Transparent Cellulose/Lignin Composite Films with Adjustable Haze and UV-Blocking Performance for Light Management

Light-management films that can control solar transmission through themselves, especially those based on renewable and biodegradable materials, are significant for diverse photon-related applications such as energy-efficient buildings, photovoltaics, and optoelectronic devices. Herein, composite transparent films with adjustable haze and UV-blocking capabilities are developed based on the main components of lignocellulosic biomass (cellulose and lignin), and their promising applications in light management are also demonstrated. Carboxymethyl cellulose (CMC) with a good film-forming property is used as the substrate matrix, and cellulose nanocrystals (CNC) with a nanoscale rod-like shape are used as functional fillers. The obtained CMC–CNC composite films exhibit adjustable optical properties (high transparency of >90% and haze of 3.17–13%) and surprisingly enhanced mechanical strength and thermal stability when compared with pure CMC films. Furthermore, lignosulfonates (LS), as industrial lignin products, are combined to endow the CMC–CNC–LS composite films with excellent UV-shielding performance (98.17% UVB and 89.38% UVA), but they well maintain the high transparency and haze. We demonstrate that the composite films are able to avoid color changes of UV test cards by shielding UV light and that they achieve uniform illumination when light transmits through, indicating their promising potential for practical applications in light management. In addition, the effect of CNC and LS contents on the morphological, chemical, mechanical, and thermal properties of composite films is investigated. Our work provides novel insights into the fabrication of sustainable light-management films based on lignocellulose-derived materials by tuning their light-scattering and light-absorbing properties.