Enhancing the processability and mechanical performance of collagen-based biofilms through supercritical carbon dioxide plasticisation

Abstract

The hierarchical structure and high molecular weight of bovine collagen fibres, along with their widespread availability, make this animal protein a promising candidate for biofilm production. However, unlike conventional thermoplastics, collagen processing is challenging due to its complex intra- and intermolecular interactions. This study investigated the use of supercritical carbon dioxide (sCO₂) as a plasticising agent to modify these interactions during a pretreatment phase prior to film formation via extrusion-compression moulding. Different supercritical conditions were tested, and the combined effect of sCO₂ and glycerol (Gly), a common plasticiser, was evaluated. Microstructural analyses of the pretreated powders and resulting biofilms revealed an unconventional plasticisation mechanism, characterised by the loss of the triple-helix structure and the formation of a randomly cross-linked network. This effect was particularly pronounced under supercritical conditions at higher temperatures (80 °C and 80–300 bar), where the loss of surface water from the collagen fibres and interactions between functional groups in denatured fibres led to enhanced plasticity. As a result, the extruded films exhibited a reduction in stiffness of up to 20 % and an increase in elongation at break by more than 50 %. In contrast, pretreatments at lower temperatures and pressures (35 °C and 80 bar) caused only minor chain scission, preserving the triple-helix structure and yielding rigid films with limited deformability. These findings demonstrated that controlling supercritical conditions in the presence of glycerol during collagen pretreatment is an effective strategy to enhance the processability and mechanical performance of collagen-based biofilms.