ROLE OF FIBER ADHESION IN NATURAL FIBER COMPOSITE PROCESSING FOR AUTOMOTIVE APPLICATIONS 1 James Holbery, Leo Fifield, Kayte Denslow, Anna Gutowska, Kevin Simmons Pacific Northwest National Laboratory – P.O. Box 999, Richland, WA 99352, USA Abstract The prediction and characterization of the adhesion between fiber, surface treatment, and polymer is critical to the success of large-scale natural fiber based composites into automotive semi-structural applications. The two primary limiting factors in natural fiber composites are in large part dominated by fiber moisture uptake due to fiber structure, and limits in high- temperature processing. In this study, we have developed several fiber surface modification techniques and analyzed the fiber-polymer adhesion to more clearly understand the critical parameters controlling moisture uptake, swelling, and structural degradation due to interface degradation. We will present preliminary surface modification findings on hemp fiber sources, and attempt to resolve the role that fiber interface adhesion characterization plays in understanding and predicting fiber performance within polymer matrices. Background Adhesion forces between two surfaces are comprised of both short and long-range forces. Short-range forces play a significant role at atomic or molecular distances (typically a few nm) and are defined by the electronic properties, as in the case of atoms or molecules, or the local chemical and geometrical properties, as in the case of macroscopic bodies in close proximity. Very important is the medium that separates particles (atoms, molecules, or small clusters) or macroscopic bodies; for example, the presence of moisture between a fiber and polymer can significantly impact interface adhesion. Short-range forces arise from either electromagnetic interaction potentials, dominating long-range forces at molecular distances, or can be of a mechanical origin, i.e., due to geometric or steric interaction. The overall sum of the contributing long and short range forces determines whether an interaction between two bodies is attractive or repulsive and thus determines the cohesion or adhesion between identical or different bodies. A primary consideration in adhering cellulose-based fibers to a polymer is the moisture present in the fiber during reaction. It is costly to dry lignocellulosics to less than 1% moisture, but the -OH group in water is more reactive than the -OH group available in the lignocellulosic components, rendering hydrolysis to be faster than substitution. The most favorable condition for surface reaction is one that requires a trace of moisture and the rate of hydrolysis is relatively slow. Three factors determine the rate at which moisture is removed from lignocellulosic materials: temperature, relative humidity, and air velocity. The ability to control and minimize energy input during this process is one opportunity foreseen within processing cellulose materials, and the forest products industry in general. The ability to eliminate water absorption during service of cellulose-based composite components is paramount in industrial 1 This manuscript has been authored by Battelle Memorial Institute, Pacific Northwest Division, under Contract No. DE-AC06- 76RL0 1830 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. Page 1