959 8. V. A. KARGIN and I. I. GORIN.~, Vysokomol. soyed. 7: 220, 1965 (Translated in Polymer Sei. U.S.S.R. 7: 2, 237, 1965) 9. Ye. D. yAKHNIN, Dokl. Akad. Nauk SSSR 164: 1107, 1965 10. V. E. VASSERBERG, A. A. BALANDIN, F. E. ENGLINA and T. V. GEORGIEVSKAYA, Dokl. Akad, Nauk SSSI~ 169: 610, 1966 11. Ye. D. SItCHUKIN, R. K. YUSUPOV, Ye. A. AMELINA and P. A. REBINDER, Kolloid. zh. 31: 913, 1969 12. C. A. GARBER and P. H. GEIL, Makromol. Chemie 113: 246, 1968 13. A. Ye. FAINERMAN, Yu. S. LIPATOV and V. S. MAISTRUK, Dokl. Akad. l~auk SSSR 188: 152, 1969 14. V. A. KARGIN, S. Kh. FAKIROV and N. F. BAKEYEV, Dokl. Akad. Nauk SSSR 159: 885, 1964 15. J. S. MACKIE and A. RUDIN, J. Polymer Sci. 49: 407, 1961 16. Yu. G. YANOVSKII, E. I. FRENKIN and G. V. VINOGRADOVA, Mekhanika polimerov, 757, 1968 17. V. P. SOLOMKO, V. V. NIZHNIKH and V. M. ZHARTOV'SKII, Dokl. Akad. Nauk Ukrain. SSR, seriya B, No. 9, 832, 1968 18. Yu. Yu. KERi~HA and Yu. S. LIPATOV, Khim. prom. Ukrainy, ~o. 5 (41), 10, 1968 19. J. W. DODD, P. HOLLIDAY and B. E. PARKEN, Polymer 9: 54, 1968
Yu. M. ]~AT.TI~'SKII¢A~al. REFERENCES
1. V. Ya. KABANOV, N. M. KAZIiKIROVA, A. A. NESTERENKO and V. I. SPITSYN,
Vysokomol. soyed. B10: 855, 1968 (Not translated is Polymer Sci. U.S.S.R.) 2. V. Ya. KABANOV, R. E. ALIEV and N. M. KAZIMIROVA, Vysokomol. soyed. BU: 834, 1969 (Not translated in Polymer Sci. U.S.S.R.) 3. K. Kh. RAZIKOV, Kh. U. USMANOV and U. A. AZIZOV, Vysokomol. soyed. 7: 1798, 1965 (Translated in Polymer Sei. U.S.S.R. 7: 10, 1980, 1965) 4. M. L. ROLLINS, A. M. CANNIZZARO, F. A. BLOUIN and G. C. ARTHUR, J. Appl. Polymer Sci. 12: 71, 1968 5. V. Ya. KABANOV, N. M. KAZIMIROVA and V. I. SPITSYN, Vysokomol. soyed. Ag: 1758, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 8, 1983, 1967) 6. M. R. KISELEV, E. L YEVKO and V. M. LUK'YANOVICH, Zavod. labor. 32: 201, 1966
AN ELECTRON MICROSCOPE STUDY 0F CRYSTALIJ~ATION IN THIN POLYMER LAYERS* Yu. M. ~AT,TWSKH,M. B. KONSTAlVTIlVOPOL'SKAYA,N. l~I. TITOVA and V. A. KARGnV (dec.) L. Ya. Karpov Scientific Research Institute of Physical Chemistry
(Received 8 February 1971) THE behaviour of polymers situated at t he b o u n d a r y of two phases is known to differ from t h a t in t he bulk [1, 2]. The mobility is reduced in t he boundary layers due to interaction with the surface of the other phase and t he geometrical restriction of the number of macromolecular conformations. Earlier studies had shown polypropylene with a 60% v / v glass powder cont e n t [3] to be almost incapable of crystallization; this was regarded as evidence of a v e r y substantial restriction of movement of t he structural elements. The influence of the solid surface on the crystallization kinetics of the polymers in thin layers has been established [4]. The object of this work was to study the influence of a hard surface on structure formation in polymers. Electron-microscopic observations were made of the crystallization of polymers on solid surfaces of different chemical compositions. We assumed th e surface energy of the material in contact with t he polymer surface to affect molecular motion at the phase boundary, which would affect the crystallization characteristics. EXPERIMENTAL
We studied isotactic polypropylene (Moplen). The structures produced on fiat, solid surfaces and in systems filled with a dispersed fine powder were studied. The polymer ~lms were produced from solutions with different thermal histories be* Vysokomol. soyed. A14: No. 9, 2048-2052, 1972.
Crystallization in thin polymer layers
2297
cause it is known [5, 6] that the temperature and the duration of heating the solution before pouring it on supports have an effect on the polymer structure in the solution and on the morphology of the resulting films. Electron photomierograms were produced to determine the state of phase of the polymer. Crystallization of pO~ypropylene (PP) on solid surfaces from solutions not subjected to heat treatment. Solutions of 0"001-0"lye concentration were used in the crystallization experi. ments. The original PP suspension in decalin was heated to the boiling point and the resulting solution was immediately poured on electron microscope grid supports with a carbon or quartz film base; the latter were at room temperature. The solvent was evaporated at room temperature and the amorphous samples (the state of phase was assessed from the morphological picture and the absence of crystal reflections) were tempered at 94 or 165°C for 2 hr. The samples were shadowed with palladium to increase the contrast. RESULTS
Tempering at 94°C yielded particles on both the supports which were amorphous according to electron-scattering (Fig. la). This was found in all the original solution concentrations. One could have assumed the amorphous state of P P under these conditions to be the result of an insufficiently high tempering temperature. To verify this and to create more favourable crystallization conditions, the films were tempered at 165°C. This temperature elevation did not produce a n y drastic morphological changes in P P films produced from 0.02% solution (Fig. lb), but the general electron diffraction picture showed reflections in the samples produced on both bases. These belonged to the a-modification of P P (Fig. lc). A 0.1% P P solution on a carbon base crystallized in typically dendritic crystals (Fig. 2a), while a quartz base did not give any morphologically typical structures at first (Fig. 2b). The tempering of films produced from 0.02% solutions on the quartz and carbon bases showed crystallization to be inhibited at 94°C regardless of the chemical nature of the bases, or retarded at 165°C; the crystal phase formed in the latter case, but the electron-microscope picture remained unchanged. However, the effect of the quartz base on crystallization spread further in depth during tempering t h a n t h a t of the carbon base. The experiments made so far had not led to the detection, in the majority of cases, of dendritic crystals typical for PP; the fact t h a t structures formed were evident only in the electron pictures, as there was only a slight morphological change during crystallization of the P P films. We were therefore interested to find conditions which would give rise to dendritic crystals. The solutions used for this purpose had a different thermal history. P P crystallization on solid surfaces from solutions subjected to heat treatment. The heat t r e a t m e n t of the solutions was t h a t described earlier [6]. The structure formation in dilute P P solutions was very slow. This agreed with earlier findings [5] on the formation kinetics of structures in polymer solutions. The original P P suspension in dec&lin was heated to its boiling point and placed in a thermostat at 94°C for 3-4 hr (such heating possibly produces some de-
2296
Y u . M. MALINSKII e$ al.
gradation of PP, but even if this is the case, it is not likely to interfere with the effect of the type of base on the crystallization which takes place in the polymer film). A droplet of the solution was then placed at t h a t temperature on the electron microscope grid, the solvent was evaporated and the sample tempered 2 hr at 94 or 165°C.
.: ~ i . i ~
~. ~ ,:
N Fio. 1. A polypropylene film produced from a 0.02~ solution which was not heat-treated-" a--after crystallization at 94°C on carbon and quartz, b--ditto at 165°C, c--electron diffraction picture after crystallization at 185°C. Films produced from solutions with a 0.002-0.1% P P concentration showed typical dendritic crystals on both the bases even before tempering; these were like those shown in Fig. 2a and remained also afVer tempering. This means t h a t there was no further strueturation during tempering. The influence of the type of base on crystallization was detected on films produced from 0.001% solution; the films were amorphous on both the bases before
Crystallization in thin polymer layers
2299
tempering. Tempering on a quartz base at 94°C left the whole film amorphous (Fig. 2c), while dendritic crystalls appeared on the carbon base (Fig. 2d). The amorphous structure of the P P film on the quartz base, and the crystalline one on the carbon base was confirmed b y the electron diffraction picture, i.e. there were no reflections in the first case, typical for a crystalline polymer (Fig. 3a), b u t microdiffraction showed in the second case (Fig. 3b) the typical fibrils of P P spherulites [7].
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FIe. 2. A polypropylene film produced from: a, b--a 0"lye, c, d--a 0"00lYe solution not subjected to heat treatment after crystallization at: a, b - 165°C, c, d - - 9 4 ° C on: a, d - - c a r b o n , b, c-- quartz. More favourable crystallization conditions for films produced from 0.001% polymer solutions were created b y tempering at 165°C. The carbon base was found to give rise to well-defined facets which terminated in thinner needles (Fig. 4).
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FIG. 3. Electron diffraction pictures of polypropylene produced from a 0.001 Yo heat-treated solution after crystallization at 94°C on: a--quartz, b--carbon. (The observed d e p e n d e n c e o f t h e crystal m o r p h o l o g y on t h e crystallization t e m p e r a t u r e - d e n d r i t e s a t 94°C a n d facets a t 1 6 5 ° C - - a g r e e d w i t h t h a t f o u n d before [8]). No crystals t y p i c a l o f P P could be d e t e c t e d on quartz; t h e p o l y m e r r e m a i n e d a m o r p h o u s u n d e r these conditions.
FIG. 4. The structures present in polypropylene film produced from a 0.001 ~o heat-treated solution after crystallization at 165°C on a carbon base. FIG. 5. The structures present in polypropylene--glass powder filrnR after c r y s t a l l i z a t i o n on: a--quartz, b-- carbon.
T h e use o f h e a t - t r e a t e d solutions for P P film p r o d u c t i o n t h u s h a d a critical c o n c e n t r a t i o n ( 0 , 0 0 1 ~ ) below which t h e solid base can completely suppress crystallization.
Crystallization in thin polymer layers
2301
The structuration of P P in filled systems. The test series was carried out with a 0.001 solution, because the type of base had been found earlier to play a decisive part on crystallization in the polymer film. The filler was powdered glass with 1-2 g particle diameter. The original powdered glass suspension in the PP solution was heated 3 hr to 94°C, after which the solution was not shaken and the supernatant was transferred to another flask (this operation was carried out to remove traces of the atactie fraction and other admixtures which probably remained adsorbed on the glass), a new portion of glass was added and the whole kept another 3 hr at 94°C. The glass suspension in the PP solutions was then poured on the carbon or quartz base and tempered 2 hr at 94°C.
The P P was found to wrap the glass in a film on both types of bases, covering mostly all the particle surfaces, but sometimes only individual particles. All the glass particles were coated with amorphous P P on the quartz base (Fig. 5a). The P P crystallized dominantly at some distance from the glass surface when on the carbon base, and the thin polymer film adjacent to the latter was electron-optically blank; the polymer is probably amorphous in this layer (Fig. 5b). There were some cases, however, in which dendritic growth started immediately at the glass surface, and this was probably due to an activity difference between various particles on the glass surface. The literature contains numerous results indicating the physical and chemical heterogeneity of solid surfaces [9-11] and points out the extremely uneven surface distribution of adsorptive particles of varying activities, up to completely inactive ones. Our results fully agreed with these findings. EVALUATION OF RESULTS
This report describes the tests with solutions which had not been subjected to prolonged heating. The electron scattering studies showed the films produced from such solutions to be amorphous. Structures started to form in such films on the base during tempering, but this depended on the reaction between the solid surface and the macromolecules of the polymer. I t was actually proved t h a t the solid surface type plays a decisive part in structure formation, in the studied concentration range, i.e. in the layer in contact with the solid surface. Crystallization was either fully suppressed (at 94°C) or difficult (at 165°C), and the effect of the quartz base penetrated deeper t h a n t h a t of the carbon base. The bond between P P and quartz was thus stronger and this seems to be due to induction forces combining here with the dispersionary intermolecular ones. The effect of the base type on the behaviour of polymer crystals during tempering was also observed by others [12]. The authors explained this by referring to the theory of physieo-chemical reactions between the base and the polymer, and this was also the treatment given by us to our results. The influence of the type of adjacent phase on the polymer chain conformation in the surface layer was also pointed out elsewhere [13]. The use of a heat-treated P P solution for the film production showed the
~02
Yu. M. MA~NsYJIel a~.
solution concentration to affect the PP crystallization on the two bases. The quartz base, using a 0.001 ~ solution, was found to completely suppress crystallization while it occurred on the carbon base. From 0.002~ concentration onwards, the type of base had no effect, As the tempering of films made of greater than 0.002°~o solutions did not produce any structural changes on the bases, one can say that the reason for the lessening of the effect of the base, when increasing the solution concentration, is the existence of structuration in the solutions used. Heat-treated solutions of 0.002~/o and greater concentrations contained polymer already in an oriented state. The existence of a supermolecular structure in dilute solutions has already been reported in the literature [5, 14]. The film forming on the base retained the structure originally present in the solution. Both types of bases gave rise to typical dendritic structures of PP. Very dilute solutions (~0.001%) do not seem to contain orderly arranged structures, and the film produced from them will have a structure forming in it dependent on the type of interaction between the solid surface of the base and the polymer macromolecules; this also applied to untreated solutions. The observed suppression of crystallization on quartz seems to be connected with an almost complete lack of mobility in the polymer next to the quartz surface and this is due to strong intermolecular reactions. Raising the tempering temperature of polymer films produced from a 0.001% solution from 94 to 165°C resulted in a greater molecular mobility which sufficed for crystallization to take place on the carbon base, and for the formation of the higher order of crystals, but the picture remained unchanged in the case of the quartz base. The results of the electron microscopic study of PP crystallization in mixtures with glass powder on various solid bases showed that the structuration will depend in such systems on the total physical interaction of the polymer with the base and the filler; this confirmed the inference of there being a strong reaction between PP and quartz. All the polymer which had enveloped the glass particles was amorphous on the quartz base. Although the polymer crystallized on the carbon base, this only happened at some distance from the glass filler. This taken as evidence of glass delaying the crystallization in the boundary layer on the carbon surface. The examination of the above results showing the differing effects of different type surfaces on the crystallization and the morphology of the polymer in the boundary layers agreed with the findings published by a number of investigators [15-19]. CONCLUSIONS
(1) The formation of crystal structures will take place in polypropylene films on solid surfaces, but depends to a large extent on the physical reaction of the polymer with the base.
Crystallization in thin polymer layers
2803
(2) T h e c r y s t a l l i z a t i o n s t u d y of p o l y p r o p y l e n e in filled s y s t e m s on d i f f e r e n t solid b a s e s e s t a b l i s h e d t h a t t h e a c t i v i t y of t h e filler on c r y s t a l s t r u c t u r e f o r m a t i o n d e p e n d s on t h e t y p e of solid b a s e used. Translated by K. A. AT.T.~W
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