Nacre-mimetic bionanocomposites of high montmorillonite (MTM) clay content, prepared from hydrocolloidal suspensions, suffer from reduced strength and stiffness at high relative humidity. We address this problem by chemical modification of xyloglucan in (XG)/MTM nacre-mimetic nanocomposites, by subjecting the XG to regioselective periodate oxidation of side chains to enable it to form covalent crosslinks to hydroxyl groups in neighbouring XG molecules or to the MTM surface. The resulting materials are analysed by FTIR spectroscopy, thermogravimetric analysis, carbohydrate analysis, calorimetry, X-ray diffraction, scanning electron microscopy, tensile tests and oxygen barrier properties. We compare the resulting mechanical properties at low and high relative humidity. The periodate oxidation leads to a strong increase in modulus and strength of the materials. A modulus of 30 GPa for cross-linked composite at 50% relative humidity compared with 13.7 GPa for neat XG/MTM demonstrates that periodate oxidation of the XG side chains leads to crucially improved stress transfer at the XG/MTM interface, possibly through covalent bond formation. This enhanced interfacial adhesion and internal crosslinking of the matrix moreover preserves the mechanical properties at high humidity condition and leads to a Young's modulus of 21 GPa at 90 %RH.
[Show abstract][Hide abstract] ABSTRACT: Bio-composites comprised of the polysaccharide xyloglucan (XG) and montmorillonite (MTM) clay has potential as a ‘green’ replacement of conventional petroleum-derived polymers in the packaging industry. These materials have been shown to possess excellent material properties, even in high relative humidity. Although interfacial interaction between XG and MTM, and the molecular structure of XG can be identified as key parameters for the complex formation process and the resulting tensile properties, these properties are usually difficult to address using experimental methods. Here we use molecular dynamics (MD) simulations to study the adsorption of fully atomistic models of both native and chemically modified XG to MTM clay surfaces in explicit water. We show that the driving force for adsorption is a favorable change in enthalpy, and furthermore that native XG adsorbs stronger than modified XG. This highlights the importance of molecular structure details to molecular adhesion. The present study provides insights into the molecular scale adsorption mechanisms and can therefore help in designing routes for further improvements of bio-composite materials.
Journal of Materials Chemistry A 05/2014; 2(25):9541-9547. DOI:10.1039/C4TA01459F · 7.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Epoxy films containing self-assembly of 2D colloidal α-zirconium phosphate nanoplatelets (ZrP) in smectic order were prepared using a simple, energy-efficient fabrication process suitable to industrial processing. The ZrP nanoplatelets in epoxy form a chiral smectic mesophase with simultaneous lamellar order and helical arrangements. The epoxy nanocomposite films are transparent and flexible, and exhibit exceptionally high tensile moduli and strengths values. The findings have broad implications for development of multi-functional materials for engineering applications.
[Show abstract][Hide abstract] ABSTRACT: Although numerous kinds of water-borne, nacre-mimetic films with excellent properties have been fabricated via different assembly methods, it remains difficult to put those kinds of lightweight materials into practical applications because they are sensitive to water in the environment. Herein, a simple superhydrophobic modification method was used to enhance the repellency of film to water and/or corrosive liquids in the environment. Furthermore, it lowered the gas transmission rate of the films dramatically and improved the heat and flame shield capabilities. This approach could also be applied to other kinds of nacre-mimetic films, proving a versatile, low-cost, fast, and facile method to produce large area and thick, water-borne, multifunctional films with excellent repellency to water and some corrosive liquids in the environment, which will pave the road for the nacre-mimetic films to practical applications.
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