Preparation,Properties And Application Of Bamboo-Based Phosphorylation Cellulose Nanofibrils

With the rapid development of high-value application of biomass materials,cellulose nanofibrils(CNFs)have a broad development prospect due to its renewable,completely biodegradability,light weight,high strength and easy chemical modification.In a general way,CNFs are prepared by mechanical exfoliation method with high energy consumption.In order to reduce the energy consumption of mechanical method,cellulose materials are usually pretreated first.Common methods include 2,2,6,6-tetramethylpiperidine oxide(TEMPO)method and enzyme treatment method.However,the reagents used in the TEMPO oxidation process have more side effects,while enzyme treatment had lower yield,which greatly limit the further development and application of CNFs.In this paper,phosphorylation,a novel and environmentally friendly chemical pretreatment method,combined with mechanical fibrillation by ultra-fine grinder to prepare phosphorylated cellulose nanofibrils(PCNFs)using bamboo-based cellulose as raw material.The effects of preparation technology and lignin content on the properties of PCNFs were investigated.Then,PCNFs were prepared into films and aerogels with excellent mechanical properties and flame retardant properties by solvent casting and freeze drying,respectively.And the relevant performance indexes were investigated.The main research results are as follows:(1)Combine orthogonal experiment combined with single factor experiment,the best process for preparing PCNFs was determined based on the transmittance and rheological properties.The curing time was 20-30 min,the phosphate concentration was 2 wt%,and the grinding spacing was-150?m.(2)In order to study the effect of lignin on the properties of PCNF materials,bamboo-based PCNFs with different lignin content were prepared and its basic properties were characterized.The results showed that with the increase of lignin content,the diameter of the nanofibrils increased,and the rheological viscosity and modulus of the suspension decreased,while the thermal stability and the rate of residual char increased.(3)PCNF films were prepared by solvent casting method.The internal microstructure,tensile properties and combustion properties of the films were characterized,and the effects of phosphorus containing groups and lignin on the mechanical and flame retardant properties of the films and the mechanism of action were analyzed and discussed.The results showed that B-PCNF film indicated high strength and toughness with tensile strength of 115.9 MPa and elongation at break of 53.1%;B_HL-PCNF film has excellent flame retardancy and thermal stability under the synergistic effect of lignin and phosphorus containing groups.The heat release capacity was as low as 22.8 J/g·K,and the total heat release was only 1.3 k J/g.(4)B_HL-PCNF aerogel was prepared by freeze-drying method.The internal microstructure,compression properties and combustion properties of the aerogel were characterized,and the effects of adding cellulose nanocrystals(CNC)and boride on the mechanical properties and flame retardant properties of aerogels were analyzed and discussed,respectively.The results showed that the addition of CNC improved the mechanical properties of aerogels,while decreased the flame retardant properties.The mixed addition of borax and boric acid made aerogel possess remarkable resilience and flame retardance.More importantly,boron/phosphorus/lignin made the limit oxygen index value of cellulose aerogel as high as 44.1%under the synergistic effect.According to the research and discussion,the performance optimization of PCNF functional materials was successfully realized through the regulation of lignin content and the addition of boride,greatly expanded the application of cellulose materials in the field of films,such as degradable packaging materials.It also provided a new idea for the preparation of cheap and efficient flame retardant and heat insulation materials instead of silica aerogel.