Evaluation of the Dyeing Process for Paiche (Arapaima Gigas) Leather Using Colorant Extracted from Walnut Leaves (Juglans Neotropica) for Scaling-Up

The technological development of paiche leather tanning is projected as a high-impact economic activity and requires the application of clean technologies, such as replacing highly toxic synthetic chemicals. This study aimed to evaluate the extraction process of naphthoquinone from walnut leaves for dyeing chrome-free tanned paiche leather and to establish the feasibility of scaling it up. The active principle extracted in an aqueous medium was characterized using HPLC chromatography and UV spectrophotometry. A factorial design was implemented to evaluate leather dyeing, and the results were scaled up at the pilot level. The factors studied were dyeing time (60, 90, and 120 minutes) and walnut dye concentration (161.6, 209.8, and 250.0 g/L), with Color Intensity in the dyed leather as the response variable. Juglone (5-hydroxy-1,4, naphthoquinone) was identified as the primary dye-producing compound with maximum absorption at 210 nm in aqueous solution. The results of the experimental design fit a linear model, with a determination coefficient (R²) of 77.36% and an adjusted coefficient of 74.34%. The values obtained for the finished leather at the pilot scale, including tear resistance (88.90 N), tensile strength (8.34 N/mm²), elongation percentage (53.76 %), dry (4/5), wet (4), and artificial sweat rub (4) and lightfastness (5), indicate that walnut-dyed leather can be used in the manufacturing of footwear and clothing. The process is technically scalable to an industrial level.