Almond Shell‐Derived Cellulosic Microfibres: Extraction, Characterisation and Applications in Sustainable Paper‐Based Packaging

ABSTRACT

This study develops pathways for the valorisation of almond shell (AS) industrial byproducts through the extraction of lignocellulosic fibres for reinforcement in fibre‐based packaging applications. AS biomass was pretreated under mild alkaline conditions to improve digestibility, followed by organosolv, soda and kraft pulping. The organosolv process achieved the highest total yield (85.68%) but retained substantial lignin, while soda pulping achieved moderate delignification. Kraft pulping was the most effective in lignin removal, producing cellulose‐rich microfibres that were subsequently treated with elemental chlorine‐free (ECF) bleaching to obtain bright, high‐purity AS microfibres. Compositional, physicochemical and structural analyses indicated that AS‐derived fibres are primarily microfibres (0.166–0.256 mm) with high fines content (80.86%–91.36%). Kraft‐derived microfibres demonstrated the highest cellulose purity, crystallinity, viscosity, carboxyl content and hexenuronic acid, reflecting superior structural integrity and surface functionality. In contrast, organosolv microfibres retained more lignin, resulting in lower viscosity but higher hard‐to‐remove water. Surface analysis confirmed progressive lignin removal and increased polysaccharide exposure from organosolv to kraft and bleached microfibres. The higher fines content increased water retention and reduced drainage; however, it also enhanced the potential for inter‐fibre bonding. The addition of 5% bleached AS microfibres into refined hardwood pulp maintained tensile strength (45.1 ± 0.7 Nm/g vs. 46.5 ± 0.4 Nm/g), with only a slight decrease in tear strength, supporting their use as functional fillers. These results demonstrate that AS residue biomass is a promising, low‐cost and sustainable feedstock for lignocellulosic microfibre production, with strong potential for integration into fibre‐based packaging systems and alignment with circular bioeconomy strategies.