Continual reduction of landfill space along with rising CO₂levels and environmental pollution, are global issues that will only grow with time if not correctly addressed. The lack of proper waste management infrastructure means gloablly commodity plastics are disposed of incorrectly, leading to both an economical loss and environmental destruction. The bioaccumulation of plastics and microplastics can already be seen in marine ecosystems causing a negative impact on all organisms that live there, ultimately microplastics will bioaccumulate in humans. The opportunity exists to replace the majority of petroleum derived plastics with bioplastics (bio-based, biodegradable or both). This, in conjunction with mechanical and chemical recycling is a renewable and sustainable solution that would help mitigate climate change. This review covers the most promising biopolymers PLA, PGA, PHA and bio-versions of conventional petro-plastics bio-PET, bio-PE. The most optimal recycling routes after reuse and mechanical recycling are: alcoholysis, biodegradation, biological recycling, glycolysis and pyrolysis respectively.

Poly(lactic acid) (PLA) was degraded to methyl lactate (Me-La) by an imino monophenolate Zn(1)2 catalyst in the presence of THF, as the solvent, and methanol, as the protic source. As well as solution based polymerization and degradation, catalyst stability was also assessed and discussed. The chemical degradation of four different commercial samples of PLA, varying in molecular weight, was studied. The effect of PLA concentration (0.05 to 0.2 g mL-1), reaction temperature (40 to 130 °C), and catalyst concentration (4 to 16 wt%) on conversion, yield and selectivity were studied and statistically analyzed. Mass transfer limitations were examined by utilizing two different PLA particle sizes and altering the stirring speed. Results revealed that the main variables affecting PLA degradation by Zn(1)2 are temperature and catalyst concentration. It was possible to observe Me-La formation even at 40 °C although the reaction times were significantly longer compared with the highest temperatures. Conversions of 100%, as determined by 1H NMR spectroscopy and GPC, were possible in short times (<15 min) depending on the reaction temperature and catalyst concentration. A reaction mechanism for the production of Me-La from PLA degradation, which considers oligomers as an intermediate product, is presented and values of the kinetic constants provided from this modelling. The activation energy for the initial PLA degradation step was found to be 42 – 66 kJ mol-1, generally decreasing with catalyst loading. This work presents a discrete metal complex catalyst that can be used for the chemical recycling of PLA to Me-La.

The use of a simple, cheap and effective organocatalyst, has been exploited for the transesterification/degradation of commercial polymers.

The catalyzed methanolysis of end-of-life poly(lactic acid) (PLA) products by an ethylendiamine Zn(II) complex to form biodegradable methyl lactate was studied experimentally at 70 °C, 90 °C and 110 °C. The PLA samples consisted of typical consumer waste materials including a cup, a toy and 3D printing material. High selectivities and yields (>94%) were possible depending on temperature and reaction time. Additionally, and in order to develop a predictive kinetic model,kinetic parameters (pre-exponential factor and activation energies) of the PLA transesterification reaction were first obtained from virgin PLA. These parameters were subsequently used to estimate the conversion of PLA, selectivity and yield of methyl lactate after 1 h and 4 h of reaction, and the results were compared with the experimental values of the end-of-life PLA. Despite the presence of unknown additives in the PLA waste material and uncontrolled particle size, the model was able to predict the overall conversion, selectivity and yield to an average deviation of 5, 7 and 12% respectively. Greater agreement between model and experimental values are observed for the higher temperatures and the longer reaction time. Larger deviations were observed for the PLA toy which we attribute to the presence of additives, since despite its lower molecular weight, it possessed a higher structural strength.