Monitoring interactions through molecular dynamics simulations: effect of calcium carbonate on the mechanical properties of cellulose composites

Abstract

This study describes the preparation and characterization of full atomistic models of amorphous cellulose and calcium carbonate (CaCO3) nanocomposite to assess its mechanical properties within and beyond the elastic limit via molecular dynamics simulations. The interactions by hydrogen bond and conformation of the cellulose molecules from the assessment of torsional angles were specifically monitored during the tensile stretching simulations to get deep understanding of the possible structural changes produced in the material during the deformation. On the one hand, the results showed a favorable interaction of the cellulose matrix with the calcium carbonate nanoparticle, with the electrostatic contribution being dominant over the van der Waals component. The determined mechanical elastic constants indicated that the inclusion of the CaCO3 nanoparticle provided an increase on the rigidity of the composite system of 15%, 18% and 19% in the Young, shear or bulk modulus, respectively. On the other hand, using extension and compression simulations, the recovery capacity of the material systems was also assessed in terms of plastic deformation. The elastoplastic behavior was observed for either the neat or the CaCO3 nanocomposite, with an elastic limit around 2.5%. The results also showed that the presence of the CaCO3 nanoparticle produced higher values of plastic deformation in the composite material compared to the neat cellulose system and thus decreased the flexibility of the material. A hysteresis mechanism was identified together with irreversible conformational changes on the cellulose molecules which would explain the plastic deformation observed on the cellulosic systems. It was concluded that the higher plastic deformations observed in the nanocomposite system would be a result of the disruption of the network of hydrogen bonds and the associated decrease on the number of possible interactions. Graphical Abstract: [Figure not available: see fulltext.].