The physico-mechanical and structural characteristics of blend film of poly (vinyl alcohol) with biodegradable polymers as affected by disorder-to-order conformational transition

• Binary blend films of PVA/some biopolymers at their coil-overlap concentration were investigated.
• Coil overlap concentration is a critical factor in determining the concentration of blend films.
• The conformational change of κ-carrageenan had a considerable effect on PVA hydrophobicity.
• PVA/κ-carrageenan blend showed high water resistant and barrier properties.
• κ-carrageenan inclusion improved the mechanical and structural properties of the PVA film.

The binary blend films of poly (vinyl alcohol) (PVA) were prepared with selected biodegradable polymers (Na-alginate, gelatin, chitosan, κ-carrageenan and carboxymethyl cellulose) at the point of their chain entanglement. The water resistance, water vapor permeability and mechanical assays were considered as a benchmark to select the superior blend film. The highest water resistant and water barrier property belonged to the blend that contains κ-carrageenan. Introducing the biodegradable polymers into PVA led to an increase in tensile strength, among which κ-carrageenan being further effective than the others. Accordingly, the influence of conformational change of κ-carrageenan chains from disorder-to-order mode on PVA matrix was monitored by hydrophobicity assay, FT-IR, FE-SEM and XRD. The conformational change of κ-carrageenan increased PVA hydrophobicity. κ-carrageenan chains which are presented as the ordered form, noticeably decreased the surface free energy of the PVA-based film. The emergence of new characteristic bands regarding κ-carrageenan found in the fingerprint region of PVA at above κ-carrageenan coil-overlap concentration. FE-SEM exhibited that PVA surface became uniform along with the disappearance of cracks after κ-carrageenan inclusion. The pronounced κ-carrageenan peak appeared in diffraction pattern of PVA after the conformational transition of κ-carrageenan chains.

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