Cellulose fibrils in the cell wall of plant fibres are responsible for their extraordinary high tensile strengths. These fibrils or fibril bundles are isolated out of different commercial pulps with diameters below 100 nanometers and lengths of several tens of micrometers. They are used for the reinforcement of matrices like (bio)polymers. Chemical modification aims on varying polarities and functionalities of the fibrils.

Application areas are e.g. in packaging, medicine, textiles, adhesives, surface coatings, or food processing.

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Isolation of CNF

• Solely mechanical isolation out of wood, wheat straw or oat straw pulp by application of an inlinedispersing system (ultra-turrax) and a high pressure shear homogenisator (up to 1800 bar)

Modification of CNF

• A good interface/binding between cellulose nanofibrils (CNF) and matrix is a precondition for nanocomposite production. Chemical modification routes are used to tailor the polarity of CNF for applications in different matrices

Nanocomposites

• The incorporation of CNF leads to a property enhancement (e.g. increase of strength and stiffness) of different (bio)polymers like hydroxypropyl-cellulose, poly ethylene oxide, polyurethane, polyvinyl acetate, or poly lactic acid and others
  

• Mechanical tests (tension tests, dynamic mechanical thermal analysis)
• Light microscopy, force microscopy
• Scanning and transmission electron microscopy
• IR-/UV-spectroscopy
• Mechanical isolation of cellulose nanofibrils (inline- and high pressure disperser, up to 1800 bar)
• Wet chemistry (chemical modification)
• Compounding of cellulose nanofibrils/(bio)polymers

Contact: Tanja Zimmermann

Utilisation of cellulose-nanofibrils for wood adhesives
Nano scaled cellulose fibrils derived from wood pulp are added into wood adhesives to improve their application and bonding properties and thus upgrade the performance and safety of wood bonds. Due to their high reactivity the fibrils are expected to strengthen both the cohesion properties of 1 K PUR adhesives as well as the adhesion of the polymer-wood interface. In water based polyvinylacetate adhesives the cellulose fibrils shall be used to substitute protective colloids while stabilising the dispersed phase of the polymers and improving the moisture and temperature resistance of the adhesive. The research will also focus on the optimization of a controlled processing of the fibrils and the reaction of the fibril-polymer composites, in order to recommend the key parameter for a pilot plant.
Contact: Tanja Zimmermann

Composites consisting of nanofibrillated cellulose and biopolymers

Nanofibrillated cellulose (NFC) is a hydrophilic material with a large surface area due to fibrillar structures with diameters below 100 nm. The molecular and supramolecular arrangement of the anhydroglucose units (the building blocks of cellulose) gives rise to crystalline domains of exceptionally high stiffness and strength. Therefore, NFC has attracted increasing attention for the reinforcement of polymers. In particular, the development of green nanocomposites with biopolymers seems promising. However, biopolymers are often hydrophilic, leading to poor adhesion between the two components. In addition, NFC is generally obtained as a never dried and low concentrated aqueous suspension. Even though this creates several disadvantages (high transportation and storage costs, susceptibility towards microbial degradation and difficulties in further processing the material) simple drying of NFC is no option, as it leads to irreversible agglomeration of the isolated fibrillar structures and therefore loss of its advantageous properties. In this project, more sophisticated concepts are developed for drying NFC aqueous suspensions and for optimization of the adhesion between NFC and biopolymer matrices, using chemical modification of the NFC surface. The project is performed in collaboration with Luleå Technical University (LTU, Sweden).
Contact: Tanja Zimmermann

Development of sustainable composite materials

Due to its high specific strength, modulus and aspect ratio, microfibrillated cellulose (MFC) is an adequate reinforcing agent for nanocomposite applications. But to realize the targeted property im-provements, the natural fibers must be homogeneously dispersed in the host polymeric matrix, which is non-trivial. In general, due to its strong hydrophilic character and high aspect ratio, a non homogeneous dispersion of MFC in most common apolar polymer matrices is obtained, thus de-creasing the final mechanical properties of the nanocomposite material.
To expand the use of these nanoelements to non polar environments, the chemical modification of MFC surface hydroxyl groups in order to decrease its inherent hydrophilicity, is strongly promis-ing.  In the European project SustainComp (see http://www.sustaincomp.eu), we are currently in-corporating chemically modified MFC in hydrophobic biopolymeric matrices (i.e., such as Poly(lactic acid) to elaborate novel bionanocomposites with tunable properties. In this context, the MFC surface esterification has already proved to be a successful method to prepare hydrophobic cellulose nanofibers, thus allowing the design of bionanocomposites with targeted properties.
Contact: Philippe Tingaut