Effect of pre-treatment temperatures on the film-forming properties of collagen fiber dispersions

Collagen fiber dispersions were formed and the influence of pre-treatment temperatures on the fiber structure and film-forming properties was investigated. A pre-transition at 33.0 °C and a main denaturation transition at around 42.8 °C were observed according to the dynamic temperature sweep of the dispersions. Accordingly, the dispersions were pre-treated at specific temperatures to obtain different structure of collagen fiber. The storage modulus and loss modulus of dispersions decreased sharply at > 39 °C. Also, the viscosity had a similar trend and the power law exponent n became larger. Microstructure and SDS-PAGE analysis showed that high temperature (≥45 °C) destroyed the fiber network and more low molecular weight fragments dissolved in dispersions. The tensile strength and elongation at break of films all decreased with the increase of temperature while the water solubility increased, attributing to the degeneration of collagen. The film hydrophilicity also increased due to more collagen turning into gelatin. However, the water vapor permeability and oxygen permeability of collagen fiber films were improved with the increase of temperature, indicating that suitable heating could improve their barrier properties. Moreover, the layered fiber network in films gradually disappeared with the increase of pre-treatment temperature. All films had typical characteristic infrared peaks of collagen and the values of AIII/A1450 gradually decreased from 1.2976 to 1.0802, indicating reduced contents of triple helix. The intensity of the XRD peaks at ~8° also decreased and higher temperatures promoted the stripping of collagen molecules from collagen fiber, where collagen molecular chains closely contact with each other.