BNNS/PVA bilayer composite film with multiple-improved properties by the synergistic actions of cellulose nanofibrils and lignin nanoparticles.

To avoid complex and toxic chemical cross-linking reaction, cellulose nanofibrils (CNF) was used to enhance the performance of hexagonal boron nitride nanosheet (BNNS)/polyvinyl alcohol (PVA)/lignin nanoparticle (LNP) composite film. The results showed that CNF and LNP had synergistic actions on enhancing the tensile strength, thermal conductivity and stability of the film. The 4 wt% CNF-reinforced composites exhibited the higher through-plane thermal conductivity (up to 1.76 W/mK) than that without CNF (1.44 W/mK), revealing an increase of 22.2% at the same BNNS loading. Meanwhile, the maximum decomposition rate (Rmax) was roughly 0.6%/oC, a decrease of 14.3% compared with the composite film without LNP. Furthermore, the rigidity of composite film was strengthened by incorporating CNF and LNP, the tensile strength of the composite film showed the highest value of 35.0 MPa with 4 wt% CNF and 0.01 g LNP, while this of BNNS/PVA/LNP film and BNNS/PVA/CNF film was only 30.66 MPa and 30.62 MPa, respectively. The green and flexible fabrication approaches will be helpful to build up eco-friendly BN composites with wide applications in thermal management of electronics.