LAUSR

Using a combination of characterization techniques, we have been able to establish two types of relaxation mechanisms when moisture is introduced into typically cross-linked phenolic resins. The inherent rigidity of this class of polymer originates from the extensive intra- and intermolecular hydrogen bonding. To raise structural stability at elevated temperatures, inter methylene bridges between the aromatic units (chemical cross-links) need to be formed usually with specific cross-linking agents such as hexamethylenetetramine. Given the rigidity of the polymer, segmental mobility decreases quickly as cross-linking reaction proceeds, thus limiting the degree of cross-linking to be well short of the theoretical values. This leaves a significant fraction of unreacted and/or partially reacted components in the phenolic network. In the presence of moisture, the disruption of hydrogen bonding provides one mechanism for cross-linked phenolic resins to relax. Our analysis showed that a second relaxation mechani...