Impact of hemp woody core surface chemical modification on wettability of epoxyurethane composites

Abstract

ABSTRACT Hemp woody core (HWC) that is a by-product of hemp industry was subjected to pre-treatment with alkali (mercerisation) and further functionalisation with epoxidised soybean oil (ESO) or (3-aminopropyl)triethoxysilane (APS). Mercerisation resulted in more developed surface area and rearrangement of fibrils into denser packing. FTIR spectroscopy analysis revealed the presence of hydrogen bonds of HWC with modifier in case of ESO application as well as hydrogen and Si-O-C covalent bonds in case of APS application. Two types of Si-containing epoxyurethanes were filled with 60% of HWC with different surface modification: the first polymer contained diglycidyl ether of bisphenol-A (DGEBA), while the second one contained ESO as an epoxy component. The investigation of the surface properties of composites found that the ones based on ESO epoxyurethane were more hydrophobic than their respective counterparts. Hydrophilicity was reduced by functionalisation of HWC providing a contact angle augment from 54°for DGEBA-containing sample with raw HWC to 86° for the one with oil modified HWC. The results of water uptake test showed that regardless of the matrix the composites reinforced with functionalised HWC exhibited about 40% less gain in weight at the saturation level than their analogues reinforced with untreated or alkali treated HWC. Graphical abstract