THE IMPACT OF INITIAL PARTICLE-SIZE ON THE FRAGMENTATION OF CELLULOSE BY THE CELLULASES OF THERMOMONOSPORA-FUSCA

This paper explores the impact of initial particle size on the rate and extent of cellulose fragmentation. Microcrystalline cellulose Avicel PH 102 was sieved with a set of US standard sieves to obtain six monodisperse, particle size ranges. Three of these size ranges (74-mu-m < x < 105-mu-m, 46-mu-m < x < 63-mu-m, 38-mu-m < x < 46-mu-m) were made into 5% suspensions and hydrolyzed with 0.1 and 0.25 mg ml-1 Thermomonospora fusca crude cellulase. Samples were removed very 20 min during hydrolysis and analyzed for reducing sugar, free enzyme and particle size distribution. The results showed that initial particle size had no impact on the rate and extent of reducing sugar production or on enzyme binding. However, the rate and extent of cellulose fragmentation was strongly affected by initial particle size. The change in the volume fraction distribution with time was also influenced by initial particle size, with larger particles giving rise to a bimodal distribution and smaller particles to a skewed distribution. The changes in the volume fraction distributions with time suggested fragmentation to be the dominant reaction for larger particles and erosion to be the dominant reaction for smaller particles. These experiments show that fragmentation is not the rate limiting step in the enzymatic hydrolysis of cellulose.