Petroleum-based plastics are often used in the production of fibers for the textiles industry. The main drawback of using these synthetic fibers is that they come from nonrenewable sources, contributing to climate change. Synthetic fibers also have extremely long environmental lifetimes evidenced by the growing ubiquity of microplastics. Natural fiber welding (NFW) is a technology platform focused on disrupting the overuse of non-biodegradable plastics by enabling new ways to mold and shape natural fibers. This process involves disrupting hydrogen bonding within cellulose fibers, physically altering the fiber structure, resulting in stronger and more durable fibers. Ionic liquids (ILs) are good candidates for solvating the fibers in the NFW process. We have found that the IL 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]) in combination with an organic cosolvent is an ideal candidate for NFW by analyzing welded fibers via scanning electron microscopy and mechanical property testing. Several families of tunable natural fiber-based composite materials for textile, packaging, automotive, and building product applications are headed to market with global brands. NFW technologies leverage abundant natural materials and enable these biodegradable substrates to be molded into morphologies that are typically attained only by using synthetic plastics. The use of (ILs) enables new, atom-efficient manufacturing that can create value-added products from inexpensive fibrous substrates like cotton, hemp, flax, silk, and wool. A key aspect of bringing NFW technologies to market is the recapture and recycling of IL-based solvents that manipulate and fuse fiber substrates. This is accomplished primarily by reconcentrating the IL by distillation and requires real-time monitoring of solvent concentrations in wash solution. On-line monitoring improves process control, increasing the economic viability of NFW processes. Herein we demonstrate techniques for on-line IL monitoring using a combination of conductivity measurements, refractometry, and ATR-FTIR spectroscopy. Specifically, we monitor the C=O stretching vibration at ca. 1176 cm<sup>-1</sup> as a function of IL concentration in a simulated wash solution. Our data show a wide concentration range over which the absorbance of the C=O stretch increases linearly. We also demonstrate that the C=O stretch remains free from interference in the presence of naturally occurring contaminants which are endemic to raw cotton fibers.

Online monitoring of ionic liquid based natural fiber welding solvents via ATR-FTIR

ACS Fall 2021

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