THE EFFECT OF INITIAL PORE VOLUME AND LIGNIN CONTENT ON THE ENZYMATIC-HYDROLYSIS OF SOFTWOODS

Four Douglas-fir pulps, a refiner mechanical pulp (RMP) salphonated RM P, delignified RMP and a kraft pulp were used to determine whether the lignin content and initial pore volume affected cellulase adsorption and substrate hydrolysis. When compared on the basis of lignin content , it was apparent from the cellulase treatment of the sulphonated RMP that the proportion of lignin did not affect enzyme adsorption when th e fibres were sufficiently swollen. However it was observed that the i nitial adsorption of cellulase does not always translate to fast and c omplete hydrolysis. Pore volume data revealed that although modificati on of lignin resulted in a dramatically increased fibre saturation poi nt the median pore width was not increased accordingly. In contrast, t he delignified RMP had a higher median pore width and was hydrolyzed m ore completely, suggesting that steric hindrance from the residual lig nin may be the rate limiting characteristic in this situation. Hydroly sis of the kraft pulp indicated that the larger average particle size of this substrate might have been an inhibiting factor, since it was h ydrolyzed more slowly than the delignified RMP despite having a higher median pore width and lower lignin content. (C) 1998 Elsevier Science Ltd. All rights reserved.