title: Montmorillonite-levan nanocomposites with improved thermal and mechanical properties.
abstract: This work reports on the structure and properties of novel nanocomposites composed of exfoliated montmorillonite clay blended with levan, a polysaccharide produced by Bacillus sp. Dry levan is very brittle, making it difficult to obtain stand-alone films. MMT-levan composites were prepared by solution blending in water, coating on plastic surfaces, partial drying at 50°C, and conditioning in air at 50-60% relative humidity. This process results in freestanding, transparent, and flexible films of pure levan and MMT-levan composites plasticized by 10-15 wt% water. XRD patterns from levan-MMT composites indicate an MMT interlayer spacing 0.62 nm greater than that of the starting MMT, suggesting re-stacking of MMT platelets coated by adsorbed, uncoiled levan molecules. FTIR results suggest that levan adheres to MMT via water-mediated hydrogen bonding between the levan's hydroxyl groups and MMT surface oxygens. MMT-levan composites have improved thermal stability and a well-defined glass transition temperature that increases with MMT loading. The tensile moduli of levan-MMT composites increase by as much as 480% relative to pure levan. The XRD and mechanical property results suggest that MMT reinforces levan through a filler network structure composed of MMT platelets bridged by adsorbed levan molecules, enhanced when the MMT loading becomes high enough (5-10wt% MMT) to induce an isotropic-nematic transition in MMT platelet orientation.
authors.affiliation: Department of Chemical Engineering, University of South Carolina, Columbia, SC 29208, United States.
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Chen
authors.forename: Hongsheng
authors.initials: H
authors.lastname: Gao
authors.forename: Harry J
authors.initials: HJ
authors.lastname: Ploehn
mesh_terms: D001546:Bentonite / Q000737:chemistry*; D005630:Fructans / Q000737:chemistry*; D055595:Mechanical Phenomena; D053761:Nanocomposites / Q000737:chemistry*; D013696:Temperature
chemical_list: D005630:Fructans; D001546:Bentonite; C072599:levan
keywords: Isotropic–nematic; Levan; Montmorillonite; Nanocomposite; Polysaccharide