Transforming wood into a high-performance engineering material via cellulose nanocrystal impregnation

Abstract

A significant challenge in this world today is innovating sustainably sourced materials for advanced engineering applications. Cellulose nanocrystals (CNCs) have excellent potential in these advanced applications as reinforcement in softwood because of their inherent biodegradability, universal accessibility, and exceptional mechanical properties. This research aimed to design a novel method to impregnate cellulose nanocrystals into marginal-quality softwood to enhance its mechanical properties for advanced engineering and architectural applications. In this research, southern yellow pine (SYP) wood underwent sodium hydroxide treatment to remove lignin from the wood cells. Then, SYP samples were submerged into a surface-functionalized (by either acetic acid or benzoic acid) CNC solution and subjected to ultrasonication treatment to penetrate functionalized-CNC into the SYP. A vacuum pressure treatment for air pocket removal and functionalized-CNC impregnation followed this. After treatment, the wood was dried and underwent mechanical testing following ASTM D1037 and ASTM D2339 standards. Delignified and functionalized-CNC impregnated SYP increased the modulus of rupture (MOR) by 68% and the modulus of elasticity (MOE) by 72%. Localized MOE maps were also generated under an atomic force microscope (AFM) to characterize the material. It was found that the areas with a CNC presence have a significantly greater elasticity modulus (<20 GPa) compared to the rest of the region consisting of SYP (3.00 - 8.55 GPa) using the Hertzian Contact model. The results support a novel methodology to improve the mechanical properties of wood delignification and functionalized CNC impregnation.