Development and optimization of natural dye-based crayons from Rumex abyssinicus using Box-Behnken methodology

Abstract This study presents the first exploration of natural dye extracted from Rumex abyssinicus for crayon formulation, leveraging its local availability and environmental sustainability. The work focused on evaluating the effects of paraffin wax, talc, extracted dye, and temperature on the crayon's properties. Characterization techniques, including UV–vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), tensile strength testing, visibility, and durability assessments, were employed to analyze the formulated crayon. A Box-Behnken design within the Response Surface Methodology framework was used to optimize the formulation by varying paraffin wax (4, 6 and 8 g), dye (0.5, 1.25 and 2 g), talc (5, 7 and 9 g), and temperature (80, 90 and 100 °C), while keeping stearic acid (0.5 g) and beeswax (1 g) constant. UV–vis spectroscopy revealed a maximum absorbance of 0.830 at λ max of 298.7 nm, indicating strong pigment retention. The crayon exhibited a tensile strength of 1.48 N/mm 2 and a percentage elongation at break of 1.34%, reflecting its durability and flexibility. These findings demonstrate the feasibility of utilizing Rumex abyssinicus dye in eco-friendly crayon production, offering a sustainable alternative with desirable mechanical and aesthetic properties.