Phosphorylation of cellulose hydroxy groups is an emerging method of introducing anionic groups to cellulose fibers to prepare high-performance and functional biodegradable materials for cutting-edge applications. However, it still lacks in-depth and systematic research. In this work, a bleached softwood kraft pulp was first phosphorylated with (NH4)2HPO4 and urea at 150 Celsius degrees for 0-40 min, and the structures and properties of the phosphorylated pulps were systematically investigated in terms of reaction time and the amount of (NH4)2HPO4 added. The phosphorous and weak acid group contents, and weight recovery ratio increased with increasing reaction time, while the pulp maintained its fibrous morphology and cellulose I crystal structure. Almost all the ammonium phosphate groups in the phosphorylated pulp behaved as weak acids and only phosphate ester groups (neither carboxy nor carbamate groups) were introduced into the pulp in present study. A longer reaction time or a greater amount of (NH4)2HPO4 added resulted in lower water swelling behavior, indicating that some intrafiber and/or interfiber crosslinking occurred in the pulp. Furthermore, mechanically ductile, flame-retardant cellulose films with tunable optical properties were prepared by simple mechanical disintegration of phosphorylated cellulose (PhC) fibers and successive filtration/pressing/drying. When mechanical disintegration conditions were optimized, the resultant PhC films exhibited an average density, tensile strength, Young’s modulus, tensile toughness, and folding resistance of 1.4 g/cm3, 150 MPa, 8.5 GPa, 8.2 MJ/m3, and 4580 times, respectively. The PhC film hazes were widely controllable from 9% to 91%, while they maintained high light transmittances (&gt;90%) at a 550-nm wavelength. Finally, the PhC films were used for light management of light-emitting diodes and effectively improved the luminescence uniformity of the devices.

Phosphorylated pulp fibers prepared under various conditions, and the preparation, properties and application of phosphorylated cellulose films

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