Cellulose nanofibers in ice: microstructural effects on mechanical response

Abstract

Abundant in cold regions, ice rarely exists as a pure single-phase compound but rather contains insoluble particulates and fibrous matter from the local environment. Such second phase materials can drastically change the formation mechanism, microstructure, and properties of the resulting composite ice. Cellulose nanofibers (CNFs) were investigated for their ability to strengthen ice and studied with optical microscopy, ice fabric analysis, and mechanical property measurements. With increasing concentration, the CNFs bridged across grain boundaries and were distributed throughout grain interiors, forming a percolated network within the ice microstructure. The CNFs in ice were found to modify the ice fabric from an S2 classification to one with an irregular distribution of c-axis for intermediate CNF wt%, and appeared to shift back towards S2 as CNF was increased to 1.0 wt%. The addition of up to 1.0 wt% CNF to ice increased the flexural strength from 3.1 MPa to 5.8 MPa in 3-point bending and from 1.7 MPa to 3.8 MPa in 4-point bending, while increasing the compressive strength from 2.6 MPa to 7.2 MPa. The increase in strength correlated with ductility imparted by the CNFs which thereby increased the apparent toughness by a factor of 2 – 10 compared to pure ice. These insights reveal the mechanistic response of CNFs in ice and open future avenues that utilize ice as a high-performance material for structures in cold regions.