KR-102961823-B1 - Method for evaluating crystallinity of polymer

Abstract

The method for evaluating the degree of crystallization of a polymer according to the present invention utilizes infrared spectroscopy to double the accuracy of the evaluation and obtains values that show a trend similar to the degree of crystallization measured using differential scanning calorimetry (DSC). Therefore, it has the advantage of easily and accurately evaluating the degree of crystallization without using DSC.

Inventors

• 공정호
• 성백형
• 유희민

Assignees

• (주)영진테크

Dates

Publication Date

20260507

Application Date

20211118

Claims (6)

1. (a) A step of obtaining a first graph with the wavenumber of the infrared wavelength on the x-axis and the absorption rate on the y-axis by measuring the infrared absorption spectrum of a polymer specimen to be measured for crystallinity using a Fourier transform infrared spectrophotometer; (b) a step of obtaining a second graph by selecting the wavenumber (x peak ) of the crystal region in the first graph, x 1 and x 2 of the low points on both sides of the wavenumber x peak , and the absorption rates y 1 and y 2 at x 1 and x 2 , and then performing curve fitting; (c) A step of measuring the absorption rate (y peak ) at the wavenumber (x peak ) of the crystal region in the second graph above; (d) a step of identifying the absorption rates y1 and y2 at wavenumbers x1 and x2 of both low points of the x peak in the second graph, and constructing a calibration curve with wavenumber (x) and absorption rate (y) as variables based on x1 and x2 and y1 and y2 ; (e) A step of obtaining the absorption rate y cal when the x value in the calibration curve is the wavenumber (x peak ) of the determination region; (f) A step of obtaining the difference in absorption rate Δyc of the crystal region from the difference value between the y peak and ycal ; (g) A step of repeating the process of steps (b) to (f) above for an amorphous region to obtain the difference in absorption rate Δy a of the amorphous region; (h) A step of obtaining the degree of crystallinity by dividing Δy c by Δy a , Method for evaluating the degree of crystallization of a polymer.
2. A method according to claim 1, wherein the two low points of the x peak are selected by first selecting the right low point x 2 , then drawing a tangent line from the right low point x 2 toward the left graph of the peak, and selecting the point of tangency as the left low point x 1 .
3. A method according to claim 1, wherein the curve fitting is performed using a Lorentzain function or a Gaussian function.
4. In claim 1, the method wherein the polymer specimen has a thickness of 0.02 to 10 mm.
5. In paragraph 1, A method in which the crystallinity evaluation value measured by the method for measuring the crystallinity of a polymer according to claim 1 and the crystallinity measured by differential scanning calorimetry (DSC) have a linear proportional relationship.
6. In paragraph 5, A method in which the degree of crystallization (x') measured by the polymer degree of crystallization measurement method according to claim 1 and the degree of crystallization (y') measured by the differential scanning calorimeter (DSC) satisfy the following relationship: y' = ax' + b In the above equation, a and b are constants, and the correlation coefficient ( R² ) is 0.9 or greater.

Description

Method for evaluating crystallinity of polymer The present invention relates to a method for evaluating the degree of crystallization of a polymer, and more specifically, to a method for improving accuracy in evaluating the degree of crystallization of a polymer using a Fourier transform infrared spectrophotometer. Crystallinity is a core characteristic of crystalline polymers and is directly related to product stiffness. Since measuring crystallinity enables product quality control, product comparison, and property prediction, measuring polymer crystallinity is the most fundamental and important technology. The degree of crystallization of polymers is generally calculated using instruments such as WAXD (Wide Angle X-ray Diffraction), DSC (Differential Scanning Calorimeter), and DMA (Dynamic Mechanical Analysis). However, there are various problems with the method of measuring the degree of crystallization using the aforementioned instruments. The accuracy of crystallinity measurement using WAXD is reduced as it is affected by defects within the crystal, such as amorphous regions, impurities, and polymer chain ends. Measuring the degree of crystallization using DSC calculates the degree of crystallization by measuring the energy input to raise the temperature of the polymer; however, there is a problem in that the degree of crystallization may vary depending on additional crystallization of the polymer during the measurement process and the data processing method of the observer. The measurement of crystallinity using DMA calculates the degree of crystallinity by utilizing the change in storage modulus due to changes in the polymer structure at the polymer transition temperature of the storage modulus. However, this method has the problem that it is difficult to apply to linear polymers with a fast crystallization rate. Accordingly, Korean Patent No. 10-2246834 presents a method for measuring the degree of crystallinity of a homopolypropylene polymer using DMA, based on the minimum value of the loss tangent (tan D1) in a temperature range above the glass transition temperature of the polymer sample and the loss tangent value (tan D2) at a temperature where the rate of change of the loss tangent is zero within a predetermined temperature range. Polymers are processed into various molded products in addition to films and sheets; however, the aforementioned methods require cutting, grinding, or heating the polymer molded product to be measured to a specific size in order to measure its degree of crystallization. Consequently, there is a problem in that these methods are difficult to utilize when, for example, the degree of crystallization of molded products needs to be measured on a production line—that is, when non-destructive, non-contact measurement is required. FIG. 1 shows the operation screen of a program used for curve fitting according to the present invention. Figures 2 to 4 show the x peak and both lows of the crystal region in the FT-IR spectrum. Figures 5 and 6 illustrate calibration curves for the crystalline region and the amorphous region, respectively. Figure 7a is the FT-IR spectrum for the four types of polymer specimens used in the example. Figure 7b illustrates a method for finding the left low point in the decision region of Figure 7a. Figures 8a and 8b are the results of curve fitting the crystalline region and the amorphous region in the graph of Figure 7, respectively. Figures 9 to 12 show the results of DSC analysis for four types of polymer specimens used in the examples. Figure 13 is a graph analyzing the correlation between the degree of crystallization measured in the comparative example and the degree of crystallization measured by DSC in the reference example. Figure 14 is a graph analyzing the correlation between the degree of crystallization measured in the example and the degree of crystallization measured by DSC in the reference example. The present invention will be described in more detail below. The present invention relates to a method for measuring the infrared absorption spectrum of a polymer to be measured by transmission using a Fourier transform infrared spectrophotometer (FT-IR) and evaluating the degree of crystallization of the polymer based on the absorption rates of the crystalline and amorphous regions. Infrared transmission methods not only enable non-contact and non-destructive measurements of polymer specimens but also allow for measurements of specimens with a certain thickness and enable the free selection of measurement points within the surface of the specimen. However, for a method of evaluating crystallinity by infrared transmission to replace existing methods, such as the DSC method, it is necessary to have a consistent trend and match well with the measurements obtained by the existing method. Accordingly, the inventors of the present invention have completed the present invention by researching a method to obtain results that match well with crystal