The study focuses on the vacuum microwave treatment of low-moisture potato starch. Typical temperature and drying profiles are presented and explained with the help of other process parameters such as sample weight, pressure, incident and absorbed microwave power. Subsequently water absorption capacity of vacuum microwave treated and conduction heated samples was investigated at 55°C. During vacuum microwave treatment, 50 g samples were treated with incident powers of 460, 500 and 750 W at 3800 Pa for durations between 30 and 300 s. Water absorption capacity increased exponentially with the net absorbed energy but could not be functionally correlated to end temperature and incident power. During conduction heating, starch samples were treated at temperature values of 120, 130, 140, 150 and 160°C, till constant weight.The water absorption capacity was observed to increase with increase in treatment temperature.
The development of energy-efficient textile manufacturing procedures is a crucial factor for cost reduction, potentially leading to the further establishment of technical textiles for industrial applications. In the textile sector, drying processes are responsible for the largest share of the total energy demand required by the manufacturing process. The performed investigations reveal that this fact also applies to infrared-based drying and curing procedures involved in the manufacturing of textile reinforcing structures for construction applications. The relationship between the temperature of the coated textile grid-like structure during drying and curing and infrared emitter power was analyzed and optimized. In addition, a thermodynamic concept was developed to replace the iterative setting of production parameters, such as infrared emitter power and machine speed. Thus, measurable process control parameters were identified that decisively influence the drying and curing process of textile reinforcements. The results of these investigations form the basis for procedural improvements (optimization variables: energy, time, and quality) as well as for the continuous monitoring of the drying and hardening process of textile reinforcements.
It is known that the water binding capacity of starch increases after vacuum microwave treatment. Microwave radiation absorbed by the starch sample affects its sensible, latent internal and chemical (bond and conformational) energy levels. A phenomenological model was developed based on energy sinks in starch, practically described as increasing temperature, breaking bonds between water and amylopectin/amylose molecules, changing the phase of water from liquid to vapor and structural rearrangements at short (single/double helices) and long (crystalline/amorphous) order. The model was validated by experimental data for different vacuum microwave treatment parameters, viz. incident power (460, 500 and 750 W), duration (30 to 340 s) and sample mass (10 to 70 g) at 4000 Pa. The results provide an insight into the physical aspects of the process and would facilitate its development on an industrial scale.
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