Pyrolysis and thermal behavior of unginned cotton piles: effects of mildewing and impurities

Cotton is an important natural material in the textile industry. A large number of unginned cotton piles in the ginning plant cause the frequent fire accidents every year. There are not only cottonseeds and cotton leaves but also those mildewing samples in unginned cotton piles. In this work, series of TGA, DSC, and SEM tests were conducted to analyze the thermal characteristics of typical samples in the unginned cotton piles. The results show that cotton mildewing causes the decrease of the strong pyrolysis temperature and the lower heat absorption at the early stage of pyrolysis. In addition, the activation energy of mildewed cotton in air atmosphere is significantly smaller than that of normal one. Cotton could be more dangerous in fire after mildewing. The SEM micrographs show that the morphological structure of cotton fibers is damaged obviously after mildewing. Additionally, compared with cotton, the endotherm of cotton leaves and cottonseeds are smaller in initial pyrolysis stage in N2 atmosphere and smaller activation energy in air atmosphere. Therefore, compared with ginned cotton, the fire hazard of unginned cotton would be higher. The thermal data of the mildewed cotton and impurities would be important to evaluate the fire hazard of unginned cotton piles and the design of fire protection system.