Mechanical properties of mixtures—II. Mixing amorphous with amorphous, and crystalline with crystalline polymers

900

G. L. SLONIMSKIIet al.

(2) Globulation of the polymer molecules and gel formation also occur in solutions PVA containing dimethylformamide. The rate of formation of globules is dependent on temperature and on the composition of the DMFA-water binary mixture. (3) When globular PVA is heated dsnaturization occurs as a result of rearrangement of the local, intramolecular bonds to form intermolecular bonds. (4) The magnitude of the i n ~ r n a l stresses in coatings obtained from PVA solutions on a glass substrate is aifccted by the composition of the binary mixture. (5) Films formed globular PVA are weak and when the solvent is completely removed under vacuum they break down so a powder. Translated by E. O. PHILLIPS

REFERENCES 1. P. I. ZUBOV, Dissertation, Moscow, 1949; P. I. ZUBOV, Z. N. ZHURKINA and V. A. KARGIN, Dokl. Akad. Nauk SSSR 67: 659, 1949 2. P. I. ZUBOV, Z. N. ZHURKINA and V. A. KARGIN, Kolloid. zh. 16: 178, 1954 3. P. I. ZUBOV, Z. N. ZHURKINA and V. A. KARGIN, Kolloid. zh. 19: 420, 1957; T. V. DOROKHINA, A. S. NOVIKOVA and P. I. ZUBOV, Vysokomol. soyed. 1: 36, 1959; A. C. NOVIKOVA, T. V. DOROKHINA and P. I. ZUBOV, Dokl. Akad. Nauk SSSR 105: 514, 1955 4. Yu. S. LIPATOV and P. I. ZUBOV, Vysokomol. soyed. 1: 88, 432, 1959; P. I. ZUBOV, Yu. S. LIPATOV and Ye. A. KANEVSKAYA, Dokl. Akad. Nauk SSSR 141: 2, 1962 5. N. F. PROSHLYAKOVA, P. I. ZUBOV and V. A. KARGIN, Ko]loid. zh. 20: 199, 202, 1958 6. I. N. VLODAVETS and P. A. REBINDER, Dokl. Akad. ]qauk SSSR 145: 617, 1962; I. N. VLODAVETS and P. A. REBINDER, Vestnik Akad. Iqauk SSSR No. 11. 80, 1962 7. P. I. ZUBOV and L. A. LEPILKINA, Vestnik Akad. Nauk SSSR No. 3, 49. 1962

MECHANICAL PROPERTIES OF POLYMER MIXTURES--H. MIXING AMORPHOUS WITH AMORPHOUS, AND CRYSTALLINE WITH CRYSTALLINE POLYMERS* G. L. SLONIMSKII, I. N. MUSAYELYAN, V. V. KAZANTSEVA and B. M. OZEROV Institute of Elementary Organic Compounds, U.S.S.R. Academy of Sciences (Received 1 June 1963)

IN [1] we dealt with features of the mixing of amorphous with crystalline polymers. These two types of polymer were found to be incompatible, and thus affected the mechanical properties of polymer mixtures. * Vysokomol. soyed. 6: No. 5, 818-822, 1946. J

Mechanical properties of polymer mixtures --II.

901

I t is also interesting to find out about the behaviour of mixtures of polymers of the same type, amorphous with amorphous and crystalline with crystalline. TEST SPECIMENS

The studies were conducted on mixtures of amorphous polypropylene (molecular weight 25,700) with polyisobutylene (mol. wt. approx. 100,000), and of crystalline isotactic polypropylene (mol. wt. 347,000) with polyethylene (reel. wt. approx. 20,000). Mixtures 1:0, 3:1, 1:1, 1:3 and 0:1 were prepared from solutions of weighed amo~mts of the appropriate polymers in decalin at 130-140° by precipitation in acetone followed by vacuum drying at 100°. From the mixtures of amorphous propylene with polyisobutylene films were compression moulded at 150° and P ~ 100 kg/cm 2. The mixtures of crystalline polypropylene with polyethylene were held in compression moulds at 240° and i ) = 100 kg/em2, and after this they were cooled at 0.5°/min. RESULTS AND DISCUSIONS

Temperature (deformation and unit stress) deformation curves were taken in tension for all the test specimens at various different temperatures. Besides this X-ray diffraction patterns were taken of the polyethylene mixture with crystalline polypropylene and an optical structural analysis was conducted by means of a MIN-8 polarization microscope. We can see from Fig. 1 t h a t isotactic propylene produces coarse spherulitie structures with quite distinct boundaries. Where the polypropylene concentration is greater (3 : 1) the film shows very well developed polypropylene spherulites with fine polyethylene spherulitic inclusions between them. The polypropylone spherulites change as the polyethylene concentration rises; their boundaries become less distinct and some are irregular. Mixtures of crystalline polypropylone with polyethylene thus have a definitely non-homogeneous structure. It was not possible by means of the microscope to determine the degree of compatibility in the mixtures of amorphous polypropylene and polyisobutylene. But a study of the mechanical properties also demonstrates t h a t such incompatibility does exist. Figure 2 shows the elongation versus the composition of polyisobutylene mixtures with amorphous polypropylene, as plotted from the unit stress versus tensile strain graphs. There is a shallow minimum at 20 ° (Fig. 2, curve 1), which in our opinion is due to lack of compatibility between the polymers [2]. At higher temperatures (40 and 60 °) considerably less deformation is seen in the pure polymers and in all the mixtures studied. At these temperatures both the polyisobutylene and the amorphous polypropylene have considerable yield, and this prevents the development of any significant high-elasticity deformation, due to which the total deformation fails rapidly with the temperature. As the viscosity of amorphous polypropylene is lower t h a n t h a t of polyisobutylene (3.46× l0 s and 2.03× 10 TM poise respectively at 40°), the graph shows a more rapid drop in the extension ratios for the compositions where the amorphous polypropylene predominates.

902

G.L.

FIG. 1. Photomicrograph ( x 182) of m i x t u r e s of crystalline polypropylene w i t h p o l y e t h y l e n e in the following ratios: a - - 1 : 0; b - - 3 : 1; c - - 1 : 1; d--1:3;e--0: 1.

SLONIMSKH Ct a~.

Mechanical properties of polymer mixtures --II.

903

Figure 3 shows the temperature-deformation curve of isotactie polypropylene mixtures with polyethylene. The yield point, which is found from the melting point of the crystalline mixtures, rises with the polypropylene concentration.

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Fig. 2. Extension ratio versus composition of mixtures of polyisobutylene with amorphous polypropylene at" 1--20°; 2--40°; 3--60 °. C,% 100

50

2

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FIG. 3. T e m p e r a t u r e v e r s u s deformation for mixtures of crystalline polypropylene with polyethylene, in the following ratios: 1 - 0 : l; 2 - 1 : 3 ; 3--1:1; 4--3:1; ~--1:0. Figure 4 shows t h a t the strength of crystalline polypropylene is slightly higher than t h a t of polyethylene. There is gradual increase in strength from the mixtures with low polypropylene concentration to those consisting mainly of this material. Due to partial amorphization there is a drop in strength with rising temperature, both for the pure polymers and for mixtures of the two. At 20 ° both crystalline polypropylene and polyethylene are known to develop considerable forced high-elasticity deformations, the total of deformation

G; L. SLONIMSKII et

904

al.

increasing with temperature in the crystalline polymers. When the deformation of crystalline m i x t u r e s was studied it was found that they all fractured with only slight deformation (not more than 10% extension) at 20% ~,k rlcrn 2

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FIG. 4. Strength of mixtures of polyethylene with crystalline polypropylene versus: A - - t e m p e r a t u r e a ~ d B - - c o m p o s i t i o n . A: a - - l : 0 ; b - - 3 : l ; c - - l : l ; d - l : 3 ; e - 0 : 1. B: 1--20°; 2--60°; 3--100°; 4--110°; 5--120°; 6--140°; 7--150°; 8--165 °. The break in the curves on Fig. 4 and 5 is due to the fact t h a t the instrument could not take the data.

Figure 5A shows measurements of deformability for 20 ° and higher temperatures. Both for the pure polyethylene and polypropylene and their mixtures the extension ratio versus temperature curves had a maximum in all cases. I f the curves in Fig. 5 are compared with the corresponding temperature-deformation curves of Fig. 3, we can see that the mixtures do not develop marked deformability until after a considerable amount of polyethylene has been melted; this is the component which has the lower melting point. In this kind of system the molten polyethylene acts as high-molecular plasticizer to the crystalline polypropylene. Polymer systems of this kind are able to develop considerable deformation b u t a further rise in temperature, which increases the yield of the system, reduces the total extension ratio. Thus we can see that it is not until the melting point of one of the components has been reached that mixtures of two crystalline polymers develop any marked deformability. Figure 5 shows the summarized data on extension ratios as dependent on composition for various different temperatures. I t is obvious that the behaviour of mixtures of isotaetie polypropylene and polyethylene is due to the incompatability of these two polymers, which means that they crystallize separately with distinct interfaces between t h e

905

Mechanical properties of polymer m i x t u r e s - I I .

spherulites. In the solid this kind of structure is responsible for the material fracturing so easily as the stresses required for the development of the required elastic d e f o r m a t i o n c a n n o t b e c r e a t e d in t h e - m a t e r i a l , This m e a n s t h a t the

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FIG. 5. Extension ratio of mixtures of polyethylene with crystalline polypropylene versus: A --temperature ax~d B--composition. A: a--1 : 0; b--3 : 1; c--1 : 1; d--1 : 3; e - 0 : 1. B: 1--20°; 2--60°; 3--100°; 4--120°; 5--140°; 6--150°; 7--160°; 8--170 °.

reason for the r~latively low Strength a n d .deformability of crystalline poly~ner m i x t u r e s is t h e i r v e r y i n h o m o g e n e o u s structure. CONCLUSIONS

(1) Mixtttres o f crystalline p o l y p r o p y l e n e with p o l y e t h y l e n e show micro-nonh o m o g e n e i t y due to t h e i r incompatibility. (2) As these m i x t u r e s are n o t homogeneous, the mechanical properties show a peculiar d e p e n d e n c e on the composition. (3) A n u n d e r s t a n d i n g of the peculiarities of t h e mechanical properties can be gained b y s t u d y i n g the t e m p e r a t u r e dependences of the s t r e n g t h a n d formability o f a m o r p h o u s a n d crystalline polypropylenes, p o l y e t h y l e n e a n d polyisobutylene. Translated by V. ALFORD REFERENCES V. V. KAZANTSEVA and G. M. O Z E R O V , Vysokomol. soyed. 6: 219, 1964 2. N. F. KOMSKAYA and G. L. SLONIMSKII Zh. Fiz. khim. 30: 1529, 1956 1. G. L. SLONIMSKII, I. Y. M U S A Y E L Y A N ,