Reinforcement of Natural Fibers via Supercritical Fluid Infiltration of Nanoparticles

Abstract

In recent years, consumer products have been increasingly utilizing sustainable materials to attempt to reduce the product’s carbon footprint. For example, the automotive industry has incorporated a variety of natural fiber polymer composites on vehicles in the last 20 years, including wheat straw in the Ford Flex and flax fibers on the Polestar Precept and the Porsche Cayman GT4 Clubsport. However, natural fibers exhibit lower strength and stiffness in comparison to synthetic reinforcing agents, such as glass fiber. In this work, the authors are developing a technique to improve the mechanical performance of flax fibers for use in structural composites. Supercritical fluids, including supercritical-carbon dioxide (scCO2), have been shown to swell and plasticize amorphous polymers, resulting in increased mass transport and absorption of additives. The weak intercellular region within flax fibers, commonly called the middle lamella, consists mainly of amorphous pectin. In this work, the authors hypothesize that scCO2 could be used to swell amorphous polymers in a fiber’s structure (e.g. pectin) and enable reinforcement with nanoparticles, resulting in fiber performance enhancement. Pectin films were created for proof-of-concept experiments and treated with scCO2 at pressures ranging from 1200-4000psi in the presence of titanium dioxide nanoparticles (TiO2). TiO2 nanoparticles were shown to be able to enter pectin films upon treatment with scCO2 for 24 hours. The same treatment process was used on dew retted, mechanically extracted flax fibers and after treatment for 24 hours, the average tensile strength of the fibers was improved by over 40%. Overall, this method of incorporation of nanoparticles within natural fibers could enable development of low-density, low-carbon footprint polymeric composites for use in structural industrial applications.