| Cellulose nanocrystals extracted from different sources possesses different chemical and physical properties.In this paper,two different kinds of cellulose nanocrystals were prepared from short cotton and tunicate sea squirts by using H2SO4 hydrolysis,respectively.Cellulose nanocrystals were modified through the following methods:（1）Physical modifications:under alkaline conditions,dopamine and tannic acid can self-polymerization to form polymer coatings on the surface of cellulsoe nanocrystals.（2）Chemical modifications:hydroxyl groups on the surface of cellulose nanocrystals were oxidized to carboxyl and aldehyde groups by using TEMPO/NaBr/NaClO oxidation system and NaIO4,respectively,moreover,chemical grafting polyimide on the surface of cellulsoe nanocrystals,hydrophobicity modified cellulose nanocrystals by chemical grafting Octadecylamine.The products were characterized by some means such as FTIR,UV,XPS and TEM.The resulting products with different modifications are applied to the following systems:（1）Polydopamine-coated cellulose nanocrystals reinforced PVA matrix:The nanofiller not only improved the mechanical properties of the composite（when the addition of nanoparticles in an amount of 6 wt%,the tensile strength reached a maximum,increased by 75.8%,as the addition of nanoparticles at 15 wt%,modulus increased by 221%）and the thermal stability of the material（heat degradation temperature increased by 50°C）,but also gave the material UV shielding effect and oxidation resistance.In addition to this,the results also showed the oxygen permeability（OP）and water vapor permeability（WVP）of the films decreased with the addition of nanoparticles at 6 wt%and 15 wt%.（2）Polydopamine-coated cellulose nanocrystals chemically grafted polyimide were applied to reinforce epoxy resin matrix:improve mechanical properties of the composite（when the filler content was 0.75 wt%,the tensile strength and breaking elongation of the composite material reached the maximum,with an increase of 41.7%and 75%,respectively,and the modulus of the composite material reached the maximum at the addition of 1 wt%,with an increase of 10%）and the friction performance（the friction coefficient of the composite material was a minimum value of 0.68 with the addition of nanoparticles of 0.75 wt%.Compared to pure epoxy resin,the friction coefficient was reduced by 26.5%.At the same time,the friction loss rate of the composite material was at a minimum value,decreased by37.5%）.（3）Conductive films based on tunicate cellulose nanocrystals:polydopamine-coated graphene oxide as conductive substance was added into the matrix.When the content was 0.5 wt%,the modulus and tensile strength modulus and tensile strength both reached the maximum,increased by 85.7%and 78.9%,respectively.When the filler content increased to 1 wt%,the volume resistivity decreased from 109?.m to105?.m. |
