Study On The Morphological Regulation Of Nanocellulose And Its Optical Haze Of Nanopaper And Rheological Properties Of Suspension

Cellulose nanopartical(CNP)includes nanocellulose filaments(CNF)and cellulose nanocrystal(CNC)extracted from plant fibers with unique physical and chemical properties.CNP has excellent film-forming properties.The transparency and haze of the prepared nanopaper are closely dependent on its size,morphology and other structures.In addition,the rheological properties of suspension systems are particularly important in industrial development.The rheological properties of cosmetic emulsions,food additives,industrial paints,and cleaning products depend on the morphology and size of the nanoparticles.At present,the prepared nanocellulose is mostly rod-shaped,and a few are spherical.The traditional preparation method still has disadvantages such as environmental pollution and low product yield.Few people have explored how to efficiently prepare cellulose nanoparticles with different morphologies and the performance of cellulose nanoparticles with different morphologies.The use of controlling the topography and size of CNF and CNC to control the optical properties of nanopaper still needs to be studied.And the change of nanoparticle morphology and size will also affect the rheological properties of its suspension system.Therefore,it is important to explore new methods for preparing CNPs with different sizes.In this paper,bleached bamboo pulp was used as the raw material to prepare CNF by enzymatic pretreatment combined with high-pressure homogenization,and CNC-1 and CNC-3 with different morphologies were prepared by acid hydrolysis/enzymatic hydrolysis;and then CNF was used as raw material under mild hydrolysis to prepare CNC-2 and CNC-4 with different sizes were prepared by acid hydrolysis/enzymatic hydrolysis.CNPs with different morphologies were prepared by vacuum suction filtration and solution casting method to produce nano paper with high transparency and adjustable haze;and inorganic salts NaCl,MgCl2,AlCl3,Na2CO3,Na3PO4 with different anion and cation strengths were added to study the rheological properties of nanocellulose particle suspensions with different morphologies.The conclusions obtained are as follow:1.Studies have shown that CNF is prepared from bleaching bamboo pulp fibers by enzyme pretreatment and high-temperature homogenization,and CNC-1 and CNC-3 are prepared by acid/enzymatic hydrolysis;CNC-2 and CNC-4 is prepared from CNF by acid/enzymatic hydrolysis,respectively.The obtained cellulose nanoparticles showed various morphologies,fibrous(CNF),short rod(CNC-1),rod(CNC-3),and spherical(CNC-2 and CNC-4).The yield of the CNF was 84%,and the yield of the CNC prepared by enzymatic hydrolysis using CNF as high as 76%,which showed good crystallinity and thermal stability.2.Cellulose nano-paper prepared using CNF has high transparency(89%at 600 nm)and high haze(77%).With the changes of the morphology of the cellulose nanoparticles CNF and CNC,the transparency of the nano-paper remained at a high level,and the haze decreased from 77%to 5%as the size decreased.And by mixing CNF and CNC in any continuous ratio to prepare nano-paper,the optical haze value can be accurately controlled.The morphology control of cellulose nanoparticles has realized the adjustment of its optical haze.3.The morphology and size of the nanoparticles affect the rheological properties of the suspension.CNF and CNC suspensions have a "shear thinning"behavior,and the viscosity reduce with decreasing size at high shear rate stages.Suspension concentration also affects its viscosity value.When the CNF suspension concentration is<0.25 wt%,the steady-state viscosity decreases with increasing shear rate.When the CNF suspension concentration is>0.25 wt%,the relationship about shear rate and viscosity is divided into three stages:viscosity reduction stage-viscosity stationary stage-viscosity reduction stage.When the concentration of CNC suspension is more than 0.25 wt%,its steady-state viscosity decreases continuously as the shear rate increases;when the concentration of CNC suspension is less than 0.25 wt%,its steady-state viscosity decreases as the shear rate increases,the viscosity value approaches that of pure water.Adding metal salts of different valence states to the nanocellulose suspension,with the increase of the amount of metal salts,the ionic strength increases,the electric double layer on the surface of the nanocellulose is destroyed,and the electrostatic repulsion weakens,which makes the nanocellulose suspension has the gelation.As the cation strength increases,the gelation becomes more and more obvious,the viscosity of the suspension increases,and the storage modulus and loss modulus also increase.In contrast,the increase in the strength of the anion is not very obvious for the gelation of the nanocellulose suspension.