Changes of lignin structure of poplar wood chips in autohydrolysis pretreatment and bleachability of chemi-thermomechanical pulp

In this work, poplar wood chips (PWCs) were subjected to autohydrolysis pretreatment with different levels of intensity, and the autohydrolyzed PWCs were used to make chemi-thermomechanical pulp (CTMP). The changes of the lignin structure of PWCs and the bleachability of the CTMP with autohydrolyzed PWCs as raw materials were both investigated. The results showed that the lignin structure changed to some extent in both CTMP pulping and the following bleaching process. The contents of conjugated carbonyl and quinone groups in the lignin structure were negatively correlated with the CTMP bleachability. Compared to the quinone groups, the conjugated carbonyl groups had a much greater impact on the bleachability. The present work would play a vital role for the application of autohydrolysis to the poplar CTMP pulping and the subsequent bleaching processes.