Experimental design of a millifluidic flow-focusing method for biomimetic nanocellulose and hemicellulose-based biopolymer fibres

TL;DR

This study develops a millifluidic flow-focusing method to align nanocelluloses within biopolymer hydrogels, aiming to create biomimetic, biobased fibres with enhanced mechanical properties for sustainable material applications.

Contribution

It introduces a novel millifluidic setup with 3D printed geometries to control nanocellulose orientation in biopolymer fibres, advancing sustainable fibre fabrication techniques.

Findings

Successful nanocellulose alignment demonstrated via birefringence observations.

Optimized flow conditions achieved anisotropic nanocellulose hydrogels.

Versatile circuit geometries enable tailored fibre properties.

Abstract

The mechanical performance of plant fibres is linked to the presence of crystalline elements dispersed within an amorphous cohesive matrix. The more the crystalline reinforcement is aligned with the fibre axis, the better the mechanical properties of the fibre. With the aim of developing entirely biobased biomimetic fibres as alternatives to synthetic or resource-consuming fibres, we have studied the fabrication of hydrogel filaments made from mixtures of nanocelluloses, biobased crystalline nanoparticles acting as reinforcement, and xyloglucans, a plant wall hemicellulose with a strong affinity for cellulose surfaces. These will ensure cohesion between the nanocelluloses. To optimize the orientation of the nanocelluloses within the filaments, and thus potentially improve the mechanical properties of the fibres, we present a study on the development of a millifluidic method of flow-focusing. The developed setup uses external sheath flows to focus and align a nanocellulose suspension central flow. Different configurations in terms of concentrations, circuit designs and flow velocities are tested. 3D printed circuits are explored to produce versatile geometries and optimize the process design. To qualify the orientations during the process, observations with a polarized microscope (POM) are made, as the alignment of the nanocellulose crystalline structures creates birefringence in suspensions. Significant optical phase shifts related to the nanocellulose particles' orientations are visible by color gradients, varying with the suspensions' concentrations and flow velocities. Results demonstrate successful tuning of nanocellulose orientation into anisotropic hydrogels using different millifluidic circuit geometries, with the introduction of xyloglucans to produce new types of biosourced fibres.