In-depth understanding on the early stage of phenolic resin thermal pyrolysis through ReaxFF-molecular dynamics simulation

Abstract

• The early pyrolysis of PR is clarified from the view of cleavage reaction. • The cleavage reaction of PR occurs beside (CR b ) and on (CR o ) the backbone. • The H• from CR b is the initial species, leading to the formation of H 2 and H 2 O. • The decreasing char yield is caused by the loss of the terminal phenol from CR o . Acquiring deep understanding of the pyrolysis process of phenolic resin (PR) and its mechanism is of pivotal importance to develop new applications. Herein, novolac resin (NR) is used as the structural model to investigate the pyrolysis mechanism by carrying out a series of reactive force field molecular dynamics simulations. The structural evolution of NR and the formation process of small molecular species at nine different kinds of NR analogous models are investigated. The results show that the early pyrolysis process of NR involves mainly two aspects: the cleavage reactions beside backbone (CR b ) and on backbone (CR o ). The hydrogen radical produced from the cleavage of the methylene C—H bond, which belong to the CR b process, is the initial species detected during the pyrolysis process, and leads to the formation of H 2 O and H 2 . Besides, the C—C bond cleavage of the methylene bridge is predominant in the CR o process, which takes place with almost equal probability. It mainly results in the formation of phenols, diphenols, polyphenols, and cross-linked structures. The volatilization of the phenol compounds stripped from the terminal groups is a critical process to reduce the char yield of the PR. Moreover, the main small-molecule species detected during the early pyrolysis of NR are H 2 O, H 2, and CO, and the higher energy is necessary to generate CO than H 2 O and H 2 . This work deepens the understanding of the PR pyrolysis mechanism and provides valuable insights to develop its applications.