## 3 Results and Discussion
### Validation of the Bionanocomposites
#### 3.2.1 First Service Life: Mechanical Performance and Fracture Surface of Dog-Bone Specimens
Higher temperatures generally result in stronger vibrations of the water molecules and more free void volume due to increased segmental motion, resulting in a higher diffusion coefficient [97; 106]. Although the permeation coefficient (\(P\)) combines the solubility coefficient (\(S\)) and diffusion coefficient (\(D\)), it is predominantly influenced by the diffusivity and shows a similar temperature dependency, showing an exponential growth pattern when the temperature of the environment increases [107]. Finally, the influence of the PEG plasticizing agent and NFC nanoparticles on the nature of water absorption was investigated. Figure 10 plots the mean values for the \(M_{s}\), \(D\), \(S\), and \(P\), in which an evident influence of the compositions on the water uptake performance could be found. Compared to neat PLA, the \(M_{s}\) and \(S\) were higher for the  
Figure 10: Influence of the composition on the mean of absorbed mass at saturation (\(M_{s}\)), solubility coefficient (\(S\)), diffusion coefficient (\(D\)), and permeability coefficient (\(P\)) of the PLA, plasticized PLA/PEG, and PLA/PEG/NFC nanocomposite materials. Figure 9: Influence of the immersion temperature on the mean of absorbed mass at saturation (\(M_{s}\)), solubility coefficient (\(S\)), diffusion coefficient (\(D\)), and permeability coefficient (\(P\)) of the PLA, plasticized PLA-PEG, and PLA-PEG-NFC nanocomposite materials. plasticized PLA-400 and PLA-1500 due to the hydrophilic nature of PEG, together with its plasticizing effect [105; 106]. Furthermore, NFC seems to have contributed to the composites attracting more water and can result in swelling, microcracking, and capillarity phenomena in the matrix [108; 109]. This offers new possible penetration pathways resulting in higher amounts of water absorbed by the composite [105; 109; 110; 111]. A similar pattern was found in the plasticized materials regarding the diffusion (\(D\)) and permeation (\(P\)) coefficients. Both \(D\) and \(P\) increased in the blends with the presence of PEG. In this regard, the higher the molar mass of PEG, the greater \(D\) and \(P\) were obtained. Therefore, higher hydrophilicity due to plasticizer was correlated to faster water penetration and permeation. However, lower diffusion coefficients can be observed with the presence of NFC in all cases. This reduction was more accentuated for low NFC percentages (1%) and the PEG of higher molar mass. Although the hydrophilic character of the NFC may indicate an increase in the diffusivity, the generation of a more cohesive and entangled structure, especially in the PLA-1500, with better dispersed low percentages of NFC nanoparticles and a crystalline structure with greater lamellar thickness resulted in a more tortuous advance of the penetrant and, consequently, lower diffusion coefficients. Even though a more cohesive structure in the bionanocomposites modulated diffusivity, they still revealed more water incorporation and solubility coefficients, probably due to the possible generation of micro- and nanovoids in the matrix-filler interphase during immersion that subsequently resulted in higher permeability. However, the exception for the 1 and 3 wt% of NFC in the PLA-400-NFC and the 1 wt% in the PLA-1500-NFC materials must be highlighted. Such low percentages of nanoparticles effectively reduced the films' overall permeability through a lower diffusivity and stability during immersion. Overall, it can be said that higher temperatures favored the absorption of water and the diffusivity, solubility, and permeability. The presence of PEG as a plasticizer and NFC as a reinforcement nanofiller also increases the absorbed mass of water at saturation and the solubility coefficient. Finally, the diffusivity and permeability increased with PEG, but they could be modulated with small percentages of NFC nanoparticles.