| 摘要 |
A method of improving the effectiveness of a photostabilizer in reducing the deleterious effects of actinic radiation on a polypropylene composition, which method involves compounding a melt-extrudable thermoplastic polypropylene composition having a melt flow rate in a range of from about 18 to about 100 g/10 minutes at a temperature of 230 .degree.C and a load of 2.16 kg. The polypropylene composition includes a first thermoplastic polypropylene having a melt flow rate lower than 18 g/10 minutes at a temperature of 230 .degree.C and a load of 2.16 kg, a polydispersity greater than about 2.6, and a Z-average molecular weight greater than about 300,000; a second thermoplastic polypropylene having a melt flow rate higher than 18 g/10 minutes at a temperature of 230 .degree. C and a load of 2.16 kg, a polydispersity equal to or less than 2.6, and a Z-average molecular weight equal to or less than 300,000 as determined by gel permeation chromatography; and a photostabilizer. The weight ratio of the first polypropylene to the second polypropylene is in a range of from about 95:5 to about 10:90. Alternatively, such improvement may be accomplished by thermally cracking a thermoplastic polypropylene composition which includes a thermoplastic polypropylene having a melt flow rate lower than about 18 g/10 minutes, a photostabilizer, and a cracking catalyst. Cracking is carried out under conditions sufficient to give a melt-extrudable thermoplastic polypropylene composition having a melt flow rate in a range of from about 30 to about 90 g/10 minutes, a polydispersity greater than 2.6, and a Z-average molecular weight greater than 300,000 as determined by gel permeation chromatography.
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