Chitin is the main building block element in the exoskeleton of shellfish. [Raabe, D.; Sachs, C.; Romano, P., Acta Materialia 2005, 53, (15), 4281-4292. Neville, A.; Parry, D.; Woodhead-Galloway, J., Journal of Cell Science 1976, 21, (1), 73-82.] Chitin nanofibers were conveniently extracted by removing minerals, proteins and extractives through acid, alkali and ethanol treatment, respectively, according to reference. [Ifuku, S.; Nogi, M.; Yoshioka, M.; Morimoto, M.; Yano, H.; Saimoto, H., Carbohydrate Polymers 2010, 81, (1), 134-139.] Defibrillation of nanofiber structures was carried out from lobster exoskeleton at pH 3. Chitin nanofiber diameter was between 3 to 4 nm and length of 700 to 1000 nm according to Atomic Force Microscope (AFM); details of the fibril structure will be presented (see Scanning Transmission Electron Microscope image Figure 1(a) below); degree of acetylation ranged between 86-88% and residual protein content was about 1.1%. Since chitin is influenced by pH due to the presence of amine groups, hydrocolloidal properties (i.e., transparency and fibril aggregation) at pH 3, 7 and 12 will be compared. The structural effect of fibril aggregates was exploited for membrane and hydrogel production. A nanopaper structure was produced from a colloidal dispersion at pH 4, 7 and 12 following vacuum filtration to obtain a wet cake that is dried in a semi-automated paper-making machine (see image of chitin nanopaper membrane Figure 1(b) below) and mechanical properties studied. A systematic reduction of mechanical properties with pH was observed. A freestanding hydrogel from chitin fibril networks was formed at 1.0.wt. % by changing pH from 3 to 7 (see image of the hydrogel Figure 1(c) below). Rheological properties of this material will be presented. Structural-property relationship and possible applications will be discussed. In conclusion, preliminary results show that chitin properties strongly depend on pH; chitin fibril structure is influenced at high pH leading to the formation of aggregations and consequence optical transparency decreases. Fibril aggregation can have a negative effect by lowering tensile or optical properties but can be exploited in a positive way for making materials, i.e, freestanding hydrogel. Figure 1. <img src='https://acs-archive-assets2.s3.amazonaws.com/240nm/uploads/36790_figure1.jpg' alt='' />

Membrane and hydrogel properties from chitin fibril structures: Structure and properties at neutral pH

247th National Meeting (2014)

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