Meaning
Thermogravimetric processes measure the rate at which volatile substances are released from a solid sample held at a constant temperature. During resin preparation, isothermal desorption determines the time required to remove moisture or solvents from hygroscopic polymers before moulding. Maintaining the sample at a constant temperature allows engineers to measure the diffusion rate of volatiles without causing thermal decomposition.
Moisture Release
Polymers like polyamide and polycarbonate absorb atmospheric moisture, which causes hydrolytic degradation during melt processing if not removed. When isothermal desorption is analyzed in a laboratory setting, it reveals the optimum drying temperature and duration for the bulk resin. Moulders apply this drying profile to their hopper dryers to ensure that the moisture content falls below the threshold required for defect-free moulding.
Material Behavior
Virgin resins generally display consistent release rates that follow standard diffusion models. In contrast, regrind materials may contain surface contaminants or moisture-retentive additives that disrupt these profiles, requiring longer drying times or higher temperatures to reach the same level of dryness. Inadequate drying results in cosmetic defects like splay marks and a reduction in the impact strength of the finished parts.
Drying Efficiency
Drying too long at elevated temperatures wastes energy and can cause thermal discolouration of the resin. Precise desorption data prevents over-drying and helps maintain high throughput in the production line.
