Cellulose Structure & Fiber Formation Studied with Molecular Dynamics : Cellulosa Struktur och Fiberbildning Studerad med Molekylär Dynamik

Sammanfattning

Cellulose is a renewable material with important applications in fibers, biomaterials and sustainable materials. Its properties depend on how cellulose chains are arranged and how they interact with each other. The early stages of cellulose organization are difficult to study experimentally at the molecular level. The aim of this thesis was to examine how molecular dynamics (MD) simulations can be used to describe early structural changes, H…O hydrogen bond contacts and fiber-like organization in cellulose Iα and cellulose Iβ two-chain models. Each model contained two cellulose chains with 16 glucose residues per chain. The simulations were analyzed using structural snapshots, root mean square deviation (RMSD) and manually identified H…O hydrogen bond contacts. Intrachain contacts were counted within each chain, while interchain contacts were counted between the two-chains. The results showed that both cellulose Iα and cellulose Iβ changed during the simulations. Cellulose Iα showed higher RMSD ranges than cellulose Iβ in several longer simulations, while cellulose Iβ showed larger short-time RMSD variation in the 1.2 ns simulation. The high RMSD values indicated large-scale displacement in the simplified unrestrained models and were more common than interchain H…O contacts in both models. No simulations, but they appeared in selected longer simulations. The clearest interchain contact formation was observed for cellulose Iα at 500 ns in the 1000 ns simulation. The study shows that MD simulations can describe early local rearrangement and temporary chain-chain contacts in simplified cellulose models. The models did not show complete fiber formation, and the results should be interpreted as trends in two-chain systems.