Assessing the softening behavior of rosin during heating using variable-temperature low-field nuclear magnetic resonance

Abstract This study investigates the softening behavior of rosin during heating using variable-temperature low-field nuclear magnetic resonance (LF NMR) technique, aiming to demonstrate the potential of LF NMR in characterizing softening transitions including softening point. The NMR signals from three types of industrial rosins during heating from 30 °C to 140 °C were analyzed by applying both mono- and multi-component interpretation methods to evaluate signal amplitudes and relaxation time distributions. These parameters were used to assess the effect of heating temperature on the softening properties of rosin. The temperature-dependent NMR signal amplitude exhibited characteristic S-shaped growth, from which the temperature corresponding to the inflection point, where the signal amplitude increased most rapidly, was proposed as the softening point of rosin. The softening point values were mathematically determined through Boltzmann function modeling and subsequently compared with those measured using the ring-and-ball method. The LF NMR-derived softening point values showed close agreement with ring-and-ball results with deviation of 0.1–1.7 °C, validating NMR reliability for softening point analysis.