Molecular dynamics insights into the tensile behavior of CNT-reinforced PLA and PGA nanocomposites

Abstract

Polylactic acid (PLA) and polyglycolic acid (PGA) are biodegradable and biocompatible aliphatic polyesters with potential for biomedical and load-bearing systems applications. However, their mechanical performance may not be appropriate for applications requiring high stiffness and strength. Carbon nanotubes (CNTs) can improve the mechanical response of polymer matrices, although their tendency to aggregate may limit effective reinforcement. Surface functionalization with 3-aminopropyltriethoxysilane (APTES) was therefore considered to enhance CNT–polymer interfacial interactions. In this work, Molecular Dynamics (MD) simulations were used to analyze the effect of cooling rate on the pure biopolymers. For the PLA system, the impact of reinforcement position was also evaluated at three distinct locations. Results indicate that the temperature has a significant effect on pure polymers, while its influence is less pronounced in reinforced polymers. PLA and PGA structures with a degree of polymerization of 25 were constructed by using MedeA software. All simulations were performed in LAMMPS using the Polymer Consistent Force Field (PCFF) force field. Tensile tests were conducted under an isothermal-isobaric ensemble (NPT) at a strain rate of 10 8 s −1 , while a canonical ensemble (NVT) was used to determine interaction energies. Results for the interaction energies show enhanced interfacial adhesion as a result of the APTES functionalization. Furthermore, placing the reinforcement at the center of the polymer matrix yielded the most favorable performance. This configuration resulted in an increase in Young's modulus from 3.637 GPa to 4.038 GPa for PLA (11% increase), and from 6.452 GPa to 6.929 GPa for PGA (7% increase).