Conc. of metal ions (mg/g) Functionalization of halloysite nanotubes for the preparation of carboxymethyl cellulose-based nanocomposite films Long-Feng Wang, Jong-Whan Rhim Department of Food Engineering Introduction: Halloysite nanotubes (HNTs), a kind of layered alumino-silicate with a molecular formula of Al2Si2O5(OH)4·nH2O , have attracted great attention as a reinforcing nanofiller for the preparation of nanocomposite materials due to their large surface area, high surface reactivity, high mechanical strength with a relatively low cost . HNTs were treated with acid to prepare uniformly charged acid treated HNTs (aHNTs). Functionalized aHNTs were prepared through adsorbing metal ions by immersing the aHNTs into saturated solutions of three different metal salts. The number of metal ions attached to the aHNTs and their functionality were dependent on the type of metal ions. The functionalized aHNTs exhibited strong antimicrobial activity against food-borne pathogenic bacteria, L. monocytogenes and E. coli. The CMC-based film showed a significant increase in mechanical, water vapor barrier, and thermal stability properties after forming a composite with HNTs. In particular, CMC-based films incorporated with the functionalized aHNTs showed strong antimicrobial activity against L. monocytogenes and E. coli. CMC/aHNT CMC/aHNTAg CMC/aHNTZn CMC/aHNTCu CMC/HNT CMC Material and methods: For acid treatment, one gram of nanotubes was dispersed into 100 mL of 0.5 M sulfuric acid, stirred continuously , and washed, collected by centrifugation and dried to obtain aHNTs. For the functionalization, the aHNT was dispersed into saturated solutions of metallic salts, AgNO3, Zn(NO3)2, and Cu(COOCH3)2, respectively, for 1 h with stirring. CMC/HNTs nanocomposite films were prepared using a solution casting method . The microstructure , Zeta potential , concentration of metal ions adsorbed , and X-ray diffraction (XRD) for HNTs were investigated. The films were characterized and the packaging properties and antimicrobial activity of nanocomposite films were performed. Results and discussion:. Table. Tensile and water vapor barrier properties of CMC/HNTs nanocomposite films. Films Thickness (μm) TS (MPa) E (%) EM (GPa) WVP (×10-9 g.m/m2.Pa.s) CMC 48.6±2.8a 38.7±3.0a 34.5±4.7bc 1.25±.0.19c 1.67±0.03d CMC/HNT 49.4±5.5a 44.2±2.4b 31.1±2.5b 0.94±0.07a 1.44±0.12bc CMC/aHNT 49.2±1.5ab 47.7±5.4c 28.1±2.4a 1.02±0.22a 1.33±0.12b CMC/aHNTAg 50.2±1.3b 45.2±5.7b 28.7±4.0b 1.08±0.11a 1.14±0.02a CMC/aHNTZn 54.1±5.8c 48.9±6.5c 29.7±4.2d 1.14±0.23b 1.34±0.10b CMC/aHNTCu 54.5±2.2c 48.4±3.9c 29.0±2.0bc 1.24±0.09c 1.52±0.07c Fig. 4. SEM images of CMC and CMC/HNTs nanocomposite films. The values are presented as mean±standard deviation. Any two means in the same column followed by the same letter are not significantly (p > 0.05) different by Duncan's multiple range tests. Table. Zeta potential and concentration of metal ions of HNTs. Halloysit es ZP (mV) Conc. of metal ions (mg/g) HNT 0.08±0.01 - aHNT -32.63±2.56 aHNTAg -33.67±2.64 220.7±15.2 aHNTZn -18.97±1.49 10.6±0.1 aHNTCu -19.63±1.54 3.6±0.1 Fig. XRD diffraction patterns of HNTs, aHNTs, and functionalized aHNTs. Fig. 7. Antibacterial activity of HNTs and CMC/NHTs nanocomposite films. Conclusion: √ Functionalized HNTs were prepared. √ The functionalized HNTs showed strong antibacterial activity against L. monocytogenes and E. coli. √ The functionalized HNTs were incorporated into CMC to form bio-nanocomposite films. √ The composite films had increased mechanical, water vapor barrier, and thermal stability properties with strong antimicrobial activity. √ The functionalized HNTs has a high potential to be used as a reinforcing filler to prepare a functional nanocomposite films, which can be applied in the active food packaging or biomedical applications. (a) Fig. FTIR spectra of (a) HNTs and (b) CMC/HNTs nanocomposite films. (b) Acknowledgment: This research was supported by the Agriculture Research Center (ARC 710003) program of the Ministry of Agriculture, Food and Rural Affairs, Republic of Korea. Fig. STEM images of (a) neat HNT and (b) aHNT. Fig. Light transmittance spectra of CMC/HNTs nanocomposite films. Fig. TGA and DTG thermograms of CMC/HNTs nanocomposite films.