Phosphorylation of Cellulose in the Presence of Urea. Mechanism of Reaction and Reagent Impact.

Abstract

A mechanism of cellulose phosphorylation in presence of urea is proposed. This model is correlated with the thermal stability of phosphorylating reactive mixture and the yield of phosphorylation for two different reagents: phosphoric acid and lauryl phosphate monoester. Three main successive reactions are involved in the formation of cellulose phosphate: (1) generation of ammonia by urea decomposition, (2) formation of phosphoramidate as intermediate reactive due to the reaction of ammonia with phosphate species, and (3) grafting the phosphate moiety to substrate due to the transfer of phosphate from phosphoramidate to cellulose. The proposed in vitro mechanism is supported by similar phosphorylation processes observed in some biochemical reactions. The limiting factor in the phosphorylation of cellulose is the formation of phosphoramidate intermediate.

The Strength and Fire Properties of Paper Sheets Made of Phosphorylated Cellulose Fibers

“…In other words, including hydrophilic phosphate groups in the cellulose chain acted as a refining or beating process and enhanced internal fibrillation between fibers. These processes are known from the literature, and the creation of P-O-C bonding on the cellulose surface was reported in the following reports [ 2 , 4 , 5 , 13 , 20 , 21 ]. However, the problem of leaching urea and cellulose degradation at a high phosphorylation degree cannot be ignored in the case of some particular applications [ 20 , 22 ].…”

“…They have also pointed out that phosphorylation productivity is tightly related to cellulose concentration (1 wt%, 2 wt%, and 5 wt%), the amount of urea, pH, and temperature. The viable proposed mechanism in the research of Belosinschi et al [ 13 ] was based on applying reagents consisting of phosphoric acid and lauryl phosphate to attain the thermal stability of phosphorylated cellulose. This procedure was introduced as low-fiber degradation, low energy expenditure, and low use of chemical agents, with good efficacy of phosphorylated fibers.…”