Novel anisotropic materials from functionalised colloidal cellulose and cellulose derivatives

This feature article describes selected examples of the properties and the methods of preparation of cellulose micro and nano crystallites (whiskers) and derivatives, with aspects related to fabrication of various anisotropic materials. Nanometre sized cellulose crystallites have a variety of novel anisotropic properties markedly different from those of common forms of cellulose. They can be obtained from a variety of native cellulose sources through partial hydrolysis with strong acids or via mechanical defibrillation. We discuss different fabrication techniques and surface modifications of cellulose whiskers which determine their wettability, surface charge and range of applications. Concentrated suspensions of cellulose whiskers of high aspect ratio can form chiral nematic liquid crystalline phases which retain their structure upon evaporation, producing iridescent films. At present, the bulk of the research on cellulose whiskers is focused on creation of composite materials in which they enhance mechanical properties and improve their biodegradability. The high strength of the cellulose nanocrystals has also been utilised in the fabrication of reinforced composite films with applications for anisotropic microcapsule preparation. Microrods and multifunctional microampules from hydrophobised cellulose have recently been recognised as being able to produce super-stable foams with long shelf life and allow the foam structural elements to encapsulate a range of liquid and solid additives.