Engineering Nanocellulose Materials for High Ballistic Impact Performance
Abstract
The objective of the proposed research is to investigate the size, microstructure, and surface chemistry dependent mechanics of neat nanocellulose thin films from a molecular viewpoint, and establish design principles for maximizing the performance of these nanostructured materials under microballistic impact. In pursuit of this overarching objective, our first aim will be to establish a coarse-grained molecular dynamics modeling framework for nanocellulose fibrils. Building on this capability, our second aim will be to relate nanocellulose fibril microstructure in thin films to ballistic impact performance. The main knowledge gap we wish to address is how the chiral nematic ordering of cellulose nanofibrils and their interfacial sliding, separation and fracture influences the ballistic performance of films. The central technical challenge that will be overcome with this research is to establish atomistically informed systematic coarse-grained models of nanocellulose fibrils that will enable modeling film behavior at the mesoscopic scale of micro-ballistic experiments while retaining key structural and interfacial details. Building on our past research sponsored by ARO, we will specifically focus on films made from high-aspect ratio nanocellulose fibrils that we anticipate will yield both greater strength and toughness, specifically cellulose nanofibers (CNFs) and tunicate cellulose crystals (t-CNCs). Strong anisotropy and large aspect ratios of nanocellulose fibrils render standard spherically symmetric bead-spring models inadequate for describing the mechanics of these systems, which will require the development of efficient orientation-dependent anisotropic potentials for 1D nanomaterials as a major thrust of our research. Our research will aim to explain the role of nanofibril structural ordering, surface chemistry, and dimensions on the mechanical behavior of self-assembled films from nanocellulose. Nanocellulose films are transparent and have great potential to be used in Army relevant applications where visibility combined with fracture toughness is vital, such as protective eyewear, windows, electronic device screens and substrates, as well as strong and lightweight materials. The anticipated outcome of these studies will be predictive models that accelerate efforts towards making high performance load-bearing materials from nanocellulose. Analytical models aimed at understanding the mechanical behavior nanostructured membranes will help guide and explain future experiments and material designs, for example by clarifying how energy dissipation mechanisms such as cone wave propagation depend on molecular design principles. Understanding how to scale micro-ballistic tests to macro-scale material performance will be important for selecting and designing new materials. Discovering how Bouligand or chiral nematic ordering of fibrils controls wave propagation in nanocellulose films is important for many active research areas such as impact tolerant materials, acoustic metamaterials and optomechanical devices. Understanding the ballistic properties of nanocellulose is particularly important for the Army as these materials are already considered promising for their exceptional quasi-static mechanical properties, but their high strain-rate performance is unknown. This is challenging to probe experimentally due to difficulties associated with sample preparation and scales (length and time) of observation of classical techniques. The proposed research on systematic coarse-graining of long-aspect ratio nanocellulose fibrils informed from atomistic simulations will be broadly useful for computational materials design and mechanics approaches pertinent to nanomaterials.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 11, 2018
- Source ID
- W911NF1710430
Entities
People
- Sinan Keten
Organizations
- Army Contracting Command
- Northwestern University
- United States Army