Effects of multi-strain pretreatment on thermochemical properties and component structure of paulownia

This study aims to delve into the impact of long-term multi-strain pretreatment on the thermochemical characteristics of paulownia. The nine-month experimental analysis reveals that the fourth month marks a crucial turning point in the pretreatment process. From Stage I (0–4 months) to Stage II (4–9 months), the pyrolysis temperature range continuously narrows, reducing a maximum of 31.47%. The char yield initially increased by 10.25% and then decreased by 6.95%. Calorific value showed a slow initial decline of 3.98–4.08%, followed by a subsequent increase of 7.66%. The ignition point continued to rise by 5.61%− 5.78%. The compositional experimental results indicate that in the first stage, strain primarily depolymerize the high-polymer lignin, resulting in a decrease in calorific value. The increase in the relative content of syringyl lignin (S) contributes to the rise in char yield. In Stage II, the S units are converted into guaiacyl lignin (G), which has a lower char yield, while the exposed hemicellulose and cellulose undergo severe erosion. The relative content of lignin and enzymatic products with stubborn structures increases, leading to an increase in calorific value. However, the higher breaking temperature of bonds in these structures results in a continuous increase in the ignition point. This study clearly establishes that after nine months of pretreatment, the paulownia exhibits characteristics of rapid pyrolysis, high calorific value and ignition point, which provides a reliable basis for uncovering the potential reuses of paulownia. •Various fungi and bacteria were used to pretreat paulownia.•The multi-strain pretreatment time was up to nine months.•The fourth month marks a crucial turning point in the pretreatment process.•After pretreatment, the pyrolysis temperature range was shortened by 31.47%.•Calorific value decreased in Stage I and increased in Stage II.