Antonella Marra

Polylactic acid/zinc oxide biocomposite films for food packaging application

Although PLA is much more expensive than polyolefins, such as PP and PE, there is a great interest to propose PLA based material as alternative films for food packaging being PLA derivable from natural source, compostable and biodegradable. For this purpose the research has the task to investigate and propose PLA materials with enhanced properties to be effectively and efficiently alternative to polyolefin films for food packaging application. In this contribution, biocomposite films of PLA with 1, 3 and 5wt% of ZnO have been investigated to determine mechanical, barrier and antimicrobial (against Escherichia coli) properties. It is found that the biocomposite films are characterized by a good dispersion of the ZnO particles in PLA matrix, although no previous treatment was performed on ZnO particles, such as silanization, to decrease its incompatibility with the polymer. The biocomposite films have shown good mechanical properties, decrease of permeability to CO2 and O2, and only a slight increase to water vapour. Particularly important is that, for the biocomposite with 5wt% of ZnO, the % Reduction for E. Coli test reached the value of 99.99 already after 24h.

Preparation and characterization of nanocomposites based on PLA and TiO2 nanoparticles functionalized with fluorocarbons

Poly(l-lactic acid)–TiO2 nanocomposite films were prepared by twin-screw mixer and compression molding. Compatibility between polymer matrix and nanoparticles were improved by modification of the TiO2 surface with fluorocarbons plasma treatment. 2 and 5 were the % in weight of modified functionalized TiO2 (fTi) used in this work. Not modified TiO2 nanoparticles were also used at the same % for comparison. The nanocomposites were analyzed in terms of molecular mass, structure, morphology, thermal stability, mechanical properties and UV absorbance. It was found that TiO2 nanoparticles affected slighly the PLA molecular weight during mixing and the phenomenon was more marked for functionalized nanoparticles (fTi). All the films presented a good dispersion of nanoparticles in PLA matrix. However, a better interfacial interaction was found for nanocomposites containing modified nanoparticles, and this was reflected in the improved mechanical properties. Moreover, all the nanocomposites showed extension of UV absorption area and increase of the thermal stability. Both UV adsorption and thermal stability increased by increasing TiO2 content and at a given composition for nanocomposites containing modified TiO2.

Effect of TiO2 and ZnO on PLA degradation in various media

This work shows the effect of 2 and 5 wt% TiO2 nanoparticles (modified by fluorocarbons and not) and of 1, 3 and 5 wt% ZnO particles on PLA degradation evaluated under UV irradiation, hydrolytical 1N NaOH solution, enzymatical proteinase K solution, and isothermal condition. The presence of TiO2 nanoparticles and ZnO particles decreases the degradation processes of PLA under UV light exposure and increases the PLA hydrolytic degradation. The enzymatic degradation is faster with TiO2 nanoparticles than with ZnO particles, respect neat PLA; whereas the opposite effect is identified in the PLA enzymatic degradation. Correspondence to: CAntonella Marra, Istituto per i Polimeri Compositi e Biomateriali (IPCB), Consiglio Nazionale delle Ricerche (CNR), Via Campi Flegrei 34, Comprensorio Olivetti, 80078 Pozzuoli (NA), Italy, E-mail: marranto.nella@libero.it

Effect of PLA/ZnO Packaging and Gamma Radiation on the Content of Listeria innocua, Escherichia coli and Salmonella enterica on Ham during Storage at 4 °C

The effect of ZnO and low γ-radiation on PLA based-films was investigated to be used for food packaging application. Ham slices were inoculated with E. coli, L. innocua and S. enterica and then covered with PLA and PLA/5% ZnO films. The samples were irradiated with a γ-radiation dose of 0.3 kGy at dose rate of 13.5 kGy/h. Microbiological analysis was performed at 0, 1 and 5 days on samples stored at 4 °C. Results showed that no onsistent reduction of bacteria was obtained, even at the fifth day of storage, when the ham was covered with PLA/5% ZnO film and no γ-radiation was performed. The use of γ-radiation results necessary to reduce the bacteria growth. In fact E. coli and S. enterica were not detected after 5 days of storage; whereas in the case of test with L. innocua a reduction of 1.3 log CFU/g was observed after 5 days of storage. The antibacterial results indicate that the presence of ZnOin PLA film is effective only for E. coli. The differences of the results obtained here with those reported in literature (where ZnO particles are reported to be very effective as antimicrobial material) are accounted for the different methodologies used. In conclusion considering the positive results, even if small, obtained here at least only for the E. Coli and considering that PLA/5% ZnO film shows, compared to plain PLA film, good tensile properties (especially Young’s modulus and stress at yielding) and good permeability (to O2 and CO2) induce to consider the PLA/5% ZnO composite film usable for food packaging when long shelf life and food safety are required, considering also that it is biodegradable and compostable.