This thesis aims to advance scientific grasp and develop innovative modeling techniques for nanofibrillated nanocomposites using various polymer-nanofibril combinations. The aim is to enable the commercialization of nanofibril technology across multiple applications, including both established and niche markets. Manufacturing polymer nanocomposites with nanofillers using conventional processes remains challenging, and the industry has yet to fully exploit the potential of these hierarchical nanostructured materials, known as ”Revolutionary Super Materials”. This work seeks to develop advanced manufacturing technologies informed by multiscale models to produce tunable polymer nanocomposites with well-dispersed nanofibrils, specifically those with diameters of 100 nm or less, which is challenging with traditional methods.

Initially, a sequential multiscale model was developed to study polymer nanocomposites. Interfacial, mechanical, and fracture properties of surface-modified nanofibrillated rubber-toughened polypropylene (PP) nanocomposites, using maleic anhydride (MA) compatibilizer grafting, were investigated through molecular dynamics (MD) and micromechanical modeling. Scanning electron microscopy helped determine the morphology and dispersion of these nanocomposites. Realistic structures were modeled using representative volume elements with various aspect ratios, curvatures, orientations, alignment angles, and bundle sizes. Interfacial properties were determined via MD pull-out simulations, with atomistic mechanical properties scaled up using multiscale modeling to examine the effects of nanofibrillation parameters such as size, orientation, and dispersion.

The interactions between rubber nanofibrils, particularly interfibril forces, were also examined. MD simulations revealed that parallel-aligned nanofibrils experience a significant attractive force, leading to rapid coalescence even below the glass transition temperature (T_g). When the separation distance between nanofibrils reaches 10 nm, the interaction shifts from attraction to repulsion. These findings were then incorporated for the development of a quantitative model for nanofibril interactions and to refine MD interatomic potentials for comprehensive interfibril interaction modeling.

Additionally, we developed a continuum model to predict the pseudoelastic behavior of hyperelastic nanocomposites under finite-plane elastostatics. The model addresses challenges such as irreversible softening, large deformations, and nonlinear stress-strain responses, incorporating damage function and variables into the kinematics of reinforcing fibers. Using variational principles, we derived the Euler equation and boundary conditions, successfully predicting the Mullins effect in human aortas and the Manduca muscle.

These findings could significantly advance the design and analysis of nanocomposites mimicking biological soft tissues and contribute to the development of eco-friendly manufacturing technologies for lightweight, sustainable nanocomposites.