The quest for alternative biodegradable materials such as cellulose to replace plastics is attracting tremendous attention among the materials science community in addition to being directly aligned with the public interest. Most cellulose nanomaterials comprises of a combination of small (~nm) but strong nanofibers and long (~ μm) but weak microfibers. We investigate the role of interactions of such fibers, spanning across different length-scales, in improving the mechanical properties of the nanocomposite. To qualitatively understand the interface mechanics in the composite material, we devise a bottom-up multi-scale coarse-grained (CG) modeling scheme. The levels of the CG scheme are as described: (a) Cellulose molecular chain level (~ Å); (b) Elementary fibril level (~ nm); and (c) fiber level (μm). We characterize the length and diameter of the fibers using Atomic Force Microscopy and thereby choose the 2nd and the 3rd level of the CG scheme to model the nano and the microfibers respectively to reproduce analogous experimental conditions. We construct hybrid models by mixing the nano and micro fiber models. Changing the mass % of the separate nano fibers help explore the fundamental reason behind why the hybrid show greater strength and toughness than the material separately fabricated using only nano or microfibers. From the quantitative aspect, we obtain that the fracture resistance enhance efficiently by around 57 times when the nanofiber content is about 85.7%. Independent molecular simulations of inter-fiber sliding in the nano-, micro- and hybrid fibers elucidate the formation and breaking of hydrogen bonds and clearly explain the role of hydrogen bonding across their interfaces which directly imparts the superior mechanistic properties in the hybrids. Implementing the above CG scheme, we also study the interaction between two neighboring fibers (nano & micro) shedding fundamental insight on the mechanical response of cellulose nanomaterials under various representative loads. Such multi-scale modeling investigations, in addition to being very timely, can also be extended to other fundamental building blocks and directly influence the material design of novel hybrid materials having tunable interfacial properties.

Mechanics of cellulose nanomaterials using a bottom-up scalable modeling scheme

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.