A method for evaluating the melt viscosity of non-crystalline polymers using DSC
By combining DSC with the thermodynamic brittleness index and the MEYGA equation, the problem of inefficient viscosity measurement of amorphous polymer melts is solved, providing a fast and low-cost viscosity measurement method.
Patent Information
- Application Number
- CN202311673366.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-07
- Publication Date
- 2025-12-26
- Estimated Expiration
- 2043-12-07
AI Technical Summary
Existing technologies are difficult to use efficiently and conveniently to measure the viscosity of non-crystalline polymer melts, and traditional methods require a large number of samples and complex high-temperature and high-pressure conditions.
Thermal scanning was performed using a differential scanning calorimeter (DSC) at a heating rate of ±10 K/min. The thermodynamic brittleness index was calculated by analyzing the thermal capacity curves, and the viscosity of the amorphous polymer melt was indirectly calculated using the MEYGA equation. A small number of samples and simplified test conditions were used.
It enables rapid and low-cost measurement of the melt viscosity of amorphous polymers, simplifies the testing process, and reduces sample requirements and testing complexity.
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Figure CN120121665B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of judging non-crystalline polymer melt viscosity testing, and specifically relates to a method for evaluating non-crystalline polymer melt viscosity by using DSC. BACKGROUND
[0002] Accurate acquisition of polymer melt viscosity is of great significance in the fields of material science, chemical engineering, polymer processing, etc. It not only affects the ease of polymer forming, but also directly affects the mechanical properties of the product. In addition, viscosity helps to understand the glass transition and enthalpy relaxation. Traditionally, the method for determining the polymer melt viscosity is usually offline measurement, which requires a large amount of sample and a long time to melt the sample, and the test conditions are complex, requiring high temperature (about 150-300℃) and high pressure (50-100MPa). These difficulties make it inconvenient to determine the polymer melt viscosity. Therefore, it is crucial to find an accurate and efficient method to obtain the polymer melt viscosity. The present application proposes a method for evaluating the viscosity of non-crystalline polymer melt using a differential scanning calorimeter (DSC). In the DSC experiment, a specific temperature program is used to measure the heat capacity change of the sample, and the related parameters of viscosity are inferred by analyzing the heat capacity curve.
[0003] In the prior art and theory before the present application, the methods mentioned in two documents, "Impact of fragility on enthalpy relaxation in glass" by Mauro J C et al. J. Physical Review E 2008, 78(2), 021502 and "New Experimental Evidence for Thermodynamic Links to the Kinetic Fragility of Glass-Forming Polymers" by Wu G et al. J. Macromolecules 2021, 54(12), 5595-5606, are most relevant to the present application. Mauro J C et al. proposed the MEYGA equation to address the problem of large error in extrapolating low temperature for VTF and AM viscosity equations, which has clear physical meaning and greatly improved precision. Wu G et al. proposed a formula for the thermodynamic fragility index of non-crystalline polymers. However, no relevant reports have been found on directly evaluating the viscosity of non-crystalline polymer melt by DSC method. SUMMARY
[0004] In view of the problems existing in the prior art, the purpose of the present application is to provide an efficient and simple method for indirectly evaluating the viscosity of non-crystalline polymer melt by DSC with the aid of one viscosity-temperature data point.
[0005] The concept and scheme of the present application are described as follows:
[0006] The basic concept of the present application is to obtain the heat capacity curves at the heating and cooling rates by performing a thermal scan on the non-crystalline polymer at a heating rate of ±10 K / min by DSC. The thermodynamic fragility index is calculated according to the thermal kinetic parameters reflected on the heat capacity curve, and the viscosity of the non-crystalline polymer melt is indirectly calculated by the MYEGA equation combined with a known viscosity-temperature data point, which specifically includes the following steps:
[0007] Step 1: Prepare the non-crystalline polymer sample to be tested and a sapphire wafer with a mass similar to that of the non-crystalline polymer sample.
[0008] Step 2: Perform a multi-stage heating and cooling test on the non-crystalline polymer sample and the sapphire wafer by a differential scanning calorimeter under a high-purity nitrogen atmosphere, with a temperature rise rate of ±10 K / min, and then obtain the heat capacity curve of the non-crystalline polymer sample by the "sapphire C p determination" DIN 51007. p
[0009] Step 3: In the heat capacity C p curve, the glass transition temperature (T g ) of the non-crystalline polymer sample is determined by the extrapolation of the starting point; a straight line is drawn at the second intersection of the heating and cooling curves, which is parallel to the extrapolated straight line, a vertical line is drawn at the T g point, and the distance of the vertical line is obtained, which is the specific heat capacity change (ΔC p ); finally, the heating and cooling curves intersect to obtain two blank areas, and the average value of the areas of the two areas is calculated, which is defined as the relaxation enthalpy (ΔH R ) (see Figure 2 ).
[0010] Step 4: Calculate the thermodynamic fragility index (m) of the non-crystalline polymer by formula (1):
[0011]
[0012] wherein T g is the glass transition temperature, K; ΔC p is the specific heat change, J / g·K; and ΔH R is the relaxation enthalpy, J / g.
[0013] Step 5: Obtain a viscosity-temperature data point, and fit the MEYGA equation by the undetermined coefficient method to obtain the high-temperature limit viscosity (η ∞ ).
[0014]
[0015] where T is temperature, K; η(T) is viscosity at temperature T; η ∞ is high temperature viscosity limit, Pa·s.
[0016] Step 6: η ∞ and m, T g are substituted back into the MEYGA equation to obtain the viscosity-temperature curve of the amorphous polymer. Step 7: The viscosity-temperature curve of the amorphous polymer is plotted.
[0017] Further, the test conditions in Step 2 are as follows:
[0018] iv. Closed aluminum crucible is used: in order to avoid sample loss and interaction with the external environment, a closed aluminum crucible is used to protect the sample;
[0019] v. The sample mass is 5mg-10mg: the sample amount in the range of 5mg to 10mg is selected for testing; this range provides sufficient sample amount to obtain accurate results and avoids excessive sample consumption;
[0020] vi. Nitrogen flow rate is 50mL / min: during the test, nitrogen is used as an inert gas to avoid reaction of the sample with oxygen; the flow rate of nitrogen is set to 50mL / min to maintain a constant atmosphere.
[0021] Further, the test process of the differential scanning calorimeter is as follows: according to Tg, the temperature range of the test is determined as (T g -55)~(T g +45)K; during the test, a continuous temperature rising and falling program is adopted; 5min isothermal is adopted during heating and cooling to ensure that the sample reaches a constant temperature.
[0022] Further, the amorphous polymer sample needs to be pretreated before the determination of the heat capacity C p curve, and a temperature rising and falling program of ±20K / min is adopted to eliminate the influence of thermal history.
[0023] Further, in Step 5, one viscosity-temperature data point can be obtained by consulting literature or using a viscometer.
[0024] Further, in Step 5 and Step 6, the temperature T range for evaluation is not lower than the glass transition point T g .
[0025] The superiority of the present application compared with the existing test technology is that the method has simple test conditions, small sample amount, short time consumption, lower test cost, and has a more extensive application scenario, and provides a universal method for evaluation of the melt viscosity of amorphous polymers. BRIEF DESCRIPTION OF DRAWINGS
[0026] Figure 1: Schematic diagram of DSC test procedure for non-crystalline polymers.
[0027] Figure 2 : Specific heat temperature diagram of polystyrene (PS) during heating and cooling.
[0028] Figure 3 Viscosity-temperature of polystyrene (PS) Line graph. Detailed Implementation
[0029] The present invention will be further described below with reference to the accompanying drawings.
[0030] The weight-average molecular weight M produced by Sigma-Aldrich w 280×10 3 Taking polystyrene (PS) as an example, this paper illustrates the method of using DSC to evaluate the melt viscosity of non-crystalline polymers.
[0031] Step 1: Prepare the polystyrene (PS) sample to be tested and grind it thoroughly. Take a sample amount of 7.5 mg and prepare a sapphire disc with a mass close to 7.5 mg.
[0032] Step 2: Under a high-purity nitrogen atmosphere, differential scanning calorimetry was used to perform multi-stage heating and cooling tests on both the amorphous polymer sample and the sapphire wafer (heating rate ±10K / min). Then, the sapphire was subjected to C... p The Cp curve of the heat capacity of polystyrene (PS) was obtained by the determination method (DIN 51007) as follows: Figure 2 .
[0033] Step 3: At the heat capacity C of polystyrene (PS) p In the curve, the glass transition temperature (T0) of polystyrene (PS) is determined by extrapolating the starting point. g The value is 369.81 K. At the second intersection of the heating and cooling curves, draw a straight line parallel to the extrapolated line. At T... g By introducing a perpendicular line from the point and obtaining the distance between the perpendicular lines, the change in specific heat capacity (ΔC) can be obtained. p The value is 0.13 J / g·K. Finally, the intersection of the heating and cooling curves yields two blank regions. The average area of the two regions is calculated to obtain the relaxation enthalpy (ΔH). R The value is 0.6 J / g (see...) Figure 2 ).
[0034] Step 4: Calculate the thermodynamic brittleness index of polystyrene PS using formula (1), which is m = 77.19.
[0035] Step 5: Given that the viscosity of polystyrene (PS) at 250℃ is 317.2 Pa·s, the logarithm of the high-temperature limiting viscosity (lgη) is obtained by fitting the MEYGA equation using the method of undetermined coefficients. ∞) is 1.26.
[0036] Step 6: η ∞ and m, T g Substituting back into the MEYGA equation gives the viscosity-temperature dependence of polystyrene PS as in equation (3), with the viscosity-temperature dependence of PS as in equation (4). The plot of η Figure 3 .
[0037]
Claims
1. A method for evaluating the melt viscosity of non-crystalline polymers by DSC, characterized in that, The method comprises the following steps: Step 1: preparing the non-crystalline polymer sample to be tested and a sapphire wafer with a mass similar to that of the sample; Step 2: The amorphous polymer sample and the sapphire wafer are both subjected to a multi-step temperature ramping test with a differential scanning calorimeter under a high-purity nitrogen atmosphere at a temperature ramping rate of ±10 K / min, and the heat capacity curve of the amorphous polymer sample is obtained by means of the "sapphire normalization" method according to DIN 51007. Step 2: The amorphous polymer sample and the sapphire wafer are both subjected to a multi-step temperature ramping test with a differential scanning calorimeter under a high-purity nitrogen atmosphere at a temperature ramping rate of ±10 K / min, and the heat capacity curve of the amorphous polymer sample is obtained by means of the "sapphire normalization" method according to DIN 51007. Step 2: The amorphous polymer sample and the sapphire wafer are both subjected to a multi-step temperature Step 3: The heat capacity In the curve, the extrapolation starting point method is used to determine the glass transition temperature of the non-crystalline polymer sample ; At the second intersection point of the heating and cooling curves, a straight line is drawn parallel to the extrapolation line, a vertical line is drawn at point, and the distance of the vertical line is obtained, which is the change in heat capacity ; Finally, the heating and cooling curves intersect to obtain two blank areas, and the average value of the areas of the two areas is calculated, which is defined as the relaxation enthalpy ; Step 4: Calculate the thermodynamic fragility index of the amorphous polymer using equation (1) : （1）， wherein, is the glass transition temperature, K; is the change in specific heat, J / g K; is the relaxation enthalpy, J / g; Step 5: Obtain a viscosity-temperature data point, fit the MEYGA equation with the pending coefficients to obtain the high temperature limit viscosity ; （2）， wherein is the temperature, K; is the viscosity at a temperature of is the high temperature viscosity limit, Pa-s; Step 6: The and , MEYGA equation is re-substituted to obtain the viscosity-temperature ~ curve for the non-crystalline polymer. plot for the non-crystalline polymer.
2. The method for evaluating the melt viscosity of non-crystalline polymers by DSC according to claim 1, characterized in that, The test conditions in step 2 are as follows: i. Using a closed aluminum crucible: in order to avoid sample loss and interaction with the external environment, a closed aluminum crucible is used to protect the sample; ii. The sample mass is 5 mg to 10 mg: the sample amount in the range of 5 mg to 10 mg is selected for testing; this range provides sufficient sample amount to obtain accurate results and avoids excessive sample consumption; iii. Nitrogen flow rate 50 mL / min: during the test, nitrogen is used as an inert gas to avoid the reaction of the sample with oxygen; the flow rate of nitrogen is set to 50 mL / min to maintain a constant atmosphere.
3. The method for evaluating the melt viscosity of non-crystalline polymers by DSC according to claim 1, characterized in that, The test process of the differential scanning calorimeter is as follows, and the temperature range of the test is determined according to Tg ; During the test, a continuous temperature rising and falling program is adopted; 5 min of isothermal is adopted for both heating and cooling to ensure that the sample reaches a constant temperature.
4. The method for evaluating the melt viscosity of non-crystalline polymers by DSC according to claim 1, characterized in that, Non-crystalline polymer samples in the determination of heat capacity The curves were pre-treated with a temperature program of ± 20 K / min before the measurement to eliminate the influence of thermal history.
5. The method for evaluating the melt viscosity of non-crystalline polymers by DSC according to claim 1, characterized in that, In step 5, one viscosity-temperature data point is obtained by consulting literature or using a viscometer.
6. The method for evaluating the melt viscosity of non-crystalline polymers by DSC according to claim 1, characterized in that, In steps 5 and 6, the temperature at which the evaluation is performed The temperature is not less than the glass transition point .