Study of cellulose structure and its relation to reactivity

Information is presented to show that the total volume of micropores in acetic acid swollen fibers correlates closely with acetylation reactivity. Pore size distribution measurements indicate that the pores with diameters of 25–75 Å may be particularly influential for promoting reactivity since fibers which perform well in acetylation processing have a characteristically high volume of pores in this size range. Internal surface area also correlates with acetylation reactivity if allowances are made for the large fraction of surface area which is associated with pores that are too small for reagent penetration. This lower limit is calculated to be 20–25 Å. Based on estimates of void spaces within and between the cellulose structural building units, acetylation of acetic acid swollen fibers should occur on the external surfaces of the elementary fibrils, the microfibrils and the lamellae as well as on the internal surfaces of the microfibrils and the lamellae. The overall effect of cellulose structure on reactivity seems to be the control of the inward flow of reagents to reaction surfaces but not the outward transport of reaction products. Internal void volume may function to accommodate reaction products as they swell inwardly and thus provide a means for allowing the reaction to go to completion. The relationship between cellulose structure and reactivity can be extended to chemical reactions other than acetylation.