Plasticizing collagen hydrolysate with glycerol and low-molecular weight poly(ethylene glycols)

The plasticizing efficiency of glycerol (GLY)and poly(ethylene glycols) of molecular mass 300-3350 Da (PEG 300-PEG 3350) for films of collagen hydrolysate (H) was assessed on the basis of the glass transition temperature depression (Delta T-g). The plasticizing effect of hydrophilic plasticizers was separated from the plasticizing effect of water absorbed to H films by means of two-stage differential scanning calorimetry (DSC). The first stage of DSC, conducted in a temperature interval of 25-150 degrees C led to removal of absorbed water. The T-g values of un-plasticized films estimated in second DSC stage (after cooling the measured sample to 25 degrees C without withdrawal the sample from the instrument and running it again in the temperature range of 25-350 degrees C) correspond to value of dehydrated gelatin films and H films contain only structurally (more firmly) bound water (approximately 2.5% mass). With plasticized H films a decrease in T-g depending on the type and concentration of employed plasticizer was observed. With glycerol, T-g decreases with the film increasing glycerol concentration in film, with poly(ethylene glycols) it attains a certain limit level at their approximately 20% concentration in film. At 20% concentration the plasticizers under study gave a T-g depression (Delta T-g) - corresponding their plasticizing efficiency for H films - was found as follows: GLY = -66.8 degrees C, PEG 300 = -48.8 degrees C, PEG 400 = -47.1 degrees C, PEG 600 = -50.3 degrees C and PEG 3350 = -9.6 degrees C. (C) 2008 Elsevier B.V. All rights reserved.