Phosphorylated cellulose nanofibrils (PCNFs) made from woody biomass have aroused immense interest because of their promising applications in various fields, including flame retardancy, adsorption, and separation. However, traditional production methods show high chemical and energy consumption, while the obtained PCNFs have lower charge density. In this study, PCNFs with higher charge density (2.09−3.79 mmol•g −1 ) were produced by tuning heat soaking pretreatment of cellulose fibers in phosphate salt and urea solutions, followed by curing and mechanical fibrillation. An optimized pretreatment can be achieved by heat-assisted soaking at 80 °C for 25 min, which was effective to produce PCNFs with greater performance (e.g., higher charge and crystallinity) compared to those of traditional methods. Furthermore, the optimized route is more sustainable with a substantial decrease in resource consumption including chemicals (33.6%), water (55.8%), and energy (65.3%), and the production costs would be saved by 62.0% in comparison with the traditional route. Such a sustainable and economic process has great potential in the industrial production of PCNFs.

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