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Douglas E. Hirt, Ph.D. -- Research Activities Improving the Wettability of Deep-groove Fibers The primary objective of this research is to modify the surfaces of polypropylene capillary surface material (CSM) (or deep-groove) fibers through the use of migratory additives, i.e., material added to the melt that exhibits controlled migration to the surface of the fiber. The goal is to create hydrophilic surfaces for liquid transport and biomedical applications. PP was selected as the base polymer as it has wide use as woven and non-woven fabrics for hygiene, medical, absorbent, and filter applications. Methods to modify this hydrophobic polymer can be classified into two categories. One is to change functionalities on the fiber surfaces through chemical reaction or treatment, e.g., generating polar function groups by exposure to plasma conditions. Another is to physically apply hydrophilic additives by topical coating with spin finishes. However, in the case of CSMs that contain axial grooves, a significant portion of the solvent may be trapped in the grooves due to the capillary pressure created by the small radii of curvature present in the cavities. As a means to overcome the permanence and coverage issues with solution-coating techniques, we study the surface modification of CSM fibers using migratory additives. The additives investigated in this study include IRGASURF HL560 (a commercial product from Ciba), linear polyethylene glycols (PEGs), multi-arm polyethylene oxides (PEO), hydroxyl-terminated dendritic polyesters, and highly regular PE-g-PEO comb polymers, which are synthesized by Prof. Ken Wagener and his students at the University of Florida. Surface Modification of Biodegradable Polymers
Poly(L-lactic acid) (PLA) and poly(hydroxyalkanoates) (PHAs) are biodegradable polymers with favorable biocompatibility, and they have been used as bioabsorbable materials in the medical and pharmaceutical fields. The major objective of this research is to modify PLA/PHA film surfaces with the ultimate aim of making bioactive surfaces. Our modification method focuses on photoinduced surface grafting, which has the advantages of low cost of operation, mild reaction conditions, selectivity of UV light absorption, and permanent alteration of the surface chemistry. Hydrophilic polymers (e.g, polyacrylic acid, polyacrylamide) are photografted from the film surfaces to enhance wettability. An important aspect of this work is to determine whether the surface-modification process influences specific bulk properties (e.g., crystallinity, tensile strength, modulus, permeability, molecular weight). We also examine the effect of surface modification on cell proliferation for tissue-scaffold applications.
Using Multilayer Films to Fabricate Reactive, Submicron Patterned Surfaces
Highly layered structures are important to microfabrication and nanofabrication technologies as tools for understanding and controlling surface structures through manipulation of chemical and physical interactions. In collaboration with Dr. Scott Husson, we are investigating a new approach to create submicron patterned surfaces with surface chemical functionality using multilayer polymer films. Alternating layer structures of two immiscible polymers, linear low density polyethylene (LLDPE) and ethylene-acrylic acid copolymer (EAA), were formed by co-extrusion with subsequent compression molding. When a structure is microtomed to reveal its cross-section, a striped pattern is observed in which every other layer is reactive due to the acid groups. Specific functional groups on the polymers (or subsequently created there via surface chemistries) could serve as binding sites for mass-transfer processes. The thicknesses of the individual layers could range from millimeters to nanometers, the latter case providing the opportunity for hundreds or thousands of layers in a compact geometry. Moreover, the multilayer films can be produced from inexpensive polymers and the films are easily bendable to create devices on a macroscopic scale. |
Last Updated:April 18, 2009
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