CN112858111B - Method for measuring interfacial tension between polymer melts in high-pressure gas - Google Patents
Method for measuring interfacial tension between polymer melts in high-pressure gas Download PDFInfo
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Abstract
The invention provides a method for measuring interfacial tension between polymer melts in high-pressure gas, which comprises the following steps: firstly, preparing a sample to be detected; placing a sample to be tested in a high-pressure cavity of a high-pressure visual device, adjusting the temperature of the high-pressure cavity to saturation temperature, introducing test gas to sweep the high-pressure cavity, introducing the test gas until the pressure in the high-pressure cavity reaches test pressure, keeping the test pressure and the saturation temperature for a certain time, then heating to the test temperature and starting timing, shooting and recording the change condition of the shape of the short fiber in the high-pressure cavity along with time in real time until the short fiber retracts into a spherical shape; calculating shape related factors in the short fiber retraction process, drawing by taking the shape related factors as vertical coordinates and time as horizontal coordinates, performing straight line fitting, and calculating the interfacial tension between polymer melts under the test condition by combining the slope of a linear equation obtained by fitting. The invention has low requirement on the measurement condition and good applicability, and can improve the accuracy of the measurement result.
Description
Technical Field
The invention belongs to the field of interfacial tension measurement between polymer melts, and relates to a method for measuring interfacial tension between polymer melts in high-pressure gas.
Background
The interfacial tension is the sum of the excess free energy of the molecules of the two substances per unit area with respect to the same number of molecules within the phase, which are present at the interface. The performance and the structure of the polymer are dense and inseparable, the interfacial tension is a basic parameter for determining the compatibility among polymer components, the key role is played for the evolution of the microstructure of the multiphase polymer and the formation of the final phase morphology, and meanwhile, the interfacial tension can play a role in predicting and regulating the dispersion of the filler, thereby being beneficial to realizing the diversification of the performances of the polymer and the alloy thereof.
Factors influencing interfacial tension comprise polymer type, polymer molecular weight, temperature, hydrostatic pressure, addition of micromolecules and the like, high-pressure gas is introduced into polymer blending, the gas is fused into the polymer to interact with the polymer, the function of a plasticizer is achieved, basic physical properties of the polymer such as crystallization behavior, surface tension, rheological behavior and the like are changed, the viscosity ratio and the interfacial tension of two phases during polymer blending are further influenced, and the phase morphology and the performance of the blend are influenced. Meanwhile, in the process of foaming the polymer by using the high-pressure gas, the interfacial tension between polymer melts is one of the important parameters influencing the nucleation and growth of foam cells. Therefore, the method can accurately and effectively measure the interfacial tension between polymer melts in the high-pressure gas, and has important significance for researching the foaming process of the polymer high-pressure gas and regulating and controlling the cell structure of the polymer foaming material.
The technology for measuring interfacial tension between polymer melts under normal pressure is mature, but as mentioned above, when high-pressure gas is introduced into a polymer blend system, the interaction between the high-pressure gas and the polymer can cause changes in physical properties of the polymer, and further cause changes in interfacial tension between the polymer melts, so that the interfacial tension value measured under normal pressure cannot accurately reflect the actual interfacial tension of the polymer in the high-pressure gas atmosphere. Currently, there is a lack of systematic research and effective means for measuring interfacial tension between polymer melts in a high pressure gas atmosphere. Some researchers measure the interfacial tension between polymer melts in high-temperature and high-pressure gas by using a pendant drop method, but the method calculates the interfacial tension according to the density difference of the two polymer melts and the shape of a balance drop, so that the requirements on the form and the size of the drop of the melt are very high, however, when the drop is squeezed into a substrate in the measuring process, if the volume is too small, the drop will retract into a needle head, and if the volume is too large, the drop will occur due to a thin neck phenomenon and fall off before measurement, and the measuring difficulty is very high. Meanwhile, the density difference of the two polymer melts is small, and the measuring result is also easy to cause inaccuracy. Furthermore, due to the high viscosity of the polymer, it takes a long time to obtain a symmetrical equilibrium droplet that meets the measurement requirements, which may cause thermolysis of the thermolabile polymer material. Due to the limitations, the applicability of the method is limited, and few polymer systems for measuring interfacial tension between polymer melts in a high-pressure gas atmosphere by using the method are reported at present. Therefore, there is a need to develop a method for measuring interfacial tension between polymer melts in a high-pressure gas atmosphere, which has better applicability, easier realization of measurement conditions, and higher measurement result accuracy.
Disclosure of Invention
Aiming at the problem that the prior art lacks an effective means for measuring the interfacial tension between polymer melts in a high-pressure gas atmosphere, the invention aims to provide a method for measuring the interfacial tension between the polymer melts in the high-pressure gas, so as to reduce the requirement on the measurement condition, improve the applicability of the method and improve the accuracy of the measurement result.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for measuring interfacial tension between polymer melts in high-pressure gas comprises the following steps:
preparing a polymer A into short fibers, annealing to eliminate internal stress, and preparing a polymer B into a sheet; clamping one short fiber between two thin sheets, and then carrying out annealing treatment to ensure that the short fiber is fully contacted with the thin sheets to obtain a sample to be detected; the polymer A and the polymer B are incompatible polymers;
placing a sample to be tested in a high-pressure cavity of a high-pressure visual device, adjusting the temperature of the high-pressure cavity to saturation temperature, opening an air inlet valve and an air outlet valve of the high-pressure cavity, introducing test gas to sweep the high-pressure cavity to remove air in the high-pressure cavity, closing the air outlet valve, then introducing the test gas until the pressure in the high-pressure cavity reaches a test pressure P, wherein the pressure is more than 0.1MPa and less than or equal to 40MPa, keeping the test pressure and the saturation temperature for 1 min-48 h, then heating to the test temperature and starting timing, and shooting and recording the change condition of the short fiber in the high-pressure cavity along with time in real time from the heating to the test temperature until the short fiber retracts to a spherical shape;
the saturation temperature is above 0 ℃ and below the melting point or viscous flow temperature of polymer a and polymer B under the conditions of the test pressure; the test temperature is above the melting point or viscous flow temperature of polymer a and polymer B at the test pressure conditions and below the decomposition temperature of polymer a and polymer B;
selecting at least 5 pictures shot at different time points from the shot and recorded data of the short fiber shape changing along with the time, measuring the radius R of the widest part vertical to the length direction of the short fiber before the short fiber retracts to be spherical, and measuring the radius R when the short fiber retracts to be spherical 0 And the radius R of the short fiber subjected to annealing treatment in the step (i) e ；
F (x) is calculated according to the expressions (1) to (2) R )、f(x Re ) Calculating a shape correlation factor in the short fiber retraction process according to the formula (3), then drawing by taking the shape correlation factor as a vertical coordinate and time as a horizontal coordinate and performing straight line fitting, calculating the interfacial tension between polymer melts under the test condition according to the formula (4) by combining the slope of a straight line equation obtained by fitting,
y＝R 0 (f(x R )-f(x Re )) (3)
σ 12 ＝kη (4)
in the formulas (1) to (5), Re is the radius of the short fiber annealed in the step (i), and R is 0 The radius of the short fiber when the short fiber retracts to be spherical, R is the radius of the widest part vertical to the length direction of the short fiber before the short fiber retracts to be spherical, y is a shape correlation factor, sigma 12 Is the interfacial tension between the melts of polymer A and polymer B, k is the slope of the fitted linear equation, η is the effective viscosity, η m Is at leastZero shear viscosity, η, at equilibrium of polymer B interaction with test gas under test pressure and test temperature conditions f Is the zero shear viscosity at which the polymer a and test gas interact to equilibrium under test pressure and test temperature conditions.
In the second step of the technical scheme of the method for measuring the interfacial tension between the polymer melts in the high-pressure gas, the shapes of the short fibers are ensured not to change in the saturation period by controlling the saturation temperature, the test pressure and the saturation time. The inventor finds in the experimental process that the short fiber morphology changes during saturation due to overshoot of the saturation temperature, excessive test pressure, and excessive saturation time, so that the saturation temperature, the test pressure, and the saturation time should be controlled properly according to the type of the polymer a and the actual test requirements in actual operation.
In the second step of the technical scheme of the method for measuring the interfacial tension between the polymer melts in the high-pressure gas, no bubbles are generated in the short fibers after the short fibers are heated to the testing temperature until the short fibers retract into a spherical shape. Whether the short fibers generate bubbles during the retraction to spherical shape is mainly related to whether the short fibers are in close contact with the sheet and whether the short fibers have bubbles in themselves.
In the technical scheme of the method for measuring the interfacial tension between polymer melts in the high-pressure gas, the length of the short fibers is preferably 0.1-5 mm, the diameter of the short fibers is preferably 0.01-5 mm, and the ratio of the length to the diameter of the short fibers is preferably 1-10. The method of making the staple fibers may be a spinning process, such as a melt spinning process, a wet spinning process or an electrospinning process, in which spinning process it is ensured that the staple fibers are free of air bubbles.
In the technical scheme of the method for measuring interfacial tension between polymer melts in high-pressure gas, the thickness of the sheet prepared from the polymer B is preferably 1-10 mm, and the volume of the sheet is preferably 25-10000 mm 3 . The shape of the polymer sheet is not limited, and may be, for example, circular, polygonal, or the like.
In the second step of the technical scheme of the method for measuring interfacial tension between polymer melts in the high-pressure gas, after the temperature of the high-pressure cavity is adjusted to the saturation temperature, an exhaust valve of the high-pressure cavity is opened and test gas is introduced to purge the high-pressure cavity so as to exhaust air in the high-pressure cavity, so that a sample to be measured is ensured to be in a pure test gas atmosphere during subsequent tests, wherein the test gas is carbon dioxide, nitrogen, hydrogen, air, methane, propane, butane, pentane, helium or argon. When the test gas is air, adjusting the temperature of the high-pressure cavity to saturation temperature, directly opening the air inlet valve of the high-pressure cavity and introducing the test gas until the pressure in the high-pressure cavity reaches the test pressure for saturation without performing the operation of opening the air inlet valve and the air outlet valve of the high-pressure cavity, introducing the test gas to purge the visible high-pressure cavity and closing the air outlet valve.
In the second step of the technical scheme of the method for measuring interfacial tension between polymer melts in high-pressure gas, the heating to the test temperature and the timing are started, namely, the timing is started when the temperature is raised to the test temperature and is 0.
In the first step of the technical scheme of the method for measuring the interfacial tension between polymer melts in the high-pressure gas, when short fibers are annealed, the annealing temperature is higher than the glass transition temperature of the polymer A and lower than the melting point or viscous flow temperature of the polymer A; when a short fiber is sandwiched between two sheets and then annealed, the annealing temperature should be greater than the glass transition temperature of polymer a and polymer B and less than the melting point or viscous flow temperature of polymer a and polymer B.
The melting point or the viscous flow temperature of the polymer A and the polymer B is referred to herein, and when a polymer is an amorphous polymer, the melting point or the viscous flow temperature is referred to herein as the viscous flow temperature of the polymer, and when a polymer is a crystalline polymer, the melting point or the viscous flow temperature is referred to herein as the melting point. Similarly, the melting points or viscous flow temperatures of the polymer A and the polymer B involved in step (II) are also determined in this manner, except that the corresponding melting points or viscous flow temperatures are the values of the polymers measured under the test pressure conditions.
For example, for step (r):
when the polymer A is a non-crystalline polymer, the annealing temperature is lower than the viscous flow temperature of the polymer A when the short fiber is annealed; when polymer a is a crystalline polymer, the annealing temperature should be less than the melting point of polymer a when the staple fiber is annealed.
When both polymer a and polymer B are amorphous polymers, after sandwiching a short fiber between two sheets, the annealing temperature at the time of annealing treatment is less than the viscous flow temperature of polymer a and polymer B; when both polymer a and polymer B are crystalline polymers, one short fiber is sandwiched between two polymer sheets, and the annealing temperature at the time of annealing treatment is less than the melting points of polymer a and polymer B; when one of the polymers A and B is a crystalline polymer and the other is an amorphous polymer, the annealing temperature of the annealing treatment is lower than the smaller value of the viscous flow temperature and the melting point of the polymers A and B after one short fiber is sandwiched between two polymer sheets.
In the technical scheme of the method for measuring the interfacial tension between the polymer melts in the high-pressure gas, the high-pressure visual device is obtained by loading a high-pressure cavity connected with a high-pressure pump in an optical microscope with a temperature control device and a charge coupling device.
In the step of the technical scheme of the method for measuring the interfacial tension between the polymer melts in the high-pressure gas, when pictures before the short fibers retract into spherical shapes and are shot at different time points are selected, the selected pictures should reflect the shapes of the short fibers at different stages as much as possible. Generally, polymer systems are different (namely, specifically selected polymer A is different from polymer B), conditions such as testing temperature, testing pressure, testing gas and the like are different, and the total length of the short fiber shrinking into a spherical shape is different from dozens of minutes to several hours, so in actual operation, the time interval and the number of the specifically selected adjacent pictures are determined according to the shrinking process of the short fiber, and the principle that the selected pictures can reflect the shapes of the short fiber at different stages as much as possible is taken as a principle, for example, a feasible scheme is that the time interval between the selected adjacent pictures is 1 s-50 min, and the adjacent pictures refer to pictures at adjacent positions after the selected pictures are sequenced according to the shooting time sequence; theoretically, the more the number of the selected pictures is, the more accurate the linear equation obtained by calculation and fitting is, and the number of the selected pictures can not be lower than 5 in principle, for example, the step (c) can select 5 to 20 pictures before the short fibers shot at different time points retract into the spherical shape from the shot and recorded data of the shape of the short fibers changing along with time, and measure the radius R of the widest part perpendicular to the length direction of the short fibers before the short fibers retract into the spherical shape. Further, when the radius R at the widest part perpendicular to the length direction of the short fiber before the short fiber retracts into a spherical shape is measured, the final radius value can be determined by measuring the radius value on the same picture for multiple times and averaging, so that the measurement error is reduced.
In the above-mentioned technical solution of the method for measuring interfacial tension between polymer melts in high-pressure gas, the polymer a and the polymer B are determined as long as they are incompatible polymers, for example, the polymer a and the polymer B are selected from polypropylene, polyethylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, polymethyl methacrylate, polycarbonate, polyamide, polylactic acid, polycaprolactone and polyacrylic acid, and the polymer a and the polymer B are different and partially compatible or completely incompatible.
In the technical solution of the method for measuring interfacial tension between polymer melts in high-pressure gas, the high-pressure gas includes supercritical fluid, for example, when the test gas is carbon dioxide, when the test pressure is greater than 7.22MPa and the saturation temperature is greater than 31.1 ℃, the carbon dioxide in the high-pressure chamber is converted into supercritical carbon dioxide.
In the second step of the technical scheme of the method for measuring the interfacial tension between the polymer melts in the high-pressure gas, the operation of adjusting the temperature of the high-pressure cavity to the saturation temperature is performed, then the operation of exhausting the air in the high-pressure cavity and introducing the test gas to the test pressure is performed, so that the action time of the high-pressure gas and the action time of the polymer in the high-pressure cavity are consistent, the problem that the action time of the high-pressure gas and the action time of the polymer are inconsistent due to the change of the environmental temperature is avoided, and the accuracy of the test result is improved. There is no special requirement for the heating rate of adjusting the temperature to the saturation temperature test temperature in the second step, and a conventional heating rate in the field can be adopted, and in order to prevent temperature overshoot, a slower heating rate is preferably adopted when the temperature approaches the test temperature. When the average value is obtained by repeating the experiment, the same temperature rising rate needs to be ensured to ensure that the action time of the high-pressure gas and the action time of the polymer are consistent.
In the step of the technical scheme of the method for measuring interfacial tension between polymer melts in high-pressure gas, the melting points or viscous flow temperatures of the polymer A and the polymer B under the condition of test pressure are determined by a high-pressure differential scanning calorimeter (HP-DSC) test.
Compared with the prior art, the technical scheme provided by the invention has the following beneficial technical effects:
1. the invention provides a method for measuring interfacial tension between polymer melts in high-pressure gas, which utilizes fiber retraction to measure interfacial tension between polymer melts in the high-pressure gas, utilizes a high-pressure visual device to firstly saturate a sample to be tested under the conditions of saturation temperature and test pressure so as to enable the high-pressure test gas and the sample to be tested to generate interaction, then heats the sample to the test temperature, shoots and records the change condition of the form of short fibers in a high-pressure cavity along with time under the conditions of test temperature and test pressure until the short fibers retract into a spherical shape in real time, and combines rheological parameters of polymers in the corresponding high-pressure gas and a theoretical formula of a fiber retraction method to calculate the interfacial tension between the polymer melts, thereby ensuring the accuracy and reliability of test results. The method does not need to rely on the density difference of the polymer melt and the shape of the balance liquid drop to calculate the interfacial tension, and compared with the existing pendant drop method for testing the interfacial tension between the polymer melts in the high-pressure gas, the method does not need to wait for the melt liquid drop form to reach the balance for a long time, on one hand, the testing time can be shortened, on the other hand, the measuring difficulty can be reduced, so that the applicability is higher, the method is also applicable to polymer materials which are easy to be thermally degraded, and the problem of accurately measuring the interfacial tension between the polymer melts in the high-pressure gas is solved.
2. The measuring method provided by the invention has the advantages of simple sample preparation method, easiness in control of observation and measurement processes, high experimental efficiency, convenience and accuracy in obtaining the interfacial tension among polymer melts under different polymers, measurement temperatures and gas pressures, and wide application range.
Drawings
Fig. 1 is a schematic structural view of a high-voltage visual device employed in the embodiment, in which: 1-gas cylinder, 2-plunger pump, 3-air inlet valve, 4-high pressure cavity, 5-exhaust valve, 6-thermocouple, 7-temperature controller, 8-eyepiece, 9-objective, 10-heat stage, 11-objective stage, 12-computer.
FIG. 2 is a schematic diagram of a sample to be tested consisting of PMMA staple fibers and PS flakes in the example.
FIG. 3 shows PS and PMMA at 190 ℃ and 6MPa CO 2 Steady state scan of (1).
FIG. 4 shows the retraction process of PMMA staple fibers in a PS sheet.
FIG. 5 is a schematic diagram showing the measurement of the radius of PMMA staple fibers during retraction in a PS sheet.
FIG. 6 is a graph of the shape correlation factor as a function of time for PMMA staple fibers retracted within a PS sheet.
Detailed Description
The method for measuring interfacial tension between polymer melts in high pressure gas provided by the present invention is further illustrated by the following examples. It should be noted that the following examples are only for illustrating the present invention and should not be construed as limiting the scope of the present invention, and those skilled in the art can make certain insubstantial modifications and adaptations of the present invention based on the above disclosure and still fall within the scope of the present invention.
Examples
In this example, the interfacial tension between the Polymethylmethacrylate (PMMA) and Polystyrene (PS) melts in high pressure carbon dioxide was measured.
The structural schematic diagram of the high-pressure visual device adopted in the embodiment is shown in fig. 1, and comprises a gas cylinder 1, a plunger pump 2, a high-pressure cavity 4, a thermocouple 6, a temperature controller 7, a microscope and a computer 12. An air inlet valve 3 and an air outlet valve 5 are arranged on the high-pressure cavity 4, the high-pressure cavity 4 is of a hollow cylinder structure, visual windows are arranged on the upper bottom surface and the lower bottom surface, and the temperature is controlled by the heat station 10. The microscope is an optical microscope with a hot stage and a Charge Coupled Device (CCD), the microscope comprises an eyepiece 8, an objective lens 9, a hot stage 10 and an objective table 11, the objective lens 9 of the microscope is arranged above a visible window of the high-pressure cavity, and light of a microscope light source sequentially passes through a light through hole, a sample to be detected in the high-pressure cavity, the objective lens 9 and the eyepiece 8. The gas cylinder 1 is used to supply a test gas. The plunger pump 2 is used for compressing the test gas to obtain corresponding high-pressure test gas. The gas cylinder 1, the plunger pump 2 and the high-pressure cavity 4 are connected through pipe fittings in sequence. The inlet valve 3 is mounted on the pipe between the plunger pump 2 and the high pressure chamber 4. An exhaust pipe is arranged on the high-pressure cavity 4, and an exhaust valve 6 is arranged on the exhaust pipe. The temperature control device of the heating table 10 consists of a thermocouple 7 and a temperature controller 8, and a temperature sensing probe of the thermocouple is positioned in the high-pressure cavity. The charge coupled device of the microscope is connected with the computer 12, shooting and recording the form change of the visible short fiber in the high-voltage cavity in real time from the temperature rise to the testing temperature, and transmitting the data to the computer.
At high pressure CO 2 As test gas, PMMA was used as polymer A, PS was used as polymer B, and PMMA and PS were tested at 190 ℃ under 6MPa of high pressure CO 2 Interfacial tension between the intermediate melts.
The method comprises the following specific steps:
putting PMMA granules and PS granules into a vacuum oven at 80 ℃ for drying for 24 hours.
Preparing PMMA granules into PMMA fibers with the diameter of 0.28mm by using melt spinning equipment, cutting the PMMA fibers into small sections with the length of 0.8mm to obtain PMMA short fibers, and then placing the PMMA short fibers in an oven at 80 ℃ for annealing for 12 hours to eliminate internal stress. The annealed PMMA staple fibers should not contain bubbles.
Molding PS granules at 180 deg.C under 10MPa for 10min by vacuum molding machine to obtain PS sheets with size of 10mm × 10mm × 1 mm; a piece of PMMA short fiber is placed between two identical PS sheets, and then annealing treatment is carried out in a vacuum oven at 100 ℃ for 12h to ensure that the PMMA short fiber is fully contacted with the PS sheets, so as to obtain a sample to be measured, as shown in figure 2.
Secondly, placing the sample to be measured in a high-pressure cavity of a high-pressure visual device, and fixing the high-pressure cavity to a heat pipeIn the table, the high-pressure chamber was heated to 30 ℃ and maintained at that temperature, the inlet and outlet valves of the high-pressure chamber were opened, and CO was introduced via a plunger pump 2 Purging the high-pressure cavity to remove air in the high-pressure cavity, exhausting for 3min, closing the exhaust valve, and introducing CO 2 And (3) keeping the testing pressure and the saturation temperature for 0.5h until the pressure in the high-pressure cavity reaches the testing pressure of 6MPa, then heating to the testing temperature of 190 ℃ and starting timing (namely starting timing when the temperature is increased to the testing temperature of 0), and shooting and recording the change condition of the form of the short fiber in the high-pressure cavity along with time in real time from the temperature increase to the testing temperature until the short fiber retracts to a spherical shape. Fig. 4 shows an image of the retraction process of PMMA staple fibers in PS flakes, during which we found that at 40min, the PMMA staple fibers retracted into a spherical shape.
Selecting 7 pictures shot at different time points before the short fiber retracts into a spherical shape from the shot and recorded data of the change of the shape of the short fiber along with time, measuring the radius R of the widest part vertical to the length direction of the short fiber before the short fiber retracts into the spherical shape, and measuring the radius R when the short fiber retracts into the spherical shape 0 And the radius Re of the short fiber subjected to annealing treatment in the step I; a schematic diagram of the radius measurement of the different forms of staple fibers is shown in figure 5.
F (x) is calculated according to the expressions (1) to (2) R )、f(x Re ) Calculating a shape correlation factor in the short fiber retraction process according to the formula (3), then drawing by taking the shape correlation factor as a vertical coordinate and time as a horizontal coordinate and performing straight line fitting, calculating the interfacial tension between polymer melts under the test condition according to the formula (4) by combining the slope of a straight line equation obtained by fitting,
y＝R 0 (f(x R )-f(x Re )) (3)
σ 12 ＝kη (4)
in the formulae (1) to (5), R e Is the radius, R, of the short fiber subjected to annealing treatment in the step (i) 0 Is the radius of the short fiber when it is retracted into the spherical shape, R is the radius of the widest part vertical to the length direction of the short fiber before the short fiber is retracted into the spherical shape, y is the shape-related factor, sigma 12 The interfacial tension k between the melts of the polymer A and the polymer B is the slope of a linear equation obtained by fitting, eta is the effective viscosity, eta is m Zero shear viscosity, η, for equilibrium of polymer B interaction with test gas at test pressure and test temperature f Is the zero shear viscosity at which the polymer a and test gas interact to equilibrium under test pressure and test temperature conditions.
Specifically, f (x) is calculated from the expressions (1) to (2) R )、f(x Re ) Then, calculating a shape correlation factor y in the short fiber retraction process according to the formula (3), then drawing by taking the shape correlation factor as a vertical coordinate and time as a horizontal coordinate, as shown in fig. 6, and then performing straight line fitting to obtain the slope of a straight line equation by fitting: y is 8 × 10 -7 t。
PS and PMMA at 190 deg.C and 6MPa 2 The zero shear viscosity under conditions was measured by the following procedure:
and (3) drying the PMMA granules and the PS granules in a vacuum oven at 80 ℃ for 24h, and performing compression molding on the PMMA granules and the PS granules for 10min at 180 ℃ and 10MPa by using a vacuum molding press to respectively prepare a PMMA sample and a PS sample which are required by rheology and have the diameters of 20mm and the thicknesses of 10 mm. The samples were loaded into a high pressure rheometer (Anton Paar) at 190 ℃ and 6MPa CO 2 After 2h of medium equilibration, a steady state scan was started, and the results are shown in FIG. 3. From this, high-pressure CO of 6MPa at 190 ℃ was measured 2 Under the condition, the zero shear viscosity of PMMA is 10226Pa · s, the zero shear viscosity of PS is 3940Pa · s, and the effective viscosity eta is 7898Pa · s according to the formula (5).
Substituting the slope of the linear equation obtained by fitting and the effective viscosity eta value into the formula (4):
σ 12 ＝kη＝8×10 -7 ×7898(N/m)＝6.3(dyn/cm)
namely, high-pressure CO at 190 ℃ and 6MPa is obtained by calculation 2 Under the condition, the interfacial tension between the polymer PMMA and PS melts is 6.3 dyn/cm.
Claims (6)
1. A method for measuring interfacial tension between polymer melts in high-pressure gas is characterized by comprising the following steps:
preparing a polymer A into short fibers, annealing to eliminate internal stress, and preparing a polymer B into a sheet; clamping one short fiber between two thin sheets, and then carrying out annealing treatment to ensure that the short fiber is fully contacted with the thin sheets to obtain a sample to be detected; the polymer A and the polymer B are incompatible polymers;
in the first step, when short fibers are annealed, the annealing temperature is higher than the glass transition temperature of the polymer A and lower than the melting point or viscous flow temperature of the polymer A; sandwiching a staple fiber between two sheets, and annealing at a temperature greater than the glass transition temperature of polymer A and polymer B and less than the melting point or viscous flow temperature of polymer A and polymer B;
placing a sample to be tested in a high-pressure cavity of a high-pressure visual device, adjusting the temperature of the high-pressure cavity to saturation temperature, opening an air inlet valve and an air outlet valve of the high-pressure cavity, introducing test gas to sweep the high-pressure cavity, closing the air outlet valve, then introducing the test gas until the pressure in the high-pressure cavity reaches a test pressure P, wherein P is more than 0.1MPa and less than or equal to 40MPa, keeping the test pressure and the saturation temperature for 1 min-48 h, then heating to the test temperature and starting timing, shooting and recording the change condition of the shape of the short fibers in the high-pressure cavity along with time in real time from the time of heating to the test temperature until the short fibers retract into a spherical shape;
the saturation temperature is above 0 ℃ and below the melting point or viscous flow temperature of polymer a and polymer B at the test pressure conditions; the test temperature is above the melting point or viscous flow temperature of polymer a and polymer B under the test pressure conditions and below the decomposition temperature of polymer a and polymer B;
the high-pressure visual device is obtained by loading a high-pressure cavity connected with a high-pressure pump into an optical microscope with a temperature control device and a charge coupling device, the high-pressure cavity is of a hollow cylinder structure, and visual windows are arranged on the upper bottom surface and the lower bottom surface of the high-pressure cavity;
controlling the saturation temperature, the test pressure and the saturation time to ensure that the short fiber is not changed in shape during the saturation period;
selecting at least 5 pictures shot at different time points from the shot and recorded data of the short fiber shape changing along with the time, measuring the radius R of the widest part vertical to the length direction of the short fiber before the short fiber retracts to be spherical, and measuring the radius R when the short fiber retracts to be spherical 0 And the radius R of the short fiber subjected to annealing treatment in the step (I) e ；
F (x) is calculated according to the expressions (1) to (2) R )、f(x Re ) Calculating a shape correlation factor in the short fiber retraction process according to the formula (3), then drawing by taking the shape correlation factor as a vertical coordinate and time as a horizontal coordinate and performing straight line fitting, calculating the interfacial tension between polymer melts under the test condition according to the formula (4) by combining the slope of a straight line equation obtained by fitting,
y＝R 0 (f(x R )-f(x Re )) (3)
σ 12 ＝kη (4)
in the formulae (1) to (5), R e Is the radius, R, of the short fiber subjected to annealing treatment in the step (i) 0 Is the radius of the short fiber when it is retracted into the spherical shape, R is the radius of the widest part vertical to the length direction of the short fiber before the short fiber is retracted into the spherical shape, y is the shape-related factor, sigma 12 Is the interfacial tension between the melts of polymer A and polymer B, k is the slope of the fitted linear equation, eta is the effective viscosity, eta is m Zero shear viscosity, η, for equilibrium of polymer B interaction with test gas at test pressure and test temperature f Is the zero shear viscosity at which polymer a reaches equilibrium with the test gas interaction under the test pressure and test temperature conditions.
2. The method of claim 1, wherein step (ii) ensures that no bubbles are formed in the staple fibers after the temperature is raised to the test temperature until the staple fibers are spherical.
3. The method of claim 1 or 2, wherein the short fiber has a length of 0.1 to 5mm and a diameter of 0.01 to 5mm, and the ratio of the length to the diameter of the short fiber is 1 to 10.
4. The method for measuring interfacial tension between polymer melts in a high-pressure gas according to claim 1 or 2, wherein the sheet made of the polymer B has a thickness of 1 to 10mm and a volume of 25 to 10000mm 3 。
5. Method for measuring interfacial tension between polymer melts in high pressure gas according to claim 1 or 2, characterized in that the test gas is carbon dioxide, nitrogen, hydrogen, air, methane, propane, butane, pentane, helium or argon.
6. The method for measuring interfacial tension between polymer melts in a high-pressure gas according to claim 1 or 2, wherein the polymer A and the polymer B are selected from the group consisting of polypropylene, polyethylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, polymethyl methacrylate, polycarbonate, polyamide, polylactic acid, polycaprolactone, and polyacrylic acid.
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