Effect of the state of water and relative humidity on ageing of PLA films

- No PLA hydrolysis at 50% RH.
- PLA hydrolysis is highly accelerated at 100% RH and in liquid water.
- PLA hydrolysis is faster in saturated vapour conditions than in liquid water.
- Degradation products are accumulated in PLA in contact with water in vapour phase.
- Degradation products accelerate PLA hydrolysis.

Various types of food are now commercialized in packaging materials based on poly(lactic acid) (PLA) due to its eco-friendly nature. However, one of the main limitations related to PLA is its reactivity with water. For food applications, it is of critical importance to better understand the hydrolysis of PLA driven by water molecules either in liquid or in vapour state. This work focuses on the modifications of PLA induced by water when simulating contact with semi-dry foods (aw ≈ 0.5), high moisture foods (aw ≈ 1) and liquid foods (aw ≈ 1). This study undoubtedly shows that both the chemical potential of water and its physical state influence the hydrolytic degradation of PLA films. From a practical point of view, PLA packaging is very well suited for semi-dry foods, but is highly sensitive to high moisture and liquid foods.