Molecular dynamics simulation of calcium carbonate nano filled PLA/PPC composites: interfacial properties and water vapor barrier

Abstract

In recent years, polymer bio-nanocomposites have attracted much attention in the fields of industry and agriculture due to their desirable overall performance and environmentally friendly properties. Among them, polylactic acid (PLA) and polypropylene carbonate (PPC), as renewable polymers, have a number of advantages but also have their respective limitations, and their blending is expected to complement each other’s strengths. In addition, the addition of appropriate compatibilizers such as calcium carbonate (CaCO₃) nanoparticles can improve performance. Considering the high cost and time consuming experimental studies, the present study was carried out using molecular dynamics (MD) simulations for PLA/PPC/CaCO₃ bio-nanocomposites with different mass fractions (0–5 wt%), with samples denoted by ACCax (0 ≤ x ≤ 5). FFV calculations revealed that CaCO₃ nanoparticles interacted with PLA and PPC chains and changed the distribution and folding of polymer chains; the T_g results showed that a small amount of CaCO₃ added to the composites shifted the T_g towards higher temperatures, which improved the compatibility of the two polymer chains; and the inter-component interaction energy results showed that, for the ACCax nanocomposites, the filling threshold of CaCO₃ in PLA/PPC blends was 3 wt%. The radial distribution function (RDF) results indicated that the interactions between components were hydrogen bonding and van der Waals force, and the strength depended on the nanoparticle content. The interaction between PLA and CaCO₃ was mainly hydrogen bonding, and the interaction between PPC and CaCO₃ was mainly van der Waals force, and the comparative analysis showed that nanoparticles in the samples containing 3 wt% of CaCO₃ interacted more strongly with the PLA chain. Comparative analysis showed that the nanoparticles in the sample containing 3 wt% CaCO₃ interacted more strongly with the PLA chains, and the order of the RDF peaks in each sample was ACCa3 > ACCa2 > ACCa1 > ACCa5. The analysis of the water adsorption sites on the composites, the energy distribution, and the mean square displacements (MSD) of water in the different samples, as well as the diffusion coefficients, showed that the filler with 3 wt% of CaCO₃ had a better dispersibility in the matrix, the free volume of the system was reduced, and the diffusion channel of water vapour was widened, which led to promising success in the field of biodegradable membranes for food packaging or waterproofing for agriculture. In conclusion, MD simulation is a powerful tool for predicting the gas permeability of polymers, blends and nanocomposites.