Thermoplastic polyurethane (TPU) resins are widely used in various industries due to their excellent properties such as high elasticity, abrasion resistance, and chemical resistance. However, TPU resins are hygroscopic and can absorb moisture from the environment during storage and transportation. Moisture in TPU resins can cause polymer rearrangement, molecular weight reduction, and significant loss of physical properties. Therefore, it is crucial to properly dry TPU pellets before processing to prevent these consequences.
There are several effective methods for drying TPU resins. One method involves mounting the dryer hopper directly onto the equipment feed hopper. The dryer hopper is filled with dried TPU pellets while the equipment feed hopper is filled with undried pellets. The dried pellets flow into the equipment feed hopper through a valve or slide gate. (Hopper Dryer direct-mounting)
Another method involves using a small hopper receiver that is fed by a closed loop dry air conveyor from a larger dryer hopper. The larger dryer hopper contains undried TPU pellets (at the top) while the small hopper receiver contains dried pellets (from the bottom of the larger dryer hopper). The dried pellets flow into the small hopper receiver through the conveyor. (Drying Loaders floor-stand mounting)
Desiccant dryers are also effective methods for drying TPU pellets. Desiccant dryers use desiccant material such as silica gel or activated alumina to absorb moisture from TPU pellets. The desiccant material is regenerated periodically by heating it to remove absorbed moisture. (Dehumidifying dryers)
For drying sticky TPU resins, mixing-type drying hopper machine is suggested to use for preventing bridging during drying. Even drying effect can be achieved by adopting drying TPU resin with mixing drying machine. (Crystallizing Drying machine)
Once the TPU pellets are dried, it is critical to retain low resin moisture levels during processing. Ambient air humidity will have a significant impact on how quickly TPU resins re-absorb moisture when exposed to the environment. Therefore, it is recommended to process TPU resins in a controlled environment with low humidity.
To determine and control the moisture of TPU resin, measuring the moisture content is recommended. Moisture analyzers can be used to determine when TPUs are dry enough. These instruments can determine moisture content to as low as 0.01% (100 ppm). We recommend drying TPU at 50-80 for 4-8 hours by dehumidifying dryers to obtain a low moisture content as required.
In conclusion, proper drying of TPU pellets is crucial for maintaining their properties and preventing defects in the final product. By using effective drying methods and controlling the environment during processing, manufacturers can ensure that their TPU products meet the desired quality standards. It is important to note that the amount of moisture that can be tolerated in processing depends on process temperature, residence time of the molten polymer, and chemistry of the TPU being processed. Higher temperatures, longer residence times, and higher durometer resins impose more stringent drying requirements to prevent moisture-related defects.
In addition to following proper drying procedures, it is also important to store TPU pellets in a dry environment. Pellets should be stored in sealed containers with desiccant packs or in a dry room with low humidity levels.
By taking these steps to properly dry and store TPU pellets, manufacturers can ensure that their products meet the desired quality standards and perform as intended.
Contact David at (0086) 18948606110 for more information about TPU drying.
Email: david@orste.com
Contact Person: Mr. David
Tel: 86-18948606110
Fax: 86-769-8202-6886
