Understanding Process-Property-Structure for Elastoplastic Behaviour of Polymer Nanocomposites with Agglomeration Anomalies and Interfacial Property Gradients

Polymer nanocomposites are inherently tailorable materials and capable of providing higher strength to weight ratio than traditional hard metals. However, their disordered microstructural nature makes processing control and hence tailoring properties to desired values a challenge. Additionally, interfacial region, also called interphase, is a key material phase in these heterogeneous materials and its extent depends on variety of microstructural features like dispersion.<br/>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 polymer bulk. Past works have shown that particle functionalization can help tweak these interactions in attractive or repulsive directions and can produce slow or fast decay of stiffness properties in polymer nanocomposites. In absence of any nano or micro-scale local property measurement, 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 that were obtained by previous researchers by atomic force microscopy and fluorescence microscopy.<br/>This is further combined with a microstructural design of experiments for agglomerated nanocomposite systems. Agglomerations are particle aggregations that are processing artefacts that result from lack of processing control. Twin screw extrusion process can reduce extent of aggregation in hot pressed samples via erosion or rupture depending on screw rpms and toque. 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 if we break down agglomeration via erosion. Rupture is relatively less effective in helping improve nanocomposite yield strength. We also observe an inflexion point where incremental increase brought on by rupture is slowed down due to increasing SCZ vs saturated interfacial fortification.