Process–structure–property relation for elastoplastic behavior of polymer nanocomposites with agglomerates and interfacial gradients

Polymer nanocomposites, inherently tailorable materials, are potentially capable of providing higher strength to weight ratio than conventional hard metals. However, their disordered nature makes processing control and hence tailoring properties to desired target values a challenge. Additionally, the interfacial region, also called the interphase, is a critical material phase in these heterogeneous materials and its extent depends on variety of microstructure features like particle loading and dispersion or inter-particle distances. Understanding process-structure–property (PSP) relation can provide guidelines for process and constituents’ design. Our work explores nuances of PSP relation for polymer nanocomposites with attractive pairing between particles and the bulk polymer. Past works have shown that particle functionalization can help tweak these interactions in attractive or repulsive type and can cause slow or fast decay of stiffness properties in polymer nanocomposites. In this work, we develop a material model that can represent decay for small strain elastoplastic(Young’s modulus and yield strength) properties in interfacial regions and simulate representative or statistical volume element behavior. The interfacial elastoplastic material model is devised by combining local stiffness and glass transition measurements from atomic force microscopy and fluorescence microscopy. This model is combined with a microstructural design of experiments for agglomerated nanocomposite systems. Agglomerations are particle aggregations arising from processing artifacts. Twin screw extrusion process can reduce extent of aggregation in hot pressed samples via erosion or rupture depending on screw rpms and torque. We connect this process-structure relation to structure–property relation that emerges from our study. We discover that balancing between local stress concentration zones (SCZ) and interfacial property decay governs how fast yield stress can improve by breaking down agglomeration via erosion. Rupture is relatively less effective in helping improve nanocomposite yield strength. We also observe an inflection point where incremental increase brought on by rupture is slowed due to increasing SCZ and saturation in interphase percolation.