PDF《Hytrel》

Processing Precautions for Hytrel H-33430 Hytrel Injection Molding Guide HYT-403 (R2) Extrusion of Hytrel HYT-409 (R1) Melt Casting HYT-451 (R1) Rotational Molding of Hytrel Polyester Elastomers HYT-452 (R1) Blown Film of Hytrel Polyester Elastomers Drying Hytrel polyester elastomer must be dried prior to processing. It is critical to ensure that the resin is dry during processing to make quality parts that would give good service performance. Hytrel is resistant to hydrolysis. It does not react with moisture in the air, but will absorb the mois- ture if left exposed. Equilibrium moisture levels as determined by ASTM D570 depend on grade (see Table 2). At temperatures substantially above the melting point, excess moisture causes hydrolytic degrada- tion of the polymer. Such degradation results in poor physical properties and brittleness. No visual defects may be apparent but poor in-service perfor- mance can occur, particularly at low temperatures. Generally, no degradation of the polymer or imper- fections in the molding or extrusion occur if the moisture content is less than 0.10%, the maximum moisture specification for all grades of Hytrel. When dry polymer is subjected to 50% relative humidity, 0.10% moisture increase occurs in about

2 hr, whereas ........