ABSTRACT
The aim of this research work was the comparative study of the different properties of interest in the case of plastic materials for food use before and after being subjected to treatment by high hydrostatic pressure (HHP) as well as the impact of additivation with antimicrobials. This method of food preservation is currently on the rise and is of great interest because it is possible to extend the shelf life of many foods without the need for the use of additives or thermal processing, as is the case with other preservation methods currently used. The effects of HHP treatment (680 MPa for 8 min) on plastic materials commonly used in the food industry were studied. These materials, in sheet or film form, were polyethylene (PE), polyethylene terephthalate (PET), polystyrene (PS), multilayer polyethylene terephthalate-ethylene-vinyl alcohol copolymer-polyethylene (PET-EVOH-PE), multilayer polyethylene-polyethylene terephthalate (PE-PET), polyvinyl chloride aluminum (PVC-AL), and polylactic acid (PLA), which were provided by manufacturing companies in the sector. PE, PP, and PLA activated with tyrosol, zinc oxide, or zinc acetate were also tested. The phenomena and properties, such as overall migration, thermal behavior, oxygen barrier, and physical properties were analyzed before and after the process. The results show that the HHP process only slightly affected the properties of the materials. After pressurization, oxygen permeability increased greatly in PVC-AL (from 7.69 to 51.90) and decreased in PLA (from 8.77 to 3.60). The additivation of the materials caused a change in color and an increase in oxygen permeability. The additivated PE and PP showed migration values above the legal limit for certain simulants. The HHP treatment did not greatly affect the mechanical properties of the additivated materials. The main increases in the migration after HHP treatment were observed for PE activated with tyrosol or zinc oxide and for PS activated with zinc oxide. Activated PLA performed the best in the migration studies, irrespective of the HHP treatment. The results suggest that activated PLA could be used in HHP food processing as an inner antimicrobial layer in contact with the food packed in a container with the desired oxygen permeability barrier.
ABSTRACT
Chitosan/bacterial cellulose composite films containing diamond nanoparticles (NDs) with potential application as wound dressing are introduced. Microstructural studies show that NDs are uniformly dispersed in the matrix, although slight agglomeration at concentrations above 2 wt % is seen. Fourier transform infrared spectroscopy reveals formation of hydrogen bonds between NDs and the polymer matrix. X-ray diffraction analysis indicates reduced crystallinity of the polymer matrix in the presence of NDs. Approximately 3.5-fold increase in the elastic modulus of the composite film is obtained by the addition of 2 wt % NDs. The results of colorimetric analysis show that the composite films are transparent but turn to gray-like and semitransparent at high ND concentrations. Additionally, a decrease in highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) gap is also seen, which results in a red shift and higher absorption intensity towards the visible region. Mitochondrial activity assay using L929 fibroblast cells shows that the nanocomposite films are biocompatible (>90%) after 24 h incubation. Multiple lamellapodia and cell-cell interaction are shown. The results suggest that the developed films can potentially be used as a flexible platform for wound dressing.
