Modified biobased materials from polyhydroxyalkanoates for packaging and engineering applications

This work relates to the development of new biobased and biodegradable blends, composites and nanocomposites from polyhydroxyalkanoates (PHAs). PHAs are the renewable-resource-based biodegradable thermoplastic biopolyesters synthesized by bacteria. This dissertation focuses on two members of the PHA family; polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV). Renewable-resource-based polymers are a strategic option to meet the growing need for sustainable materials for the next generation owing to the depletion of global oil reserves, increase in fossil-fuel based resin prices and environmental concerns.; The main goal of this dissertation is to focus on a renewable-resource-based biodegradable polymer and modify as well as develop it so as to make the resulting biobased materials comparable or even better than conventional polymers in properties. In the first part of this work, novel toughened PHB-based green materials were successfully developed through reactive extrusion of PHB and functionalized natural rubber in presence of a compatibilizer followed by injection molding. Maleated polybutadiene with high grafting and low molecular weight was determined to be an efficient compatibilizer for the PHB-rubber blend system thereby improving the toughness of PHB by 440%. The resultant toughened PHB exhibited impact strength (124 J/m) superior to specific toughened conventional polymers. Montmorillonite clay treated with neopentyl (diallyl)oxy tri(dioctyl) pyrophosphato titanate was used as a reinforcement for toughened PHB in order to develop novel biodegradable nanocomposites. The titanate-based surface modified clay, PHB, toughening partner and specific compatibilizer were processed by extrusion followed by injection molding. The novel aspect of the titanate-based modification was that the nanocomposites still maintained nearly the same impact strength value as that of toughened PHB yet improved the modulus. The diffraction patterns suggest exfoliation of the organically modified clays and this was further supported by transmission electron microscopy and melt rheological analysis coupled with theoretical modeling. Toughened and compatibilized PHB showed significantly lower biodegradation rate than virgin PHB however titanate-modified clay-nanocomposites regained the biodegradation rate.; The second part of this dissertation involved the reactive blending of a plasticized biobased polymer with PHBV matrix in order to get a novel and flexible biodegradable material. A thermoplastic starch (TPS) system was developed by blending of corn starch, glycerol (byproduct of soy-based biodiesel industries) and poly-(butylene adipate-co-terephthalate) (PBAT). Following optimization by structure-property-processing correlation, this thermoplastic starch system was blended with PHBV to obtain a biodegradable flexible polymer blend and further reinforced with talc and processed into cast films. The incorporation of talc promoted disruptive mixing, homogeneity and subsequently reduced the droplet size of the components ultimately giving improvement in physical properties. The talc-filled films showed remarkable improvement in barrier properties and this was ascertained to be because of a combination of the tortuosity effect and the nucleating effect of the talc and the improved mixing. The ability of PHBV-TPS system as well as the talc-filled composites to resist ageing was also established.