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

Abstract

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.