Performance and 4D Printing of Thermoplastic Polyurethane/Cellulose Nanocrystal-Poly(vinyl acetate) Nanocomposites

Thermoplastic polyurethane (TPU) is a linear block copolymer composed of hard and soft segments that possesses unique strength, toughness, and shape memory properties. Owing to the high modulus, strength, and biocompatibility, cellulose nanomaterials have been proposed to modify TPU for obtaining high-strength and high-performance green fused filament fabrication (FFF) consumables. However, achieving a high-level dispersion of cellulose nanofillers in the TPU matrix remains a challenge as the abundant hydroxyl groups on the surface of cellulose nanomaterials tend to undergo self-aggregation. Industrial melt compounding, rather than solution compounding, is still a challenging method to achieve this. Herein, by using poly(vinyl acetate) (PVAc)-modified cellulose nanocrystal (CNC) powder (CNC-PVAc) containing a mixture of CNC grafted by PVAc and PVAc homopolymer latex, the homogeneous dispersion of CNC in TPU was achieved by a simple melt blend. The results show that the addition of CNC-PVAc with 4 wt % loading enhances mechanical properties and crystal integrity, with a tensile strength of up to 32.2 MPa. When the content of CNC-PVAc is 6%, the nanocomposites have the best shape memory properties, with a recovery rate of 83.76% and excellent four-dimensional (4D) printing performance at a 0° printing angle. This work provides an industrial route for the preparation of high-performance TPU/CNC-PVAc nanocomposites to meet the strength and performance requirements of the FFF parts.