Investigation of nanoparticle-polymer interaction in bio-based nanosilica-filled PLA/NR nanocomposites: molecular...

Molecular dynamics (MD) simulation, by employing the COMPASS force field, was utilized to investigate structural and thermal characteristics as well as interfacial interactions between components of nanocomposite consisting of poly(lactic acid) (PLA)/natural rubber (NR)/nanosilica, abbreviated as PSxN, where 1 ≤ x ≤ 7 and it represents the parts of SiO₂ nanoparticles added to the PLA/NR (PN) blend. Analysis of the obtained results including density (ρ), fractional free volume (FFV), glass transition temperature (T_g), interaction energy (E_interaction), and radial distribution function (RDF) of these nanocomposites was performed. Comparing E_interaction of nanocomposites with that of the PN blend showed that the interactions between the chains of the two polymers are highly dependent on the added amounts of silica nanoparticles, so that by adding silica to the PN blend to obtain PS1N and PS3N nanocomposites, the amount of E_interaction was reduced to a smaller positive value, which indicates the tendency of the nanocomposite's components to interact with each other. By further addition of silica nanoparticles to have PS5N and PS7N nanocomposites and then by analysis of the RDF results, it was found that the nanoparticles were not well dispersed in these two nanocomposites and they were accumulated in the NR rubbery phase. Therefore, the percolation threshold for silica loading on the PN blend is at most 3 parts (x = 3). These results as well as the other obtained simulation results were compared with the available experimental data, and the agreement observed between them approved the simulation procedure and validated the obtained results.