THE INFLUENCE OF MECHANOCHEMICAL ACTION ON THE PHOTOSENSITIVITY OF REFINER PULPS

The effect of mechanical refining on the formation of photoactive lign in chromophores in black spruce wood chips was investigated with a lab oratory-scale Sprout-Bauer 12'' disc refiner. The effect of the degree of refining on the generation of chromophores was evaluated. Radical scavengers and antioxidants were used to impregnate pulps before and d uring refining, in an attempt to verify the radical mechanism previous ly proposed for the mechanochemical transformations of lignin structur es. Electron spin resonance (ESR) spectrometry did not provide evidenc e for the generation of free radicals during mechanical pulping. By mo nitoring the degree of photoyellowing using reflectance spectroscopy, the amount of chromophores in the pulps was found to be independent of the extent of the mechanical defibration. The addition of radical sca vengers during the refining process did not lead to brighter pulps or to a significant reduction in photoyellowing of the pulps. These resul ts cast doubt on the mechanochemical formation of photoactive lignin c hromophores during mechanical pulping.