Difference Between Novolac and Resole

Novolac and resole are the products of phenol and formaldehyde, and are known as phenolic resin . The differences between novolac and resole are as follows  

Novolac is produced using excess phenol and an acid or metal salt catalyst, whereas resole is produced using excess formaldehyde and a basic catalyst. 

Novolacs are mostly supplied in the solid form, whereas resoles are mostly supplied as a solution (using water or alcohol as a solvent). 

Novolac is not self-curing it requires an extra curing agent, whereas resole is self-curable without an additional catalyst. 

Novolac has a long shelf-life, whereas resole has a limited shelf life ( 1 year). 

---

The work on nanocomposites utilizing novolacs and resols can be considered preliminary and promising. The very subtle differences between novolacs and resols appear to have the potential to contribute to significantly different nanocomposite systems. The distinct separation of the silicate layers may provide the basis for the properties of nanocomposites prepared as novolacs or resols. 

Phenolic novolacs are produced by condensation reactions (Step polymerization), and a typical schematic is given below. It is clear that one of the major differences between novolacs and resoles is that, in their initially advanced stage, novolacs do not contain the methylol groups, which are so essential to the thermal cure of phenolic resole resins and adhesives. 

The RSST charts also point out another important difference between resoles and novolacs. Fig. 2 shows that resole reactions take place in two distinct stages with initiation temperatures at about 40-50°C and 100-140°C, respectively. 

---