Upcycling Canola: Closed-Loop Water Retting System for Sustainable Fiber Production from Waste Canola Stalks

A closed-loop water retting system is developed and fabricated in this study to process discarded canola stalks into fibers. The effects of retting parameters are studied using Latin Hypercube statistical design, modeled using Altair HyperStudyTM, and subjected to a multi-objective optimization. The retting time is reduced from a range of ≈168–1080 h for the conventional water retting system to 60 h for the developed closed-loop system. The fiber yield increased from ≈0.84% to 11.26%, the crystallinity index (CI) increased from ≈55.6% to 67.3%, and linear density decreased from ≈73.6 to 51.7 Tex with the increase in retting time, temperature, and water flow rate. However, the overall trends are complicated due to the heterogeneity in the structures and properties of the starting plant materials. The optimal retting parameters are 60 h-time, 60 °C-temperature, and 150 mL min⁻¹-water flow rate. Under these conditions, canola fibers exhibited ≈11.26% yield, ≈67.32% crystallinity index, and ≈56.24 Tex linear density. Canola fibers exhibited a multifiber structure surface (mean fiber diameter ≈957.8 µm) and non-cellulosic component dominant cross-section due to their higher pectic polysaccharides content (≈32.5–41.8%). The canola fiber production accounts for ≈169.42 kg CO₂e/tonne, which is significantly lower than the emissions associated with equivalent flax fiber production (≈403.15 kg).