DEVELOPMENT OF POLYVINYL ALCOHOL BASED COMPOSITES AS ADVANCED PACKAGING MATERIAL

Abstract

In the food packaging industry, polymer and its composites have been used for low-cost high-performance packaging materials. Synthetic polymers like polyethylene, polypropylene, and polyethylene terephthalate are used extensively as the main polymers for food packaging. Due to their non biodegradability, the usage of these polymers has led to various environmental concerns and focus has been shifted towards biodegradable polymers such as polylactic acid, polyvinyl alcohol (PVOH), polycaprolactone, polyglycolic acid, polybutylene succinate, and polybutylene adipate-co-terephthalate. PVOH, as one of the potential biodegradable polymers, is a water-soluble, non-toxic, odorless, and possess various physicochemical properties such as viscosity, film-forming, emulsifying, dispersing power, tensile strength, and flexibility. Apart from these, thermostability, adhesiveness, high tolerance towards solvents and gas barrier properties makes it suitable for its wide application in various industries like adhesives, emulsion polymerization, fabric and paper sizing, fiber coating, film for packaging and farming. Also, PVOH and its composite as coating material on paper and as smart packaging film with improved physicochemical and barrier properties with the addition of platelet-like minerals montmorillonite (MMT), kaolin and talc and natural compound like plant extract, essential oils have been explored. In this work, attempts have been made to increase the process speed of coating preparation by a single step process at varying pigment concentration. Coating dispersion was applied on Kraft paper using a laboratory rod coater and dried in hot air oven at 80°C for 5 minutes. Further, thermal stability, water vapor transmission rate (WVTR) and grease resistance of PVOH/kaolin and PVOH/talc coated paper were studied. Additionally, trials were also done to analyze the effect of single and bilayer coating on paper properties. Thereafter, a permeability model was used to predict the orientation of pigments to the surface of paper. It was noted that viscosity of both kaolin and talc-based dispersion increased with the increase in pigment concentration. Thermal studies showed that at 600°C residual mass (%) of PVOH film increased from 0.6% to 9.89% and 15% with the addition of 25% (by weight) kaolin and talc pigment. At high pigment concentration (40% - 50%, by weight) the greatest reduction in WVTR was observed for both the pigments. Excellent coverage of the paper surface, and high grease resistance was observed for all coating formulations. This study concluded that talc acts as a better insulator than kaolin, and for the pigments studied in this case, talc, with its higher aspect ratio and chosen particle size, also provided better barrier properties. In the second section of the study, polyphenols present in pomegranate peel were extracted, and their adsorptive interaction with kaolin clay was investigated by the UV spectroscopic method. Adsorption isotherm data were best fitted to the Langmuir model. Moreover, the kinetic study revealed that the trend was in significant agreement with pseudo-second-order. The results showed that the maximum quantity of adsorbed polyphenol on kaolin was 24.96 mgGAE/g of kaolin at 25°C. Adsorbed polyphenols on kaolin were further characterized by zeta potential, Fourier Transform Infrared spectroscopy (FTIR), and X-Ray Diffraction (XRD). FTIR analysis showed that polyphenols were adsorbed on kaolin via hydrogen bonding. Zeta potential analysis showed less negative value conforming to the adsorption of polyphenols on kaolin. Intercalation of polyphenols between kaolin platelets was also observed by XRD analysis. Further, Polyphenol-kaolin nanofiller was incorporated in the composite films. The prepared films were characterized for structural, mechanical, thermal, morphological, and barrier properties. Color and 2, 2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity of films were studied for the appearance and antioxidant activity of the composite films. Total phenolic content of polyphenols released from composite films after 24 hours in distilled water and food simulant showed 36% and 27% release of polyphenols into the solvent, thus continuously replenishing the polyphenols onto the food surface. Finally, the active and intelligent films based on PVOH/methoxy-kaolin with betalains rich beetroot (Beta vulgaris) extract, extracted at low temperature from fresh beetroot, was prepared. Betacyanin and betaxanthin were found to be the main component of beetroot extract with an extraction yield of 11.74 mg/100 g and 7.9 mg/100 g of fresh beetroot, respectively. Beetroot extract showed that stability of betalains components was maintained from pH range 3-9, and degradation starts under highly alkaline environment i.e. above pH 9. Beetroot extract showed a total phenolic content defined as gallic acid equivalent (GAE), of 1.4 mg GAE/g of fresh beetroot and an antioxidant activity of 93.07%. The physical and functional properties of PVOH/methoxy-kaolin film containing 15%, 20%, 30% (v/v) beetroot extract was characterized using FTIR, XRD, and Thermogravimetric Analysis (TGA). An increase in XRD determined crystalline plane separation (d-spacing) of methoxy-kaolin was observed due to the addition of beetroot extract in the PVOH/methoxy-kaolin matrix. The addition of beetroot extract showed loss on both thermal and mechanical properties. Methoxy-kaolin showed positive effects by reducing the water vapor permeability of the Colorimetric films. Colorimetric films showed a response to 8 mM ammonia solution with a change in Color from pink to yellow. Colorimetric films with 30% beetroot extract showed a high response to ammonia solution and high antioxidant activity. The study showed the potential of PVOH as advanced packaging materials which can be used for the preparation of coating dispersion by incorporating high content of platelet-like minerals. Furthermore, PVOH was successfully utilized as matrix by incorporating two different plant extracts and showed antioxidant and colorimetric functional properties.