Mechanical properties of a fiber reinforced composite depend not only on its constituents but also on the interfacial adhesion which is a thermodynamical quantity. Therefore, to design a composite having specific properties, it is essential to know the surface thermodynamics of the constituents. In this study dispersion component of surface energy and acid-base characteristics of the untreated hemp fibers, alkali treated hemp fibers, acetylated hemp fibers, and unsaturated polyester resin were determined using Inverse Gas Chromatography. Concurrently, a novel eco-friendly method of treating natural fibers was developed using Ophiostoma ulmi fungus. Treated fibers showed improved acid-base characteristics which mean that work of adhesion between fiber and resin due to acid-base interactions is expected to improve in a composite. To ascertain this, the hemp-polyester composite were manufactured using resin transfer molding process and influence of dispersive and acid-base interactions on the structural properties and durability of the composites was studied.