Green preparation of poly(vinyl alcohol)/phosphorylated nanocellulose composite film with excellent flame retardancy, high transparency and high strength

Abstract

Novel and environmentally benign flame-retardant plastic films that maintain outstanding physical performance are urgently needed for high-tech fields. Herein, sodium hydroxide (NaOH) was innovatively used to pre-swelling dried sugarcane pulp to effectively enhance the immersion of urea and ammonium dihydrogen phosphate, obtaining phosphorylated cellulose with high phosphorus loading. By combining with micro-fluidization, the in-situ stripping of phosphorylated cellulose was achieved, successfully preparing phosphorylated nanocellulose (PNC) with phosphorus content as high as 12.2 wt% and a three-dimensional network, breaking through the problem of low phosphorus content in traditional PNC preparation from sugarcane pulp. PNC was further introduced into PVA film, significantly improving its flame retardancy and mechanical properties, while maintaining good transparency. With 12.5 wt% PNC, the composite film pasted the VTM-0 grade of UL-94, and reach a limiting oxygen index (LOI) of 28.0%. The tensile strength of the composite film also increased from 56.6 MPa of pure PVA film to 70.8 MPa, and the visible light transmittance remained at 81.9%, which was comparable to pure PVA (85.8%). This work overcomes the long-standing trade-off between flame retardancy, transparency and mechanical performance via designing bio-based flame retardants and constructing nanostructures, establishing an innovative paradigm for the development of sustainable high-performance packaging materials for electronic and electrical packaging.