Preparation And Properties Of Vermiculite/CMC Biomimetic Composites

The development of high-performance clay film materials with single-layer clay nanosheets as structure unit has wide application value.Natural vermiculite minerals belong to phyllosilicates.They are abundant,environmentally friendly and inexpensive and can be peeled off into single-layer vermiculite nanosheets with a thickness of 1-1.5 nanometres.The exfoliated monolayer vermiculite sheets have good film-forming ability,as well as excellent heat resistance,electrical insulation,flame retardancy,thermal insulation and UV shielding capability.They can be used as a nanostructure unit to develop high-performance film materials for broad application in the field of high voltage insulation,heat insulation,electronic packaging,UV shielding and others.Sodium carboxymethyl cellulose（CMC）,a kind of natural polysaccharide,is easily crosslinked with different metal cations because of its rich carboxyl and hydroxyl groups.Inspired by the"brick-and-mortar"structure of natural nacre and the synergistic interaction of interfacial hydrogen and ionic bonding,this thesis focuses on the preparation and properties of bioinspired vermiculite/CMC nanocomposite.（1）A two-step ion exchange and ultrasound method were used to weaken the van der Waals/Coulomb forces between vermiculite layers for exfoliating them into nanosheets.The morphology and structure of the exfoliated vermiculite nanosheets were characterized,and their size were analyzed.The results of XRD and XPS prove susscessful intercalation and exfoliation.The average diameter and thickness of the nanosheets obtained from AFM images were about 1.87μm and 3.12 nm,respectively.（2）Based on the exfoliated vermiculite nanosheets,a layered vermiculite/CMC nanocomposite was prepared by vaccum-assisted filtration method to mimick the"brick-and-mortar"structure of natural nacre.Moreover,Cu²⁺crosslinking was used to construct synergistic interaction of interfacial ionic and hydrogen bonding.SEM image confirmed that the nanocomposite has nacre-like layered structure.The interfacial hydrogen and ionic bondings between vermiculite nanosheets were analyzed by FTIR and XPS.（3）The bioinspired vermiculite/CMC nanocomposites with 30%vermiculite nanosheets and cross-linked with 3 wt%Cu Cl₂exhibits excellent mechanical property with a tensile strength of 254.9±19.5 MPa,which are better than that of lnatural nacre.In addition,the bioinspired nanocomposite shows an improved heat resistance and UV shielding properties.We believed that these finding would provide a new route for the development of bioinspired high-performance nanocomposites with enhanced functionalities in the future.