Quantitative analysis method of PLA in PHA

Abstract

The invention discloses a quantitative analysis method of PLA (polylactic acid) in PHA (polyhydroxyalkanoate). The method comprises the following steps: respectively testing PHA samples mixed with PLA in different proportions by using a differential scanning calorimeter to obtain a differential scanning calorimetry curve; establishing a standard fitting curve according to the linear relation between the curve intensity and concentration at the PHA melting point peak of 155-157 DEG C and the curve intensity and concentration at the PLA melting point peak of 171-173 DEG C; and the PLA is quantitatively analyzed according to the curve intensity of a PLA melting point peak at 171-173 DEG C in a differential scanning calorimeter. The quantitative analysis method provided by the invention is simple and efficient, and requires less sample amount.

Description

Technical Field

[0001] The invention relates to a method for analyzing polymer content, in particular to a method for quantitatively analyzing PLA in PHA. Background Art

[0002] PLA (polylactic acid) is a high molecular polymer obtained by polymerization of lactic acid as raw material. PLA is added to PHA (polyhydroxyalkanoate) to achieve modification.

[0003] Usually, the quantitative analysis of PLA in PHA is performed by nuclear magnetic resonance spectroscopy, which requires the use of a special solvent to dissolve the sample before testing. The operation steps are cumbersome and the detection efficiency is low. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a quantitative analysis method for PLA in PHA which does not require solvent dissolution of the sample to be tested and requires a small amount of sample.

[0005] Technical solution: The quantitative analysis method of PLA in PHA of the present invention comprises the following steps:

[0006] (1) PHA samples mixed with different proportions of PLA were tested by differential scanning calorimetry to obtain differential scanning calorimetry curves;

[0007] (2) determining the melting point peak temperature range of PLA and the melting point peak temperature range of PHA according to the differential scanning calorimetry curve, and marking the corresponding melting point peak curve intensities respectively;

[0008] (3) The melting point peak curve intensity of PLA is recorded as x1, the melting point peak curve intensity of PHA is recorded as x2, and the baseline intensity is recorded as x0. (x1-x0) / (x2-x0) is the abscissa x, the content ratio of PLA to PHA is the ordinate y, and the standard fitting curve is obtained by fitting: y=ax+b; wherein a is the slope of the standard fitting curve, and b is the intercept of the standard fitting curve;

[0009] (4) The PHA sample mixed with PLA was tested by differential scanning calorimetry, and the concentration of PLA in the PHA sample mixed with PLA was calculated based on the standard fitting curve.

[0010] Wherein, in step (1), the amount of the PHA sample is 1 to 10 mg.

[0011] Wherein, in step (1), the temperature rise range during the differential scanning calorimeter test is 100 to 200°C.

[0012] Wherein, in step (1), the parameters of the differential scanning calorimeter test are: heating rate of 3 to 10°C / min; purge nitrogen flow rate of 50 to 70 ml / min; protective nitrogen flow rate of 40 to 60 ml / min.

[0013] Wherein, in step (2), the melting point peak of PLA is determined to be 171-173° C., and the melting point peak of PHA is determined to be 155-157° C., and the peak intensities of 171-173° C. and 155-157° C. are marked respectively.

[0014] Wherein, in step (2), the baseline intensity at 180°C to 200°C in the differential scanning calorimetry curve is selected as x0.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant effects: According to the linear relationship between the curve intensity of the PLA melting point peak of 171-173°C and the concentration, the present invention establishes a standard fitting curve, and realizes quantitative analysis of PLA by using the peak intensity of the PLA melting point peak of 171-173°C using a differential scanning calorimeter. The present invention can directly perform differential scanning calorimetry test on the sample to be tested, and the sample to be tested does not need to be dissolved by a solvent, thereby improving the detection efficiency. The method of the present invention is simple, can quickly perform quantitative analysis of PHA in PHA, and requires less sample volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a comparison diagram of the differential scanning calorimetry curve of PHA without PLA and the differential scanning calorimetry curve of PHA containing PLA in step (1) of the embodiment of the present invention;

[0018] Figure 2 is the fitting curve graph obtained in step (2) of the embodiment of the present invention;

[0019] Figure 3 is a differential scanning calorimetry curve of PHA containing PLA of sample 6 in step (3) of an embodiment of the present invention;

[0020] Figure 4 is a differential scanning calorimetry curve of PHA containing PLA of sample 7 in step (3) of an embodiment of the present invention;

[0021] Figure 5 is a differential scanning calorimetry curve of PHA containing PLA of sample 8 in step (3) of the embodiment of the present invention;

[0022] Figure 6 is a differential scanning calorimetry curve of PHA containing PLA of sample 9 in step (3) of the embodiment of the present invention;

[0023] Figure 73 is a differential scanning calorimetry graph of the PLA-containing PHA of sample 10 in step (3) of an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The present invention is described in further detail below.

[0025] A quantitative analysis method for PLA in PHA comprises the following steps:

[0026] (1) As shown in Table 1, 5 groups of PLA particles and PHA particles with different proportions were weighed and blended, wherein the total mass of each group of samples was 5 mg. In samples 1-5, the mass of PLA was 0.5 mg, 1 mg, 1.5 mg, 2 mg, and 2.5 mg, respectively, and the mass of PHA was 4.5 mg, 4 mg, 3.5 mg, 3 mg, and 2.5 mg, respectively. After the granular PHA and PHA were blended, 5 groups of PHA with different proportions of PLA were obtained by melt blending, and the obtained 5 groups of PHA samples were tested by differential scanning calorimeter respectively; the test conditions of the differential scanning calorimeter were as follows: the sample crucible was an aluminum crucible, the temperature range was 100-200 ° C, the temperature rise rate was 5 ° C / min, the purge nitrogen flow rate was 50 ml / min, and the protective nitrogen flow rate was 60 ml / min.

[0027] (2) According to the obtained differential scanning calorimetry curve, the melting point peak of PLA is determined to be 171-173°C, and the melting point peak of PHA is determined to be 155-157°C. The curve intensities of 171-173°C and 155-157°C are marked respectively, and then qualitative analysis and component analysis are performed:

[0028] ①Qualitative analysis:

[0029] Depend on Figure 1 From the differential scanning calorimeter graph of PHA without PLA and the differential scanning calorimeter graph of PHA modified with PLA, it can be seen that PLA has a unique characteristic melting point peak at 171-173°C, and PHA has no melting point in this area. It can be qualitatively judged that PLA has been blended and modified into PHA.

[0030] ②Quantitative analysis:

[0031] The melting point peak curve intensity of 171-173°C is x1, the curve intensity of 155-157°C is x2, the baseline intensity is x0, (x1-x0) / (x2-x0) is the abscissa x, and the content ratio of PLA to PHA is the ordinate y. The standard fitting curve is fitted: y=ax+b; wherein a is the slope of the standard fitting curve, and b is the intercept of the standard fitting curve; the fitting curve data are shown in Table 1, and the obtained curve is shown in Figure 2 shown.

[0032] Table 1 Fitting curve data of 5 groups of PHA samples

[0033]

[0034] (3) Differential scanning calorimetry tests were performed on 5 groups of PHA samples mixed with different contents of PLA, wherein the contents of PLA in the 5 groups of samples are shown in Table 2 below; then, according to the standard fitting curve obtained in step (2), the concentrations of PLA in the 5 groups of PHA samples mixed with different contents of PLA were calculated.

[0035] like Figure 3-7 The following are differential scanning calorimetry curves of 5 groups of PHA samples mixed with PLA, namely samples 6 to 10. The results of the standard fitting curve are shown in Table 2.

[0036] It can be seen that the results of theoretical and actual calculations are within a reasonable error range, and this accuracy can meet the analytical requirements of process control.

[0037] Table 2

[0038]

Claims

1. A quantitative analysis method for PLA in PHA, characterized in that: The following steps are involved: (1) PHA samples mixed with different proportions of PLA were tested by differential scanning calorimetry to obtain differential scanning calorimetry curves; (2) determining the melting point peak temperature range of PLA and the melting point peak temperature range of PHA according to the differential scanning calorimetry curve, and marking the corresponding melting point peak curve intensities respectively; (3) The melting point peak curve intensity of PLA is recorded as x1, the melting point peak curve intensity of PHA is recorded as x2, the baseline intensity is recorded as x0, (x1-x0) / (x2-x0) is used as the abscissa x, and the content ratio of PLA to PHA is used as the ordinate y, and the standard fitting curve is obtained by fitting: y=ax+b; wherein a is the slope of the standard fitting curve, and b is the intercept of the standard fitting curve; (4) The PHA sample mixed with PLA was tested by differential scanning calorimetry, and the concentration of PLA in the PHA sample mixed with PLA was calculated based on the standard fitting curve.

2. The quantitative analysis method of PLA in PHA according to claim 1, characterized in that: In step (2), the melting point peak of the PLA is 171-173°C, and the melting point peak of the PHA is 155-157°C.

3. The quantitative analysis method of PLA in PHA according to claim 1, characterized in that: In step (2), the baseline intensity at 180°C to 200°C in the differential scanning calorimetry curve is selected as x0.

4. The quantitative analysis method of PLA in PHA according to claim 1, characterized in that: In step (1), the mass of the PHA sample is 1 to 10 mg.

5. The quantitative analysis method of PLA in PHA according to claim 1, characterized in that: In step (1), the temperature rise range during the differential scanning calorimeter test is 100 to 200°C.

6. The quantitative analysis method of PLA in PHA according to claim 1, characterized in that: In step (1), the heating rate during the differential scanning calorimeter test is 3 to 10° C. / min.

7. The quantitative analysis method of PLA in PHA according to claim 1, characterized in that: In step (1), the purge nitrogen flow rate during the differential scanning calorimeter test is 50 to 70 ml / min.

8. The quantitative analysis method of PLA in PHA according to claim 1, characterized in that: In step (1), the protective nitrogen flow rate during the differential scanning calorimeter test is 40-60 ml / min.

9. The quantitative analysis method of PLA in PHA according to claim 1, characterized in that: In step (1), the crucible used in the differential scanning calorimeter test is an aluminum crucible.

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