Abstract

Unplasticized Polyvinyl Chloride (uPVC) is a vital structural thermoplastic whose macroscopic mechanical responses are governed by atomistic dynamics often inaccessible via traditional experimentation. This study aims to provide molecular-level insights into the macroscopic mechanical response and viscoplastic performance of amorphous uPVC. Atomistic Molecular Dynamics Simulations (MDS) were conducted using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) package and a reparametrized  CHARMM  force field.  Amorphous simulated cells were equilibrated through a rigorous multi-stage thermal protocol within the Isothermal-Isobaric (NPT) ensemble. Uniaxial tensile tests were performed at a constant strain rate across temperatures ranging from 200 K to 350 K.

Findings revealed that increasing temperature systematically reduced yield stress and significantly diminished material stiffness. Quantitative topological analysis demonstrated that initial elastic deformation is enthalpy-driven by non-bonded intermolecular interactions, whereas large strain hardening is entropy-driven, characterized by significant chain uncoiling and segmental alignment. This research establishes a predictive framework linking microstructural dynamics to macroscopic performance. The results confirm that elevated thermal energy facilitates molecular mobility and lowers energy barriers for conformational transitions, offering a robust contribution to the fundamental understanding of yield mechanisms in glassy thermoplastics and providing valuable insights for the design of polymer components under varying thermal conditions.