Approaches for Surface Energy Control of Nonwoven Fibers for Alcohol Repellency and Electret Charge Protection.

LAVOIE, JOSEPH HENRY. Approaches for Surface Energy Control of Nonwoven Fibers for Alcohol Repellency and Electret Charge Protection (Under the direction of Saad Khan, Orlando Rojas, and Eunkyoung Shim). Bulk polymer additives are commonly used in the nonwovens manufacturing industry for a variety of applications. One such application is the modification of surface properties for controlled repellency of solvents. This is particularly relevant in the field of electret air filtration materials, which have been shown to be rapidly discharged in the presence of oil and alcohol vapors or aerosols. Increased resistance to wetting by these low surface tension fluids can be challenging, but the use of additives to create nonwoven fabrics capable of repelling oils and alcohols allows these products to be manufactured cheaply and easily. While the use of melt additives is established in the prior art, there are many factors in the efficacy of the additives on the resultant properties of the final product, not all of which are well understood. Chief among these is the impact of additive migration on surface properties of manufactured fibers. In this work we seek to explore the effects of melt additive migration on meltblown nonwoven fibers as well as the kinetics and resultant microstructure of additive migration in the polymer matrix. Fibers containing fluorochemical melt additive compounds were characterized by several different analytical techniques. Scanning Electron Microscopy (SEM) images of nonwoven fiber mats allow for the quantitative evaluation of median fiber diameter. By monitoring changes in fiber diameter with respect to additive concentration and fiber manufacturing parameters, we are able to elucidate the correlation between these critical parameters. X-ray Photoelectron Spectroscopy (XPS) was used to characterize the kinetics of the changing surface composition of the fiber mat, as migration of the additive to the surface occurs over time. In an effort to gain a more thorough understanding of the migration process, Time-ofFlight Secondary Ion Mass Spectroscopy (TOF-SIMS) was used to generate compositional maps of fiber cross-sections. These 2D maps of fluorine content throughout the core and surface of fibers offer a unique view of additive migration and allow for additional understanding of the role of fiber diameter and nonwoven manufacturing methods on the resultant surface properties of the material. Migration of additives was monitored over several months, allowing for the evaluation of compositional changes over multiple timescales. This changing composition was then related to repellency of alcohol solutions via contact angle data. By collecting composition and contact angle data in tandem, thresholds in surface fluorine content for repellency were identified, as well as protection of charge against isopropanol vapor discharging methods. In addition to bulk polymer melt additive approaches, we also utilized novel surface modification methods for the creation of extremely low surface energy nonwoven webs. In this study, we utilized the non-specific binding of unfolded natural polymers to highly inert hydrophobic surfaces like polypropylene to generate an activated surface capable of further functionalization. Through the use of sequentially deposited charged moieties, an extremely conformal, rough, and densely decorated silica surface was created on fiber surfaces. After functionalization of the silica surface with a highly fluorinated silane molecule through a simple vapor phase silane reaction, the multi-scale roughness of the coated nonwoven web in combination with the low surface energy of the fluorinated surface enabled extremely high water contact angles (>160°) and significant improved repellency of low surface tension oils and alcohols. © Copyright 2018 Joseph Henry Lavoie All Rights Reserved Approaches for Surface Energy Control of Nonwoven Fibers for Alcohol Repellency and Electret Charge Protection by Joseph Henry Lavoie A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Chemical Engineering Raleigh, North Carolina 2018