Jet-cooked papermaking starches studied using H-1 NMR-relaxometry and viscometry

Two wet-end starches (potato and barley), one surface sizing starch (barley) and one coating binder starch (barley) were jet-cooked. Samples were collected and stored at 90, 60 and 40 degrees C. H-1 NMR-relaxometry and viscometry were used to monitor the jet-cooked solutions as they cooled to room temperature. Samples stored at different temperatures were also monitored using H-1 NMR-relaxometry and viscometry. A sediment formed into the surface sizing and coating binder starches stored at 90 degrees C. The sediment and supernatant were separated and collected, and measured using H-1 NMR-relaxometry. The T-2 relaxation rates of jet-cooked starches showed significant differences between potato and barley starches, as had also been examined in previous studies. The NMR method was also sensitive to differences in solids content and chemical modification (degree of cationization, degree of oxidation and molecular weight). The cooking temperature, cooking speed and viscosity did not influence T-2 relaxation rates. The sediment separated from the surface sizing and coating binder starches held at 90 degrees C had a significantly higher relaxation rate than the supernatant, indicating that the sediment contained a high amount of retrograded starch.