Method for measuring prediction model of crystallinity of polylactic acid product through near infrared

Abstract

The invention relates to the technical field of polylactic acid product crystallinity, in particular to a method for measuring a prediction model of polylactic acid product crystallinity through near infrared. Measuring the melting enthalpy of different polylactic acid samples by adopting a DSC differential scanning calorimeter, wherein the ratio of the sample melting enthalpy of the polylactic acid product to the standard melting enthalpy is the crystallinity of the sample; the method comprises the following steps: carrying out infrared characterization on polylactic acid samples with different crystallinity degrees by adopting a Fourier transform infrared spectrometer FTIR, and drawing a curve by taking the crystallinity degrees as abscissas and A1383 / A1358 as ordinates; according to the method for measuring the prediction model of the crystallinity of the polylactic acid product through near infrared, a new method is provided for measuring the crystallinity by researching the detection capability of a near infrared spectrum 5-Y-analysis technology on the crystallinity of the polylactic acid.

Description

Technical Field

[0001] The invention relates to a method for measuring the crystallinity of a polylactic acid product, and in particular to a method for determining a prediction model of the crystallinity of a polylactic acid product by near infrared. Background Art

[0002] Near infrared (Nm) spectroscopy is a new detection technology that can quickly and accurately perform nondestructive testing on the physical, mechanical and chemical properties of organic samples such as powders, liquids and solids. It has been widely and rapidly applied in many fields and has achieved field testing, online testing and product quality control. In terms of materials, the use of NIR to determine the chemical composition, density, strength, etc. of materials is very extensive, but the research on the determination of material crystallinity is very rare.

[0003] Crystallinity is an important material property index of polylactic acid products, especially in the manufacture of heat-resistant products such as cups, straws, lunch boxes, knives, forks and spoons. Crystallinity is related to the quality of polylactic acid and polylactic acid derivative products. The traditional measurement of polylactic acid crystallinity is not only complicated and time-consuming, but also requires the use of chemicals to separate the sample material during measurement, which is not conducive to large-scale measurement. The measurement of polylactic acid crystallinity by X-ray diffraction method takes a long time, and the experiment generates X-ray radiation, which causes certain harm to the working environment and the health of the experimenters. Summary of the invention

[0004] The present invention aims to solve the above-mentioned defects and provides a method for a prediction model of the crystallinity of polylactic acid products by near infrared measurement.

[0005] In order to overcome the defects in the background technology, the technical solution adopted by the present invention to solve the technical problem is: the method comprises the following steps:

[0006] The first step is to prepare a polylactic acid sample with a crystallinity between 30% and 95% by controlling the crystallization temperature and time;

[0007] The second step is to use DSC differential scanning calorimeter to measure the melting enthalpy of different polylactic acid samples. The ratio of the sample melting enthalpy of the polylactic acid product to the standard melting enthalpy is the sample crystallinity;

[0008] The third step is to use Fourier transform infrared spectrometer FTIR to characterize the polylactic acid samples with different crystallinity. The attenuated total reflection ATR mode is used for testing, and the spectrum peak 1383cm -1 The absorbance A 1383 and 1358cm -1 The absorbance A 1358 , calculate its ratio A 1383 / A 1358 ;

[0009] Step 4: Use crystallinity as the horizontal axis, A 1383 / A 1358 As the ordinate, a curve is drawn and polynomial fitting is used to obtain the regression equation y = -7E-05x2 + 0.0136x + 0.8456, R 2 = 0.9972, substitute the measured ordinate y A 1383 / A 1358 The ratio can be used to calculate the crystallinity x on the horizontal axis.

[0010] According to another embodiment of the present invention, the temperature range of the DSC differential scanning calorimeter measurement in the second step is room temperature to 100°C, and the heating rate is 10°C·min -1 , the protective gas is nitrogen.

[0011] The beneficial effect of the present invention is that the method of the prediction model for near-infrared determination of the crystallinity of polylactic acid products provides a new method for determining the crystallinity by studying the detection capability of near-infrared spectroscopy 5-Y-analysis technology for the crystallinity of polylactic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0013] Figure 1 It is a schematic diagram of the structure of infrared characterization of polylactic acid samples by infrared spectrometer (FTIR);

[0014] Figure 2 Yes A 1383 / A 1358 Schematic diagram of the structure corresponding to the degree of crystallinity. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] The method of the prediction model of the near infrared determination of the crystallinity of polylactic acid products comprises the following steps:

[0017] The first step is to prepare samples with different crystallinity by controlling the crystallization temperature and time, and prepare polylactic acid samples with a crystallinity between 30% and 95%;

[0018] The second step is to use DSC differential scanning calorimeter to measure the melting enthalpy of different polylactic acid samples. The ratio of the sample melting enthalpy of the polylactic acid product to the standard melting enthalpy is the sample crystallinity;

[0019] The third step is to use Fourier transform infrared spectrometer FTIR to characterize the polylactic acid samples with different crystallinity. The attenuated total reflection ATR mode is used for testing, and the spectrum peak 1383cm -1 The absorbance A 1383 and 1358cm -1 The absorbance A 1358 , calculate its ratio A 1383 / A 1358 ;

[0020] Step 4: Use crystallinity as the horizontal axis, A 1383 / A 1358 As the ordinate, a curve is drawn and polynomial fitting is used to obtain the regression equation y = -7E-05x2 + 0.0136x + 0.8456, R 2 = 0.9972, substitute the measured ordinate y A 1383 / A 1358 The ratio can be used to calculate the crystallinity x on the horizontal axis.

[0021] In the second step, the temperature range of DSC differential scanning calorimeter measurement was room temperature to 100°C, and the heating rate was 10°C min -1 , the protective gas is nitrogen.

[0022] like Figure 1 , 2 As shown, 1383cm -1 The two peaks at 1383cm-1 can be attributed to the carbonyl CH bending vibration peaks on the polymer chain. Polylactic acid is a linear molecule with a side methyl group. Its main chain contains only methine CH groups except ester groups. As the crystallinity increases, the peaks at 1383cm-1 are -1 The absorption peak signal of 1358cm -1 The absorbance decreases.

[0023] Use near-infrared to continuously monitor the finished polylactic acid products, and determine their crystallinity in real time based on the pre-set fitting curve.

[0024] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for predicting the crystallinity of polylactic acid products by near infrared determination, characterized in that: The method comprises the following steps: The first step is to prepare a polylactic acid sample with a crystallinity between 30% and 95% by controlling the crystallization temperature and time; The second step is to use DSC differential scanning calorimeter to measure the melting enthalpy of different polylactic acid samples. The ratio of the sample melting enthalpy of the polylactic acid product to the standard melting enthalpy is the sample crystallinity; The third step is to use Fourier transform infrared spectrometer FTIR to characterize the polylactic acid samples with different crystallinity. The attenuated total reflection ATR mode is used for testing, and the spectrum peak 1383cm -1 The absorbance A 1383 and 1358cm -1 The absorbance A 1358 , calculate its ratio A 1383 / A 1358 ; Step 4: Use crystallinity as the horizontal axis and ratio A 1383 / A 1358 As the ordinate, a curve is drawn and polynomial fitting is used to obtain the regression equation y = -7E-05x2 + 0.0136x + 0.8456, R 2 = 0.9972, substitute the measured ordinate y A 1383 / A 1358 The ratio can be used to calculate the crystallinity x on the horizontal axis.

2. The method for predicting the crystallinity of polylactic acid products by near infrared determination as claimed in claim 1, characterized in that: In the second step, the temperature range of the DSC differential scanning calorimeter measurement is room temperature to 100°C, and the heating rate is 10°C·min -1 , the protective gas is nitrogen.

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