Proton, thermal and mechanical relaxation characteristics of a complex biomaterial (de-fatted date-pits) as a function of temperature

Abstract

Thermal (differential scanning calorimetry, DSC), proton (low-frequency nuclear magnetic resonance, LF-NMR), and mechanical (differential mechanical thermal analysis, DMTA) relaxations were measured for defatted date-pits as a function of temperature. DSC showed three types of relaxations, lower one structural relaxation (i.e. − 5 °C), followed by a glass transition (i.e. 136 °C) and solids melting–decomposition (i.e. 171 °C). LF-NMR showed three pools of protons, rigid, semi-rigid and mobile. Rigid protons showed two types of relaxations, first one low temperature increase (− 80 to − 40 °C), plateau region (− 60 to − 40 °C) and a positive peak at 120 °C, and semi-rigid showed maximum peak at − 5 °C and minimum peak at 150 °C. Mobile protons showed low relaxation (− 80 to − 40 °C), a maximum peak at 70 °C and a minimum peak at 130 °C. The maximum peak (i.e. − 5 °C) of semi-rigid protons was similar to the DSC structural change, while the maximum peak of rigid protons (120 °C) was similar to DSC glass transition (i.e. 136 °C). The minimum peak of the semi-rigid protons (i.e. 150 °C) was similar to the solids melting–decomposition (171 °C). DMTA showed five regions of mechanical relaxations, glassy region (i.e. onset at 32 °C), glass transition (i.e. 32–85 or 87 °C), first reaction region with a plateau or peak (85–140 °C), second reaction region (87–174 °C), and softening or decomposition region (223 or 242 °C). Mechanical glass showed completely different relaxation as compared to the protons and thermal relaxations. This study showed that LF-NMR, DSC and DMTA could be used to explore the relaxations of a material at nano-, micro- and macro-levels.