Polymeric composites for biodegradable and antimicrobial food packaging applications

Disposal of petroleum based plastic packages like Polyethylene (PE), Low Density Polyethylene (LDPE) or Polypropylene (PP) leads to a serious environmental problem worldwide due to the fact that most of them are generally non-biodegradable. Therefore, biodegradable packaging is gaining importance for their daily use. Thus, attention is needed to be given for the preparation of some novel biodegradable packaging material which can meet the present demand and can be applied for practical use; such as food packaging. Researchers of Tomas Bata University in Zlin, Czech Republic already started to work on this aspect to achieve commercial grade polyol based hydrogel food packaging which is prepared with Polyvinylpyrrolidone (PVP), Sodium-CarboxyMethyl Cellulose and other ingredients (polyethylene glycol, Agar-agar, glycerol and water) to form hydrogel film designated as "PVP-CMC" hydrogel, which is biodegradable but showing very low levels of mechanical properties. Food packaging material point of view, each package should be biodegradable, but also exhibits quite good mechanical properties. Hence, in this Master Thesis, focus has been given to improve the mechanical properties of the existing biopolymer based hydrogel (i.e. PVP-CMC) food package which is already reported as biodegradable under natural conditions. In this Master Thesis, three different kinds of polymeric films were prepared by modifying PVP-CMC with three different additives like: Sepiolite (Sep), PVA Nanofiber (PVA) and Bacterial cellulose (BC). Each case, additive concentration was varied (i. e. 0.05, 0.10, 0.15 and 0.20 g additive was added in 150 mL polymer solution). The biopolymer based films were prepared by the solvent casting method and designated as "PVP-CMC-Sep", "PVP-CMC-PVA" and "PVP-CMC-BC" respectively. Structural properties of the above mentioned films were characterized by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction method (XRD) as well as Scanning Electron Microscopy (SEM) which analysed the surface morphology of the films. FTIR, XRD and SEM analysis confirmed that the modified PVP-CMC films are true biocomposites. The mechanical properties of these four films, including PVP-CMC (without additive) were investigated by the tensile strength test which shows: 47.79±13.85 MPa (PVP-CMC-BC-0.10)>33.75±7.19 MPa (PVP-CMC-Sep-0.15)>25.21±5.97 MPa (PVP-CMC-PVA-0.20)>20.53±2.37 MPa PVP-CMC respectively. Thus, thermal, permeability, biodegradability and antimicrobial tests of the polymeric films were performed for the selected PVP-CMC-Sep-0.15, PVP-CMC-PVA-0.20, PVP-CMC-BC-0.10 films (as test samples) which showed a considerable range of mechanical property after modification of PVP-CMC hydrogel films by Thermal Gravimetric Analysis (TGA), Water Vapour Transmission (WVT) test, soil burial test and disc diffusion method, respectively. As a result of antimicrobial test by disc diffusion method, it is observed that films have mostly antimicrobial effect on both bacteria of Escherichia coli and Staphylococcus aureus. On the contrary, the films do not play antifungal role for neither fungus of Aspergillus niger nor Candida albicans. It was noticed that more than half of the weight was lost after first 7 days of biodegradability test period that is 21 days due to degradation of polymeric films by the soil bacteria present in the garden soil. It was observed that all films are biodegradable in nature. It can be concluded that as PVP-CMC-BC-0.10 showed the highest tensile strength and highest barrier property as compared to the other additive based biocomposites. Therefore, PVP-CMC-BC based composites hydrogel film can be recommended as a good polymeric biomaterial for food packaging.