Analysis of interfacial nanostructure and interaction mechanisms between cellulose fibres and calcium silicate hydrates using experimental and molecular dynamics simulation data

Understanding the effects of cellulose fibre on the nanostructure of and adhesion energy at the cellulose fibre-calcium silicate hydrate (C-S-H) interface is essential for designing high-performance cement-based composites (CBCs). Therefore, the chemical structure of cellulose fibre surface and microstructure of the fibre-cement matrix interface were investigated using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Molecular dynamics (MD) simulations were used to study the adhesion energy and nanostructure at the cellulose fibre-(C-S-H) interface by comparing crystalline I-beta and amorphous celluloses (AC). The results revealed that the adhesion energy at the AC-(C-S-H) interface was approximately 35% greater than that at I beta-(C-S-H) interface. Given that the AC configuration was disordered and presented greater deformation than I-beta, the AC-(C-S-H) interface was denser than the I-beta-(C-S-H) interface. Electrostatic interactions between -OH groups and Ca2+ ions caused the Ca2+ in C-S-H to migrate towards the interface; the Ca2+ ions exhibit a bridging effect at the interface. Additionally, the -OH groups in the cellulose fibre and C-S-H could also interact with each other via hydrogen bonding. The electrostatic and hydrogen bonds increased the interfacial adhesion energy, which was beneficial for improving the performance of cellulose fibre-reinforced CBCs.