Further study on double-melting endotherms of isotactic polypropylene

✍ Scribed by Xinyuan Zhu; Deyue Yan; Susheng Tan; Tao Wang; Donghang Yan; Enle Zhou

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 143 KB
• Volume: 77
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(20000705)77:1<163::aid-app22>3.0.co;2-l

✦ Synopsis

The origins of the single-and double-melting endotherms of isotactic polypropylene crystallized at different temperatures were studied carefully by differential scanning calorimetry, wide-angle X-ray diffraction, and small-angle X-ray scattering. The experimental data show that spontaneous crystallization occurs when the crystallization temperature is lower than 117°C; thus the lamellae formed are imperfect. At a lower heating rate, the recrystallization or reorganization of these imperfect lamellae leads to double endotherms. On the other hand, when the crystallization temperature is higher than 136°C, two major kinds of lamellae with different thickness are developed during the isothermal process, which also results in the double-melting endotherms. In the intermediate temperature range the lamellae formed are perfect, and there is only a single peak in the distribution of lamellar thickness. This explains the origin of the single-melting endotherm.