Preparation of tapioca starch film filled with ZnO nanorods

GUZ, LUCAS; CANDAL, ROBERTO; GOYANES, SILVIA

Capital Federal

Workshop; II Workshop on Bio-degradable Polymers and Biocomposites III Workshop BIOPURFIL, Bio-based Polyurethane Composites with Natural Fillers; 2015

INTEMA-CONICET; ITPN-CONICET

INTRODUCTIONZinc oxide nanoparticles are one of the compounds that is listed as generally recognized as safe (GRAS) by the U.S. FDA (21CFR182.8991) and have antibacterial activity and high UV absorption. The addition of ZnO nanorods (ZnO-nr) into starch film could lead to a biopolymeric film with UV shielding property and antibacterial activity.There are some reports on the effect of ZnO nanorods incorporation on the properties of starch films. However, ZnO-nr was synthesized using a gas phase synthesis [1].In this work, ZnO-nr synthesized by a scalable combination of sol-gel and hydrothermal process were used as nanofiller in tapioca starch films.MATERIALS AND METHODSZnO nanorods were synthesized using a combination of sol-gel and hydrothermal process. Briefly, ZnO NPs used as seeds were synthesized by mixing NaOH (15 mM) and Zn(CH3COO)2 (10 mM) in methanol. For the nanorods growth, seeds suspension (3 ml) were added to HMT/Zn(NO3)2 solution (90 ml, 8 mM) and heated 3 h at 90°C.Tapioca starch film was prepared by casting method [2]. For starch/ZnO-nr film, ZnO-nr (1% w/w of total solids) were dispersed in water by sonication for 45 min. This suspension was used to prepare the starch and glycerol dispersion for film preparation.The films were characterized by SEM, UV-vis absorption, reflection and antimicrobial activity using the agar diffusion method and in suspension in liquid medium.RESULTS AND DISCUSSIONThe average size of the synthesized ZnO-nr was 15 ± 5 nm diameter and 240 ± 50 nm length. The ZnO-nr were homogeneously distributed in the starch matrix and maintained its hexagonal rod shape after the incorporation to the film as can be seen on film cryogenic surface microscopy.Starch film showed very high transmittance in the UV-vis spectrum; however the addition of a very low amount (1%) of ZnO-nr decreased UV transmission to 0%. In the UV range (280-400 nm) starch/ZnO-nr film showed zero reflection, indicating that almost all UV light was absorbed. Starch film showed no inhibition of E. coli growth on agar plates. Starch/ZnO-nr film inhibited the growth of bacteria on the surface of the film but no significant inhibition zone was observed. A similar result was obtained inoculating the surface of the film with E. coli suspension. The effect was even more significant illuminating the films with 20 W/m2 of UVA light. In liquid medium, the starch film was completely biodegraded after 24 hs. Starch/ZnO-nr film was not biodegraded after 24 hs and remained in the culture medium, but didn?t inhibited E. coli growth. Only 4.2 % of the total Zn was released from the film, measured by atomic absorption.In this work we synthesized a new biopolimer with high UV absorption and antibacterial activity on surface without Zn2+ liberation. This film resist more time bacterial biodegradation than starch film.REFERENCES[1] Nafchi A, Alias A, Mahmud S, Robal M, J. of Food Eng. 113-4 (2012), 511-519.[2] Famá L, Gañan Rojo P, Bernal C, Goyanes S, Car. Pol. 87-3 (2012), 1989-1993.