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Changes in the structure of capron on heat treatment
CHANGES IN THE STRUCTURE OF CAPRON* ON HEAT TREATMENT * K . A. MOSKATOV a n d D. YA. TSVANK1N Scientific Research and Experimental Design Institute of Food Machinery Construction: Institute of Hetero-organic Compounds, U.S.S.R. Academy of Sciences (Received 7 February 1961)
DEPENDING on the method of preparation and treatment polyamides of different degrees of structural order can be obtained [1-3]. Rapid cooling from the melt usually gives material with a low degree of structural order. This can be shown by means of X-ray diffraction patterns, which show broad, diffuse reflections, and also by density measurement, determination of the transparency of films etc. The degree of crystallinity of these specimens of low structural order can be increased considerably by subsequent treatment. The density of the material then increases and the X-ray pattern shows sharp, clear reflections. The crystallinity can be increased by treatment at high temperatures in toluene, water or chloroform. Naturally, different polyamides do not behave in the same way under this type of treatment. For example it has been found t h a t E n a n t ++cannot be obtained in the amorphous, disordered state [4]. The process of crystallization of Capron is of special interest [5]. X-ray analysis has shown t h a t highly crystalline Capron has a monoclinic structure [6]. However when Capron is cooled rapidly the hexagonal structure encountered in m a n y other polyamides is sometimes observed. In the present work the effect of heat t r e a t m e n t on the structure of Capron was studied by X-ray analysis. This subject is of considerable scientific and practical interest because changes in structure alter, for example, the mechanical properties of the specimens. In recent years m a n y industrial plants have made use of various components made from polyamides, working under load and at high speeds. It is very important to discover what factors cause premature wear of the components. Observation has shown t h a t the working life of the components is determined to a considerable extent by their thermal treatment. It has been found experimentally t h a t in a number of cases specimens with a predominantly monoclinic structure are more wear-resistant [7, 8, 9]. In this connection some polyamide materials used for the manufacture of power-plant * Nylon 6, polyeaproamide. Vysokomol. soyed. 4: No. 2, 201-206, 1962. Polyoenantharaide. 75
76
K . A . MOSKATOV and D. YA. TSVANKIN
components
were chosen for investigation. P r o b l e m s
directly connected with
c h a n g e s in t h e m e c h a n i c a l p r o p e r t i e s o f C a p r o n o n h e a t t r e a t m e n t a r e n o t i n c l u d e d in this w o r k a n d will be e x a m i n e d s e p a r a t e l y .
EXPERIMENTAL Two samples of Capron resin were selected for examination of the changes taking place in the structure of the material of heat treatment. Sample A was a Capron resin produced by the K i e v synthetic resin combine, and sample B was Grade B Capron produced by the Klinskii synthetic resin combine. The specimens were prepared by heating under pressure, in the form of bars of rectangular cross-section measuring 6 × 4 × 55 mm, in confortuity with GOST* 4648-56. The preparation of the specimens conforms with the method of manufacture of power-plant components. H e a t t r eat m en t was carried out in boiling water in an enclosed bath for 2, 4, 6, 7, 10 and 15 hours. At the end of the heat-treatment period the specimens were cooled slowly. A typical graph of the change in temperature with time is shown in Figure 1. F o r obtaining the X - r ay patterns an outer layer, 2-3 m m 100
l ,
80
~ 6O ~ 4O
ll)
o
Time of stay
z
~'
~
8
Io
' I>.
Time (hours) FT~. 1. Graph of heat tr e a t m e n t of sample A (from 55 ° cooling in still air). thick, was cut from the specimens. The X - r a y patterns were obtained with a standard apparatus with copper irradiation and a nickel filter. Figures 2a and b show the most characteristic patterns of samples A and B. The patterns of specimens heat treated for 2, 4 and 6 hours are intermediate between those of the original specimens and those treated for 7 hours. The patterns of specimens from sample A, heated for 10 and 15 hours are similar to that of sample A heated for 7 hours. I t is i m p o rt an t to note t h a t in all the patterns there is a reflection corresponding to second-order reflection from the repeat unit along the chain. This reflection corresponds to 020 for monoclinic systems and 002 for hexagonal systems. The position of this reflection is the same in all the patterns and corresponds to a repeat unit along the chain of 16"6 A. The lines attributed to the monoclinic structure are most clearly visible on the diffraction pattern of the specimens of sample B heated for 7 hours. I n addition to strong lines with d2~0~ 4.38 A and d00~~ 3"65 A there are weak circles with d ~ 2.35, 2" 17 and 1.95 A. The first of these is evidently formed by 202 and 402 reflections, the second by 271 and * (All-Union) State Standard Specification.
FIG. 2. X-r ay diffraction patterns: a - - s a m p l e A; b--sample B. a: / - - o r i g i n a l specimen; 2--specimen treated for 7 hours; b: / - - o r i g i n a l specimen; 2, 3, 4--specimens treated for 7. l0 and 15 hours res~eet, ivelv.
78
K . A . MOSKATOV and D. YA. TSVAI~KIX
171, and the third can be attributed to 271 and 371 as well as 204 reflections. These three weak lines are not visible on the photograph. The hexagonal lines can be seen most clearly in the p at t er n of the original specimens. There is a strong 100 line with d=4"12 A and also very weak 101, 102 and 103 reflections. I n order to examine the changes taking place in the structure of samples A and B on heat t r e a t m e n t it is convenient to divide all the diffraction patterns obtained into three groups. I n the first group are the patterns with hexagonal and monoclinic lines. This group includes the diffraction patterns of sample B after 15 hours' treatment and those of sample A after t r e a t m e n t for 7, 10 and 15 hours. The distinctive feature of the patterns of the second group is a comparatively strong line corresponding to the hexagonal structure. Instead of the two basal 200 and 002 monoclinic lines in the patterns of this group there is a broad ring of the amorphous halo type, with sharp edges. Another distinctive feature of this group is a broad ring in the region of d--2.30-2.11 A. The intensity of this ring falls sharply as 0 approaches a low value and decreases slowly toward the edge of the pattern. The hexagonal structure lines are stronger in the second group o f patterns than in the first group, where the 101, 102 and 103 lines
l
2
2
6
s
7
15
FIG. 3. I n te n s i ty distribution curves in the basic interference region for X - r a y diffraction patterns of the three main types: / - - f i r s t type of pattern, with two monoclinic lines and one hexagonal line; 2--second type of pattern with a hexagonal line and a broad ring obgained by merging of the two monoelinic lines; 3 - - t h i r d type of pattern with two monoclinie lines. Ordinate--intensity, in arbitrary units.
Changes in structure of Capron on heat treatment
79
ahnost merge with the background. The diffraction patterns of the original samples A and B and that of sample B heat treated for 10 hours belong to this group (Fig. 2, al and bl). In the third group are the patterns with no hexagonal lines but with clear, comparatively sharp lines corresponding to the monoclinic structure. This type of pattern is given by sample B after heating for 7 hours (Fig. 2, b2). Intensity distribution curves in the region of low values of 0 for patterns of the three groups are shown in Figure 3. The curves were obtained by photometric measurement of the diffraction patterns. From the intensity of interference the relative strength of the background was calculated. This increases with decrease in 0 and is present in almost all the patterns. Up to now we have been discussing diffraction patterns taken a few (lays after the heat treatment. The patterns were then photographed again, eight months after the first stage of the work. With the exception of sample B, heat-treated for 7 hours, the patterns of all the specimens remained the same as before. Three equivalent specimens were studied. The pattern of one of' these as before contained only monoclinic lines, i.e. it belonged to the third group; however, instead of continu(ms circles a broken ring pattern was obtained, indicating the tbrmation of texture in the specimen. The two other specimens gave patterns of the first type and not the third, as before. DISCUSSION
W e shall e x a m i n e t h e v a r i a t i o n in s t r u c t u r e o f s a m p l e s A a n d B w i t h i n c r e a s ing t i m e of h e a t t r e a t m e n t . T h e d i f f r a c t i o n p a t t e r n s o f t h e o r i g i n a l s a m p l e s b e l o n g to t h e s e c o n d g r o u p ; t h e y c o n t a i n clear h e x a g o n a l lines t o g e t h e r w i t h diffuse a n d m e r g i n g m o n o c l i n i c lines. A f t e r p r o l o n g e d h e a t t r e a t m e n t (15 hours) s a m p l e s A a n d B give p a t t e r n s w i t h clear lines c o r r e s p o n d i n g to b o t h h e x a g o n a l a n d m o n o c l i n i c s y s t e m s . T h u s as a r e s u l t of h e a t t r e a t m e n t t h e b a s a l 200 a n d 002 m o n o c l i n i c lines in t h e d i f f r a c t i o n p a t t e r n s e p a r a t e a n d in a d d i t i o n in p l a c e of a b r o a d , a s y m m e t r i c halo t h r e e w e a k lines, d = 2 . 3 5 , 2.19 a n d 1.95 A, a p p e a r . A t t h e s a m e t i m e t h e i n t e n s i t y of t h e h e x a g o n a l lines d e c r e a s e s . I n s a m p l e A t h i s t r a n s i t i o n o c c u r s w i t h o u t a n y i n t e r m e d i a t e stages. I n s a m p l e B a p u r e m o n o c l i n i c s t r u c t u r e is f o r m e d a f t e r 7 h o u r s ' h e a t t r e a t m e n t , a f t e r l 0 h o u r s it a g a i n gives a p a t t e r n of t h e s e c o n d t y p e a n d f i n a l l y a f t e r 15 h o u r s ' t r e a t m e n t s a m p l e B gives a p a t t e r n s i m i l a r to t h a t o f s a m p l e A a f t e r 7 h o u r s ' treatment. T h e i n t e r m e d i a t e s t a g e w i t h a p u r e m o n o c l i n i c s t r u c t u r e is e v i d e n t l y u n s t a b l e b e c a u s e on ageing, as m e n t i o n e d a b o v e , h e x a g o n a l lines a p p e a r in t h e d i f f r a c t i o n p a t t e r n or t h e r e is e v i d e n c e o f t h e f o r m a t i o n of t e x t u r e . T h e c o n v e r s i o n of a b r o a d r i n g i n t o two, clear, m o n o c l i n i c tincs as in t h e t r a n s i t i o n f r o m a d i f f r a c t i o n p a t t e r n of t h e s e c o n d t y p e to t h e first can in p r i n c i p l e b e e x p l a i n e d in t w o w a y s . I n f a c t t h e b r o a d e n i n g of t h e lines in t h e p a t t e r n c a n be a s s o c i a t e d w i t h b o t h a c h a n g e in d i m e n s i o n s of t h e c r y s t a l l i n e r e g i o n s a n d w i t h a n i n c r e a s e in t h e s t a t e of o r d e r of t h e l a t t i c e s t r u c t u r e . I n o u r case we a r e c o n c e r n e d w i t h 200 a n d 002 reflections, w h i c h c h a r a c t e r i z e t h e o r d e r i n g of t h e c e n t r e s of t h e c h a i n s in t h e e q u i v a l e n t p l a n e , i.e. in a p l a n e p e r p e n d i c u l a r
80
K. A. MOSKATOVand D. YA. TSVANKIN
to the axes of thb chains. As is seen from Figure 2a a n d b and also f r o m the intensity distribution curves (curve 2, Fig. 3) the monoclinie lines in the p a t t e r n s o f t h e second group are almost c o m p l e t e l y merged. I n order to assess the effect of the dimensions of the regions on the b r o a d e n i n g o f t h e basal monoelinie lines, the i n t e n s i t y of scattering in groups consisting o f 50 a n d 100 chains a r r a n g e d in a t r u e monoclinic lattice was calculated. The calculation was m a d e b y m e a n s o f formulae derived previously [10] in a m a n n e r similar to the calculation of diffraction in p o l y e t h y l e n e [11]. Since we are i n t e r e s t e d o n l y in the separation of two basic reflections the first t e r m in t h e general expression for i n t e n s i t y o f scattering was calculated, giving t h e f u n d a m e n t a l c o n t r i b u t i o n to the t o t a l i n t e n s i t y in t h e given range o f angles [12]. T h e results o f the calculations are shown in Fig. 4 'curves 1 a n d 2). As would
7' 5
1
7
9
11
13
IS 17 S~SxlOZ ~"
FIG. 4. /--intensity distribution curves calculated for regions consisting of 50 chains: 2--intensity distribution curves for regions of 100 chains; 3--intensity distribution on diffraction by an impaired lattice; k=0.1. Ordinate--intensity, in arbitrary units. be e x p e c t e d for diffraction in regions containing 50 chains the 200 a n d 002 m a x i m a are only slightly separated. F o r diffraction in regions containing 100 chains t h e m a x i m a are s e p a r a t e d v e r y clearly. F o r complete merging of the m a x i m a diffraction should occur in groups containing 20-30 chains. I t is seen from a comparison of curves 1 a n d 2 in Fig. 4
C h a n g e s in s t r u c t u r e o f C a p r o n o n h e a t t r e a t m e n t
81
t h a t with a decrease in the number of chains, in addition to broadening of the lines their intensity also decreases. Consequently in diffraction in groups consisting of 20-30 chains the intensity maxima will be only slightly distinguishable from the background, whereas in the diffraction patterns of the second group the general 200-002 ring will be fairly intense. ILl order to model diffraction in regions of disturbed structure we made use of a scheme of radially progressing disorder [13]. For the calculations in this case it was assumed that Ap, the deviation from the true interchain distance, is directly proportional to this distance
Ap =kp.
O)
The distribution of scattering intensity can then be obtained in the following way. The intensity distribution curve, constructed for the true lattice, I(S), where S:=4u sin 0/). must be averaged at each point in the interval AS--kS, where k is the same as in (1). I t is obvious t h a t when k is sufficiently large the maxima will merge and form one continuous ring. An averaged curve of this type, constructed for k=0.1 and for diffraction caused by regions containing 100 chains is shown in Fig. 4 (curve 3). In this case the maxima are completely merged and in contrast to the previous case (diffraction caused by bundles of macromolecules with a small number of chains in the bundle) the intensity of the ring is very high. Thus the more probable cause of the broadening of the monoclinic lines is ~ disturbance of the lattice of the chain centres in the equivalent plane and not the formation of small ordered groups containing 20-40 chains. An additional argument in favour of this supposition is the fact t h a t if small groups with a true lattice are formed low angle diffraction should be observed, either in the form of continuous scattering or separate reflections, corresponding to regions of dimensions of the order of 20-30 A. On the other hand with our specimens only a large repeat unit of the order of 80 A is observed. The results of an investigation of low angle scattering will be published separately. Since in passing from the first to the second group there is no change in the repeat unit along the chain the change in structure evidently involves only an improvement of the lattice in the equivalent plane and the appearance of highly ordered regions of monoclinic structure in addition to the hexagonal regions. This is not accompanied by any marked broadening of the hexagonal 100 line. The other hexagonal lines are very weak and it is difficult to say anything definite about them. On passing from a pattern of the first type to the second the hexagonal lines weaken, and on passing from the second to the third type they disappear completely, indicating a decrease in the number of hexagonal regions. It should be noted t h a t in tlle hexagonal structure the distance between the chains in the equivalent plane is 4.12 × 1.16=4.75 A. This is exactly the same as the distance between molecules of normal paraffins in the hexagonal 6 Polymer 1
82
K.A. MOSKATOVand D. YA. TSVANKIN
modification. I t is well known t h a t in this type of modification the molecules rotate around their own axes. Since the distance between the chains is too small for the molecules to rotate independently of one another it is evident t h a t coordinated rotation of the chains occurs. Consequently the problem of azimuthal ordering in the hexagonal structure of Capron is of great interest--whether this structure is a " n o r m a l " crystalline structure or a structure of the rotationalcrystalline type [14]. From the point of view of X-ray analysis the fundamental criterion must be the rate of decrease in intensity of the reflections in the patterns. In the diffraction patterns of the hexagonal modification of normal paraffins there are only two lines, indicating a sharp drop in intensity with increasing values of 0. In our patterns there are four lines and in the texture patterns the number is greater. However, account should be taken here of the fact t h a t the weak lines in a texture pattern are more definite than in a powder pattern. Moreover, the repeat unit along the axis of the chain in paraffins is 2.54 A, hence lines of the 101 type in paraffins correspond to large angles where the fall in intensity is marked. The problem of the nature of the hexagonal structure in polyamides cannot be regarded as solved at present, though the similarity of the diffraction patterns of the hexagonal modifications of polyamides and normal paraffins is an argument in favour of the idea t h a t they have the same type of structure. I t is natural to suppose t h a t on rapid cooling from the melt a hexagonal structure of the rotational-crystalline type would be formed in Capron. In fact if the hexagonal structure in Capron were an ordinary crystalline structure with regular, azimuthal rotation it would be difficult to explain why the monoclinic structure does not form on chilling', because these structures differ little from one another. In conclusion the authors express their sincere gratitude to A. I. Kitaigorodskii for valuable advice and constant interest in the work. CONCLUSIONS
(1) X-ray diffraction patterns have been obtained of two samples of Capron resin, heat treated for various times in boiling water. (2) In specimens subjected to prolonged heat t r e a t m e n t regions of monoclinic structure predominate. There are also regions of hexagonal structure. (3) As a result of the heat t r e a t m e n t of Capron an improvement in the state of order of the monoclinic regions occurs and the number of hexagonal regions decreases. Translated by E. O. PHILLIPS REFERENCES 1. N . V . MIKHAILOV and V. O. KLESMAN, I)ok]. Akad. ~Nauk SSSR 41 : 99, 1953; Kolloid. zh. 16: 191, 272, 1954 2. T. M. FRUNZE, V. V. KORSHAK and V. A. MOSHKARKIN, Vysokomol. soyed. 1: 342, 1959
Compatibility of polyethylene polypropylene system
83
3. W. O. BAKEIt and C. S. FULLER, J. Amer. Chem. Soc. 62: 3275, 1940; 6 4 : 2399, 1942; 6 5 : ll20, 1943 4. E. Z. FAINBERG, V. O. GOItBACHEVA and N. V. MIKHAILOV, Vysokomol. soyc(I. 1: 17, 1959 5. V. O. KLESMAN, Dissertation, VNIIV, 1952 6. D. It. HOLMES, C. W. BUNN and D. J. SMITH, J. Polymer Sei. 17: 159, 1955 7. K. A. MOSKATOV, Sb. Primenenie plastmass i novykh materialov v mashinostroyenii. (Collected Papers. The Application of Plastics and New Materials in Machine Construction.) No. 4, Izd. I T E I N GNTK RSFSR, Moscow, 1960 8. K. A. MOSKATOV, Trenie i iznos v mashinakh. (Friction and Wear in Machines.) No. XV, Izd. Nauk SSSR, Moscow, 1961 9. K. A. MOSKATOV, Dissertation, K. A. Timiryazcv A~zriculttlral Academy, Moscow~ 1961 10. D. Ya. TSVANKIN, Dokl. Akad. Nauk SSSR 120: 1076, 1958 l l . D . Ya. TSVANKIN, Nauchnye dokl. vysshei shkoly, fiz.-mat, nauki, No. 5, 267, 1958 12. D. Ya. TSVANKIN, Dissertation, Institut vysokomolekulyarnykh soyedinenii, Aka
THE COMPATIBILITY OF THE POLYETHYLENE-POLYPROPYLENE SYSTEM* ]~. V. MIKHAILOV, n . Z. FAINBERG, V. O. GORBACHEVA a n d CHEN TSIN-KHAI Scientific-Research Institute of Synthetic Fibre (Received 9 February 196l) THE blending of p o l y m e r s in a m u t u a l solvent or in the m o l t e n state is widely used a t the present time as one of the m e t h o d s of m o d i f y i n g t h e properties o f p o l y m e r i c materials. I n the p r e s e n t work an a t t e m p t was m a d e to develop a m e t h o d of blending h y d r o c a r b o n p o l y m e r s from solution [1]. I t seemed of direct interest to s t u d y the simplest system, p o l y e t h y l e n e - p o l y p r o p y l e n e . Our :intention w h e n planning this work was to examine the possibility of plasticization of one p o l y m e r b y the other, which should lead to modification of the physico-chemical properties of the h o m o g e n e o u s m i x t u r e of p o l y m e r s in c o m p a r i s o n with the original polymers. I t was i m p o r t a n t to discover w h e t h e r the properties of the b l e n d wouht differ f r o m those of a c o p o l y m e r of the same composition. The m i x t u r e of polymers, low-pressure p o l y e t h y l e n e a n d isotactic p o l y p r o p y le~m, was p r e p a r e d b y m e a n s o f a m u t u a l solvent (o-xylene or white spirit) or f r o m the melt, using various ratios of p o l y e t h y l e n e to p o l y p r o p y l e n e b y weight. * Vysokomol. soyed. 4: No. 2, 237-241, 1962.
DEPENDING on the method of preparation and treatment polyamides of different degrees of structural order can be obtained [1-3]. Rapid cooling from the melt usually gives material with a low degree of structural order. This can be shown by means of X-ray diffraction patterns, which show broad, diffuse reflections, and also by density measurement, determination of the transparency of films etc. The degree of crystallinity of these specimens of low structural order can be increased considerably by subsequent treatment. The density of the material then increases and the X-ray pattern shows sharp, clear reflections. The crystallinity can be increased by treatment at high temperatures in toluene, water or chloroform. Naturally, different polyamides do not behave in the same way under this type of treatment. For example it has been found t h a t E n a n t ++cannot be obtained in the amorphous, disordered state [4]. The process of crystallization of Capron is of special interest [5]. X-ray analysis has shown t h a t highly crystalline Capron has a monoclinic structure [6]. However when Capron is cooled rapidly the hexagonal structure encountered in m a n y other polyamides is sometimes observed. In the present work the effect of heat t r e a t m e n t on the structure of Capron was studied by X-ray analysis. This subject is of considerable scientific and practical interest because changes in structure alter, for example, the mechanical properties of the specimens. In recent years m a n y industrial plants have made use of various components made from polyamides, working under load and at high speeds. It is very important to discover what factors cause premature wear of the components. Observation has shown t h a t the working life of the components is determined to a considerable extent by their thermal treatment. It has been found experimentally t h a t in a number of cases specimens with a predominantly monoclinic structure are more wear-resistant [7, 8, 9]. In this connection some polyamide materials used for the manufacture of power-plant * Nylon 6, polyeaproamide. Vysokomol. soyed. 4: No. 2, 201-206, 1962. Polyoenantharaide. 75
76
K . A . MOSKATOV and D. YA. TSVANKIN
components
were chosen for investigation. P r o b l e m s
directly connected with
c h a n g e s in t h e m e c h a n i c a l p r o p e r t i e s o f C a p r o n o n h e a t t r e a t m e n t a r e n o t i n c l u d e d in this w o r k a n d will be e x a m i n e d s e p a r a t e l y .
EXPERIMENTAL Two samples of Capron resin were selected for examination of the changes taking place in the structure of the material of heat treatment. Sample A was a Capron resin produced by the K i e v synthetic resin combine, and sample B was Grade B Capron produced by the Klinskii synthetic resin combine. The specimens were prepared by heating under pressure, in the form of bars of rectangular cross-section measuring 6 × 4 × 55 mm, in confortuity with GOST* 4648-56. The preparation of the specimens conforms with the method of manufacture of power-plant components. H e a t t r eat m en t was carried out in boiling water in an enclosed bath for 2, 4, 6, 7, 10 and 15 hours. At the end of the heat-treatment period the specimens were cooled slowly. A typical graph of the change in temperature with time is shown in Figure 1. F o r obtaining the X - r ay patterns an outer layer, 2-3 m m 100
l ,
80
~ 6O ~ 4O
ll)
o
Time of stay
z
~'
~
8
Io
' I>.
Time (hours) FT~. 1. Graph of heat tr e a t m e n t of sample A (from 55 ° cooling in still air). thick, was cut from the specimens. The X - r a y patterns were obtained with a standard apparatus with copper irradiation and a nickel filter. Figures 2a and b show the most characteristic patterns of samples A and B. The patterns of specimens heat treated for 2, 4 and 6 hours are intermediate between those of the original specimens and those treated for 7 hours. The patterns of specimens from sample A, heated for 10 and 15 hours are similar to that of sample A heated for 7 hours. I t is i m p o rt an t to note t h a t in all the patterns there is a reflection corresponding to second-order reflection from the repeat unit along the chain. This reflection corresponds to 020 for monoclinic systems and 002 for hexagonal systems. The position of this reflection is the same in all the patterns and corresponds to a repeat unit along the chain of 16"6 A. The lines attributed to the monoclinic structure are most clearly visible on the diffraction pattern of the specimens of sample B heated for 7 hours. I n addition to strong lines with d2~0~ 4.38 A and d00~~ 3"65 A there are weak circles with d ~ 2.35, 2" 17 and 1.95 A. The first of these is evidently formed by 202 and 402 reflections, the second by 271 and * (All-Union) State Standard Specification.
FIG. 2. X-r ay diffraction patterns: a - - s a m p l e A; b--sample B. a: / - - o r i g i n a l specimen; 2--specimen treated for 7 hours; b: / - - o r i g i n a l specimen; 2, 3, 4--specimens treated for 7. l0 and 15 hours res~eet, ivelv.
78
K . A . MOSKATOV and D. YA. TSVAI~KIX
171, and the third can be attributed to 271 and 371 as well as 204 reflections. These three weak lines are not visible on the photograph. The hexagonal lines can be seen most clearly in the p at t er n of the original specimens. There is a strong 100 line with d=4"12 A and also very weak 101, 102 and 103 reflections. I n order to examine the changes taking place in the structure of samples A and B on heat t r e a t m e n t it is convenient to divide all the diffraction patterns obtained into three groups. I n the first group are the patterns with hexagonal and monoclinic lines. This group includes the diffraction patterns of sample B after 15 hours' treatment and those of sample A after t r e a t m e n t for 7, 10 and 15 hours. The distinctive feature of the patterns of the second group is a comparatively strong line corresponding to the hexagonal structure. Instead of the two basal 200 and 002 monoclinic lines in the patterns of this group there is a broad ring of the amorphous halo type, with sharp edges. Another distinctive feature of this group is a broad ring in the region of d--2.30-2.11 A. The intensity of this ring falls sharply as 0 approaches a low value and decreases slowly toward the edge of the pattern. The hexagonal structure lines are stronger in the second group o f patterns than in the first group, where the 101, 102 and 103 lines
l
2
2
6
s
7
15
FIG. 3. I n te n s i ty distribution curves in the basic interference region for X - r a y diffraction patterns of the three main types: / - - f i r s t type of pattern, with two monoclinic lines and one hexagonal line; 2--second type of pattern with a hexagonal line and a broad ring obgained by merging of the two monoelinic lines; 3 - - t h i r d type of pattern with two monoclinie lines. Ordinate--intensity, in arbitrary units.
Changes in structure of Capron on heat treatment
79
ahnost merge with the background. The diffraction patterns of the original samples A and B and that of sample B heat treated for 10 hours belong to this group (Fig. 2, al and bl). In the third group are the patterns with no hexagonal lines but with clear, comparatively sharp lines corresponding to the monoclinic structure. This type of pattern is given by sample B after heating for 7 hours (Fig. 2, b2). Intensity distribution curves in the region of low values of 0 for patterns of the three groups are shown in Figure 3. The curves were obtained by photometric measurement of the diffraction patterns. From the intensity of interference the relative strength of the background was calculated. This increases with decrease in 0 and is present in almost all the patterns. Up to now we have been discussing diffraction patterns taken a few (lays after the heat treatment. The patterns were then photographed again, eight months after the first stage of the work. With the exception of sample B, heat-treated for 7 hours, the patterns of all the specimens remained the same as before. Three equivalent specimens were studied. The pattern of one of' these as before contained only monoclinic lines, i.e. it belonged to the third group; however, instead of continu(ms circles a broken ring pattern was obtained, indicating the tbrmation of texture in the specimen. The two other specimens gave patterns of the first type and not the third, as before. DISCUSSION
W e shall e x a m i n e t h e v a r i a t i o n in s t r u c t u r e o f s a m p l e s A a n d B w i t h i n c r e a s ing t i m e of h e a t t r e a t m e n t . T h e d i f f r a c t i o n p a t t e r n s o f t h e o r i g i n a l s a m p l e s b e l o n g to t h e s e c o n d g r o u p ; t h e y c o n t a i n clear h e x a g o n a l lines t o g e t h e r w i t h diffuse a n d m e r g i n g m o n o c l i n i c lines. A f t e r p r o l o n g e d h e a t t r e a t m e n t (15 hours) s a m p l e s A a n d B give p a t t e r n s w i t h clear lines c o r r e s p o n d i n g to b o t h h e x a g o n a l a n d m o n o c l i n i c s y s t e m s . T h u s as a r e s u l t of h e a t t r e a t m e n t t h e b a s a l 200 a n d 002 m o n o c l i n i c lines in t h e d i f f r a c t i o n p a t t e r n s e p a r a t e a n d in a d d i t i o n in p l a c e of a b r o a d , a s y m m e t r i c halo t h r e e w e a k lines, d = 2 . 3 5 , 2.19 a n d 1.95 A, a p p e a r . A t t h e s a m e t i m e t h e i n t e n s i t y of t h e h e x a g o n a l lines d e c r e a s e s . I n s a m p l e A t h i s t r a n s i t i o n o c c u r s w i t h o u t a n y i n t e r m e d i a t e stages. I n s a m p l e B a p u r e m o n o c l i n i c s t r u c t u r e is f o r m e d a f t e r 7 h o u r s ' h e a t t r e a t m e n t , a f t e r l 0 h o u r s it a g a i n gives a p a t t e r n of t h e s e c o n d t y p e a n d f i n a l l y a f t e r 15 h o u r s ' t r e a t m e n t s a m p l e B gives a p a t t e r n s i m i l a r to t h a t o f s a m p l e A a f t e r 7 h o u r s ' treatment. T h e i n t e r m e d i a t e s t a g e w i t h a p u r e m o n o c l i n i c s t r u c t u r e is e v i d e n t l y u n s t a b l e b e c a u s e on ageing, as m e n t i o n e d a b o v e , h e x a g o n a l lines a p p e a r in t h e d i f f r a c t i o n p a t t e r n or t h e r e is e v i d e n c e o f t h e f o r m a t i o n of t e x t u r e . T h e c o n v e r s i o n of a b r o a d r i n g i n t o two, clear, m o n o c l i n i c tincs as in t h e t r a n s i t i o n f r o m a d i f f r a c t i o n p a t t e r n of t h e s e c o n d t y p e to t h e first can in p r i n c i p l e b e e x p l a i n e d in t w o w a y s . I n f a c t t h e b r o a d e n i n g of t h e lines in t h e p a t t e r n c a n be a s s o c i a t e d w i t h b o t h a c h a n g e in d i m e n s i o n s of t h e c r y s t a l l i n e r e g i o n s a n d w i t h a n i n c r e a s e in t h e s t a t e of o r d e r of t h e l a t t i c e s t r u c t u r e . I n o u r case we a r e c o n c e r n e d w i t h 200 a n d 002 reflections, w h i c h c h a r a c t e r i z e t h e o r d e r i n g of t h e c e n t r e s of t h e c h a i n s in t h e e q u i v a l e n t p l a n e , i.e. in a p l a n e p e r p e n d i c u l a r
80
K. A. MOSKATOVand D. YA. TSVANKIN
to the axes of thb chains. As is seen from Figure 2a a n d b and also f r o m the intensity distribution curves (curve 2, Fig. 3) the monoclinie lines in the p a t t e r n s o f t h e second group are almost c o m p l e t e l y merged. I n order to assess the effect of the dimensions of the regions on the b r o a d e n i n g o f t h e basal monoelinie lines, the i n t e n s i t y of scattering in groups consisting o f 50 a n d 100 chains a r r a n g e d in a t r u e monoclinic lattice was calculated. The calculation was m a d e b y m e a n s o f formulae derived previously [10] in a m a n n e r similar to the calculation of diffraction in p o l y e t h y l e n e [11]. Since we are i n t e r e s t e d o n l y in the separation of two basic reflections the first t e r m in t h e general expression for i n t e n s i t y o f scattering was calculated, giving t h e f u n d a m e n t a l c o n t r i b u t i o n to the t o t a l i n t e n s i t y in t h e given range o f angles [12]. T h e results o f the calculations are shown in Fig. 4 'curves 1 a n d 2). As would
7' 5
1
7
9
11
13
IS 17 S~SxlOZ ~"
FIG. 4. /--intensity distribution curves calculated for regions consisting of 50 chains: 2--intensity distribution curves for regions of 100 chains; 3--intensity distribution on diffraction by an impaired lattice; k=0.1. Ordinate--intensity, in arbitrary units. be e x p e c t e d for diffraction in regions containing 50 chains the 200 a n d 002 m a x i m a are only slightly separated. F o r diffraction in regions containing 100 chains t h e m a x i m a are s e p a r a t e d v e r y clearly. F o r complete merging of the m a x i m a diffraction should occur in groups containing 20-30 chains. I t is seen from a comparison of curves 1 a n d 2 in Fig. 4
C h a n g e s in s t r u c t u r e o f C a p r o n o n h e a t t r e a t m e n t
81
t h a t with a decrease in the number of chains, in addition to broadening of the lines their intensity also decreases. Consequently in diffraction in groups consisting of 20-30 chains the intensity maxima will be only slightly distinguishable from the background, whereas in the diffraction patterns of the second group the general 200-002 ring will be fairly intense. ILl order to model diffraction in regions of disturbed structure we made use of a scheme of radially progressing disorder [13]. For the calculations in this case it was assumed that Ap, the deviation from the true interchain distance, is directly proportional to this distance
Ap =kp.
O)
The distribution of scattering intensity can then be obtained in the following way. The intensity distribution curve, constructed for the true lattice, I(S), where S:=4u sin 0/). must be averaged at each point in the interval AS--kS, where k is the same as in (1). I t is obvious t h a t when k is sufficiently large the maxima will merge and form one continuous ring. An averaged curve of this type, constructed for k=0.1 and for diffraction caused by regions containing 100 chains is shown in Fig. 4 (curve 3). In this case the maxima are completely merged and in contrast to the previous case (diffraction caused by bundles of macromolecules with a small number of chains in the bundle) the intensity of the ring is very high. Thus the more probable cause of the broadening of the monoclinic lines is ~ disturbance of the lattice of the chain centres in the equivalent plane and not the formation of small ordered groups containing 20-40 chains. An additional argument in favour of this supposition is the fact t h a t if small groups with a true lattice are formed low angle diffraction should be observed, either in the form of continuous scattering or separate reflections, corresponding to regions of dimensions of the order of 20-30 A. On the other hand with our specimens only a large repeat unit of the order of 80 A is observed. The results of an investigation of low angle scattering will be published separately. Since in passing from the first to the second group there is no change in the repeat unit along the chain the change in structure evidently involves only an improvement of the lattice in the equivalent plane and the appearance of highly ordered regions of monoclinic structure in addition to the hexagonal regions. This is not accompanied by any marked broadening of the hexagonal 100 line. The other hexagonal lines are very weak and it is difficult to say anything definite about them. On passing from a pattern of the first type to the second the hexagonal lines weaken, and on passing from the second to the third type they disappear completely, indicating a decrease in the number of hexagonal regions. It should be noted t h a t in tlle hexagonal structure the distance between the chains in the equivalent plane is 4.12 × 1.16=4.75 A. This is exactly the same as the distance between molecules of normal paraffins in the hexagonal 6 Polymer 1
82
K.A. MOSKATOVand D. YA. TSVANKIN
modification. I t is well known t h a t in this type of modification the molecules rotate around their own axes. Since the distance between the chains is too small for the molecules to rotate independently of one another it is evident t h a t coordinated rotation of the chains occurs. Consequently the problem of azimuthal ordering in the hexagonal structure of Capron is of great interest--whether this structure is a " n o r m a l " crystalline structure or a structure of the rotationalcrystalline type [14]. From the point of view of X-ray analysis the fundamental criterion must be the rate of decrease in intensity of the reflections in the patterns. In the diffraction patterns of the hexagonal modification of normal paraffins there are only two lines, indicating a sharp drop in intensity with increasing values of 0. In our patterns there are four lines and in the texture patterns the number is greater. However, account should be taken here of the fact t h a t the weak lines in a texture pattern are more definite than in a powder pattern. Moreover, the repeat unit along the axis of the chain in paraffins is 2.54 A, hence lines of the 101 type in paraffins correspond to large angles where the fall in intensity is marked. The problem of the nature of the hexagonal structure in polyamides cannot be regarded as solved at present, though the similarity of the diffraction patterns of the hexagonal modifications of polyamides and normal paraffins is an argument in favour of the idea t h a t they have the same type of structure. I t is natural to suppose t h a t on rapid cooling from the melt a hexagonal structure of the rotational-crystalline type would be formed in Capron. In fact if the hexagonal structure in Capron were an ordinary crystalline structure with regular, azimuthal rotation it would be difficult to explain why the monoclinic structure does not form on chilling', because these structures differ little from one another. In conclusion the authors express their sincere gratitude to A. I. Kitaigorodskii for valuable advice and constant interest in the work. CONCLUSIONS
(1) X-ray diffraction patterns have been obtained of two samples of Capron resin, heat treated for various times in boiling water. (2) In specimens subjected to prolonged heat t r e a t m e n t regions of monoclinic structure predominate. There are also regions of hexagonal structure. (3) As a result of the heat t r e a t m e n t of Capron an improvement in the state of order of the monoclinic regions occurs and the number of hexagonal regions decreases. Translated by E. O. PHILLIPS REFERENCES 1. N . V . MIKHAILOV and V. O. KLESMAN, I)ok]. Akad. ~Nauk SSSR 41 : 99, 1953; Kolloid. zh. 16: 191, 272, 1954 2. T. M. FRUNZE, V. V. KORSHAK and V. A. MOSHKARKIN, Vysokomol. soyed. 1: 342, 1959
Compatibility of polyethylene polypropylene system
83
3. W. O. BAKEIt and C. S. FULLER, J. Amer. Chem. Soc. 62: 3275, 1940; 6 4 : 2399, 1942; 6 5 : ll20, 1943 4. E. Z. FAINBERG, V. O. GOItBACHEVA and N. V. MIKHAILOV, Vysokomol. soyc(I. 1: 17, 1959 5. V. O. KLESMAN, Dissertation, VNIIV, 1952 6. D. It. HOLMES, C. W. BUNN and D. J. SMITH, J. Polymer Sei. 17: 159, 1955 7. K. A. MOSKATOV, Sb. Primenenie plastmass i novykh materialov v mashinostroyenii. (Collected Papers. The Application of Plastics and New Materials in Machine Construction.) No. 4, Izd. I T E I N GNTK RSFSR, Moscow, 1960 8. K. A. MOSKATOV, Trenie i iznos v mashinakh. (Friction and Wear in Machines.) No. XV, Izd. Nauk SSSR, Moscow, 1961 9. K. A. MOSKATOV, Dissertation, K. A. Timiryazcv A~zriculttlral Academy, Moscow~ 1961 10. D. Ya. TSVANKIN, Dokl. Akad. Nauk SSSR 120: 1076, 1958 l l . D . Ya. TSVANKIN, Nauchnye dokl. vysshei shkoly, fiz.-mat, nauki, No. 5, 267, 1958 12. D. Ya. TSVANKIN, Dissertation, Institut vysokomolekulyarnykh soyedinenii, Aka
THE COMPATIBILITY OF THE POLYETHYLENE-POLYPROPYLENE SYSTEM* ]~. V. MIKHAILOV, n . Z. FAINBERG, V. O. GORBACHEVA a n d CHEN TSIN-KHAI Scientific-Research Institute of Synthetic Fibre (Received 9 February 196l) THE blending of p o l y m e r s in a m u t u a l solvent or in the m o l t e n state is widely used a t the present time as one of the m e t h o d s of m o d i f y i n g t h e properties o f p o l y m e r i c materials. I n the p r e s e n t work an a t t e m p t was m a d e to develop a m e t h o d of blending h y d r o c a r b o n p o l y m e r s from solution [1]. I t seemed of direct interest to s t u d y the simplest system, p o l y e t h y l e n e - p o l y p r o p y l e n e . Our :intention w h e n planning this work was to examine the possibility of plasticization of one p o l y m e r b y the other, which should lead to modification of the physico-chemical properties of the h o m o g e n e o u s m i x t u r e of p o l y m e r s in c o m p a r i s o n with the original polymers. I t was i m p o r t a n t to discover w h e t h e r the properties of the b l e n d wouht differ f r o m those of a c o p o l y m e r of the same composition. The m i x t u r e of polymers, low-pressure p o l y e t h y l e n e a n d isotactic p o l y p r o p y le~m, was p r e p a r e d b y m e a n s o f a m u t u a l solvent (o-xylene or white spirit) or f r o m the melt, using various ratios of p o l y e t h y l e n e to p o l y p r o p y l e n e b y weight. * Vysokomol. soyed. 4: No. 2, 237-241, 1962.