The physicochemical properties of plant fibres are determined by the fibre morphology and structural features of the cell wall, which is composed of three main layers that differ in chemical composition and architecture. This composition and hierarchical structure are responsible for many of the mechanical properties that are desirable for industrial applications. As interactions between the lignocellulosic polymers at the molecular level are the main factor governing the final cohesion and mechanical properties of plant fibres, atomic force microscopy (AFM) is well suited for the observation and measurement of their physical properties at nanoscale levels. Given the complexity of plant cell walls, we have developed a strategy based on lignocellulosic assemblies with increasing complexity to understand the influence of the different polymers on the nanomechanical properties. Measurements of the indentation moduli performed on one type of lignified cell wall compared with those performed on the corresponding lignocellulosic films clearly show the importance of the lignin in the mechanical properties of cell walls. Through this strategy, we envision a wide application of bioinspired systems in future studies of the physical properties of fibres.
Using AFM, ellipsometric and profilometric measurements, we have investigated the topography and the thickness of the cellulose nanocristal (NCC) films prepared by two different methods: the first one is obtained by evaporation of concentrated suspension of NCC in petridish to produce a self-supported film; the second one is produced by dipping thin NCC layer on silicon substrate by Langmuir-Blodgett (LB) technique. Glucomanan (GM) functionalized AFM tip was brought into contact with these two kinds of NCC films in order to measure the adhesion between GM and NCC. The impact of the substrate and the thickness of NCC films on the measured adhesion forces were also studied: the mean measured adhesion force between the two polysaccharides was 17 nN regardless of the way the films were prepared. Adhesion properties can help us understand biochemical processes in the plant cell wall.
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