Work

Direct melt extrusion of polyhydroxyalkanoate solvent-rich gels after polymer extraction and melt processing with integrated solvent recovery

Year: 2025

Type: article

Abstract: Melt extrusion was evaluated for polyhydroxyalkanoate (PHA)-solvent gels. Gels in 2-butanol were produced with polyhydroxybutyrate (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) co-polymer blends. Gels were formed by extracting PHA from dried biomass, or by dissolving it in 2-butanol, at up to 135 °C followed by cooling the solutions to room temperature. Excess solvent was pressed from the gel to make a compact gel cake. Cakes with less than 95 wt.% 2-butanol were grated into a granulate that could then be consistently fed and melt-processed in a twin-screw extruder. Gels showed significantly reduced PHA melt temperatures. For example, PHB melting temperature was reduced from 180 °C (neat polymer) to 115 °C in a 60 wt.% 2-butanol gel. The PHA molecular weight decomposition rates were independent of 2-butanol presence, and they were reduced 6-fold from 180 to 160 °C. Gel extrusion accomplishes polymer drying, solvent recovery, and melt processing altogether. More than 98 wt.% solvent removal with 77 wt.% solvent recovery was achieved using a vacuum pump and condenser attached to one extruder vent port. Extrudate quality was consistent, but it was influenced by the selected die temperature and barrel conditions that controlled gel residual solvent content at the die. PHA gel extrusion was characterized, and experiments are reported herein. Process efficiencies (solvent recovery and specific mechanical energy), and extrudate qualities were assessed. Insights were gained with thermogravimetry, differential scanning calorimetry, rheology and microscopy. The outcomes suggest benefits from directly combining solvent-based PHA recovery from biomass with gel-based PHA formulation and melt-processing into bioplastic articles.

Source: Journal of Cleaner Production

DOI: 10.1016/j.jclepro.2025.145818

Authors: Sanjay Pal, Philip Kridiotis, Ana Jiménez Vergel, Zarja Medved, Raquel Barbosa, Alan Werker

Institutions: Wetsus, European Centre of Excellence for Sustainable Water Technology, The University of Queensland, Delft University of Technology

Language: English

Topic: biodegradable polymer synthesis and properties

Subfield: Biomaterials

Field: Materials Science

Domain: Physical Sciences

SDG: Responsible consumption and production

Open Access status: hybrid

Estimated APC paid: $4,660