Enhanced mechanical and oxygen barrier performance in biodegradable polyurethanes by incorporating cellulose nanocrystals with interfacial polylactide stereocomplexation

Using bio-derived cellulose nanocrystals (CNCs) to reinforce the mechanical properties of biodegradable polyurethanes (PUs) is a promising approach especially when attempting to fabricate fully sustainable materials with high performance. However, the way to efficiently improve the dispersion and interfacial strength of CNCs in PU matrices is still an open question. In the current work, poly-l-lactide (PlLA) grafted CNCs (CNC-g-l) and a PU elastomer with poly-d-lactide as partial soft segments (d-PU) were first prepared separately, and then the fully biodegradable PU nanocomposites were fabricated by solution blending of CNC-g-l and d-PU. The surface grafting of PlLA can improve the thermal stability of CNCs, but has marginal effect on that of the nanocomposites. The improved dispersion of CNCs and enhanced interfacial strength, as evidenced by scanning electron microscopy, wide-angle X-ray diffraction and rheology measurements, are achieved by the construction of interfacial polylactide stereocomplexation (sc-PLA). The optimal improvement in mechanical properties of the nanocomposites is realized when only 1 wt% CNC-g-l is incorporated in the d-PU matrix. With the assistance of interfacial sc-PLA, the nanocomposite can gain 40% reduction in oxygen transmission rate at the optimal CNC-g-l content of 5 wt%. This study may provide a new method to improve the dispersion and interfacial strength of CNCs in biodegradable PUs and achieve simultaneously mechanical and barrier performance enhancement.