Simple production of cellulose nanofibril microcapsules and the rheology of their suspensions

TL;DR

This paper presents a simple, scalable method to produce cellulose nanofibril microcapsules with porous shells and explores how their suspension rheology can be tuned by internal phase composition, including the addition of polyacrylic acid.

Contribution

The study introduces a novel, scalable fabrication technique for cellulose nanofibril microcapsules and demonstrates how internal phase modifications can control suspension rheology.

Findings

Suspensions of neat capsules are viscous liquids with viscosity depending on volume fraction.

Adding PAA induces elasticity and yield stress in the suspensions.

Rheological properties can be tailored by changing internal phase composition.

Abstract

Microcapsules are commonly used in applications ranging from therapeutics to personal care products due to their ability to deliver encapsulated species through their porous shells. Here, we demonstrate a simple and scalable approach to fabricate microcapsules with porous shells by interfacial complexation of cellulose nanofibrils and oleylamine, and investigate the rheological properties of suspensions of the resulting microcapsules. The suspensions of neat capsules are viscous liquids whose viscosity increases with volume fraction according to a modified Kreiger-Dougherty relation with a maximum packing fraction of 0.73 and an intrinsic viscosity of 4. When polyacrylic acid (PAA) is added to the internal phase of the microcapsule, however, the suspensions become elastic and display yield stresses with power-law dependencies on capsule volume fraction and PAA concentration. The elasticity appears to originate from associative interactions between microcapsules induced by PAA that resides within the microcapsule shells. These results demonstrate that it is possible to tune the rheological properties of microcapsule suspensions by changing only the composition of the internal phase, thereby providing a novel method to tailor complex fluid rheology.