| 摘要 |
1,201,060. Extruding polypropylene strands. ESSO RESEARCH & ENG. CO. 1 Dec., 1967 [19 Dec., 1966], No. 54884/67. Heading B5A. [Also in Division C3] Polypropylene is heated to a temperature exceeding 550‹ F. in the presence of a gas containing at least 7 mole per cent of oxygen and extruded, a portion of the extrudate being sampled to measure a parameter of the molecular weight of the polypropylene and the conditions of extrusion being controlled in response to said measured parameter whereby polypropylene of desired molecular weight is obtained in a reproducible and predictable manner. The parameter measured may be the shear stress or swell, and the controlled conditions may be temperature, extrusion speed and back pressure. Polypropylene may be introduced and mixed with gas from line 29 in hopper 28 and mixing zone 31, the polymer being extruded as strands through die 36, cooled in bath 37, pelletized in 22 and the viscosity of a sample measured in rheometer 23, the temperature of heaters 30 being controlled in accordance with the measured viscosity. The extruder has a cooling chamber 33, back-pressure control valve 35 and impurities are removed at screen pack 34. |
