Waste valorization through synergistic co‐pyrolysis of cotton stalk and high‐density polyethylene: thermal and kinetic insights

Abstract This study used thermogravimetric analysis to investigate kinetics and synergistic behavior during the co‐pyrolysis of cotton stalk (CS), high‐density polyethylene (HDPE), and their blends, which contained 50% to 90% CS. The experiments were performed under a N 2 atmosphere at heating rates of 5, 10, and 20 °C min −1 over a temperature range of 30–800 °C. The CS thermograms show that it decomposed in three stages, whereas HDPE decomposed in a single step. The blends exhibited three‐stage decomposition similar to CS. Model‐free isoconversional methods, including the Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), and Starink methods, were used to estimate the apparent activation energy ( E a ). Pre‐exponential factors were calculated using the Kissinger method for all feedstocks. The average E a values for CS were 163, 166, and 162 kJ mol −1 , and for HDPE were 279, 276, and 277 kJ mol −1 , using the KAS, FWO, and Starink methods, respectively. For the blend containing 10 wt% HDPE, the E a values were close to those of CS. Increasing the HDPE content from 20 to 50 wt% reduced the E a by approximately 9% to 19%. The lowest E a of 132 kJ mol −1 was obtained for the blend containing 50 wt% HDPE across all kinetic models. The co‐pyrolysis experiments demonstrated that a synergistic effect exists between CS and HDPE during co‐pyrolysis, suggesting that these blends have strong potential for the production of value‐added chemicals.