Molecular weight decrease in the early pyrolysis of crystalline and amorphous cellulose

Abstract

Samples of ordinary “ash‐free” cellulose papers and similar samples decrystallized by swelling in liquid ammonia were pyrolyzed in vacuo to a weight loss ranging from <0.1% to nearly 20%. The samples were then nitrated and their molecular weight distributions determined by gel permeation chromatography. When weight loss reached 1%, both the ordinary and the ammonia‐swelled celluloses showed a large drop in average degree of polymerization (D.P.). However, the ordinary cellulose showed this sharp drop long before there was any measurable weight loss; the ammonia‐swelled cellulose changed D.P. only gradually in the early stages. Further, x‐ray diffraction measurements showed that by the time the D.P. of the ammonia‐swelled cellulose had dropped appreciably, the material had developed a significant crystalline pattern. These results support the suggestion that initial rupture of the cellulose molecule occurs at strain points at the crystalline–amorphous boundaries.