Esterification of viscose fibres with orthophosphoric acid and study of their physicochemical and mechanical properties

Abstract

Esterification of viscose fibres with aqueous solutions of orthophosphoric acid and urea at different ratios of components was investigated. It was shown that in phosphorylation of cellulose with these solutions, onesubstituted cellulose phosphates are formed and a side process of formation of cellulose carbamates takes place together with accumulation of phosphate groups. A decrease was found in the mechanical strength of the phosphorylated cellulose preparations and the degree was a function of the concentration of orthophosphoric acid and urea as the phosphorylating solution. Phosphorus-containing viscose fibres (up to 0.5 mmole/g of phosphate groups) obtained in solutions of orthophosphoric acid and urea with a 0.25-0.63 and 3.33-4.17 M concentration have the most satisfactory mechanical properties and stability in phosphate buffer with pH 7.5.Phosphorylation of cellulose in an aqueous solution of orthophosphoric acid in the presence of urea is the simplest and most industrially acceptable method of giving it additional biological activity [1]. Cellulose phosphate is biocompatible with human tissues, is resorbed with no inflammatory reaction, and neither it nor the products of biodegradation have any toxic effect on the body. The physicochemical properties of highly substituted cellulose phosphate are characterized relatively completely in the literature [1], which served as the basis for using it as a sorbent for stabilization of donor blood. At the same time, there is almost no information on the use of phosphorylated cellulose for obtaining resorbable surgical sutures. Moreover, the following are also necessary for successfully using cellulose phosphate in surgery in addition to these properties: sufficiently high dry and wet mechanical strength and knot strength; a rate of reduction in strength commensurate with wound healing times.The lack of a detailed study of the effect of the conditions of fabricating phosphorus-containing cellulose fibres on their physicomechanical properties and the shortage of quality resorbable materials make the study of esterification of cellulose by orthophosphoric acid pressing.We investigated the effect of the conditions of phosphorylation of viscose cord fibres on the physicochemical and mechanical properties of the cellulose phosphates obtained. Viscose cord fibre (Khimvolokno IA, Svetlogorsk) with a linear density of 184 tex was used as the initial material.Esterification of viscose fibre with orthophosphoric acid was conducted with the method in [1], improved to attain the maximum mechanical strength. Viscose fibres were placed in phosphorylating mixtures of different composition heated to 353±2 K (the bath ratio varied from 1:5 to 1:20 g/ml) and held in them for 30 min. The excess solution was then wrung out of the samples to 100% weight gain, dried to the air-dried state, and treated with heat in a thermostat at 418±2 K for 1

A highly efficient chemical approach to producing green phosphorylated cellulosic macromolecules

“…In fact, in addition to the high phosphate content, the length of the phosphorylated bers is the greatest and the level of nes is lower (Table 2). The quantication of the amount of graed phosphorus as a function of the amount of urea used clearly shows that a large proportion of the cellulosic bers have been phosphorylated with a high percentage compared to the previous works, which do not exceed 13% of P. [20][21][22]36,[42][43][44][45][46][47] Moreover, we carried out several tests by varying the concentration of phosphoric acid, considering the degradation effects of cellulosic chains, which can be generated by the release of acid at high temperatures. 3 It was found that the content of the P element in the phosphorylated samples (PKP1 and PKP4) decreased sharply from 14.87 to 11.05% in an acid concentration of 2 and 3 M, respectively.…”

Heat Soaking Pretreatment for Greener Production of Phosphorylated Cellulose Nanofibrils with Higher Charge Density

“…The increase in urea concentration had active impacts on the reaction in terms of enhancing charge when heat-treating for the same time (90 min). Similar studies have reported to increase charge of the phosphorylated cellulose fibers by increasing urea usage. , …”

“…However, the charge density of P-H80-25 showed no significant difference compared to that of P80-25, which probably indicates that a longer heat-treatment time (e.g., 90 min) would be required to sufficiently implement the active effects of urea. In addition to heat-driven fiber swelling in the presence of urea, urea can act as a catalyst to promote the reaction . Decomposition of urea in the curing stage with release of ammonia causes accumulation of ammonium phosphate in the reaction system, which is an active phosphorylating agent .…”

“…Similar studies have reported to increase charge of the phosphorylated cellulose fibers by increasing urea usage. 11,31 However, the charge density of P-H80-25 showed no significant difference compared to that of P80-25, which probably indicates that a longer heat-treatment time (e.g., 90 min) would be required to sufficiently implement the active effects of urea. In addition to heat-driven fiber swelling in the presence of urea, urea can act as a catalyst to promote the reaction.…”

“…In addition to heat-driven fiber swelling in the presence of urea, urea can act as a catalyst to promote the reaction. 31 Decomposition of urea in the curing stage with release of ammonia causes accumulation of ammonium phosphate in the reaction system, which is an active phosphorylating agent. 31 Therefore, another probable explanation is that an increase in urea concentration contributes to catalysis of the phosphorylation and hence larger amounts of the phosphate groups onto cellulose fibers.…”