Formaldehyde-Free and Phenol-Free Non-toxic Phenolic Resins with High Thermostability

Today, phenolic resins are polymers still widely used, with a global production of about 12 million tons/per year. However, their syntheses need the use of formaldehyde and phenol, which are highly toxic. Notably, formaldehyde is carcinogenic. Therefore, the reagents used for the synthesis of phenolic resins must be substituted by non-toxic compounds to preserve the health of users. These resins are extensively used as a char precursor for composite-based thermal protection systems. For thermostability, aromatic structures are preferred, so this work proposes to study the substitution of formaldehyde by aromatic aldehydes, as well as the substitution of phenol by less toxic phenolic analogues. The resin composition, chemistry, and reaction mechanisms of polymerization were deeply studied. The thermostability and thermomechanical properties were also investigated. It was possible to use terephthalaldehyde as formaldehyde replacement and 2-hydroxymethylphenol as phenol replacement to obtain resins without phenol or formaldehyde, with extremely interesting thermomechanical properties [temperature at 5% of mass loss (Td5%) = 390 °C, char yield = 62%, and Tα > 200 °C]. In addition, the synthesis of these resins remains easy to implement and upscale.