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The possibility of using the interference micromethod for plotting phase diagrams of polymer-crystallizing plasticizer systems
Polymer Science U.$.$,R. VoL 26, 1~'o. 2, pp. 520-522, 1983 Printed in Poland
0032-B950/88 $10.00+.00 O 1984 Pergamon Press Ltd.
THE. POSSIBILITY OF USING THE INTERFERENCE MICROMETHOD FOR PLOTTING PHASE DIAGRAMS OF POLYMER-CRYSTALLIZING PLASTICIZER SYSTEMS* V. A. GoLovr~, Yr. M. LOTM~.~TSV.V, S. M. YERSHOV and M. D. DEMCHENKO D. I. Mendeleyev Chemico-teehnoiogical Institute, Moscow
(Received 5 January 1982) A description was given of methods a n d results, which confirm the possibility of using the interference micromethod for determining the solubility in polymers of crystallizing plasticizers at temperatures lower t h a n the melting point of plasticizers. THe, interference micromethod has recently become popular in studying amorphous seI)aration in polymer-plasticizer systems [1]. A t the same time this m e t h o d m a y be used for examining crystalline t y p e phase equilibrium. A description is given in the literature of a t t e m p t s of using the interferetme micromethod for studying phase equilibria in crystallization of salts from dilute solutions [2]; a single crystal of the substance examined was placed into the measuring cell, where it came into contact with solutions of different concentration. A great disadvantage of these methods is the fact t h a t to prevent volumetric crystallization in solution, investigations have to be carried out with comparatively low degrees of supercooling. Furthermore, ensuring contact between the edges of the single crystal and surfaces of semi-transpar,~nt glass involves some difficulty. I n view of the fact t h a t in the presence of a crystal in homogeneous supercooled polym('r solutions, where n o r m a l l y the front of crystallization spreads rapidly in the volume, which restricts the possibility of investigating kinetics of establishing b o u n d a r y concentration, studies should be carried out using a continuous range of solutions of variable composition. I n this case crystallization of the plasticizer is possible a n d will only be observed in a region of solutions supersaturated a t a given temperature, while concentration on the interface between the region of plasticizer solutions in the polymer a n d the two-phase region, eot~raining plasticizer crystals, corresponds to equilibrium solubility of the crystalline plasticizer in the polymer at a given temperature. This s t u d y therefore deals with the possibility of using the interference micromethod for investigating crystalline separation a n d establish b o u n d a r y concentration during crystallization of the plasticizer in plasticized systems of variable composition. Investigations were carried out in a system of 2,4-dinitrotoluene (DNT)-SK~'-26-1 (butadiene acrylonitrile carboxylated rubber containing 1% COOH groups, 57/~=4 ~: 104). The plasticizer was purified b y two-fold reclTstallization from alcohol; T m e l t = 343°K. Experimental devices and methods of calculation related to interferograms were, described previously [3]. According to the foregoing, components in the interference cell were mixed with T > >Ttael t of the individual DNT, which made it possible to obtain a continuous r e # o n of solutions of variable composition with a concentration ranging from t h a t of pure D N T to pure * Vysokomol. soyed. A25: No. 2, 443-444, 1983. 520
Plotting phase diagrams of polymer-crystallizing plasticizer systems
521
polymer. The sample obtained was cooled to a chosen temperature of investigation (T < Tmelt), aft~,r which crystallization was initiated b y t h e addition of a seeding polymer to the zone of supercooled plasticizer. The plasticizer both outside and inside the region of solutions o f mixed composition crystallized in the meantime. Tmel, of the plasticizer in SKN-26-1D N T systems was determined b y a method using a differential scanning calorimeter [4] a.t a rate of heating of 1.5 deg/min. Curves of concentration distribution Obtained b y the methods described for the plasticizer in the zone of contact of the plasticized polymer with a two-phase region, containing plasticizer crystals, are shown in Fig. 1.
7-0 60 0"2 qO
O'l
0
O'lt Fro. 1
0"8 X~ rnrn
0.2
O'G
/-0
Fro. 2
FIG. 1. Curves of concentration distribution of the plasticizer ~ ( X ) in the zone of contact o f the plasticized polymer with the two-phase region, containing plasticizer crystals, a t 35 (1-3) a n d 60 ° (4-6). Duration of crystallization 1 (1, 4), 24 (2), 50 (3), 5 (5), 57 min (6). Fro. 2. Comparison of liquidus curves in a system of SKN-26-1-DNT, obtained b y the interference micromethod (1) a n d b y D T A (2).
The minimum time possible according to experimental conditions when distribution of plasticizer concentration could be measured after the introduction of the crystalline seeding polymer, is ~ 1 rain. During subsequent thermostatic control the plasticizer is transferred from the two-phase region into the region of the plasticized polymer of variable composition. As shown b y these results, a constant concentration of the plasticizer is quickly established on the b onndary of the plasticized polymer with a two-phase region at increased temperatures; this concentration remains unchanged during subsequent thermostatic control. W i t h a reduction of temperature some time is required for establishing equilibrium b o u n d a r y concentration. The methods proposed were used to determine the solubility of the crystallizing plasticizer at different temperatures. Figure 2 shows a comparison of results with values of equil i b , i u m Tmelt obtained b y I)TA; satisfactory agreement is seen between results of the two methods. Deviation in solubility values found is under 2%, which enables the interference micromethod to be recommended for determining the solubility of the plasticizer in the polymer when rd'
Translated by E. SEMERE
622
V. A. GOLO~IN et al. REFERENCES
1. A. Ye. CEALYKE, Vyeokomol. soyed. 17: 11, 2603, 1975 2. G. E. KRUEGER and E. W. MILLER, J. Chem. Phye. 21: 11, 2018, 1953 3. A. Pa. MALKIN and A. Ye. CHALYKH, Di!X&ya i vyazkoet’ polimerov. Iletody isledovaniya, p. 201, Khimiya, Moscow, 1979 4. E. A. DZHAVADYAN, 0. 8. GALYUE and B. A. ROSENBERG, Zavodsk. lab., 3, 228, 1979
0032-B950/88 $10.00+.00 O 1984 Pergamon Press Ltd.
THE. POSSIBILITY OF USING THE INTERFERENCE MICROMETHOD FOR PLOTTING PHASE DIAGRAMS OF POLYMER-CRYSTALLIZING PLASTICIZER SYSTEMS* V. A. GoLovr~, Yr. M. LOTM~.~TSV.V, S. M. YERSHOV and M. D. DEMCHENKO D. I. Mendeleyev Chemico-teehnoiogical Institute, Moscow
(Received 5 January 1982) A description was given of methods a n d results, which confirm the possibility of using the interference micromethod for determining the solubility in polymers of crystallizing plasticizers at temperatures lower t h a n the melting point of plasticizers. THe, interference micromethod has recently become popular in studying amorphous seI)aration in polymer-plasticizer systems [1]. A t the same time this m e t h o d m a y be used for examining crystalline t y p e phase equilibrium. A description is given in the literature of a t t e m p t s of using the interferetme micromethod for studying phase equilibria in crystallization of salts from dilute solutions [2]; a single crystal of the substance examined was placed into the measuring cell, where it came into contact with solutions of different concentration. A great disadvantage of these methods is the fact t h a t to prevent volumetric crystallization in solution, investigations have to be carried out with comparatively low degrees of supercooling. Furthermore, ensuring contact between the edges of the single crystal and surfaces of semi-transpar,~nt glass involves some difficulty. I n view of the fact t h a t in the presence of a crystal in homogeneous supercooled polym('r solutions, where n o r m a l l y the front of crystallization spreads rapidly in the volume, which restricts the possibility of investigating kinetics of establishing b o u n d a r y concentration, studies should be carried out using a continuous range of solutions of variable composition. I n this case crystallization of the plasticizer is possible a n d will only be observed in a region of solutions supersaturated a t a given temperature, while concentration on the interface between the region of plasticizer solutions in the polymer a n d the two-phase region, eot~raining plasticizer crystals, corresponds to equilibrium solubility of the crystalline plasticizer in the polymer at a given temperature. This s t u d y therefore deals with the possibility of using the interference micromethod for investigating crystalline separation a n d establish b o u n d a r y concentration during crystallization of the plasticizer in plasticized systems of variable composition. Investigations were carried out in a system of 2,4-dinitrotoluene (DNT)-SK~'-26-1 (butadiene acrylonitrile carboxylated rubber containing 1% COOH groups, 57/~=4 ~: 104). The plasticizer was purified b y two-fold reclTstallization from alcohol; T m e l t = 343°K. Experimental devices and methods of calculation related to interferograms were, described previously [3]. According to the foregoing, components in the interference cell were mixed with T > >Ttael t of the individual DNT, which made it possible to obtain a continuous r e # o n of solutions of variable composition with a concentration ranging from t h a t of pure D N T to pure * Vysokomol. soyed. A25: No. 2, 443-444, 1983. 520
Plotting phase diagrams of polymer-crystallizing plasticizer systems
521
polymer. The sample obtained was cooled to a chosen temperature of investigation (T < Tmelt), aft~,r which crystallization was initiated b y t h e addition of a seeding polymer to the zone of supercooled plasticizer. The plasticizer both outside and inside the region of solutions o f mixed composition crystallized in the meantime. Tmel, of the plasticizer in SKN-26-1D N T systems was determined b y a method using a differential scanning calorimeter [4] a.t a rate of heating of 1.5 deg/min. Curves of concentration distribution Obtained b y the methods described for the plasticizer in the zone of contact of the plasticized polymer with a two-phase region, containing plasticizer crystals, are shown in Fig. 1.
7-0 60 0"2 qO
O'l
0
O'lt Fro. 1
0"8 X~ rnrn
0.2
O'G
/-0
Fro. 2
FIG. 1. Curves of concentration distribution of the plasticizer ~ ( X ) in the zone of contact o f the plasticized polymer with the two-phase region, containing plasticizer crystals, a t 35 (1-3) a n d 60 ° (4-6). Duration of crystallization 1 (1, 4), 24 (2), 50 (3), 5 (5), 57 min (6). Fro. 2. Comparison of liquidus curves in a system of SKN-26-1-DNT, obtained b y the interference micromethod (1) a n d b y D T A (2).
The minimum time possible according to experimental conditions when distribution of plasticizer concentration could be measured after the introduction of the crystalline seeding polymer, is ~ 1 rain. During subsequent thermostatic control the plasticizer is transferred from the two-phase region into the region of the plasticized polymer of variable composition. As shown b y these results, a constant concentration of the plasticizer is quickly established on the b onndary of the plasticized polymer with a two-phase region at increased temperatures; this concentration remains unchanged during subsequent thermostatic control. W i t h a reduction of temperature some time is required for establishing equilibrium b o u n d a r y concentration. The methods proposed were used to determine the solubility of the crystallizing plasticizer at different temperatures. Figure 2 shows a comparison of results with values of equil i b , i u m Tmelt obtained b y I)TA; satisfactory agreement is seen between results of the two methods. Deviation in solubility values found is under 2%, which enables the interference micromethod to be recommended for determining the solubility of the plasticizer in the polymer when rd'
Translated by E. SEMERE
622
V. A. GOLO~IN et al. REFERENCES
1. A. Ye. CEALYKE, Vyeokomol. soyed. 17: 11, 2603, 1975 2. G. E. KRUEGER and E. W. MILLER, J. Chem. Phye. 21: 11, 2018, 1953 3. A. Pa. MALKIN and A. Ye. CHALYKH, Di!X&ya i vyazkoet’ polimerov. Iletody isledovaniya, p. 201, Khimiya, Moscow, 1979 4. E. A. DZHAVADYAN, 0. 8. GALYUE and B. A. ROSENBERG, Zavodsk. lab., 3, 228, 1979