Design and engineering of starch-based polymer materials as substitutes for persistent non-biodegradable plastics

Replacing carbon-carbon backbone persistent hydrocarbon plastics with biobased and biodegradable plastics offers value proposition of reduced carbon footprint and an environmentally responsible end-of-life. This work focuses on design and engineering of starch based polymeric materials as substitutes for non-biodegradable plastics. The biodegradability of these bioplastics in aqueous environment was evaluated.Starch foams are being used as replacement for petroleum-based foams in insulation and cushion protection applications. However, moisture sensitivity remains a problem resulting in collapse of cell structure and loss of mechanical integrity. First section of the thesis focuses on engineering high-performance starch foams with enhanced moisture resistance using reactive extrusion processing technology. Chitosan, polyvinyl butyral (PVB) and sodium trimetaphosphate (STMP) were used with water as a plasticizer and a blowing agent to make foams with desired physico-mechanical properties. The resulting foams were hydrophobic, insoluble in water, and showed improved moisture resistance. The biodegradability of the foams was not impacted - they were completely biodegradable as established by ASTM/ISO standards. Crosslinking of starch with STMP increased the compressive strength of the foams by three times compared to control foams. Optimization of process parameters ensured an efficient, cost-effective route towards commercialization. In the second section, our group's chemically modified thermoplastic starch (MTPS) prepared by reactive extrusion technology was explored in three different applications. First, MTPS, was melt blended with glycol modified polyethylene terephthalate (PETG) using transesterification chemistry to synthesize MTPS-g-PETG in situ graft copolymer with 33% grafting. Mechanical and thermal properties of the blend were evaluated and compared with neat PETG. The addition of starch into PETG molecular backbone did not result in PETG biodegradability. This finding refutes many claims of biodegradability of non-biodegradable polymers by the addition of starch and similar additives. in the marketplace. Second, the use of MTPS as a biobased and biodegradable nucleating agent and barrier property enhancer in polylactide (PLA) was explored. Our findings establish that MTPS accelerates the rate of crystallization of PLA (polylactide polymers) by up to 98 times at 100°C, reducing the half time for crystallization from 20 mins to less than 1 minute. Oxygen barrier properties of PLA was improved 127% without causing detrimental impact on mechanical properties or biodegradability. Third application focuses on using MTPS as a carrier for iodine, which is a very effective and strong antimicrobial agent. The antimicrobial starch-iodine complex in pellet form was manufactured by extrusion processing. The new MTPS-iodine complex was incorporated in various proportions to commercial fully biodegradable-compostable polyester films. The morphological, mechanical, and antibacterial properties of these films were evaluated and compared with current commercial additives used to obtain antibacterial properties. The last section focuses on the end-of-life evaluations for biobased and biodegradable plastics using kinetics approach. The effect of temperature on biodegradation of cellulose and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) in an aqueous environment seeded with a biologically aggressive microbial inoculum was studied. A global equation was derived from the reparametrized Arrhenius equation and the kinetic rate law to estimate the time required for 90% removal of polymer from the low temperature ocean environment. The t90 (time required to remove 90% of the polymer carbon from the environment) for PHBV at 10°C ranged from 6.2-6.9 years. The t90 of cellulose at 10 C was found to be 1.1-1.2 years. ASTM/ISO standards for measuring and reporting ocean biodegradability is static and conducted at one temperature (30°C), whereas ocean temperatures can vary from −1.8 °C to 33.4 °C. The kinetic analysis and model developed can provide a method to estimate time for complete removal of the biodegradable polymer carbon in ocean environments.