16.4.1 PROCESSING

The nanocomposites of cellulose and chitosan has been motivated by their chemical similarities, the functional properties (antimicrobial, water transpiration) and the improvements in materials (mechanical, physical and barrier) properties achieved in parallel by blending the cellulose and chitosan by dissolution using acidic media and ionic liquids.32 Various organic solvents and mixture of acids have been used to process the composites of chitosan and cellulose. Most reactions consume and pro­duce toxic waste, which is hazardous to the environment. Furthermore, some com­ponents of the processing tend to release the atomic oxygen, which attacks the mac­romolecular chains and degrades them, and severely compromising the mechanical properties of the composites. In order to overcome the above-mentioned issues ionic liquids have been used to dissolve and process cellulose and chitosan composites. A binary system consisting of acidic ionic liquid glycine hydrochloride and neutral ionic liquid 1-butyl-3-methylimidazolium chloride is used as a cosolvent to gener­ate electrospun fibers of chitosan and cellulose. The prepared composite fibers were shown to have excellent thermal and mechanical properties.33 In a similar approach, environmental friendly composites of chitosan and cellulose were prepared using a mixture of sodium hydroxide and thio-urea solvent. The solvent led to chain depoly­merization of both polymers by sustaining the film forming capability. The crystal­line property of the prepared nanocomposites was close to that of cellulose film.34

Interestingly, a blend of chitosan and cellulose also showed an improvement in water vapor even when the blends were not well-miscible. The authors proposed that intermolecular hydrogen bonding of cellulose is supposed to be break down to form cellulose-chitosan hydrogen bonding, while intramolecular and intrastrand hydrogen bonds hold the network flat. These blends membranes demonstrated ef­ficient antimicrobial activity against E. coli and S. aureus3

Chitosan dissolves readily in water or acidic medium which allows one to pre­pare chitosan-based nanocomposites via solution casting3640 or spinning methods.41 Layer-by-layer (LBL) assembly method is also adopted to develop nanocomposites, by alternatively dipping in to chitosan solution and nano-cellulose suspension.4243