Polycaprolactone (PCL) is an important polymer due to its mechanical properties, miscibility with a large range of other polymers and biodegradability. Two main pathways to produce polycaprolactone have been described in the literature: the polycondensation of a hydroxycarboxylic acid: 6-hydroxyhexanoic acid, and the ring-opening polymerisation (ROP) of a lactone: ε-caprolactone (ε-CL). This critical review summarises the different conditions which have been described to synthesise PCL, and gives a broad overview of the different catalytic systems that were used (enzymatic, organic and metal catalyst systems). A surprising variety of catalytic systems have been studied, touching on virtually every section of the periodic table. A detailed list of reaction conditions and catalysts/initiators is given and reaction mechanisms are presented where known. Emphasis is put on the ROP pathway due to its prevalence in the literature and the superior polymer that is obtained. In addition, ineffective systems that have been tried to catalyse the production of PCL are included in the electronic supplementary information for completeness (141 references).

This review takes an in-depth look at the chemical modifications that have been carried out on nanocrystalline cellulose.

Developing new, alternative ways to recycle plastics is an important and pressing challenge for industry and academy, given its significant impact on CO₂ emissions as well as improvement of resource-efficiency and reduction of landfilling. Currently, re-use and mechanical recycling are the most employed routes to exploit post-consumer plastics; however, chemical recycling, which involves the depolymerization of polymer chains to reclaim the original monomers or intermediate oligomers, is gaining much attention. Chemical recycling allows for the transformation of various types of plastic waste from single-polymer and mixed waste streams back into their original components. By creating a new, secondary virgin-quality raw material, chemical recycling can help close the loop and reduce the consumption of fossil resources. The energy barrier for depolymerization is normally high; thus, these reactions tend to require high temperatures and/or pressures; therefore, diminishing the reaction temperature and pressure through incorporation of catalysts has led to a whole field of study, looking for catalysts that promote solvolysis under mild reaction conditions. In this review, we assess the different depolymerization conditions for polyethylene terephthalate (PET) in the literature, according to three proposed green chemistry metrics that allow us to compare the energy economy (ε coefficient), the environmental factor (E) and the combined effect of both (ξ). These green chemistry metrics parameters allowed us to make a numerical comparison of different studies and to determine their relative feasibility, which can assist in finding better routes for viable implementation of chemolytic depolymerization for present and future studies in the field of chemical depolymerization of PET and other polymer materials.