Polylactic Acid and Polylactic Acid-Based Nanocomposite Photooxidation

Abstract

The importance of photooxidation in promoting formation of anhydride functional groups and thus promoting hydrolysis/biodegradation of polylactic acid and PLA nanocomposites were elucidated. PLA-based nanocomposites were prepared by adding 5% wt filler content of sodium montmorillonite (ClNa), sodium montmorillonite partially exchanged with Fe(III) (ClFe), organically modified montmorillonite (Cl20A), unmodified sepiolite (SEP), and fumed silica (SiO2). The pure PLA and nanocomposites were UV-light irradiated in artificial accelerated conditions representative of solar irradiation (λ > 300 nm) at 60 °C in air. The chemical modifications resulting from photooxidation were followed by IR and UV-visible spectroscopies. The infrared analyses of PLA photooxidation show the formation of a band at 1845 cm(-1) due to the formation of anhydrides. A photooxidation mechanism based on hydroperoxide decomposition is proposed. The mechanism proposed is confirmed by an increase in anhydride formation rate: the main responsible for this acceleration was identified as transition metals contained in the nanofillers as impurities and involved in the catalytic hydroperoxide decomposition.

Oxidative degradation of polylactide (PLA) and its effects on physical and mechanical properties

“…Three calorimetric scans were performed for each sample at a heating/cooling rate of 10°C/min. The first heating scan, in which the thermal history was Gardette [24] and Bocchini [25] showed that PLA photo oxidation by UV-light irradiation leads to the formation of carbonyl products, identified as anhydride functions, characterized by a new band at 1845 cm -1 . Nevertheless in our case of thermal oxidation, we have not observed new bands, especially this expected band for anhydride functions at 1845 cm -1 (Figure 1).…”

Physical, Mechanical, Thermal and Morphology Properties of Biodegradable Polymer Nanocomposites and Its Comparison

“…This was attributed to the C-O stretching vibrations that impeded in this region [17]. Another strong absorption band at 1750cm-1 was corresponded to the C=O stretching vibration as detected in Figure 1(d) [18]. Moreover, the peak at 2946cm-1 was also visibly detected in Figure 1(d) assigned to the -CH groups in PLA [19].…”

Comparative study of filler influence on polylactide photooxidation

“…In the same article they also explain that under the conditions typical of outdoor exposure other reaction such as Norrish II are improbable. The photooxidation of PLA-nanocomposites with different types of nanoparticles was also studied [19]. As a general statement the nanoparticle addition does not change the mechanism but, on the basis of the nanoparticle type, an increase of anhydride formation was noted.…”

“…The resistance to ultraviolet (UV) light is a key factor for most outdoor applications of polymeric materials. In the last few years, the impact of light on polymer/clay nanocomposites has been studied [11][12][13][14][15][16][17][18][19]. The clay nanocomposites show a significant reduction of the oxidation induction time (OIT).…”

“…The most probable hypothesis was the presence of interactions between the nanofillers and the stabilizers: the antioxidants can be adsorbed on the nanofillers thus preventing their protective action [13][14][15][16][17][18]. In a previous article the photo-oxidation mechanism of PLA [19] was investigated. The proposed mechanism was the formation of anhydride functional groups by a radical peroxide mechanism ( Figure 1).…”