Solvent- and formaldehyde-free phenolic resin derived from salicyl alcohol

Phenolic resins (PRs) have a broad application foundation in various fields owing to their excellent mechanical properties, thermal resistance, and chemical stability. However, as products of fossil resources, reducing their reliance on such resources is a key developmental goal for PRs. Salicyl alcohol, also known as 2-hydroxybenzyl alcohol (HBA), can be obtained from natural sources and is a high-quality raw material for synthesizing high-performance PRs without the addition of phenol or formaldehyde. In this study, polymerized HBA (PHBA) was synthesized via solvent- and catalyst-free bulk polymerization. The cured PHBA resins showed good thermal stability (thermal decomposition temperature: 325 °C, char yield: 60.3%) along with good mechanical properties (tensile and bending strengths of 30.1 and 147 MPa, respectively). By controlling the polymerization temperature and time, the viscosity of PHBA could be adjusted to suit different solvent-free processes, such as resin transfer molding (RTM) and the hot-melt film process, broadening the applicability of this type of PR. Furthermore, PHBA could be reinforced with not only natural materials, such as poplar wood boards, jute fibers, and Moso bamboo powder but also carbon fibers using solvent-free processes. These composites possessed excellent mechanical properties, and no formaldehyde was detected, indicating that PHBA has potential for preparing composites as aerospace and building materials. Overall, this study introduces a high-performance, environmentally friendly PR with excellent application prospects.