Relationship Between Morphological And Rheological Properties Of Lignocellulose Micro/nanofibrils And Its Application In Emulsions

Lignocellulose as the most abundant natural biomass resource have attracts growing interest in many fields due to its renewability and biodegradability.Cellulose micro/nanofibrils produced from lignocellulose are candidates for development of Pickering emulsion because of its small size,nontoxicity and biocompatibility.Lignin is one of the most important components in the lignocellulose,which generally will be removed in advance by using chemical reagents before the preparation of cellulose micro/nanofibrils,resulting in environmental pollution.The emulsions stabilized by cellulose micro/nanofibrils containing lignin are more suited to the green production and application.At present,cellulose micro/nanofibrils is produced,stored and used mainly as suspensions.Therefore,the relationship between morphological properties and rheological properties of cellulose micro/nanofibrils was established,and the effect of morphological properties of cellulose micro/nanofibrils on its emulsifying capacity and stabilization mechanism in Pickering emulsion was studied.Subsequently,the influence of lignin content on the morphological properties of lignin-containing cellulose nanofibrils(LCNFs)in suspensions was studied with the aid of the relationship between morphological properties and rheological properties of cellulose micro/nanofibrils.Finally,the lignocellulose based-suspensions(LBS)containing lignin particles(LPs),microfibrils(MFs)and LCNFs was obtained from lignocellulose with high lignin content.Furthermore,its emulsifying capacity and stabilization mechanism were investigated.This work can offer practical guidance of micro/nano-lignocellulose on the preparation and application of Pickering emulsions.(1)The morphological changes during grinding treatments,the relationship between morphological properties and rheological properties of cellulose micro/nanofibrils were systemic studied.The morphological changes of cellulose were the process of “unfibrillated cellulose(A10)-incompletely nanofibrillated cellulose(A20)-completely nanofibrillated cellulose(A40)” with increasing the mechanical fibrillation.The size of cellulose was decreased and the aspect ratio of cellulose was increased with increasing grinding treatments.Cellulose with different morphologies showed the different rheological properties.A10 had weak fiber network structure,thus exhibiting low viscosity,weak gel-like behavior,infirm anti-deformation capacity and poor dynamic stability of suspension.A40 had a strong capacity of entanglement and created an entangled fiber network structure,so its suspension exhibited high viscosity,strong elastic gel-like behavior,large apparent yield stress and small creep compliance,suggesting that the cellulosic fiber suspension obtained by more mechanical fibrillation had excellent anti-deformation capacity and dynamic stability.(2)Subsequently,cellulose micro/nanofibrils were used to stabilize the Pickering emulsion to study the effect of morphological properties on emulsifying capacity and stabilization mechanism.The unfibrillated fibers tended to obstruct the oil droplets from coalescence via depletion flocculation,which exhibited weak interfacial adsorption.The partially fibrillated fibers formed a sparse covering layer,and the residual large fiber connected the adjacent droplets forming a weak droplet-fiber network.The completely nanofibrillated fibers was irreversibly adsorbed on the surface of droplets,which also formed the dense covering layer against coalescence.Thus,A40 showed the best emulsifying capacity,and the corresponding emulsion exhibited high viscosity,strong gel-like behavior,high yeild stress values,excellent anti-deformation capacity and high dynamic stability.A10 had the weakest emulsifying ability,and the emulsion stabilized by A10 exhibited low viscosity,weak gel-like behavior,low yeild stress values,bad anti-deformation capacity and low dynamic stability.The emulsifying capacity of A20 was intermediate between A40 and A10.(3)In order to promote the efficient utilization of lignocellulose,LCNFs was prepared using the pulp with different bleaching levels.The influence of lignin content on the morphological properties of LCNFs during its preparation by mechanical fibrillation was studied.The low degree of fibrillation was found in the lignocellulose with high lignin content,and a large amount of large sized lignin particles adhered on the surface of nanofibers.On the contrary,the high degree of fibrillation was found in the cellulose with low lignin content,and the residual lignin was grinded into lignin nanoparticles and adhered on the surface of nanofibers.The LCNFs suspensions with low lignin content exhibited big viscosity,large yield stress,strong gel strength and excellent anti-deformation.It is worth noting that LCNFs suspension with lignin content of 6.52% had the highest viscosity,largest yield stress,strongest anti-deformation capacity in all suspensions.Therefore,lignin will prevent the mechanical fibrillation when it accounts for a high percentage in raw materials,and residual lignin can promote mechanical fibrillation.(4)LBS containing LPs,LCNFs and MFs were produced from BCTMP with high lignin content by grinding treatment and high-shearing treatment.The incompletely nanofibrillated LCNFs was obtained after mechanical fibrillation.Then,the LPs were partially peeled from the fiber surface by high-shearing treatment,and dispersed in the LBS.Simultaneously,endmost nanofibrillated LCNFs were cut off from the incompletely cellulose and also dispersed in the suspension.Then Pickering emulsion stabilized by LBS was prepared,and the stabilization mechanism was studied.LBS exhibited outstanding emulsifying capacity because of the synergy of irreversible adsorption of LCNFs and LPs,and because the mutually-supporting and mutually-constrained fiber network structure created by MFs and drops.Therefore,emulsions stabilized by LBS exhibited excellent dynamic stability and anti-deformation capacity.