The Research On Esterification Modification On Nanocellulose And Its Application

Nanocellulose were widely used in papermaking,packaging,food,cosmetics and medicine and so on,due to its light weight,degradable,excellent mechanical properties,large specific surface area,biocompatibility,and renewable characteristics.In recent years,with the development of the modification technology,the modification of nanocellulose have become possible in a green and highly efficient manner.How to give new functionality to nanocellulose through chemical modification,thus broadening the field of application of nanocellulose have become the focus of research.In this paper,cellulose nanocrystals（CNC）were esterified by in situ solvent exchange.Subsequently,the modified and unmodified CNC were separately mixed with polar polymers such as poly（vinyl alcohol）（PVA）,poly（methyl methacrylate）（PMMA）and poly（acrylic acid）（PAA）to form a film.The effects of the interaction between pure and modified CNC and the above-mentioned polymer on the compatibility of the two phases and the microstructure and macroscopic properties of the composite were thoroughly investigated,in order to provide theoretical guidance for the preparation of high performance nanocomposites.The specific research work were as follows:1.In the first system,firstly,CNC were prepared by acid hydrolysis with cotton fiber as raw material.TEM analysis showed that CNC had a rod-like structure and its size was in the nanoscale.The CNC crystal shape had not changed by the analysis of the XRD.TGA showed that the thermal stability of the CNC was reduced.CNC then were modified through the green in-situ solvent exchange method.The CNC and its esterification products were characterized by FT-IR and ¹³C-NMR.The crystallization and thermal stability of CNC with different substitution degree were studied by XRD and TGA.The results showed that L-malic acid（MA）was successfully grafted onto CNC.After the CNC esterification modification,the original crystal structure of CNC were retained,but the degree of crystallinity slightly decreased,and the esterification reaction only occurred on the surface of CNC.And the thermal stability of modified CNC have improved.2.In the second system,PVA/CNC and PVA/CNC-g-MA composite films were formed by a casting technique with PVA as a matrix,CNC and CNC-g-MA as reinforcement components.When the same amount was added,there was stronger hydrogen bonding and better compatibility between PVA matrix and CNC-g-MA was demonstrated by FT-IR,XRD and SEM characterization.Using tensile,TGA,DSC,DMA and water absorption tests have found that CNC-g-MA can further improve the mechanical properties,barrier properties and thermal propertiesof PVA film when the same amount was added.When the amount of CNC-g-MA was 3 wt%,the tensile strength and Young’s modulus of PVA/3 wt%CNC-g-MA composite film were 96 MPa and 3.30 GPa,which were 28%and 20%higher than that of pure PVA film.3.In the third system,different contents of PMMA/CNC and PMMA/CNC-g-MA composite films were prepared by physical blending.The structure and compatibility of PMMA composite membranes were characterized by FT-IR,XRD and SEM.The results show that the CNC-g-MA and PMMA have stronger hydrogen bonds.When the amount of CNC and CNC-g-MA were low（1 wt%）,both can be uniformly dispersed in the PMMA matrix.Both CNC and CNC-g-MA can improve the thermal stability and mechanical properties of PMMA composite films through tensile,TGA,DSC and DMA.The effect of CNC-g-MA on the thermal and mechanical properties of PMMA composite film was more significant when the same amount were used.When the content of CNC-g-MA was 1 wt%,the tensile strength,elongation at break and Young’s module of PMMA/1 wt%CNC-g-MA composite film were 62.1 MPa,30%and 1.49 GPa,which were 60.9%,118.6%and 20.2%higher than that of pure PMMA film,respectively.The transparency test showed that the light transmittance of PMMA/1 wt%CNC-g-MA composite film was close to that of pure PMMA film while improving the other properties of PMMA,the transparency of the composite film was not affected much.4.In the fourth system,PAA/CNC and PAA/CNC-g-MA composite films were prepared by casting technology with PAA as a matrix,CNC and CNC-g-MA as reinforcement components.The effects of CNC and CNC-g-MA on the structure,dispersibility,mechanical properties,thermal properties,swelling ratio and optical transparency of PAA composite films were investigated.The study found that PAA and CNC-g-MA have stronger hydrogen bonding,the addition of CNC-g-MA improves the thermal stability and mechanical properties of PAA membranes while improving the swelling properties of composite membranes compared with PAA/CNC composite film.In depth analysis of the mechanical properties of PAA composite film found that when the amount of both CNC and CNC-g-MA were 3 wt%,the maximum tensile strength of PAA composite films reaching 30.4 MPa and 55.6 MPa,which were 85%and 239%higher than that of pure PAA film indicating that CNC-g-MA had better enhancement effect on PAA.