Concentration and Humidity Effect on Gelatin Films Studied by NMR

Gelatin films were prepared using different initial concentrations (1 to 30%) in H2O (w/v). The solid films were kept at four different environmental conditions at 20%, 43%, 75%, and 90% relative humidity, until complete equilibrium was achieved. Spin–spin relaxation (T2) and spin–lattice relaxation (T1) times of the samples were determined using a low-field nuclear magnetic resonance (NMR) spectrometer operated at 40 MHz proton (1H) Larmor frequency and were correlated with the molecular mobility of the system influenced by the humidity conditions and initial concentration. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were performed as well to investigate the thermal properties of the samples. The results indicate an increase in molecular mobility of the gelatin films with the increase of storage humidity independent of the initial concentration and suggest that the dynamic of the films depends on the amount of the water in the amorphous region of the film.