Environmental issues urge for the substitution of petrochemical-based raw materials with more environmentally friendly sources. The biggest advantages of PLA over non-biodegradable plastics are that it can be produced from natural sources (e.g., corn or sugarcane), and at the end of its lifetime it can be returned to the soil by being composted with microorganisms. PLA can easily substitute petroleum-based plastics in a wide range of applications in many commodity products, such as disposable tableware, packaging, films, and agricultural twines, partially contributing to limiting plastic waste accumulation. Unfortunately, the complete replacement of fossil fuel-based plastics such as polyethylene (PE) or poly(ethylene terephthalate) (PET) by PLA is hindered by its higher cost, and, more importantly, slower degradation as compared to other degradable polymers. Thus, to make PLA more commercially attractive, ways to accelerate its degradation are actively sought. Many good reviews deal with PLA production, applications, and degradation but only in the medical or pharmaceutical field. In this respect, the present review will focus on controlled PLA degradation and biodegradation in technical applications. The work will include the main degradation mechanisms of PLA, such as its biodegradation in water, soil, and compost, in addition to thermal- and photo-degradation. The topic is of particular interest to academia and industry, mainly because the wider application of PLA is mostly dependent on discovering effective ways of accelerating its biodegradation rate at the end of its service life without compromising its properties.

The stepwise hydrogenation of 9-ethylcarbazole to 9-ethyl-perhydrocarbazole (Pl 12[H]) via partially hydrogenated intermediate(s) was studied over a number of supported ruthenium and rhodium catalysts. The reaction pathways were modelled and the rate constants for individual hydrogenation steps were compared. It was found that the selectivities to the reaction intermediates and products were highly dependent on the electronic structure of the particular metal and the nature of the support used. Ruthenium was found to be the most active metal for this reaction but it suffered from a poor selectivity to the desired product due to the formation of a kinetically stable intermediate, 9-ethyl-octahydrocarbazole (Pl 8[H]) in short reaction time. On the other hand, rhodium catalysts with moderate activity gave a higher selectivity to the fully hydrogenated product under comparable conditions. It was also found that the presence of a hydrophilic support such as alumina or rutile can give kinetically favoured cis-isomers of the 9-ethyl-perhydrocarbazole. Regarding application of the reversible hydrogen storage concept, the storage material should be able to switch between fully hydrogen loaded and unloaded forms during hydrogenation (material regeneration) and dehydrogenation (delivery of hydrogen gas) in short times. Formation of any stable intermediates and stereo-non-favoured isomers with a particular type of catalyst can result in significant implications to the overall storage capacity as well as operation times for hydrogen gas delivery and regeneration. Thus, this study yields valuable information on the suitability of various metal catalysts for use in hydrogen storage systems based on the liquid organic hydride (LOH) concept.