Synergism Effect between Nanofibrillation and Interface Tuning on the Stiffness-Toughness Balance of Rubber-Toughened Polymer Nanocomposites: A Multiscale Analysis

M Zeidi and CB Park and CI Kim, ACS APPLIED MATERIALS & INTERFACES, 15, 24948-24967 (2023).

DOI: 10.1021/acsami.3c04017

Asthe design and scalable technology development of tough, yetstiff, polymer nanocomposites receive attention in the automotiveindustry, fundamental understating of underlying toughening mechanismsat the nanoscale is inevitable. However, mechanical tests on rubber- toughenednanocomposites have shown that their overall fracture properties aresignificantly smaller than theoretical predictions. Our previous studyshowed that major factors in this regard are the simultaneous operationof different toughening mechanisms and the nanostructural featuresof the interface. As a result, it may be necessary to employ multiscaleand multimechanism modeling strategies to accurately account for thecontribution of each toughening mechanism. In this study, the effectsof nanofibrillation (i.e., size, orientation, and dispersion) andinterfacial tuning on the mechanical properties of nanofibrillatedrubber-toughened nanocomposites are examined using molecular dynamics(MD) simulations. We report that by interfacial modification via graftingcompatibilizer at the interface, nanofibrillated rubber-toughenedpolypropylene (PP) nanocomposite can achieve superior mechanical propertiesas a result of enhanced interfacial load transfer. Compared to pureethylene propylene diene monomer rubber (EPDM)/PP system, an increaseof 49% in energy absorbed per unit volume during fracture was achievedfor 30% functionalized nanocomposites. Such an increase in energydissipation was caused by a transition in the dominant crack propagationmechanism from interfacial slippage to crack-arresting behavior, owingto enhanced interfacial adhesion. MD simulations in conjunction withthe multiscale model revealed that such a change in mechanism is causedby the formation of strong covalent bonds, interfacial friction, andthe presence of a highly entangled polymeric network at the interface.Although the multiscale framework can be viewed as a road map formodeling the interface of various nanocomposite systems, the resultsobtained from our study may offer valuable insights for developingrobust and scalable fabrication processes for nanofibrillated rubber-toughenednanocomposite structures, which pose significant technological challenges.

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