Preparation And Application Of Multi-scale Cellulose Nanospheres Powder

As environmental protection and sustainable development gain increasing global attention,cellulose nanomaterials from renewable natural resources have attracted significant interest in both academia and industry.Cellulose nanospheres（CNS）,a novel type of cellulose nanomaterial,can be derived from natural cellulose using methods akin to those for rod-shaped cellulose nanocrystals or by processing regenerated cellulose and fibroin cellulose.Early-stage CNS research faces several challenges,such as determining the influence of preparation methods on structure and morphology,addressing high energy consumption and complex preparation steps,understanding the formation mechanism,and identifying potential applications and advantages.This study addresses these challenges by comparing the structural and morphological characteristics of CNS obtained through inorganic acid hydrolysis and various preparation routes,selecting phosphoric acid hydrolysis as the preferred method for producing powdered CNS.The investigation also examines the impact of hydrolysis duration on structural properties,explores the formation mechanism of CNS.Lastly,considering the advantages of CNS powder in promoting crystallization,enhancing the matrix,and facilitating dispersion,the preliminary applications of CNS in cellulose regeneration films and cellulose derivative hydrogel films were examined.The main research contents of this study are as follows:1.Short cotton linter pulp was used as the raw material for preparing CNS through different pretreatment methods,utilizing both sulfuric acid hydrolysis and phosphoric acid hydrolysis.Two preparation processes were ultimately established:CNSS was prepared by ultrasonic-assisted hydrolysis with 64 wt%H₂SO₄ at 45°C for 3.5 h,while CNSP was prepared by water bath hydrolysis with 85%H₃PO₄ at 50°C for 10 h.The particle size of CNSS ranged between 25-45 nm,with an average size of 34 nm,whereas CNSP exhibited a particle size range of 350-500 nm and an average size of 442 nm.The two types of CNS displayed distinct crystal structures;CNSS had a cellulose I polymorph,with a crystallinity of 91%,while CNSP exhibited a cellulose II polymorph,with a crystallinity of 69%.The presence of phosphate groups on the CNSP surface endowed it with higher thermal stability compared to CNSS,which bore sulfate groups.Additionally,CNSP demonstrated superior powder properties compared to CNSS.2.By adjusting the phosphoric acid hydrolysis reaction time between 4 and 11 hours,we successfully obtained CNS powders with yields ranging from 65-82%,varying sizes（530 nm-1.3μm）and crystallinities（69-75%）.The thermal stability of CNS produced through phosphoric acid hydrolysis in a nitrogen environment decreased with increasing hydrolysis time.Dispersion tests confirmed the excellent redispersibility of the CNS powder in DMSO.Additionally,we observed that the molecular weight of the samples rapidly decreased with prolonged hydrolysis time before reaching a constant value.Considering that the crystal structure of CNS remained as cellulose II and did not change with the acid hydrolysis time,we propose a cooperative mechanism for CNS assembly involving dissolution-regeneration and acid degradation.3.The application of CNS powder as nano-fillers in cellulose regenerated membranes and cellulose derivative hydrogel membranes was explored In the CNS/cellulose composite regeneration film system,the addition of CNS promoted the crystallization of cellulose molecular chains during regeneration,increasing the crystallinity of cellulose composite regeneration films,with the crystallinity rising as the CNS content increased.The enhanced crystallinity resulted in improved mechanical properties of the regenerated cellulose films,with the tensile strength increasing from 9.25 MPa to a maximum of 51.25 MPa.Meanwhile,the addition of CNS maintained the transparency of regenerated cellulose films at over 75%.In the CNS/carboxymethyl cellulose（CMC）hydrogel composite film system,the incorporation of CNS was speculated to increase the crosslinking bond strength of CMC according to FTIR results.Due to the hydrophilicity of CNS,the water absorption capacity of the hydrogel was enhanced,and when the CNS content reached 5 wt%,the hydrogel composite film achieved its maximum swelling effect,with a swelling ratio exceeding1400%.Compared to pure CMC hydrogel films,the addition of CNS increased the elastic modulus and tensile strength of the hydrogel films,displaying the highest elastic modulus（4.57 GPa）and tensile strength（47.80 MPa）when the CNS content reached 5 wt%.