# Chemical pre-treatment to improve anaerobic digestion of polylactic acid packaging

Celia Marin-Collado, Gael Huet, Anir Benihya, Emmanuelle Gastaldi, Florian

Monlau, Cecilia Sambuisti, Sandra Domenek

► To cite this version:

Celia Marin-Collado, Gael Huet, Anir Benihya, Emmanuelle Gastaldi, Florian Monlau, et al. Chemical pre-treatment to improve anaerobic digestion of polylactic acid packaging. JCAT 53 - 53. Journée de Calorimétrie et Analyse Thermique, May 2023, Palaiseau, France. pp.sciencesconf.org:jcat53:478449. hal-04375386

HAL Id: hal-04375386

https://hal.science/hal-04375386v1

Submitted on 5 Jan 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

Public Domain
# Chemical pre-treatment to improve anaerobic digestion of polylactic acid packaging

Celia Marín Colladoª, Gaël Huetᵇ, Anir Benihyaª, Emmanuelle Gastaldiᵇ, Florian Monlauᶜ, Cecilia Sambusitiᵈ, Sandra Domenekª

## Contact:

Sandra Domenek: sandra.domenek@agroparistech.fr

Celia Marín Collado: celia.marincollado@agroparistech.fr

## Introduction

Polylactic acid (PLA) is a promising bio-based alternative to conventional petrol-based plastic packaging. Despite its **biodegradable** qualities in industrial composting, PLA biodegradability remains low in mesophilic anaerobic digestion (1,2). In anticipation of the selective collection of biowastes, efforts are being made to foster and accelerate **PLA food packaging digestibility** together with biowaste by applying pretreatments strategies (2).

Among the different types of **pre-treatments, thermo-alkaline** methods seemed to be the most promising (1).

<figure><img src="image_1.png" /></figure>

This study aims to better understand the impact of PLA's morphology and geometry during thermo-alkaline hydrolysis, to gain knowledge on PLA kinetic biodegradation and solubilization (2). For this purpose, several PLA available in the market has been selected and are described below.

<table><thead><tr><td>Name</td><td>Composition</td><td>Geometry</td><td>Morphology</td><td>Glass transition temperature (T<sub>g</sub>)(°C)</td></tr></thead><tbody><tr><td>PLA 1.1</td><td>93% L-lactic acid</td><td>pellet</td><td>amorphous</td><td>57.4 ± 0.7</td></tr><tr><td>PLA 1.2</td><td>93% L-lactic acid</td><td>film</td><td>amorphous</td><td>57.2 ± 0.1</td></tr><tr><td>PLA 3</td><td>98% L-lactic acid</td><td>film</td><td>semi-crystalline</td><td>60.3 ± 0.1</td></tr></tbody></table>

## Materials and methods

Thermo-alkaline pretreatments was performed on the various PLA polymers (amorphous vs semicrystalline, and pellet vs film). KOH was purchased at Sigma Aldrich and used at 20 % w/v (3.57 M equivalents, pH of 13.5). Polymers were hydrolyzed at a solid loading of 50g/L, 20 % w/v KOH, at 80 °C and 100 rpm stirring in a water bath for 24 h, 48 h and 72 h respectively.

The following analysis were performed:

**Differential Scanning Calorimetry (DSC):** program heating-cooling-heating between -20 °C and 200 °C, at a rate of 10 °C/min in a Mettler Toledo DSC (DSC 1, USA) under N₂ 50 ml/min. Results were analyzed using STARe software.

**Prospects: Size Exclusion Chromatography (SEC).**

<figure><img src="image_2.png" /></figure>

## Results and discussions

<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /></figure>

► The crystallinity degree of all the samples increased with the thermo-alkaline pre-treatment duration. The initial increase of the amorphous samples was faster.

► The solubility percentage of all the samples increased with the pre-treatment duration. The different geometry (PLA 1.1 and PLA 1.2) seems to have no impact.

<table><thead><tr><th>Name</th><th>Pre-treatment duration (hours)</th><th>pH</th><th>T<sub>g</sub> (°C)</th><th>Crystallinity (%)</th></tr></thead><tbody><tr><td rowspan="3">PLA 1.1</td><td>24</td><td>11.5 ± 0.8</td><td>51.4 ± 0.1</td><td>34.4 ± 2.2</td></tr><tr><td>48</td><td>5.0 ± 0.0</td><td>38.7 ± 0.2</td><td>47.0 ± 4.9</td></tr><tr><td>72</td><td>4.3 ± 0.1</td><td>47.4 ± 2.3</td><td>52.4 ± 3.9</td></tr><tr><td rowspan="3">PLA 1.2</td><td>24</td><td>10.8 ± 0.1</td><td>52.9 ± 0.2</td><td>27.5 ± 0.2</td></tr><tr><td>48</td><td>4.9 ± 0.1</td><td>48.1 ± 0.5</td><td>34.9 ± 4.8</td></tr><tr><td>72</td><td>4.2 ± 0.1</td><td>48.6 ± 0.4</td><td>43.4 ± 2.9</td></tr><tr><td rowspan="3">PLA 3</td><td>24</td><td>12.9 ± 0.1</td><td>54.9 ± 0.5</td><td>58.0 ± 1.2</td></tr><tr><td>48</td><td>5.6 ± 0.1</td><td>50.6 ± 0.1</td><td>63.8 ± 1.5</td></tr><tr><td>72</td><td>4.7 ± 0.1</td><td>52.1 ± 0.1</td><td>70.4 ± 2.6</td></tr></tbody></table>

► A decrease in pH is observed with an increase in pre-treatment duration due to the PLA hydrolysis.

### DSC thermograms

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

► Thermograms show values for melting temperature (T<sub>m</sub>) and the enthalpy of crystallization. The enthalpy increased with the pre-treatment duration, the crystallinity degree increases over time and so does the melting temperature (T<sub>m</sub>) of the material.

## Take Home message

Overall, this poster emphasizes the importance of effective end-of-life management of PLA packaging and presents a novel approach to enhancing its biodegradability. The thermo-alkaline hydrolysis pre-treatment offers a promising solution for meeting industrial anaerobic digestion times and fostering PLA degradation for methane production. The findings of this study contribute to the development of sustainable waste management practices and support the transition to a circular economy.

## References

(1) Guillaume Cazadehore. Thèse de doctorat. Méthanisation des plastiques biodégradables : performance et diversité microbienne. Université de Pau et Pays de l'Adour, 11/03/2022.

(2) Cazaudehore, G., Guyoneaud, R., Vasmara, C., Greuet, P., Gastaldi, E., Marchetti, R., Leonardi, F., Turon, R., & Monlau, F. (2022). Impact of mechanical and thermo-chemical pretreatments to enhance anaerobic digestion of poly(lactic acid). *Chemosphere*, *297*, 133986. https://doi.org/10.1016/j.chemosphere.2022.133986

<footnote>ªUMR SayFood (AgroParisTech/INRAE/Université Paris Saclay), Palaiseau, France.</footnote>

<footnote>ᵇUMR IATE (Univ Montpellier/INRAE), Montpellier, France.</footnote>

<footnote>ᶜTotalEnergies, PERL - Pôle D'Etudes et de Recherche de Lacq, Pôle Economique 2, BP 47 - RD 817, 64170 Lacq, France</footnote>

<footnote>ᵈTotalEnergies, CSTJF - Avenue Larribau, 64018 Pau, France</footnote>