Preparation And Study Of Eucalyptus Pulp Nanocellulose And Its PVA Composites

As a natural polymer material,cellulose is abundant in nature and has a wide range of sources.The nanocellulose prepared by various methods has high specific surface area,high strength,good thermal stability,etc.As a natural ideal polymer fillers have been widely used.In this thesis,NCC was prepared from eucalyptus pulp by ultrasonic oxidation method.The effects of oxidation time,oxidation temperature,ammonium persulfate concentration and their interaction on NCC yield were studied by response surface methodology,and the best process conditions were obtained.The microstructure,crystal structure and thermal stability of NCC were studied.The results show that the experimentally prepared NCC is a carboxylated nanocellulose with a diameter of20~40 nm,which is a mixture of cellulose type I and cellulose type II.In this paper,NCC was added to PVA to prepare PVA/NCC composite flim by solution casting method.The effect of NCC on the performance of PVA film was studied.The results show that the addition of a certain amount of NCC can be uniformly dispersed in the composite film,improve the tensile strength and reduce the elongation at break.When the NCC content is 5%,the tensile strength reaches the maximum value(46.76 MPa),increased by 49.48%;the addition of NCC improved the thermal stability of the PVA film,which solved the problem of difficult thermoplastic processing to some extent;improved the water contact angle of the PVA film,and reducing the equilibrium swelling degree and water absorption rate of the composite film;when the NCC content is higher than 5%,the dissolution rate of the composite film is lowered,and the water resistance of the PVA film is improved.In this paper,PVA/NCCcomposite hydrogels were prepared under repeated freeze-thaw conditions.The effects of the number of freeze-thaw cycles and the addition of NCC on the properties of PVA hydrogels were investigated.The results showed that with the increase of the number of freeze-thaw cycles,the gel fraction of the PVA hydrogel increased,the water content decreased,and the mechanical properties were improved.Under the same preparation conditions,the addition of NCC improved the tensile strength and elongation at break of the PVA hydrogel.Optimized hydrophilic properties,improved gel fraction and water content;improved cross-linking network of composite hydrogel,improved crystallinity,improvedthermal stability;After adding NCC,the equilibrium swelling degree of the hydrogel is increased,the swelling property is improved,the water loss rate is lowered,and the water retention performance is improved.