In this study, bionanocomposite films based on poly(lactide) (PLA) plasticised with poly(ethylene glycol) (PEG) (7.5 wt%) and reinforced with various contents of nanofibrillated cellulose (NFC) (1, 3, 5 wt%) were prepared. The hydrothermal degradation was investigated through immersion in several aqueous environments at temperatures of 8, 23, 58, and 70 °C as a function of time (7, 15, 30, 60, 90 days). The effect of water immersion on the physicochemical properties of the materials was assessed by monitoring the changes in the morphology, thermo-oxidative stability, thermal properties, and molar mass through field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). The hydrothermal degradation behaviour was not critically affected regardless of the nanofibrillated cellulose content. All the materials revealed certain integrity towards water immersion and hydrolysis effects at low temperatures (8 and 23 °C). The low hydrothermal degradation may be an advantage for using these PLA biocomposites in contact with water at ambient temperatures and limited exposure times. On the other hand, immersion in water at higher temperatures above the glass transition (58 and 70 °C), leads to a drastic deterioration of the properties of these PLA-based materials, in particular to the reduction of the molar mass and the disintegration into small pieces. This hydrothermal degradation behaviour can be considered a feasible option for the waste management of PLA/PEG/NFC bionanocomposites by deposition in hot aqueous environments.
Bionanocomposites of polylactide (PLA), plasticized with poly(ethylene glycol) (PEG) (7.5 wt%, 400 and 1500 g/mol) and reinforced with nanofibrillated cellulose (NFC) (1, 3, and 5 wt%) were sequentially compounded, and injection and compression molded. All of the stages caused structural and morphological consequences, more relevant in the plasticized PLA, especially with low molar PEG. Small percentages of NFC (1 and 3 wt%) acted as crystalline nucleating agents and improved thermo-oxidative stability. Given the substantial degradation caused by (re)processing, a downgrading validation strategy was applied, assessing the mechanical and water contact performance during fictional first and second service life applications. After the first processing, PEG increased the ductility and reduced the strength and elastic modulus, while NFC buffered the fall in stiffness and increased rigidity compared to their PLA-PEG counterparts. Once reprocessed, PEG increased the water affinity of the blend, especially for low molar mass PEG. Low percentages of NFC (1 and 3 wt%) modulated water diffusivity and permeability, regardless of the water temperature. Overall, although reprocessing caused significant degradation, the mechanical valorization possibilities of these green bionanocomposites were proven, and are pointed out as sustainable candidates for food packaging or agricultural applications where modulated mechanical or water contact behaviors are required.
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