Effect of surface treatments and filler loading on the properties of hemp fiber/natural rubber composites

The aim of this present work was to study the effect of surface treatment methods, i.e., silane and permanganate on curing characteristics, dynamic mechanical, mechanical morphological and thermal properties of hemp fiber filled natural rubber composites. Hemp fiber surfaces were pretreated with an alkali solution and followed by a KMnO4 solution or (3-triethoxysilylpropyl) tetrasulfide (Si69). After that, the chemical, physical and morphological properties of untreated and treated hemp fiber samples were investigated by attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. It was found that the KMnO4 and silane (Si69) treatments affected the surface characteristics of hemp fibers. The curing characteristics of the rubber composites, i.e., scorch and curing times increased with increased fiber loading, except for 15 parts per hundred ofrubber (phr) fiber level. The curing characteristics improved with the addition of KMnO4 or silane treated hemp fiber compared to unfilled natural rubber composites. At 5 phr fiber loading, it was found that silane treated hemp fiber filled natural rubber composite showed greater tensile strength and crosslink density in comparison with KMnO4 treated and untreated hemp fiber filled rubber composites. Good interface interaction between the silane treated hemp fiber and rubber matrix was observed in SEM images. Additionally, the thermal stability of rubber composites was unaltered with the incorporation of KMnO4 or silane treated hemp fibers.