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.

中文翻译：

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使用非卤化溶剂回收 PHA 共聚物 P(HB-co-HHx)：对分子量和 HHx 含量的影响

可生物降解和生物相容的聚羟基链烷酸酯 (PHA) 是传统塑料的有前途的替代品。根据其单体的链长，它们被分为短链长 (scl-) 或中链长 (mcl-) PHA 聚合物。单体的类型、组成和分子量 (MW) 决定了聚合物的性能。为了加速 PHA 作为散装材料的使用，需要将下游相关成本降至最低。本研究的重点是评估非卤化溶剂，尤其是作为 scl-PHA 非溶剂的丙酮，用于回收聚（3-羟基丁酸酯-co-3-羟基己酸酯）-P(HB-co-HHx)-与mcl-HHx 含量 >15 mol%，平均分子量 (Mw) < 2 × 105 Da。根据共沸物的形成、沸点差异和毒性来选择溶剂和沉淀剂。非卤化溶剂-沉淀剂对就萃取聚合物的 MW 特性 (MWC) 进行了评估。丙酮和 2-丙醇作为一种低毒和共沸溶剂-沉淀剂对，在不同的提取温度和多次提取时间下进行了评估。通过使用不纯的丙酮进行​​提取并实施多级提取过程来进一步评估提取过程。此外，用三种不同的溶剂萃取的 P(HB-co-HHx) 通过 1H 和 13C-APT NMR 进行表征。通过乙醇沉淀分别用丙酮和乙酸乙酯萃取，沉淀剂的筛选对 MWC 产生负面影响。据观察，与在室温下提取相比，在 70°C 下用丙酮提取从细胞中提取的 PHA 比例更高，但 Mw 平均下降了 9%。2-丙醇含量高达 30% 的丙酮仍然能够像纯丙酮一样有效地提取 95% 的聚合物。此外，当丙酮和乙酸乙酯用于多阶段提取过程时，两阶段过程足以从细胞中提取 98-99% 的聚合物。1H 和 13C-APT NMR 分析证实了提取的聚合物的单体分数和结构，并揭示了无规共聚物结构。所提出的策略可以进一步发展为生态和经济上可行的 PHA 下游工艺，从而有助于低成本 PHA 的商业化。当在多阶段提取过程中使用丙酮和乙酸乙酯时，两阶段过程足以从细胞中提取 98-99% 的聚合物。1H 和 13C-APT NMR 分析证实了提取的聚合物的单体分数和结构，并揭示了无规共聚物结构。所提出的策略可以进一步发展为生态和经济上可行的 PHA 下游工艺，从而有助于低成本 PHA 的商业化。当在多阶段提取过程中使用丙酮和乙酸乙酯时，两阶段过程足以从细胞中提取 98-99% 的聚合物。1H 和 13C-APT NMR 分析证实了提取的聚合物的单体分数和结构，并揭示了无规共聚物结构。所提出的策略可以进一步发展为生态和经济上可行的 PHA 下游工艺，从而有助于低成本 PHA 的商业化。