Phenolic Foams Toughened with Triethylene Glycol by In Situ Polymerization and Prepolymerization Processes

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.