Polylactic acid and polylactic acid-based nanocomposite photooxidation.

Area of Science:

• Polymer Science
• Materials Science
• Photochemistry

Background:

• Polylactic acid (PLA) is a biodegradable polymer with growing applications.
• Understanding PLA degradation mechanisms is crucial for its effective use and disposal.
• Photooxidation is a key environmental degradation pathway for PLA.

Purpose of the Study:

• To elucidate the role of photooxidation in PLA and PLA nanocomposite degradation.
• To investigate the formation of anhydride functional groups during PLA photooxidation.
• To identify the influence of nanofillers on PLA photooxidation and degradation.

Main Methods:

• Preparation of PLA nanocomposites with various nanofillers (ClNa, ClFe, Cl20A, SEP, SiO2).
• UV-light irradiation of pure PLA and nanocomposites under accelerated conditions (60 °C, λ > 300 nm).
• Analysis of chemical modifications using IR and UV-visible spectroscopies.

Main Results:

• Photooxidation of PLA and its nanocomposites leads to the formation of anhydride groups, indicated by an IR band at 1845 cm⁻¹.
• A photooxidation mechanism involving hydroperoxide decomposition is proposed.
• Transition metals present as impurities in nanofillers accelerate anhydride formation by catalyzing hydroperoxide decomposition.

Conclusions:

• Anhydride formation is a critical step promoted by photooxidation, leading to increased hydrolysis and biodegradation of PLA.
• Nanofillers, particularly those containing transition metals, can significantly influence the rate of PLA photooxidation.
• The findings provide insights into controlling the degradation rate of PLA-based materials.