Study on Hydrothermal Depolymerization of Polylactic Acid Based on Circulation of Aqueous Lactic Acid Solution

doi:10.19491/j.issn.1001-9278.2020.08.001

Abstract

Abstract:

The degradation behavior of poly(lactic acid) (PLA) was investigated at a high temperature of 180 °C under the circulating hydrothermal condition, and their weight variation, generation of lactic acid, thermal weight?loss process, and chemical structure were evaluated by mass?loss rate, high performance liquid chromatography, thermogravimetric analysis, Fourier?transform infrared spectroscopy and liquid chromatography?mass spectrometry. The results indicated that the greater the cycle number, the faster the weight loss of PLA. The weight loss process was completed within 40 minutes by a hydrothermal reaction at 180 ° C. The production rate of lactic acid was accelerated with an increase of cycle number, but there was almost no variation in final volume. The PLA conversion rate was not reduced by the chemical cycling process, indicating a good cycle stability. The stability of PLA was enhanced with the progress of hydrothermal process, and the more cycles resulted in a much better stability. In the hydrothermal process, the hydroxyl index and carbonyl index of PLA exhibited an increasing trend with an increase of cycle number, suggesting that the chemical cycle process could accelerate the degradation of PLA.

Key words: poly(lactic acid), hydrolytic degradation, chemical cycle, cycle stability

CLC Number:

TQ321

Chenxi BI, Aimin LI. Study on Hydrothermal Depolymerization of Polylactic Acid Based on Circulation of Aqueous Lactic Acid Solution[J]. China Plastics, 2020, 34(8): 1-8.

Figures/Tables 9

Fig.1. Mass change of PLA samples under multiple cycles

Fig.2. LA yield of PLA samples under multiple cycles

Fig.3. Thermal stability of PLA samples during hydrothermal degradation

水热时间 /min	$T - 5 ? %$ /℃			$T - 10 ? %$ /℃
水热时间 /min	C1	C2	C3	C1	C2	C3
10	206.612	201.701	208.259	239.598	231.745	231.130
20	190.968	221.033	226.723	221.115	243.342	324.403
30	197.489	246.567	330.017	223.781	344.043	—

水热时间 /min	$T - 5 ? %$ /℃			$T - 10 ? %$ /℃
水热时间 /min	C1	C2	C3	C1	C2	C3
10	206.612	201.701	208.259	239.598	231.745	231.130
20	190.968	221.033	226.723	221.115	243.342	324.403
30	197.489	246.567	330.017	223.781	344.043	—

Tab.1. T-5?% and T-10?% of PLA samples under hydrothermal degradation conditions

Fig.4. FTIR of PLA samples after multiple cycles with different degradation times

Fig.5. Different indices of characteristic peaks of PLA samples after multiple cycles with different degradation times

Fig.6. Hydrolysis mechanism of PLA

Fig.7. Different adducts of theoretical products in hydrothermal solution

Fig.8. LC?MS spectrum of products in hydrothermal solution

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