The synthesis process of the phenolic resin adhesive was developed in the 19th century, and its excellent environmental resistance and high bonding strength make it one of the main wood adhesives.

Nanocellulose is a type of nanomaterial with high strength, high specific surface area and high surface energy. Additionally, it is nontoxic, harmless, biocompatible and environmentally friendly and can be extracted from biomass resources. The surface groups of cellulose show high surface energy and binding activity on the nanoscale and can be modified by using various methods. Because nanocellulose has a high elastic modulus, rigidity and a low thermal expansion coefficient, it is an excellent material for polymer reinforcement. This paper summarizes the reinforcement mechanisms of nanocellulose polymer composites with a focus on the role of theoretical models in elucidating these mechanisms. Furthermore, the influence of various factors on the properties of nanocellulose reinforced polymer composites are discussed in combination with analyses and comparisons of specific research results in related fields. Finally, research focus and development directions for the design of high-performance nanocellulose reinforced polymer composites are proposed.

With the rapid development of flexible wearable electronics, the demand for stretchable energy storage devices has surged. In this work, a novel gradient-layered architecture was design based on single-pore hollow lignin nanospheres (HLNPs)-intercalated two-dimensional transition metal carbide (Ti₃C₂T_x MXene) for fabricating highly stretchable and durable supercapacitors. By depositing and inserting HLNPs in the MXene layers with a bottom-up decreasing gradient, a multilayered porous MXene structure with smooth ion channels was constructed by reducing the overstacking of MXene lamella. Moreover, the micro-chamber architecture of thin-walled lignin nanospheres effectively extended the contact area between lignin and MXene to improve ion and electron accessibility, thus better utilizing the pseudocapacitive property of lignin. All these strategies effectively enhanced the capacitive performance of the electrodes. In addition, HLNPs, which acted as a protective phase for MXene layer, enhanced mechanical properties of the wrinkled stretchable electrodes by releasing stress through slip and deformation during the stretch-release cycling and greatly improved the structural integrity and capacitive stability of the electrodes. Flexible electrodes and symmetric flexible all-solid-state supercapacitors capable of enduring 600% uniaxial tensile strain were developed with high specific capacitances of 1273 mF cm⁻² (241 F g⁻¹) and 514 mF cm⁻² (95 F g⁻¹), respectively. Moreover, their capacitances were well preserved after 1000 times of 600% stretch-release cycling. This study showcased new possibilities of incorporating biobased lignin nanospheres in energy storage devices to fabricate stretchable devices leveraging synergies among various two-dimensional nanomaterials.