The colour fastness of silk fabrics dyed with extracts obtained from the palm kernel shell (PKS) of African oil palm tree was evaluated at first in order to clarify the dyeing characteristics of this dyestuff. It was found in the colour fastness test to washing that the colour of the dyed silk fabric became deeper with the number of washing by basic Marseille soap solution and no fading occurred after up to thirty washings. The sample colour also became darker until 10 h of exposure to artificial sunlight illumination by a simulator and then brightened very gradually to 150 h in the colour fastness test to light. While the colour fastness to rubbing for the dyed fabrics was low under wet conditions, it was high under dry conditions. The PKS extracts contain the component substances which have reducing properties. Such unoxidised dye precursors are adsorbed onto the silk fabrics in the process of the dyeing and are oxidised to be colouring matters during the washing and light irradiation. On the other hand, attempts at colour stabilisation treatments to prevent darkening after dyeing by washing showed that treating the PKS-dyed silk fabric with Na₂CO₃·1.5H₂O₂ solution was the most effective. This treatment process oxidises the adsorbed component substances and prevents colour change due to the further oxidation. Furthermore, it was found that the colour of the PKS-dyed silk fabric turned black, very dark brown, brown or brown-close to black by the treatments with FeCl₂, CuCl₂, AlCl₃ or VOSO₄ aqueous solution, respectively. These are mordant effects by the metallic ions and post-mordanting was more effective in darkening the colour.

Biomass-derived biodegradable fibers have attracted considerable attention as sustainable alternatives to petroleum-derived non-biodegradable synthetic fibers. Curdlan, a linear β-1,3-glucan, is a promising renewable resource that exhibits unique physicochemical properties owing to its triple-helical crystalline structure. The regenerated fibers of curdlan can be fabricated by wet spinning; these fibers exhibit excellent ductility but poor mechanical strength compared to other polysaccharides such as cellulose. In this study, a new post-treatment was developed to enhance the mechanical properties of regenerated curdlan fibers by exploiting their high ductility when swollen with water. Curdlan was dry-jet wet spun using an ionic liquid as the solvent and water as the coagulant. The regenerated fibers were subsequently post-drawn in water to a maximum of four times the original fiber length, followed by air-drying. The resultant fiber showed a 1.4-fold increase in the briefringence (Δn) value, which represents the orientation degree; moreover, the tensile strength was two times higher (20 cN tex^‒1; 300 MPa) than that of the untreated fiber. It was also observed that an increase in the degree of post-drawing was more effective in enhancing the regenerated curdlan fiber than an increase in the initial draw ratio from 10 to 20 during wet spinning.