Internal modification of novolac phenolic resin with polyethylene glycol

Polyethylene glycol 400 (PEG) has been used as a reactive plasticizer for commercial novolac phenolic resin (NR). The blends of oligomeric NR and PEG in mass ratios of 90:10, 80:20, and 70:30 were prepared and studied for their thermal properties by differential scanning calorimetry. The uncured blends have a single glass transition temperature (Tg), which is significantly lower than that of the neat oligomeric resin. It has been found that PEG facilitates cross-linking reactions in the resin at the content of 10 wt%. The results of infrared analysis of cured NR-PEG samples revealed a strong physicochemical interaction between the PEG and the NR, as well as an incorporation of the additive into the cross-linked polymer matrix. Polymer composites based on glass fabric (GF) and PEG-modified NR were prepared and studied for their viscoelastic properties. According to results of dynamic mechanical analysis, the introduction of 10% PEG significantly improves the storage modulus (E´) of the GF/NR composite (by 30%), whereas GF/NR-PEG (20%) composite shows viscoelastic behavior similar to that of neat NR. Further increasing the PEG content to 30% led to a significant drop in the storage modulus, indicating the presence of regions with low cross-link density in the material. Overall, the results of this study indicate that PEG is an efficient toughening agent for novolac phenolic resin, which can significantly improve the mechanical properties of cured resin in a wide temperature range.