| Popis: |
The reactions of cellulose with phosphoric acid under different temperature conditions were investigated to prepare a new class of cellulose excipients which have controlled, low degrees of crystallinity and reduced levels of polymerization. The results showed the depolymerization of cellulose by phosphoric acid to be a first order reaction with rate constant values corresponding to 4.79 × 10 −3 and 0.314 per hour at 25 and 55°C (after 1 h pretreatment at 22°C), respectively. Products prepared from reactions at 25, 30, 35, 45, and 55°C for 216, 120, 72, 15, and 4.5 h, respectively, exhibited degrees of polymerization values ranging from 64 to 88. The degree of crystallinity of the products prepared at 25, 30, 35, and 45°C ranged from 32 to 45%, whereas that of the product isolated at 55°C was 80%. The activation energy, calculated using the Arrhenius relationship, was 25.3 kcal/mol. A temperature sequencing method, wherein the cellulose is treated at room temperature (22–25°C) for 1–14 h, and then at 50°C for 2–10.5 h, resulted in the preparation of low crystalline cellulose materials with degree of crystallinity and degree of polymerization values ranging between 19–43% and 45–138, respectively. |
Full Text from ScienceDirect