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Method for the continuous registration of swelling and its application in studying the vulcanization of thiokol
Method for the continuous registration of swelling
1955
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9.
$. E. HAUSK, Maker. Design. Engng. 62: 101, 1965 R. D. BURKHART and N. L. ZUTTY, J. Polymer Sci. A I : 1137, 1963 R. A. TERTERYAN, A. I. DINTSES and M. V. RYSAKOV, :Neftekhimiya 3: 719, 1963 F. E. BROWN and G. E. HAM, J. Polymer Sci. A2: 3623, 1964 V. A. KARGIN, M. B. KONSTANTINOPOL'SKAYA, R. A. TERTERYAN and Z. Ya. BERESTNEVA, Dokl. AN SSSR 164: 112, 1965 L. B. NIELSEN, J. Polymer Sei. 42: 357, 1960 H. BARTL and J. PETER, Kautschuk u n d Gummi, No. 2, 23, 1961 E. M. BARALL, R. S. PORTER and J. F. JOHNSON, Analyt. Chem. 35: 73, 1963 R. A. TERTERYAN, A. I. DINTSES and M. V. RYSAKOV, :Neftekhimiya 5: 340, 1965
METHODS OF INVESTIGATION METHOD FOR THE CONTINUOUS REGISTRATION OF SW-EIJ,1NG AND ITS APPLICATION IN STUDYING THE VULCANIZATION OF THIOKOL* B . YA. TEITEL'BAUM a n d A. YE. TAVRII~ A. Ye. Arbuzov I n s t i t u t e of Organic and Physical Chemistry, U.S.S.R. Academy of Sciences
(Received 18 May 1967) T o s t u d y swelling of v u l c a n i z e d p r o d u c t s , we d e v e l o p e d a device which enables process kinetics to be a u t o m a t i c a l l y registered b y c o n t i n u o u s l y m e a s u r i n g the t h i c k n e s s of t h e swelling specimen; in this device some features of the m e t h o d s d e s c r i b e d b y V a s e n i n [1] a r e u t i l i z e d . The measuring mechanism (Fig. 1) is based on the part of the device registering temperature-deformation curves of polymers [2]. The specimen studied, shaped as a flat disc of 6-8 m m diameter and up to 2 m m thick, is placed on the base of the device between two porous glass plates, a measuring rod resting on the upper one. The weight of the rod and components is balanced by an arm with an adjustable counterweight. I f necessary, a load can be applied to the rod, which exerts pressure on the specimen and counteracts swelling. A soft iron core is fixed to the opposite end of the arm, which is inserted in the induction data unit, as the specimen swells. The data unit is a coil with two coaxial windings, the primary being supplied b y stabilized alternating current of 50 c/s and the secondary connected to the measuring circuit. The current in the secondary coil, after rectification, is registered by an electronic potentiometer (EPP-09 or PS-1). The electrical circuit of the device [3] is assembled on the chassis of a VT-2A labora* Vysokomol. soyed. A1O: :No. 7, 1684-1687, 1968.
1956
B. YA. TEITEL'BAUMand A. YE. TAVRII~
tory vacuum-meter. The sensitivity of the data unit is adjusted by changing the current in the primary winding and the zero point of recording can be displaced. The data unit has linear characteristics within a fair range of the passage of the core. The scale of the potentiometer is calibrated by measuring the vertical passage of the rod a n d the corresponding deflection of the pen on the scale. The passage of the rod is measured either by a micrometer screw fixed above the rod, or b y graduated scales. Linear dimensions can be determined with an accuracy of m i n i m u m ~=5 /1. The following experimental methods were used. A load was applied to the rod to give a clamping force of 5 g/cm 2, ensuring a tight fit of the plates to the specimen without any considerable inhibition of swelling. The thickness of the specimen was determined from the difference of readings effected without and with it. Then, the lower part of the measuring mechanism was immersed in a thermostatically controlled vessel containing the solvent and the chart mechanism of the potentiometer simultaneously switched on. F r o m the registration curve of swelling both the equilibrium degree of swelling and the intermediate value could be determined at a n y point of time.
\7
"
% 8
2 f 3 /
~g20V
~e I
I
FIG. 1. Layout of device used for automatic registration of swelling: a - - measuring mechanism; b - - i n d u c t i o n displacement data unit; c - - d a t a unit supply; d--rectifying unit; e--recording instrument. / - - S p e c i m e n , 2--porous glass plates, 3-- supporting base, 4--measuring rod, g - - s u p p o r t i n g rods, 6--guide ring, 7 - - a r m with counterweight, 8--core of induction data unit, 9--weight, 10--supporting b a s e , / / - - v e s s e l containing solvent. By the above method swelling kinetics in benzene were studied of vulcanized thiokol products obtained from mixtures of di-(#-chloroethyl) formal thiokol containing 2% trichloropropane units ( M n - - 3 7 0 0 ) - 100 parts b y weight, MnO2--5 parts b y weight, diphenylguanidine (DPG)--0.5 parts b y weight. Unfilled vuleanizates also contained 30 parts b y weight carbon black. Vulcanization was carried out at room temperature for 800 hr. The prolonged duration of vulcanization led us to assume t h a t the degree of crosslinking in unfilled and filled vulcanizates is practically the same. To determine the extent of volumetric swelling from the thickness -¢ariation of the specimen, the isotropism of swelling h a d to be independently determined. For this purpose rectangular plates of vulcanizates
Method for the continuous registration of swelling
1957
of 6 x 4 × 2 mm were vertically placed on thin horizontal needles fastened in metal holders. The samples were measured by a microcathetometer (KM-6) and then immersed for 6-7 hr in benzene in a glass vessel with parallel plane walls; subsequent measurements were carried out in this position. Up to five samples were tested at the same time: swelling was determined for the length, width and thickness of plates. Swelling of thv thiokol vulcanizates, as shown by measurement, was fully isotropic, enabling the volumetric swelling of vulcanizates to be determined from variations of linear dimensions. The data of both methods were compared. Tabulated data indicate t h a t reproducibility in both methods is quite satisfactory. The equilibrium swelling Qp obtained by automatic registration was somewhat lower t h a n t h a t obtained by measurement with a cathetometer, which is due to the presence of a certain load on the sample when measurement was carried out by the first method. The temperature dependence of Qp of unfilled vulcanizates has the opposite sign to the dependence predicted by the Flory-Rehner equation [14], which m a y be explained by the presence in the vulcanization network of weak salt bonds formed by reaction of thiol groups with manganese dioxide, the rate of decomposition of which during swelling depends on the temperature factor. Kinetic curves of swelling of unfilled vulcanizates (Fig. 2, curves 2, 4) also con-
ho,mm 0.6 " 0"# O2 0
~
# -
3
1
2
2 Time,hi"
FIG. 2. Curves showing swelling of thiokol vuleanizates in benzene: /--filled with carbon black, 20°; 2--unfilled, 20°; 3--filled with carbon black, 50°; 4--unfilled, 50°. Sample thickness h0= 1.6 mm. firm this assumption. They have an unusual appearance; after the initial rise no saturation takes place, but a long, almost linear section of ascent is seen, which only later becomes horizontal, corresponding to Qp. A similar pattern was observed by Poddubnyi et al. [5] when investigating swelling of carboxyl-conraining rubbers. I t can be assumed t h a t the appearance of linear sections on the swelling curves of unfilled vnlcanizates is due not only to the decomposition of salt bonds, but also to the decomposition of weak bonds of the vulcanized network due to the reaction of the polymer with carbon black. A comparison of swelling curves 4 and 3 (Fig. 2) clearly shows this effect. However units formed b y strong chemical bonds between thiokol and carbon black must be absent from the vulcanization network, as the experimental value of Qp (at 20 °) of a filled vulcanizate coincides
1958
B. YA. TEITEL'BAUM and A. YE. TAVI~-~
with the corresponding value for unfilled vulcanizates calculated for the quantity of thiokol contained Lu the filled specimen. EQUILIBRIUM
SVCELLING
Qp
OF THIOXOL
~ULCAIqIZATES
Type of vuleanizate
T,
°C
According to swelling curves
Unfilled Ditto
20 20 20 50 20 20 20 50
0-381 0.398 0.396 0.451 0.302 0.293 0.296 0.372
99
Filled Ditto 9P ~9
Ilq B E N Z E N E
Measured by a cathetometer 0.415 0.403 0.408 0"313 0"306 0"311
The automatic registration of swelling is very convenient when investigating effects due to reorganization and even degradation of the network by agents penetrating the polymer with solvent. For example, during swelling of degraded thiokol (perhaps containing a few thiol groups) in a 1% benzene solution of DPG under a load of 0.28 kg/cm 2 (Fig. 3, 1) a gradual reduction of thickness
h,/TIlTI 1
2"4
~2
-~
1"6 0"8 0
I
#
8
12
D'me , hp
FIG. 3. Curves showing swelling of thiokol in benzene containing 1% DFG: 1--undecomposed thiokol at 20°, 2--thiokol vulcanizate at 50°C. Arrow shows the moment when 5% low molecular weight thiokol was added to the solution. was observed which proves t h a t the sample flowed. This effect is obviously due to the cleavage of polysulphide bonds of the polymer by the effect of DPG and subsequent polysulphide exchange. The effect of DPG on the swelling vulcanizates of degraded thiokol does not cause flow even at increased temperature (50°); however subsequent addition to a low molecular weight thiokol solution (5%) results in complete breakdown of the sample (Fig. 3, 2). This degradation is apparently due to thiol-disulphide exchange. The investigations carried out by the authors on degradation of thiokol vulcanizates in benzene indicate t h a t
Method of determination of molecular weight distribution of PETP
1959
this process depends on m a n y factors: concentration of low molecular weight thiokol and base, extent of load on the sample, temperature, sulphur content in the polymer and conditions of vulcanization. The results of these investigations will be discussed later. The authors are grateful to V. A. Byl'ev for his part in the discussions. CONCLUSIONS
(1) A device is proposed for continuous registration of polymer swelling by an electric potentiometer. (2) A s t u d y of swelling ofthiokol vulcanizates shows that, as well as the main network, salt bonds participate in forming the vulcanization structure on cold vulcanization, and in filled vulcanizates, bonds formed by reaction of the polymer with carbon black are readily decomposed during swelling. I t was shown t h a t swollen vulcanizates can undergo flow and degradation with low molecular weight thiokol in the presence of a base, diphenylguanidine. Translated by E. SEMERE REFERENCES
1. R. M. VASENIN, Vysokomol. soyed. 6: 1700, '1964 (Translated ill Polymer Sci. U.S.S.R. 6: 9, 1882, 1964) 2. B. Ya. TEITEL'BAUM, Peredovoi nauehno-tekhnicheskii i proizvodstvennyi opyt (Advanced Scientific-Technical and Industrial Experience). TslTETN, 1961, No. P-61-4/2; B. Ya. TEITEL'BAUM and M. P. BIANOV,Vysokomol. soyed. 3: 594, 1961 (Not translated in Polymer Sci. U.S.S.R.) 3. B. Ya. TEITEL'BAUM, Vysokomol. soyed. A10: 969, 1968 (Translated in Polymer Sci. U.S.S.R. 1O: 4, 1129, 1968) 4. P. FLORY and I. REItNER, J. Chem. Phys. II: 52I, 1943 5. I. Ya. PODDUBNYI, Ye. G. ERENBURG and Ye. I. STAROVOITOVA, Dokl. AN SSSR 120: 535, 1958
RAPID METHOD OF DETERMINATION OF THE MOLECULAR WEIGHT DISTRIBUTION OF POLYETHYLENE TEREPHTHALATE* YU. P. VYRSKII, O. A. KLAI'OVSI(AYA,~ . V. ANDRIANOVA and O. F. ALKAYEVA Scientific Research Institute of Plastics (Received 12 October 1967)
POL¥]~T//YLENE terephthalate (PETP) is widely used for preparing films and fibres of high strength, satisfactory chemical resistance, thermal stability, resistance to photochemical degradation and high dielectric properties [1]. The opti* Vysokomol. soyed. A1D: No. 7, 1688-1693, 1968.
1955
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9.
$. E. HAUSK, Maker. Design. Engng. 62: 101, 1965 R. D. BURKHART and N. L. ZUTTY, J. Polymer Sci. A I : 1137, 1963 R. A. TERTERYAN, A. I. DINTSES and M. V. RYSAKOV, :Neftekhimiya 3: 719, 1963 F. E. BROWN and G. E. HAM, J. Polymer Sci. A2: 3623, 1964 V. A. KARGIN, M. B. KONSTANTINOPOL'SKAYA, R. A. TERTERYAN and Z. Ya. BERESTNEVA, Dokl. AN SSSR 164: 112, 1965 L. B. NIELSEN, J. Polymer Sei. 42: 357, 1960 H. BARTL and J. PETER, Kautschuk u n d Gummi, No. 2, 23, 1961 E. M. BARALL, R. S. PORTER and J. F. JOHNSON, Analyt. Chem. 35: 73, 1963 R. A. TERTERYAN, A. I. DINTSES and M. V. RYSAKOV, :Neftekhimiya 5: 340, 1965
METHODS OF INVESTIGATION METHOD FOR THE CONTINUOUS REGISTRATION OF SW-EIJ,1NG AND ITS APPLICATION IN STUDYING THE VULCANIZATION OF THIOKOL* B . YA. TEITEL'BAUM a n d A. YE. TAVRII~ A. Ye. Arbuzov I n s t i t u t e of Organic and Physical Chemistry, U.S.S.R. Academy of Sciences
(Received 18 May 1967) T o s t u d y swelling of v u l c a n i z e d p r o d u c t s , we d e v e l o p e d a device which enables process kinetics to be a u t o m a t i c a l l y registered b y c o n t i n u o u s l y m e a s u r i n g the t h i c k n e s s of t h e swelling specimen; in this device some features of the m e t h o d s d e s c r i b e d b y V a s e n i n [1] a r e u t i l i z e d . The measuring mechanism (Fig. 1) is based on the part of the device registering temperature-deformation curves of polymers [2]. The specimen studied, shaped as a flat disc of 6-8 m m diameter and up to 2 m m thick, is placed on the base of the device between two porous glass plates, a measuring rod resting on the upper one. The weight of the rod and components is balanced by an arm with an adjustable counterweight. I f necessary, a load can be applied to the rod, which exerts pressure on the specimen and counteracts swelling. A soft iron core is fixed to the opposite end of the arm, which is inserted in the induction data unit, as the specimen swells. The data unit is a coil with two coaxial windings, the primary being supplied b y stabilized alternating current of 50 c/s and the secondary connected to the measuring circuit. The current in the secondary coil, after rectification, is registered by an electronic potentiometer (EPP-09 or PS-1). The electrical circuit of the device [3] is assembled on the chassis of a VT-2A labora* Vysokomol. soyed. A1O: :No. 7, 1684-1687, 1968.
1956
B. YA. TEITEL'BAUMand A. YE. TAVRII~
tory vacuum-meter. The sensitivity of the data unit is adjusted by changing the current in the primary winding and the zero point of recording can be displaced. The data unit has linear characteristics within a fair range of the passage of the core. The scale of the potentiometer is calibrated by measuring the vertical passage of the rod a n d the corresponding deflection of the pen on the scale. The passage of the rod is measured either by a micrometer screw fixed above the rod, or b y graduated scales. Linear dimensions can be determined with an accuracy of m i n i m u m ~=5 /1. The following experimental methods were used. A load was applied to the rod to give a clamping force of 5 g/cm 2, ensuring a tight fit of the plates to the specimen without any considerable inhibition of swelling. The thickness of the specimen was determined from the difference of readings effected without and with it. Then, the lower part of the measuring mechanism was immersed in a thermostatically controlled vessel containing the solvent and the chart mechanism of the potentiometer simultaneously switched on. F r o m the registration curve of swelling both the equilibrium degree of swelling and the intermediate value could be determined at a n y point of time.
\7
"
% 8
2 f 3 /
~g20V
~e I
I
FIG. 1. Layout of device used for automatic registration of swelling: a - - measuring mechanism; b - - i n d u c t i o n displacement data unit; c - - d a t a unit supply; d--rectifying unit; e--recording instrument. / - - S p e c i m e n , 2--porous glass plates, 3-- supporting base, 4--measuring rod, g - - s u p p o r t i n g rods, 6--guide ring, 7 - - a r m with counterweight, 8--core of induction data unit, 9--weight, 10--supporting b a s e , / / - - v e s s e l containing solvent. By the above method swelling kinetics in benzene were studied of vulcanized thiokol products obtained from mixtures of di-(#-chloroethyl) formal thiokol containing 2% trichloropropane units ( M n - - 3 7 0 0 ) - 100 parts b y weight, MnO2--5 parts b y weight, diphenylguanidine (DPG)--0.5 parts b y weight. Unfilled vuleanizates also contained 30 parts b y weight carbon black. Vulcanization was carried out at room temperature for 800 hr. The prolonged duration of vulcanization led us to assume t h a t the degree of crosslinking in unfilled and filled vulcanizates is practically the same. To determine the extent of volumetric swelling from the thickness -¢ariation of the specimen, the isotropism of swelling h a d to be independently determined. For this purpose rectangular plates of vulcanizates
Method for the continuous registration of swelling
1957
of 6 x 4 × 2 mm were vertically placed on thin horizontal needles fastened in metal holders. The samples were measured by a microcathetometer (KM-6) and then immersed for 6-7 hr in benzene in a glass vessel with parallel plane walls; subsequent measurements were carried out in this position. Up to five samples were tested at the same time: swelling was determined for the length, width and thickness of plates. Swelling of thv thiokol vulcanizates, as shown by measurement, was fully isotropic, enabling the volumetric swelling of vulcanizates to be determined from variations of linear dimensions. The data of both methods were compared. Tabulated data indicate t h a t reproducibility in both methods is quite satisfactory. The equilibrium swelling Qp obtained by automatic registration was somewhat lower t h a n t h a t obtained by measurement with a cathetometer, which is due to the presence of a certain load on the sample when measurement was carried out by the first method. The temperature dependence of Qp of unfilled vulcanizates has the opposite sign to the dependence predicted by the Flory-Rehner equation [14], which m a y be explained by the presence in the vulcanization network of weak salt bonds formed by reaction of thiol groups with manganese dioxide, the rate of decomposition of which during swelling depends on the temperature factor. Kinetic curves of swelling of unfilled vulcanizates (Fig. 2, curves 2, 4) also con-
ho,mm 0.6 " 0"# O2 0
~
# -
3
1
2
2 Time,hi"
FIG. 2. Curves showing swelling of thiokol vuleanizates in benzene: /--filled with carbon black, 20°; 2--unfilled, 20°; 3--filled with carbon black, 50°; 4--unfilled, 50°. Sample thickness h0= 1.6 mm. firm this assumption. They have an unusual appearance; after the initial rise no saturation takes place, but a long, almost linear section of ascent is seen, which only later becomes horizontal, corresponding to Qp. A similar pattern was observed by Poddubnyi et al. [5] when investigating swelling of carboxyl-conraining rubbers. I t can be assumed t h a t the appearance of linear sections on the swelling curves of unfilled vnlcanizates is due not only to the decomposition of salt bonds, but also to the decomposition of weak bonds of the vulcanized network due to the reaction of the polymer with carbon black. A comparison of swelling curves 4 and 3 (Fig. 2) clearly shows this effect. However units formed b y strong chemical bonds between thiokol and carbon black must be absent from the vulcanization network, as the experimental value of Qp (at 20 °) of a filled vulcanizate coincides
1958
B. YA. TEITEL'BAUM and A. YE. TAVI~-~
with the corresponding value for unfilled vulcanizates calculated for the quantity of thiokol contained Lu the filled specimen. EQUILIBRIUM
SVCELLING
Qp
OF THIOXOL
~ULCAIqIZATES
Type of vuleanizate
T,
°C
According to swelling curves
Unfilled Ditto
20 20 20 50 20 20 20 50
0-381 0.398 0.396 0.451 0.302 0.293 0.296 0.372
99
Filled Ditto 9P ~9
Ilq B E N Z E N E
Measured by a cathetometer 0.415 0.403 0.408 0"313 0"306 0"311
The automatic registration of swelling is very convenient when investigating effects due to reorganization and even degradation of the network by agents penetrating the polymer with solvent. For example, during swelling of degraded thiokol (perhaps containing a few thiol groups) in a 1% benzene solution of DPG under a load of 0.28 kg/cm 2 (Fig. 3, 1) a gradual reduction of thickness
h,/TIlTI 1
2"4
~2
-~
1"6 0"8 0
I
#
8
12
D'me , hp
FIG. 3. Curves showing swelling of thiokol in benzene containing 1% DFG: 1--undecomposed thiokol at 20°, 2--thiokol vulcanizate at 50°C. Arrow shows the moment when 5% low molecular weight thiokol was added to the solution. was observed which proves t h a t the sample flowed. This effect is obviously due to the cleavage of polysulphide bonds of the polymer by the effect of DPG and subsequent polysulphide exchange. The effect of DPG on the swelling vulcanizates of degraded thiokol does not cause flow even at increased temperature (50°); however subsequent addition to a low molecular weight thiokol solution (5%) results in complete breakdown of the sample (Fig. 3, 2). This degradation is apparently due to thiol-disulphide exchange. The investigations carried out by the authors on degradation of thiokol vulcanizates in benzene indicate t h a t
Method of determination of molecular weight distribution of PETP
1959
this process depends on m a n y factors: concentration of low molecular weight thiokol and base, extent of load on the sample, temperature, sulphur content in the polymer and conditions of vulcanization. The results of these investigations will be discussed later. The authors are grateful to V. A. Byl'ev for his part in the discussions. CONCLUSIONS
(1) A device is proposed for continuous registration of polymer swelling by an electric potentiometer. (2) A s t u d y of swelling ofthiokol vulcanizates shows that, as well as the main network, salt bonds participate in forming the vulcanization structure on cold vulcanization, and in filled vulcanizates, bonds formed by reaction of the polymer with carbon black are readily decomposed during swelling. I t was shown t h a t swollen vulcanizates can undergo flow and degradation with low molecular weight thiokol in the presence of a base, diphenylguanidine. Translated by E. SEMERE REFERENCES
1. R. M. VASENIN, Vysokomol. soyed. 6: 1700, '1964 (Translated ill Polymer Sci. U.S.S.R. 6: 9, 1882, 1964) 2. B. Ya. TEITEL'BAUM, Peredovoi nauehno-tekhnicheskii i proizvodstvennyi opyt (Advanced Scientific-Technical and Industrial Experience). TslTETN, 1961, No. P-61-4/2; B. Ya. TEITEL'BAUM and M. P. BIANOV,Vysokomol. soyed. 3: 594, 1961 (Not translated in Polymer Sci. U.S.S.R.) 3. B. Ya. TEITEL'BAUM, Vysokomol. soyed. A10: 969, 1968 (Translated in Polymer Sci. U.S.S.R. 1O: 4, 1129, 1968) 4. P. FLORY and I. REItNER, J. Chem. Phys. II: 52I, 1943 5. I. Ya. PODDUBNYI, Ye. G. ERENBURG and Ye. I. STAROVOITOVA, Dokl. AN SSSR 120: 535, 1958
RAPID METHOD OF DETERMINATION OF THE MOLECULAR WEIGHT DISTRIBUTION OF POLYETHYLENE TEREPHTHALATE* YU. P. VYRSKII, O. A. KLAI'OVSI(AYA,~ . V. ANDRIANOVA and O. F. ALKAYEVA Scientific Research Institute of Plastics (Received 12 October 1967)
POL¥]~T//YLENE terephthalate (PETP) is widely used for preparing films and fibres of high strength, satisfactory chemical resistance, thermal stability, resistance to photochemical degradation and high dielectric properties [1]. The opti* Vysokomol. soyed. A1D: No. 7, 1688-1693, 1968.