## 1 Introduction  
Biopolymers comprise a sustainable alternative and promising opportunity for almost every conventional fossil-based plastic application. Among the biopolymers, poly(lactide) (PLA) has been the frontrunner due to its attractive properties that meet the demands in packaging, agriculture, biomedicine, or automotive applications [1, 2]. PLA can be made from agricultural products such as corn, sugar beets, and wheat, is easily biodegradable, and can be processed through conventional techniques due to its comparable rheological properties to traditional polymers. Although the use of PLA is growing, its actual contribution to the plastic industry is still limited due to shortcomings, especially related to its mechanical behavior or water permeability. The low deformation at break and high modulus restricted its application to the rigid thermoformed industry. Morphologies such as films or sheets usually require high flexibility at room temperature, transparency, and high barrier properties. Several strategies have been proposed to overcome these issues. The relatively stiff and brittle nature of PLA can be improved by modifying its physical properties through copolymerization with other monomers, blending with other polymers, and plasticization strategies [3, 4]. Among the low molecular weight plasticizers for PLA [5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16], poly(ethylene glycol) (PEG) is one of the most suitable candidates due to its good miscibility with PLA, improvement of chain mobility, biodegradability, and allowed use in food-contactable applications [17; 18; 19; 20]. The combination of PLA and small percentages of PEG up to 10% demonstrated complete miscibility, promoted a decrease in the tensile strength and elasticity modulus, and endorsed higher elongation at break and impact resistance. In this regard, the PEG molar mass has been identified as a relevant feature in the physico-chemical performance of plasticized PLA [8; 21]. However, other characteristics, including thermal stability and water swelling, and diffusion in PLA/PEG blends, are still the target of optimization for widening the application of such alternatives. Reinforcing PLA-based materials with natural fillers has been explored for the generation of green composites [22; 23; 24]. Cellulose-based reinforcements are among the most promising renewable fillers, especially concerning availability and biodegradability, which can modulate mechanical or permeability performance, among others [25; 26; 27; 28; 29]. Nanofibrilated cellulose (NFC) is an attractive renewable nanomaterial with a high surface-to-volume ratio, crystallinity, anisotropic performance, surface functionality, and excellent mechanical properties [30]. When hydrophobic matrices such as PLA are combined with hydrophilic fillers such as NFC, dispersion and compatibility concerns must be addressed through the surface functionalization of NFC or using coupling agents that allow for the proper interaction of both components in the composite. In this line, the acetylation of NFC and using PEG as a plasticizer and compatibilizer may become a sustainable alternative for spreading the use of PLA/NFC bionanocomposites. The preparation and processing of bionanocomposites are critical stages because they define their properties and behaviors [22; 31]. Several strategies have been reported for building products made of bionanocomposites, including filament winding, electrospinning, solution casting, 3D printing, extrusion, injection, or compression molding [32]. In particular, injection or compression molding are some of the most extended industrial processing setups. Both methods involve heat and pressure, which can cause mechanical and thermal degradation in PLA-based materials. The consequences of reprocessing PLA have been the center of numerous studies and highlighted thermo-mechanical degradation [33].