Molecular-Scale Understanding of the Embrittlement in Polyethylene Ocean Debris

Christopher Garvey (1) , Marianne Impéror-Clerc (1) , Stéphan Rouzière (1) , Gwenaël Gouadec (2) , Olivier Boyron (3) , Laura Rowenczyk (4) , Anne-Françoise Mingotaud (4, 5) , Alexandra A. ter Halle (4, 6)

1 LPS - Laboratoire de Physique des Solides
2 MONARIS - De la Molécule aux Nanos-objets : Réactivité, Interactions et Spectroscopies
3 C2P2 - Laboratoire de Chimie, Catalyse, Polymères et Procédés, R 5265
4 IMRCP - Interactions moléculaires et réactivité chimique et photochimique
5 IMRCP - IDeAS - IMRCP - Interfaces Dynamiques et Assemblages Stimulables
6 IMRCP - SMODD - IMRCP - Systèmes Moléculaires Organisés et Développement Durable

The fate of plastic waste is a pressing issue since it forms a visible and long-lived reminder of the environmental impact of consumer habits. In this study, we examine the structural changes in the lamellar arrangements of semicrystalline poly-ethylene (PE) packaging waste with the aim of understanding the physical mechanisms of embrittlement in PE exposed to the marine environment. PE microplastics and macroplastics from identifiable PE packaging were collected in the Atlantic Ocean and compared to new PE boxes. Several experimental techniques interrogate the effects of environmental exposure on their bulk and surface properties. Size exclusion chromatography determines the molecular weight distribution of the PE polymer chains and differential scanning calorimetry gives the crystallinity. Small-and wide-angle X-ray scattering examines the packing of PE chains into semicrystalline lamellae. Longitudinal acoustic mode Raman spectroscopy provides a complementary measurement of the length of PE polymer chains extending through the crystalline lamellar domains. While there is a high degree of uncertainty in the time scale for the changes, the overall picture at the molecular scale is that although PE becomes more crystalline with environmental exposure, the lamellar order present in new packing boxes is disrupted by the weathering process. This process has important implications for embrittlement and subsequent degradation.

Mots clés: polymer; plastics; polyethylene; weathering; X-ray scattering; Raman spectroscopy; differential scanning calorimetry; size exclusion chromatography

Domaines: Polymères; Biodiversité et Ecologie

Christopher Garvey, Marianne Impéror-Clerc, Stéphan Rouzière, Gwenaël Gouadec, Olivier Boyron, et al.. Molecular-Scale Understanding of the Embrittlement in Polyethylene Ocean Debris. Environmental Science and Technology, 2020, 54 (18), pp.11173-11181. ⟨10.1021/acs.est.0c02095⟩. ⟨hal-02990062⟩