Abstract
Biodegradable and biocompatible polyhydroxyalkanoates (PHAs) are promising alternatives to conventional plastics. Based on the chain length of their monomers they are classified as short chain length (scl-) or medium chain length (mcl-) PHA polymers. The type of monomers, the composition and the molecular weight (MW) define the polymer properties. To accelerate the use of PHA as a bulk material, the downstream associated costs need to be minimized. This study focuses on the evaluation of non-halogenated solvents, especially acetone as a scl-PHA non-solvent, for the recovery of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) – P(HB-co-HHx) – with an mcl-HHx content >15 mol% and a MW average (Mw) < 2 × 105 Da. Solvents and precipitants were chosen regarding zeotrope formation, boiling point differences, and toxicity. Non-halogenated solvent-precipitant pairs were evaluated regarding the MW characteristics (MWCs) of the extracted polymer. Acetone and 2-propanol as a low toxic and zeotropic solvent-precipitant pair was evaluated at different extraction temperatures and multiple extraction times. The extraction process was further evaluated by using impure acetone for the extraction and implementing a multi-stage extraction process. Additionally, P(HB-co-HHx) extracted with three different solvents was characterized by 1H and 13C-APT NMR. The screening of precipitants resulted in a negative influence on the MWCs by ethanol precipitation for extractions with acetone and ethyl acetate, respectively. It was observed, that extractions with acetone at 70°C extracted a higher fraction of PHA from the cells compared to extractions at RT, but the Mw was decreased by 9% in average. Acetone with a 2-propanol fraction of up to 30% was still able to extract the polymer 95% as efficient as pure acetone. Additionally, when acetone and ethyl acetate were used in a multi-stage extraction process, a two-stage process was sufficient to extract 98–99% of the polymer from the cells. 1H and 13C-APT NMR analysis confirmed the monomer fraction and structure of the extracted polymers and revealed a random copolymer structure. The presented strategy can be further developed to an ecological and economically feasible PHA downstream process and thus contributes to the commercialization of low-cost PHAs.
Highlights
Plastic pollution of land and sea is a ubiquitous problem, which results in microplastic in the animal and human food chain
With the objective to compare the MW characteristics (MWCs) of P(HB-co-HHx) extracted with ethyl acetate or acetone and precipitated by different solvents (1-propanol, 2-propanol, ethanol, n-heptane), material was extracted from freeze-dried cells
A cell solvent suspension with a cell concentration of 0.1 g mL−1 was used for the recovery experiments and the PHA was precipitated by adding the three-fold volume of the respective non-solvent
Summary
Plastic pollution of land and sea is a ubiquitous problem, which results in microplastic in the animal and human food chain. Biodegradable alternatives, such as microbial synthesized polyhydroxyalkanoates (PHAs), have the potential to partially substitute fossil-based and non-biodegradable plastics (Sudesh et al, 2000; Chen, 2009; Brigham and Sinskey, 2012; Kourmentza et al, 2017; Brigham, 2018). Large amounts of halogenated solvents – e.g. chloroform – are traditionally used in the extraction process (Pérez-Rivero et al, 2019). The downstream process accounts for a large portion of the PHA production price
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
