Effect of polystyrene addition on the monomer recycling of phenol novolac

The liquid-phase cracking of two different types of phenol novolacs, the precursors to commonly used crosslinked resins, was studied using a 200-ml autoclave at 430-450 degreesC under an initial nitrogen pressure of 2.0 MPa. Both phenol novolacs gave almost 100 wt.% conversion with a hydrogen-donor solvent (tetralin), and about 85 wt.% yield of oil product, including 43-76 wt.% of monomer compounds such as phenol and cresols. Phenol novolac containing >90 mol% of ortho-ortho and ortho-para bonds could be cracked in a non-hydrogen-donor solvent (decalin) with formation of only a small amount of coke. However, novolac containing > 26 mol % of para-para bonds could not be degraded in decalin and produced a large amount of coke. When polystyrene was added to the latter novolac, an enhanced conversion of 51.1 and a 43.6 wt.% yield of distillable oil were obtained at 440 degreesC without a large amount of coke formation. Hydrogen gas at pressures > 5 MPa also enhanced cracking reactivity. (C) 2002 Elsevier Science Ltd. All rights reserved.