Subject Number :S-16-2014
Support Type : Common use (including technical support necessary for the training),
Proposal Title (English) : Structural identification of cellulose nanocrystal/nanofibril hybrids and composites using soft X-ray techniques
Username (English) : M.Y. Ismail1, M. Huttula2, M. Patanen2, H. Liimatainen1, T.Ohigashi3,N. Kosugi3
Affiliation (English) : 1Fibre and Particle engineering unit, University of Oulu, 2Nano and Molecular Systems unit, University of Oulu, 3UVSOR Synchrotron, Institute for Molecular Science

Nanocellulose hybrids are high strength materials consisting of cellulose nanofibrils or nanocrystals embedded in a continuous biopolymeric matrix with additives such as mineral nanoparticles. In the present work, the structure of the hybrid formed of nanosilica, nanocellulose (cellulose nanofibrils) and chitosan matrix is studied. The critical factors affecting the mechanical performance of these materials are the interaction between the constituents and their spatial distribution. So far, these properties have mainly been analysed using electron microscopy techniques (TEM and SEM), but they possess limited ability to localize nanocellulose and biopolymers within the hybrid structure (e.g. to determine interactions between minerals and nanocelluloses). Therefore, novel methods are desired to better address the structural details of the hybrids. Previously, soft X-ray spectroscopy has shown to be able to identify the localized distribution of biopolymers, but based on our best knowledge this methodology has not been used for nanocellulose hybrids. This report shows significant new outcomes on structural characteristics of nano-scale hybrids based on nanocelluloses.
Chitin is one of the most abundant natural biopolymers and it is used for the production of chitosan by deacetylation [1]. Chitosan is antibacterial, non-toxic, and biodegradable; thus, it can be used for the production of biodegradable films which are potential green alternatives for commercially available synthetic counterparts. However, poor mechanical and thermal properties of chitosan restrict its wide spread applications. Consequently, hybrids fabricated from chitosan matrix reinforced by nanofibers are attractive materials to develop sustainable products [2].
The aim of the present work was to obtain a nano-scale spatial distribution of constituents within the hybrid. The hybrids had constant nanocelluloses:chitosan ratio of 50:50, and variable nanosilica content (5-30%). The samples (thickness of 100 nm) were prepared from solution casted hybrid films using an ultramicrotome. Pure nanocellulose, nanosilica and chitosan samples were used as references.
The samples were exposed to soft X-ray radiation at BL4U beamline at UVSOR synchrotron. The absorption at carbon 1s-edge was recorded for investigation of the nanocellulose and the matrix distribution, with photon energies between 280 and 300 eV. The Si 2p absorption edge around 100 to 130 eV was utilized for the same spatial parts of the sample for observing the distribution of nanosilica on the hybrid.
Figure 1 presents examples of the image data of the 30% nanosilica sample. In the first preliminary interpretation the nanosilica (Si2p on leftmost) appears to be concentrated on the fiber bundles of the sample. The nanocellulose fibers were found to provide somewhat characteristic absorption structure (Fig.2.), matching the intense absorption patterns on the Fig.1. Similarly the appearance of smaller “dots” of nanosilica on the fibers were also found in the sample containing only 5% of the nanosilica.
The obtained data seem to provide a strong evidence of the agglomeration of the nanosilica at the nanofibers. Indications on the spectral changes in the Si rich regions suggest also possible chemical binding mechanism of the nanoselluloce and nanosilica. The present data will give valuable information of behavior of the additive mineral which will affect the mechanical properties of composite hybrid materials.

Figure 1. STXM images for 30% nanosilica sample.

Figure 2. The C1s absorption reference for nanocellulose fibers.

[1] Abdul Khalil H.P.S. Chaturbhuj K. Saurabha, Adnan A.S., et al., Carbohydrate Polymers 150 (2016) 216–226
[2] Moon, R. J., Martini, A., Nairn, J., Simonsen, J., Youngblood, J., Chemical Society Reviews 40 (2011) 3941–3994.