Pressure-mediated reconstruction of hydrogen bonding networks under ambient temperature towards high-strength cellulosic bulk materials

Pressure moulding offers an efficient route to process the infusible cellulose into bulk materials. However, generally, it needs the assistance of heat, which leads to local decomposition of the cellulose molecules and heterogeneity of the as-prepared bulk materials. Considering the multi-scaled relaxation behavior in the structure, interaction and movement of cellulosic molecules, herein, we propose a scheme of pressure-mediated moulding for preparing cellulosic bulk materials under ambient temperature. In brief, microcrystalline cellulose is moulded under a specific pressure in the range of 100–900 MPa, and undergoes a period of pressure retention and pressure relief. Experimental optimizations and characterizations demonstrate that an elevated pressure, reasonable pressure retention and slow pressure relief processes contribute to a densified bulk material with high crystallinity index. The densified and highly ordered structure exhibits a compressive strength up to 575.3 MPa, which is higher than that of almost all commercial plastics. Further investigations reveal the mechanism for illustrating the formation and mechanical improvement of the moulded material, which is expressed as pressure-mediated reconstruction of hydrogen bonding networks in cellulosic bulks. Specifically, the hydrogen-bonding networks break under applied high pressure in the pressurization and pressure retention phases, which ensures the motions of cellulosic molecules; and the slow pressure relief allows the subsequent reconstruction of hydrogen bonding networks, leading to an increasing density from 0.96 g/cm3 to 1.55 g/cm3 and an improving crystallinity index from 85.07