The current work presents the study
of the toughening effect of
in situ polymerization modification process (In-MP) and prepolymerization
modification process (Pre-MP) on triethylene glycol (TEG)-modified
phenolic foams (PFs). TEG in situ polymerization-modified phenolic
resin (T-In-PR) and TEG prepolymerization-modified phenolic resin
(T-Pre-PR) with different molecular structures have been synthesized
by two processes using TEG as a modifier. The comparison of the molecular
structure and properties of the resins shows that the molecular weight
distribution of T-Pre-PR is uniform and its basic properties of resin
are better than T-In-PR. The number of benzene ring linkage bridges
in the T-Pre-PR structure increases from three to four, which can
improve the toughness while stabilizing the intermolecular connection
strength. The TEG-modified PFs prepared with TEG-modified phenolic
resins exhibit excellent toughness. The fracture displacement of T-Pre-PF
was 85.13% higher than those of ordinary PFs, and the pulverization
rate was 55.85% lower than those of ordinary PFs. Compared with T-In-PF,
the cell shapes of T-Pre-PF were uniform polygonal structures and
formed a stable honeycomb-like structure. The cell size distribution
of T-Pre-PF was more concentrated than those of T-In-PF and ordinary
PFs, and the level of damage of cell wall was low. The maximum bending
strength of T-Pre-PF was 0.263 MPa, and the maximum compression strength
was 0.160 MPa, which were higher than those of T-In-PF. The findings
demonstrate that Pre-MP is more suitable for the preparation of PFs
with internal toughening modification by TEG than In-MP.