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

Abstract

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 (Δ 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 °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 °C without withdrawal the sample from the instrument and running it again in the temperature range of 25–350 °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 (Δ T g) – corresponding their plasticizing efficiency for H films – was found as follows: GLY = −66.8 °C, PEG 300 = −48.8 °C, PEG 400 = −47.1 °C, PEG 600 = −50.3 °C and PEG 3350 = −9.6 °C.