Transparent and Hazy All-Cellulose Composite Films with Superior Mechanical Properties

A general and scalable strategy to achieve transparent and hazy cellulose films with excellent mechanical properties, especially folding endurance, remains an obstacle. Herein, we incorporate transparent carboxymethyl cellulose (CMC) into opaque but hazy paper of uniformly distributed lignocellulosic fiber network by a facile and scalable impregnation to fabricate transparent and hazy all-cellulose composite films with strong mechanical properties. The CMC serves as a matrix to enhance the transparency and smoothness, whereas the isotropic intertwined network of long and slender lignocellulosic fibers simultaneously acts as a reinforcing phase to improve the mechanical properties and a light scatting source to enhance the optical haze. Consequently, the resulting composite film combines a high transparency (up to 90%) and optical haze (up to 82%) at 550 nm with superior mechanical properties (140 MPa tensile strength, 8.5 MJ m–3 toughness, and 3342 folding times). Moreover, this composite film demonstrated ultrasmoothness (Rq: 0.9 nm) and improved flame retardant performance. Mechanically robust, transparent, and hazy composite films with ultrasmoothness and enhanced fire retardancy may extend their opportunities in flexible optoelectronics.