Further nanoindentation experiments have been carried out to study the elastic modulus of wood cells (Gindl and Schoberl 2004) or that of dry pulp fibre walls (Adusumalli et al. With an AFM-based indentation method, it was possible to test the mechanical properties of wet cellulose and observe the Young’s modulus, which resulted in elucidating the kPa range (Hellwig et al. Further AFM-based colloidal probe measurements on cellulose were performed on gel beads made of cellulose to show the impact on the mechanical properties in the wet state (Hellwig et al. When immersed in water, the fibres exhibited a decrease in the elastic moduli by 100 and in the viscosity by at least three orders of magnitude (Czibula et al. Compared with the dry state, the elastic moduli decreased by a factor of 10, and the viscosity decreased by a factor of 10–20. Here, the RH was varied, and the elastic moduli and viscosity characteristics of fibres were examined. Additionally, the viscoelastic properties of pulp fibres could be investigated with AFM.
Atomic force microscopy (AFM) has been used to investigate the surface properties of cellulose-based materials in dry and wet states (Chhabra et al. In a more comprehensive approach, coated cellulose fibres were investigated with the help of brightfield microscopy, Raman spectroscopy and confocal laser scanning microscopy (Janko et al. 2009) to study changes in the molecular structure of cellulose caused by water or sodium hydroxide. Raman spectroscopy was applied by (Fechner et al.
The distribution of coatings on fibres and the distribution in the fibre network can be investigated with fluorescence microscopy (Bump et al. The efficiency of coating strategies and the uptake of liquids into cellulose fibres are issues that have been successfully addressed with various characterisation methods. To improve the strategies to strengthen wetting properties, it is essential to understand how these coatings change the mechanical and wetting properties of individual cellulosic fibres. 2015) or modified with TiO 2 nanoparticles or fluorinated silanes to obtain self-cleaning surfaces used for the separation of different liquids, such as water and oil (Chauhan et al. To control the wetting properties, paper fibres or the entire fleece can become hydrophobic with the application of polymer coatings (Janko et al. How the relative humidity (RH) affects the elastic modulus, stiffness and strength of materials has been studied by various authors (Ganser et al. In particular, material swelling and the loss of mechanical stability in a humid or wet environment must be addressed. 2011 Gurnagul and 9 Hayes and Feenstra 2003 Liana et al.
Introducing paper as a functional material in the fields of microfluidics, electronics, sensor technologies, and medicine is equally promising and challenging (Bump et al. These results verify the basic functionality of the hydrophobic coating on fibres and paper fleeces but call into question the homogeneity of the coating. The water uptake also induced a change in the local mechanical properties, as measured by atomic force microscopy. Contact angle measurements proved the hydrophobic character of the coated fleece, which was also confirmed by Raman spectroscopy measurements that investigated the water uptake in single fibres. The scanning electron and fluorescence microscopy results revealed the distribution of the coating on the paper fleeces and fibres. Coated and uncoated fibres were characterised by using scanning electron microscopy, contact angle measurements, Raman spectroscopy and atomic force microscopy with the objective of correlating macroscopic properties such as the hydrophobicity of the fleece with microscopic properties such as the coating distribution and local nanomechanics. Here, we investigate the effects of a terpolymer P(S-co-MABP-co-PyMA) coating on cotton linters and eucalyptus fibres to improve the resistance of cellulose fibres against wetness. Polymer coatings on cellulosic fibres are widely used to enhance the natural fibre properties by improving, for example, the hydrophobicity and wet strength.