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 conven- tional thermoplastics, collagen processing is challenging due to its complex intra- and intermolecular in- teractions. 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 in- teractions 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 demon- strated 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.