Mechanical properties of waste cotton and their changes during early pyrolysis

Waste cotton is a textile material with high mechanical properties. Understanding the mechanical properties of waste cotton and their changes at an early pyrolysis stage is important for its thermochemical recovery. In this study, a universal testing machine equipped with a heating furnace was adopted to study the mechanical properties of a cotton towel in the temperature range of 25–250 °C under N2 atmosphere. The devolatilization behaviors of the cotton towel in the same temperature range were investigated using thermogravimetric-Fourier transform infrared (TG-FTIR) analysis. A reactive force field molecular dynamics (ReaxFF MD) model was employed to reveal the tensile deformation mechanism. Results showed that the cotton yarn tensile displacement increased with increasing temperature within 25–250 °C. Cotton degradation was onset at 150 °C, while at 200 °C, initiation of rapid CO2 emission was observed; sharp reductions in the mechanical strength observed at approximately 150 °C and 200 °C were mainly due to the degradation of hemicellulose and amorphous cellulose, respectively. CO2 was the primary volatile compound and its concentration correlated well with the mechanical strength. The ReaxFF MD simulation results indicated that the breaking strength of the cotton yarn depended mainly on the mechanical strength of the amorphous cellulose; the non-bonded interactions contributed more to the mechanical strength of the amorphous cellulose than the bonded interactions. The correlations between the mechanical strengths of the yarn bundle and towel, as well as the number of yarns they contained, have been proposed. © 2020 Elsevier B.V.