Structural and morphological features of microcrystalline сellulose from industrial hemp hurd

Abstract

Currently, there is increased interest in growing hemp as well as in large-scale hemp products. The main research focuses on the use of seeds and fibres. At the same time, the remaining hurd is proposed to be used for mulching, making insulation and bedding for animals. Due to the cellulose’s high content in its composition with a relatively low content of inorganic components, it can be a promising raw material for obtaining microcrystalline cellulose (MCC). Therefore, our work aimed to obtain MCC from hemp husks, establish its physicochemical characteristics and compare them with the indicators of MCC previously obtained from another flax culture. Air-dry hemp hurd, waste after the fibre extraction from technical hemp, was used for the research. It has the following characteristics: humidity of 8 %, the proportion of organic components to dry weight of 97.3 % (cellulose – 48.4, hemicellulose – 25.8, lignin – 20.9 % mass) and inorganic components – 2.7 %. To obtain microcrystalline cellulose, the hemp hurd was subjected to organo-solvent cooking. The structure and morphology of the MCC were studied using methods such as XRD, XRF, FTIR-ATR, low-temperature nitrogen sorption-desorption, AFM, TGA, and DSC. It was found that by the organo-solvent cooking method, it is possible to obtain MCC with a yield of 83.2 %. The resulting product was a white, tasteless, and odourless substance with 96.9 % organic components (including 98.5 % cellulose and 1.5 % lignin) and 3.1 % inorganic components (including 91.4 % SiO₂). The XRD method confirmed the presence of a crystalline component in the obtained MCC due to the availability of the intensity of the peak reflex in the region 2θ = 22–23° which corresponds to the plane 002 of the crystal lattice of natural cellulose I. Based on these data, the crystallinity index was calculated – 0.88. The FTIR spectrum of the sample shows typical functional groups corresponding to MCC. There are two distinct mass loss steps in thermograms (TGA). It was found that the obtained samples had a specific surface area of 2.6 m²/g and a pore diameter of 3.6 nm, which indicates an MCC's non-porous structure. The AFM method shows that the particles are distributed throughout the scan, while there are no clusters of particles and their agglomerates, the height of which elements varies from 5.0 to 11.1 nm. Surface roughness Ra = 1.3–1.4 nm.