Thermal analysis method of water-containing polymer

Abstract

The invention discloses a thermal analysis method of a water-containing polymer, and belongs to the technical field of chemical analysis. The thermal analysis method comprises the following steps: putting a to-be-detected sample containing a water polymer into a sample container, and dropwise adding silicone oil into the sample container until the to-be-detected sample is completely coated by the silicone oil; taking another container as a reference container, and adding the same amount of silicone oil; placing the sample container and the reference container in a differential scanning calorimeter, and performing a differential scanning calorimetry test comprising at least one complete heating and cooling cycle in an inert gas or air atmosphere to obtain a heat flow-temperature curve; and analyzing the thermal transformation behavior of the to-be-tested sample according to the heat flow-temperature curve. According to the method, on the premise that the structure of the water-containing polymer is not damaged, moisture volatilization during heating can be inhibited, and a cyclic heating and cooling test is supported, so that a real melting and crystallization curve is obtained. The method is suitable for various water-containing polymers such as polymer aqueous solutions, hydrogel and paste, and is high in universality.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical analysis, and particularly relates to a thermal analysis method of a water-containing polymer. BACKGROUND

[0002] Hydrophilic polymers are a kind of high molecular materials rich in hydrophilic functional groups in side groups or main chains, and have important application value and research prospect in the fields of food processing, energy environment, biomedicine and new energy materials. At present, common hydrophilic polymers such as polyamide (PA), polyvinyl alcohol (PVA) and ethylene-vinyl alcohol (EVOH) copolymer have been widely used in many industrial fields such as water treatment, fuel cells and food packaging. During the forming process of polymer solution, a polymer paste is often formed, and the structure of the polymer paste directly affects the processing performance of the material.

[0003] Due to the action of hydrophilic functional groups, such polymers can be dissolved or swollen in water to form various water-containing dispersion systems such as polymer aqueous solution, hydrogel and paste. In these systems, the interaction between the polymer and water molecules will significantly affect the motion behavior of the molecular chain, and then change the melting and crystallization characteristics of the polymer. As a common means of analyzing the thermal properties of polymers, differential scanning calorimetry (DSC) can provide melting peaks and crystallization peaks by detecting the heat flow changes during the heating or cooling process, so as to obtain key parameters such as crystallization temperature, crystallization rate, melting point and crystallinity. However, for water-containing polymer systems, water molecules are easy to volatilize under heat during the DSC test, which leads to the continuous change of the water content of the system, so that the measured melting and crystallization behavior cannot truly reflect the actual state, which seriously affects the reliability of the data and the accurate acquisition of related process parameters.

[0004] At present, the conventional DSC test still lacks effective means to inhibit the volatilization of water, and it is difficult to accurately characterize the thermal behavior of water-containing polymers under conditions close to the actual conditions. Therefore, in the thermal analysis process of water-containing polymers, how to effectively inhibit the volatilization of water at high temperature, and truly and stably measure the melting and crystallization behavior has become a key problem to improve the processing applicability and use performance of such materials.

[0005] Therefore, it becomes a technical problem to be solved by those skilled in the art to provide a method for thermal analysis of water-containing polymers, which has the characteristics of effectively inhibiting the volatilization of water and truly reflecting the melting and crystallization behavior, and can solve the problem of inaccurate data caused by water volatilization in the existing DSC test. SUMMARY

[0006] The present application aims to provide a thermal analysis method for water-containing polymers, which can inhibit the volatilization of water molecules during heating without destroying the structure of the water-containing polymers, so that repeated temperature rising and falling can be carried out to obtain the real melting and crystallization curves of the water-containing polymers.

[0007] To achieve the above object, the present application adopts the following technical solutions: The thermal analysis method for water-containing polymers disclosed by the present application comprises the following steps: S1. Placing a sample to be tested of a water-containing polymer in a sample container, and adding silicone oil dropwise into the sample container until the sample to be tested is completely covered by the silicone oil; S2. Taking another container as a reference container, and adding an equal amount of silicone oil into the reference container as in step S1; S3. Placing the sample container and the reference container in a differential scanning calorimeter, and performing a differential scanning calorimetry test containing at least one complete temperature rising and falling cycle under an inert gas or air atmosphere to obtain a heat flow-temperature curve; S4. Analyzing the thermal transition behavior of the sample to be tested according to the heat flow-temperature curve.

[0008] In some embodiments of the present application, the physical form of the sample to be tested in step S1 includes a solid state, a solution state, a gel state and a paste state.

[0009] In some embodiments of the present application, the mass of the sample to be tested is 3-5 mg.

[0010] In some embodiments of the present application, the sample container and the reference container are crucibles.

[0011] In some embodiments of the present application, the inert gas is nitrogen.

[0012] In some embodiments of the present application, the thermal transition behavior includes melting behavior and crystallization behavior.

[0013] In some embodiments of the present application, the process of the at least one complete temperature rising and falling cycle comprises: rising the temperature from 0-25℃ to 100-150℃ at a rate of 1-50℃ / min, and keeping the temperature constant for 1-10 min; and then lowering the temperature to 0-25℃ at a rate of 1-50℃ / min.

[0014] In some embodiments of the present application, in the heat flow-temperature curve, an upward melting endothermic peak appears in the temperature rising stage to represent the melting behavior, and a downward crystallization exothermic peak appears in the temperature falling stage to represent the crystallization behavior.

[0015] The non-polar liquid silicone oil in the application has a boiling point higher than 100 DEG C, does not have a significant phase transition during the test, has a density less than 1.00 g / cm 3 at 25 DEG C, has a viscosity greater than 0.91 cPa s at 25 DEG C, and does not react with the polymer / water system at high temperature.

[0016] Compared with the prior art, the application has the following beneficial effects: The application provides an innovative solution to the key problems in the prior art, such as easy evaporation of water in a water-containing polymer during thermal analysis test, sample structure damage, data distortion and difficult repeated measurement. The application method effectively constructs a physical barrier environment without interfering with the crystallization and melting behavior of water itself, significantly inhibits the escape of water molecules during heating, so that the water-containing polymer sample can maintain its complete physical structure and stable water content in multiple temperature cycle, thereby successfully obtaining a heat flow curve reflecting the real phase change behavior, and overcoming the long-term problems of melting peak and crystallization peak deformation, temperature drift and even signal disappearance caused by water loss in the traditional method.

[0017] Based on the above technical means, the application realizes accurate and reliable characterization of the thermal performance of various forms of water-containing polymers such as polymer aqueous solution, hydrogel and paste. Experiments show that the method can clearly record the complete melting-crystallization process of the water-containing polymer, and sensitively distinguish the thermal performance difference between samples with different water contents, and the obtained data truly reflects the thermodynamic properties of the material itself. More importantly, since water evaporation is effectively inhibited, repeated heating and cooling processes will not significantly affect the sample state and test results, ensuring excellent repeatability and data stability of the experimental method, and providing a solid data foundation for in-depth study of the thermal behavior, phase diagram drawing and process optimization of water-containing polymers.

[0018] In summary, the application not only provides a simple and versatile test method, but more importantly, it first realizes high-fidelity and repeatable measurement of the intrinsic thermal performance of water-containing polymers in conventional DSC testing. The method significantly improves the analysis capability of related material research and quality control, and has wide application prospect and important practical value in the fields of biomedical materials, food industry, cosmetics and high-performance water-based materials. BRIEF DESCRIPTION OF DRAWINGS

[0019] The accompanying drawings illustrate the application; Figure 1 The accompanying drawings illustrate the application; The accompanying drawings illustrate the application; Figure 2 The accompanying drawings illustrate the application; The accompanying drawings illustrate the application; Figure 3The following are DSC curves for water under silicone oil protection: (a) heating curve and (b) cooling curve. Appendix Figure 4 The DSC curves for water are shown in (a) for temperature rise and (b) for temperature fall. Appendix Figure 5 DSC curves (a) showing the heating curve and (b) showing the cooling curve of EVOH paste with different water contents after repeated heating and cooling under silicone oil protection; Appendix Figure 6 The DSC curves (a) showing the heating and (b) showing the cooling of EVOH pastes with different water contents after repeated heating and cooling. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific examples. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] The experimental reagents, instruments, and manufacturers used in this invention are as follows: Differential scanning calorimeter (model DSC 3+, Mettler Toledo Co., Switzerland).

[0022] The following is a flowchart of the thermal analysis method for aqueous polymers disclosed in this invention. Figure 1 As shown; specifically, it includes the following steps: S1. Place the water-containing polymer sample to be tested in a crucible and add silicone oil dropwise until the sample is completely coated with silicone oil; the physical form of the sample to be tested includes solid form, solution form, gel form and paste form; the mass of the sample is 3~5mg.

[0023] S2. Take another crucible as a reference crucible and add the same amount of silicone oil as in step S1; The sample crucible and reference crucible are set up as shown in the attached figure. Figure 2 As shown.

[0024] S3. Place the sample crucible and the reference crucible in a differential scanning calorimeter under an inert gas (such as nitrogen) or air atmosphere, and perform a differential scanning calorimetry test including at least one complete heating and cooling cycle to obtain a heat flow-temperature curve; the at least one complete heating and cooling cycle includes: heating from 0 to 25°C to 100 to 150°C at a rate of 1 to 50°C / min, holding at the temperature for 1 to 10 min; and then cooling to 0 to 25°C at a rate of 1 to 50°C / min.

[0025] S4. Analyzing the thermal transition behavior of the sample to be tested according to the heat flow-temperature curve, the thermal transition behavior including melting behavior and crystallization behavior. In the heat flow-temperature curve, an upward melting endothermic peak appears in the heating stage to represent the melting behavior, and a downward crystallization exothermic peak appears in the cooling stage to represent the crystallization behavior.

[0026] The non-polar liquid silicone oil in the present application has a boiling point higher than 100°C, does not undergo significant phase transition during the test process. The density of the silicone oil at 25°C is less than 1.00 g / cm 3 , the viscosity at 25°C is greater than 0.91 cPa·s, and does not react with the polymer / water system at high temperature.

[0027] Example 1 This example uses water as the test sample to evaluate the inhibitory effect of silicone oil on water evaporation by differential scanning calorimetry. The specific test is as follows: Accurately take 5 μL (5 mg) of deionized water and place it in the sample crucible, use the sample dropper to drop silicone oil on top of the water droplet, so that the water droplet is completely covered by silicone oil, and drop the same amount of silicone oil in the reference crucible.

[0028] Place the prepared sample crucible and reference crucible on the sample side and reference side of the differential scanning calorimeter, respectively, and perform differential scanning calorimetry. The following temperature program is executed: heating from 25°C to 110°C at a rate of 10°C / min; constant temperature for 2 minutes; then cooling to 0°C at a rate of 10°C / min. The test is carried out in a nitrogen atmosphere.

[0029] Record the heat flow (dH / dT)-temperature (°C) curve during the heating and cooling process, the results are shown in Figure 3 The results show that: During the heating stage, no water evaporation endothermic peak near 100°C appears on the curve, indicating that the water molecules covered by the silicone oil do not undergo significant volatilization under this test condition.

[0030] During the cooling stage, a clear exothermic peak appears at about 4°C, which corresponds to the crystallization phase transition of water, indicating that the crystallization behavior of water is not inhibited by the covering of silicone oil.

[0031] From the above sample preparation method and DSC thermal analysis curve, it can be seen that the silicone oil covering layer formed on the surface of water can effectively inhibit the volatilization of water molecules during the heating process, while not affecting the inherent crystallization characteristics of water during the cooling process.

[0032] Comparative Example 1 Comparative Example 1 and Example 1 are compared, the sample crucible does not add silicone oil, and air is used as a control in the reference crucible; the rest of the conditions are the same. The specific test is as follows: A sample crucible was prepared by dropping 5 mg of deionized water in the sample crucible using a sample dropper capillary, and air was used as a reference in the reference crucible. The prepared sample crucible and reference crucible were placed in the sample side and reference side of the differential scanning calorimeter, respectively, and differential scanning calorimetry was performed. The following temperature program was executed: heating from 25 °C to 110 °C at a rate of 10 °C / min; isothermal for 2 min; and then cooling to 0 °C at a rate of 10 °C / min. The test was performed under a nitrogen atmosphere.

[0033] The heat flow (dH / dT) - temperature (°C) curves during the heating and cooling processes were recorded, and the results are shown in FIG. 1. Figure 4 The results show that, during the heating process, a significant endothermic peak was observed at about 90 °C, which was attributed to the evaporation of water. During the subsequent cooling process, no expected exothermic peak of water crystallization was observed near 0 °C.

[0034] Example 2 In this example 2, the EVOH paste was tested by the method of the present application.

[0035] The test sample was a mixture of ethylene-vinyl alcohol copolymer (EVOH) resin (F171B, Kuraray Co., Japan) and water, i.e., EVOH paste, provided by a foreign manufacturer. According to the different water contents of the sample, the sample was divided into two groups, i.e., high water content and low water content.

[0036] The test sample was cut into a thin piece of about 5 mg and placed in a sample crucible. Silicon oil was dropped on the surface of the sample using a sample dropper capillary to completely cover the sample. At the same time, an equal amount of silicon oil was dropped in the reference crucible. The prepared sample crucible and reference crucible were placed in the sample side and reference side of the differential scanning calorimeter, respectively. The temperature was raised from 25 °C to 110 °C at a rate of 10 °C / min, and then cooled to 25 °C at a rate of 10 °C / min after isothermal for 2 min. Subsequently, the heating and cooling processes were repeated.

[0037] According to the different water contents of the sample and the number of heating and cooling, the sample was recorded as “high (low) water content, xth heating (cooling)”.

[0038] The heat flow (dH / dT) - temperature (°C) curves during the heating and cooling processes were recorded, and the results are shown in FIG. 2. Figure 5 The results show that, for the sample with high water content, the heating curves of the first and second heating both showed an endothermic peak at about 87 °C, and the cooling curves of the first and second cooling both showed an exothermic peak at about 38 °C. For the sample with low water content, the heating curves of the first and second heating both showed an endothermic peak at about 100 °C, and the cooling curve of the first and second cooling showed an exothermic peak at about 42 °C.

[0039] The above DSC curve shows that after the protection of silicone oil, the EVOH paste exhibits complete melting-crystallization behavior during the heating and cooling process, which indicates that the sample preparation method of the present application can effectively inhibit the volatilization of water molecules and effectively distinguish the thermal performance difference between polymers with different water contents, so as to obtain the real thermal behavior characteristics. The repeated heating and cooling does not affect the test results, which indicates that the method has good repeatability and reliability for the thermal performance test of water-containing polymers.

[0040] Comparative Example 2 Comparative Example 2 and Example 2, the sample is not protected by silicone oil. The specific operation of the comparative example is as follows: The mixture of ethylene-vinyl alcohol copolymer (EVOH) resin and water (i.e. EVOH paste) from a foreign manufacturer is used as the sample to be tested.

[0041] First, the sample is cut into a thin piece with a mass of about 5 mg and placed in a sample crucible, and air is used as a reference in the reference crucible. The prepared sample crucible and reference crucible are placed on the sample side and reference side of the differential scanning calorimeter, respectively, and the test program is set as follows: heating from 25℃ to 110℃ at a rate of 10℃ / min, holding for 2 min; then cooling to 25℃ at the same rate.

[0042] Thereafter, the same heating and cooling cycle is repeated immediately at the same position to investigate the change of the thermal behavior of the sample before and after the volatilization of water. In order to distinguish, the two cycles are marked as "first heating / cooling" and "second heating / cooling", respectively.

[0043] The heat flow-temperature curves of the two cycles are recorded and analyzed, and the results are as follows: Figure 6 In the first heating process, an obvious endothermic peak is observed at about 75℃, which is attributed to the evaporation of water in the sample; and in the subsequent first cooling process, no significant exothermic peak is observed. In the second cycle, whether heating or cooling, no significant heat flow change is detected.

[0044] The above results show that in the first heating stage, the water molecules in the sample volatilize due to heating, thereby producing an evaporation endothermic peak near 75℃; since the melting temperature of pure EVOH resin is about 160℃, which is much higher than the upper limit temperature (110℃) of this test, no melting or crystallization signal of the polymer itself is observed throughout the process. In the second cycle, since the water has been completely volatilized in the first heating process, the sample is essentially dry EVOH resin, so its heat flow curve does not change significantly, further confirming that the endothermic peak observed in the first cycle is derived from the evaporation of water, rather than the thermal transition of the resin itself.

[0045] The above merely describes the preferred embodiments of the present application, which are only illustrative but not restrictive; those skilled in the art understand that many changes, modifications, and even equivalent variations can be made to the present application within the spirit and scope defined by the claims of the present application, and all shall fall within the protection scope of the present application.

Claims

1. A thermal analysis method for aqueous polymers, characterized in that, Includes the following steps: S1. Place the water-containing polymer sample to be tested in a sample container and add silicone oil drop by drop until the sample to be tested is completely coated with silicone oil; S2. Take another container as a reference container and add the same amount of silicone oil as in step S1; S3. Place the sample container and the reference container in a differential scanning calorimeter, and perform a differential scanning calorimetry test including at least one complete heating and cooling cycle in an inert gas or air atmosphere to obtain a heat flow-temperature curve; S4. Analyze the thermal transformation behavior of the sample under test based on the heat flow-temperature curve.

2. The thermal analysis method for an aqueous polymer according to claim 1, characterized in that, In step S1, the physical state of the sample to be tested includes solid state, solution state, gel state, and paste state.

3. The thermal analysis method for an aqueous polymer according to claim 1, characterized in that, The mass of the sample to be tested is 3~5mg.

4. The thermal analysis method for an aqueous polymer according to claim 1, characterized in that, The sample container and the reference container are crucibles.

5. The thermal analysis method for an aqueous polymer according to claim 1, characterized in that, The inert gas is nitrogen.

6. The thermal analysis method for an aqueous polymer according to claim 1, characterized in that, Thermal transformation behavior includes melting behavior and crystallization behavior.

7. A thermal analysis method for an aqueous polymer according to claim 1, characterized in that, The at least one complete heating and cooling cycle includes: heating from 0 to 25°C to 100 to 150°C at a rate of 1 to 50°C / min, holding at the temperature for 1 to 10 min; and then cooling down to 0 to 25°C at a rate of 1 to 50°C / min.

8. A thermal analysis method for an aqueous polymer according to claim 1, characterized in that, In the heat flow-temperature curve, an upward melting endothermic peak appears during the heating stage to characterize the melting behavior, and a downward crystallization exothermic peak appears during the cooling stage to characterize the crystallization behavior.

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