Unique properties of PGA, and its modifications and applications.

The aerobic composting and anaerobic digestion of plastics is a promising route to recovering the multidimensional value from biodegradable single-use plastics. At present, the collection, separation, and management of biodegradable plastic waste are extremely challenging, and the majority of these plastics still end up in landfills or incineration facilities. This is because not all biodegradable plastics can be treated using organic waste management options (composting). In addition, end-users at a domestic and industrial level are often unaware of the compostability potential of biodegradable plastics, which results in the mismanagement of these types of plastic. A greater understanding of the compostability of biodegradable plastics will generate the required knowledge base for interventions that support their market penetration, use, and proper management. In this review, we clarify the concepts of biodegradability and compostability in bioplastics, in particular commercial synthetic biopolyesters, which have increasing technical and economic importance, and discuss how macromolecular design, blending, and additives can be used to modify their compostability. Future trends on the uptake of compostable and biodegradable bioplastics are also discussed.

Furandioate-adipate copolyesters are an emerging class of bio-based biodegradable polymers with great potential to replace fossil-derived terephthalic acid-based copolyesters such as poly(butylene adipate- co -terephthalate) (PBAT). Furandioate-adipate polyesters have almost exclusively been prepared with conventional primary (1°) alcohol diols, while secondary (2°) alcohol diol monomers have largely been overlooked until now, despite preliminary observations that using methyl-branched diols increases the T g of the resultant polyesters. Little is known of what impact the use of 2° alcohol diols has on other properties such as material strength, hydrophobicity, and rate of enzymatic hydrolysis—all key parameters for performance and end-of-life. To ascertain the effects of using 2° diols on the properties of furandioate-adipate copolyesters, a series of polymers from diethyl adipate (DEA) and 2,5-furandicarboxylic acid diethyl ester (FDEE) using different 1° and 2° alcohol diols was prepared. Longer transesterification times and greater excesses of diol (diol/diester molar ratio of 2:1) were found to be necessary to achieve M w s > 20 kDa using 2° alcohol diols. All copolyesters from 2° diols were entirely amorphous and exhibited higher T g s than their linear equivalents from 1° diols. Compared to linear poly(1,4-butyleneadipate- co -1,4-butylenefurandioate), methyl-branched, poly(2,5-hexamethyleneadipate- co -2,5-hexamethylenefurandioate) (0:7:0.3 furandioate/adipate ratio) displayed both higher modulus (67.8 vs 19.1 MPa) and higher extension at break (89.7 vs 44.5 mm). All other methyl-branched copolyesters displayed lower modulus but retained higher extension at break compared with their linear analogues. Enzymatic hydrolysis studies using Humicola insolens cutinase revealed that copolyesters from 2° alcohol diols have significantly decreased rates of biodegradation than their linear equivalents synthesized using 1° alcohol diols, allowing for fine-tuning of polymer stability. Hydrophobicity, as revealed by water contact angles, was also found to generally increase through the introduction of methyl branching, demonstrating potential for these materials in coatings applications.

The rise in demand for biodegradable plastic packaging with high barrier properties has spurred interest in poly(lactic acid-co-glycolic acid) (PLGA) copolymers with a relatively high glycolide content. In this work, we examined how reaction conditions affect the synthesis of PLGA25 (L:G 25:75) through the ring-opening polymerisation of d-l-lactide (L) and glycolide (G), using tin 2-ethylhexanoate (Sn(Oct)2) as the catalyst and 1-dodecanol as the initiator. The effects of varying the initiator concentration, catalyst concentration, reaction time, and temperature on the molecular weight, monomer conversion, and thermal properties of PLGA25 were investigated. Increasing the reaction temperature from 130 to 205 °C significantly reduced the time required for high monomer conversions but caused greater polymer discolouration. Whilst increasing the [M]:[C] from 6500:1 to 50,000:1 reduced polymer discolouration, it also resulted in longer reaction times and higher reaction temperatures being required to achieve high conversions. High Mn and Mw values of 136,000 and 399,000 g mol−1 were achieved when polymerisations were performed in the solid state at 150 °C using low initiator concentrations. These copolymers were analysed using high temperature SEC at 80 °C, employing DMSO instead of HFIP as the eluent.