Transparent Bioplastics from Super-Low Lignin Wood with Abundant Hydrophobic Cellulose Crystals

Bioplastics (BPs) prepared from lignocellulose are an excellent replacement for petrochemical-plastics (PCPs) due to their renewability and biodegradability. The presence of residual/added/regenerated lignin reduced the water sensitivity; however, these BPs possessed a deep color and low transmittance and were prone to photodegradation. Herein, we developed a UV- and water-insensitive, colorless, transparent, and sustainable wood-derived BP (W-BP) by pressing delignified wood (DW) with 0.21% lignin and abundant hydrophobic crystal plane (200) of cellulose. The DW was obtained by the pretreatment of the wood sample with NaOH/Na2SO3 followed by H2O2 steam conditioning. The abundant hydrophobic crystal plane (200) of cellulose in DW was demonstrated by a large ratio of the crystal plane (200) to (110), the presence of two-dimensional (2D) nanosheets of defibrated cellulose, and a low moisture uptake of 8.7% of the freeze-dried DW. The aged W-BP with a thickness of about 50 μm displayed good photostability with a ΔE* value of 2.3 and a transparency of 84% transmittance at 550 nm. Additionally, W-BP also possessed water stability with a wet tensile strength of 74 MPa and a low water uptake of 28.3%. These values exceeded those of lignocellulosic BPs and some commercial PCPs. The W-BP could replace transparent PCPs and provide indirectly experimental support to the lignin–cellulose interaction.