The mechanical performance is critical for hydrogels that are used as strain sensors. p-Aramid nanofiber (ANF) is preferable as an additive to the reinforce the mechanical performance of a poly(vinyl alcohol) (PVA). However, due to the limited hydrogen bond sites, the preparation of ultra-stretchable, ANF-based hydrogel strain sensor is still a challenge. Herein, we reported an ultra-stretchable PVA hydrogel sensor based on tea stain-inspired ANFs. Due to the presence of numerous phenol groups in the tannic acid (TA) layer, the interaction between PVA and the ANFs was significantly enhanced even though the mass ratio of TA@ANF in the hydrogel was 2.8 wt‰. The tensile breaking modulus of the PVA/TA@ANF/Ag hydrogel sensor was increased from 86 kPa to 326 kPa, and the tensile breaking elongation was increased from 356% to 602%. Meanwhile, the hydrogel became much softer, and no obvious deterioration of the flexibility was observed after repeated use. Moreover, Ag NPs were formed in situ on the surfaces of the ANFs, which imparted the sensor with electrical conductivity. The hydrogel-based strain sensor could be used to detect the joint movements of a finger, an elbow, a wrist, and a knee, respectively. This ultra-stretchable hydrogel described herein was a promising candidate for detecting large-scale motions.

The recycling use of wood sawdust to process composite boards has received much attention in recent years. To avoid the use of chemical adhesives, natural cellulose-based materials were often used as adhesives to combine wood sawdust. Rather than utilizing nanocellulose, the report herein describes a method to prepare a robust composite board that is based on microfibrous cellulose, which is a low-cost commercial product. To effectively cross-link wood sawdust and microfibrous cellulose, phosphoric acid-activated glutaraldehyde was used as catalyst. Compared to its uncross-linked counterpart, the modulus of elasticity and modulus of rupture of the composite board that had been cross-linked by glutaraldehyde and phosphoric acid were significantly strengthened to 3.45±0.06 GPa and 36.5±3.5 MPa, respectively. Moreover, the moisture resistance of the cross-linked composite board was also enhanced. After soaking in water for 24 h, the mass swelling ratio and thickness swelling ratio of cross-linked composite board had only changed 49% and 21%, respectively. These performances even exceeded that of composite board prepared from nanocellulose. The method described in this work may have applications in commercial processing and the recycling of wood sawdust.