Recovery of Poly（lactic acid） Through Ferric Chloride⁃catalyzed Alcoholysis

doi:10.19491/j.issn.1001-9278.2020.11.013

Abstract

Abstract:

This paper reported an investigation on the reaction mechanism and influence factors of the alcoholysis of poly（lactic acid）（PLA） catalyzed with ferric chloride（FeCl₃）. The effects of reaction temperature， reaction time， and addition amounts of catalyst and ethanol solution on the alcoholysis reaction were investigated in detail. The chemical structure of the alcoholysis product was characterized with ¹H-NMR， FTIR， and GPC. Furthermore， the degradation kinetics of the alcoholysis reaction was also explored. The results showed that the optimum process conditions were determined as a reaction temperature of 130 ℃， a reaction time of 24 h， a C₂H₅OH/PLA mass ratio of 3/1 and a FeCl₃/PLA mass ratio of 3/40. Under the above optimum conditions， the alcoholysis reaction led to a depolymerization rate of 99.81 % and an ethyl lactate yield of 73. 60 wt% for PLA. It was found that PLA could be completely depolymerized into ethyl lactate under the catalysis of FeCl3， acting as a first-order reaction with a reaction activation energy of 10.28 kJ/mol.

Key words: poly（lactic acid）, alcoholysis, ferric chloride, ethyl lactate

CLC Number:

TQ 321

MA Qiaoyun, WENG Yunxuan, ZHANG Caili. Recovery of Poly（lactic acid） Through Ferric Chloride⁃catalyzed Alcoholysis[J]. China Plastics, 2020, 34(11): 73-80.

Figures/Tables 16

Fig.1. FTIR of pure PLA and its alcoholysis product

Fig.2. 1H?NMR of PLA powder precipitated from ethanol and PLA raw material

Fig.3. FTIR of PLA ethanololysis products and ethyl lactate standard samples

Fig.4. 1H?NMR of PLA ethanololysis product and ethyl lactate standard sample

Fig.5. FTIR of residues at different PLA depolymerization rates

Fig.6. FTIR of products at different PLA depolymerization rates

残留物	解聚率/ %	数均相对分子质量	重均相对分子质量	相对分子质量分布
a	0	89 722	136 974	1.527
b	66	28 522	45 112	1.581
b	66	8 326	8 507	1.021
c	84.71	22 563	25 216	1.117
c	84.71	8 282	8 446	1.020
d	91.04	20 293	22 006	1.084
d	91.04	8 278	8 466	1.023
e	99.81	15 546	16 005	1.029
e	99.81	7 615	7 853	1.031

Tab.1. Molecular weight and its distribution of PLA residues at different depolymerization rates

Fig.7. TG and DTG spectra of PLA residues at different depolymerization rates

Fig.8. Reaction mechanism of PLA alcoholysis reaction catalyzed by FeCl3

Fig.9. Effect of FeCl3 dosage on PLA ethanololysis reaction

Fig.10. Effect of ethanol dosage on PLA alcoholysis reaction

Fig.11. Effect of temperature on PLA ethanololysis reaction

Fig.12. Effect of reaction time on PLA ethanololysis reaction

Fig.13. Effect of reaction temperature on the ethanololysis rate of PLA catalyzed by FeCl3

反应温度/℃	线性回归方程	R²
120	y=-2.667 7+0.340 45x	0.969 18
130	y=-2.823 9+0.367 07x	0.991 37
140	y=-3.054 5+0.410 75x	0.999 87
150	y=-3.061 4+0.421 6x	0.999 56

Tab. 2. Linear regression results

Fig.14. Arrhenius analysis diagram of ethanololysis rate constant catalyzed by FeCl3

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