As plastic production and consumption increase globally, so does the amount of plasticwaste to be disposed of and managed. Most worldwide plastic waste ends in landfills, open dumps, or leaks into the environment. Hence, new alternatives, such as developing biobased and biodegradable polymers, have been proposed to tackle the ever-growing plastic waste problem and help reduce the amount of plastic coupled with organic waste reaching landfills or incineration facilities. It is essential to understand the degradation behavior of these novel polymers to guarantee their ultimate biodegradation together with organic waste. Among them, poly(lactic acid) (PLA), a popular biobased and compostable polymer produced from renewable sources has garnered much interest due to its low environmental footprint and ability to replace conventional polymers and be disposed of in industrial compost environments. Although PLA is industrially compostable when subjected to a suitable set of conditions (i.e., aerobic thermophilic conditions for an extended period), its acceptance in industrial composting facilities is affected adversely due to longer timeframes to degrade than the readily biodegradable organic fraction of waste. So, PLA’s requirement to be fully exposed to thermophilic conditions for prolonged periods to biodegrade has restricted its adoption and hindered its acceptance in industrial composting facilities. This dissertation proposes three different approaches to improve PLA biodegradation under mesophilic conditions to open new avenues of biodegradation, such as home/backyard composting and guaranteeing industrial composting biodegradation at similar times as that of readily biodegradable materials. For the first approach, a reactive blend of PLA with thermoplastic starch (TPS) was produced and evaluated for biodegradation under mesophilic (37°C) and thermophilic (58°C) conditions. Films were tested for biodegradation by analysis of evolved CO2 for 180 days in simulated composting conditions in an in-house built direct measurement respirometer (DMR). The films' average molecular weight (Mn) and crystallinity (Xc) were tracked throughout the test duration, and the kinetic degradation rate was calculated. The introduction of TPS positively affected accelerating PLA hydrolysis during the lag phase in both mesophilic and thermophilic conditions due to increased chain mobility, resulting in faster degradation of PLA at both biodegradation conditions. The second approach involved the introduction of biostimulants in compost to target different stages of biodegradation and enhance the enzymatic activity of microorganisms. PLA and biostimulants, Fe3O4 nano-powder, skim milk, gelatin, and ethyl lactate were introduced into the compost media at 37°C. The CO2 evolution, Mn, and Xc of PLA, PLA added with single biostimulants, and PLA added with a combination of biostimulants were evaluated to investigate the degradation of PLA. To attain Mn values of ≲10 kDa for PLA, PLA added with skim milk experienced a biodegradation acceleration of 15%, 25% with gelatin, and 22% with ethyl lactate. Fe3O4 enhanced the biodegradation rate by 17% whereas the combination of gelatin and Fe3O4 resulted in a substantial increase of biodegradation rate of around 30%. The last approach explores the use of enzymatic pretreatments. PLA films were pretreated with proteinase K enzyme at 37°C for 7 and 10 days and at 58°C for 2 and 5 days. These films were later introduced in inoculated vermiculite at 37°C and 58°C in the DMR to investigate the effect of pretreatment by simulating home and industrial composting settings. The results showed a higher CO2 evolution and visible degradation for PLA films pretreated with proteinase K compared to the untreated control PLA films. This dissertation presented three innovative methods to speed up PLA film biodegradation in composting. It provides potential solutions to remove the barrier for degrading PLA in home and industrial composting conditions and to help address the plastic pollution challenge by effectively degrading biodegradable polymers with organic waste.
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