Study of plasticised PLA based bionanocomposites reinforced with nanofibrillated cellulose

In this study polylactide (PLA)-based nanocomposites plasticised with poly(ethylene glycol) (PEG) and nanofibrillated cellulose (NFC) were evaluated. Their physico-chemical properties were assessed by field emission scanning electron microscopy (FE-SEM), gel permeation cromatography (GPC), tensile testing machine, thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The effect of PEG with molecular weight of 400 g·mol-1 and 1500 g·mol-1 (PEG-400 and PEG-1500) and the influence of nanofibrillated cellulose (NFC) with different concentration (0, 1, 3, 5 wt%) on the polylactide, were analysed. No pores or cracks were observed in the evaluation of the cryo-fracture surface, suggesting an adequate processing strategy. The study of molar mass variation revealed that the additional processing step for the blends and composites promoted slight chain scission of PLA. The addition of NFC provoked a slight decrease in molar mass possibly due to the shear effects caused by the presence of nanofibrils during processing. With the incorporation of PEG-1500, the tensile strength and modulus decreased, whereas the elongation at break increased by 70%. Further, the nanocomposites showed increased rigidity and lower tensile strength in comparison to the blends. The microscopic evaluation of the fracture surface after tensile test suggested the possible agglomeration of NFC as the cause for this behaviour, especially for high NFC contents. The study of the thermal and thermo-oxidative stability highlighted the presence of PEG, as it decomposed at lower temperatures than the PLA. Finally, the presence of PEG decreased the glass transition temperature and the degree of crystallinity. Complementarily, the addition of NFC nanoparticles increased the PLA crystallinity due to its nucleation effects. This behaviour occurred for NFC contents between 1 and 3% wt., which suggested feasible nanoparticle agglomeration for higher concentrations.