Spherulitic banding in metallocene catalysed polyethylene spherulites

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• 作者：Janimak ; J.J. ; Markey ; L. ; Stevens ; G.C.
• 关键词：Polymer spherulites ; Spherulitic banding ; Polyethylene spherulites
• 刊名：Polymer
• 出版年：2001
• 出版时间：February 1, 2001
• 年：2001
• 卷：42
• 期：10
• 页码：4675-4685
• 全文大小：387 K

文摘

Atomic force microscopy (AFM) and transmission electron microscopy (TEM) have been used to examine the influence of molecular weight on the melt-crystallised morphology of a series of permanganically etched metallocene catalysed high-density polyethylenes (mHDPEs). The effect of increasing molecular weight is manifest by different morphologies, viz. banded spherulites and lamellar domains structures above a critical molecular weight, and sheaf-like structures below a critical molecular weight. In addition, the incipient spherulite development has been detected in a low molecular weight mHDPE. AFM height imaging of permanganically etched sections has revealed an apparent band period spacing decreasing from the centre of any given spherulite in non-diametral sections of isothermally crystallised samples. This observation was also confirmed by exhaustive TEM measurements on similar non-diametral sections. AFM height measurements show that band height amplitude varies across bands as a function of radial position and is a characteristic feature of all the banded spherulitc structures studied. The band amplitude and period are dependent on molecular weight and are sensitive to the degree of etching with fast etching rates for low molecular weight mHDPEs. Both the AFM and TEM measurements of the apparent band spacing converge with radial distance to the true band period spacing. Homopolymers and copolymers show a different relationship of true band spacing with molecular weight.