Abstract:

In order to improve the performance of collagen film, a colorant consisting of cochineal carmine and sorghum
red pigment was used to dye the collagen film. The optimum dyeing process was determined with respect to different
dyeing conditions such as colorant concentration, temperature, pH value and time. The results showed that the best dyeing
efficiency could be obtained by using 3% colorant at 40 ℃ and pH 5.0 for 8 min. The measurement of contact angle
and water absorption ratio indicated that the surface hydrophilicity of the dyed collagen film was improved obviously.
The Fourier transform infrared spectrum showed that the dyed molecules reacted with collagen film. The differential
scanning calorimetry (DSC) and thermogr avimetric (TG) analysis suggested that the denaturation temperature and initial
decomposition temperature of the dyed collagen film were increased by 20 ℃ and 100 ℃ or so, respectively. Mechanical
tests confirmed that the tensile strength of the dyed collagen film was higher than that of native collagen film.

Key words: edible collagen film, composite colorants, cochineal carmine, sorghum red pigment, dyeing properties