TEMPO-oxidized cellulose nanofiber/kafirin protein thin film crosslinked by Maillard reaction
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Mixtures of cellulose nanofiber and protein have gained attention as a material having potential application such as bio-plastics and biopolymer based packaging film. Herein, an efficient protocol for the formation of kafirin protein thin film plasticized with PEG-300 and reinforced with 0.5% TEMPO-oxidized CNF was developed. In this regards cellulose nanofibers were prepared using a high-pressure homogenizer at ≈ 241 MPa pressure for 30 cycles and the resultant nanofibers was found to be of average diameter 89–60 nm under SEM observation. Further, ultrasound-mediated regio-selective oxidation of nanofibers was carried out using 2,2,6,6-tetramethylpiperidine (TEMPO) catalyst. FTIR and Solid-state 13C CP/MAS NMR spectroscopy reveals successful surface modification of nanofiber. The conductometry titration data demonstrated 32.81% substitution of the hydroxyl group by carbonyl group. Furthermore, the effect of TEMPO-oxidized cellulose nanofiber content (0–1%) on kafirin protein structure and nanocomposite film was thoroughly investigated. The cross-linking between carbonyl group of nanofiber and amine groups of kafirin protein is attributed to the possible Maillard reaction at 80 °C, which was evidenced by FTIR. An increase in cross-linking between nanofiber and protein results in the simultaneous increase in crystallinity and thermal stability when 0.5% of TO-CNF was incorporated in kafirin. Meanwhile, additional attempts have been made to improve mechanical strength and water vapor transmission rate. Swelling studies suggests better stability with no swelling, however, at pH 10.6 film starts to swell over a period of time and then starts to disintegrate. Overall, when comparing 0% with 0.5% of TO-CNF, 0.5% has shown better stability.
KeywordsCellulose nanofiber Kafirin protein Cross-linking Maillard’s reaction Nanocomposite film
The Author is thankful to UGC BSR for the financial assistance to carry out this research work. We would like to acknowledge IIT Bombay, SAIF Facilities to help us to carry out Solid state 13C CP/MAS NMR.
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